Audiogram
The term audiogram indicates a graph, used in tonal Audiométrie, which makes it possible to visualize the auditive capacity of a subject.
The tonal audiogram is generally based on pure sounds at frequencies chosen arbitrarily and conventionally (to 125 Hz, 250 Hz, 500 Hz, 750 Hz, 1000 Hz, 1500 Hz 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, 8000 Hz, 15000 Hz). One measures the threshold of hearing for these various frequencies. One does it by addressing the sound in turn to each ear by means of a helmet or loudspeakers (audiogram in air route) then by a vibrator applied to cranium on each side (audiogram in osseous way).
One compares then these results with the normal threshold for the same frequencies, in order to determine the auditive deficit and to study the audiogram which graphically represents this deficit according to the frequency.
One can use in certain cases a semi-automatic system (Von Békésy) which was improved by a Toulouse team (Pr Azaïs, Pr Josserand, Dr. Auriol) to lead to patent (INRS N° 89 080397) of C. Meyer-Bisch: Audioscan (marketed by Essilor).
One uses a controlled frequential sweeping on constant, gradually increased level and leaving systematically not-heard towards heard. The beaches of swept frequencies and the levels explored are ordered automatically by a system itself controlled to the answers of the examined subject. I.e.:
- - the system carries out the first frequential sweeping with a constant reference level;
- - the subject holds supported an order as a long time as he hears something and slackens it when he does not perceive any more any sound;
- - if a zone of “silence” (known as of “not hearing”) is detected, the program will memorize the frequency from which the subject does not understand anything any more and the frequency from which he hears something again.
- - the program then determines the center frequency of this zone of silence and on the basis of this one, it will carry out a new frequential sweeping but with a higher level of diffusion of 5 dB for example.
- - the subject holds supported an order as a long time as he hears something and slackens it when he does not perceive any more any sound;
Methods not implying an intentional answer of the subject also exist:
- - auditive evoked Potential or PEA;
- - the Oto sound emissions or OAS whose measurement results from splendid work of Kemp and Wilson. They showed that if the auditive system functions, the ear answers by a kind of echo any audible sound which is addressed to him.
See too
External bonds
- For more details, to see the site of Essilor.
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