In article , Fleetie
wrote:

Another idea would be to use an electron gun. Electrons don't propagate
well through air, because they collide with air molecules. This effect
would increase with increasing local air pressure and density, again
reducing the received signal.

I recall reading about one of these around 4 decades ago. The idea was to
put a beta-emitting isotope on a central pillar and measure the variations
in current reaching a surrounding (open ended) tube to determine the sound
pressure variations.

No idea if it failed to become popular because it worked poorly, or because
it relied on 'evil' radiation. :-)

Slainte,

Jim

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