Hi again Kevin;
Well, it's a start; but we're not there yet.
A few good numbers are still missing, I'm afraid. Like Qts, Qes, Xmax, and like that
You're halfway right about what the polyfill does in the box! What happens is, the sound takes a bit longer to find it's way thru the stuff out to the enclosure walls, and then back again, so the sound is fooled into thinking the walls are farther away, ergo, the driver thinks it's in a bigger box
Generally speaking; a bigger sealed box IS a better box(to a point)normaly a bigger box will give a cleaner, dryer sound with less "Boominess"
You may want to check and see if your impedance is set properly. Having a DVC(dual voice coil)driver does complicate things a bit. If the voice coils are connected in series, the amp will see 8 ohms, if in parallel; only 2.
If you're getting low volume, but lots of travel, you may also want to check what cross-over point you have. If you're crossed down around 40hz or below, with a big bass boost dialed in, the driver may not be seeing much other than the real low stuff, and with an SPL of 94.5 db, you should be gettin' lots of noise
I'm gonna sneak off now and do a little Googling for a Fusion 12 with numbers that match what you currently have, and see what we can come up with!
If you should find out any more info, let me know!!
Rich.
