Norsonic nor1217, Instruction Manual

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12 Chapter 4
Technical description
100 10 k 20 k 1 k
0
1
2
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4
Frequency [Hz]
+/- 30 deg – Horizontal reference
Directional response
An outdoor microphone system like Nor1217 may
form a part of a sound level meter when applied for
environmental noise monitoring. The combination of
microphone and instrument shall therefore satisfy all
requirements in the international standards for sound
level meters, specified in IEC 61672-1. The Nor1217
in combination with Nor140 is type approved by PTB,
Germany. Ideally, the microphone shall have the same
sensitivity for sound from any direction. The IEC 61672-
1 specifies tolerance limits for the directional response.
The directional response of a microphone is the ratio
of the free field response at a particular frequency as
a function of angle of sound incidence to the response
in the reference direction.
The upper adjacent figure shows the directional re-
sponse for Nor1217, when the reference axis is verti-
cal, for the frequencies 1000 Hz, 4000 Hz and 8000
Hz.
IEC 61672-1 specifies tolerance limits for any frequen-
cy. The limits are depending on the angle from the ref-
erence axis and the standard specify tolerance limits
for angles up to ± 30°, up to ± 90° and up to ± 150°
from the reference axis. The lower adjacent figure
shows the typical max. deviation for the sector up to
± 30° from a horizontal reference axis together with the
applicable tolerance limits for a Class 1 sound level
meter.