Thermoacoustic Engine - How do these Hofler Tubes Generate Sound?

This thermoacoustic engine, also known as a Hofler Tube, has no moving parts.

A strong temperature gradient across closely spaced plates in the middle of the tube creates a thermodynamic cycle of oscillating air that produces sound

This small thermoacoustic sound source was invented by Naval Postgraduate School Professor Tom Hofler and built by NPS Engineer Jay Adeff.

The hofler tube can use a flame or electrical heat source at 308 °C to produce sound pressure levels as high as 149 dB SPL at 930 Hz.

The heat power to radiated sound power efficiency has been measured to be 2.8%. Sufficient information has been included so that others may construct the device.

Dr. Bruce Denardo of the Naval Postgraduate demonstrates a Hofler Tube during a 2015 Maos visit.