Like regular speakers in your system, I am not so sure it is good to have multiple brands/sizes of subwoofers in your system. I tried that once and it did not work well, as such I did 2 same subs for music and 2 additional matching subs for movies. That was nice.
That is common advice but one I like to correct. It isn’t really a problem.
The argument against using different types and brands of subs is that the dynamic limits of the different subs make it so the weakest sub becomes your weak link. Partially but not necessarily totally true.
Then you have the arguement about ported vs sealed. Again, there is truth to the argument but it’s also an overstatement to say never do it.
Rather, using multiple dissimilar subs adds variables you need to account for and it can complicate integration.
I’m a big believer in the use of multiple subs which have a bandwidth focused more in the midbass region. I then like to use one sub that has greater low end extension than the midbass subs. In my case I have a mix of sealed and ported, but the ported is the deep bass sub and is tuned below 20hz.
There is no problems with this approach but there are complications to address. For example my extension is actually worse with the ported sub added to the equation because the port is out of phase with that of the sealed subs. Fix for that is a targeted allpass filter. That and, honestly, I don’t really care that I might be missing bass output below 15hz where the cancelation occurs.
As for dynamic differences. If they are wildly different then that is a problem. However if we are talking about modest differences of say 3-4dB then It can be managed. My own approach, which i took from geddes, doesn’t set all subs at the same output level. Instead I set each additional sub in the system that is closer to me at a lower level than that of the first sub. My setup currently is operating with 5 subwoofers. The 18” porter sub is the first sub added in my setup routine and is set such that the level is flat with it added, or close to that. I then add each successive sub and only allow it to bring the total output up about 1dB or so. When all is done I get the right room curve I want but the midbass module subs are not playing as loud. That means that it, for example, the subs output is 3dB’s lower in peak output and its playing 3dB lower in level, its total dynamic range in the system is the same. I haven’t limited anything.
