Audio Traveler AA222, Operation Manuals, Page: 26 / 141

AA222 Operation Manual Page 26
General Theory about Air and Bone
Conduction
Hearing threshold levels can be determined by air conduction and
bone conduction audiometry. In air conduction audiometry the test
signal is presented to the test subject by earphones. In bone-
conduction audiometry the test signal is presented by a bone vibrator
placed on the mastoid or forehead of the patient. It is recommended to
start hearing threshold level determinations with air conduction
measurements followed by bone conduction measurements.
Hearing threshold levels can be determined using test tones with fixed
frequencies or a test signal with frequency varying with time according
to predetermined rate of change.
Air Conduction
The purpose of air conduction audiometry is to establish the hearing
sensitivity at various frequencies. The test can specify the AC loss, but
it cannot distinguish between abnormality in the conductive
mechanism or sensor-neural mechanism.
Headset Placement:
Remove eyeglasses and earrings if possible and position the
headband directly over the top of the head. Place the rubber
cushions so that the diaphragms are aimed directly at the
opening into the ear canal. Pull down the yokes of the phones
and adjust for tight fit. If the cushions are not tight to the ears,
the test result will be false at lower frequencies.
Background noise:
Background noise can also give false test results, especially at
lower frequencies. If necessary, the audiometric headphone can
be equipped with our Audiocup Exclosures type 21925. Please
contact the distributor.
Instruction of subject:
Prior to hearing threshold level measurements, the following
instruction of the subject about the test tones and the response