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of the ear mould substitute for the convenience of the user who may wish
to make his ,own special substitutes.
Airtight rubber seal
O,Smm-0,020" wire to fill
capillary partially
Standard pressure
microphone
Pressure equalisation
capillarry 0,6 mm- 0,024"
f592!i9
Fig. 1.4. The "normal" 2
cm3
Coupler DB 0138.
The 6 cm3
Couplers.
To enable
acou~tical
tests to be made on headphones used in audiometers
and in telephone systems, two 6 cm3 couplers
are
available for the Artificial
Ear Type 4152. One of these couplers, the one normally included in the
4152 ear, fulfils the requirements of the N.B.S. 9A Coupler and A.S.A.
Z. 24.5-1951, the other being in
accordance
with the requirements of the
A.S.A. Z. 24.9-1949 Type 1 Coupler.
Sectional views of the couplers are shown in Fig. 1.6. According to the
standards the couplers should be used in connection with microphones
supplied with a front cavity. As the Microphone Cartridge Type 4132 is made
wit}} a flat front, a Coupler Adaptor Ring DB 0111 is supplied with the
couplers.
By
unscrewing the normal protection cover from the microphone cartridge
and mounting the coupler adaptor ring instead, measurements can be made
in complete agreement with the standards.
However, the openings of the couplers are big enough that, by acc;ident
a small object might be dropped into the cavity and damage done to the
unprotected microphone diaphragm. To
avoid
this risk of damaging the
6
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