from TFA:
"In an acoustic suspension, sealed box, or infinite baffle application, there is an optimum system Q value to obtain the flattest frequency response, and a phase response identical to a 2nd order Butterworth filter."
-i'm suprised he didn't prove it.
needs pics or animations. diverges frequently. could use section headings. these were problably left out because it is just a post on a forum and not a howto, at least that's the impression i gathered.