What big amp are you running? (The PF 500 is you backup, I guess.) You only write "SVT". Do you refer to the 300W tube model? Not an SVT-3Pro or something similar? The SVT-610HLF uses speakers that have traded sensitivity for extended bass. In order to "get you back" to the SPL given by the sealed, middy 810 you will need substantially more power than either those amps can deliver (cleanly), IME.
A true 1000W amp will give you much more articulate and accurate lows, cleaner and more dynamic mids and less "choking" once the volume goes up.
Boosting mids around 1000-1500 Hz might work better than in the low treble region 3kHz.
By the way, anderbass, blocking a port will lower the cabinet tuning, not roll off lows.
Last edited by AlexanderB : 09-01-2013 at 04:52 AM.