One or two subs

Marty is right that room resonances will be largely determined by the room dimensions, regardless of the number of subs. Careful placement of the sub or subs can help a bit, but the walls will still be the most important factors. (Like, it's very hard to reproduce a sound with a 30 foot wave in a 26 foot room, no matter where the sub is or even if there are multiple subs. On the other hand, the room will tend to emphasize sounds with 26 and 52 foot waves.)

Using multiple subs to try to reduce the impact of room resonances is difficult and not very effective, especially since the output of the subs will be reinforcing or cancelling at different frequencies as a function of how far apart they are and where they are relative to the listening position, as well as dealing with room resonance factors.

Kalbi23,

You don't have to take my or anyone else's word on the subject. Just google "multiple subwoofers in a home theater" and you will find that most experts agree on the superiority of that approach. Multiple subwoofers makes it possible to have much more even bass response throughout the room.

The issue for you is whether it is wiser to spend more money for a bigger/better single subwoofer vs. buying multiple cheaper subwoofers. That is a more difficult choice. Most listeners would find that a single bigger subwoofer will give more impact (hit-you-in-the-gut effect) and deeper bass, but multiple smaller subwoofers gives more even coverage, better pitch definition and better overall sound for music reproduction. If you place a high priority on impressive home theater sound effects, the bigger badder woofer would probably be a better choice.

James wrote:

Using multiple subs to try to reduce the impact of room resonances is difficult and not very effective, especially since the output of the subs will be reinforcing or cancelling at different frequencies as a function of how far apart they are and where they are relative to the listening position, as well as dealing with room resonance factors.

Well.....

The point of adding a second sub is precisely the phenomenon James describes as a problem. The delta between the response deviations of multiple subs averages back to the norm (anechoic response) - provided you place them carefully.

As to the larger point James is making, again, overall, I'd say "true" (regarding effort, with one caveat) and "false" (regarding potential for good results):

Attempting this exercise by ear is a major PITA. I'm 100% sure that many folks will quit before they get it right.

Doing it with a real time analyzer is much easier and likelier to produce a good result (with more than negligible time required).

Doing it with a high quality automatic room EQ package is a snap and IME will certainly produce excellent results. OTOH, this approach IME often provides excellent results with one subwoofer, so..point taken.

Bottom line: If you take the time, two unEQ'd subs will almost certainly produce smoother bass than one unEQ'd sub.

Two. I have three and there is bass without excessive boom. Everything blends better with multiple subs.