Audio Traveler AA222, Инструкции по эксплуатации

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AA222 Operation Manual Page 31
When masking is supplied via normal audiometric headphones
during the BC test, the earphone over the test ear can be
moved a little forward, letting the ear open. This will prevent the
so-called occlusion effect at lower frequencies, especially 125-
750 Hz. In practise, this effect can be regarded as less
important.
Masking Procedure - Step by Step (Hoods
Plateau)
In air and bone conduction measurements the hearing threshold levels
of both ears are determined separately. Therefore, under specified
conditions, masking noise shall be applied to the ear not being tested
(contra lateral ear).
A) Find the unmasked thresholds for air conduction and then for
the better ear by bone conduction - see air and bone
conduction.
B) Notify the subject that masking will be used. Tell him that he will
be hearing some noise, but to disregard it as best as he can and
respond only to the test signal, as he did previously.
When air conduction is made, both ears are covered by earphones.
The noise is presented through one earphone and the test signal
through the other.
When bone conduction is made, the noise is presented through one
earphone placed on the non-test ear. The other earphone is placed in
front of the test ear and thereby not covering the ear. The bone-
conduction vibrator is placed on the mastoid process of the test ear.
C)
Select Tone and output: Left or Right, Bone L R. Dial the “HL
dB” (30) to the right and the masking noise will automatically be
switched on.-
Set the “HL dB” (26) dial to the test ear at the level
of the unmasked threshold by means of rotary switch.
D) Increase the masking in 10 dB steps with the rotary switch
channel 2 (allow approximately 2 seconds at each step), and
have the subject letting you know when he first starts to hear the
noise.