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

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

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

Thank you very much for the link, Les creative edge.

In the first half of the interview, I didn't hear anything on the subject of speakers, rooms, subwoofers, subwoofer placement, or psychoacoustics that I didn't already know. Not trying to be a smartass, but those are topics I have studied. Now I did learn some of the "why" behind limitations at the microphone end of the chain, and behind the fallacy of pursuing "ideal" room dimensions.

Much of the surround-sound discussion in the second half was EXTREMELY educational to me, as historically I've been a two-channel guy. Toole obviously can teach me a great deal about multichannel, so a few minutes ago I ordered his book. I have you to thank, Les creative edge, for making me aware that Toole's book contains a lot of valuable information I am not familiar with.

Back to the first half of the interview. Fascinating that Todd Welti, whose work I'm familiar with, was actually commissioned by Toole to investigate multisubs. I hadn't appreciated that it was Toole's idea first.

As far as subwoofer configuration goals, Toole apparently places top priority on bass efficiency rather than smoothness, as he prefers four in the corners over four at the wall midpoints. My top priority is smoothness, which comes at the expense of efficiency because destructive interference is the mechanism by which maximum smoothness is achieved.

The comparison I would like to see, but which I don't think anyone has made, is four subs at the midwall locations vs four subs in a thought-out asymmetrical configuration. I bet they both would sound pretty darn good.

Again thank you very much for this discussion and the link, without which I would have continued in my mistaken belief that there probably wasn't much in the book that would be new to me. At some point I wish to become competitive in the home theater sound system marketplace, and Toole's book will be a primary resource.

Duke

Gozren, I tip my hat to you for wading through all that and finding something useful. We kinda went off on a tangent or three there.

Very best of luck with your project... and if you get a chance to listen to the interview with Dr. Toole (episode 14 at the link Les creative edge posted), it's great stuff.

Duke