BRUEL & KJAER 2206 - Page 8

Battery 1.5 Vo------<rr
On
OQff
'2206 ----------,
I
Condenser
I Microphone
Polarization
Voltage
Adapter
(Source
follower)
~~ (Type~4-1_48_) ...__-1
L- -- - _...._____. J
~ Pl.,oeloct~ ~ - - - -~
Microphone
I (Type 4117) I
I I
l220!_ _______ j
Meter
Voltage Voltage
Converter Regulator
~~-----
Hold
1
I L-----'
I
lsi ow
I
I
2206
l._f
208
only _j Rectifier
Output
740632
Fig.1. Block diagram for the miniature sound level meters
Description
The Type 2206 Precision Sound
Level Meter and Type 2208 Noise
Event
Meter are two variations of
the same basic instrument. Both
meet the internationally apprbved
standards
for general purpose
sound level meters, while the Type
2206 also satisfies the require-
ments for precision sound level me-
ters.
Various special features have
been
included in the two instru-
ments so that a sound level meter
can be obtained with only those fea-
tures necessary for its particular
use. This gives an instrument that
is both inexpensive, and simple to
operate. Reference to the block dia-
gram in Fig .1 shows the similarities
and differences between the instru-
ments.
The microphone normally sup-
plied with the Type 2208 is the 1"
diameter Piezoelectric Microphone
Type 4117. This is a high quality,
low cost measuring microphone de-
signed primarily for use in general
purpose sound level meters. Its
high capacitance allows it to be
used
with amplifiers having moder-
ate input impedance to give ade-
quate
low frequency performance.
The high capacitance also permits
the use of relatively long connection
cables between the microphone and
the
sound level meter (reducing the
2
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Briiel & Kj(8r Potentiometer Ronge, __ dB Ro<tilier, __ L- lim. Froq. :_Hz 'VIr . Spoed: __ mmf- . Popo< Spoed:_....,..c.
C-hogon 50 25 , 10 75
dB dB Condenser Microphone 4148:=f dB dB
860
Moosuring Obj.:
Microphones
Piezoelectric Microphone 4117
~~u~~n~:~;~ 30 15
Meters
()0 Free Field
---2010
---·105
~
o.u:._
Sign.: 0 0
430
10dB
2 15
Qp 1124 10
20 Hz 50
100
200
500 1000
2000 5000
0 0
10000 20000 40000
D A B C lin.
Multiply Fre<{vency Scole by
Z.ro t.....l:
1612/2112 A B C lin.
17
2221
Fig.2. Typical frequency response curves for the microphones
possibility of reflections from the op-
erators body) without serious loss of
sensitivity. A typical frequency re-
sponse
curve is shown in Fig.2. The
performance of the 2208 with this
microphone is in accordance with
IEC R 1 23 for general purpose
sound level meters.
The Type 2206 features a special
8 & K condenser microphone sys-
tem, and the drcuitry for 2208 has
also been designed to accept this
system. The Type 4148 1 /2" Con-
denser Microphone requires 28 V
polarization voltage, and was devel-
oped for these miniature instru-
ments. It is mounted on the meter
by means of the UA 0208 Adaptor,
and when fitted, the requirements
of IEC, ANSI and DIN for precision
sound level meters are met. The
Adaptor contains a source follower
(FET) to transform the high imped-
ance of the condenser microphone
into a low output impedance. A typi-
cal frequency response curve for
the 1 /2" Condenser Microphone is
also shown in Fig.2. When fitted
with the 1 /2" Condenser Micro-
phone and Adaptor, the 2208 be-
comes a
Precision Sound Level Me-
ter in accordance with IEC, ANSI
and DIN.
The Piezoelectric Microphone, or
Condenser Microphone and Adap-
tor, can be replaced by a JJ 0037
Adaptor, which permits connection
with miniature coaxial cables, thus
allowing the sound level meters to
be used as indicating instruments
for 8 & K accelerometers. It should
be noted however, that when the