free air subs in a 10.5 cuft ported trunk?

[tbird635]

Ok...here's the scenario....
I have a 1972 MGB roadster with what I calculate to be approx 10.5 cu ft of trunk space. Years ago back in the 90's I had an almost identical car with 2 Radio Shack 12" subs mounted in the rear bulkhead as a semi sealed enclosure. The sound quality was shaky at best.
So I decided to go with 2 10" Kicker free air subs in almost the same setup. Mounted in the rear bulkhead where the trunk wall meets the passenger compartment. (both cars I mounted the subs in 3/4 mdf board screwed and siliconed to the bulkhead with holes cut for the drivers. ) 07C104 is the Kicker part number this time around.
After listening to them a bit, I decided to port the enclosure as it had very low output . I put in A 4" Precision Port , basically glued flange to flange. No tube length. And cut down one flange. Basically a 2" flared port.
I figure its tuned to maybe 25 hz. It sounds better with the port, but it all sounds 20 hz or lower.
As my calculations may not be correct, and I should reduce the enclosure volume, is it viable to reduce volume with stuff in the trunk?
and are my calculations correct? How do I determine the resonant frequency of my enclosure? Is 25 hz too low for a car?
It has some serious kick on rap, but Im more of a classic rock guy.
Finally, did I pick the wrong speakers, and should I have made a smaller enclosure?
T/S parameters:

Size10 -inchImpedance4 ohmsCone MaterialPolymineralSurround MaterialFoamIdeal Sealed Box Volume (cubic feet)N/AIdeal Ported Box Volume (cubic feet)N/APort diameter (inches)N/APort length (inches)N/AFree-AirYesDual Voice CoilNoSensitivity87.3 dB at 1 watt
Frequency Response30 - 500 HzRMS Power Range (Watts)50-150Peak Power Handling (Watts)300Top Mount Depth (inches)5 1/16Bottom Mount Depth (inches)N/ACutout Diameter or Length (inches)9 1/4Vas (liters)64.38Fs (Hz)29.4Qts0.451

• 10" 4-ohm subwoofer
• polymineral cone
• double-stitched foam surround
• suitable for free-air use
• power handling: 50-150 watts RMS
• peak power handling: 300 watts
• frequency response: 30-500 Hz
• sensitivity: 87.3 dB
• top-mount depth: 5-1/16"
• sealed box volume: 1.0 - 2.4 cu. ft.
• ported box volume: 1.25 - 1.75 cu. ft.
• warranty: 1 year

[TheBaronGroog]

They should be fine for your use, however with IB cone area is king so would go larger if possible.

Is the boot completely sealed other than the port hole? Otherwise it may be cancelation that's causing your issues.

You've tuned your trunk to 24-26Hz if your calcs are correct, you'd need to add 5cf of ballast to get it to tune to 40Hz area-bit of a PITA!

[dangus]

I wonder if an aperiodic membrane would make the sub more tolerant of variations in box volume?
AP Enclosures-The Aperiodic Cookbook | Tutorials | Team Audionutz

[TheBaronGroog]

AP is a good idea, not tried it myself, but provided you're willing to do some experimenting it should offer some good results-allows you to effictively tune the Fs of the driver from my little reading on it-only down side is that I've heard it drops sens by up to 6dB