Sub crossover freq for MMGs?

[Mike Anderson]

I finally got a subwoofer for my Magnepan MMGs. I went with the Dayton Titanic 10".

Any advice on the proper crossover frequency for this setup?

Thanks,
Mike

[Mike Anderson]

Oh, and my room is about 15'x20', with 8' ceilings.
Thanks

[Geoffcin]

Oh, and my room is about 15'x20', with 8' ceilings.
Thanks

I would try 80hz or 100hz. Your also going to want to play with moving the sub around to see if you can get the smoothest responce.

Good luck!

[Mike Anderson]

^ Thanks.

I should also add that my amp is a Musical Fidelity A3.2, with plenty of power. I already get a fair amount of bass when it's cranked up loud enough.

I'm not looking for knock-down-drag-out booming bass, just something to round out my sound a little -- something subtle, not terribly noticeable. I don't want it to sound like I'm using a subwoofer.

Also, this is in my living room, not a dedicated listening room. So placement is constrained; the wife just isn't going to put up with a 14" cube just sitting wherever it wants to live. Hopefully it won't be a problem; I have a space for it pretty much right in between and in line with the MMGs.

[JoeE SP9]

With planar speakers the lowest crossover frequency that works is the best. This is probably true for any speaker. I have my electrostatics crossed over at 80hz. I have tried lower but my panels don't like going that low at higher volumes.http://forums.audioreview.com/images/icons/icon6.gif

[Mike Anderson]

OK, at this point I've set the crossover at 40hz; it sounds fairly transparent that way. However, no matter what I seem to do, I get a dip in level right around 65 hz. I think I must have a room problem. Not only that, but if I play a test tone at 65 hz using only the MMGs, one of my MMGs (the one closest to the corner of the room) rattles rather loudly. It only stops if I grab the frame of the speaker and hold it firmly.

Anyway, I made a series of test tones starting at 30 hz and increasing in 5hz steps up to 160 hz. I've got it set so that (to my ears anyway) it sounds as flat as possible, excepting for the dip at 65 hz; I'm not sure what to do about that.

I also made a sweeping/rising test tone starting at 30hz and increasing very slowly up to 22000hz. If I have any kind of volume coming out of the amp, it's a freaking disaster! There's huge peaks and valleys in the volume, stuff is rattling and rumbling all over the place; criminy, thank God my music doesn't sound that bad! Still, I sure wish I knew what to do to even it all out and to get rid of the rumbles and rattles.

I tested the MMGs by themselves, and they don't really start to drop off until about 60-55 hz. Shouldn't that tell me what the crossover frequency should be, if I could figure out the slope of the MMGs as compared to the subwoofer? How would I do this mathematically?

Thanks,
Mike

[JoeE SP9]

OK, at this point I've set the crossover at 40hz; it sounds fairly transparent that way. However, no matter what I seem to do, I get a dip in level right around 65 hz. I think I must have a room problem. Not only that, but if I play a test tone at 65 hz using only the MMGs, one of my MMGs (the one closest to the corner of the room) rattles rather loudly. It only stops if I grab the frame of the speaker and hold it firmly.

Anyway, I made a series of test tones starting at 30 hz and increasing in 5hz steps up to 160 hz. I've got it set so that (to my ears anyway) it sounds as flat as possible, excepting for the dip at 65 hz; I'm not sure what to do about that.

I also made a sweeping/rising test tone starting at 30hz and increasing very slowly up to 22000hz. If I have any kind of volume coming out of the amp, it's a freaking disaster! There's huge peaks and valleys in the volume, stuff is rattling and rumbling all over the place; criminy, thank God my music doesn't sound that bad! Still, I sure wish I knew what to do to even it all out and to get rid of the rumbles and rattles.

I tested the MMGs by themselves, and they don't really start to drop off until about 60-55 hz. Shouldn't that tell me what the crossover frequency should be, if I could figure out the slope of the MMGs as compared to the subwoofer? How would I do this mathematically?

