 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/((Fn4C*Fn2+A)^2+Fn2*(D*Fn2B)^2))  My thanks to Bill McFadden, for providing these equations for determining the frequency response of ported systems. 
