Dual Center Channel...

[Dual-500]

Brad,
You may have convinced yourself it sounds good, but this really is a bad practice and I don't care how well it is done. Either you are hearing the effect of frequency combining, or you are hearing the tweeters cancelling, but there is no way this kind of setup is even close to flat. If you drop two rocks side by side in a pond, and watch the waves come together, that is what your set up is doing. When those waves meet, depending on the wavelength and frequency, they will either be is phase and boost the output at those frequencies, or they will be out of phase and cancel some frequencies. Either way this venture veers away from a flat frequency response, and depending on where you sit in the room, you will hear different tonalities and timbres coming from this setup.

Not recommended at all.

I'm genuinely interested, please tell me a little more about "Flat" frequency response please.

How is it achieved in any given environment? (let's limit discussion to HT envirnoments) Let's consider it in terms of "Dynamic System Performance" (not static anechoic chamber performance) which will include the environment. i.e. system excitation + environment = performance.

With consideration given to near field, far field, reverberent field and overall system levels.

How to eq the system? Do we even use electronic level correction basee upon room acoustic performance? If so, how to do it? A SPL meter? RTA? Where to place mic(s) and so on. What SPL to use during correction tuning.

Or simplify matters and install a pair of whatevers that perform "flat" in the lab, use no eq correction and call it a day?

What kind of system and under what conditions will reproduce audio without changes based upon listener location in the room?

Isn't this happening in the typical room all the time anyway? Isn't the enviroment more dynamic than static?

I maintain the OP is hearing the net result of an environment responding acoustically to excitation provided from a reproduction system. How do we make that "Flat" over the dymanics of theatre within the audible range of frequencies?

[luvtolisten]

http://www.falstad.com/ripple/[/url]

When the applet comes up, click on one source and look at the wave pattern. Now click on two sources, and see that wave pattern. The first has a nice clean wave, and the second with two sources shows considerable interference in the wave patterns. This is what is happen with you two center setup.

http://www.falstad.com/ripple/

But if you click "ADD BORDERS" (or walls) for one source and 2 sources all bets are off. The theory make hold up if you had no walls, but in a real environment, there is little difference between one source or 2 source wave patterns.

[Dual-500]

http://www.falstad.com/ripple/

But if you click "ADD BORDERS" (or walls) for one source and 2 sources all bets are off. The theory make hold up if you had no walls, but in a real environment, there is little difference between one source or 2 source wave patterns.

That's right.

And in the listening environment what reaches the ears = source + environment.

The environment being a variable based upon the excitation it's receiving at any given point in time. The environment will respond to frequency and intensity in different ways. The environment will respond to complex passages with numerous frequencies present differently than to a less complex waveform.

Ultimately, we can utilize treatments for the environment, location of system and electronic response corrections (equalization) to end up with the final product which is always the sum total of source + environment.

Flat Frequency responce when speaking in terms of the total system simply cannot be effectively achieved.

Even if we installed a system that had near field and gain performance to completely control the room - true flat response would only exist in the test or setup of the system at whatever set points were chosen for the tuning. Change any of that and all bets are off. Add to that the dynamic nature of the signals the system will reproduce.

Translation, flat frequency response in a listening environment COULD be achieved but only under static conditions - i.e. a given stimulus signal and given intensity. Change either and the system (environment + source) performance will also change and no longer be "Flat".

With proper test equipment and equalization, a room could be tuned flat. Flat with test tones or pink noise. Depending upon the available maximum system gain, it may perform flat going between the two. In practical application that would be essentially impossible to achieve however.

Music and Theatre are dynamic in nature and not static. Tuning a system (source + environment) for HT applications ultimately is a compromise between many factors. The end result being, when it sounds best to the tuner.

[pixelthis]

That's right.

And in the listening environment what reaches the ears = source + environment.

The environment being a variable based upon the excitation it's receiving at any given point in time. The environment will respond to frequency and intensity in different ways. The environment will respond to complex passages with numerous frequencies present differently than to a less complex waveform.

Ultimately, we can utilize treatments for the environment, location of system and electronic response corrections (equalization) to end up with the final product which is always the sum total of source + environment.

Flat Frequency responce when speaking in terms of the total system simply cannot be effectively achieved.

Even if we installed a system that had near field and gain performance to completely control the room - true flat response would only exist in the test or setup of the system at whatever set points were chosen for the tuning. Change any of that and all bets are off. Add to that the dynamic nature of the signals the system will reproduce.

Translation, flat frequency response in a listening environment COULD be achieved but only under static conditions - i.e. a given stimulus signal and given intensity. Change either and the system (environment + source) performance will also change and no longer be "Flat".

With proper test equipment and equalization, a room could be tuned flat. Flat with test tones or pink noise. Depending upon the available maximum system gain, it may perform flat going between the two. In practical application that would be essentially impossible to achieve however.

Music and Theatre are dynamic in nature and not static. Tuning a system (source + environment) for HT applications ultimately is a compromise between many factors. The end result being, when it sounds best to the tuner.

Nope, when its accurate.
I HAVE HEARD some "good" systems, after fixing they were GREAT systems.
And we are talking about active centers, not passive mikes, different thang.
And no, you cant get a room flat, there will always be compromises in HT, sure, but
why shoot yourself in the foot from the get-go? YOU HAVE ENOUGH PROBLEMS
without creating new ones.
THE LEVELS of the different channels are not that critical in PROLXII , for example,
but a lot more so in DD. About 10 years or so ago I broke down and got a sound meter.
THE DIFFERENCE was amazing, really.
JUST because something is "decent" doesnt mean its enough.

[Dual-500]

Nope, when its accurate.
I HAVE HEARD some "good" systems, after fixing they were GREAT systems.
And we are talking about active centers, not passive mikes, different thang.
And no, you cant get a room flat, there will always be compromises in HT, sure, but
why shoot yourself in the foot from the get-go? YOU HAVE ENOUGH PROBLEMS
without creating new ones.
THE LEVELS of the different channels are not that critical in PROLXII , for example,
but a lot more so in DD. About 10 years or so ago I broke down and got a sound meter.
THE DIFFERENCE was amazing, really.
JUST because something is "decent" doesnt mean its enough.

