I dont wanna sound to much like a newb, but what is Qtc? It sounds like a T/S parameter
It "sort of" is. The Qts is the total "Q" of a speaker, a T/S parameter. The Qtc is the "Q" of the
system (speaker in the enclosure). And since it's dependent upon the enclosure, the Qtc will vary by enclosure size. "Q" is basically a measure of the system to resonate, or a measure of damping.
The Qtc basically tells us everything about the low frequency response of the "system".....low frequency extension, transient response, group delay, frequency response, sensitivity, peak output, etc etc. Higher Qtc's have less damping, and hence less low frequency extension, less sensitivity, worse transient response and group delay, more peaky frequency response, but with more peak output. Lower Qtc's have better damping, and have better low frequency output, better sensitivity, better transient response and group delay, flatter frequency response but with less peak output.
A Qtc of .707 (Butterworth alignment) gives us maximally flat frequency response and the lowest F3 out of any other sealed enclosure (any other Qtc). Qtc of .5 is critically damped and is "transiently perfect". A Qtc of .577 (Bessel) has maximally flat delay.