2 subwoofers and frequency response

Thanks Bob,Shiitaki, Martykl and Summitav.
You all have been very informative!!!
Ok so I have one JL audio Fathom F110. My room is 14X16 Iam using the audessy system on my Marantz av8003.

the owners manual states that one F110 would be :

27-111 Hz(1.5db)
-3db @ 25hz/120hz
-10 db @ 19 hz/155hz

so adding a second sub would change this how?
I realize that there are a lot of variables but
what would be your best educated guess?

Doug,

First caveat, I couldn't find output data for the JL110, only the JL113 (available at HTshack.com subwoofer test archives).

The 113 will reproduce 20hz at 95db (quasi-anechoic) with 10% THD, which means that it probably provides more than enough clean output for a room your size for music or movies (unless you require lower distortion for your tastes or you listen/watch very loud). The Audyssey will provide smooth response, meaning that you don't need a second sub to achieve that. In short, a single 113 in your room with Audyssey will probably be very, very good. The only reason you might want a second sub would be if you cross over high enough to require stereo subwoofers to maintain imaging and directionality.

The question is: How far short of the 113 does the 110 fall? Don't know the answer to that one. Maybe someone else has seen data for the 110.

Marty

Adding more woofers in a given acoustic space accomplishes many things - and introduces a challenge or two. Dual woofers allows for more dynamic range and efficiency in the bass - more power and surface area equals all the above, plus can help eliminate distoration, provide higher accuracy potential, and more. Getting another woofer in the system, allows you to lower the output of each - again, more efficiency.
Another common concept is dual woofers smoothing the bass response, by locating them in different possitions in relation to the bass modes and the seating possitions/speaker locations. This can be tricky to pull off with maximum effectiveness, however, in a multiple seating arrangment, where you sit proximally closer to one woofer vs the other, cause phase issues, and so forth.
Dual woofers can also be out of phase with each other, and relative to the rest of the speakers in the system.
Yes, Stereo Subwoofers also increases efficiency, and can help locate the bass and proper phase with each speaker with some added ease and effectiveness. (an EQ often helps here, regardless).
Whether to add another sub depends on lots of variables. Sure, in smaller/medium sized spaces, and in less ambitious systems, multiple subs might not makes sense. Still, to be certain, more can indeed be better in an "all out" system, where maximum impact, and system efficiency is demanded. I think the benefits outweighs the negatives - but ONLY as long as the rest of the system in wisely constructed and dialed in, and a there's a little knowledge involved with what's going on with the rest of the set up. Othewise, default to "keep it simple, stupid" is probably the wiser route - stay with the single
...in this case throw a smaller sub in a corner, and a bigger one right up in the middle of front wall between main speakers, and let today's advanced digital EQ's help you out with the rest.

Oh, didn't see your post on room size. I'd probably stick with one well placed sub in that smallish space. Two will get croweded aweful fast, unless you get real creative. Also, you have enough output from that single sub in that space. Also, the very lowest feq's won't be properly represented in that space anyway (could have gone with high output 10" woofer in that space, also). Bass will be on the thick and slow side on the bottom, as room won't absorb enough bass for a proper RT60. In rooms like this, I like to stay with woofer(s) that don't play down as low as larger, because natural boundary reinforcement and RT60 balance better this way. Otherwise you spend your time and technology tying to TAKE AWAY bass energy, and eqing out the large hump at the bottom from boundary re-inforcement, bass nodes, and lack of absorption. Better to have too little that's properly blended than too much that's compromised.
Yeah, stay with the single and EQ it out. My advice, anyway.