Two Subwoofers... Comb Effect

One key is to keep the x-over as low as practical. This will make sure you can't localize the bass. My Maggies, 1.6s are x'd-over at about 40-45hz. Seamless and invisible.
Phase, however, is another matter and does make a difference.
I wish I had a fully variable 0->180 control rather than the 0 OR 180 I now have. Small point, but don't forget that sound travels at about 14"/millisecond, so a small movement of the sub can produce phase changes, too.

Thanks Todd,
That Harmon International link is not only interesting....it is the first quasi scientific documentation that appears to prove that multi subs are the only real way to go.

Sorry....I meant thanks Duke!

Halcro, Todd Welti et al published a couple of thoroughly scientific (nothing "quasi" about them) papers on the same subject in the Journal of the Audio Engineering Society a few years ago. What you see at the link above is the version he wrote for non-engineers.

Another very scientific proponent of multiple subwoofers is Earl Geddes, though he hasn't published any peer-reviewed papers on the subject. His approach differs from that described in the Welti papers somewhat; Earl advocates asymmetrical placement. Here is a brief study he did comparing four-corners placement with asymmetrical placement of four subs:

http://www.gedlee.com/downloads/sub%20study%20.pdf

I use a simplified quasi-Geddes placement strategy; I do not elevate one of the subs as he recommends.

Duke

I was logged in on the account of a physically challenged friend (with his permission) when I posted above.

Duke