Originally Posted by dla26
Good suggestion. I've sent an e-mail. I hope he still has the results on his hard drive. He did this analysis last summer.
While I wait for this info, anyone have any suggestions as to what sub I should be looking for? Or does it really hinge on which frequencies are missing?
Try to earn some more WAF points and buy another Ultra.
I was in a very similar situation and wanted to compliment my Ultra with some smaller, probably sealed, sub. I'm glad I did not.
I bought another Ultra, and in the process of fine-tuning the system I figured out that two subs canceled each other at certain frequencies when they were in different tuning modes, e.g. one in 20Hz mode and another one in 15Hz mode. That happened because they had different phase shifts (group delays) in different modes. For the best result I had to put them both in the same mode.
Every sub model has its own group delay, and if you want to achieve the best possible sound from your system try to use the subs with the identical group delays, i.e. the same model.
You can compromise and run two subs with different group delays, but in this case, most likely, you would have to sacrifice some frequencies due to the sound cancellation.