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Hand-held Analyzer 2250 Light – User Manual

13.2 Tone Assessment According to ISO 1996-2, Annex D

When assessing noise, it is generally recognised that noise containing audible pure tones is

more annoying than noise with the same A-weighted broadband level that does not contain

audible tones. When assessing noise that contains tones or narrow bands of noise, an

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

) 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

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

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:

080160

1 2 ... 121 122 123 124 125 126 127 128 129 130 131 ... 211 212

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