Thanks,
MikeRaise the crossover point. A good place to start is the -3db point for the Maggies. Use the -3db point you have measured. If you still have a serious dip at the crossover point raise it in 5hz increments until you have minimized the dip. If you go to high the bass will begin to sound muddy and you will degrade that clean Magnepan sound. Going too high will also give a serious hump at the crossover point. MMG's do not have a lot of surface for the bass. Consequently the roll off is in the area that smaller bookshelves usually have. In any case, I don't think you bought MMG's because of their prodigious bass. In any panel speaker, the larger the diaphragm the better and deeper the bass. The amount of bass produced by any panel is determined by panel size, room placement, room dimensions and furnishings. Use measurements to get the sound in the ball park. Use your ears to fine tune things. The rattle you hear is probably a result of the nearness of the corner. It may be exciting panel resonances. Larger Maggy's benefit from stands that stiffen the frame. There is no reason to believe that MMG's would not benefit from the same. http://forums.audioreview.com/images/icons/icon6.gif

[Feanor]

That is assuming you use a line-level crossover so you feed you amp and hence the MMGs only the >80Hz signal. I don't recall you amp set up, but to this your need a preamp/main set up or "main in" connectors on your integrated or receiver.

You have a good sized room while the MMGs have a limited "loudness" capability for rock or classical orchestral crescendos or the like. Setting the crossover high, (80Hz), largely compensates for this shortcoming. If you have a decent quality sub, (which you do), setting it higher would be better still in this regard, but you will begin to loose stereo separation so it would be a trade off.

[JoeE SP9]

I agree. I think 80Hz is an excellent frequency to start. It takes the burden of low bass off the MMG's without getting into the area where directionality becomes a factor.http://forums.audioreview.com/images/icons/icon6.gif

[Mike Anderson]

My amp (Musical Fidelity A3.2, an integrated amplifier) has a preamp (line level) out. I'm assuming it's the same signal that goes into the main amp section. Obviously, I'm running that into the RCA line-level input of the subwoofer.

But I'm confused about a couple things.

First, although I'm using my ears instead of a meter, it sounds like my MMGs have a fairly flat response down to about 55hz. So why would I set the crossover as high as 80hz? Wouldn't this necessarily create a hump in the 55-80 range?

Perhaps my problem is that I don't know the slopes of the rolloffs for the two speakers, so I'm having a hard time picturing this all in my mind. Perhaps I should just bite the bullet and get an SPL meter. Is a $50 digital Radio Shack meter going to be more accurate than my ears?

I experimented with a large range of crossover freqs, and found that anything as high as 80hz made it really boomy on any recording with substantial bass; if I then back off on the subwoofer gain to eliminate the boominess, it becomes difficult to tell that there is any subwoofer at all. No matter what I do, it seems like I still get a dip at 65hz, which makes me think it's a room problem.

I will say that at 40hz, I'm still having a hard time getting a good rock and roll punch.

[Mike Anderson]

"MMG's do not have a lot of surface for the bass. Consequently the roll off is in the area that smaller bookshelves usually have. In any case, I don't think you bought MMG's because of their prodigious bass."

I don't know if you've tried out the MMGs, but you might be surprised: if you drive them with a sufficiently powerful amp, it makes a big difference. I don't know what bookshelf speakers do, but I'm definitely getting good bass down to 55hz or so.

[JoeE SP9]

<quote>"MMG's do not have a lot of surface for the bass. Consequently the roll off is in the area that smaller bookshelves usually have. In any case, I don't think you bought MMG's because of their prodigious bass."</quote>

I don't know if you've tried out the MMGs, but you might be surprised: if you drive them with a sufficiently powerful amp, it makes a big difference. I don't know what bookshelf speakers do, but I'm definitely getting good bass down to 55hz or so.
I have owned Maggy's in the past. Several of my friends currently own 3.6r's, 1.6QR's and some old Model 2's. I have owned MG1's, MG2's and MG3A's. So, I am familiar with the bass characteristics of the breed. What musical selections are you using to gauge the low end? Bear in mind that a large percentage of popular music doesn't really have any low bass. I agreed that 80Hz was a good place to start. I would consider it an upper limit. The reason I can use 80Hz is because I use an electronic crossover that sends everything above 80Hz to my panels. By getting everything below 80Hz away from my panels I get around the boom. I have found an external active crossover to be much more flexible in adjusting frequency and level than the ones built into most subwoofers.http://forums.audioreview.com/images/icons/icon6.gif

[Mike Anderson]

What musical selections are you using to gauge the low end?

