Descripti011; The Anechoic Chamber - BRUEL & KJAER 4212 Instructions And Applications

Description.
The Hearing Aid Test Box Type 4212, a sectional view of which is seen in
Fig. 3 is a lacquered mahogany Test Box with relatively small outside
dimensions.
It
consists basically of a small anechoic chamber with built-in
loudspeaker, and built-in regulating precision microphone which enables
very accurate measurements to be carried out according to the Comparison
Method. On the outside of the Test Box is mounted an artificial ear designed
in such a way that measurements may be made both on hearing aids with
insert types of earphones and with built-in earphones (e.g. hearing aid
spectacles, hair-clips Pte.). In accordance with the standards the coupler has
a volume of 2 cc.
Union
nut ~
Coupler (2cc) ----------
~
Microphone 4132
~ ~fj
Cathode Follower 2613 -
~
Spring arrangement
Holder for
Perforated
Glasswool
Rockwool
Perforated protecting cover
Microphone cables
Rockwool
Glasswool
springs
attenuator
Loudspeaker terminals
fStJII~
Fig. 3. Sectional view of the Hearing Aid Test Box Type 4-212.
The Anechoic Chamber.
As can be seen from Fig. 3, the Test Box consists of an "inner box" and
an "outer box" with lid. The lid , which is supplied with a handle and a lock
5