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Air Conduction
Hearing threshold levels can be determined by presenting test signals to the test subject with the included
earphones (air conduction – AC). The purpose of AC audiometry is to establish the hearing sensitivity at
various frequencies. The test can specify the AC loss but cannot distinguish between abnormality in the
conductive mechanism and sensor neural mechanism.
Headset Placement:
Remove eye glasses and ear rings 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 results may be false at lower frequencies.
Background Noise:
Background noise can also produce false test results, especially at lower frequencies. If
necessary, the DD65 can be equipped with noise excluding enclosures. Please contact the
distributor for more information.
Instruction of Subject:
Prior to hearing threshold level measurements, the following instructions should be given. "You
will now hear a variety of pitches with various loudness levels. Please push the signal button
when you hear a tone and release the button when you no longer hear it. If not using the
response button, ask the patient to "raise their left or right hand when you hear the tone in the
left or right ear".
Threshold Determination:
The test normally starts at 1000 Hz on the patient's better ear with the L/R switch adjusted
accordingly.
Familiarization:
Present a tone at 1000 Hz which can easily be perceived (i.e. 50dB) If necessary, increase with
steps of 10 dB until the tone is clearly perceived.
Threshold Determination:
The hearing threshold is defined as the lowest level at which more than half of the stimuli are
heard. This threshold is found by the following procedure.
1)
Present a tone which is 10 dB lower than the level at which familiarization was finished.
2)
Decrease the level in steps of 10 dB until response fails.
3)
Increase the level in steps of 5 dB until the subject responds again.
4)
Repeat 2) and 3) two or three times until the threshold appears at the same level.
The time intervals in between the stimuli should be varied to prevent the subject to react on the
rhythm.
5)
Change to the next frequency and repeat the procedure until all frequencies are measured.
Repeat the procedure at 1000 Hz. If the difference to the previously found threshold is then
5dB or less go to the other ear. If the difference is 10 dB or higher, repeat the test at the
other frequencies, until agreement to 5 dB or less has been obtained.
6)
Proceed until both ears have been tested.
Screening Procedure:
It is common to test at one dB level for preliminary hearing screenings as is often done in schools and
primary practice clinics. In this instance you would follow the same familiarization and instruction
procedures as stated above, but present a single dB level (i.e. 25dB) at just 4 frequencies (500, 1000,
2000 & 4000 Hz) in each ear. In this instance, you simply record a response or no response to the single
tone presentations at each frequency.
D-0127810-A – 2020/05
AS608 - Instructions for Use - US
Page 13
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