Mismatched Dual Subwoofers

Subs output frequencies are such long wavelength they cannot be localized. As such it simply does not matter what subs are used together, in fact there are advantages to using different ones. Because the main benefit of multiple subs is multiple different bass modes, at different frequencies and in different locations, so one way of increasing differences is to use different subs. I say this knowing full well many, perhaps most, will say something else, being as they are still stuck in the old paradigm not having caught up with 20 years ago.   

See my system page. https://systems.audiogon.com/systems/8367 One Talon Roc powered sub, two sealed subs, two ported subs. This is deliberate. Because once you take the time to understand what is going on, then what you are worried about being a problem turns out to be an advantage.  

I use a pair of Rythmik F12 subs with a Paradigm Reference 12 all sealed with a huge HSU ported sub. I feel it is an excellent set up and love every minute of it. They are place randomly around the room, in fact one of the Rythmiks is on a solid steel table about 40" off the floor. 

Absolutely agree with Millercarbon, except I prefer sealed to ported subs (not sure that it matters particularly in a multiple sub array, it's just my preference).  I have two Rythmik 12SE subs and one dual 10" sealed DIY sub in addition to the 10" woofers in my full-range Kef Reference 207/2 speakers.  Using the subwoofer crawl I was able to dial in bass response below 200 Hz to ~+/- 2dB at the primary listening position.  Multiple subs is not a cure all, but it is effective in managing room modes at a single location.

Mat, it is not optimal but you can do it. I believe your STR will ping each sub individually and correct it's frequency response. Just hook one sub up to each channel, set up your microphone and go through your room control routine.

Sealed cabinets tend to start rolling off earlier than ported, but at a lower rate. All rooms have bass reinforcement, with often times the most at the higher end of the low bass, the same area where ported subs have higher output. As you go down lower though the curves often cross, with the sealed cabinet actually having greater output than ported. This accounts for hearing ported as more powerful, sealed as smoother/deeper.   

Using lots of them works so well because while each sub still has its own set of lumpy modes, its output can be lower because there are more subs and they all add together for smooth deep bass everywhere in the room. The single location limitation is a problem with using EQ, not DBA.

Is 2 subs better than 1 sub ? My problem is I have a Def tech supercube 4000, 8" with 2 8" radiators. Now they dont make it anymore Im thinking of a Rel T7x now. Will this be a problem having 2 different sub makers ? Thxs