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Old 10-22-2013, 05:59 PM
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Question Anyone have a guess on car audio math equation

I was doing a bit of research on how to mathematically calculate 4th orders, and stumbled across this,

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)

but no where on the website does it say what "b" stands for! All the effort of finding this and I can't even try to use it... So maybe one of you smart people could pitch in and help me out.

The Subwoofer DIY Page - 4th Order Bandpass Systems: Box Calculations
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Old 10-22-2013, 07:27 PM
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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
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Old 10-22-2013, 10:35 PM
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Thanks! I guess I'm just blind sometimes.
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Old 10-22-2013, 11:01 PM
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No worries! I just found that site a couple days ago.

It's kinda fun to go through the whole equation.
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