Accurate? Another term that gets misused.

I haven't heard a definition for "Flat Response" yet. You and I agree, a room can't be made to be flat. Good starting point.

Accurate? Yes, we strive for accurate. But, like "Flat Response" it ain't happening. Accurate is goal, not a destination. We get as close as possible to accurate.

Take a given room and test 10 different system/installations in it and what do you have? 10 different sets of results. They can all be tweaked towards "Accurate" and all 10 setups sound good. But all 10 will be inherently different.

Take one "Decent" system and setup/install in 10 different rooms and once again, even after tweaking, the net result is different in each room.

That's my simple point. The OP in this thread made a change that to him sounds good. It get's criticized and shot down as not being "Flat Response" or "Accurate" and that's not the case. Factors are not being taken into consideration. The listening environment plays a role in the end result. That role varies from room to room, some more than others. It's simply not a constant that can be conveniently ignored or disregarded when discussing net results.

The only point in the naysayer discussion was driver interaciton at the source and resultant comb effects. The room wasn't even in the equation, and the room is probably the big player here.

Shoot your self in the foot? Negative. There are times when nearfield radiation increases will net better sound regardless of resultant side effects derived from comb interaction. I didn't say EVERY time, I said sometimes. No ABSOLUTES here.

I doubt anyone on this thread would argue that if the components from the dual center channels loudspeakers were package into an integrated unit in such a way as to reduce comb effects from optimum driver placement that the result would not likely be inproved. However, that in and of itself doesn't negate the potential that what he did resulted in an improvement.

I submit the results the OP is getting using 2 -vs- 1 center channel speakers is an improvement just as he says it is. The increase in near field radiation could be improving upon overall environmental acoustic conditions (reverberant field control) that the side effect of comb interaciton is negated.

Thanks for the input - good discussion.

[Sir Terrence the Terrible]

http://www.falstad.com/ripple/

But if you click "ADD BORDERS" (or walls) for one source and 2 sources all bets are off. The theory make hold up if you had no walls, but in a real environment, there is little difference between one source or 2 source wave patterns.

You need to look again, and pay attention to the first few seconds of the reflection pattern. The 2 sources with borders filled the room with reflections far quicker than the single source, and they had a much more complex interaction far more quickly than the single source. The first wave of the single sources had smooth perfect half arch until it hit a border, the 2 source had waves colliding very quickly, which created a complex interaction within the first few seconds of the launch of the wave.

[Sir Terrence the Terrible]

Accurate? Another term that gets misused.

It gets misused because it takes work to achieve it, and few have really tried.

I haven't heard a definition for "Flat Response" yet. You and I agree, a room can't be made to be flat. Good starting point.

The room can't be flat, but at least the system that goes into it can. With good EQ, proper placement, and room treatments, you can get awful close - close enough for the cigar.

Accurate? Yes, we strive for accurate. But, like "Flat Response" it ain't happening. Accurate is goal, not a destination. We get as close as possible to accurate.

Whether it happens or not depends highly on the skill of the individual(a person well educated in small room acoustics) and interpretation of the measurements obtained from the room. From 200hz downward it all depends on placement, treatments, and EQ. From 200hz up, it is on the shoulders of the equipment itself. Nothing can achieve a ruler flat response, but a well calibrated system/room interaction will certainly remove far more peaks and valleys than a untreated room, or uncalibrated system.

Take a given room and test 10 different system/installations in it and what do you have? 10 different sets of results. They can all be tweaked towards "Accurate" and all 10 setups sound good. But all 10 will be inherently different.

Here you are correct, but this is stating the obvious.

Take one "Decent" system and setup/install in 10 different rooms and once again, even after tweaking, the net result is different in each room.

This all highly depends on the shape of the different rooms, and how the system is placed in it.

This I don't agree with, only because I have actually done it. I had one system of which I set up in one room (14x17x8), tore down and set up in another room (12x15x10). Before tweaking, their response in both rooms(especially above 200hz or so) was pretty darn close, but below 200hz is where I saw the most deviation, and because of where I placed the sub (in the middle of the room against the front wall) and mains (at least three feet from any wall toed in), even below 200hz the response curves for each room were not that far off. Once I tweaked the system for both rooms, the both had almost identical frequency curves.

That's my simple point. The OP in this thread made a change that to him sounds good. It get's criticized and shot down as not being "Flat Response" or "Accurate" and that's not the case.

It got shot down because it is a poor practice not grounded anywhere in home theater, or the theater for that matter. There is a reason why movie theaters only have one center channel, and there is a reason why THX, Dolby, and Dts only recommends a single center channel in home theater environments. There are acoustical principles that support a single channel, and not two center speakers spaced apart.

Factors are not being taken into consideration. The listening environment plays a role in the end result. That role varies from room to room, some more than others. It's simply not a constant that can be conveniently ignored or disregarded when discussing net results.

If you start off on the wrong foot acoustically speaking from the speakers, then the room is not going to change that one bit. The applet demo clearly shows that. Even with no borders, there is considerable acoustical wave interference with two sources playing the same signals. Throw the walls up, and the interference just gets easier to hear.

The only point in the naysayer discussion was driver interaciton at the source and resultant comb effects. The room wasn't even in the equation, and the room is probably the big player here.

If you start off with lobing from the speakers, the room is not going to change that as that is a function of driver interaction. If you start off with comb filtering coming from the speakers, the room will just make it worse. A room does not make a bad set up choice better, it can often make it far worse.

Shoot your self in the foot? Negative. There are times when nearfield radiation increases will net better sound regardless of resultant side effects derived from comb interaction. I didn't say EVERY time, I said sometimes. No ABSOLUTES here.

Rather than creating "grey areas" look at the gentleman's set up. He has two speakers closely packed together recessed in a cavity like environment. He has two tweeters closely packed together which efficiently interact with each other (Proximity Effect) to boost and cancel signals based on their wavelengths. He has two spaced woofers (which we know causes lobing for off axis listeners) set up in a cavity which creates a boundary reinforcement effects and comb filtering. This is all happening even before the first fractured wave (what you get from this kind of set up) hits the wall once. Being in the near field will just make this more audible in the form of more diffusion to the image.

