Pure Tone Audiometry

The testing of hearing is most often carried out by establishing the threshold of hearing, the softest sound which can be perceived in a controlled environment. It is typical to do this testing with pure tones by providing calibrated tones to a person via earphones, allowing that person to increase the level until it can just be heard. Various strategies are used, but pure tone audiometry with tones starting at about 125 Hz and increasing by octaves, half-octaves, or third-octaves to about 8000 Hz is typical. Hearing tests of right and left ears are generally done independently. The results of such tests are summarized in audiograms.

Audiograms compare hearing to the normal threshold of hearing, which varies with frequency as illustrated by the hearing curves. The audiogram is normalized to the hearing curve so that a straight horizontal line at 0 represents normal hearing.
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Hearing loss
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Audiogram Showing Presbycusis

The progressive loss of high frequency sensitivity with aging is typical, and is called presbycusis. The loss of the high frequencies can make it difficult to understand speech, since the intelligible differences in speech sounds are often in the range above 2000 Hz.

When hearing aids are used, it is important to amplify the high frequencies, since it is uncommon for there to be significant loss at low frequencies. Audiograms are important for the prescribing of hearing aids.

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Older persons may have difficulty understanding speech clearly because of progressive loss of high frequency hearing.

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Audiograms Showing Hearing Loss

Audiograms can help with the diagnosis of various types of hearing disorders. Specific geometries of curves are found to be typical of presbycusis, and a characteristic notch in the hearing curve may be the signature of damage by a sudden loud sound like a gunshot or a firecracker explosion close to the ear.

The curves are normalized so that a straight horizontal line represents equal loudness.
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