2 subwoofer???

Hi All,

I've heard that using two subwoofers eliminates many problems associated with having only one. If this is true, can they be any 2, or do they have to be similar or identical subs?

thanks in advance,
Audiogon is fabulous! Thanks for all the input, and it seems as though we have some real discussion going on.

It looks as though the subs have to be identical, eh?

the rustler
Hi Dbld,

A basic premise of the second school of thought is that room acoustics dominates in the bass region. So the idea is to use what inevitably happens in the room to your advantage as much as possible.

Consider the single subwoofer situation: There's a path length from the subwoofer to your listening position, and then there's another path length from the subwoofer to the opposite wall and back to your listening position. At a certain frequency, the difference between those two path lengths is equal to one-half wavelength. At that frequency you will get cancellation at the listening position. Higher up there will be a frequency where the path length difference is equal to one wavelength, and at that frequency there will be reinforcement at the listening position.

Obviously you have more than one wall in the room so the situation is more complex, but you get the idea. You can get quite large peaks and valleys in the in-room reponse at various locations depending on how the reflection patterns coincide.

Now if you put a second woofer in the room positioned such that its path lengths do not concide with those of the first woofer, the peaks and dips from their outputs will never exactly coincide (in other words, they will be "decorrelated"). So the net result will be a smoothing of the response throughout the room.

Here's an example setup: One subwoofer located near the left front corner but elevated up several feet off the floor, and the other subwoofer along the right wall a little bit behind the listening position but well away from the corner.

There may be a way to mathematically predict optimum locations for randomizing the interaction patterns of multiple subwoofers in a room, but that's out of my league.

There is great merrit to what Duke just said.

For my symetrical stereo sub set-up there are obvious peaks and nulls when playing test tones. It is possible to get things relatively flat by using the controls on the subs. But when you do this the music looses a lot in my opinion.

Judicious use of an EQ like the one from Velodyne has crossed my mind, but it does sound awfully good as is.

If space and living conditions permit I would try exactly what Duke recomends.

Good luck!
Thanks, Bignerd100.

Giving credit where credit's due, my primary source for the above-mentioned first school of thought is David Griesinger, and my primary source for the second school of thought is Earl Geddes.

Just for the record, Earl recommends having more than two low frequency sources in the room, and preferably a mixture of vented and sealed. So I doubt that he'd have a problem with using two non-identical subwoofers.

I've gotten great results with matched, dual subs. In addition to a fuller and more natural base, the addition of the second sub has resulted in a wider soundstage, added a bit more clarity to both instruments and voices and contributed to a smoother response in the low to mid-range. My listening room is over 3500 cu. ft. with many openings and a vaulted ceiling that climbs to 13 ft. The second sub has definitely made a difference in this large space. After experimenting with several locations, I concluded that placing both subs along the same wall, with each sub slightly outside of the LF and RF speakers respectively produced the smoothest and most natural sounding bass.