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Audiometry; Hearing test; Audiography (audiogram)
An audiometry exam tests your ability to hear sounds. Sounds vary based on their loudness (intensity) and the speed of sound wave vibrations (tone).
Hearing occurs when sound waves stimulates the nerves of the inner ear. Eventually the sound travels along nerve pathways to the brain.
Sound waves can travel to the inner ear through the ear canal, eardrum, and bones of the middle ear (air conduction), or through the bones around and behind the ear (bone conduction).
The INTENSITY of sound is measured in decibels (dB):
Sounds greater than 85 dB can cause hearing loss after a few hours. Louder sounds can cause immediate pain, and hearing loss can develop in a very short time.
The TONE of sound is measured in cycles per second (cps) or Hertz:
The normal range of human hearing is about 20 Hz - 20,000 Hz. Some animals can hear up to 50,000 Hz. Human speech is usually 500 - 3,000 Hz.
The first steps are to see whether you need an audiogram. The specific procedures may vary, but they generally involve blocking one ear at a time and checking your ability to hear whispers, spoken words, or the sound of a ticking watch.
A tuning fork may be used. The tuning fork is tapped and held in the air on each side of the head to test the ability to hear by air conduction. It is tapped and placed against the mastoid bone behind each ear to test bone conduction.
Audiometry provides a more precise measurement of hearing. To test air conduction, you wear earphones attached to the audiometer. Pure tones of controlled intensity are delivered to one ear at a time. You are asked to raise a hand, press a button, or otherwise indicate when you hear a sound.
The minimum intensity (volume) required to hear each tone is graphed. An attachment called a bone oscillator is placed against the bone behind each ear (mastoid bone) to test bone conduction.
No special preparation is needed.
There is no discomfort. The length of time varies. An initial screening may take about 5 to 10 minutes. Detailed audiometry may take about 1 hour.
This test can detect hearing loss at an early stage. It may also be used when you have difficulty hearing from any cause.
Common causes of hearing loss include:
Kileny PR, Zwolan TA. Diagnostic audiology. In: Cummings CW, Flint PW, Haughey BH, et al, eds. Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2010:chap 133.
Norton SJ, Bhama PK, Perkins JA. Early detection and diagnosis of infant hearing impairment. In: Cummings CW, Flint PW, Haughey BH, et al, eds. Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2010:chap 190.
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