Norsonic nor1218, Instruction Manual

10

Chapter 4

Technical description

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Frequency [Hz]

+/- 30 deg – Horizontal reference

Directional response

An outdoor microphone system like Nor1218 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. Ideally, the mi-
crophone shall have the same sensitivity for sound 
from any direction. The IEC 61672-1 specifies toler-
ance 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 Nor1218, 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.