indicated on the
red
MICR. SENS.
scale
of
the meter. Note
that
for
the B & K standard 1 inch microphone, the sensitivity (approx.
50
mV
per
N/m
2
)
will
be
set
on
the upper
of
the
two
MICR. SENS.
scales.
For the B & K
1/2
inch microphones (sensitivity approx.
10
mV
per
N/m
2
)
and
the
1/8
inch microphones (sensitivity approx.
1
mV
per
N/m
2
)
the upper
of
the
two
MICR. SENS.
scales
should
also
be
used-
the attenuator
scale
accounts
for
the required factors
of
ten. For the B & K
1/4
inch microphone the sensitivity (approx. 2
mV
per
N/m
2
)
should
be
set
on the lower
of
the MICR. SENS.
scales-
the attenuator
scale
again accounts
for
the factor
of
ten.
Note:
Slight attenuation
is
inevitably
caused
by
the
input
stage
capacity. Its significance
is
discussed in section 4.3.
3.2. MEASUREMENT
OF SOUND
Where
sound measurements
are
to
be
made in accordance
with
I
EC
179
or Dl N 45 633 parts 1 and 2 the
2209 must
be
fitted
with
the Extension
Rod
UA
0196, 1 inch microphone 4145
and
RAndom Incidence Corrector
UA
0055
or
with
the Extension Rod
UA
0196 and
Half
Inch Microphone
Type 4133. The procedure
is
as
follows:
1.
Calibrate the meter
as
described in section 3.1.1. Note: Before
fitting
the
input
stage,
set
the
input
socket switch
(see
Fig.4.8
and
section 4.3)
to
its 10
Hz
position (screw
fully
anticlockwise). This
V\(ill
reduce sub-audio sound disturbances
such
as
wind noise.
2.
If
measurements
are
to
be
made
with
a one inch microphone at sound
incidence on the microphone diaphragm other than normal incidence,
fit
the Random Incidence Corrector in place
of
the normal micro-
phone protection grid. Note:
Care
should
be
taken
to
avoid anything
touching the diaphragm
of
the microphone.
3.
Set the WEIGHTING NETWORK switch
to
"Lin"
or
"C"
and
select
the required
function
of
the METER SWITCH.
4.
Hold the instrument steadily
but
as
far
away
from
the
body
as
practical (preferably
use
a
tripod
or
other
firm,
non-interfering
support. The microphone
should
be
at least 1 metre
from
the
observer's body),
with
the microphone directed towards the measur-
ing object.
17
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