2 subwoofers and frequency response

Thanks Summitav
so if it is +/- 3db @ 22hz how many DB would it change? I had a fellow audiophile say that each sub would allow you to hear the FR at 3db louder what do you think ?

Hi Bob,
Thanks for the white paper link but nothing came up just the title white papers with nothing under it

I found it nice article

Thanks Queefee,
I will try placing them as close to each other on the front wall. I guess my question would be if my f110 fq response is 22 hz then how low would 2 take me? I understand that placement has a lot to do with it but have you measured how low 2 will go compared to one?

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?