Center channel Impedance.

[StevenSurprenant]

Normally a surround system uses a single speaker for the center channel, but I have always considered that the main flaw in the design. In most home setups, the sound comes from above or below the screen and I find that very distracting. Most people get used to it and the brain compensates by creating a virtual audio image across the screen. In my case, that has never happened. My solution was to use a Yamaha receiver that has an ambience channel. This is comprised of 2 extra speakers that enhance the sound by creating extra ambiance, but also has the ability to add center channel information to those 2 speakers. When placed correctly, these extra speakers will bring the center channel information up to the center of the screen. It works very well.

I have Magnepan wall speakers and I was reading about using their center channel speakers with two additional wall speakers flanking both sides of the screen to get the same effect that I mentioned above. All their speakers are 5 ohm. The way they set it up was to wire the 2 wall speakers in series (10 ohms) and then wire the center speaker in parallel with those two for a combined impedance of 3.3 ohms. My receiver is rated at 6/8 ohms, but the specs also shows a peak output at 2 ohms. In addition, I understand that the Magnepans impedance is lowest below 200 Hz. I set the speakers to small and the crossover to 200 Hz to reduce the current to these speakers. Also, because there are now three speakers, the volume was reduced accordingly to match the main speakers. Still, I can't get it out of my mind that at times the current draw is going to be excessive and shorten the life of the receiver.

I then wired all 3 of the speakers in series for a total of 15 ohms impedance. I actually liked this way better because now all 3 speakers are at the same volume, whereas before in the previous setup, the 2 wall hanging speakers were not as loud as the center channel speaker. I realize that I have to increase the preamp section of the center channel higher than the main speakers which in turn makes that channel the limiting factor of the maximum output of the entire system (at least I assume so). I have yet to run out of power so I don't believe this to be an issue. I believe this solves the problem with too high a current drain compared to the previous configuration.

This brings me to my question...

Is it okay to run speakers at 15 ohms and is there anything else that I need to be concerned about? Is my logic correct?

You might be asking, if the ambiance speakers worked so well, why would I want to do this? The answer... The ambiance speakers only do their magic when they are engaged. If I wanted to run without them and just with Dolby or DTS, they do not function. Also I cannot run 7.1 surround and the ambiance channels at the same time. Besides, I already had an extra pair of Magnepan speakers stored away that I wasn't using.

[Sir Terrence the Terrible]

Normally a surround system uses a single speaker for the center channel, but I have always considered that the main flaw in the design. In most home setups, the sound comes from above or below the screen and I find that very distracting. Most people get used to it and the brain compensates by creating a virtual audio image across the screen. In my case, that has never happened. My solution was to use a Yamaha receiver that has an ambience channel. This is comprised of 2 extra speakers that enhance the sound by creating extra ambiance, but also has the ability to add center channel information to those 2 speakers. When placed correctly, these extra speakers will bring the center channel information up to the center of the screen. It works very well.

I have Magnepan wall speakers and I was reading about using their center channel speakers with two additional wall speakers flanking both sides of the screen to get the same effect that I mentioned above. All their speakers are 5 ohm. The way they set it up was to wire the 2 wall speakers in series (10 ohms) and then wire the center speaker in parallel with those two for a combined impedance of 3.3 ohms. My receiver is rated at 6/8 ohms, but the specs also shows a peak output at 2 ohms. In addition, I understand that the Magnepans impedance is lowest below 200 Hz. I set the speakers to small and the crossover to 200 Hz to reduce the current to these speakers. Also, because there are now three speakers, the volume was reduced accordingly to match the main speakers. Still, I can't get it out of my mind that at times the current draw is going to be excessive and shorten the life of the receiver.

I then wired all 3 of the speakers in series for a total of 15 ohms impedance. I actually liked this way better because now all 3 speakers are at the same volume, whereas before in the previous setup, the 2 wall hanging speakers were not as loud as the center channel speaker. I realize that I have to increase the preamp section of the center channel higher than the main speakers which in turn makes that channel the limiting factor of the maximum output of the entire system (at least I assume so). I have yet to run out of power so I don't believe this to be an issue. I believe this solves the problem with too high a current drain compared to the previous configuration.

This brings me to my question...

Is it okay to run speakers at 15 ohms and is there anything else that I need to be concerned about? Is my logic correct?

You might be asking, if the ambiance speakers worked so well, why would I want to do this? The answer... The ambiance speakers only do their magic when they are engaged. If I wanted to run without them and just with Dolby or DTS, they do not function. Also I cannot run 7.1 surround and the ambiance channels at the same time. Besides, I already had an extra pair of Magnepan speakers stored away that I wasn't using.

This is such a bad idea, I don't know where to start. Are you calibrating your center channel with a SPL meter or calibrating software? A properly calibrated system does not need two center speakers. Two speakers reproducing the same signals introduces dispersion pattern interference that is not very good for dialog clarity.

There is a reason movie theaters and home theaters only have one speaker reproducing the center channel information.

Your claim about the sound of the center speaker being over or under the screen is simply not correct at any level. The ear/brain mechanism does a great job of putting the dialog where your eyes are, as the offset is not far enough to create a discontinuity. Even with highly directional loudspeakers, the sound is not pulled down or up from them unless you are sitting extremely close to them. At that point any picture on the screen is basically unwatchable. Your idea that a single center speaker reproducing the dialog is flawed is in itsef flawed.

The ambient channels of a Yamaha receiver cannot carry dialog. All it can carry is DSP generated and processed ambience, and that is it. If you love muddled dialog, then keep doing what you are doing, However if dialog clarity is more disireable, ditch the two center, and use one calibrated one.

[StevenSurprenant]

This is such a bad idea, I don't know where to start. Are you calibrating your center channel with a SPL meter or calibrating software? A properly calibrated system does not need two center speakers. Two speakers reproducing the same signals introduces dispersion pattern interference that is not very good for dialog clarity.

There is a reason movie theaters and home theaters only have one speaker reproducing the center channel information.

I don't mean to to contrary, but I found the opposite to be true, dialog clarity has increased, even though I know what you are saying makes sense. I suppose that there are other variables in play here. It might be that they are planer dipole speakers and not so much point sources. I don't know.

Here are links to what others have said...

Magnepan center channel field test - wendell diller - Planar Speaker Asylum (http://db.audioasylum.com/mhtml/m.html?forum=mug&n=141501&highlight=StephanD&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dotl%26ses sion%3D20110318073732)

The Audio Beat - Monday at Magnepan (http://www.theaudiobeat.com/visits/monday_at_magnepan.htm)

The Audio Beat - Magnepan's Tri-Center: The Sound of Things to Come for Home Theater?; Magnepan speakers (http://www.theaudiobeat.com/blog/magnepan_tricenter.htm)

The Audio Beat - Magnepan's 3.7/Tri-Center System: The Second Time Around; Magnepan 3.7 and Tri-Center speakers (http://www.theaudiobeat.com/blog/magnepan_37_tricenter_system.htm)

Tri-Center (http://www.audiocircle.com/index.php?topic=92895.0)


On the other issue of "Your idea that a single center speaker reproducing the dialog is flawed is in itsef flawed." . I'm not in agreement with you except for the distance factor from the speaker. The further from the center speaker we are, the better it integrates. In most home settings, that distance isn't achievable. Oh, I also agree with you on the ear/brain mechanism, except that, for me, it takes an effort to ignore where the sound is actually coming from.

Sir... My intention is not to be argumentative. You have been a great contributor to this site and have exhibited that you have an in depth knowledge of audio. However, theory doesn't always apply, nor do our tastes always mesh. From your equipment list that you posted, your "TV" room is the exception and not the norn. Your screen is bigger than my entire wall, hence I have to assume that your room is much much larger than what I have. From that, it makes sense that your center would integrate better than what is available to me or to most people.

Just a thought...

It seems odd to me that many people compare their home systems to a theater. I quit going many years ago because of the sound (too loud). Theaters are great at producing loud sound with little distortion and the large room size is great for creating that spacious ambiance. Where theaters fall short is creating a depth to the image (it's wallpaper, if you know what I mean)..Home theaters are much better in that regard. Neither is better. all things considered.

BTW, I bet your theater systems sounds terrific.

Thanks...

Oh, one more thing...

|The ambient channels of a Yamaha receiver cannot carry dialog. All it can carry is DSP generated and processed ambience, and that is it.|

Not true, at least I don't think so. The model I have has a feature called "Dialog Lift". Granted it is a function of the ambience feature, but from what I can hear, it does just what it claims without adding additional ambience.

Normally, I am not a fan of processed sound. My 2 channel system only has a volume knob and that's it. There is no pre-amp or switching capability either. It sounds very good (to me), but I like it and the surround system equally. Needless to say, I've heard better, but at a higher cost.

[E-Stat]

There is a reason movie theaters and home theaters only have one speaker reproducing the center channel information.
And yet, I've never seen a center speaker hung below the screen at a cinema. Ever been to an IMAX where they give the sound presentation intro that includes showing the location of the speakers themselves via backlighting through the screen? Maybe not. Here are some examples:

Centers not below screen here (http://i174.photobucket.com/albums/w118/Brainstorm3417/Malco_Brochure.jpg)

Nor here... (http://www.leesound.com/bw_photos/photo13.jpg)

Nor here... (http://forum.ecoustics.com/bbs/messages/47069/288071.jpg)

Nor here... (http://drhart.ucoz.com/Cinema/thx-speaker-layout-baffel-wall616w.jpg)

Nor here... (http://forum.ecoustics.com/bbs/messages/3/308262.jpg)


Even with highly directional loudspeakers, the sound is not pulled down or up from them ...
Unless of course you use tall line sources for the mains.

rw

[E-Stat]

Most people get used to it and the brain compensates by creating a virtual audio image across the screen. In my case, that has never happened.
Such is the same for me, too.


My solution was to use a Yamaha receiver that has an ambience channel. This is comprised of 2 extra speakers that enhance the sound by creating extra ambiance, but also has the ability to add center channel information to those 2 speakers.
I'm not sure that is the best approach either.


I have Magnepan wall speakers and I was reading about using their center channel speakers with two additional wall speakers flanking both sides of the screen to get the same effect that I mentioned above.
Interesting approach, but might still involve the same challenge with loss of separation.


Is it okay to run speakers at 15 ohms and is there anything else that I need to be concerned about?
Wiring different speakers in series is not ideal. Multiples of the same is fine. An amplifier won't have trouble driving the load, but the time response to the speakers will be affected. I might try using two of the identical speakers as the center with their height aligned with the mains. Just like they do at commercial cinemas.

rw

[Sir Terrence the Terrible]

And yet, I've never seen a center speaker hung below the screen at a cinema. Ever been to an IMAX where they give the sound presentation intro that includes showing the location of the speakers themselves via backlighting through the screen? Maybe not. Here are some examples:

Centers not below screen here (http://i174.photobucket.com/albums/w118/Brainstorm3417/Malco_Brochure.jpg)

Nor here... (http://www.leesound.com/bw_photos/photo13.jpg)

Nor here... (http://forum.ecoustics.com/bbs/messages/47069/288071.jpg)

Nor here... (http://drhart.ucoz.com/Cinema/thx-speaker-layout-baffel-wall616w.jpg)

Nor here... (http://forum.ecoustics.com/bbs/messages/3/308262.jpg)

Unfortunately Ralph, most home theaters use televisions and not screens. All of your examples are of movie theaters, and most setups are not done that way. When you use a set(and you know this very well), you either have to put the center speaker in front of the set below it, or on top of the set. These are your only choices for this setup.



Unless of course you use tall line sources for the mains.

rw

You can't really use line sources for the center position with flat panels, but you are correct.

[E-Stat]

All of your examples are of movie theaters, and most setups are not done that way.
I merely point out that you must choose your own set of compromises in imperfect environments. While I have not heard an HT using tall line sources with a split equivalent center, my guess is that I would prefer its non-distracting image coherence to using the more common below the screen approach. I seriously doubt that Wendell Diller or either Winey would make such a suggestion without first trying it out.

rw

[Sir Terrence the Terrible]

I don't mean to to contrary, but I found the opposite to be true, dialog clarity has increased, even though I know what you are saying makes sense. I suppose that there are other variables in play here. It might be that they are planer dipole speakers and not so much point sources. I don't know.

