Mismatched Dual Subwoofers

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.

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.