Audiometry examination tests a person’s hearing level. Sounds vary based on their loudness (intensity) and the speed of sound wave vibrations (tone).
Hearing occurs when sound wave stimulates the nerves of the inner ear. Eventually the wave travels along nerve pathways to the brain.
Sound wave 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 about 80 - 120 dB
- A jet engine is about 140 - 180 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:
- 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.
How the Test is Performed
Audiometry provides a more precise measurement of hearing. To test air conduction, you need to wear earphones attached to the audiometer. Pure tones of controlled intensity are delivered to one ear at a time. You will be 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.
How to Prepare for the Test
No special preparation is needed.
How the Test Will Feel
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.
Why the Test is Performed
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:
- The ability to hear a whisper, normal speech, and a ticking watch is normal.
- The ability to hear a tuning fork through air and bone is normal.
- In detailed audiometry, hearing is normal if you can hear tones from 250 Hz - 8,000 Hz at 25 dB or lower.
What Abnormal Results Mean
There are many different kinds and degrees of hearing loss. In some types, you only lose the ability to hear high or low tones, or you lose only air or bone conduction. The inability to hear pure tones below 25 dB indicates some hearing loss.
The following conditions may affect test results: