"I ran WinIsd at 600W, and with a 4.3ft^3 box that has (2) 3"x18" ports, the port Velocity is really high at 40m/s @ 20hz (that box is tuned ~20.90 give or take).
With a 20hz Butterworth 2nd HPF, the Xmax is listed as 13.45 @ 17.55hz at 0 Degree coil temp, at 200*F it jumps up to 16.6mm At 1000W the Xmax jumps to >21mm at 200*, with >60m/s por velocity.
No wonder you are hearing chuffing, doesn't seem like a good match to that box."
What were you looking at in WinISD to figure all that out. Would you mind telling me the way to find that kind of info? Right now I'm modeling drivers and looking at graphs, but it sounds like I'm missing a lot.