I will be referring to the focal 15KX in the examples as it was what i was working with at the time. (i wish i could afford it!)

Vas = 280.3L fs = 25.8, QTS = 0.39, QES = .40, QMS = 9.71

anyways, Dr. Leach says to choose your QTC. so lets go with 0.707. Then estimate the value of QMC. he suggests using 5-10 for unfilled systems, and 2-5 for filled systems. so lets use 3.5.

Then calculate the electrical quality factor QEC by the equation QEC = QMC*QTC/(QMC-QTC)... .886

Then calculate the compliance ratio alpha

alpha = (QEC/QES)^2 - 1 = 3.91

then VAB is simply Vas(280.3L) / alpha. or 71.76L

and fc is fs*sqrt(alpha+1) = 57.19hz. to accomodate the effects of filling this volume must be reduced further. Leach suggests 25% for uncompressed home fiberglass insulation. So Vb = 71.76/1.25 = 57L So final box volume would be 57L + bracing + driver displacement.

This varies significantly from winISD which gives me an enclosure size of 121L and an Fc of 46.8hz(extrapolated from the phase plot...freq when phase = 90)

unibox gives 131L with an Fc of 54.4hz with Ql = 30 and Qa = 5. would QMC be the parallel combination of these two? In which case i'll recalculate the Leach way with a QMC of 4.3. I get a VAB of 81L and FC of 54.6.

It seems leach and unibox are very close with their calculation of Fc. which means both should calculate the compliance ratio similarly, but why the big difference in Vab? Both in my acoustics class and my audio engineering class, Vab was always Vas/alpha.

What am I missing? I like Dr. Leach's method because it follows with his PSPICE loudspeaker models that I use to simulate driver + crossover interactions. If it is grossly inaccurate however, I need to find something new!.

jt