Not music -- using Wavelab, I generated a series of pure sine wave test tones, starting at 30 hz and increasing in 5 hz increments.

Here's how it works with the MMGs only: I start at 160hz, and step down. I notice a slight dip right around 65-70hz, and then it's loud again at 60hz. A very slight decrease at 55hz, and at 50 hz the dropoff is substantial.

Adding the subwoofer obviously increases level in the 55hz and below frequency, and I can get levels in that range to match a level in the 80hz range if I set the crossover somewhere below 60hz and fiddle with the gain repeatedly. But there's always a dip right around 65hz, no matter what I do; there must be a room-generated node at this frequency.

Again, this is using nothing but my ears, no meter.

A problem is that once I set it using the test tones, the music is all over the place.

Using a well-recorded jazz piece with lots of acoustic bass (e.g. Diana Krall's "Stop This World"), there's loads of bass, and in spots it's boomy. If I then go to a rock album (e.g. Foo Fighter's "Colour and the Shape"), there's not much at all below 80hz or so, and it has no punch unless I really jack up the gain on the subwoofer. On the other hand, with something like a modern electronica/house recording, the bass is just too boomy and dominating.

Optimally, I'd have a remote control for the subwoofer gain, I suppose, and adjust it to the music.

[Mike Anderson]

I have found an external active crossover to be much more flexible in adjusting frequency and level than the ones built into most subwoofers.

Well I guess I'll just have to go buy one of those then! Perhaps you can explain this all to my wife.

Anyway, I'm being quite picky here. Once I fiddle with it enough, I've generally got things where I want them. I find it best to back off on the subwoofer gain a bit, and that usually keeps things from getting too boomy. Seems the ears can tolerate a slight absence of bass better than an abundance of it.

[JoeE SP9]

Well I guess I'll just have to go buy one of those then! Perhaps you can explain this all to my wife.

Anyway, I'm being quite picky here. Once I fiddle with it enough, I've generally got things where I want them. I find it best to back off on the subwoofer gain a bit, and that usually keeps things from getting too boomy. Seems the ears can tolerate a slight absence of bass better than an abundance of it.You must remember that most popular music is mastered for playback on gear that is no where near as good as what you use. Using test tones will get things close. The ear is the final arbiter. I think a lot of what you are hearing is just plain poor mastering. Once you get good equipment you have to get used to lousy mastering. Actually the differences in bass quality and quantity are normal. Some recordings sound good and quite a few don't. As far as absolute bass level is concerned use your ears! By the way, I have owned a RS SPL meter for more than 20 years. They do come in handy and are a good thing to have around. I have found if you have the bass level high enough to actually hear it, it is probably to loud. Remember most rock albums don't have any real bass while something like a well recorded Diana Krall does. If you set your rig so Diana Krall sounds right you are probably very close to the correct settings. I know this may make a lot of popular music sound bass shy but that's the price you pay for good gear.http://forums.audioreview.com/images/icons/icon6.gif

[Mike Anderson]

If you set your rig so Diana Krall sounds right you are probably very close to the correct settings

Yes, that's basically just what I did: After tuning with the test tones, I put on Krall and a few other high-quality recordings, and set the subwoofer gain so that it's about as loud as it can get without being boomy.

Thanks for the feedback though, it helps me know I'm on the right track.

[JoeE SP9]

Yes, that's basically just what I did: After tuning with the test tones, I put on Krall and a few other high-quality recordings, and set the subwoofer gain so that it's about as loud as it can get without being boomy.

Thanks for the feedback though, it helps me know I'm on the right track.
Over time you will probably find that setting the subwoofer gain as you have done leaves it a little to high. One of my friends did exactly as you have done. When we had our irregular monthly beer, snack and music get together at his house the three guests (two other lunatic fringe audiophiles and myself) unanimously thought the woofer level was just a tad too high. He turned it down just a little and has left it there. We alternate with our meetings. He was eager to show of his new DIY transmission line sub, so the get together was at his house. We all liked it a lot! I am now in the process of building two for myself. Most people have the level set too high when they first get a good sub. I did and so did all of my fellow audiophiles. http://forums.audioreview.com/images/icons/icon6.gif

[Mike Anderson]

^^ I'm sure you're right, but let me get it out of my system, and some time next week I'll turn it down!

