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Hearing Tests

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Hearing Tests

Intensity and Frequency

Hearing tests measure loudness in decibels (intensity) and pitch in

Hertz (frequency). The lowest number of decibels (dB) you can hear at

different frequencies (Hz) is measured and plotted on a graph called

an audiogram.

Frequency: Frequency is the number of vibrations per second, expressed

as Hertz (Hz). The sounds of speech are in the range of 250 Hz to 4000

Hz. These are commonly tested in a hearing test.

Intensity: Sound waves made by something vibrating gently have little

intensity (the sound is soft). If an object vibrates strongly, sound

waves have greater intensity (the sound is loud).

* When sound waves are made by something vibrating slowly, a foghorn

or a drum, a low frequency sound occurs.

* When sound waves are made by something vibrating quickly, a

whistle or a small bell, a high frequency sound occurs.

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TYPES OF STANDARD HEARING TESTS

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Pure tone audiometry

You listen to a range of beeps and whistles, called pure tones, and

indicate when you can hear them. The loudness of each tone is reduced

until you can just hear the tone. The softest sounds you can hear are

your hearing thresholds marked on an audiogram.

Air conduction

Hearing is measured with pure tones through headphones. The sounds go

via the air, down the ear canal, through the middle ear, and to the

cochlea in the inner ear. The air conduction hearing thresholds are

indicated on the audiogram by X for left and 0 for right.

Bone conduction

Placing a small vibrator on the mastoid bone be...

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...rical activity generated in response to sound

along the nerve pathway, also called brainstem, to the brain. It takes

approximately one hour and is usually carried out while the baby is in

natural sleep. If this is not possible occasionally it is performed

while the person is under GA.

Tympanometry and Acoustic Reflex: Tympanometry gives information about

the middle ear.

· Normal - Compliance: 30 to 150, Middle ear Pressure: -150 to 50

· Middle ear dysfunction - no peak compliance recorded (flat trace)

· Eustachian tube dysfunction - Compliance: 30 to 150, Middle ear

Pressure: <-150 or> 50

· Perforation/grommet: either no seal obtained or large cavity volume

When a person has a normal tympanogram it may be possible to test for

the presence of a muscle reflex - acoustic reflex - in the middle ear.
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