Audiometry

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Ear anatomy

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):

• A whisper is about 20 dB
• Loud music (some concerts) is around 80 - 120 dB
• A jet engine is about 140 - 180 dB

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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:

• Low bass tones range around 50 - 60 Hz
• Shrill, high-pitched tones range around 10,000 Hz or higher

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.

Audiometry; Hearing test; Audiography (audiogram)

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.