BRUEL & KJAER 2221 - Measurement Analysis

It is good practice before starting measurements to check the proper functioning of the
sound level meter and its calibration. Always use the windscreen supplied when measure-
ments are made outdoors or in very dusty environments. Keep the instrument at arms
length (or mounted on a tripod) to minimize body reflections which can produce reading
errors of up to a few dB in the range 300 to 500 Hz.
3.5.2 Considerations Regarding the Type of Sound Field
12
The condenser microphone fitted to the Type 2221/22 is designed to have a linear free
field response for oo incidence. Use of the supplied Random Incidence Adaptor DZ 9566
results in a linear response under diffuse field conditions. The use of the Random
Incidence Adaptor is described in the Fig.3.4 and. in the following text. When performing
measurements to national and international recommendations, the sound level meter
should be used as prescribed in the relevant standard.
Mount
Random
Incidence
Adaptor
Diffuse
Accurate
reading
ANSI
Free
Best angle
of incidence
75°
Inaccurate
reading
Remove
Random
Incidence
Adaptor
Diffuse
Inaccurate
reading
No
Remove
Random
Incidence
Adaptor
Free
Best
angle
of incidence
oo
Accurate
reading
Free
Mount
Random
Incidence
Adaptor
Accurate
reading
820331
Fig. 3.4. Flow chart for use of the Random Incidence Adaptor regard-
ing standards and type of sound field
IEC Standards:
When performing measurements requiring the use of a sound level meter to IEC stan-
dards the Random Incidence Adaptor DZ 9566 should NOT be mounted on the
microphone.