Here are links to what others have said...

Magnepan center channel field test - wendell diller - Planar Speaker Asylum (http://db.audioasylum.com/mhtml/m.html?forum=mug&n=141501&highlight=StephanD&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dotl%26ses sion%3D20110318073732)

The Audio Beat - Monday at Magnepan (http://www.theaudiobeat.com/visits/monday_at_magnepan.htm)

The Audio Beat - Magnepan's Tri-Center: The Sound of Things to Come for Home Theater?; Magnepan speakers (http://www.theaudiobeat.com/blog/magnepan_tricenter.htm)

The Audio Beat - Magnepan's 3.7/Tri-Center System: The Second Time Around; Magnepan 3.7 and Tri-Center speakers (http://www.theaudiobeat.com/blog/magnepan_37_tricenter_system.htm)

Tri-Center (http://www.audiocircle.com/index.php?topic=92895.0)

So let me get this straight, a guy that works for a speaker company tells you that dual or even a trio of center speakers is best. And you believe this? This guys want to sell speakers, but he must understand something called "wave interference" as demonstrated on this page.

2-Point Source Interference Patterns: Changing Separation Distance (http://www.physicsclassroom.com/mmedia/waves/ipd.cfm)

You notice that when the speakers are separated, there is a very complex interaction between the two waves.This causes wave interference that causes cancellations and boosts to the frequency response. As the sources are moved until they almost are one source, that interference pattern decreases, and eventually would go away completely. This is what happens when dialog in split between two speakers, and why only one speaker works best for this application.



On the other issue of "Your idea that a single center speaker reproducing the dialog is flawed is in itsef flawed." . I'm not in agreement with you except for the distance factor from the speaker. The further from the center speaker we are, the better it integrates. In most home settings, that distance isn't achievable. Oh, I also agree with you on the ear/brain mechanism, except that, for me, it takes an effort to ignore where the sound is actually coming from.

This is nonsense. The fusion point is based on the size of the speakers, and the distance between the drivers. I sit 5.4" from a mini-monitor, and its drivers are long integrated with each other at that distance. It would be integrated at 2ft, and that can be easily measured using speaker measurement software like MLSSA. I can sit 10ft away from my Dunlavy SC-V, and all of the drivers sound is fully integrated at that distance. I can sit 5ft away from the system in my signature, and the drivers sound is fully fused at that distance. All of these distances are easily achievable in most hometheaters.


Sir... My intention is not to be argumentative. You have been a great contributor to this site and have exhibited that you have an in depth knowledge of audio. However, theory doesn't always apply, nor do our tastes always mesh. From your equipment list that you posted, your "TV" room is the exception and not the norn. Your screen is bigger than my entire wall, hence I have to assume that your room is much much larger than what I have. From that, it makes sense that your center would integrate better than what is available to me or to most people.

Theory does not always apply, but in this case, it does and can easily be demonstrated. Once again, look at the example above as it is a simulation of exactly what would happen when two spaced speakers are playing the same signal. You can also measure what the interference does to the overall frequency response coming from those two speakers. The effect leads to comb filtering, and comb filtering has a diffusive effect on the sound, not a cohesive effect.

This is not designed to be augmentative as well, but as a person who mixes movie soundtracks for a living, I completely understand how to get articulate dialog from a single speaker set up. You are essentially creating a phantom image between the two speakers. Phantom images have notches in the frequency response depending on how far the speakers are spread. The sound goes from a notch very close to the speakers, to full out cancellation and boosting further away. This is not good for dialog. Movie soundtracks are designed with a single discrete source for each channel across the front and sides, and matrixed or discrete channels in the back rear.



Just a thought...


It seems odd to me that many people compare their home systems to a theater. I quit going many years ago because of the sound (too loud). Theaters are great at producing loud sound with little distortion and the large room size is great for creating that spacious ambiance. Where theaters fall short is creating a depth to the image (it's wallpaper, if you know what I mean)..Home theaters are much better in that regard. Neither is better. all things considered.

Actually this is not quite correct. Movie theater sound system create depth in a DIFFERENT way than home theaters do. The sense of depth in home theater speakers comes from the complex interaction of front wall reflections at low and mid bass frequencies. Side wall reflections create a sense spaciousness. Since movie theaters are pretty reflection free at mid and high frequencies, in order to create depth, we pull images out in to the room using the surrounds. If you mirror the signals coming from the fronts to the surrounds, the image will pull into the room all the way back to the backwall with current 6.1 and 7.1 configurations.


BTW, I bet your theater systems sounds terrific.

Thanks for the compliment.

It seems from reading on the net, most folks that use this dialog left feature have their speakers far too close to the floor, or sitting on it. This is a total compromise and will induce boundary reinforcing effects to the signal. You can lift the dialog higher, but it still won't reduce the effect of the boundary reinforcement unless the center speaker is off the floor. Lift it off the floor, and closer to the television screen, and the eye/ear mechanism can do its magic.

[Sir Terrence the Terrible]

I merely point out that you must choose your own set of compromises in imperfect environments. While I have not heard an HT using tall line sources with a split equivalent center, my guess is that I would prefer its non-distracting image coherence to using the more common below the screen approach. I seriously doubt that Wendell Diller or either Winey would make such a suggestion without first trying it out.

rw

Ralph, you don't get coherence from this setup, you get destructive wave pattern interference. That is not good at all, and why you won't find many people trying this kind of set up.

[E-Stat]

Ralph, you don't get coherence from this setup, you get destructive wave pattern interference. That is not good at all, and why you won't find many people trying this kind of set up.
You continue to apply point source radiation rules to dipolar line sources. Like apples and kumquats. Once again, you must choose your choice of compromise(s). I find voices coming from below everything else distracting. Perhaps that is not the case for you. I'll repeat: there are a sum total of ZERO cinemas compromised in that way. I suspect they know what they are doing even if you don't.


In this case you are compromising an even frequency response.
Perhaps. Since there are always frequency anomalies at virtually every concert and theater, I don't find those distracting.

rw

[Sir Terrence the Terrible]

I merely point out that you must choose your own set of compromises in imperfect environments. While I have not heard an HT using tall line sources with a split equivalent center, my guess is that I would prefer its non-distracting image coherence to using the more common below the screen approach. I seriously doubt that Wendell Diller or either Winey would make such a suggestion without first trying it out.

rw

I understand your point. However some compromises just makes things worse, or creates more compromises. In this case you are compromising an even frequency response.

Remember Wendell and Winey are in the business of selling speakers, and naturally they would recommend something that....well... sells more speakers.

[Sir Terrence the Terrible]

You continue to apply point source radiation rules to planar line sources. Like apples and kumquats. Once again, you must choose your choice of compromise(s). I find voices coming from below everything else distracting. Perhaps that is not the case for you. I'll repeat: there are a sum total of ZERO cinemas compromised in that way. I suspect they know what they are doing even if you don't.

rw

The only difference between a point sources and planar line sources is in vertical directivity. It still has a very wide horizontal dispersion pattern, and that is where the problem lies. They are placing these speakers side by side, and that will create an interference pattern in the horizontal plane.

If planar line sources had both limited vertical and horizontal dispersion patterns, then you would not have a problem.

[E-Stat]

The only difference between a point sources and planar line sources is in vertical directivity. It still has a very wide horizontal dispersion pattern...
While you have a great deal of expertise in a wide range of audio topics, these statements are simply not supported by fact. The horizontal dispersion of dipolar planar line sources is anything but identical to that of point sources. Which requires different thinking and placement approaches. Having lived with them for nearly forty years, I am somewhat familiar with their characteristics.


If planar line sources had both limited vertical and horizontal dispersion patterns, then you would not have a problem.
Thank you for agreeing! Vertical dispersion is easily solved by using a tall panel. Horizontal dispersion is addressed in different ways depending upon the design. Magneplanars use mirror imaged tweeters and more toe-in to mitigate the effects. My electrostats - which most soundly (pun intended) refute your assertion about dispersion - use angled panels to address the question of horizontal beaming.

rw

[bobsticks]

How does Harry Pearson do it at Sea Cliff? I thought I'd read that he uses two Maggies horizontally for purposes of dispersion.

Why do I think I'm muddying the waters?

[E-Stat]

How does Harry Pearson do it at Sea Cliff? I thought I'd read that he uses two Maggies horizontally for purposes of dispersion.
His arrangement is quite impressive sounding but is unable to get around the vertical height issue with the center. He uses a stacked pair of CC5s set horizontally atop a stand with the top of the array at about three feet - just below the line of sight to the screen. 20.1s are used for mains, 3.6s are used for rears along with four Nola subs. Given the width of his 100" screen and that of Room 1, he is unable to use a split center approach. The resolution, however, of that MC audio system is phenomenal.

rw

[Sir Terrence the Terrible]

While you have a great deal of expertise in a wide range of audio topics, these statements are simply not supported by fact. The horizontal dispersion of dipolar planar line sources is anything but identical to that of point sources. Which requires different thinking and placement approaches. Having lived with them for nearly forty years, I am somewhat familiar with their characteristics.

I have no doubt about your knowledge of this type of speaker, you own them. But to say they will NOT have a dispersion interference pattern at some point is simply not true, especially when they are playing the same signal.



Thank you for agreeing! Vertical dispersion is easily solved by using a tall panel. Horizontal dispersion is addressed in different ways depending upon the design. Magneplanars use mirror imaged tweeters and more toe-in to mitigate the effects. My electrostats - which most soundly (pun intended) refute your assertion about dispersion - use angled panels to address the question of horizontal beaming.

Even if you are controlling both the horizontal and vertical dispersion of a speaker, multiples of them tightly spaced together playing the same signal will still have wave interference PERIOD. When you toe these speakers in, the output has to intersect somewhere, and that is where you will experience wave interference. Dipoles Enhance this effect with their reflected energy combining with the direct energy from the speaker. We haven't even discussed the phase interference of this setup. We are talking tightly spaced tri-speaker setups playing a mono signal, not two stereo pairs playing two discrete signals. .

[StevenSurprenant]

Wiring different speakers in series is not ideal. Multiples of the same is fine. An amplifier won't have trouble driving the load, but the time response to the speakers will be affected. I might try using two of the identical speakers as the center with their height aligned with the mains. Just like they do at commercial cinemas.rw

Thanks E-STAT... That answers my question. For all "practical" purposes all the speakers are identical, except the center is curved.

About "challenge with loss of separation", I'm not sure what you mean.

From the seating position the speakers are about equal distant and the information is the same for each of them. It seems to me that this creates a virtual speaker much larger than any one of them. Think of it as a "Very Large Antenna array" that they use for astronomical radio. Same concept, smaller scale. When I move off center the wave form of the separate speakers will begin to diverge causing the lobing that "Sir" mentions. At the same time, the speaker I am closest to will be heard less as I move out of its directional pattern. I doubt that I can detect this minute time delay between the speakers or any lobing that is created, at least I've never heard it.

This is more directed at "Sir" ...

As you are fully aware of, dipole, line arrays, dipole line arrays, box speakers, Multi-driver speakers and about every configuration has its inherent flaws and wave patterns. Throw in different room dimensions and reflecting surfaces, cross talk to both ears from the left and right speakers and you have this incredibly complex wave pattern that is hitting our ears from every direction. It's a wonder that we can hear anything coherent.

"Sir"... Wave interference, combing, lobing, room reflections, speaker directivity, wave patterns from point sources versus line arrays, dipole, bipole, direct radiating speakers, and time alignment is all audio 101. Everyone who has followed this hobby knows this stuff. The only thing that is in contention is the audibility of these affects.

Heck, if I wanted to take it too an extreme, I would build a wall between my speakers right up to my face to prevent the right and left speaker from reaching the wrong ear (cross talk). Even though this cross talk has a large effect on soundstaging and more minor effects on wave interference, it is not worth the effort or concern to address.

