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Old 10th December 2008, 06:40 PM   #31
badman is offline badman  United States
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Quote:
Originally posted by Wayne Parham
What's with the attitude, Markus? I've usually considered you to be fairly level headed over the last few months of reading your postings. Your last few posts seem fairly uncharacteristic of you.

Look at his location for a clue. NJ winter will make a grouch out of anybody!

Hence, my relocation from NJ this winter to SoCal
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Old 10th December 2008, 06:54 PM   #32
gedlee is offline gedlee  United States
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But then there is that SoCal Effect
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Old 10th December 2008, 07:03 PM   #33
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Quote:
Originally posted by markus76
Sorry Wayne, but I really don't see any difference in "SFM" and "Gedlee Multisub".
Well, in a general context, you're right. They're both multisubs. That's the most important part, really, and in that sense I would agree. Especially in light of the fact that the more sound sources are used, the less important placement becomes.

Perhaps we should focus on the multisub feature, and not make this a Geddes verses Welti thing; however, Geddes has long made a point that the pseudo-random feature makes his proposition different from Welti's.
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Old 10th December 2008, 07:05 PM   #34
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Old 10th December 2008, 07:13 PM   #35
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Wayne, Welti doesn't dictate symmetrical setups for SFM. So for me there is no "Geddes verses Welti thing". There's only one effect on the low frequency response when adding multiple subs. Varying their position, level, phase and bandpass let's you smooth the frequency response at a particular listening area.
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Old 10th December 2008, 07:15 PM   #36
badman is offline badman  United States
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Quote:
Originally posted by gedlee
But then there is that SoCal Effect
Wondering just what freezin' yer keister in Michigan does to ya? One plus about cold weather though, it makes a warm body close by that much better.



Back on topic, I'm working out a multisub install myself right now. We'll be looking at a group of sealed 12"s, (2x modified classic JBL AlNiCos modded for higher Qts and lower Fs along with cone stiffening/dampening in 7.5 ft^3 cabs) and 1 Castle Acoustics Classic (nice sub, small sealed 12).

I have a complex room with a lot of openings, so my plan is to put 2 at floor level, with varied distance to the sidewalls, and one a little higher up in the room to distribute the floor-celing modes.

I've had multiple subs before but they were less "subs" and more "low woofers", as they were playing up more like 70, 80Hz. I'm inclined to keep the subs low and have mains that go low too. While the geddes approach with less filtration makes some sense, what it doesn't appear to address is localization from distortion artifacts and higher frequency content, so I'll stick with 'mains' to 40 or thereabouts and subs below that.

Per one of the posters in this thread, it will look funny to have subs smaller than the mains (vented 15"s), but I'm inclined to think that the cabinet volume will make up for it
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Old 10th December 2008, 07:24 PM   #37
gedlee is offline gedlee  United States
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Originally posted by badman
While the geddes approach with less filtration makes some sense, what it doesn't appear to address is localization from distortion artifacts and higher frequency content, so I'll stick with 'mains' to 40 or thereabouts and subs below that.

Well actually I have dealt with that and talked about it before. This is exactly the reason why I use bandpass subs as they have acoustic LP filters which takes away any HF effects that might cause the subs to be localizable - which can happen. Closed box doen't have this advantage, otherwise I'd just use those.

With "mains to 40" and "subs below that" you won't get any multi-sub benifits at all. There would be no point in doing it.
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Old 10th December 2008, 07:53 PM   #38
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Quote:
Originally posted by markus76
Wayne, Welti doesn't dictate symmetrical setups for SFM. So for me there is no "Geddes verses Welti thing". There's only one effect on the low frequency response when adding multiple subs. Varying their position, level, phase and bandpass let's you smooth the frequency response at a particular listening area.
SFM is an approach that uses signal processing in addition to source placement. It's newer than Welti's original work, where he modeled room/speaker setups with MatLab and then made acoustic measurements of a variety of configurations. His conclusions at that time were that subs should be placed at two wall midpoints, four midpoints or four corners. Those were what I would call "Welti configurations" and are what I believe Earl considers them to be also, from discussions here and elsewhere.

Again, I tend to agree that we should look at this as a multisub thing, not Welti and not Geddes but rather a generic approach that uses multiple subs to smooth room modes. Each room is different, so there probably shouldn't be a cookie cutter approach other than to say use multiple subs and to set them by measurement.

The thing is, historically, Harman International promoted symmetrical configurations suggested by Toole, Welti and others. Geddes promoted a similar setup but with a pseudo-random placement instead of a symmetrcial arrangment. Both have moved some, but Geddes, in particular, made it a point to suggest that the two approaches were different.
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Old 10th December 2008, 08:26 PM   #39
badman is offline badman  United States
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Quote:
Originally posted by gedlee



Well actually I have dealt with that and talked about it before. This is exactly the reason why I use bandpass subs as they have acoustic LP filters which takes away any HF effects that might cause the subs to be localizable - which can happen. Closed box doen't have this advantage, otherwise I'd just use those.

With "mains to 40" and "subs below that" you won't get any multi-sub benifits at all. There would be no point in doing it.
Well, apart from the increased displacement ability of multiple units, and reduced thermal effects (at least that's my take) of multiple voice coils vs. one larger one. Also, let's not forget that -12dB @ 80Hz wouldn't be a ton of attenuation, and is what a typical sub crossover will give you, so you'll have smoothing contributions due to continuing output over the corner frequency up in the upper bass.
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Old 10th December 2008, 08:27 PM   #40
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Quote:
Originally posted by badman
I've had multiple subs before but they were less "subs" and more "low woofers", as they were playing up more like 70, 80Hz. I'm inclined to keep the subs low and have mains that go low too. While the geddes approach with less filtration makes some sense, what it doesn't appear to address is localization from distortion artifacts and higher frequency content, so I'll stick with 'mains' to 40 or thereabouts and subs below that.
This is very important. There are two competing priorities in any mutisub setup.

One priority is to smooth room modes with dense interference, which requires distributed sound sources in the modal region. The modal region can actually extend up pretty high, into the lower midrange in small rooms. The Schroeder frequency is the point where room modes become close enough to be indistinguishable, and so marks the approximate point where wave motion in the room begins to act as a reverberent field. This can be as high as 200Hz in small rooms.

The second (but equally important) priority is to prevent localization problems, which means you have to low-pass the subs lower the further away from the mains they are. In some medium size and larger rooms you also have to deal with inverse square falloff clues if the subs are too far from the mains. Once you get into rooms that large, multisubs aren't generally a good solution anymore but there is a sort of grey area transition between "big" and "small" rooms.

It is attractive to find solutions that allow the mains to go low enough to provide adequate bass, providing two bass sound sources built-in. Sometimes subs can be placed just a few feet away, far enough to provide smoothing of the midbass frequencies but close enough that they can overlap up to a fairly high point. Sometimes large format midrange and woofer subsystems can be made to overlap enough to provide this smoothing, which also smooths floor bounce. Subs placed further should usually be low-passed lower. The further away they are, generally, the more effective they are at smoother lower frequencies anyway. This also helps in regards to preventing localization.
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