Originally Posted by basshead81
Just to note the TV42 looks to be tuned to extend deeper then the TV36.
TV42- +/-3db 11-150hz
TV36- +/-3db 14-150hz
Thanks, Bass! That's interesting. I don't think that implies that the TV42 is actually tuned deeper than the TV36 though. I suspect that the port tune is the same, and if so, that's somewhat more important for potential cancellation somewhere around the port tune. I think that it simply means that the TV42 continues to carry more SPL a little deeper than the TV36 does.
In most rooms, frequencies below about 15-20Hz won't be as subject to room modes as higher bass frequencies would be, so a difference in SPL (and therefore in FR shape) at the lower bass frequencies won't be quite as significant as cancellation at the tuning point would be. At least, I believe that would be generally correct.
I think that a good analogy would involve comparing the Cap 4000ULF and the Cap 2400ULF. They are both tuned to about 10 or 11Hz, but the Cap 4000 has more SPL at 10Hz, and it continues to extend a little deeper. And yet, because the tuning point is the same, they seem to be able to pair well in a room.
This issue of different tuning points, creating potential cancellation, seems to be a little complicated though. I know that you aren't getting cancellation from your low-tuned JTR sub, paired with your much higher tuned PSA subs. And, I have seen the same thing with mid-bass modules paired with low-tuned subs. But, subs with port tunes only a few Hz apart seem to be much more subject to cancellation at about the port tune of the higher of the two, from what I have seen.
I'm not sure whether anyone has come up with any sort of formula, or rule-of-thumb, to explain how much difference in port tune is actually problematical. If so, I haven't seen one. My best thought at the moment is either to have the port tunes very close together, or pretty far apart, as they are in your room. But, even if that were generally correct, placement within a given room might still be a factor.