"Phil Allison" wrote in message ...
"William Sommerwerck"

It's been done. William Michael Watson Dayton-Wright built conventional
dynamic speakers with bags of SF6 in the woofer box.

** For what advantage ?
The speed of sound is about half in SF6 but that is no help in a sealed
box where resonance depends only on the stiffness of the volume of
gas trapped behind the woofer.
The smaller the volume or the larger the woofer, the stiffer it becomes.

The lower speed of sound makes the bag appear to have a larger acoustic volume
than the air it replaces.


He got clean bass to below 16Hz from a small cabinet.

** Really?

Really. The bass cabinet was about 20" by 20" by 12". At 16Hz, there was no
/audible/ output from the speaker, but everything loose in the room was
rattling.

The spec sheet for these speakers included a harmonic distortion curve. If I
recall correctly, the speaker had something like 5% harmonic distortion at
20Hz at 90dB output. (Don't hold me to the exact numbers, but the distortion
was very low.)

He also claimed that aluminum wool was a better damping material than
Fibreglas, fiberfill, or foam. He said the linearity of the driver's movement
depended in part on the thermal linearity of the damping material, and that
aluminum wool did a better job. I didn't fully understand this, so don't jump
on me.

Ever heard his SF6-filled electrostatics? We sold a pair to a man with a
large, dead basement. With each speaker powered by bridged Crown M300 amps,
the system could play at ear-splitting levels with no strain.