Support Services Handout Series
Number 5002 Audiology Sheet
Understanding the Audiological Evaluation

•  Hertz (Hz):

The measurement standard for the frequency or pitch of sound. The pitches on an audiogram are usually 250 Hz (lowest pitch measured) through 8000 Hz (highest pitch measured).

•  O and X:

Symbols used to record thresholds on an audiogram. The symbol 0 stands for the right ear and is usually recorded in red. The symbol X, typically marked in blue, represents the left ear.

•  Pure Tone
   Average(PTA):

The average of the three thresholds at 500 Hz, 1000 Hz. and 2000 Hz. The PTA is often used to describe an individual's hearing loss. For example, when a hearing loss is described as 80 dB, that number probably represents the PTA.

•  Speech Detection
   Threshold (SDT):

The loudness level at which a person begins to be aware of speech sounds, without necessarily understanding words. The SDT may reflect the level at which the person is aware of words or sentences, or of individual sounds that represent various parts of the frequency range. The individual sounds most often used during testing are oo and aa (low pitch), ee (mid-pitch), and sh or s (high pitch).

•  Discrimination Testing:

Usually described by a percentage score or the terms poor, fair, good, or excellent, this test evaluates a person's ability to understand one- syllable words at a comfortable listening level. This test may be done twice--first in quiet, and then with background noise.

How Loud Is Loud?

The following numbers represent the approximate loudness levels of various sounds, to help clarify the meanings of decibel readings on the audiogram.

0 dB:

Approximate threshold for normal hearing

30 dB:

Whisper at five feet

60 dB:

Average conversational level

90-110 dB:

Loud auto horn, close loud scream

100-110 dB:

Motorcycle engine

150-170 dB:

Jet engine

normal range

0 -25 dB

mild loss

26-40 dB

moderate

41-55 dB

moderate severe

56-70 dB

severe

71-90 dB

profound

91 dB or >

Configuration

•

Flat: Hearing loss remains essentially the same at all frequencies.

•

Sloping: Hearing is better in the low frequencies than in the high frequencies.

•

U-shaped or Cookie Bite: Hearing is better in the low and high frequencies than in the middle frequencies.

•

Rising: Hearing is better in the high frequencies than in the low frequencies.

Note: If sound awareness is available to a person in the higher frequencies (pitches) this usually suggests greater potential to understand spoken language. Much of the information in speech that helps differentiate one sound from another is located in the higher frequencies. Vowel sounds have their energy in the lower pitches while many consonant sounds have their energy in the higher pitches.

Testing for Type of Hearing Loss

Three types of audiological testing-air conduction, bone conduction, and tympanometry-can help determine whether a hearing loss is conductive, sensorineural, or mixed.

Air conduction testing: Subject uses a headphone. The test evaluates the whole ear system-outer, middle, and inner ear.

Bone conduction testing: An oscillator is usually placed behind the ear on the mastoid bone to evaluate the inner ear only.

Tympanometry: A test used to evaluate the middle ear system. The test generates a graph called a tympanogram that indicates whether the middle ear is functioning well.

Test Implications

When a person with a hearing loss hears sound at the same level via both air and bone conduction, the loss is considered sensorineural. The middle ear system is fine; the difficulty is in the inner ear where the nerves are housed.

People who hear within normal range during the bone conduction test (the test that directly measures the inner ear nerves) but who show hearing loss during the air conduction test (the test under headphones which must direct sound through the middle ear before it reaches the inner ear) may have a conductive loss. The inner ear is fine, the difficulty is in the middle ear and the sound can therefore not efficiently reach the inner ear nerves.

If different degrees of hearing loss are found via air and bone conduction testing, the loss is mixed. Sound is prevented in the middle ear from reaching the inner ear, which also has nerve damage.

Tympanometry evaluates the condition of the middle ear system. If an abnormal pattern is seen, it may suggest a possible conductive hearing loss at the time of testing. Tympanometry does not evaluate sensorineural hearing loss.

The ability to process and interpret sound, as well as the ability to speak, depend on the interaction of numerous factors in each individual's background. Two people with similar audiograms may function very differently.