Subwoofers - crazy upgrade!

Regarding the comments about stack vs spread out, yeah it's better to spread out.  It doesn't just fill in the nulls, it also makes response more even from seat to seat which is very important in home theater, and it also provides active cancellation, which is grossly overlooked.  Most people in typical rooms have an obnoxious spike around 35-40 hz, often another not so big one around 55 hz maybe.  So what do we do about this, stack the subs and make it even more obnoxious?  LOL.  No.  Spreading them out provides active cancellation that brings that spike down.  The alternative to this is a whole bunch of bass traps.  

Usually the best thing to do in terms of even response is to put them in the middle of each wall midpoint.  However that's usually not very feasible.  Second best, which also provides gain from the corners, is to put one in each corner, which is most popular.  Another method is to put them on the 25% points of the long wall if your room is long.  

As mentioned above, Harman has a ton of whitepapers on the subject, often written by Floyd Toole.  

I’m using a 12 inch SVS sub.  Should I add my old 10 inch  Martin Logan’s?

@elamar I’m using a 12 inch SVS sub.  Should I add my old 10 inch  Martin Logan’s?

If you've mapped out your rooms standing bass waves using the crawl to position your subs in and can invest in some inexpensive custom length interconnects from Monoprice or Blue Jeans Cable, I would certainly give it a try.

The likelihood should be a noticeable difference in room pressurizing and low frequency presentation.

Mapping your room only need be done once. It's the key for optimal -3dB subwoofer/s room integration unless you're using a four sub distributed array (Swarm). All the best.  

I love my 2 direct servo 12 inch sealed Rythmik F12G subs.

https://youtu.be/WBpDJ38shtk

@erik_squires  The use of built-in DSP and calibration on a sub is priceless

100% agree with this.  If I hadn’t experienced it recently, I’m don’t think I would fully grasp the magnitude of the improvement to the room from DSP to the sub (and woofers).  DSP was able to successfully address and significantly reduce room nodes.  The room got notably quieter...almost like magic.  The room wasn’t even noticeably noisy or boomy.  After I had braced my suspended floor, I thought things were dialed in pretty well, but a few surgical narrow cuts using the PEQ on the DSP was eye opening.  

The purist in me was always a bit squeamish to even try it, but since I bi-amp with solid state amps to the sub and woofers, and run tubes to the midbass/tweeters, I was able to install the DSP to only the low frequencies.  It really made an audible improvement...at least in my case.  Highly recommended!