‘Theoretically there was no normal hearing power, but practically there was, and was found to vary from 32 to 35,000 vibrations per second. This could be tested by properly constructed tuning-forks, as oculists tested by lenses the normal visual range.’ – Professor Marcel Natier in the British Medical Journal, 1904.
The tuning fork is a fascinating object because its history reveals how theories of sound, music, hearing loss and communication have intersected in the past to inform the way we measure hearing loss today. The possibility of hearing through bone conduction by vibrations travelling through the bones around our ears had been discovered in 1550 but it was not until 1711 that the tuning fork was invented to utilise the potential of this discovery. John Shore, trumpet and lute player in the Royal Court, was attributed with its invention as a musical instrument, which allegedly came about because he had split his lip and was unable to play his trumpet.Tuning forks became widely used in music for tuning purposes and for establishing pitch rather than as instruments in themselves because they produce pure tones.
In 1827, Sir Charles Wheatstone was the first to use the tuning fork to assess hearing and realised that when both ears were blocked, sound lateralised (travelled) to the side nearest to the origin of the sound. Wheatstone is famed for his work with telegraphy and for inventions like the Wheatstone bridge and the Cooke -Wheatstone telegraph yet there is less known about his role in establishing standards for hearing testing. He grew up in a musical family however and was for some time apprentice to a musical instrument maker, which may indicate his interest in tuning forks. His interest could be explained further by the fact that studies of acoustics were proliferating in the late nineteenth century, especially as comparative pieces to the more widely studied subject, optics, as the epigraph to this piece also suggests. The late nineteenth century is notable furthermore because it was a time in which measurement and standardisation became of defining importance to science and tuning forks were used in this way to define standards of pitch and frequency, which were then related to speech and to hearing.
Wheatstone’s essential role in developing hearing tests as well as pioneering telegraphy further points to the close link between hearing loss and communication. It is well known that Alexander Graham Bell attributed his invention of the telephone to his work with the deaf and more recently historians like Mara Mills have described how measuring and classifying normal hearing and hearing loss was essential to the development of the telephone network.
The Weber Test.
In 1834, Ernst Heinrich Weber realised that Charles Wheatstone’s discovery could be used to differentiate between conductive and sensori-neural hearing loss when there is either a unilateral hearing loss or a difference in hearing between one ear and the other. This works by placing the handle of a vibrating tuning fork in the centre of the skull. If the sound is heard in the better ear this indicates sensori-neural hearing loss but if it is heard in the worst eat, this indicates conductive hearing loss. This works because when someone has sensori-neural hearing loss, the sound is localised through bone conduction in the better ear but for someone with bone conductive hearing loss the sound travels (is localised) to the worst ear. Although various kinds of tuning fork hearing tests proliferated in the late 19th and early 20th century, the Weber Test and the Rinne test were the most common and remain in use today.
The Rinne Test.
Heinrich Adolf Rinne developed this hearing test in 1855 in order to differentiate between conductive hearing loss and sensori-neural hearing loss. This works by measuring how long the tuning fork tone can be heard thorough air conduction (by holding the fork close to the ear) compared to bone conduction (by placing the handle of the fork on the mastoid). If the fork is heard longer through bone conduction then this indicates conductive loss but if it is heard longer through air conduction then this indicates sensori-neural loss.By 1985, it was established that these tests were to be conducted by using forks vibrating at C on the scientific scale through frequencies 128hz- 8192 hz. This roughly reflected the frequency at which most speech is usually heard, on a spectrum from 16hz to 20khz.
Thank you to Anne Hanley and Sean McNally – the stars of the featured videos!
REFERENCES AND FURTHER READING
Blauert J, The Psychophysics of Human Sound Localisation, (MIT Press, 1997)
Mills M, ‘Deafening: Noise and the Engineering of Communication in the Telephone System’ in Grey Room, Spring Issue, No. 43, (Inc. and the Massachusetts Institute of Technology 2011) pp.118-14
Newby. H.A & Popelka G.R, Audiology ( Prentice Hall Inc, 1985)p.104-105
Ng, M & Jackler R K, ‘Early History of Tuning Fork Tests’ in History of Otology (The American Journal of Otology) Vol. 19, No.1, Jan 1993 (pp 100-105)
Rees T, ‘Historical notes: a brief chronicle of the tuning fork’, in Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2009 <http://www.hps.cam.ac.uk/whipple/explore/acoustics/historicalnotes/,> (accessed 20 November 2014]