Basic Sound Chamber Tests 59
3.3.1 Explaining the Coupler Types
The HA-1 direct access coupler is used to test in-the-ear and canal aids, and
aids with molds connected. Figure 3.3.1B shows the direct access coupler. The
sound bore of the aid is sealed directly to the 2-cc cavity of this coupler with
Fun-Tak putty, provided with the instrument.
The HA-2 coupler approximates the human ear with an earmold attached. See
Figure 3.3.1A. Note the tube that simulates the earmold. Button-type receivers
connect directly to this coupler. Behind-the-Ear (BTE) hearing aids connect to
this coupler by means of an ear-level adapter, as shown in Figures 3.3.1C.
OUTER O-RING
INNER O-RING
MICROPHONE
O-RING
Figure 3.3.1A Figure 3.3.1B
Standard 2-cc Coupler (HA-2) Direct access coupler (HA-1)
0.4" (10 mm)
NUB CONNECTS TO
TOP OF HA-2 COUPLER
Figure 3.3.1C—Ear-level Adapter (used with HA-2)
The length and thickness of the tubing of the ear-level adapter can have a sig-
nificant effect on the frequency response of an aid. If an aid is being compared
against the manufacturer’s specifications, the tubing should be carefully chosen
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