The Thermophones, incredible sounds from converting thermal energy into acoustic energy

Credit : photo Angélique Gilson for Diagonale Paris-Saclay.

Project leaders : Jacques Rémus, designer artist, Christophe d’Alessandro (AA) et Diana Baltean Carlès (ETCM), in collaboration avec Catherine Weismann (ETCM)Virginie Daru (AERO), Brian Katz (AA)

The project "Thermophones" program won the Arts and Sciences in 2015 Diagonal Paris-Saclay.

An auto-oscillation, usable as a musical tone can be generated by the thermoacoustic effect through the introduction of a heat source located in a sound pipe. Compared with a flute pipe, the resulting tones of these "thermophones" are quite unique, by their timbre and power. The phenomenon of conversion between thermal and acoustic energy has been predominately studied for refrigeration, or as a pump, but rarely used for generation of musical sounds. The purpose of this project is to study the sonic properties in the audible range of thermophones, especially their musical control.
Jacques Remus, musician and visual artist, sculptor and musical machine manufacturer, created the thermoacoustic sound pipe several years ago, which he dubbed "thermophones". They consist of a steel, glass, or aluminum pipe, circular or square in section; open at both ends (flute) or open at one end and closed at the other end (bourdon). Inside the tube, there is a rigid "stack" (stack of plates or metal grids or grid of ceramic rectangular channels). The stack is heated by an electrical resistance at one end. As yet, the thermophones do not include a cold heat exchanger for controlling the temperature of the other end of the stack, and the temperature may vary along the tube.
The sound of a Thermophone is dominated by the fundamental resonance frequency of the pipe, due to its length. The establishment of the sound depends on the heat input, the geometry, but also the inclination of the pipe. The sound may be interrupted by partially sealing the end with a fine metal screen, for example.
The project aims to study the thermophone as a musical instrument. In particular, to study its acoustic properties (impedance of the pipe with a stack, the onset time, and frequency stability) to tune it; to estimate the sound intensity as a function of operating parameters; to control and modulate the loudness; analyze and control the timbre of the sound radiated. This will be compared to the organ pipe flute. For this, it is desired to make series of measurements of the acoustic impedance of thermophone, requiring the creation of a measurement system for a thermophone prototype.
From the point of view of modeling, theories commonly used in thermoacoustics, including the linear theory developed by N. Rott between 1960 and 1980 and formalized by G. Swift in 1990, must be adapted to study thermophones, which are thermoacoustic standing wave engines with a specific purpose and design. A study was conducted in 2015 focused mainly on initial conditions. This study showed good agreement between the calculation and approximate measures of the initial temperature and sound frequency. The study should continue to allow a sufficiently fine control of the tuning and persistence of the sound. A simplified model of a thermophone will be developed (e.g., with the DeltaEC] software. Subsequently, numerical simulations with a compressible Navier- Stokes code will be carried out to describe the transitory effects, onset of thermoacoustic instability until saturation (sound stability), allowing comparisons between calculation and experiment.

 Information Thermophones :


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LIMSI in numbers

10 Research Teams
100 Researchers
40 Technicians and Engineers
60 Doctoral Students
70 Trainees

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