Best setup for two subwoofers.

In my opinion it is okay to use different subs. I'm also an advocate of asymmetrical placement, so that the two subs are interacting with the room modes differently. The result is each sub will give you a different peak-and-dip pattern at any given listening position, and the sum of these two dissimilar peak-and-dip patterns will be smoother than either one alone.

Since you want very deep bass, you might put the sub that goes the deepest in a corner, and then put the other sub along one of the opposite walls perhaps 1/3 of the wall dimension away from a corner. This would give you good asymmetry in the horizontal plane.

Duke
dealer/manufacturer

If you want a very informed opinions, go to Scott Wilkenson's Home Theatre Geeks podcast. Home Theatre Magazine reviewer. A few weeks ago he had an episode with Dr. Floyd Toole and this guy KNOWS SPEAKERS AND SPEAKER DESIGNS! and much of the podcast was on sub woofer and sub woofer placement and design along with general speaker design.

That said TWO subs will provide for you the best compromise in bass for the most listeners in a room if each sub is equal distant down front and/or back walls or side walls. IE: Put each sub down the front wall the same distance away from each side walls. Or you can put one sub midway down the front wall or near to it and the other sub reversed down the back wall. Or try putting each sub mid way down each side wall of your room. Doing any of these will balance out bass and suppress room anomalies for more than one listener.

Again check out Home Theatre Geeks podcast and listen to the Floyd Toole episode.

Les creative edge, to the best of my knowledge none of the subwoofer studies published by Harmon researcher Todd Welti (presumably Toole's source) investigated asymmetrical placement, simply because that introduces too many variables. Another researcher, Earl Geddes, demonstrated improved smoothness from asymmetrical placement in a paper that is unfortunately no longer up on his website, possibly because it gave away too much to potential competitors. Todd's consumer-oriented paper is no longer up on the Harmon site either.

Based on conversations I've had with both Earl and Todd, the main thing is to have multiple bass sources spread fairly far apart, as that is where the greatest benefit accrues. The exact positioning of the subs is generally less critical than with a single sub.

It is interesting that Earl and Todd arrived at using distributed multiple subs as a solution to room modal behavior completely independent of one another. Neither was aware of the other's work until Todd published the first of his papers.

Duke

From what I understand the only concern one truly has to worry about with two or more subs is that they are not placed in a way where one is out of phase with the other. By setting up multiple subs in ways where they generally mirror each other or sit along side/front walls equal distance from corners will generally have each sub work in tandem reinforcing the bass signal and keeping boom and nulls to less effect. Now of course if you have subs with a variable phase control you can with effort tweak the subs to work more in phase and thus positioning errors will not be quite as much an issue in terms of phasing.

Now of course two subs if not sitting in a best compromise situation for what may be determined as the best sitting locations for listeners can still aggravate boom and tubbiness of bass along with nulls in bass.

Dr. Toole suggests the best choice if budget allows (and factoring extra electricity useage) is FOUR subs each in a corner. They will cancel out well over 85% of the room effect of boom, tubbiness and nulls. They will provide the smoothest bass for the most listeners in room. On top of that they will work more efficiently as the corners reinforce their output causing the sub amps to work less hard. He suggests you may be able to settle for even smaller subs say 4-10's rather, than 4-12's or 4-15's. In such a case where you use FOUR subs one in each corner it no longer matters what your room is shaped like. It could be square, long rectangle, short rectangle, L shaped, or whatever.

If you want the easiest placement for multiple listeners with only TWO subs again setting each up down a wall and out of a corner and where each is relative to each other similar in the room placement you will get a better compromise for more listeners in room.

If you only have ONE sub the best thing to do is to put it as close to a mid placement on a wall, front, side or back to give the best compromise for multiple listeners in room. If only one listener will likely ever listen then put the single sub in a corner but understand once another listener or more then sits he/she/they will get a compromise in sound that may not be too pleasant for them.

If this is indeed Dr. Toole's position, then I disagree with him:

"...the best choice if budget allows... is FOUR subs each in a corner.... They will provide the smoothest bass for the most listeners in room."

I question whether that's really what he said, because Todd Welti's investigation showed that four subs with one at the midpoint of each wall in a rectangular room was smoother than one in each corner.

In the paper mentioned in my second post above, Dr. Geddes compared four subs each in a corner against three subs in a specific asymmetrical configuration (one in a corner, one along an opposite wall, and one closer to the ceiling than to the floor). The three subs asymmetrical were not only smoother, they also had less frequency response variation from one listening location to another.

I have been manufacturing four-piece multisub systems since 2006, and my experience plus my customers' supports the argument for asymmetrical positioning even if it's confined to the horizontal plane. I am unaware how many of my customers tried a symmetrical configuration, but to the best of my knowledge all of them have chosen to use an asymmetrical one.

Regarding the relative phase of widely-spaced subs, it is far less critical than intuition would lead us to believe. The reason is, we cannot even detect the pitch of a bass note before several cycles have reached our ears. By then the room's effects have totally swamped the first-arrival sound. For all practical purposes, in the size rooms we listen in at home there is no such thing as "direct sound" in the bass region. By the time we hear it, it's all reverberant sound. This is precisely why a distributed multisub system offers such a significant improvement in perceived bass clarity and smoothness, instead of sounding like mud: The only place a multisub system offers improvement is in the reverberant field, but from a perceptual standpoint that's all there is in our rooms anyway.

Duke