Two subwoofers or One?

I have a pair of Martin Logan Ascenti speakers with one Descent sub. What advantages besides having them operate in stereo would I get?

My room is 14' wide by 40' long would 2 subs. be more balanced, or should I just stick with the one sub?

Any help in this matter would help.
Put your Descent (just one) exactly between your speakers and set the phase angle switch to 90 degrees, crossover point to 35 (I know it sounds low but just try it.)

Set the volume to 12 o'clock to start.

Then adjust the 25 Hz boost and cut by starting low and very slowly raise it until your perceive a marked "thump" to the bass (depends on your material of course, but anything with a continuous good beat, but doesn't have to be unusually loud) Then, back off two tick marks.

You can then adjust the volume to taste -- but here's a little tip about using a Decent or Depth easily (if you're not too anal, aesthetically -- actually it looks kinda cool I think):

Because the woofers are in an omnidirectional layout 120 degrees apart, it really doesn't matter which woofer faces "front," the other two will wind up where they're supposed to. So if you point one of the two "back" woofers to the front, you will bring the rear control panel to the left or right front. I really like this because depending on the material, I do make regular subwoofer adjustments while listening. And it's much more covenient, both to make the adjustments and to hear the results, if you can do it from in front of the speaker system rather than standing (or crouching!) behind it. FWIW

Also, on an entirely different subject, with a room like yours, you might want to try setting up your speaker system in the center of one of the long sides of the room. You might be very surprised at the increased air and better defined audio image.
The usual advantage of using two subwoofers is that you will most likely spread out nodes due to room interaction.
Unsound, I know what you're saying, but for some reason (which I haven't really analysed) the omnidirectional radiation pattern of the ML subs seems to not excite room nodes to the degree that regular front firing subs do (I don't know about down firing ones.)
Nsgarch, I'm not familiar with this particular sub, so I must bow to your experience. It might be worth mentioning that it has been suggested that due to the summing of channels of stereo (i.e. not a dedicated sub woofer channel) signals to mono that it is actually possible to deplete information.
Unsound, What you are referring to did happen when people summed the L and R electrically by using a Y connector at the preamp and then running one IC with a mono amp for the sub. But if you keep the two channels separated electrically and either use a woofer with two voice coils (and a two channel amp) OR mix the channels with a buffered circuit and then use a single amp and voice coil, then that won't happen.

Whether one gains more spatial effects when two separate subs interact in the room has been debated. I suppose if a low frequency signal like cannon fire was clearly located on say the left channel, you would notice it, but anything below 120 Hz isn't very directional and I think the room would tend to soften that effect. It's the mid-bass and midrange that gives directional cues, and those are being handled by the main speakers.

Nsgarch, I can't argue with the truth. I will say that I while most experts agree that low frequencies aren't very directional, I suspect that on some level we are aware of something askew when those frequencies harmonics appear from where they might not aught to be.
As far as subwoofers go: two are better than one. 12" woofer is better than 10" and in my case, 15" is heavenly. IMHO. warren :)

On our website there are two resources that will help you. One is a paper on speaker placement. It includes subwoofer location. The second is a paper by Todd Welti and Floyd Toole on the use of multiple subwoofers.

Here's a link to our Resource Page.
Listen to Richard (Rives) he knows what he's talking about.
This is how I set my subs. Jay (the James from James labs) gave me this advice. Not the first one, mind you, who recommended this way: Turn your crossover all the way down. Then turn it up slowly 'til the music has that "boxy" sound. You'll hear it when it is not right. Then turn the crossover down very slowly until the sound agrees with your ears. Crossover numbers mean nothing. The crossover is room dependent. Oodles on the 'gon about this. Trust your ears. warren
No doubt Nsgarch , Richard is the man . His site is very informative with many interesting articles to get you started thinking before making that call to get help with the room itself. A great "white hat" in the industry for sure!

I have always used two subs. Two subs actually augment the size and shape of the soundstage adding much to the width and vertical height. Of the many pairs of subs I have used I have placed them any where from 1.5 inches in front of or at the same plane as the mains. The reason I do this is to align the voice coils of both the mains and the subs so as to more closely match the wavelaunch of both. My hot button for using subs is the net gain in realism of stage not the effect of super deep bass. As you already know the most bass will be at the corner or along the wall,this to me does nothing for the shape or stage of the music. Please make sure you use the coupling devices that came with your speakers and your subs. Direct coupling your speakers will allow you to more quickly dial in the sound placement and all the settings needed to blend your sub or subs into your mains.Tom
"Russ_b" can be manipulated to read "Rs_sub". Heheh.
Thanks Tom for the input. I am going to demo a second sub on Friday to compair one verses two.