the reason polyfill will give you a lower response is because it will help to deflect standing waves in your enclosure. it won't eliminate them, but it will help, and w/less standing waves, there is less resonation on the cone, so the driver can use more excursion with less distortion(can play louder, and lower).
you want the perfect enclosure....make one in the shape of an egg.... zero standing waves
Perf: KYB AGX Struts Neuspeed Sport Springs 5 Strut Bars (2 F/U, F/L, R/U, R/L) Sprint Front Camber Kit $15 Rear Camber Kit Corbin's A/F Gauge MSD DIS-2 Ignition System Some Regrind Cams that need High Compression (which I don't have) Ported Intake Manifold Ported Throttle Body Nameless Cold Air Intake with a K&N Filter Custom 2 1/2 inch exhaust with Dual DTM Muffler Empty Catalytic Convertor Energy Suspension Motor Mount inserts Hurricane_GS Short Shifter Symborsky Shift Kit Clutchmasters Stage 3 Modular 225/50/16inch Wheels and Tires
Audio: Alpine CD Head Unit Alpine Flex4 25W X 4 for Fronts and Rears Alpine V-12 450W X 1 for Subs Infinity Reference Series 5 1/4 and 1 inch tweeter component systems for fronts and rears Blaupunkt 3 way 6x9's in the rears 3 MTX 5000 10" 12 ohm subs running 4 ohms mono
Flame Red SRT-4 GT40,8.5:1 Built Shortblock, Brian Crower Stage 2 Cams, etc etc etc...