Setting up Multiple Subwoofers

[kevinh]

For those interested in optimizing multiple subs in a room. This is a description of a commercial subwoofer that uses 4 sub modules. The first 2/3rd of the page describes the system and the reason for multiple subwoofers.

Towards the bottom of the page is a description of how to set the subwoofers up in a room. Most processes I have read about for setting up multiple subs seem to involve a lot of trial and error which can make them hit or miss. The process described here seems very straight forward, repeatable & simple.

DEBRA Distributed Subwoofer, 5+ pieces- James Romeyn

The system is ~ 3k USD, looks like a good value. But the process should work for anyone building or who have multiple subs.


BTW I have no involvement with the company that makes these subs.

[mdocod]

My personal experience leads me to believe that the concept is perhaps not a bad approach to solving problems of bass response in a room. It "might" solve the problem for most listening environments, however, there is no reason to believe that this is the only "good" approach to dealing with lobing and loading related issues in a listening environment.

[kevinh]

Well based on the papers by Geddes and Toole it appears that 3-4 subs are needed to solve the issues with bass in a small (ie residental) room.

[mill23bay]

Could that be related to close field coupling. Bass is hard to control, but if the sub is very near to where one is sitting it may subdue the boom and reduce that -echo bass- sound.
PeterC.

[mill23bay]

Low volumes and a bit of eq to tame the boom gives one a bit of control in a small room.
Where my listening area, is in a basement, low ceiling, a focused listening zone of very nice sound. Outside of that there is a large dip and peak in bass response.
PeterC.

[m R g S r]

They look hand crafted....

[Pallas]

There are a few good things about the writeup. Multiple sub woofers, obviously, and attacking the (IMO idiotic) conventional wisdom about low crossover points. $3k for what look like 4 Dayton RSS265's in nice cabinets with an SA1000 strikes me as a fair price, too.

Certainly, his setup will be better than 1 $3k sub. I'm not convinced that inverting the polarity of one sub will provide the benefit of having finer control of phase (delay) and separate level controls by using external processing and separate amps, though.

[kevinh]

Originally Posted by Pallas

There are a few good things about the writeup. Multiple sub woofers, obviously, and attacking the (IMO idiotic) conventional wisdom about low crossover points. $3k for what look like 4 Dayton RSS265's in nice cabinets with an SA1000 strikes me as a fair price, too.

Certainly, his setup will be better than 1 $3k sub. I'm not convinced that inverting the polarity of one sub will provide the benefit of having finer control of phase (delay) and separate level controls by using external processing and separate amps, though.

This setup process can be applied to any subwoofer array. As to the part of reversing the polarity on 1 of the subs that is something you can determine experimentally.

I need to get another sub to try this out.

[Wayne Parham]

Do not forget about flanking subs or helper woofers, as they smooth the important range above 80Hz, up to the Schroeder frequency:

• Room modes, multisubs and flanking subs

This region is a difficult range to deal with, because the sound field begins to transition between modal and statistical behavior. It is also the most noticeable range. Modes in this range tend to really cry out at you.

I've studied the modal problem for a long time, since first reading Todd Welti's papers about ten years ago. I began to setup woofers in four corners or along two wall midpoints, per his recommendations. Then, in 2005, I talked with Earl Geddes at the Great Plains Audiofest, where he debuted his Summa loudspeakers with Duke LeJeune. We talked at length about multiple subs during that show and in the months that followed. This is when Earl began suggesting his random arrangement.

There were some disagreements about where the best places were to position multiple subs, but everyone seems to agree that for deep bass response smoothness and uniformity, once you get to four subs, placement almost doesn't matter as long as they are not stacked. Whether Welti (symmetrical) or Geddes (asymmetrical), whether ordered (Welti and Romeyn) or random (Geddes), smoothness is assured below ~80Hz when four subs are used.

What is not so assured is smoothness above 80Hz. This range becomes very placement sensitive. Subs placed too far away from the mains cannot be blended at higher frequencies because they become localizable. And if a sub is placed within a few feet - where it can be blended higher - it is probably best to be tied to the main full range speaker it is flanking.

This brought me to a conclusion that a pair of flanking subs or helper woofers could be employed for blending in the midbass and lower midrange region. This strategy can be accomplished with a variety of methods, a separate helper woofer or "flanking sub", a built-in bipolar woofer or 2.5-way speaker with helper woofer placed behind and below the main woofer in the cabinet, or a three-way speaker with a midrange that has sufficient low-frequency capacity to be blended with the woofer in the 80-200Hz range.

Any of these flanking sub strategies can be used with more distant subs used to smooth lower frequency modes, positioned as described by Welti, Geddes or Romeyn. In fact, some Welti configurations can be employed with flanking subs as a matter of natural consequence. But no matter how the (distant) deep bass multisubs are configured, it is very important to employ some form of flanking sub / helper woofer arrangement to smooth the midbass. I think smoothing the higher frequency modes is a greater priority, because they are almost always the most noticeable.

[kevinh]

Wayne, thanks for the post. I see you approach as a variation of Welti and Geddes, if I am reading the link correctly if you are running say a 4 sub configuration with your 3 pi speakers for example (similar to the Geddes Harper) a 2 way with a 12 in pro woofer a horn. You would have 2 'flanking' subs close to the main speakers and then the other (2 or more) subs positioned in the room. Is this correct?

What method do you use for placing the other subs?


What I think Romeyn is doing that is a bit different for the other approaches in 2 areas. The speakers are placed with the drivers placed close to the wall ~1.5 in (<4cm), providing some loading I presume, and you reverse the polarity on 1 of the subs until you determine the best sound.

Have you tried any of these things when you have set up subs?