The primary purpose of audiometry is to determine the frequency and intensity at which sounds can be heard. Humans can hear sounds in the frequency or pitch range of 20 to 20,000 Hertz (Hz), but most conversations occur between 300 and 3000 Hz. Audiometric testing is done between 125 and 8000 Hz. The intensity levels or degree of loudness at which sounds can be heard for most adults is between 0 and 20 decibels (dB).
Both air conduction and bone conduction of sounds are evaluated by audiometry. Air conduction establishes the extent of sound transmission through the bones of the middle ear. The results of a bone conduction test determine how soft a sound an individual can hear over several frequencies or pitches.
Bone conduction audiometry determines the extent to which there is neurosensory hearing loss. An individual with a neurosensory loss may be able to hear sounds but not understand them.
Since those with hearing losses often cannot hear sounds at normal decibel levels, intensities as high as 115 dB are used to assess the extent of air conduction loss and as high as 70 dB for bone conduction loss. The difference between bone conduction loss and neurosensory hearing loss is called the air-bone gap.