>>>Yes, that's why I'm curious as to people who've actually used an RTA to look at the impact of the 2nd sub. For someone to say, "I have two subs and it's much better than one" doesn't really mean much. They might just like saying "I have 2 subs". <<<

Two or more subs excite more of the natural room modes, and at different frequencies. This causes the peaks and dips caused by these modes to be of less amplitude overall depending on placement - one sub may excite a strong "peak" while the other creates a "dip" at that frequency at the listening position, effectively reducing or eliminating the original peak.

More than one sub will equate to more efficiency (overall output by +3db over a single sub) and they will exhibit a lower extension of low frequency response than one sub alone - this is caused by mutual coupling which essentially makes two subs seem like one larger one if they are positioned relatively close to each other at the lowest frequency's wavelength. If one of your subs have a low frequency extension of 25Hz for instance, two subs could have extension to 20-22Hz or so.

These are real world and measureable benefits.

[This message has been edited by soundhound (edited August 24, 2004).]