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A bit over a century ago, compressed air gramophones
[link] were used to play music for large audiences. These
consisted of regular gramophones where the needle,
instead of driving a diaphragm, drove a comb valve that
as a pneumatic amplifier, modulating the flow of
product is just the pneumatic amplifier packaged as
its own device, with a standard electric audio signal
as well as a compressed air input. That audio signal input
drives a voice coil, which drives the comb valve. The
airflow modulated by the comb valve is then put out
through a horn to match the pressure to ambient
the same as in an electric horn speaker. (It occurs to me
just now that this is the same thing a rocket nozzle does.
Impedance matching is everywhere.)
This product enables loud audio playback on remote job
sites where compressed air is available (provided by an
engine-powered compressor) and electricity is not. (This
situation was mentioned to me the other day by someone
know, who was suggesting that a pneumatic generator
would be useful, to power electric power tools. You
such a generator to power conventional electric audio
gear, but that seems less efficient and also less rugged.)
PS: Why do we have separate categories "Product: Audio:
Speaker" and "Product: Speaker"?
Wikipedia: Compressed air gramophone
Mentioned in idea body [notexactly, Sep 28 2019]
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||Well there has to be somewhere to put all the ideas for non-audio speakers.