[PaulP]

Thanks tINY for the link to the subwoofers acticle. I just finished reading
it and found it very interesting as it appears to describe an effective way
of dealing with modes. And all harmonics as well given enough woofers.
Looks like the Holy Grail.

I can't quite grasp how it works though, there is very little information in
the document as to how, other than "Loudspeakers located at a null point
of a given mode will not couple to that mode, resulting in no excitation of
that mode."

You say something similar :

Originally Posted by tINY

If you place a speaker in the pressure anti-node (half-way between the two walls
creating it), the mode is never excited. Think of it as the wave bouncing off of
the walls and coming back to cancel itself out.

I understand standing waves and how the reflection cancels things out at
a null (and causes double levels in between). I don't at all see how a
woofer positioned in a null and generating the appropriate frequency would
not cause the mode to exist. Once the sound leaves the woofer won't it
cross the room, hit the wall and bounce back on itself like it always does ?
What is different when the woofer is in the null ?

Turns out that you can do the same thing using two speakers placed 1/4 of the way between on either side as well. As a benefit with more subs, you also get rid of the comb-filtering-like boundary effects because there is more than one transmitter of the sound.

For this to work properly, using subs, do you have to high pass the regular
speakers so they don't produce the modal frequency ?

You have to run them in mono, which usually isn't a problem below 120Hz or so.

What would be the usual way of producing mono bass from two stereo
channels ?

Paul P