Specification - BRUEL & KJAER 4212 Instructions And Applications

However, due to the absorbing material, the field in the transverse direction
in the test area of the Test Box cannot be considered as a free field. This
causes the damping of the transverse sound waves in the test area to be more
than 6 db per doubling of the distance. The effective distance between the
regulating microphone and the hearing aid is thus greater than the geometrical
distance. Because the absorbing quality of the absorbing material changes
with the frequency , the effective distance is not constant. Around frequencies
of 800- 1ooo Hz ( c/ s) a geometrical distance of 12 em equals an effective
distance of approximately 20 em .
Specification
Frequency Range: 150 Hz ( c/ s) - 5ooo Hz ( c/ s).
Dynamic Range: 40 db to approx. 90 db re 2 · 10-
4
,ubar.
Uniformity of Sound Field: The free field sound level at the measuring point
is equal to that at the regulating microphone to within the following
tolerances: At 200 Hz (c/s)
±
o.2 dB, at 2ooo Hz (c/ s):
±
o .5 dB, and at
5ooo Hz (c/ s):
.±
3 dB.
Insulation against Airborne Sound: At 200 Hz (c/ s): Approx. 35 dB, at 2ooo
Hz (c/s): Approx. 55 dB, and at 5ooo Hz (c/s) approx. 70 dB.
Effective Test Areas: 8 em
X 6
em (3"
X
2.5") .
Built-in Condenser Microphone: The sensitivity of the regulating microphone
as well as the microphone in the artificial ear is approx.
5
m V / ,ubar.
Acoustic Coupler: The artificial ear includes a 2 cc coupler and may be used
both for insert types of earphones and for hearing aids with built-in ear-
phones. A loaded spring arrangement supplies the necessary static force
on the insert types of earphones when placed in the coupler.
6
cc ASA coupler: ASA Type 1,
Z
24.9/1949 available. Not included; must be
ordered as DB 0160 .
6
cc NBS coupler: NBS 9A
=
ASA
Z
24.5/1951 available. Not included; must be
ordered as DB 0161.
Loudspeaker: The loudspeaker in the Test Box is an 8 watt specially
selected loudspeaker with a moving coil impedance of 3.2
Q
at 400 Hz ( c/ s).
Mechanical Dimensions:
Inside dimensions of the anechoic chamber:
23 (width)
X
23
(depth) X
24 (height) em
9 (width)
X
9 (depth)
X
9¥2 (height) inches
Outside dimensions of the Test Box:
Weight:
Without sand :
With sand:
28
53 (width)
X
53 (depth)
X 80 (height) em
21 (width)
X 21 (depth) X 31 (height) inches
49 kg (108 lbs.)
125 kg (275 lbs .l