Here's the answer to your question about Boyle's Law (which you will ignore,
of course)...

PV = k assumes a constant temperature. If the temperature changes, then PV
changes. The relationship is no longer linear, and as the air trapped in the
cabinet is supposedly providing a significant part of the restoring force, the
cone's displacement will not be as linear. (Duh... Get it?)

This is what WDW is talking about when he says "As SF6 is an 'ideal gas', it
operates as an 'isothermal' spring, thus avoiding the problems with
'acoustic-suspension' loudspeakers that operated partially as an isothermal
and partially as an adiabatic system. Some designers seemed to lave little
knowledge of Boyles Law or the Laws of Thermodynamics."

There is no such thing as an ideal gas, so WDW is wrong on this particular
point. However, if SF6 is significantly closer to being an isothermal gas than
air is, * then what he says makes sense. QED.

Gotcha! Finally got ya!

You may now jump up and down, Rumplestiltskin, until you break through the
floor.

* I can't find anything on this at the moment. But I'm looking.