I doubt anyone on this thread would argue that if the components from the dual center channels loudspeakers were package into an integrated unit in such a way as to reduce comb effects from optimum driver placement that the result would not likely be inproved. However, that in and of itself doesn't negate the potential that what he did resulted in an improvement.

I disagree. Have you ever heard of a tapered array, or vertical placement? If you took this same set up, and flipped it vertically, it would change the result dramatically. You would have shifted the lobing of the woofers to the vertical plane, which would(especially if you moved it out of the cavity) result in less interaction with the floor and ceiling, and create a wider horizontal dispersion pattern. If you taper one woofers response going up in frequency, it will not have the destructive driver interference at higher frequencies that an untapered response will have. A piece of foam inserted between the two stacked tweeters will reduce any interaction between them at lower frequencies in the operation range, and eliminated altogether at higher frequencies.

Anyone can say there is an improvement if not just to justify the cost of what they have done. If you do not have a reference to what is really good, then you could justify anything.
I can convince myself a speaker with a poor frequency response sounds good. Bose owners do it everyday.

I submit the results the OP is getting using 2 -vs- 1 center channel speakers is an improvement just as he says it is. The increase in near field radiation could be improving upon overall environmental acoustic conditions (reverberant field control) that the side effect of comb interaciton is negated.

Thanks for the input - good discussion.

He has done nothing to control the reverberant field, that can only be done with room treatments. What he has done in the nearfield is created all kinds of issues that negatively impact the nearfield response as well. You really cannot negate comb filtering unless you remove the source that creates it.

There is a reason that THX, Dolby, and Dts only include one center speaker in their home theater layouts, and why the ITU, AES and SMPTE committees only sanctions the use of a single center speaker. It is for all of the reasons I have mentioned here. You gain nothing with this practice except a more narrow dispersion pattern, lobing, non complimentary driver interaction, poor frequency response, and various other problems. Your attempt to justify this if one understands driver interaction and small room acoustics fails miserably.

IMAX uses two center speakers in their old IMAX configuration. The two center speakers never played together, only one is used at a time for just the reasons I have mentioned. Your driving the ambulance for the OP did not save the patient at all.

[Dual-500]

.......1) Once I tweaked the system for both rooms, the both had almost identical frequency curves.

2) It got shot down because it is a poor practice not grounded anywhere in home theater, or the theater for that matter. There is a reason why movie theaters only have one center channel, and there is a reason why THX, Dolby, and Dts only recommends a single center channel in home theater environments. There are acoustical principles that support a single channel, and not two center speakers spaced apart.

3) He has done nothing to control the reverberant field, that can only be done with room treatments. What he has done in the nearfield is created all kinds of issues that negatively impact the nearfield response as well. You really cannot negate comb filtering unless you remove the source that creates it.

You are obviously intelligent, well spoken and very knowledgeable in audio. Good discussion - thanks for participating and taking the time to do so.

1) Yes, with tweaking one can obtain similar results using test equipment. That's part of my argument here - you didn't state they sounded the same, felt the same, invoked the same experience. You went straight to test gear. I can tune two guitars with test gear and they will sound different being played.

2) Moot point. His system design could be improved upon, I already acknowledged that. Doesn't have any relevance to whether it sounds better or not with dual center channel loudspeakers.

3) Here I disagree. By virtue of adding the second center channel loudspeaker, he has absolutely improved the systems ability to control the reverberant field in the room. A good example is the HS gymnasium. Put one of our HT systems in basketball gymnasium and listen to it. Won't sound so good. Now put a 10kw pro system in it's place and the results are dramatically different even at similar sound pressure levels. Why? Nearfield radiation energy.

Air has mass. As such, standing waves have mass. There is a point when the energy from the source will overcome the standing waves making them essentially null and void. The reason we "Tweak" or "Tune" a room is to compensate for the systems lack of control of the reverberant field.

There are three basic sound field components in a typical listening environment - near field (source), far field (near field + reverberant field) and the reverberant field itself.

Ever been in a stadium or arena where you couldn't understand the announcer or music wasn't clear? Too much echo or slap back. Articulation and consonants lost. We all have. Ever been to a rock show, get there a little late with reserved seats. Walking across the parking lot you can hear the band playing like the building isn't even there? That's when they have a large enough PA system in the house to overcome the reverberant field all together and the near field of the system is expanded beyond the physical boundaries of the building. Little or no eq correction in the house system was needed or applied in such a case.

Both scenarios happen all the time. Most of our HT systems are somewhere in the middle of the two examples above - able to sound good, speech articlation is good, yet not enough power to completely overcome the room reverberant field - hence the use of tuning and treatments.

Take a room, excite the room with a near field of 2" square @ 100 db measured at the source. Let's assume optimum placement of the source in the environment for this example. Now let's expand the near field at the source to 12" square, same measured intensity of 100 db. What happens to it's ability to control room reverberations? Take it up another level - 10' square near field size, same measured intensity of 100 db.

In example 1 the acoustic power generated is 1/60 of that in the 3rd example. Same measured intensity at the source, same inverse square law applies. The 3rd example will contol standing waves much better even at the same SPL. Because of the effective acoustic power radiation. The near field power radiation can be increased (maximum system gain) to the point the reverberant field and far fields dissappear or are nulled out by the near field power radiation.

I attended a USITT seminar in Oakland, CA back in the mid 80's and my perspective for audio systems was changed forever when listening to a lecture on sound design given by a professor from the Yale School of Drama. He began by stating (paraphrased) "When approaching a design, the first thing to do is determine what emotional responses we seek to elicit from the audience, then go about the task of determining how we are going to achieve it".

Never in the discusson did his perspective migrate into specifications, response curves, db meters, sound pressure levels, hardware - these are simply the tools and properties of the trade - the means to an end.

The OP stated his system sounds better - it does. Yet, the chorus seems hell bent on leather to disprove that possibility. He already stated it's a fact.

Not suggesting he couldn't do better with it. But, neither can I definitively state it sounds worse.

The simplicity of design execution of a typical HT setup is something a hobbyist can enjoy. Let him enjoy.