As for the integration of my speakers, the distances are set, the volumes are set, and I can't tell where one speaker starts and another begins. This is all good and well, but if you want to be critical, the moment that you move out of the sweet spot, all these setting go out of wack. This occurs on your system and mine. The point is that you are being too critical here.

As for my center channel, where this all began, I've had it above the TV, below the TV, out in the room, and up against the wall. I've sat closer and further away and it sounds like the sound is coming from it and not the screen. You seem to be telling me to live with it, but I have a choice to do other wise.

While I'm at it, I'll tell you one more thing, which I have no doubt that you already know. Frequencies above about 40 Hz are directional and there is no way to hide where the speaker is. You can't make a single speaker sound like it is coming from the screen, but the effect can be reduced by increasing the distance between you and the screen/speaker. That is the only way except for placing the speaker behind the screen or using multiple speakers.

I'm not even sure we are arguing the same point. If speaker articulation (clarity) is your point, then you have nothing to worry about. Clarity of sound has always been my goal since I've gotten into this hobby. I've had Quad electrostats, Magnepan, and more, and built present speakers for my 2 channel system using some of the best components money can buy. I can hear a gnat land on a dogs back with either of my systems. I've also listened to some of the best systems available. Still, I can find fault with any system I've owned and listened to.

Two more things...

My system ( I suppose all) brings the image out into the room as you mentioned that theaters do. regardless of the mechanics, having a deep soundstage behind the speakers is what makes home audio better, it that regard, than a theater. My stereo speakers are about 3 feet from the back wall, but it routinely images 20 feet or more back depending on the source music. My Magnepan speakers are mounted "on the wall" and I still get a very deep soundstage. The imagining is not as precise as my stereo, but I would have to guess that the soundstage is almost as deep. Yet, I do agree that the back wall effects this soundstage.

About lifting the center speaker. It has set directly on top of the TV and almost touching the bottom of the screen with the same results. The eye/ear thingy doesn't work for me. I should mention that my speakers are dipole and long, like line arrays, hence floor bounce is less of an issue. Besides, they only go down to about 100Hz.

Let me ask you a question... Have you ever tried using two speakers for the center channel? Be honest.

I appreciate your thoughts and I know you are trying to help. However, I'm with E-STAT on this issue.

The more I learn, the less I know....

[Smokey]

Wiring different speakers in series is not ideal. Multiples of the same is fine. An amplifier won't have trouble driving the load, but the time response to the speakers will be affected.

Although amp will not have trouble driving the load, but by connecting speakers in series, it does change the electronic characteristic of speakers.

Sonce most amp's speaker out have constant 20 rail volts, by having two speaker in series, the rail voltage cross each speaker will drop to 10 v. Or if three way, the rail voltage cross each speaker will drop to 6.5 volts. So a speaker that have 20 volts cross it will sound different (since its electronic specification has change) than the one that have 10 volts or 6.5 volts cross it. So you are basically "starving" your speakers.

I tried two speakers in series, and notice that not only it pretty much kill speakers bass responce, it made them sound lifeless. Sounded like cheap car speakers :)

[E-Stat]

I have no doubt about your knowledge of this type of speaker, you own them. But to say they will NOT have a dispersion interference pattern at some point is simply not true, especially when they are playing the same signal.
Who is it who made such a claim? What I did was observe that your sweeping statement (completely independent of the OP's question) that there is NO difference in horizontal dispersion between point source speakers and dipolar panel line sources is most certainly not a correct assertion.


Even if you are controlling both the horizontal and vertical dispersion of a speaker, multiples of them tightly spaced together playing the same signal will still have wave interference PERIOD.
You seem to be caught in a negative feedback loop. While your point has been restated, you have returned to post #11 - to which I responded in advance in post #10. Let's review the facts:

1. Optimum center channel speaker arrangement is uniquely found in the cinema environment employing vertical symmetry of the three front channels.
2. Most HT arrangements don't allow for what is known to be ideal.

Pick your own poison by determining which parameter you choose to optimize over another.

rw

[E-Stat]

Although amp will not have trouble driving the load, but by connecting speakers in series, it does change the electronic characteristic of speakers.
Isn't that essentially what I said in the two sentences you quoted?


I tried two speakers in series, and notice that not only it pretty much kill speakers bass responce, it made them sound lifeless.
For starters, bass response for the voice track really isn't that critical. You might be surprised how many speakers use series wired components. Aren't you one of the Roger Russell disciples? You do realize that his IDS speaker is wired thusly, right?

rw

[E-Stat]

Thanks E-STAT... That answers my question. For all "practical" purposes all the speakers are identical, except the center is curved.
They are not identical. Why does the center cost only $26 less than the pair of MMG-Ws?


About "challenge with loss of separation", I'm not sure what you mean.
You have effectively split the mono center channel into two parts which are located closer to the mains reducing the effective separation between main and center.


rw

[StevenSurprenant]

They are not identical. Why does the center cost only $26 less than the pair of MMG-Ws?

You have effectively split the mono center channel into two parts which are located closer to the mains reducing the effective separation between main and center.rw

I'm not sure about the price difference. Why does any center channel cost more than a single main speaker?

From what I understand, they are the same driver. On the MMGW the panel is laid flat in it's frame while on the MMGC the same panel is stretched on a curved frame. If you look at the specs, they are identical.

Description Planar Magnetic
Freq. Resp. 100 Hz- 16 kHz + - 3 db
Sensitivity 88 db 2.83 volts
Impedance 5 ohms

They sound similar, but not totally the same.
__________________________________________________ _
"challenge with loss of separation" - I understand now and I was concerned about that. What I discovered was that the image was still in a relatively tight point in the center of the screen from left to right instead of spread out like what someone might imagine.

I suppose that it's like a 2 channel system that is playing a mono source. In my stereo room I have a smaller TV between the speakers and when I am watching an older movie with a mono source it seems like all of the sound is coming directly from the TV and that the main speakers are off. In other words, the sound is confined to a very tight point between the speakers.

Thinking further about that... If the speakers are angled correctly, as I move away from the center, I am also moving away from the radiation pattern of one speaker while remaining in the radiation pattern of the other, hence preventing image drift. As you know, dipoles have a null region at edge of their speaker plane.

I suppose that in the extreme, as long as you remain in the center between speakers (to prevent image drift), the two side center channel speakers could be placed right next to the mains and still produce a very distinct focused image midway between the mains. Even in this scenario, If the speakers radiation pattern is optimal and the speakers are angled correctly, it should still be able to maintain a focused center image when moving away from the center.

While we're talking...

There has been much talk about point sources being the optimal type of speaker. It sounds good in theory, but it has a major flaw and that is listening distance. The closer you are, the smaller the image. I'll give you a real life example. I have a recording of Peter Paul and Mary which uses a great deal of hard left and right. In certain songs, Peter is singing directly out of one speaker and Paul is singing out the other. The surface area of my Quads is a great deal larger that what I use now and when I play those tracks, the image of the voices appear much larger on the Quads than on my present system. My present system has a relatively smaller point source on the horizontal plane than the Quads. Hence, while the image height is about the same between the two speakers, image width is much broader on the Quads. I imagine that if I could sit further from my present speakers, this might change. I prefer the Quads on that CD. One of the selling points of the Quads is that it is a point source, but at a perspective of sitting further from the point source. I'm not being clear here, but hopefully you will understand.

The reason I mention this is because the Maggies tend to create a broader/taller image across the screen compared to using a smaller speaker. If I were to use smaller point source speakers for the center, the image would be more focused into a point on the center of the screen. As it is, the image is about the size of my screen. I don't know if that's better, but I like it.

The other thing, and as a electrostat aficionado you should know, is that most box speakers sound like boxes. You and I can hear the boxes, but people who don't listen to dipoles can't hear it. To me, it's in your face. That doesn't mean that dipoles are the better than box speakers. They both have their strengths.

I've heard some great speakers in my days, Quads, Martin Logan, Theil, Avalon, Wilson, and too many others to mention. Even my Phase linear's (dipole) from the 70's were impressive in their clarity. The one thing in common with all great speakers is that the first thing I noticed was the music in all its grandeur and delicacy. The speakers and electronics became invisible until the song ended.

Thanks for your thoughts, it helps me think and understand. Keep in mind that I'm not always right. As I said in a previous post, "the more I learn, the less I know."

[Feanor]

...
Two speakers reproducing the same signals introduces dispersion pattern interference that is not very good for dialog clarity.

...
I don't understand the implications of this for stereo. Of course we know that the central image in a stereo sound stage consists of the same sound coming from both left and right speakers. Isn't there dispersiona pattern interference in this case? But subjectively the central image -- singer, solo instrument -- sounds pretty good.

[E-Stat]

If you look at the specs, they are identical.
FR and efficiency, yes. Size and panel configuration, however, are different which most likely yields a slightly different radiation pattern.

rw

[StevenSurprenant]

Although amp will not have trouble driving the load, but by connecting speakers in series, it does change the electronic characteristic of speakers.

Sonce most amp's speaker out have constant 20 rail volts, by having two speaker in series, the rail voltage cross each speaker will drop to 10 v. Or if three way, the rail voltage cross each speaker will drop to 6.5 volts. So a speaker that have 20 volts cross it will sound different (since its electronic specification has change) than the one that have 10 volts or 6.5 volts cross it. So you are basically "starving" your speakers.

I tried two speakers in series, and notice that not only it pretty much kill speakers bass responce, it made them sound lifeless. Sounded like cheap car speakers :)

Good points!

My electronics knowledge is very limited, but I sort of know what you are saying. As a corollary of what you have said, does that imply that by running speakers in parallel at 4 ohms , the speakers should sound even better? I'm not being facetious, I really don't know. If I were to guess, I would think that, in parallel, there would be 20 volts across both speakers and the amp would just double the current output with no change in sound, except for the 3 db increase by having two speakers instead of one. It does make sense that more impedance means less current, but if we were speaking about the amount power needed for a certain db output, this could be attained by increasing the voltage to the output transistor gate. Ahhh... I understand now... By wiring three speakers in series, the maximum power across any one speaker would be P = V squared / R.

As an example... P = 20 volts squared/5 ohms = 80 watts for a single speaker, but in series... P = (20/3)squared / 5 ohms = 8 watts per speaker. Does that sound correct?

Now considering my speakers... They are rated down to 100 Hz at which point I assume the impedance increases, so power is not wasted below that point. I have the speakers set to small and the crossover set to 200 on them so that I have 8 watts of electrical power available to drive each speaker from 200Hz to 16kHz. Besides that, by running three speakers, each additional speaker adds a 3db increase in acoustic power for a 6db increase.

In total, I have 8 watts of electrical power available but the 6db acoustic output gained by using 2 additional speakers gives me the equivalent acoustic power of 32 watts. In other words, I would get the same output running one speaker at a maximum of 32 watts. Does this make sense? This reduces the acoustic output by about 4db compared to running a single speaker at 80 watts. Since my speaker efficiency is 88db this limits the maximum output to about 106db in a tri-speaker configuration. I'm not sure that my speaker can put out that amount of sound pressure. So, in the practical sense, I'm good to go.

Does this make any sense to you?

Thank you.

[StevenSurprenant]

FR and efficiency, yes. Size and panel configuration, however, are different which most likely yields a slightly different radiation pattern.

rw

You are correct. Being a planer and that it sits horizontally, the vertical radiation pattern is greatly reduced. In the horizontal plane, the radiation pattern is much broader, but it still sounds slightly different than the flat panels.

[Sir Terrence the Terrible]

Who is it who made such a claim? What I did was observe that your sweeping statement (completely independent of the OP's question) that there is NO difference in horizontal dispersion between point source speakers and dipolar panel line sources is most certainly not a correct assertion.

Majoring in minors a little Ralph. A mistake on a side issue does not change one thing. The OP idea is a bad idea, and there is enough science on the issue to support what I have stated.



