I have a 95 Trans Am convertible and all I have are a punch 60 amp hooked to
an Obcon 10" enclosure box (at the time it had a RF woofer) and I hit 132.5
dB a few years back at the local dB Drags. I was the only convertible and
only person with only one sub in my class. The judges made me pop my trunk
because they could not believe "I hit that hard in a convertible with just
(1) Punch 60 and (1) 10" sub." I now have a JL audio sub in the same
enclosure and I would love to see how much harder it hits now (terms of dB)
because I know I can hear and feel a HUGE difference ever since it was
installed. As for your concerns; for clarity and hit of the bass my system
sounds best with top up but not too shabby with it down. The bass is just a
little more muffled and needs to be turned a few clicks up on the volume to
get closer to what I would have with the top up.