[Mr Peabody]

SteveW, I didn't follow your example. What was the variable in each example? I realize the size but did you change seating or room size, what changed the field? You always remained a 100dB in each example so I don't see how there would be any difference. 100dB in a closet, a room or auditorium is still 100dB. And in an auditorium it would be unlikely to have 100dB at every step from source to wall. If you had 100dB at the source it would drop as the distance increases.

[Dual-500]

SteveW, I didn't follow your example. What was the variable in each example? I realize the size but did you change seating or room size, what changed the field? You always remained a 100dB in each example so I don't see how there would be any difference. 100dB in a closet, a room or auditorium is still 100dB. And in an auditorium it would be unlikely to have 100dB at every step from source to wall. If you had 100dB at the source it would drop as the distance increases.

Thanks for asking.

The concept I'm discussing is acoustic power radiation. That's the variable - acoustic power generated - near field size x intensity x air mass = acoustic energy. Simple db measurements ar only a single point in space. That's the real output of an audio system. It goes beyond what we measure at a single point in space at 1m.

Any given system as max gain which is in essence maximum acoustic power generation capability. This is of course goverened by the usual paramaters we deal with everyday on audio forums. Amp power, impedance, power handling capactiy, bandwidth, directivity and sensitivity. There is one more factor - the size of the near field or acoustic power generated. We are moving air. How much air? Air has mass, more air = more mass = more acoustic power.

We can take a 100w system in a 1000 seat gym and feed music to it and it won't sound too good. Setup the system at 1m with a test tone for max power out. Then inject the music.

Now take a 10kw pro setup, with the same horizontal and vertical "Q" and set to same level @ 1m and then inject the same music at the same level.

I will guarantee you the results will be vastly different. Why? Because the acoustic power generated is greater with the larger system.

That's what the OP did when he added the second center. The acoustic power capability of the system was essentially doubled, the near field size doubled. (let's not haggle about comb effects as they work both ways)

An audio system provides excitation to the environment. Your only considering db measurements and not considering acoustic power.

Again, we can measure your or my HT setup and set it to 100db out at 1m in a 10,000 seat arena. Then take a 50kw concert array and set it to 100db @ 1m in the same arena and at 10', 50' or 100' back, the larger system will sound better and the measured sound pressure will be greater at distance. Because the standing waves will be better controlled by the larger system by virtue of the additional acoustic power that is generated.

Acoustic power generated is what allows for the system to control the environment. The more power, the better the contol.

[Mr Peabody]

So what you are saying is because two center would have four woofer cones moving more air, than two cones would, the field has more energy? If I am understanding this correctly it makes sense and why I find large woofers more accurate in reproducing drums, in a general sense, over smaller woofers. Some speakers with small woofers can play amazingly low but still seems to fall a bit short on the body of a drum tone. Hope I didn't misunderstand and get off on a tangent

[Dual-500]

So what you are saying is because two center would have four woofer cones moving more air, than two cones would, the field has more energy? If I am understanding this correctly it makes sense and why I find large woofers more accurate in reproducing drums, in a general sense, over smaller woofers. Some speakers with small woofers can play amazingly low but still seems to fall a bit short on the body of a drum tone. Hope I didn't misunderstand and get off on a tangent

Yes exactly. In racing, there ain't no substitute for cubic inches. I audio, size matters.

In a reproduction environment we are simply taking an electrical stimulus and converting that into a mechanical stimulus. What we hear is the net result of such.

I'm not suggesting here there would be a hugh difference in his setup or results. Nor, that proper orientation of the drivers would not net an improvement.

Just saying it may sound better - the OP claims it does. So, I'm not inclined to attempt to debunk it using typical hobbyist paradigms.

I'm a hobbyist too nowadays - not bashing.

Hobbyist: Buy speaker x, amplifier y, processing setup of z and install in listening room. A skilled/experienced hobbyist will take said setup and work placement, room treatment and system tuning to arrive at a spot of optimum performance. Typically though, they only tune to one spot in the room.

Professional Sound Designer: Will assess requirements, evaluate environment, then start shaping a course of action. If they are a contractor cost, schedule and other considerations will also be taken into consideration. If working in an institution, there could be other constraints, hardware inventory, rental budget, etc. If it's a fixed install in club or church comes archtectual specs, elevations and renderings. For a touring system another set of variables. For a regional sound contractor it's a lot of pure experience in play. Make optimum use of inventory, while meeting or exceeding customer expectations. Take less gear out an you can send another crew out to handle a smaller job. Get paid twice that day.

There must be an awareness of how much PA is needed - can't use too much, drives prices out of competetive realm, not enough and sound is bad - damage to reputation.

To reinforce for instance a high school graduation ceremony in a big budget high school with large student body that's held in the football stadium with 5-10,000 seats presents unique challanges. Grandstands with infield seating in front and stage beyond that. Front fills, side fills, rear fills, time delay, etc. And it's outdoors. Gotta cover all the seats, not too loud for grandma, but speech intelligibility must be good on the upper deck and in the bleachers going up 50 rows. If it's not, you won't be coming back next year. Truck payment is tough to make when you're not working.

And instutution is about as much fun. Musical theatre in a house for public presentation - been there done that. Wireles mic's on actors, set mic'd up, apron in front of stage mic'd up. Live band behind stage mic'd up. Director demands the house including balcony and under balcony seats sound good - not too loud. And of yeah, the system must be behind scrim flats and unobtrusive - i.e. when the actors are speaking the point source localization is towards them and not a pair of stacks or flying array.

There's a degree of group think and paradigms on this thread that frankly bothers me. Somewhat narrow view of all things audio if you will.

Sometimes, it's good to blow dowm a few walls!

Cheers dude!!!

[PeruvianSkies]

So what if a person decided to connect all the speakers into their receiver in the wrong places and therefore had the surrounds mixed with the fronts and left and right were backwards and various other exchanges, but they claimed that they loved the way it sounded this way and think it is highly recommended?

By this we are saying that everyone has their own version of right and wrong setup and therefore there really isn't any correct or incorrect way of doing HT, which means to each their own and unless we can hear each others systems there is no way of really knowing?