You seem to be caught in a negative feedback loop. While your point has been restated, you have returned to post #11 - to which I responded in advance in post #10. Let's review the facts:

1. Optimum center channel speaker arrangement is uniquely found in the cinema environment employing vertical symmetry of the three front channels.
2. Most HT arrangements don't allow for what is known to be ideal.

Pick your own poison by determining which parameter you choose to optimize over another.

rw

1. You do not have to position your center speaker like the cinema environment to be considered optimal for HT. We have already discussed this ad nauseum previously. THX has already found that we are allowed 12" of vertical offset before panning images is disturbed by the offset. A center speaker can be placed under the set as long as it does not violate that rule. So you don't have to choose one over the other.

[Sir Terrence the Terrible]

I don't understand the implications of this for stereo. Of course we know that the central image in a stereo sound stage consists of the same sound coming from both left and right speakers. Isn't there dispersiona pattern interference in this case? But subjectively the central image -- singer, solo instrument -- sounds pretty good.

You are correct, there is wave interference with the mono signal. However, we equalize the heck out of that mono signal to give it the clarity and stability it has.

[StevenSurprenant]

You are correct, there is wave interference with the mono signal. However, we equalize the heck out of that mono signal to give it the clarity and stability it has.

Just curious...

Wouldn't it make more sense to correct the phase problem rather than equalize it? It seems to me that when two signals are 180 degrees out of phase that no amount of equalization can compensate for that. Where the phase angle is less than 180 degrees, equalization can have some benefit, but still changes the original waveform to be other than what it was and is more of a reflection of what the recording engineer thinks it should sound like.

[Sir Terrence the Terrible]

This is more directed at "Sir" ...

As you are fully aware of, dipole, line arrays, dipole line arrays, box speakers, Multi-driver speakers and about every configuration has its inherent flaws and wave patterns. Throw in different room dimensions and reflecting surfaces, cross talk to both ears from the left and right speakers and you have this incredibly complex wave pattern that is hitting our ears from every direction. It's a wonder that we can hear anything coherent.

On top of all of this you want to muddy the sound further with a dual center setup?


"Sir"... Wave interference, combing, lobing, room reflections, speaker directivity, wave patterns from point sources versus line arrays, dipole, bipole, direct radiating speakers, and time alignment is all audio 101. Everyone who has followed this hobby knows this stuff. The only thing that is in contention is the audibility of these affects.

The audiblity of these effects have been demonstrated with measurements correlated to what we hear.


Heck, if I wanted to take it too an extreme, I would build a wall between my speakers right up to my face to prevent the right and left speaker from reaching the wrong ear (cross talk). Even though this cross talk has a large effect on soundstaging and more minor effects on wave interference, it is not worth the effort or concern to address.

Oh brother.......(rolls eyes).


As for the integration of my speakers, the distances are set, the volumes are set, and I can't tell where one speaker starts and another begins. This is all good and well, but if you want to be critical, the moment that you move out of the sweet spot, all these setting go out of wack. This occurs on your system and mine. The point is that you are being too critical here.

How was the volume set? I'll ask this again, did you use a SPL meter with pink noise? With 3 speakers across the front, the sweet spot is quite large. It is certainly wider than my couch, so sitting out of the sweet spot is not really possible. This pretty much goes for all of my systems even if they use theater seating and multiple rows of seats.


As for my center channel, where this all began, I've had it above the TV, below the TV, out in the room, and up against the wall. I've sat closer and further away and it sounds like the sound is coming from it and not the screen. You seem to be telling me to live with it, but I have a choice to do other wise.


Then you are doing SOMTHING wrong here. I have ten HT/multichannel music system of which only three have the speakers behind the screen. Not one of the other seven exhibit this characteristic. I go to my friends house to watch movies in his hometheater with the center speaker just below the screen, no disassociation of the sound from the screen. When I am mixing soundtracks for DVD and Bluray on a system with the center speaker just below the projection screen, no disassociation of the sound from the screen. THX recommends placing its THX speakers either below or above the screen, and even with its limited vertical coverage, they don't exhibit what you speak of. I can go to each of the 25 sound editing rooms with their center speaker under a flat panel monitor at the studio I work at, and not one of them disassociates the sound from the picture like you mention.

Something is wrong with this picture, and it has nothing to do with a single center speaker sitting under or over the set.



While I'm at it, I'll tell you one more thing, which I have no doubt that you already know. Frequencies above about 40 Hz are directional and there is no way to hide where the speaker is. You can't make a single speaker sound like it is coming from the screen, but the effect can be reduced by increasing the distance between you and the screen/speaker. That is the only way except for placing the speaker behind the screen or using multiple speakers.

Correction, that would be 80hz and up, not 40hz. You really are making stuff up here. I have 7 personal examples that you are completely wrong. THX standards for HT say you are wrong, 25 sound editing rooms say you are wrong on this.

I have never heard anyone saying that using a single center speaker causes a auditory discontinuity from the picture around the net. You are the first person making this claim.


I'm not even sure we are arguing the same point. If speaker articulation (clarity) is your point, then you have nothing to worry about. Clarity of sound has always been my goal since I've gotten into this hobby. I've had Quad electrostats, Magnepan, and more, and built present speakers for my 2 channel system using some of the best components money can buy. I can hear a gnat land on a dogs back with either of my systems. I've also listened to some of the best systems available. Still, I can find fault with any system I've owned and listened to.

Wow..you can hear a gnat land on a dogs back. A little hyperbole on steriod perhaps?


Two more things...

My system ( I suppose all) brings the image out into the room as you mentioned that theaters do. regardless of the mechanics, having a deep soundstage behind the speakers is what makes home audio better, it that regard, than a theater. My stereo speakers are about 3 feet from the back wall, but it routinely images 20 feet or more back depending on the source music. My Magnepan speakers are mounted "on the wall" and I still get a very deep soundstage. The imagining is not as precise as my stereo, but I would have to guess that the soundstage is almost as deep. Yet, I do agree that the back wall effects this soundstage.

The front soundstage of a movie theater is basically a dead zone. The speakers are built into baffles that surpress rearward reflections. That combined with the fact there is acoustical treatment behind the screen as well, there is no way a movie theater can replicate the artificial "reflections" that we get in the home.

About lifting the center speaker. It has set directly on top of the TV and almost touching the bottom of the screen with the same results. The eye/ear thingy doesn't work for me. I should mention that my speakers are dipole and long, like line arrays, hence floor bounce is less of an issue. Besides, they only go down to about 100Hz. [/quote]

Have you tried aiming the speaker towards the listening position whether it is above or below the screen?


Let me ask you a question... Have you ever tried using two speakers for the center channel? Be honest.

I have never personally tried it, but I have heard a setup that used dual center speakers. I hated the diffusiveness it imparted on dialog. Yes it had more depth than a single speaker, but that is not what we hear in the dubbing stage where soundtracks are created. It is not what we hear when the individual stems are assembled. There is no where in the process that we hear a diffusive dialog except when the dialog is process that way artistically.


I appreciate your thoughts and I know you are trying to help. However, I'm with E-STAT on this issue.

The more I learn, the less I know....

Then both of you are wrong on this one. Sorry..

[Sir Terrence the Terrible]

Just curious...

Wouldn't it make more sense to correct the phase problem rather than equalize it? It seems to me that when two signals are 180 degrees out of phase that no amount of equalization can compensate for that. Where the phase angle is less than 180 degrees, equalization can have some benefit, but still changes the original waveform to be other than what it was and is more of a reflection of what the recording engineer thinks it should sound like.

Wave interference does not require the signals be 180 degrees out of phase. It is the interaction of the two in phase signals that cause this effect.

Any spaced speaker system reproducing a mono signal is going to have a notch between 2-4khz because of the distance between our ears. We equalize mono vocals spread between the two speakers to minimize the effects of notching, and give that spread mono signal more stability.

[E-Stat]

The OP idea is a bad idea, and there is enough science on the issue to support what I have stated.
Choose you own compromise. And if you want to bring science into the discussion, next time use examples of the kind of speaker used!


1. You do not have to position your center speaker like the cinema environment to be considered optimal for HT. We have already discussed this ad nauseum previously.
Indeed. Why is it that you want to discuss preferences again? Apparently you cannot hear what he and I do. Fine. Let it go!

rw

[Smokey]

You might be surprised how many speakers use series wired components. Aren't you one of the Roger Russell disciples? You do realize that his IDS speaker is wired thusly, right?

Don't know who Roger Russel is :)

If speaker have series wired components, then its specification is designed to have 20 volt rail cross whole combined resisitance to have optimum sound. That would be different from combining two speakers that have optimum sound that was designed to have 20 volts cross each speakers.


As a corollary of what you have said, does that imply that by running speakers in parallel at 4 ohms , the speakers should sound even better? I'm not being facetious, I really don't know. If I were to guess, I would think that, in parallel, there would be 20 volts across both speakers and the amp would just double the current output with no change in sound, except for the 3 db increase by having two speakers instead of one.

That would be true if amp can handle excessive double current. But most amp can't which mean with excessive current also come excessive distortion. I rather have one speaker with less distortion than two with added distortion. There is old saying in electronic that "there is no free lunch". Which you have to give up something (distortion) to gain something else (volume).


As an example... P = 20 volts squared/5 ohms = 80 watts for a single speaker, but in series... P = (20/3)squared / 5 ohms = 8 watts per speaker. Does that sound correct?

Now considering my speakers... They are rated down to 100 Hz at which point I assume the impedance increases, so power is not wasted below that point. I have the speakers set to small and the crossover set to 200 on them so that I have 8 watts of electrical power available to drive each speaker from 200Hz to 16kHz. Besides that, by running three speakers, each additional speaker adds a 3db increase in acoustic power for a 6db increase.

The formula is correct, but I am not sure adding more speakrs that have the same volume neccesary equal to added 3 db acoustice power since the loudness have not changed. I could be wrong here though so may be somebody else can chime in on this.


In total, I have 8 watts of electrical power available but the 6db acoustic output gained by using 2 additional speakers gives me the equivalent acoustic power of 32 watts. In other words, I would get the same output running one speaker at a maximum of 32 watts. Does this make sense?

I don't think that is correct. Since each speaker will have the same volume, adding more speakers with same volume does not equal "linear" added acoustic. Just like having a table fan in a room with 40 db acoustic noise. By adding more table fan to room, the noise level will not increase 3 db per fan since the noise level has not change.

For example, if you add 10 more fans to room, the noise level will increase slightly, but not 3 db per fan (or the noise level in a room with 10 table fans will make you go deaf :D). I hope you see the relation.

[E-Stat]

Don't know who Roger Russel is :)
You haven't missed anything worthwhile.


I could be wrong here though so may be somebody else can chime in on this.
You are mistaken. I get a similar +6db gain from using double New Advents. Half of the acoustic gain comes from using doubles. The other half comes from the Threshold's added power. Which is not even breathing hard driving that load.

rw

[StevenSurprenant]

That would be true if amp can handle excessive double current. But most amp can't which mean with excessive current also come excessive distortion. I rather have one speaker with less distortion than two with added distortion. There is old saying in electronic that "there is no free lunch". Which you have to give up something (distortion) to gain something else (volume).


I checked my amp specs and it supplies approximately 50% more power each time the impedance is halved which is a far cry from doubling. I realize that distortion increases with power output but as long as its below audibility, would it really matter? I only say this because at the volume I play music, I've never had too little power. At present, I use a Trends TA 10.1 digital amp on my stereo which puts out about 6 clean watts. That is more power than I need for the speakers I use and the room it's in. I built my own speakers so I'm guessing that they are about 91db efficient, at least that's what the tweeter is rated at and I don't have it padded down.


The formula is correct, but I am not sure adding more speakrs that have the same volume necessarily equal to added 3 db acoustice power since the loudness have not changed. I could be wrong here though so may be somebody else can chime in on this.

I don't think that is correct. Since each speaker will have the same volume, adding more speakers with same volume does not equal "linear" added acoustic. Just like having a table fan in a room with 40 db acoustic noise. By adding more table fan to room, the noise level will not increase 3 db per fan since the noise level has not change.

