While quite famous as a physicist for his research in electrodynamics and energy conservation , fewer of us are aware of his work in the psychology of sound and visual perception. He is credited as one of the first to challenge the way we understand pitch perception through experiments and scientific observation and laid the foundation for acoustics and psychoacoustics. He demonstrated that all sound, no matter how complex, can be mathematically broken down into constituent sine waves.
His book On the Sensations of Tone as a Physiological Basis for the Theory of Music, published in 1863, was considered for many decades as the guidebook for hearing and acoustics for musicians, musicologists and instrument designers. The language used is rather plain and non-technical in order to appeal and be useful to musicians, at whom it was aimed.
The idea that any sound can be depicted as a sum of sinewaves was first proposed by Georg Simon Ohm through the “acoustic law” that stated that the ear performs a limited Fourier analysis by determining the sinusoidal components of complex sound. [1]
Helmholtz used Fourier’s theorems to describe a resonance theory of frequency analysis performed by the inner ear as the basis of pitch and argued that the resonance place with the greatest magnitude would be a determining factor in pitch perception. Because his inner ear resonators were more sharply tuned at low frequencies, low frequencies were likely to be a dominant factor in pitch perception.[2]
In order to be able to isolate different frequencies Helmholtz created a device that is now called a Helmholtz Resonator, which basically works as an oscillator. A case could be made that he invented possibly the first sound synthesizers. When a resonator is held near the source of a sound, the air in it will begin to resonate if the tone being analyzed has a spectral component at the frequency of the resonator. By listening carefully to the tone of a musical instrument with such a resonator, it is possible to identify the spectral components of a complex sound wave such as those generated by musical instruments.[3]
Another device used in his research was the Helmholtz Sound Synthesizer. It was built not as a musical instrument but as a scientific tool used to analyse the effect of overtones in complex sound. It consisted of an array of tuning forks (which produced pure tones) vibrated by electromagnets which in turn were amplified by a Helmholtz Resonator to generate overtones. The device helped understand the nature of speech, particularly vowel sounds.[4]
While Helmholtz’s theories in psychoacoustics and pitch perception have since been challenged and new models developed [5], his theory of tonotopicity has laid the foundation for artists like Maryanne Amacher who uses combination tones to cause the ear to produce and amplify tones of its own.
It is my intention to further delve into the subject of human hearing. There seems to be a lot of scientific research on the matter, yet many questions left still, especially regarding pitch perception. I think there might be potential of finding new ways of engaging the listener and creating sonic experiences.
[1] Kromhout, M. (2020) ‘The Unmusical Ear: Georg Simon Ohm and the Mathematical Analysis of Sound’, The University of Chicago Press Journals, Volume 111, Number 3
[2] William, A. Yost (2015) Psychoacoustics: A Brief Historical Overview, Speech and Hearing Science, Arizona State University
[3] https://www.britannica.com/science/sound-physics/The-Helmholtz-resonator
[4] https://braintour.harvard.edu/archives/portfolio-items/helmholtz-sound-synthesizer
[5] https://www.cns.nyu.edu/~david/courses/perception/lecturenotes/pitch/pitch.html