Come on....

I think we are missing some of the fundamentals that go into this hobby and there are proper ways to do various things that each of us have tried in our own ways and logic tells us that we don't have to fall off a skyscraper to know it's a bad idea.

[Sir Terrence the Terrible]

You are obviously intelligent, well spoken and very knowledgeable in audio. Good discussion - thanks for participating and taking the time to do so.

1) Yes, with tweaking one can obtain similar results using test equipment. That's part of my argument here - you didn't state they sounded the same, felt the same, invoked the same experience. You went straight to test gear. I can tune two guitars with test gear and they will sound different being played.

Yes, I go straight to test gear, because it is futile to create an "emotional" system that is suitable for everyone. Everyone's emotions are different, and stimulated differently. What stirs me emotionally may not stir you, so I don't chase after subjective variables, but stick to objective ones tweaked to taste.

2) Moot point. His system design could be improved upon, I already acknowledged that. Doesn't have any relevance to whether it sounds better or not with dual center channel loudspeakers.

Oh, its quite relevant. There is a great body of evidence that does not support the dual center set up, which is why none of these organizations have come out in favor of it.

3) Here I disagree. By virtue of adding the second center channel loudspeaker, he has absolutely improved the systems ability to control the reverberant field in the room. A good example is the HS gymnasium. Put one of our HT systems in basketball gymnasium and listen to it. Won't sound so good. Now put a 10kw pro system in it's place and the results are dramatically different even at similar sound pressure levels. Why? Nearfield radiation energy.

Sorry but you have this all wrong. First, most room in houses are not big enough to even speak about the reverberant field, that is the territory of auditoriums and concert halls where the pathways of reflections(and therefore their Reverberant times)are longer. If we sit close to the speakers as we sit in HT rooms, then the reverberant field is immaterial in the equation, the pathways and reverberant times are a lot shorter. Second you are totally missing dispersion as a component of performance. If he was stacking those two speakers in the vertical plane, the woofers interactions are complimentary on the horizontal plane, and destructive in the vertical plane which equals better radiation energy. This would result in a better frequency response over a very wide horizontal plane, and less interaction with the ceiling and floor. Stacking those same two speakers in the horizontal plane creates destructive interactions in the horizontal plane(lobing) which means an uneven frequency response off axis, a poor off axis speaker performance, which negatively affects both the nearfield, and the reverberant field alike. The floor and the ceiling are fully engaged thereby creating a short reflective path towards the floor, and longer one to the ceiling, and comb filtering between the two. Not good.

Air has mass. As such, standing waves have mass. There is a point when the energy from the source will overcome the standing waves making them essentially null and void. The reason we "Tweak" or "Tune" a room is to compensate for the systems lack of control of the reverberant field.

What you are speaking of does not happen in small rooms, this is a function of a much larger room - a room approaching the size of a theater or large auditorium. Standing waves in smaller room rooms are very audible, and cannot be swamped out unless the listening seat is very close to the speakers themselves. Much of what you are talking about occurs in the very deep bass, far below what is attainable with these dual center speakers.

The reason why we tweak or tune a system has more to do with the interaction of bass waves with the surrounding surfaces. If you try to swamp a standing wave by increasing the volume, you just excite the resonant frequency more. The only way to reduce standing waves is to move the sub out of the high pressure zones within the room(along with the listening seat). That is the only way period.

In larger rooms standing waves are far less audible, as they are much lower in frequency than in small rooms, and often the sources cannot drive them hard enough(stimulate) to make them audible.

There are three basic sound field components in a typical listening environment - near field (source), far field (near field + reverberant field) and the reverberant field itself.

In the typical listening room in homes those components have ratios. The near field accounts for 80-90 percent of what we hear, and we don't sit far enough away from the sources to truly give equality to the reverberant field, the rooms are just too small. These really are larger room principles you are trying to apply to small rooms. I would apply these principles when tuning a movie theater, or dubbing stage, not a HT room. I have done all three.

Ever been in a stadium or arena where you couldn't understand the announcer or music wasn't clear? Too much echo or slap back. Articulation and consonants lost. We all have. Ever been to a rock show, get there a little late with reserved seats. Walking across the parking lot you can hear the band playing like the building isn't even there? That's when they have a large enough PA system in the house to overcome the reverberant field all together and the near field of the system is expanded beyond the physical boundaries of the building. Little or no eq correction in the house system was needed or applied in such a case.

This has nothing to do with small rooms, and you must know this right? This comparison can't even effectively translated into the typical listening room in houses, the rooms are far too small to create this effect. What dogs articulation in small rooms are early arriving reflections combining with later reflections that create diffusion and comb filtering, not long reflections which create echo's and long reverberation times. In small rooms low frequencies fill the room instantly, and mid and highs have longer build up times, more density, which makes any resonances in those frequencies inaudible. Slap echo's are audible as a twang, but not as a total echo like in large spaces.

Both scenarios happen all the time. Most of our HT systems are somewhere in the middle of the two examples above - able to sound good, speech articlation is good, yet not enough power to completely overcome the room reverberant field - hence the use of tuning and treatments.

This makes no sense to me whatsoever. I have never heard a HT room that had enough internal volume to create the scenario you have stated. I have heard auditoriums, gymnasiums and stadiums that did.

Take a room, excite the room with a near field of 2" square @ 100 db measured at the source. Let's assume optimum placement of the source in the environment for this example. Now let's expand the near field at the source to 12" square, same measured intensity of 100 db. What happens to it's ability to control room reverberations? Take it up another level - 10' square near field size, same measured intensity of 100 db.

In example 1 the acoustic power generated is 1/60 of that in the 3rd example. Same measured intensity at the source, same inverse square law applies. The 3rd example will contol standing waves much better even at the same SPL. Because of the effective acoustic power radiation. The near field power radiation can be increased (maximum system gain) to the point the reverberant field and far fields dissappear or are nulled out by the near field power radiation.

None of this is applicable to the issue at hand. All even mentioning this does is muddy the waters of the discussion. What you are saying can be done by just moving closer to the source. There is no need to increase anything, unless the source is not suitable size wise for the size of the room.

