MIDIMATE 602 & 622 Diagnostic Audiometers
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4.2
Bone Conduction thresholds
Masking is always necessary when Bone Conduction thresholds are tested because of
the reduced level of contralateral attenuation.
4.2.1
Masking with TDH39 headphones
The procedure for testing the patient’s Bone Conduction thresholds differs from that
for Air Conduction as follows:
1.
Connect the B–71 Bone Conductor into the
Bone
socket on the rear panel.
2.
Select
User Test2
(as described in Chapter 0) to see the set-up for Bone Con-
duction, unless the default settings have been changed.
3.
Make sure that there are no interfering ambient sounds, especially at low fre-
quencies, — if necessary place the patient in a sound cabin.
4.
Fit the headphones so that the red (right) phone is applied to the poorer ear for
masking, and the other phone is applied to the patient’s temple region, leaving
the ear to be tested uncovered.
5.
Use
L/R Shift
to select the masking output required
6.
Use
Softkey 4
to toggle
Air Off
.
7.
Use a tone hearing level about 10 to 20 dB above threshold, and check with the
patient to find the most sensitive part of the mastoid to place the Bone Conduc-
tor. Make sure that there is no contact between the headband, which secures the
Bone Conductor, and the headset or headband supporting the TDH39 head-
phones which could conduct vibrations from one to the other. Leave it in this po-
sition until the test is finished.
8.
Determine the threshold without masking.
9.
Use
Softkey 4
to toggle
Air On
.
10.
Test the threshold again with masking.
11.
If the threshold has changed, determine the true threshold by testing in the same
way as in §4.1.4.
12.
Switch the Bone Conductor and headphone to the opposite ears. Test the poorer
ear with masking applied to the better ear.
13.
If the bone conduction thresholds for the two ears prove to be very different, use
a masking insert phone (optional accessory) instead of the TDH39 headphones.
4.2.2
When to use a masking insert phone
The optional masking insert phone (8–75–250) has a much lower level of bone con-
duction caused by vibration than the TDH39 headphones. Use the masking insert
phone instead of the TDH39 headphones for masking when you test the Bone Con-
duction threshold of patients with much more hearing loss in one ear than in the
