MIDIMATE 602 & 622 Diagnostic Audiometers
15
other. This is to avoid “false” contralateral masking caused by the high masking level
required in the weaker ear.
The test procedure is similar to that described in §4.2.1.
4.3
Free-Field thresholds
Free-field pure-tone testing, with loudspeakers instead of headphones, is used pri-
marily when the patient for instance is a child who dislikes wearing headphones.
However, the measured thresholds will be influenced by:
•
The distance from the loudspeakers to the patient;
•
The acoustic absorption of the walls of the test room;
•
Ambient noise.
Loudspeakers (such as 8–02–450) and a two-channel power amplifier such as PA 210 (8–02–
240) for free-field testing are optional accessories.
To set up a free-field tone test, do as follows:
1.
Connect the amplifier’s left and right inputs to
FF
,
L
and
R
on the rear panel.
2.
Connect the loudspeakers to the amplifier’s outputs.
3.
Press
Menu
to display the
Select Function
menu.
4.
From the
Select Function
menu press
Softkey 1
to select the
(Tone) Out-
put ?
menu.
5.
From the
(Tone)Output ?
menu press
Softkey 3
to select
F.F
.
6.
From the
(Tone,F.F) Side ?
menu press
Softkey 1
to select
Left
.
7.
From the
(Tone,F.F,Left) Masking ?
menu press
Softkey 3
to select
FF
.
To minimize the influence of standing waves on the measured threshold, the test
tone is frequency modulated to a depth of ±5% by a warble tone. If required, you can
disable this by toggling Softkey 2 so that C/P/W is displayed instead of C/P/W.
To use the narrow band noise provided for masking as an alternative test source in-
stead of tone, do as above but with the following differences:
8.
Press
Softkey 2
to select
Right
instead of
Left
in step 5.
9.
Toggle
Softkey 4
to display
F.F On/Off
.
10.
Turn the
Hearing Level
wheel counterclockwise to reduce the tone to minimum.
11.
Use the
Masking Level
wheel to see the threshold (displayed above
Softkey 5
)
for each center frequency.
