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.