Thermophone

A thermophone is a type of transducer that converts an electrical signal into heat, which then becomes sound.

It can be thought of as a type of loudspeaker that uses heat fluctuations to produce sound, instead of mechanical vibration.

[4] The theory and practice of creating sound with electric heat emerged in the late 19th century.

[5] In 1917, Harold D. Arnold and Irving B. Crandall [de] of Bell Labs developed a quantitative theory for the thermophone.

This periodic heating and cooling creates temperature waves which the conductor propagates into the surroundings.