For example, if you add 10 more fans to room, the noise level will increase slightly, but not 3 db per fan (or the noise level in a room with 10 table fans will make you go deaf :D). I hope you see the relation

As I said, my knowledge is limited and I went by what I've heard repeated many times, especially on the speaker building sites. BTW, When I first built my speakers, I was using two SEAS drivers per box and a Newform ribbon, but I was also bi-amping through a digital crossover and so level matching speakers elements was a none issue. However, when I went to passive crossovers, two drivers would overpower the tweeter so I reduced it to one per box which sounds about right. I suppose the point here is that two drivers compared to one really does increase acoustic output. This correlates to what I've read. I didn't measure the increase, so I don't know if the suggested 3db increase is accurate. BTW, the SEAS woofers were wired in parallel.

Again, thanks for your help.

[StevenSurprenant]

Wave interference does not require the signals be 180 degrees out of phase. It is the interaction of the two in phase signals that cause this effect.

Any spaced speaker system reproducing a mono signal is going to have a notch between 2-4khz because of the distance between our ears. We equalize mono vocals spread between the two speakers to minimize the effects of notching, and give that spread mono signal more stability.

If I understand this correctly, the mono signal from, let's say the left speaker hits the left ear, travels across the face, which is about the width of the wave length at 2-4khz, and strikes the right ear. This is repeated with the right speaker. Now each ear has received information that was meant for the opposite ear which has the effect of blurring the image. (I apologize for approaching this in such a simplistic manner, but for me, this is a learning process and I have to crawl before I walk.) What you do is add information to each speaker to cancel out the cross talk across the face. Does this sound right? I didn't know that recording engineers payed any attention to this.

It's similar to what Carvers "Sonic Hologram" did and more recently, what Edgar Choueiri is doing at Princeton University.

3D3A Lab at Princeton University (http://www.princeton.edu/3D3A/index.html)

In my previous post I mentioned putting a wall in the middle of my face to eliminate cross talk, (to which you replied, "Oh brother"). I wasn't kidding, well sort of, but after reading about Choueiri's work I tried using a block of sound absorption to test this idea and yes, it did make a difference. What I discovered was that image quality improved, not enough to sit there with a block of foam strapped to my head, but the improvement was readily apparent.

Perhaps his technology would be superior to the method you use?

[StevenSurprenant]

Except for perhaps 2 systems I have heard, stereos sound like stereos and cannot be mistaken for the real thing. We constantly bicker over an inferior technology like it's a true representation of what we experience in real life. If we were both blindfolded, I doubt that you or I could be fooled into thinking that either of our systems was the real thing. Blind folded, there would be no question that we were listening to a stereo or surround system. So whats the point?

Your system is probably better than mine in almost every way, but it still sounds like a stereo/surround system.

I've heard systems that were so detailed that you could place X's on the floor, both left or right and back, where everyone was standing during the recording, how tall they were, and how far apart they were standing from the performer next to them. In a sense, it was was the closest I have been to true virtual reality. This quality is rare and what most of us listen to is HiFi in comparison. Strangely, many people don't want this level of perfection. They want that warm fuzzy sound that tubes offer or the less distinct and spacious sound that dipoles offer.

Even with all you knowledge and all the money you've spent on your system, I seriously doubt that your system approaches reality. It probably sounds like a very good surround system according to how someone else decided it should sound.

This reminds me of Mr. Bose's discovery. When he first set off to create his company he tested different speakers, some attempting accuracy and others that were anything but accurate. What he discovered was that people preferred the sound that he now offers. Surround is the same way. Someone gave the people what they wanted, not accuracy, but excitement.

In effect, surround systems are anything but accurate. For instance, the center channel that we've been discussing is an abomination. Ninety percent of the time, the sound is coming directly from the middle of the screen. If there are two people talking, left and right, we hear a mono signal in the middle. It's only when, for instance, a door opens far left or right, that we hear any directional clues to what we see on the screen during dialogs. Of course we hear the full stereo spread when there are things like space battles going on. Three center channels across make more sense to me. That way, they can be positioned across the width of the screen and create a stereo effect that is maintained within the screen dimensions. Of course, info could be added to the front speakers to create this same effect, but then that would somewhat negate the use of a center channel.

I could go on and on about the inferiority of audio systems relative to reality, but you are in this niche where you think there is only one way to do things. All your theories are correct, well most of them, but you are missing the most important part. People have different preferences. You like box speakers and horns, I don't because boxes sound like boxes and horns are irritating. I hear the boxes because I am used to dipoles. To me, that is very distracting. There are some box speakers that do a pretty good job of getting rid of the box sound, but most don't. Most horns are harsh and lack delicacy. That is my preference, but that doesn't mean that everyone should like what I do. I like dipole bass. To me, it is the best quality bass that can be had, but it can't compete with the loudness and dynamics of a box speaker.

It's odd, sometimes when I am watching a movie and things are banging and clanging, and shaking, I am truly enjoying myself, but then a thunderstorm comes along outside and I sit in awe how wonderful it sounds. It makes me realize how confined and boxy my subwoofer sounds and how small my surround system sounds. Even a movie theater pales in comparison.

I have told you in the past that by using three speakers that the dialog is clearer, but you have insisted, in so my words, that I am lying to you. Why would I do that? You insist that interference patterns from the speakers reduce the intelligibility of the audio, without even hearing it. You don't take into consideration that I am using dipole planers, or that my room is much smaller than what you are used to, and you have no idea if reflections have been tamed in my room. You know nothing about my setup and yet you insist that using 3 speakers is one of the worse things I could do. In all probability there is some truth in what you say, but the overall effect might just outweigh the negatives. You don't know.

I learned a lesson many years ago. I used to play chess constantly and as a result I got very good. I never lost. However, one day after winning, my opponent challenged me to a game of checkers. I thought, what the heck, it's much simpler than chess, so I should be able to beat him. Well... I lost every game.

The point is that you should stick with what you know and what you have experience with.

I've been down a similar road concerning the Trends TA 10.1 digital amp I use for my stereo. Some critics ran it through its paces and tested it with every piece of test equipment they could get their hands on and in the end, they declare it awful. On the other hand, most reviewers compared it with amps and used it with speakers that most of us cannot afford and in the end, everyone of them declared this amp astounding and was only bettered by true high end equipment. They liked it very much.

The point is that you could take it apart, test the heck out of it and declare it junk, or... you could just listen.

Ohh.. About that gnat landing on a dogs back... I might have exaggerated a little.

"Something is wrong with this picture, and it has nothing to do with a single center speaker sitting under or over the set. "

Why would I not hear the speaker above or below the screen where it really is? How is it that you don't? Even you said the frequencies over 80hz are directional.

I'll ask you one more question and then I'll let it drop...

We, the public, talk amoungst ourselves about movies and music, and we every once in a while, we mention how good a sound track a certain movie or CD has. Even more often, we complain about it. Most of the time, we say nothing because it's adequate.

Why is it that only a few recording studios produce quality recordings? What do they do different?

[Sir Terrence the Terrible]

If I understand this correctly, the mono signal from, let's say the left speaker hits the left ear, travels across the face, which is about the width of the wave length at 2-4khz, and strikes the right ear. This is repeated with the right speaker. Now each ear has received information that was meant for the opposite ear which has the effect of blurring the image. (I apologize for approaching this in such a simplistic manner, but for me, this is a learning process and I have to crawl before I walk.) What you do is add information to each speaker to cancel out the cross talk across the face. Does this sound right? I didn't know that recording engineers payed any attention to this.

It's similar to what Carvers "Sonic Hologram" did and more recently, what Edgar Choueiri is doing at Princeton University.

3D3A Lab at Princeton University (http://www.princeton.edu/3D3A/index.html)

No not quite. When we are monitoring the mix, we are constantly listening to what happens to the sound as various tracks get mixed in. Bass instruments mixed down the middle are nothing to worry about, but when you get to instruments or voices nearing 1K, you have to start using EQ to prevent the voices from sounding hollow as a result of the notch. We don't try to fill in the notch, it would just make it worse. We just try to minimize its audible effect.


In my previous post I mentioned putting a wall in the middle of my face to eliminate cross talk, (to which you replied, "Oh brother"). I wasn't kidding, well sort of, but after reading about Choueiri's work I tried using a block of sound absorption to test this idea and yes, it did make a difference. What I discovered was that image quality improved, not enough to sit there with a block of foam strapped to my head, but the improvement was readily apparent.

Perhaps his technology would be superior to the method you use?

He is addressing the playback side, and I am addressing the recording mixing side. You are referring to interaural crosstalk on the playback side, and that can be eliminated or at least lessened by including a center speaker for mono signals.

[Sir Terrence the Terrible]

Choose you own compromise. And if you want to bring science into the discussion, next time use examples of the kind of speaker used!

It really does not matter what speaker is used, the penalty is exactly the same. That's science as well!



Indeed. Why is it that you want to discuss preferences again? Apparently you cannot hear what he and I do. Fine. Let it go!

rw

Personally, I don't really care about what you and him do, its not even relevant. No matter what speaker technology is deployed, the effect is exactly the same. Perhaps you need to follow your own advice.

[Smokey]

E-Stat and StevenSurprenant,

I found the formula for how much acoustic power (db) changes with added source that have the same volume. It is rather interesting.

Formulas: Δ L = 10 × log n where
Δ L = level difference; n = number of equal loud sound sources.

If we have two sources of the same volume, the loudness acoustic gain is 3 db. But if we have three sources of same volume, the acoustic gain is only 4.8 db. And if we have four, the acoustic gain is 6.0. Here is table:

(Number of n equal loud sound sources) = (Level increase Δ L in dB)

1 0 = 0 db
2 = 3.0 db
3 = 4.8 db
4 = 6.0 db
5 = 7.0 db
6 = 7.8 db
7 = 8.5 db
8 = 9.0 db
9 = 9.5 db
10 = 10.0 db
12 = 10.8 db
16 = 12.0 db
20 = 13.0 db

As you can see, as we add more sources of equal volume, the changes in acoustic power changes less and less :)

[Smokey]

I At present, I use a Trends TA 10.1 digital amp on my stereo which puts out about 6 clean watts. That is more power than I need for the speakers I use and the room it's in. I built my own speakers so I'm guessing that they are about 91db efficient, at least that's what the tweeter is rated at and I don't have it padded down.

No matter how sensetive your speakers are, 6 watts of power is definitely not enough. Alot of poeple associate more power with more loudness which is not true because amp also have to have dynamic headroom which can go well above 100 watts.

If you don't have dynamic headroom to take of music spikes, the result would be excessive distortion better know as Total Harmonic Distortion (THD). That is why low power amps always have high THD :)

[E-Stat]

As you can see, as we add more sources of equal volume, the changes in acoustic power changes less and less :)
The other variable, however, is the frequent increase of amplifier power driving lower impedance. In my case, the wattage doubles with the halving of impedance providing the cumulative +6db effect.

I first discovered these two factors in high school back in '74 when I drove my first pair of double Advents with a Crown D-150. Its power also doubled into half the impedance load. Which worked great in the high school gym for the Miss RHS Pageant where they were used as the sound system for the talent. :)

rw

[E-Stat]

That is why low power amps always have high THD :)
Ridiculous. Low powered First Watt amplifiers most certainly do not have high THD even with zero NFB.

rw

[StevenSurprenant]

E-Stat and StevenSurprenant,

I found the formula for how much acoustic power (db) changes with added source that have the same volume. It is rather interesting.

Formulas: Δ L = 10 × log n where
Δ L = level difference; n = number of equal loud sound sources.

