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2250 Light – User Manual
adjustment shall be added to the A-weighted time averaged level, L
Aeq
. The first evaluation of
audible tones in noise is most often carried out by the human ear. But for comparative analysis
results, and documentation, an objective analysis may be needed.
Tone Assessment can be performed using the ISO 1996-2:2007 standard “Determination of
environmental noise levels”, Annex D: “Objective method for assessing the audibility of tones
in noise – Simplified method”. This method uses 1/3-octave measurements.
The selection of method depends on local legislation which may refer to ISO 1996-2 or a
local method.
Find more information about rating level and assessment of environmental noise in ISO 1996-2
and in Brüel & Kjær’s Environmental Booklet.
13.2.1 ISO 1996-2, Annex D – Tone Assessment Calculations
The ISO method searches a measured, time averaged (L
eq
) spectrum, for level differences
between adjacent 1/3-octave bands. If the level difference between a 1/3-octave band and the
band either side of it are higher than a certain limit, an adjustment for audible tones may be
added to the L
Aeq
level when calculating the rating level, L
r
.
In ISO 1996-2, Annex D, the spectrum is divided into three frequency ranges: Low, Middle and
High. In each frequency range a specific limit for the level differences leading to an adjustment
is defined, see Fig.13.1.
Fig.13.1 Definition of frequency ranges and level differences
The proposed frequency ranges and level differences between adjacent bands are:
• Low frequency range: includes the 1/3-octave bands from 25 Hz to 125 Hz with a level
difference for a detected tone greater than 15 dB
25 Hz
Low
Middle
High
125 160 400 500 10 kHz
1/3 - octave bands [Hz]
Proposed level
difference limits
for adjacent
bands [dB]
Level differences can be defined in Low, Middle
and High frequency range:
0
2
4
6
8
10
12
14
16
dB
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