I'm talking about the acoustic system Q. If we put a driver in an infinite baffle the Qtc = Qts (of the driver). But with an open baffle the Qtc (or perhaps Qtb) of the system goes down with the size of the baffle. What I have ascertained so far (by means of sims) is that if the baffle cutoff frequency = Qts x Fs we get sort of a max flat alignment where Fc(-3db) = Fs.......... I'm not sure "Fc" is the right term. To get on the same page would you define the differant "F" numbers as you understand them.....mike