The Subwoofer DIY Page
Ported Systems - Frequency Response Calculations
last updated: 13 April 2011
The Subwoofer DIY Page

To calculate the frequency response of a ported enclosure system, you will need to know the following:
Vb = net box volume (litres)
Fs = driver resonance frequency (Hz)
Qts = driver Q at system resonance
Fb = box tuning frequency (Hz)
Ql = box losses (Ql=7 can be assumed for most cases)

then,

Fn2 = (F/Fs)^2
Fn4 = Fn2^2
A = (Fb/Fs)^2
B = A/Qts+Fb/(Fs*Ql)
C = 1+A+(Vas/Vb)+Fb/(Fs*Qts*Ql)
D = 1/Qts+Fb/(Fs*Ql)
dBmag = 10*LOG(Fn4^2/((Fn4-C*Fn2+A)^2+Fn2*(D*Fn2-B)^2))

My thanks to Bill McFadden, for providing these equations for determining the frequency response of ported systems.