Haha funny story about your old school setup bumpin vanilla ice :P
Ya I totally hear ya about bumpin it at a stop light being disrespectful to others. That's why I really like the 4th order design, it keeps all the bass in the car and doesnt leak out the trunk this way I can play my music at a medium loud volume without trunk rattle anopying noise. Nothing worse then hearing horrid trunk rattle !Removed! sounds at a stop light. I feel like yelling at those aholes and tell them that they arnt impressing anyone with that crap rattle of a system they have and then blast them with a 30hz tone :P making them feel like crap :D
Thanks for the comment. It took a long time with alot of number crunching to design the 4th order enclosure properly so I'd get the perfect blend of sound quality and output for all types of music...
To use the following calculations, you will need to know the following:
Vas = equivalent air compliance for the driver (litres)
Fs = driver resonance frequency
Qts = driver Q at Fs
The following equations will allow you to design a 4th order bandpass system with a desired low frequency limit or a desired gain. You will need to choose a value for "S" that suits your requirements. 4th order bandpass systems where S is less than 0.7 will have a degraded transient response, but wider bandwidth and smaller box requirements.
if S = 0.7, then b = 0.7206, passband ripple = 0.00 dB
if S = 0.6, then b = 0.9560, passband ripple = 0.35 dB
if S = 0.5, then b = 1.2712, passband ripple = 1.25 dB
4th order bandpass system with desired low frequency limit
Choose a value for Fl, the lower 3dB cutoff frequency,
then,
Fl' = (Fl*Qts)/Fs
Fh = (Fl'+B)*Fs/Qts
Qbp = (Fl'*(Fl'+B))^0.5
Fb = Qbp*Fs/Qts
Vf = (2*S*Qts)^2*Vas
Vr = Vas/((Qbp/Qts)^2-1)
Pa = -40*LOG(1/(Qbp*2*S))
where,
Fh = upper -3dB cutoff frequency (Hz)
Qbp = Qtc of sealed chamber
Fb = resonance frequency of vented chamber(Hz)
Vf = net volume of vented chamber (litres)
Vr = net volume of sealed chamber (litres)
Pa = gain (dB)
4th order bandpass system with desired gain
Choose a value for Pa, the gain in efficiency,
then,
Qbp = ((10^(-Pa/40))*2*S)^-1
Fl = ((-b+(b^2+4*Qbp^2)^0.5)/2)*(Fs/Qts)
Fh = Fl+(b*Fs/Qts)
Fb = Qbp*Fs/Qts
Vf = (2*S*Qts)^2*Vas
Vr = Vas/((Qbp/Qts)^2-1)
where,
Fl = lower -3dB cutoff frequency (Hz)
Fh = upper -3dB cutoff frequency (Hz)
Qbp = Qtc of sealed chamber
Fb = tuning frequency of vented chamber (Hz)
Vf = net volume of vented chamber (litres)
Vr = net volume of sealed chamber (litres)
Pa = gain (dB)
Even at low volumes this flex is noticable, it's not a vibration though its just the air pressure in the cab changing due to the high excursion (XMAX) of the woofers. With the 6" aerport having flared ends to it there is no port noise when air passes from out of the box through the factory subwoofer cutout hole into the cab of the car, this makes for a smooth deep sound that on some subsonic frequencies you wont even hear the bass, but just feel it or see it moving your shirt.
To see your own roof flex crack your sunroof, kepp all other windows up. Open a door then slam shut semi hard and you will see your roof flex from the air pressure change.