I attended a USITT seminar in Oakland, CA back in the mid 80's and my perspective for audio systems was changed forever when listening to a lecture on sound design given by a professor from the Yale School of Drama. He began by stating (paraphrased) "When approaching a design, the first thing to do is determine what emotional responses we seek to elicit from the audience, then go about the task of determining how we are going to achieve it".

This does not sound like a function of the system itself, but the mix the system will reproduce. I learned this same principle at film school when approaching the design of a soundtrack mix. All I want my reproduction chain to do is convey the mix to the audience, not try and get an emotional response from the speakers themselves. The concept when applied to the reproduction chain places it in front of the mix itself , not exactly what we are looking for.

Never in the discusson did his perspective migrate into specifications, response curves, db meters, sound pressure levels, hardware - these are simply the tools and properties of the trade - the means to an end.

Perhaps you are right, but these tools are necessary to get a good result in the end, and the OP has not applied any of them, and his system does not reflect their use as well. In looking at the way the OP system is set up, there is no way he is getting any improvement from anything. The first rule of good sound is to use these tools as the means to and end, or you don't really have an end in their absence.

The OP stated his system sounds better - it does. Yet, the chorus seems hell bent on leather to disprove that possibility. He already stated it's a fact.

How do you know it sounds better, have you heard it? The chorus is right in this case, as the very nature of what the OP is doing defies good acoustical and set up principles in spades. If it in fact sounded better, you can bet THX, Dolby, Dts, SMPTE, AES, and ITU organizations would extol the use of dual centers. Since in fact testing has produced negative results for this kind of set up, none of them recommend it.

Facts must be verified, or they are just anecdotal without support.

Not suggesting he couldn't do better with it. But, neither can I definitively state it sounds worse.

The simplicity of design execution of a typical HT setup is something a hobbyist can enjoy. Let him enjoy.

I am puzzled by your defense of this kind of thing. You act as if this kind of set up has never been tested, and quite frankly it has. When attending USC's film school, I had Tomlinson Holmann (creator of the THX certification criteria) and Dr. Floyd Toole as my professors. My minor is in acoustical science along with a major in film and television post production with an emphasis on sound. None of what you are stating lines up one bit with what they have taught me when it comes to speaker/room interaction in small rooms. It does apply when we are talking about large rooms. It might help if your comments and observations lined up better with the circumstances at hand.

[Sir Terrence the Terrible]

Hobbyist: Buy speaker x, amplifier y, processing setup of z and install in listening room. A skilled/experienced hobbyist will take said setup and work placement, room treatment and system tuning to arrive at a spot of optimum performance. Typically though, they only tune to one spot in the room.

There is two approaches when tuning a system. You tune to one spot(which is mostly recommended as there is only one place of perfect fusion in small rooms), and there is another school of thought that tunes for as many listening positions that are in the room, which mostly leads to average sound everywhere. I tune for a perfect one spot(or as close to perfect as possible), and secondarily for other listening positiond for as best sound as they can get. This yields one almost perfect spot, and many decent spots.

Professional Sound Designer: Will assess requirements, evaluate environment, then start shaping a course of action. If they are a contractor cost, schedule and other considerations will also be taken into consideration. If working in an institution, there could be other constraints, hardware inventory, rental budget, etc. If it's a fixed install in club or church comes archtectual specs, elevations and renderings. For a touring system another set of variables. For a regional sound contractor it's a lot of pure experience in play. Make optimum use of inventory, while meeting or exceeding customer expectations. Take less gear out an you can send another crew out to handle a smaller job. Get paid twice that day.

A sound designer does not design sound systems, they design effect tracks and create live or recorded mixes. A sound system designer designs sound systems with the room and purpose in mind. I am both a sound designer, and a system designer, and I know the difference between the two.

There are one very important factor you are missing here. When we talk about the combination of near-field, far-field, and reverberant field, the sound source has to be coming from one direction, much like a PA system in the front of the auditorium or concert hall(whether it is flown, or a stage stack). In a home theater, there is no reverberant field, as you are surrounded by speakers in a 7.1 setup, and at least enveloped with a 5.1 system. You are too close to all of the speakers for a reverberant environment to really form. You only get a reverberant field when the reflections are more dominate in amplitude, have very long reflective paths that diffuses the output from the source elements, and which reduce the high frequency content of the signals. This complex interaction does not happen with multichannel set ups in small rooms.

There must be an awareness of how much PA is needed - can't use too much, drives prices out of competetive realm, not enough and sound is bad - damage to reputation.

To reinforce for instance a high school graduation ceremony in a big budget high school with large student body that's held in the football stadium with 5-10,000 seats presents unique challanges. Grandstands with infield seating in front and stage beyond that. Front fills, side fills, rear fills, time delay, etc. And it's outdoors. Gotta cover all the seats, not too loud for grandma, but speech intelligibility must be good on the upper deck and in the bleachers going up 50 rows. If it's not, you won't be coming back next year. Truck payment is tough to make when you're not working.

Once again you are back to large spaces, which have no relevance to HT rooms.

And instutution is about as much fun. Musical theatre in a house for public presentation - been there done that. Wireles mic's on actors, set mic'd up, apron in front of stage mic'd up. Live band behind stage mic'd up. Director demands the house including balcony and under balcony seats sound good - not too loud. And of yeah, the system must be behind scrim flats and unobtrusive - i.e. when the actors are speaking the point source localization is towards them and not a pair of stacks or flying array.

For eight years I was an audio engineer on Broadway, and most of the systems in those locations are already set in place for the best sound coverage in the theater. Localization in a theater environment is not what you want, consistent even sound coverage is, which is why most theater installations are a permanent part of the theater.

There's a degree of group think and paradigms on this thread that frankly bothers me. Somewhat narrow view of all things audio if you will.

This group think exists because their are principles that have been tried, tested and proven to give good results. Follow the rules, and you get an expected good result. Create your own rules, and you have something only you can enjoy.

Sometimes, it's good to blow dowm a few walls!

Cheers dude!!!

If blowing down walls is what you set out to accomplish, then you failed the mission. No offense, but your what you are stating here does not apply to the OP's situation. Not one bit I am afraid.

