Audiometry is the general term applied to a number of tests used to measure hearing.
An audiometer is an essential instrument for conducting most audiometric tests. The audiometer is basically a device that generates pure tones of known level and frequency, and delivers these to the patient through either a headphone or a bone conduction vibrator.
On an audiometer, the levels are given as Hearing Level, dB (HL). In this way, a normal hearing person will be able to hear tones at and above a 0 dB HL level.
Since these levels are average levels measured in a standard coupler, the actual sound levels at the patient's eardrum can differ considerably. One might expect up to as much as 15 dB individual deviation from the average.