BillFitzmaurice.info

In my build thread of a THTLP, I said I might build a Table Tuba (or other sub, maybe even a T18) to complement the THTLP - fill in room nulls and all that.

Someone said not to mix the THTLP with something smaller. I do remember Bill saying not to try to mix (or EQ) the THT with other subs (ie, regular front firing ones) as they won't be able to keep up.

What's the reason why not? And Table Tubas (or T18s) won't work well with the THT? Most of my listening is not at reference levels anyway (and even then, the amplifier of the THTLP is nowhere near maxed out).

It's not that they wont be able to keep up. Different speakers have different phase response and mixing cabs is said to be more likely to create cancellations at frequencies with opposing phase response. I understand the concept, but have never tested it. By my logic, which is shaky at best, the "rule" makes sense for clusters of subs in PA applications. However, in small rooms, there are so many reflections and nulls throughout a room already with one cab design, it seems it may be less important having additional cabs be 100% in phase throughout their passband. Adding TT's to your THT may help and it may hurt. Honesty, if you're happy with the response in the room as is, I wouldn't bother building any TT's unless you have another place to use them if they don't work well in the current space.

I did it in the past with a Table Tuba and a T18. However, I had to use a measurement mic and lots of trial and error on my DSP to get it right because you can actually have less bass if it's wrong. A lot of the work was finding the right delay since the two subs had different horn lengths, but once it was dialed in it sounded good and provided a nice boost. There's definitely a reason they suggest to use the same sub, but it's possible.

TT and T18 is worst case, as they're so different. THT and TT wouldn't be as difficult to work with, but I'd only do so if I had the ability to EQ them individually.

Will a minidsp 2x4HD work in making a THT and TT play along nicely with each other?

Or... How about a 32" wide THTLP with 15" driver with a minimum width 15" THTLP with a 12" driver?

Difference in widths (which I read shouldn't be a problem), but different sized drivers as well.

Any of those combinations would be OK so long as the subs aren't close to each other, which they should not be in any case. But separate EQ is a must for best results.