BRUEL & KJAER 2230 - Page 23

Sound
Incidence
"Random"
Diffuse
Optimum
accuracy
ANSI
Free
Best angle
of incidence
75°
Reduced
accuracy
Sound
Incidence
"Frontal"
Diffuse
Reduced
accuracy
No
Sound
Incidence
"Frontal"
Free
Best angle
of incidence
oo
Optimum
accuracy
Free
Sound
Incidence
"Random"
Optimum
accuracy
83 036 1
Fig. 3.5. Flow chart for use of the Sound Incidence switch regarding
standards and type of sound field
IEC Standards:
When performing measurements requiring the use of a Sound Level Meter to IEC stan-
dards the SOUND INCIDENCE switch has to be switched to "Frontal".
The Sound Level Meter should be pointed directly at the source if a free-field condition
is assumed to exist (see Fig.3.6). In a diffuse-field reduced accuracy may be expected.
For optimum accuracy, see Fig.3.5.
Fig. 3.6. Measurements to lEG standards in a free sound field
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