BRUEL & KJAER 2203 - Sound Measurement Procedure

factors between + 8 and + 14, the 2203 can be set for a K-factor of (K - 1 0), and
1
0 dB can be added to all readings.)
Determination of K -factor
The K-factor of a microphone is the difference in dB between a standard microphone sen-
sitivity of 50 mV /Pa (-26 dB re 1 V /Pa) to which B & K instruments are calibrated and
the sensitivity of the actual microphone. For example, if a microphone has a sensitivity
of -2 7 dB re 1 V /Pa, then the K-factor is 1 ,0 dB. This means that the gain of a Sound
Level Meter must be increased by 1 dB compared with its standard gain, in order to give
correct readings.
The K-factor is also influenced by the loading due to cables, adaptors, etc .. Therefore the
K-factor should be determined using several different factors according to the formula:
K = K
0
- input gain - adaptor gain
where K
0
is the open-circuit correction factor.
For the Microphone Type 41 65 supplied with the 2203, the K-factor is found as indi-
cated in Fig.3.2.
In the example, for use with the set-up shown in Fig.2.1, K
0
is found on the front of the
calibration chart(+ 0,5 dB). From this is subtracted the input gain of -2,1 dB indicated
on the back of the calibration chart. This gives a total K-factor of + 2,6 dB, to which the
2203 should then be calibrated.
If a 3m (10ft) extension cable AO 0128 is used, it has an attenuation of approximately
0,3 dB with half-inch microphones and approximately 0,1 dB with one-inch micro-
phones . This should also be taken account of in the K-factor adjustment on the meter.
Because of these complications, it is easier to use a Pistonphone Type 4220 or a Sound
Level Calibrator Type 4230, quite apart from the fact that when using these the com-
plete system is calibrated .
3.4. SOUND MEASUREMENTS
3.4.1. General
The accompanying booklet "Measuring Sound" should be read through before proceed-
ing
with measurements, as it contains much useful general information on the subject.
One or two points should perhaps be emphasized. Ensure that the microphone has the
required dynamic range, frequency range and directional characteristics. Always use a
Windscreen for outdoor measurements and in a dusty environment. Various Nose Cones
are available
for reducing wind noise (see Fig.8, Chapter 1 ), as well as Dehumidifiers.
The microphone must be mounted on the Extension Rod UA 01 96 to fulfil the require-
ments of the precision standards. If a one-inch microphone is used, a Random Incidence
Corrector may also be necessary for certain measurements. Ensure that the measuring
position is suitable and hold the Sound Level Meter at arm's length, or mount it on a
tripod, to minimize reflections from the operator. Finally, make sure that the background
noise level is not too high to make meaningful measurements.
3.4.2. Procedure for Sound Measurements
1. Calibrate the 2203 (including checking the batteries) as described in section 3.3.
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