The other thing is that it is clearly changing in character as it breaks in. I've had it on for about 12-14 hours now, and it already sounds tighter and smoother.

Despite all the questions and complaints, I really am thrilled with my setup. Music sounds better than I've ever heard it sound before; it's a chore to tear myself away from it.

[Mike Anderson]

BTW, I just moved out of Philly (to San Francisco), otherwise I'd invite you over to tune my rig properly.

I miss Philly; I was only there for a year, but my wife and I had a fantastic time. Lived in the Society Hill neighborhood.

[JoeE SP9]

^^ I'm sure you're right, but let me get it out of my system, and some time next week I'll turn it down!

The other thing is that it is clearly changing in character as it breaks in. I've had it on for about 12-14 hours now, and it already sounds tighter and smoother.

Despite all the questions and complaints, I really am thrilled with my setup. Music sounds better than I've ever heard it sound before; it's a chore to tear myself away from it.
I believe there is a thread here about speaker break in. You might want to post a comment there. The changes you hear are something that some say don't exist. I agree with you about speaker break in. Many high end speaker manufacturers also believe in it and state that their speakers need break in. I don't blame you for enjoying your rig. Mine still gives me thrills every time I crank it up.http://forums.audioreview.com/images/icons/icon6.gif

[Feanor]

...
First, although I'm using my ears instead of a meter, it sounds like my MMGs have a fairly flat response down to about 55hz. So why would I set the crossover as high as 80hz? Wouldn't this necessarily create a hump in the 55-80 range?
...
I will say that at 40hz, I'm still having a hard time getting a good rock and roll punch.
The reason you don't get the punch form the MMGs is that they just can move enough air at the lower frequencies. That is the "loudness" issue I mentioned earlier. It's also the reason that you will be better off with a higher crossover point, say 80Hz. That way your sub does more work and you will get more punch. I owned MMGs for awhile and try the various settings. 80Hz is your best bet, IMO.

As you observed yourself -- the MMGs have flat response down to about 55Hz so you will get a bit of a hump between 50 and 80Hz (or whatever high-pass frequency you use) unless you limit the signal to the MMGs in that range. This is best done with an active crossover between the preamp and the main amp that feeds the MMGs. I used to use a Paradigm X-30 active crossover unit, although a few subs have built-in high-pass, line-level filters that work at a suitable frequency.

Unfortunately the Musical Fedelity 3.2, (while it has "pre-out" connectors), doesn't have "main in" connectors. This makes it basically impossible to send a high-pass-only signal to the main amp. There is no handy solution to this problem that I can think of.

[Mike Anderson]

The reason you don't get the punch form the MMGs is that they just can move enough air at the lower frequencies. That is the "loudness" issue I mentioned earlier. It's also the reason that you will be better off with a higher crossover point, say 80Hz. That way your sub does more work and you will get more punch. I owned MMGs for awhile and try the various settings. 80Hz is your best bet, IMO.

I've experimented with it quite a bit, and I think what you say is true -- particularly if I'm looking for extra punch in rock and roll type music.

However, most of my music collection doesn't require the extra punch, being either: 1)music that is already mastered with a fair amount of bass, such that the hump would be really obnoxious; or 2) the style of music that just doesn't need it.

So for now, I think my solution will be to simply turn up the crossover freq on those occasions when I want to rock out, and at all other times I'm leaving it around 55-60.


Unfortunately the Musical Fedelity 3.2, (while it has "pre-out" connectors), doesn't have "main in" connectors. This makes it basically impossible to send a high-pass-only signal to the main amp. There is no handy solution to this problem that I can think of.

Yeah, I figured that out at some point. It's OK though, I think I'm quite happy with things now - I'm done fiddling and I'm just going to sit back and listen for a while. (Although I reserve the right to change my mind about that!)

