i have a box in the back of my truck that is 6.5 cuft with twin 5" square ports from my previous subwoofer. My new sub is a BTL18 dual 1. here is some specs. Can someone tell me with with the box tuned to 38 hz ish what my port lengths would need to be? I can't change the box from 6.5 cuft but I could change port sizing/length. DUAL 1 | DUAL 2 Fs: 32.6 Hz | 32.1 Hz Re: 0.7 Ohms/coil | 1.5 Ohms/coil Qms: 6.11 | 6.20 Qes: .28 | .26 Qts: .27 | .25 Mms: 298g | 307g Cms: 0.80mm/N | 0.80mm/N Sd: 1210cm^2 | 1210cm^2 Vas: 164.2 l | 164.2 l Spl: 94.9dB 1W/1m | 95.1dB 1W/1m Bl: 17.5 N/A | 26.9 N/A Bl: 00.0 N/A | 00.0 N/A Xmax: 16mm * | 16mm * Rms: 2000W * | 2000W * Sealed box: N/A cuft | N/A cuft Ported box: 5-8cuft | 5-8cuft Sub OD: 18.500" | 18.500" Cut ID: 16.750" | 16.750" Mounting depth: 9.750" * | 9.750" * Displacement: 0.26cuft * | 0.26cuft