advantages/disadvantages of 2 subs.....

Room 20 x 16...thinking of 2 10" subs...would this be wise?
Yes, I use 2 RELs in a room that is narrower and longer. Used one originally. Two are not necessary to produce enough bass, but , as REL puts it, two load the room better. That is, although bass is non directional, generating it from both sides or the room gives a better pattern of sound dispersal. Also , each sub will be working less to produce a given sound level. Cross them over very low and you will not be aware of their presence until you turn them off. I turn mine off when working on my system and occasionally forget to power them back up. It takes a while before I realize that something is missing.
there is a white paper by Harman Internation on the benefit of multipe subs - you can search for it in these forums. Beyond the placement issues, distortion for any sub goees up with increasing spl and decreasing hz. At the lowest frequencies, you may get audible improvement by spreading spl over two subs (if you listen loud enough and there's low pitch information in the program material). BTW, A-gon member Bob Reynolds has been very helpful to me in this area - he recommends SVS subs and provided pretty compelling distortion specs to demonstrate just what a value they are. You might want to contact him, visit the SVS web site, & check Bob's contribution to the thread entitled "best inexpensive subwoofer".

God Luck

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>Room 20 x 16...thinking of 2 10" subs...would this be wise?

For what purpose? Ported/passive radiator, bandpass, or sealed?

For most music (even electronic music) peaks in the last octave don't have 1/10th the power that they have in the rest of the spectrum. You should be OK.

I don't know about organ music.

For reference level home theater a pair of 10" sub-woofers will be woefully short. A pair of 15" sub-woofers there are short.

If you haven't noticed from the above post, I might also have pointed out that Drew is an excellent resource for this question as is member Shadome.
Dear Phasecorrect: Which speakers do you own? do you wnt to integrate the subs for a music stereo system or a home theater?

Regards and enjoy the music.