If we have two sources of the same volume, the loudness acoustic gain is 3 db. But if we have three sources of same volume, the acoustic gain is only 4.8 db. And if we have four, the acoustic gain is 6.0. Here is table:

(Number of n equal loud sound sources) = (Level increase Δ L in dB)

1 0 = 0 db
2 = 3.0 db
3 = 4.8 db
4 = 6.0 db
5 = 7.0 db
6 = 7.8 db
7 = 8.5 db
8 = 9.0 db
9 = 9.5 db
10 = 10.0 db
12 = 10.8 db
16 = 12.0 db
20 = 13.0 db

As you can see, as we add more sources of equal volume, the changes in acoustic power changes less and less :)

That's good to know and very interesting. Thank you!

[StevenSurprenant]

No matter how sensetive your speakers are, 6 watts of power is definitely not enough. Alot of poeple associate more power with more loudness which is not true because amp also have to have dynamic headroom which can go well above 100 watts.

If you don't have dynamic headroom to take of music spikes, the result would be excessive distortion better know as Total Harmonic Distortion (THD). That is why low power amps always have high THD :)

I understand what you're saying and it's true, but keep in mind that it depends on how loud a person listens. I designed my system for ultra clarity, at least that was my goal, and so I can listen at very low levels and still hear everything. Also, the system is in a very small room which also allows me to reduce the volume. I know this doesn't mean much, but I normally run my volume control at 1/4 of the max. I tried the system in a larger room and there wasn't enough power.

When I had my Quads I was pushing them with a Mark Levinson 331 which was rated at 130 watts per channel. Of course, power wasn't a problem, but personally, I think the Trends TA sounds much better. The last time I said that, the guy got mad at me and told me, in so many words, that I was out of my mind. I don't think the ML was the correct choice for my speakers, that's all. I think the Pass Labs Aleph 3 at 30 watts would have been a better choice.

I remember many years ago listening to a ML system driving Wilson Watt/Puppies and thought to myself that it was decent, but then I found another store driving the same speakers with a Pass Labs amp similar to the Aleph 3 except it put out 45 watts. The difference was astounding. Comparatively speaking, the ML system sound flat like wall paper. ML products are great, but system matching is always a must. Anyway, the sound stage with the Pass Labs was so defined that I could have walked between the performers on the stage. I remember seeing (actually hearing) the drummer placed way back in the room on the right. This was the first time (only time) that I thought that there was too much separation between instruments and performers. It was surreal. The space between the performers was as defined as the performers themselves.

I suppose that what I'm trying to say is that more power is always good, but there are some things that transcend pure power.

The soundstage I get is nowhere near what I heard at that store, but it has a certain magic. I would go for a bigger amp, but I would not trade off the sound quality. There are better amps, but at what price?

Read this...

6moons audio reviews: Trends Audio TA-10 (http://www.6moons.com/audioreviews/trends/ta10_3.html)

Also

TA-10 Modifications (http://www.michael.mardis.com/trendamp/mods-1.htm)

I've supplied a graph of the output power just in case you're interested. No need to click on the links if you're not. I would guess that the Trends amp would be similar to the Super-T on the graph.

[StevenSurprenant]

The other variable, however, is the frequent increase of amplifier power driving lower impedance. In my case, the wattage doubles with the halving of impedance providing the cumulative +6db effect.

I first discovered these two factors in high school back in '74 when I drove my first pair of double Advents with a Crown D-150. Its power also doubled into half the impedance load. Which worked great in the high school gym for the Miss RHS Pageant where they were used as the sound system for the talent. :)

rw

Nothing is ever simple, is it? Makes a person think! Arghhh...

[StevenSurprenant]

No not quite. When we are monitoring the mix, we are constantly listening to what happens to the sound as various tracks get mixed in. Bass instruments mixed down the middle are nothing to worry about, but when you get to instruments or voices nearing 1K, you have to start using EQ to prevent the voices from sounding hollow as a result of the notch. We don't try to fill in the notch, it would just make it worse. We just try to minimize its audible effect.

He is addressing the playback side, and I am addressing the recording mixing side. You are referring to interaural crosstalk on the playback side, and that can be eliminated or at least lessened by including a center speaker for mono signals.

I guess that I don't get it. It seems that we are talking about the same thing, yet somehow, it's different. I understand how the same signal reaching across the face causes a loss of imaging, but I don't quite understand what causes the notch.

The only way I can understand this is to think that the left signal reaching the right ear is out of phase with the sound from the right speaker and when the two signals combine they create peaks and troughs, hence, distorting the sound. If I understand it correctly, what we hear is a softening (less distinct) of the sound .

Just thinking...

What's different that you do compared to Choueiri is that you ( I assume) equalize both channels at the same time whereas, Choueiri actually adds information to each opposite channel to cancel the cross talk.

It seems that Choueiri's method would better solve the problem except for one thing, his method is highly dependent on listening position since there is a timing/amplitude factor involved in when the signals reach the ears and moving away from that "sweet spot" ruins that timing/amplitude.

You method is a compromise that maintains a more even response regardless of the listening position.

Am I beginning to understand you?

Thanks

[Smokey]

The other variable, however, is the frequent increase of amplifier power driving lower impedance. In my case, the wattage doubles with the halving of impedance providing the cumulative +6db effect.

But where did extra 3 db came from?

If we halv the impedance (add another speaker in parallel), wouldn't double power be needed to keep same volume as when there was only one speaker. Also remember that relation between power output and acoustic power out is not linear as for every 3 db increase in loudness require doubling the power.

For example if a speaker that is connected to 25 watt amp put out 80 db loudness, then to have:

83 loudness = 50 watts
86 db loudness = 100 watts
89 db loudness = 200 watts
92 db loudness = 400 watts


Ridiculous. Low powered First Watt amplifiers most certainly do not have high THD even with zero NFB.

I went to their web site to look at First Watt amplifiers specifications. If you look at their amp's THD, you will see that %THD are only for 1 watt output. I would like to know what is THD for full power output. I bet it does not look pretty :)


I understand what you're saying and it's true, but keep in mind that it depends on how loud a person listens. I designed my system for ultra clarity, at least that was my goal, and so I can listen at very low levels and still hear everything. Also, the system is in a very small room which also allows me to reduce the volume. I know this doesn't mean much, but I normally run my volume control at 1/4 of the max.

I mentioned before that alot of poeple associate loudness with power :D

Loudness and power are not directy related. Even 1 watt of power can make a speaker pretty loud. The extra power is not for loudness, but rather for cleanly reproducing transient peaks. Check out this web site that explain it better. I quote the most important part:

"It is obvious from the example above that adequate amplifier power is necessary to provide an accurate portrayal of music. This is especially true when attempting to reproduce realistic levels, or when driving inefficient speakers. However, even small efficient speakers may require copious amounts of power to cleanly reproduce transient peaks. In the final analysis, it is difficult to have too much power. While a small amplifier of only a few watts output can produce surprising average loudness, the dynamic peaks will usually suffer."

The Relationship of Voltage, Loudness, Power and Decibels (http://www.gcaudio.com/resources/howtos/voltageloudness.html)

[E-Stat]

But where did extra 3 db came from?
3 db from acoustic gain. 3 db from a doubling of power. If you had a transformer driven amplifier whose output was consistent, then you would get 3 db from merely doubling the speakers. Additionally, you are now running twice the power to double the speakers.


If we halv the impedance (add another speaker in parallel), wouldn't double power be needed to keep same volume as when there was only one speaker.
Nope. Re-read you own source!

"If we have two sources of the same volume, the loudness acoustic gain is 3 db."

Before the Sound Labs, I used Acoustat 2+2s which had four panels per speaker. There was also a 1+1 which used the exact same transformer for driving half the number of panels. While there were different taps to the bass transformer to optimize the frequency response, the 2+2 was twice as efficient having double the panel area. 400 watts into a double pair of Advents has 3db more output than 400 watts into a single pair.


Also remember that relation between power output and acoustic power out is not linear as for every 3 db increase in loudness require doubling the power.
Or having two sources with the same power! You still don't get it?


I went to their web site to look at First Watt amplifiers specifications. If you look at their amp's THD, you will see that %THD are only for 1 watt output.
You didn't look very far. Try again. (http://firstwatt.com/f2j.html)



I would like to know what is THD for full power output. I bet it does not look pretty :)
And you would be wrong. Again.


The extra power is not for loudness,
At least you are consistently wrong. I assure you that the measurable levels I get at 400 watts is much higher than for 4 watts. You can teach me nothing in this regard. I know exactly the difference between what the Stasis output is at 0 db and at -20 db.

rw

[StevenSurprenant]

[QUOTE=Smokey;368846
I mentioned before that alot of poeple associate loudness with power :D

Loudness and power are not directy related. Even 1 watt of power can make a speaker pretty loud. The extra power is not for loudness, but rather for cleanly reproducing transient peaks. Check out this web site that explain it better. I quote the most important part:

"It is obvious from the example above that adequate amplifier power is necessary to provide an accurate portrayal of music. This is especially true when attempting to reproduce realistic levels, or when driving inefficient speakers. However, even small efficient speakers may require copious amounts of power to cleanly reproduce transient peaks. In the final analysis, it is difficult to have too much power. While a small amplifier of only a few watts output can produce surprising average loudness, the dynamic peaks will usually suffer."

The Relationship of Voltage, Loudness, Power and Decibels (http://www.gcaudio.com/resources/howtos/voltageloudness.html)[/QUOTE]


I understand fully and have two examples to prove your point...

A long time ago, before man roamed the Earth, a friend had speakers that had peak indicators on them (little lights that would light up when the power reached the maximum that the speakers were rated at)...(cool huh!). I'm not sure what the limits were that would trigger these lights, but I assume it was over 100 watts.

His amp also had meters (VU) on it. So one day, he was cranking it for the enjoyment of himself and his neighbors and the lights on his speakers were flashing, but when he looked at his power meters on his amp, it was only showing about 30 watts. He was confused and so I explained the difference between continuous power and peak power and that the speaker lights were indicating peak power while the amp was showing continuous power.

Thinking in round numbers, let;s assume that his amp was putting out 120 watts peak and 30 watts continuous. This is a headroom of 6db (30/60/120). According the the article that you posted, this is a 4 times increase in power and only 50% increase in loudness.

Here is a link to relative loudnesses that I will use as a reference (I assume these numbers are representative of continuous power). Sound levels (dB) and relative loudness of typical noise sources in indoor and outdoor environments. (http://www.rcaanews.org/noiselev.htm)

Using the numbers for "Moderately loud - Living room music" , it shows 76db. Since my speakers are 91db efficient. This means it takes about 1/5 of a watt to drive my speakers to this volume (76db). Since my amp is about 6 watts, this makes my maximum volume about 97db at 4 watts. We'll just toss the last 2 watts out since it won't add any appreciable loudness. This gives me a headroom from 76db to 97db of 21db. Also, the peak of 97db is almost equal (according the the link I sent) to a "Bell J-2A helicopter at 100 ft . . . 100 dB"

That seems pretty respectable, don't you think? From these numbers, it seems, to me, that 6 watts is enough to create decent music. Of course, if I turn up the volume, the amount of relative headroom shrinks.

If you think it will only play a low volumes, you couldn't be more mistaken. Have you ever watched the movie "Lost in Space"? It begins with a space battle where the good guys are fighting the Genteks over a space gate they are constructing. I play that movie at a realistic volume. Even a movie theater doesn't get much louder.

Of course, listening distance and room size figure into all of this and believe me, it is minimal. Out of necessity, my stereo is in a small room. It's a funny thing, I was going to give up on this audio thing because I didn't have a suitable room to set it up in, but as it turned out, I couldn't be more pleased.

The other story (much shorter) is that in the 70's I owned a pair of Phase Linear dipole speakers and a receiver rated at 80 watts. The speakers were rated at (if I remember correctly) 350 watts. While I loved the clarity of these speakers I also loved the dynamics and loudness that my friends box speakers put out. So, one day cranked my speakers as loud as I could to see if I could get them to sound like my friends speakers. Well I couldn't (it's the nature of dipole), but in the process, I blew out one of my drivers. I was surprised since my speakers were rated to take much more power. That's when I learned that too little power was worse than too much.

However, and I'm not sure about this, at 6 watts which is way below what my present speakers can handle, I don't think I could blow a speaker even if I ran my amp into full clipping for a prolonged period of time. I'm not going to test this!

