What is a Hearing Test?
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 pass through the ear canal, hitting the ear drum. The ear drum begins to vibrate at the same frequency as the sound wave which is then transmitted through little bones connected to the ear drum called ossicles. The last ossicle called the stapes has a rounded footplate that fits precisely over a membranous little window called the oval window. Past this window is a fluid that fills the hearing organ called the cochlea. Within the cochlea the sound now transmitted within the fluid of the inner ear stimulates the nerves of the inner ear. Eventually the sound travels along nerve pathways to the brain.
Sound waves normally travel to the inner ear through the ear canal, eardrum, and bones of the middle ear by a process called air conduction, but sounds can also travel through the bones around and behind the ear, bypassing the ear canal, eardrum and the little bones; this is called 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
Sounds greater than 85 dB can cause hearing loss after a few hours of exposure. 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 or Hertz (Hz):
- 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 usually ranges between 500 and 2,000 Hz.
How the test is performed
Audiometry provides a precise measurement of hearing. To test air conduction, you wear earphones attached to the audiometer (the machine that performs the hearing test). 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.
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. In younger children, since a hearing test requires the particpation of the child there are alternative ways of measuring hearing, see our information about infant hearing screening.
Common causes of hearing loss include:
- Acoustic trauma
- Chronic ear infections
- Diseases of the inner ear
- Head injury
- Inherited conditions
- Medications that can harm the inner ear, including certain antibiotics (such as neomycin or gentamycin), diuretics, and large doses of salicylates (such as aspirin)
- Occupational hearing loss
- Ruptured eardrum
- 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 amount and type of hearing loss may give clues to the cause and outlook.
The following conditions may affect test results:
- Acoustic neuroma – a benign growth that may be present around the hearing nerve within the skull that requires surgical removal
- Acoustic trauma
- Age-related hearing loss
- Meniere’s disease
- Occupational hearing loss
- Ruptured or perforated eardrum
There are many different hearing function tests. In simple screenings, the health care provider will make a loud noise and watch to see if it startles you. Detailed screenings include brainstem auditory evoked response testing (BAER). This test uses an electroencephalogram to detect brain wave activity when sounds are made.
Another hearing test called otoacoustic emission testing (OAE) can be used in very young children (such as newborns) or when standard tests do not produce reliable results.