Two subwoofers

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