Musical instruments use many techniques to produce the oscillations we hear as sound. Some use air moving through a tube, such as a pipe organ, the trumpet, or clarinet. Other instruments use a vibrating string, such as the plucked guitar, the bowed viola, or the struck piano. All these instruments use mechanical energy to create acoustic waves. It is, however, possible to use thermal energy to produce sound.
The fire organ is a musical instrument that uses the laws of thermoacoustics to create the oscillations in the air we hear as sound. Like traditional organs, the pyrophone (“flame sound”) has one pipe for each playable note, activated by a piano keyboard. However, the sound in this instrument is produced by a temperature difference imposed across a stack of closely packed channels. The hot temperature is maintained by propane flames and the other end of the stack is kept cold by running liquid nitrogen through a heat exchanger. Boasting a range of 14 notes, the organ is one of the only instruments in existence that uses heat to make music.