Two subwoofers

Yes it is possible but careful volume matching, phasing, and cancellation issues must be addressed. I am currently using five subs(3 different mfr's) in my main HT/music system and believe me, it takes some work and patience to get it "right". I am using a pair of Klipsch RT-10d's in the front corners, a Klipsch RSW-10d next to my recliner, and SVS SB13+ next to my sofa, and also a Revel B15. Different driver sizes(10"-13"-15"), amp powers(500w, 700w, 1000w, 1000w). And yes, my bride is a keeper.

Bill

When you match the output level of a sub to the main speakers in a system, you do so at a given SPL (75db in the latest Audyssey set-up regimen IIRC). I think the OP may be asking what happens as that SPL changes. Might two different sub models behave differently as SPL rises.

Theoretically, at least, I believe that the the answer should be "yes". In every sub (and speaker, for that matter) some amplifier output is converted to acoustic output and some is lost to heat - thermal compression. The ratio of the two may differer between different designs.

In practical use, I doubt that it's likely to be meaningful (or even audible). Since most dual sub set-ups aren't stereo, the theoretical mismatch wouldn't affect stereo balance (the subs are operating in mono, anyway). The bigger theoretical issue is how thermal compression impacts the combined output of the subs vs the combined output of the main speakers as the SPL increases. This is as true with identical model subs as it is with differing subs.

It may vary case by case, but I've measured the response of my system (with identical twin Rythmik subs) at 75db and at 95db and the difference is negligible. FWIW.

Thanks all. Wow 5 subs in a single HT system. Whoa and I thought two was more than most. Yes that can be quite tricky. Bob what I meant by out of synch is that perhaps the two different subs were not in exact phase. Perhaps the drivers could be out of the exact timing being of different types of amps (class B and Class D) and one having a larger enclosure. So here's what I ended up doing. I took home a 2nd ASW610 brand new from my dealer and removed the ASW600.

After many hours of listening and trials, I became convinced this was the right move. I purchased the new ASW610 and redeployed my older ASW600 as a sub for my Dell desktop PC in another room. The two ASW610s work extremely well together being very compatible. The LFE and bass extension is far more tight and focused on the sweet spot. I realized that the older ASW610 produces more rattle and actually more vibrations in other rooms. Now those vibrations have greatly reduced which was also my interest in upgrading. So far, mission accomplished !!

I am assuming when you mean out of synch, you are referring to out of phase? I am guessing one sub set at 180 and the other 0. I pondered similar issues a few years ago. My old 15" sealed 1000 watt sub watt (B&W Nautilus ASW 850) has been a workhorse in my system. I wanted to get a replacement but of course they are not made anymore. After researching and doing comparative analysis (Internet sources and manufacturer products), I opted to get another 15" 1000 watt sealed sub, from HSU. It had all of the basic functionality of the B&W in terms of specs and controls. It was easy to blend both of these subs with a Velodyne SMS1 sub eq. Excellent room response. I have them configured directly to the right and left of the main speakers. You will need to level match them first in order to ensure that the volume is the same for a given output.

Good luck,
Audioquest4life

I use a pair of Velodyne HGS-15s controlled by an SMS-1. I recently bought a pair of SMS-1s with the thought that I might try an SMS-1 for each HGS-15 and use the third SMS-1 in another setup with an HGS-10. I can't quite get my head around the efficacy of a separate SMS-1 for each HGS-15, because it seems that it's the combined output of the subs that one wants to equalize. Nevertheless, the Manual for the SMS-1 covers using them in tandem, so I plan to try it.

db

Where you get the SMS 1's? It is not for sale on the Velodyne website anymore. I want to use two for my setup.
Thx.
Audioquest4life

I bought the two SMS-1s from a guy in Wyoming, I think. It was probably a listing on Audiogon.

db

congrats you are happy ! are the new subs servo controlled subs ? and what size are they ?
i think there are a # of YT videos extolling the value of multiple subs and i think it is a no brainer now proven they work
are those vented or sealed ? some advocate using bOTH!
I am going to try open baffle servo subs 12 "
some chaps elsewhere were debating "fast bass:" which ( to me just means it is controlled better like w/ servo subs and i am quite sure the servo subs are MUCH better than they used to be) older ones had reliability issues

funny why is it all the old guys think speaker tech just STOPPED! like 20 years ago and new speakers and subs are not better ? ? are they just lazy to keep up ? so just dismissive ?
reminds me of some of the old profs at university who just were resting on their laurels and had not done any noteworthy research in years ! we always wondered if their brains had atrophied ?
when i watch the good , honest reviewers on YT like New Record Day, Audioholics etc they sure seem to be saying the newer are better and say so! even prove it w/ measurements ! ( and YES they are LISTENING too! -love it when some curmudgeon intones whining "but do they LISTEN " to them LOL 
i am thinking of using sub for almost ALL the speakers in my 11.2 HT system! 
i found adding a sub to my center channel certainly is valid it only does below 80 Hz or   so it seems there is info there to be heard below what the speakers like to produce sadly the BEST audio is during commercials! often not shows or movies!
thx for any helpful comments  

Hopefully the OP figured it out in the last 10 years.

well nothing wrong IMHO w/reviving old threads and bringing the topic up to date!

IS THERE?
your comment smacks of ad hominem attacks we see here bunch of old guys ( mostly ) behaving like school yard bullies! and what does your snarky sarcasm contribute ? get real!
as Werner Von Braum said :"we aim for the stars! ................( but sometimes we hit London) " 

i was interested to learn what he is doing / using for a subwoofer(s) Now years later! the Allison group is full of old curmudgens who don't seem to have made many equipment changes for  decades! 
i was excited to find velodyne sub for sale for only $100 but when i went to buy it pick it up  there was big hole he had poked in the rubber surround! the day before so NO sale !