Originally Posted by dftkell
So I'm most likely going to use the 12" Ultimax and stuff it well like you said. But when you say the other woofer would work but have a lower Q, you're referring to the Dayton RS-HF, right? And if you don't mind me asking, what does having a lower Q mean?
Yes, the RS-HF has a lower Q by itself, lending itself to lower Q sealed box designs. Q comes from (way back in the day) "Quality factor" and it's a measure of damping I guess you could say. It's kinda how much control the magnet/coil system have over the cone motion, fighting the mass and the springiness of suspension. A lower Q means more control, meaning in particular better ability to stop the cone motion when the audio signal stops. Another way to think of it is as a measure of how sharp or strong the resonance of the speaker is.
Here you can see some tone burst results-the audio voltage on the bottom looks perfect, but the acoustic output (related to the cone motion) does not start nor stop instantly.
Too much ringing is heard as a looseness and/or boominess of the sound.
Many sealed box designers shoot for a final Q in the box of 0.707, because this gives the lowest -3 dB point. That's rather misguided, since Dick Small only chose -3 dB for mathematical convenience while writing his thesis. In real rooms, the -6 or even -10 decibel points may be more important. On the other hand, very low Qs start to require a huge box, since the stiffness of the air in the box drives the Q up. The Ultimax Q was I think 0.58, so even a big box pushes the Q higher really fast. The HS' Q is...0.39?? Anyway much lower, so even a smaller box doesn't push the final Q too high.
All this vaguely applies to ported boxes. Those are much more complex than sealed boxes, however we can generally apply a rule of thumb that smooth gradual rolloffs should sound good but responses with peaks will tend to sound boomy. This is not actually because of the frequency response, it is because of the TIME response (ringing).