Draft National Wind Farm Development Guidelines - July 2010

Table B-4
Suggested methods for assessment of noise characteristics
Noise
characteristic
Amplitude
modulation
Impulsiveness
Suggested assessment
procedure
Tasmania Department
of Primary Industries,
Water and
Environment (2004)
Noise measurement
procedures manual,
Also Western
Australian
Environmental
Protection (Noise)
Regulations 1997
Australian Standard
1055.1:1997 Acoustics
– Description and
measurement of
environmental noise
Part 1: General
Procedures
Comments
Amplitude modulation may be present where there is a
greater than normal degree of fluctuation of sound level.
The suggested assessment procedure indicates the
presence of amplitude modulation where there is a
regular, cyclic and audible variation in sound level of more
than 3dB.
It should be noted that LA90,T may not be appropriate for
assessing amplitude modulation. LAeq, LA01 or LAMax indices
may be more suited to identification measurements.
Further, it is noted that any assessment of amplitude
modulation should take place at the Receiver location
being assessed. It is not suitable to carry out an assessment
within the wind farm site as, at the Receiver location,
emission from several different turbines may be contributing
to the observed effect. Also, the measurement position
should not be unduly affected by facade reflections in the
area immediately around the measurement location.
This assessment requires the use of a sound level meter with
fast response and impulse response time weightings. It is
recommended that impulsiveness assessments be carried
out on calibrated digital recordings of the suspected
impulsive sound, so that the impulsive and fast time
weighting may be applied to the same audio sample. In
some cases, impulsiveness may be indicated using the
AS1055.1 assessment method when, subjectively, it is not
considered to be present. These cases should be discussed
with the relevant authority
Infrasound DIN 45680:1997
Measurement and
evaluation of lowfrequency
environmental noise,
Deutsches Institut für
Normung
DIN45680 does not prescribe acceptable noise limits but
discusses a method for assessing perceptibility. Although a
given low frequency noise or infrasound may be
perceptible, this does not imply a negative effect on
health.
The assessment frequency range of DIN 45680:1997 extends
down to 8Hz and so may exclude some frequencies which
are considered part of the infrasound range. Complaints
resulting from noise emission in this extremely low frequency
range are considered unlikely. Nonetheless, it is important
to recognise this limitation of the assessment method.
Low
frequency
noise
Tonality
DIN 45680:1997
Measurement and
evaluation of lowfrequency
environmental noise,
Deutsches Institut für
Normung
Assessment
procedures as
identified in Section
7.2 of AS4959–2010
The noise level threshold curves included in the standard
are reasonably conservative. However, they are based on
a 50% threshold level and some research suggests that a
10-12dB margin to the 10% threshold may exist.
Accordingly, it may be that some individuals can hear a
sound level which is measured to be less than the threshold
limit. Where the measured level is within 12dB of the
threshold value and the measured level is greater than the
background noise level further investigative work is likely to
be required.
Note: The assessment method proposed for amplitude modulation should be considered as nominal
and is proposed in the absence of a more suitable method specific to wind farms. It may be used as
an indicator of amplitude modulation; however, the assessment should be carried out in conjunction
with a subjective assessment of the sound by the assessor and the relevant authority. It may be more
suitable in this case to explore adjustments in the operation of particular turbines under certain
meteorological conditions, for example by using noise management settings at particular wind
speeds, to try and alleviate the issue
Page 60 Draft National Wind Farm Development Guidelines – 2 July 2010