[Mike Anderson]

BTW, just out of curiosity: What if one were to split out the signal before sending it to the pre-amp and filter it there, i.e. sending everything above 80hz to the integrated amplifer that feeds the MMGs, and sending everything under 80Hz directly to the subwoofer?

Ignoring the possible degredation of the signal that may occur by inserting extra components in the signal path, is there some reason this wouldn't sound good? Does the signal going to the subwoofer "need" to be pre-amp'd to blend properly with the signal going into the MMGs?

[Mike Anderson]

Oh, and one other question (sorry):

Can someone tell me what is the precise definition of "crossover frequency"? I understand what it means generally, but what is it exactly?

For example, if the dropoff in frequency above/below a given threshold was exactly vertical, there'd be no ambiguity in defining the crossover frequency as being this threshold. But obviously, there is some finite degree of slope in the dropoff for both the satellite speakers and the subwoofer. So how is the crossover frequency defined relative to the slope of the dropoff for the satellite speakers versus the sub?

Do the signals from the two sources always sum linearly? If so, then when the sub and the satellites have two different slopes, it's impossible to pick a crossover frequency that gives a flat response, correct?

[Feanor]

BTW, just out of curiosity: What if one were to split out the signal before sending it to the pre-amp and filter it there, i.e. sending everything above 80hz to the integrated amplifer that feeds the MMGs, and sending everything under 80Hz directly to the subwoofer?
...

The issue, of course, is volume control, that is, you would want a volume control ahead of the crossover device so the volumes of the amp and sub volume can be controlled together. Some degradation is inevidable, however with a decent volume control device, (in effect a preamp), the degradation is likely to be unnoticable.

My own amp, (the Bel Canto), doesn't have a "main in" either. However my MG 1.6's inherently have much less of the "loudness" problem than the MMG's, so I just set my sub to 50Hz which is just above the 1.6's roll-off in the mid/low 40's. Integration is pretty good.

[Feanor]

...
Can someone tell me what is the precise definition of "crossover frequency"? I understand what it means generally, but what is it exactly?
...
Do the signals from the two sources always sum linearly? If so, then when the sub and the satellites have two different slopes, it's impossible to pick a crossover frequency that gives a flat response, correct?
There are various crossover "alignments" which others can better explain than I can. However roughly speaking the crossover is where the signal is -3 decibels. The slopes are generally defined in terms of decibels per octave of attenuation; these a discussed in terms of "orders" of crossover:

1st order: 6dB/octave
2nd order: 12dB/octave
3rd order: 18dB/octave
4th order: 24dB/octave
and so on ...
No, the two sources don't necessarily sum linearly. It depends on the phase shift that is induced by the crossover. Active crossovers, which we have mostly been talking about, are designed to avoid the phase shift, (or so I understand -- I'm no engineer).

But all passive crossovers, (like the one inside the MMG), induce phase shift. Again, it relates to the "order". Each order induces a 90 degree difference in phase between the low and high pass signals. Hence a 2nd order crossover induces a 180 degree phase difference between the two -- which leads to complete cancellation at the crossover point :( In this case the remedy is to invert the polarity of one of the drivers :)

[Mike Anderson]

^^ OK, I get it, thanks for taking the time to explain this to me.

Speaking of phase, I had assumed that as long as I kept my subwoofer perfectly aligned with the MMGs, I wouldn't have to worry about phase on the subwooofer, and just set it to zero. Is that incorrect?

[Feanor]

^^ OK, I get it, thanks for taking the time to explain this to me.

Speaking of phase, I had assumed that as long as I kept my subwoofer perfectly aligned with the MMGs, I wouldn't have to worry about phase on the subwooofer, and just set it to zero. Is that incorrect?
The sub and MMGs should have no problem with phase if the fronts of the speakers line up within 1/4 of a wave length around the crossover point. At 80Hz that's 3.5 feet and more at lower frequencies, so it's not too difficult.

[Mike Anderson]

^^ That's what I had assumed (deduced?), thanks for the confirmation, and for your other advice.

I find this forum an invaluable resource -- my gratitude goes to you all for making it so.