Standalone compressed air speaker

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 served as a pneumatic amplifier, modulating the flow of compressed air.

This product is just the pneumatic amplifier packaged as its own device, with a standard electric audio signal input 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 pressure, just 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 I know, who was suggesting that a pneumatic generator would be useful, to power electric power tools. You could use such a generator to power conventional electric audio gear, but that seems less efficient and also less rugged.)

N/A [2019-09-28]

PS: Why do we have separate categories "Product: Audio: Speaker" and "Product: Speaker"?