Thanks for the info Swerd, good stuff. It definitely helps fill out the picture for me. After some googling, it seems that the most preferred Qtc is .707. Am I right in thinking that not all commercial subs go by .707? Take the
FR of the Cadence CSX15 mk2, for example, that looks like the FR of a high Qtc.
Glad to know that made sense to you.
A Qtc of 0.71 (or lower) is what I'd shoot for, but I don't know if its the most preferred.
If I had to describe in words the sound of woofers with different Q, I'd say low Q (about 0.5 to 0.7) sounds "lean" or "dry", and high Q (1 or higher) sounds "fat" or "boomy".
Yes, you're right, not all commercial subs (or commercial speakers of any kind) go for Q = 0.7. The example you linked sure looks like it has a very high Q (elevated response from about 60 Hz to well over 100 Hz). It often is used to make a cheaper woofer sound like it has more potent bass, while keeping the cabinet small.
Many people get used to listening to bass from woofers with high Q. Their poor damping allows them to ring so much that it makes the upper bass/lower midrange sound muddy. Think of how car audio can sound with cheap speakers when the bass is boosted too high. When people first hear speakers with low Q bass, they often think the speakers lack bass slam

.