Two Subs Vs. One

Trying to augment the sound from a pair of Totem Hawks in a large room (rest of system is an Olive Musica server, Eastern Electric Minimax Pre, Classe CAP-150 Amp). I am doing some in-home auditions of affordable single subs (mostly REL) and really like what they do for the sound. So far, I am leaning toward two smaller subs, one behind each speaker (ie. REL Q108E's - I like the sound better in that position and it looks better - wife factor) versus one larger one in the corner (ie. REL R-205). Can't find two demo units of the same sub to audition the two-sub option and was wondering if anyone had experience with this comparison.
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Bob_reynolds...I am not quite sure what your question is, but...

It is widely stated that a very LF sound source can't be located by a listener. Without getting into whether the statement is true or not, my contention is that it is widely stated. I believe this because it is often said in Audiogon postings which I have read (and other reviews). When something is said often enough people accept it as true.

I believe that a LF sound source can be located simply because I can do it, and I don't think that my ears are anything special. The ability to localize the sound is most obvious when it comes from behind the listener in a multichannel system. Left to right localization is also easy unless, as is often the case (particularly with LPs) the LF signal has been blended to mono. A mono LF sound will create a phantom image between two subwoofers, just like higher frequency sound. Also, if multiple subwoofers are operating out of phase, through either electrical connections or placement, the sound will have a "diffuse and directionless" quality...exactly what happens at higher frequency.
Thanks for all the advice - really appreciate it - it's always interesting to hear several logical yet contradictory and often mutually exclusive opinions on audio topics - part of the fun really.

I decided to start my sub experience with a single unit and do it in the least expensive way while still going for a quality unit. I bought a HSU research sub on-line. Easy to hide (wife factor), great reviews from mags and audiophiles, reportedly more oompf than the small RELs, 30-day refund option and if I find I want to try a second unit it is easy and cheap to do.

My room is huge, it's a bit of a sonic mess, I am very limited in placement options and a big powerful sub will not fly in the family/listening room - so spending huge cash on a top notch sub likely makes little sense. I will settle for a noticeable improvement in sound for awhile, play around with the HSU and maybe a second one at some point and see where that takes me.
You might to look at the following article which talks about how to maximize the use of subwoofers (both number and placement)
I agree with Eldartford when at very close range and at higher SPL levels.

I find I become aware of the general direction of a sub when I am within about four feet of it in 25 foot room (very close range and the lower the cut off the closer I need to be to know where it is). This tends to work only at higher SPL levels so maybe floor vibrations are providing higher frequency harmonic clues or it is the small amount of energy from the driver above the cut off....who knows.

I do agree that a sub position behind the listener does not seem to work as well...perhaps because this ends up being quite close to the listener. My preferred option is placement at a similar distance to the listener as the main speakers and for practical puproses to one side of the room or the other (rather than between the two speakers). Sub to ceiling, sub to side wall, sub to rear and front walls all being different lengths (this seems to be a good rule of thumb).

Two subs does complicate things as cancellations will also affect the sound field...probably a harder setup.