Anyway, thanks again. I really enjoy being forced to think about things.

[Sir Terrence the Terrible]

I guess that I don't get it. It seems that we are talking about the same thing, yet somehow, it's different. I understand how the same signal reaching across the face causes a loss of imaging, but I don't quite understand what causes the notch.

We are talking the same thing, but at different points in the recording/mixing/playback chain. The cause of the notch is something called the interaural time delay, or the time it takes for the signal to wrap around the head, and get to the opposite ear. That delay causes the notch.


The only way I can understand this is to think that the left signal reaching the right ear is out of phase with the sound from the right speaker and when the two signals combine they create peaks and troughs, hence, distorting the sound. If I understand it correctly, what we hear is a softening (less distinct) of the sound .

Actually it is not out of phase, but in phase and delayed. You have a signal from the left speaker hitting the left ear, and a delayed signal(interaural time delay) left speaker signal hitting the right ear. That is what causes the notch, not a flip in phase.


Just thinking...

What's different that you do compared to Choueiri is that you ( I assume) equalize both channels at the same time whereas, Choueiri actually adds information to each opposite channel to cancel the cross talk.

So you understand what we are doing in the studio. When vocals are recorded, they are on a single mono track. When we mixed them into a stereo configuration, we split that mono track between two channels equally. This causes the vocals to lose about 3db of power in the mix, so we restore that power back by bringing up the vocals by that same amount. As a result of that split, vocals will take on a diffusive quality because of the HRT effect we discussed above. We equalize to get rid of that "fuzziness" on our side of the audio chain. When you play that same track on your speakers, the effect crops up again, but is somewhat lessened because of what we have done on the mixing side.

What Choueiri is doing is trying to eliminate the effect of HRT effects on the playback side, and his idea is really quite old. Bop Carver was doing this very same thing with his sonic holography circuit, and Polk was doing this with his SDA towers in the 80's.


It seems that Choueiri's method would better solve the problem except for one thing, his method is highly dependent on listening position since there is a timing/amplitude factor involved in when the signals reach the ears and moving away from that "sweet spot" ruins that timing/amplitude.

You method is a compromise that maintains a more even response regardless of the listening position.

Am I beginning to understand you?

Thanks

Actually we are doing the same thing, but on different sides of the recording and playback chain. We do it only to vocals and instruments mixed from mono sources into a stereo configuration. He is trying to correct the effect in a broadband way on the playback side.

[E-Stat]

Since my speakers are 91db efficient. This means it takes about 1/5 of a watt to drive my speakers to this volume (76db). Since my amp is about 6 watts, this makes my maximum volume about 97db at 4 watts.
Another difference with line sources like Maggies is their output drops in a linear fashion with a doubling of distance as opposed to a logarithmic drop of point sources (3 db vs. 6 db). Most efficiency specs are stated at a distance of 3 feet or 1 meter. At 6 feet, therefore, output would be 94 db, and at 12 feet, 91 db. A point source would have dropped to 85 db at that distance!

I leverage the 6 db gain from doubling Advents in the garage in a similar quality vs. quantity manner. I usually listen in the mid 80 db level where the amp is indicating -20 db output or 4 watts (yes, an '81 Stasis has peak reading output ladders). What that means is the class A voltage amp is providing all the output where the sound is marginally better with improved focus and a softer top than when running at higher levels where the AB current mirror is also contributing. The only time I've used the full output is at Halloween. For the past two years, my closest neighbors have thrown an outdoor party for their teenaged daughter. I've taken the system over to what used to be a tennis court. It will cleanly crank Rihanna in the mid 90s at some distance when the amp is wide open at 400 watts. Last year, doing so for three continuous hours destroyed the woofer surrounds on the older pair necessitating a re-foaming job. :)

Halloween (http://home.cablelynx.com/~rhw/audio/halloween2.jpg)

rw

[Feanor]

3 db from acoustic gain. 3 db from a doubling of power. If you had a transformer driven amplifier whose output was consistent, then you would get 3 db from merely doubling the speakers. Additionally, you are now running twice the power to double the speakers.
...

"If we have two sources of the same volume, the loudness acoustic gain is 3 db."

Before the Sound Labs, I used Acoustat 2+2s which had four panels per speaker. There was also a 1+1 which used the exact same transformer for driving half the number of panels. While there were different taps to the bass transformer to optimize the frequency response, the 2+2 was twice as efficient having double the panel area. 400 watts into a double pair of Advents has 3db more output than 400 watts into a single pair.
...
rw
I know I don't understand "acoustic gain", but I'd like to. It almost seems like you're getting something for nothing in terms of energy. Do you have a reference that I could read & understand, (bearing in mind the my science/engineering background is weak).

[StevenSurprenant]

Actually we are doing the same thing, but on different sides of the recording and playback chain. We do it only to vocals and instruments mixed from mono sources into a stereo configuration. He is trying to correct the effect in a broadband way on the playback side.

Thanks for taking the time to help me through that. It's a simple concept, but when you're as thick headed as I am, sometimes it takes time to sink in.

[E-Stat]

Do you have a reference that I could read & understand, (bearing in mind the my science/engineering background is weak).
There are tons of them around. Here's (http://yu-ra.tripod.com/array.htm)one that graphically depicts the table which Smokey posted back on page 2. What actually improves is the overall sensitivity from the added cone or diaphragm area. Professional sound reinforcement makes broad use of this concept.

rw

[Feanor]

There are tons of them around. Here's (http://yu-ra.tripod.com/array.htm)one that graphically depicts the table which Smokey posted back on page 2. What actually improves is the overall sensitivity from the added cone or diaphragm area. Professional sound reinforcement makes broad use of this concept.

rw
Thanks for that. :smile5:

[StevenSurprenant]

I'm humbled!

I was scrolling through the posts and It just occurred to me that everyone that replied to my initial posting pretty much represented the backbone of this site.

Sir Terrence the Terrible - 5,841 posts
E-Stat - 4,672 posts
bobsticks - 6,647 posts
Smokey - 2,724 posts
Feanor - 5.965 posts

And then there's me at - 170 posts

I'm almost embarrassed...

All I can say is thank "you all" for helping me and opening my mind to new ideas. The saying that I am fond of repeating,' The more I learn, the less I know", truly applies here. At times I got a little defensive and I apologize for that, but understand that I listened to everything you folks said and I discounted nothing. You guys are truly great people. Thanks.

[Smokey]

However, and I'm not sure about this, at 6 watts which is way below what my present speakers can handle, I don't think I could blow a speaker even if I ran my amp into full clipping for a prolonged period of time. I'm not going to test this!

With lower power amps, you probably would not damage midrange or woofer, but you might put tweeter at risk if prolong clipping occurs. The problem is a clipped waveform (squarewave) will have much more higher frequency energy than its sinewave equivalent due to squarwave having more [high frequecny] harmonics.

So a tweeter will dissipate more power and heat from clipped wave than a non clipped sinewave.



Would like to know what is THD for full power output. I bet it does not look pretty.

And you would be wrong. Again.

FIRST WATT F2J (http://firstwatt.com/f2j.html)

I am wrong if you consider 1% THD an acceptable number for distortion. As you can see from the chart, F2 amp reaches 1% THD at 1 watt, and F2J amp reaches 1% distortion at full power output (5 Watts). 1% THD in audio world is totaly unacceptable :)

Beside I don't know why you are advocating low power amps since your self recently bought a 300 watts amp, and said that having more headroom delivered more weight and far more clarity to the presentation(post #5):

http://forums.audioreview.com/home-theater-video/just-joined-emo-tribe-36632.html


At least you are consistently wrong. I assure you that the measurable levels I get at 400 watts is much higher than for 4 watts. You can teach me nothing in this regard. I know exactly the difference between what the Stasis output is at 0 db and at -20 db.

Ofcourse there will be level differenec between 4watts and 400watts, or 4 watts and 40 watts for that matter. But most typical HT setups uses between 1 to 20 watts (RMS) of their amp and rest of power are reserve for music peaks. That is why I said [extra] power is not for loudness.

[E-Stat]

I am wrong if you consider 1% THD an acceptable number for distortion...1% THD in audio world is totaly unacceptable :)
I refer you to the last time we (and Pix) had this discussion exactly a year ago. Neither he nor you backed your assertions with demonstrable proof via the online test which I had taken. My position was stated in posts 28,32,38,64, and 81 with Pix. You entered the discussion and my responses at 90,93 and 100 cover those.

Here's (http://forums.audioreview.com/home-theater-video/my-stuff-35240.html)the thread. It was worth the review.


Beside I don't know why you are advocating low power amps since your self recently bought a 300 watts amp, and said that having more headroom delivered more weight and far more clarity to the presentation(post #5):
Sorry, but I guess I don't respond very well to those who make unqualified grandiose declarations which are not supported by fact. As for me, I've never owned a low power amp because my choice of speakers has always dictated differently. You would get consistent disagreement among horn speaker enthusiasts who are very similar with the sort. BTW, the XPA-5's output is 200 watts into 8 ohms.

rw

[StevenSurprenant]

Beside I don't know why you are advocating low power amps...

Of course there will be level differenec between 4watts and 400watts, or 4 watts and 40 watts for that matter. But most typical HT setups uses between 1 to 20 watts (RMS) of their amp and rest of power are reserve for music peaks. That is why I said [extra] power is not for loudness.

You made your point clear and I think everyone agrees, but I've had people tell me that 1,000 watts isn't enough power for those peaks. So how much is enough?

There is a reason why many people use low power amps. In many cases, they just sound better. Advocates of low power amps claim that there is more information reaching their ears and they usually attribute this to fewer gain stages. That was Nelson Pass's selling point of his Aleph 3 amp (30 watts). I listened to his amps from that era and from what I heard, he might be right.

I've listened to a butt load of amps and speakers and for the most part, the larger amps seemed to lack the micro detail of the smaller amps. This isn't a set rule. Besides, many claim that the larger amps have more control over their drivers, i.e. tighter bass.

The other thing is that many people advocate tube amps, not so much for their warm sound, but because of they claim that they create a more 3 dimensional sound stage as compared to solid state. I don't know if I can agree. The most defined sound stages I have heard were created with ss amps, notably Pass Labs and Spectral gear. Even a Linn system I heard did a pretty good job of fleshing out a decent sound stage. I have also heard tube amps that did a pretty good job too.

More power might mean that you will have ultimately louder dynamics, but dynamics is only part of the picture. As long as we keep our peaks below the distortion point, it should sound good. That's another issue (distortion). Back in the 70's my amp was rated at .3% distortion at rated output. A number of amps came out that were using a great deal of feedback to their drive transistors resulting with distortion figures of .0001% or some sort of low number. Spec wise, these things looked great on paper, but they sounded anemic.

The other thing is people with low power amps realize the limits of their system. They would never play Tchaikovsky's 1812 Overture at realistic volumes. I doubt that there are many systems that could do that.

Anyway, you are correct that peak power is important, but as long as you limit the speaker volume to the level of available peak power, there isn't an issue. If I took my speakers outside, like E-STAT did with his Advents, and drove my amp to full power, I doubt that I could disturb my neighbors. However, inside my smallish room and sitting 7 feet away from them, they are very loud.

This is all way over my head. All I know is that 6 watts is enough to play my system as loud as I want it to go without detecting any distortion.

My surround system, which has 130 watts per channel, gets played just as loud and I have yet to detect any distortion or compression from either system.

Besides, if I needed more volume I could bi-amp the system using a line level crossover (I've done this - same power - twice as many amps) or I could use a sub and limit the amount of bass going to the main speakers, or use multiple drivers as we spoke about earlier... or all the above!

You're making my head spin... Stop it!

[Feanor]

I enjoyed your reflections here, Steven.

People have different needs and different preferences -- two dimensions that we need to keep in mind whenever we give or receive advice.

My system, see under my signature, is the most satisfying that I've owned and, fortuitously, also the cheapest in a long, long time. However it conforms to my taste and needs, not necessarily to anyone else's.


