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Hearing Process:
Hearing occurs when sound waves are conducted to the nerves of the inner ear and from there to the brain. Sound waves can travel to the inner ear by air conduction (through the ear canal, eardrum, and bones of the middle ear) or bone conduction (through the bones around and behind the ear).
Definition:
An audiology exam tests your ability to hear sounds. Sounds vary according to the intensity (volume or loudness) and the tone (the speed of sound wave vibrations). Audiometry is the testing of hearing ability. Typically, audiometric tests determine a subject’s hearing levels, but may also measure the ability to discriminate between different
sound intensities, recognize pitch, or distinguish speech from background noise. Acoustic reflex and optoacoustic emissions may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear.
An equal-loudness contour is a measure of sound pressure (dB SPL), over the frequency spectrum, for which a listener perceives a constant loudness. The unit of measurement for loudness levels is the phons, and by definition two sine waves that have equal phons are equally loud.
The human’s auditory system is sensitive to frequencies from 20 Hz to a maximum of around 20,000 Hz, although the hearing range decreases with age. Within this range, the human ear is most sensitive between 1 and 5 kHz, largely due to the resonance of the ear canal and the transfer function of the ossicles of the middle ear.
Threshold of Hearing:
INTENSITY of sound is measured in decibels (dB):
• A whisper is about 20 dB
• Loud music (some concerts) is around 80 to 120 dB
• A jet engine is about 140 to 180 dB
Usually, sounds greater than 85 dB can cause hearing loss in a few hours. Louder sounds can cause immediate pain, and hearing loss can develop in a very short time.

TONE of sound is measured in cycles per second (cps) or Hertz:
• Low bass tones range around 50 to 60 Hz
• Shrill, high-pitched tones range around 10,000 Hz or higher
The normal range of human hearing is about 20 Hz to 20,000 Hz, and some animals can hear up to about 50,000 Hz.
The measured threshold of hearing curve shows that the sound intensity required to be heard is quite different for different frequencies. The standard threshold of hearing at 1000 Hz is nominally taken to be 0 dB, but the actual curves show the measured threshold at 1000 Hz to be about 4 dB. There is marked discrimination against low frequencies so that about 60 dB is required to be heard at 30 Hz. The maximum sensitivity at about 3500 to 4000 Hz is related to the resonance of the auditory canal.
Pure Tone Audiometry:
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.