Diagnostics: Audiometry

Audiometry is a painless hearing test that shows whether hearing loss is present, how significant it is, and where in the ear the problem lies.

Audiometry is usually performed by an audiologist in a quiet, soundproof room, and each ear is checked separately. It is often paired with tympanometry, a separate quick test of how the eardrum and middle ear are working.

Pure-Tone Testing: Air Conduction

In pure-tone testing, tones are played at different pitches (frequencies) and volumes (loudness). The listener presses a button or raises a hand each time a tone is heard, even when it is very faint. With headphones or earpieces, sound travels the normal path through the outer ear, eardrum, and middle ear before reaching the inner ear. This is called air conduction, and it checks the whole hearing system working together.

Pitch is measured in Hertz (Hz), from low to high. Most speech sounds fall between 500 and 4000 Hz. Volume is measured in decibels (dB); ordinary conversation is roughly 45 to 60 dB. The softest volume that can be heard at each pitch is recorded as a "threshold."

Pure-Tone Testing: Bone Conduction

The test is then repeated with a small vibrating device placed on the bone behind the ear. This device sends sound as gentle vibrations directly through the skull to the inner ear, skipping past the outer and middle ear. This is called bone conduction.

Comparing air conduction and bone conduction is the key to locating the problem. If bone conduction is normal but air conduction is poorer, the outer or middle ear is likely blocking sound. If both are equally reduced, the inner ear or hearing nerve is more likely involved.

Masking

Sometimes a steady background noise is played into the ear that is not being tested. This is called masking. It keeps the better ear from "helping out" and answering for the ear being measured, so each ear's true threshold is recorded.

Speech Audiometry

Pure tones show which pitches can be detected, but understanding words is a separate ability. In speech audiometry, spoken words are presented at different volumes and repeated back. Two common measures are the softest level at which about half of simple words can be correctly repeated, and the percentage of words understood clearly when the volume is comfortable.

Speech testing adds important information. In hearing loss caused by a blockage of the outer or middle ear, word understanding usually stays good once sound is made loud enough. When word understanding is much poorer than the pure-tone results would predict, it can point toward a problem in the inner ear or the hearing nerve.

How to Read an Audiogram

Pure-tone results are plotted on a graph called an audiogram. Pitch runs left to right, from low pitches on the left to high pitches on the right. Loudness runs top to bottom, with soft sounds at the top and loud sounds at the bottom.

Each ear has its own symbols, often a red circle for the right ear and a blue X for the left ear, with separate marks for bone conduction. A key on the graph explains the symbols. The lower a mark sits on the graph, the louder a sound must be before it is heard, so marks lower down indicate more hearing loss. The pattern of the marks (for example, worse hearing only in the high pitches) helps describe the type of hearing difficulty.

Degree of Hearing Loss

The degree of hearing loss describes how much hearing is reduced, based on the softest sounds that can be heard. Categories commonly used range from normal, to slight, mild, moderate, moderately severe, severe, and profound as thresholds rise. Higher decibel numbers mean softer sounds cannot be heard and the loss is greater. Even a mild loss can affect understanding of speech in noisy settings. More background on hearing loss is available on the hearing loss conditions page.

Type of Hearing Loss

The type of hearing loss describes where the problem is located:

• Conductive: Sound is blocked in the outer or middle ear, while the inner ear works normally. On the audiogram, bone conduction is normal but air conduction is reduced, leaving a gap between the two (an "air-bone gap"). Common causes include earwax, fluid behind the eardrum, ear infections, or problems with the small middle-ear bones.

• Sensorineural: The inner ear or hearing nerve is affected. Air and bone conduction are reduced by a similar amount, with little or no gap between them. Common causes include aging and noise exposure.

• Mixed: A combination of conductive and sensorineural loss, with reduced bone conduction and an additional gap to air conduction.

How Audiometry Relates to Tympanometry

Tympanometry is a separate, quick test that checks how the eardrum and middle ear are working. A soft probe in the ear canal changes the air pressure slightly and measures how the eardrum moves. It does not test hearing itself, but it explains the mechanics behind the audiogram.

A normal tympanogram suggests the eardrum and middle ear are moving well. A flat tracing can indicate fluid behind the eardrum, a hole in the eardrum, or an eardrum that does not move. A pattern showing negative pressure can suggest Eustachian tube dysfunction.

Combined with the audiogram, tympanometry helps confirm the type of hearing loss. A hearing loss with a normal tympanogram points toward a sensorineural cause, while a hearing loss with an abnormal tympanogram points toward a conductive cause in the middle ear. Together, these tests give a fuller picture than either one alone.

What Happens After Testing

Results are reviewed by an audiologist or physician, who explains the degree and type of any hearing loss and discusses the findings. Depending on the results, next steps that are sometimes considered include treating a reversible cause such as earwax or fluid, further testing, or hearing aids and other devices. Additional information is available on the hearing loss treatments page.

Example Audiograms

The illustrations below show simplified examples of how normal hearing, conductive hearing loss, and sensorineural hearing loss can appear on an audiogram. They are examples only and do not represent any individual's results.