[Dual-500]

Good stuff Terrence. I'll read and digest tomorrow night and comment.

Thanks for the discussion.

I do have some quesitons on tuning technique for HT applications - which by definition are unique to HT.

Cheers!

[Sir Terrence the Terrible]

So what you are saying is because two center would have four woofer cones moving more air, than two cones would, the field has more energy? If I am understanding this correctly it makes sense and why I find large woofers more accurate in reproducing drums, in a general sense, over smaller woofers. Some speakers with small woofers can play amazingly low but still seems to fall a bit short on the body of a drum tone. Hope I didn't misunderstand and get off on a tangent

Keep in mind that one larger woofer does not have the same negative side effects as using four spaced ones. If you are going to use four woofers, there has to be some way for them to couple together to effectively move more air as one driver(proximity boost). Spaced apart coupling is not effective, clustered together tightly it is. If you have ever seen a subwoofer in an IMAX installation, it has four 15" in what is called a "diamond cluster", a tight diamond shape pattern which causes the four 15" drivers to move the air as one large
driver.

If you really want to move more air, you get a larger center channel with larger drivers, not two separate speakers in the name of moving more air. Let's be logical here, just how much more air is going to be moved with those small drivers in such a small cabinet like the OP has.


If

[PeruvianSkies]

Keep in mind that one larger woofer does not have the same negative side effects as using four spaced ones. If you are going to use four woofers, there has to be some way for them to couple together to effectively move more air as one driver(proximity boost). Spaced apart coupling is not effective, clustered together tightly it is. If you have ever seen a subwoofer in an IMAX installation, it has four 15" in what is called a "diamond cluster", a tight diamond shape pattern which causes the four 15" drivers to move the air as one large
driver.

If you really want to move more air, you get a larger center channel with larger drivers, not two separate speakers in the name of moving more air. Let's be logical here, just how much more air is going to be moved with those small drivers in such a small cabinet like the OP has.


If

EXACTLY! I am glad that someone else is not smoking crack around here regarding this. Despite my differences with Sir T in other areas here, I have to say that this is one time I am in complete agreement.

[pixelthis]

Accurate? Another term that gets misused.

I haven't heard a definition for "Flat Response" yet. You and I agree, a room can't be made to be flat. Good starting point.

Accurate? Yes, we strive for accurate. But, like "Flat Response" it ain't happening. Accurate is goal, not a destination. We get as close as possible to accurate.

Take a given room and test 10 different system/installations in it and what do you have? 10 different sets of results. They can all be tweaked towards "Accurate" and all 10 setups sound good. But all 10 will be inherently different.

Take one "Decent" system and setup/install in 10 different rooms and once again, even after tweaking, the net result is different in each room.

That's my simple point. The OP in this thread made a change that to him sounds good. It get's criticized and shot down as not being "Flat Response" or "Accurate" and that's not the case. Factors are not being taken into consideration. The listening environment plays a role in the end result. That role varies from room to room, some more than others. It's simply not a constant that can be conveniently ignored or disregarded when discussing net results.

The only point in the naysayer discussion was driver interaciton at the source and resultant comb effects. The room wasn't even in the equation, and the room is probably the big player here.

Shoot your self in the foot? Negative. There are times when nearfield radiation increases will net better sound regardless of resultant side effects derived from comb interaction. I didn't say EVERY time, I said sometimes. No ABSOLUTES here.

I doubt anyone on this thread would argue that if the components from the dual center channels loudspeakers were package into an integrated unit in such a way as to reduce comb effects from optimum driver placement that the result would not likely be inproved. However, that in and of itself doesn't negate the potential that what he did resulted in an improvement.

I submit the results the OP is getting using 2 -vs- 1 center channel speakers is an improvement just as he says it is. The increase in near field radiation could be improving upon overall environmental acoustic conditions (reverberant field control) that the side effect of comb interaciton is negated.

Thanks for the input - good discussion.

Of course you cant get totally straight up and down flat outside a lab and very few high end setups, but you can get amazingly close, but not if you start off shooting yourself in the foot.
This sort of frequency cancellation is so effective that its used in several brands of headphones.
This sort of massively inaccurate setup is universally decried by all who know better.

[pixelthis]

[QUOTE]

So what if a person decided to connect all the speakers into their receiver in the wrong places and therefore had the surrounds mixed with the fronts and left and right were backwards and various other exchanges, but they claimed that they loved the way it sounded this way and think it is highly recommended?

PERSONAL EXPERIENCE?

By this we are saying that everyone has their own version of right and wrong setup and therefore there really isn't any correct or incorrect way of doing HT, which means to each their own and unless we can hear each others systems there is no way of really knowing?

what is this the situational ethics version of setting up a system?
PEOPLE PREACHING such a system claim that their is no set system of morality,
whatever you do is okay. They always fail to mention murdering people.
THERE IS AN OBJECTIVE WAY to hook any system up that is going to be best,
its called science, and you can argue that "if it feels good do it", but there is still
a certain set of objective rules to follow concerning setting up a HT.
And using two centers is not one of them




Come on....

I think we are missing some of the fundamentals that go into this hobby and there are proper ways to do various things that each of us have tried in our own ways and logic tells us that we don't have to fall off a skyscraper to know it's a bad idea.

Like using two centers.

[brad1138]

I want to point out, I have been professionally in and around the audio industry for ~20 years and a hobbyist since I got my first home stereo for my 10th B-day, 33+ years ago. I worked for 8+ years at a well respected, local, high end AV dealer that has been around for over 40 years. I am not coming at this without knowledge of HT/Stereo design theory.

I get that the 2 center approach has draw backs, I can hear them. Slightly less pinpoint/focused image from the center for 1. However in my setup and situation, it has benefits, and in the end I like the Dual center sound better than the single. I am not some AV/HT noob, I have a fairly critical ear. Of course I could convince myself the sky is orange if I really wanted to, but I have no reason to convince myself the dual centers sound better, it was/is an experiment. If I hadn't liked the sound more I would have switched back and probably posted that experience as well. Last night while watching The Hangover with my son I let him have the center seat I almost always sit in, I was about 4-5 feet off center, and the "benefits" were present there as well.