My requirements and tastes:

I enjoy the soundstage of the dipolar planar speakers
I listen at only moderate volumes
I don't require the "pounding" bass that some sorts of music demand
I prefer maximum resolution and transparency (vs. warm, harmonic richness)
I'm poor and can only affort a modest outlay.

[bobsticks]

I'm humbled!..stuff.

Steve, personally, I would turn that sentiment around on you. I suspect we're all just glad to have you as part of the community and I respect the fact that amidst this thread there have been a variety of conflictory opinions and theories expressed with a modicum of civil comportment.

A theory that I've always held is that "system synergy" and "the room" are just as, if not more important, than equipment. Yes, there are hard and fast rules to set ups and good kit is good kit and numbers are numbers, results being what they are...but take the best piece of gear and throw it in an unbalanced system and a rotten room and see what the results are.

Ultimately, I appreciate the way that you've raised some questions and expressed some opinions. That's how I started; that's how I learned. I suspect the others would say the same...

That's how we all learn.

[StevenSurprenant]

I know I don't understand "acoustic gain", but I'd like to.

It almost seems like you're getting - "something for nothing"- in terms of energy.

I think this is what Smokey has been alluding to all along... He has been telling us just that... You don't get something for nothing which makes perfect sense.

A perfect amp will double the current (and power) each time you halve the impedance. You can see this in the amps spec sheets. So, two 8 ohm speakers in parallel will consume twice as much power, but each speaker (separately) in this configuration will maintain the same acoustic output as if only one speaker were being used. Together, they will be 3db louder. That seems perfectly logical. All this happens without touching the volume knob.

Referring to the pages supplied by Smokey and E-Stat which show the acoustic power of multiple drivers... I think it is a little misleading and can be interpreted incorrectly (at least I did, at first).

This is important...The one point they don't seem to make is that everything is in reference to each (single) speaker outputting the same db in every case, irrespective to the amount of input power for the total system. In the real world, when we start adding more speakers, we start configuring them in series and parallel circuits to maintain an impedance that the amp can deal with.

For two speakers... If we wire them in parallel, the impedance drops, the current increase and the acoustic output doubles. Nice! If we wire them in series, the impedance doubles, the current to each speaker gets cut in half (is divided between both speakers), and the acoustic output goes down 3db for each speaker, but together, they have the acoustic output of a single speaker at the initial power, there is no net gain.

Someone correct me if I'm wrong.

For four speakers and in any situation where we double the number of speakers beyond that, we run into a different situation which seems to make the charts we are referencing above seem incorrect. If we have two speakers and we double them to four, assuming they are all 8 ohm, we need to wire then into two groups of series circuits (16 ohm) and then wire those groups into parallel with each other, which brings the total impedance that the amp sees to 8 ohms. I'm sure everyone understands.

This is where it gets sticky...

Without changing the input power, (combined) the 2 speakers that we wired in series only have the same acoustic power a single speaker driven at that power. Makes sense... Double the impedance -> half the current. Adding the second set of series wired speakers in parallel (without changing the input power) with the first pair, will bring the system impedance down to 8 ohms and the current/power to them will double. Combined they will have the same acoustic output as only 2 speakers in parallel..


In a nutshell, without changing the initial power from the amp, wiring two speakers in series will double the impedance and the total power will be divided between both speakers. The acoustic output of each speaker will decrease by 3db, but together they will gain that 3db back and play the same loudness as one speaker driven at the same power. Adding another set of these series wired speakers in parallel will halve the impedance and each set will play just as loudly as they did separately because the amps current will double. Together, they will play 3db louder than either group of series wired speakers. Now that should be clear as mud.

Let me repeat the most important part of this rumination. The charts that we were linked to are valid if every speaker is outputting the same acoustic power. This can only be accomplished with multiple amps, or if we wire the speakers in parallel and the amp can deliver the current needed at the lower impedances. Once we start wiring the speakers in series, the chart becomes invalid. I'm sure I don't need to explain it to you guys.

That pretty much balances the equation. If we get an acoustic increase from multiple speakers, it's because we've increased the total power. This means that we don't get something for nothing.

It seems so simple now. I know I repeated myself several times, but sometimes it helps in understanding to word it differently.

There is one after thought...

If your amp doesn't double the power into 4 ohms and you have a speaker with a tweeter at 8 ohms and a woofer (or series of woofers) at 4 ohms, the speaker will sound different than had you used a perfect amp which doubles the current at 4 ohms. In effect, the woofer/s would be at a lower volume (less current) with the lesser amp and cause the speakers to sound brighter.

Just thinking....

[Feanor]

The article linked by E-Stat asserts the fact of "accoustic gain" and links it to the area of the transducer. I'll admit I didn't understand how this wasn't "getting something for nothing", but I read the item only once so maybe it just when by a little too quickly.

The article does also discuss the issues of multiple drivers which I guess are mainly "lobing", i.e.effect of different phase of sound waves arriving at the listener from drivers being at different distances.

[E-Stat]

The article linked by E-Stat asserts the fact of "accoustic gain" and links it to the area of the transducer. I'll admit I didn't understand how this wasn't "getting something for nothing", but I read the item only once so maybe it just when by a little too quickly.
The answer is mutual coupling. You may be aware of the retired engineer over at AA who is a big Advent proponent. I've had the good fortune of visiting him during a business trip. Here (http://db.audioasylum.com/mhtml/m.html?forum=vintage&n=63149) is his explanation. It is true that such is not a consistent 6 db gain across all frequencies.

rw

[StevenSurprenant]

The answer is mutual coupling. You may be aware of the retired engineer over at AA who is a big Advent proponent. I've had the good fortune of visiting him during a business trip. Here (http://db.audioasylum.com/mhtml/m.html?forum=vintage&n=63149) is his explanation. It is true that such is not a consistent 6 db gain across all frequencies.

rw

Okay, I guess that I'll have to rethink this. Ohhh my head hurts!

I'll put my idea of electrical power aside and just think of it in terms of acoustic power.

Since this effect occurs mostly at certain frequencies and that the frequencies that this occurs at is dependent on how far apart the woofers are placed from each other, I might assume that this gain is a result of the waveforms at those frequencies being in phase with each other, hence additive in nature.

Is this closer to the idea?

[E-Stat]

I'll put my idea of electrical power aside and just think of it in terms of acoustic power...Is this closer to the idea?
I don't profess to fully understand the theory - just to apply it!

rw

[StevenSurprenant]

I don't profess to fully understand the theory - just to apply it!

rw

I understand....

Actually I was thinking of some applications for this. For instance, I thought of rebuilding my speaker boxes using the extra mid bass drivers I have in a 2.5 configuration. Since my speakers only go down to about 55Hz at -3db, I thought about adding a second woofer and crossing it over at such a point that it would bring that -3db point up to 0db and extend the bass down a little further. Anyway, this subject complicates things a bit, but it creates the possibility to increase the bass a total of 6db and could, in theory, allow me an even lower output. I'm just thinking, that's all.

Thanks again.

[Feanor]

The answer is mutual coupling. You may be aware of the retired engineer over at AA who is a big Advent proponent. I've had the good fortune of visiting him during a business trip. Here (http://db.audioasylum.com/mhtml/m.html?forum=vintage&n=63149) is his explanation. It is true that such is not a consistent 6 db gain across all frequencies.

rw
BTW I've heard of mutual coupling in another context. Thanks for that link re. stacked Advents.

I have the Big Box Pro and X-Over Pro programs for speaker crossover and cabinet designs. There they allude to mutual couple. X-Over Pro asserts that the mutual coupling will only occur where identical drivers are located within 1/8 wave length of each other. I.e. coupling is frequency dependant.

At one time I made a chart of Frequency > 1/8 wavelength:

<TABLE style="WIDTH: 121pt; BORDER-COLLAPSE: collapse" border=0 cellSpacing=0 cellPadding=0 width=161><COLGROUP><COL style="WIDTH: 73pt; mso-width-source: userset; mso-width-alt: 3441" width=97><COL style="WIDTH: 48pt" width=64><TBODY><TR style="HEIGHT: 26.4pt" height=35><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; WIDTH: 73pt; HEIGHT: 26.4pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl63 height=35 width=97>Frequency Hz</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; WIDTH: 48pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl66 width=64>1/8 wave, inches</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>20</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>84.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>40</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>42.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>80</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>21.2</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>160</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>10.6</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>200</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>8.5</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>300</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>5.7</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>400</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>4.2</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>500</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>3.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>600</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>2.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>700</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>2.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>800</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>2.1</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.7</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1200</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1350</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.3</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1500</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.1</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1800</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.9</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2200</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2400</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.7</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2700</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.6</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>3000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.6</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>4000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>5000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.3</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>6000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.3</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>7000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.2</TD></TR></TBODY></TABLE>

So according to this it's quite practical to couple a pair of 7" mid/bass drivers below about 250 Hz but not much above. But it looks fairly impractical to couple 1.25" tweeters in typical 4" mounts at any relevant frequency.

[StevenSurprenant]

BTW I've heard of mutual coupling in another context. Thanks for that link re. stacked Advents.

I have the Big Box Pro and X-Over Pro programs for speaker crossover and cabinet designs. There they allude to mutual couple. X-Over Pro asserts that the mutual coupling will only occur where identical drivers are located within 1/8 wave length of each other. I.e. coupling is frequency dependant.

At one time I made a chart of Frequency > 1/8 wavelength:

<TABLE style="WIDTH: 121pt; BORDER-COLLAPSE: collapse" border=0 cellSpacing=0 cellPadding=0 width=161><COLGROUP><COL style="WIDTH: 73pt; mso-width-source: userset; mso-width-alt: 3441" width=97><COL style="WIDTH: 48pt" width=64><TBODY><TR style="HEIGHT: 26.4pt" height=35><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; WIDTH: 73pt; HEIGHT: 26.4pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl63 height=35 width=97>Frequency Hz</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; WIDTH: 48pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl66 width=64>1/8 wave, inches</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>20</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>84.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>40</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>42.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>80</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>21.2</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>160</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>10.6</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>200</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>8.5</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>300</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>5.7</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>400</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>4.2</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>500</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>3.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>600</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>2.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>700</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>2.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>800</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>2.1</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.7</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1200</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1350</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.3</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1500</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>1.1</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>1800</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.9</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2200</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.8</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2400</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.7</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>2700</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.6</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>3000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.6</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>4000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.4</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>5000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.3</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>6000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.3</TD></TR><TR style="HEIGHT: 13.2pt" height=18><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; HEIGHT: 13.2pt; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" height=18 align=right>7000</TD><TD style="BORDER-BOTTOM: #f0f0f0; BORDER-LEFT: #f0f0f0; BACKGROUND-COLOR: transparent; BORDER-TOP: #f0f0f0; BORDER-RIGHT: #f0f0f0" class=xl64 align=right>0.2</TD></TR></TBODY></TABLE>

So according to this it's quite practical to couple a pair of 7" mid/bass drivers below about 250 Hz but not much above. But it looks fairly impractical to couple 1.25" tweeters in typical 4" mounts at any relevant frequency.

Those numbers look very good for what I was thinking of. I was thinking about crossing over close to 200hz, that's where the curve begins to drop. The 8.5 inches distance is doable. but I'd have to make the boxes very deep.

BTW, how do you like the software you are using?

Thanks.

[Feanor]

Those numbers look very good for what I was thinking of. I was thinking about crossing over close to 200hz, that's where the curve begins to drop. The 8.5 inches distance is doable. but I'd have to make the boxes very deep.

BTW, how do you like the software you are using?

Thanks.
I have Bass Box Pro and X-Over Pro from Harris Tech, see HERE (http://www.ht-audio.com/pages/Products.html). They are easy to use and have great user interface; also they come with and extensive database of driver specifications.

A couple of shortcomings are that they cannot take into account driver relative offsets, nor will they optimized values for a given topology, (although they will calculate the results of manually changed component values).

http://gallery.audioreview.com/data/audio//500/X-overPro_example.jpg