Another point no one seems to have thought about. Some have said, "just go buy", I can't afford to just go out and buy the exact correct piece(s) for my system. If I could I would probably have a, single, top of the line center behind an acoustically transparent 120" projection screen. So I look for the best sound with what I have and can afford to buy. As I posted originally, the S1s weren't being used, and I came up with a way to, IMO, improve my system for free. I am very proud of, and happy with, the system I have been able to put together over the last 20 years or so, for very little $.

Feel free to continue your (seemingly never ending) argument against it. I get your text books say it isn't a good idea (I have never been one to go by the books), and your expierience is that it doesn't sound as good. This is my experience & system and I don't need your approval.

I am always tinkering with my system. I will keep it like this for a while, I may change back at some point, especially if I get the M-Csi matching center for my M-3si's I have been looking for the right deal on, but I am very happy with the sound currently.

Thanks again,
Brad

[Sir Terrence the Terrible]

I want to point out, I have been professionally in and around the audio industry for ~20 years and a hobbyist since I got my first home stereo for my 10th B-day, 33+ years ago. I worked for 8+ years at a well respected, local, high end AV dealer that has been around for over 40 years. I am not coming at this without knowledge of HT/Stereo design theory.

If this were the case, then you should have known that what you are trying is not a good idea at all. A hobbyist or a salesman probably knows about as much about room acoustics and wave interaction as I know about rocket science. None of these amateurish credentials validates any special knowledge when it comes to the proper way of setting up a home theater.

I get that the 2 center approach has draw backs, I can hear them. Slightly less pinpoint/focused image from the center for 1. However in my setup and situation, it has benefits, and in the end I like the Dual center sound better than the single. I am not some AV/HT noob, I have a fairly critical ear. Of course I could convince myself the sky is orange if I really wanted to, but I have no reason to convince myself the dual centers sound better, it was/is an experiment. If I hadn't liked the sound more I would have switched back and probably posted that experience as well. Last night while watching The Hangover with my son I let him have the center seat I almost always sit in, I was about 4-5 feet off center, and the "benefits" were present there as well.

Brad, I do think you are really trying to justify something that acoustically speaking cannot be justified. Some of us know better, and have heard this whole schmeel before.

Anyone can say they have a critical ear, anyone can make any claim for that matter. But I have heard enough of these kinds of setups to know that you are not fooling me, but you really are fooling yourself.

Another point no one seems to have thought about. Some have said, "just go buy", I can't afford to just go out and buy the exact correct piece(s) for my system. If I could I would probably have a, single, top of the line center behind an acoustically transparent 120" projection screen. So I look for the best sound with what I have and can afford to buy. As I posted originally, the S1s weren't being used, and I came up with a way to, IMO, improve my system for free. I am very proud of, and happy with, the system I have been able to put together over the last 20 years or so, for very little $.

If this is all you have, then you would do far better by stacking the two speakers in the vertical plane(instead of the horizontal) with the two tweeters clustered together. You will get far better sound than what you are currently doing.

Feel free to continue your (seemingly never ending) argument against it. I get your text books say it isn't a good idea (I have never been one to go by the books), and your expierience is that it doesn't sound as good. This is my experience & system and I don't need your approval.

Then why in the hell did you come here reporting what you have done? Did you come here expecting a co-signer to your madness?

Alright, so everyone, just throw away years and years of acoustical knowledge and experimentation done in labs under controlled conditions. Forget the white papers that have been submitted to AES on small room acoustics and speaker/room interactions. Forget the white papers on wave propagation, and driver interaction. What do the books and white papers know, anything goes and there are no rules. I will place my center speaker behind me, my left and right rears in front of me, and my main fronts to the side and rear of the listening area. This ought to sound great, because its my experience, and my system. Oh, and I will put my sub on the ceiling in the center of the room. It ought to have the perfect frequency response there.

I am always tinkering with my system. I will keep it like this for a while, I may change back at some point, especially if I get the M-Csi matching center for my M-3si's I have been looking for the right deal on, but I am very happy with the sound currently.

Thanks again,
Brad

If you are happy, I say more power to ya

[Mr Peabody]

Pix, don't start that frequency cancelling crap again, I can't believe the last time we went through this you didn't learn anything. Well, obviously, it must be true. I will say this just once and will not go through it again posting endless links to articles to prove it to you.
In general:
1. When same frequencies meet that are IN PHASE, they will increase.
2. When same frequencies meet that are OUT OF PHASE, they will cancel each other.

[Mr Peabody]

Keep in mind that one larger woofer does not have the same negative side effects as using four spaced ones. If you are going to use four woofers, there has to be some way for them to couple together to effectively move more air as one driver(proximity boost). Spaced apart coupling is not effective, clustered together tightly it is. If you have ever seen a subwoofer in an IMAX installation, it has four 15" in what is called a "diamond cluster", a tight diamond shape pattern which causes the four 15" drivers to move the air as one large
driver.

One of the recommended ways to use dual subs is one in front of the room and one in the back of the room, so it would seem distance, as it relates to low frequencies, as in your example, isn't that relevant.

If you really want to move more air, you get a larger center channel with larger drivers, not two separate speakers in the name of moving more air. Let's be logical here, just how much more air is going to be moved with those small drivers in such a small cabinet like the OP has. If

Well, being logical, if you start with two drivers and add two more, you should effectively double the air movement.

What about the "phantom center channel"? I understand you are using two left/right speakers to create the phantom but those signals designated as center content have to be mono in order to be centered in the middle of the sound stage. Is there some reason this works horizontally and not vertically?

[Mr Peabody]

Keep in mind that one larger woofer does not have the same negative side effects as using four spaced ones. If you are going to use four woofers, there has to be some way for them to couple together to effectively move more air as one driver(proximity boost). Spaced apart coupling is not effective, clustered together tightly it is. If you have ever seen a subwoofer in an IMAX installation, it has four 15" in what is called a "diamond cluster", a tight diamond shape pattern which causes the four 15" drivers to move the air as one large
driver. If

Oh, I get it now, two centers isn't enough, he needs four, in a diamond shape around his TV, one on top, one underneath, and one on each side! diamond......