Draft National Wind Farm Development Guidelines - July 2010

the converse. These Guidelines recommend that analysis of wind direction effects on
background noise level be carried out as part of the noise impact assessment.
Noise Characteristics
Some industrial noise emissions contain characteristics that may make the noise more
annoying: tonality (humming, whining), modulation (regular variation in noise level or pitch)
and impulsiveness (hammering, banging). These characteristics can generally be
eliminated in the case of wind farm noise emissions; however these Guidelines address
their assessment and management.
AS4959–2010 provides some guidance on how to address tonality, but excludes methods
of measurement of other characteristics.
In considering noise characteristics, AS4959–2010 notes that:
When setting limits of acceptability, the limits should take into account the
fundamental characteristics of wind farm noise, including aerodynamic noise from
the rotating blades, occasional aerodynamic modulation, the mechanical noise of
the gearbox and other components and also other infrequent and short term noises
that may occur, such as braking.
If a wind farm is designed for compliance with reasonable noise limits, this should provide
for sufficient buffers between the wind farm and noise-sensitive sites to ensure that the
received noise is free of annoying noise characteristics. For example, a wind turbine
exhibits a degree of amplitude modulation (“swoosh-swoosh”) for a listener nearby. As
one moves away and the turbine noise merges with noise from other turbines and the
background noise, this characteristic tends to disappear. If however the degree of
amplitude modulation at the receiving location was greater than normal and not
consistent with the characteristics of a correctly-functioning wind farm then it may be
considered an annoying characteristic that would need to be addressed.
The relevant authority may have specific requirements for assessing some noise
characteristics and they will be responsible for determining how these characteristics are
to be addressed in the process of showing compliance with the noise criterion. These
Guidelines provide recommendations for the assessment of noise characteristics during
particular phases of the noise impact assessment process as outlined below.
Tonality – as part of the assessment phase the proponent should require the wind turbine
supplier to ensure that tonality is not present in the turbine’s noise emission at the distances
of interest (manufacturers typically accept this). An assessment of tonality may be
required as part of the pre-construction phase or the post-construction monitoring phase
and a penalty (typically 5dB) may be applied to the received noise level if tonality is
present.
Amplitude Modulation and Impulsiveness - An assessment of amplitude modulation or
impulsiveness should be required as part of the post-construction monitoring phase and a
penalty (typically 5dB) may be applied to the received noise level if any of these attributes
are present. These features may only be evident once a wind farm is operational and they
would not be dealt with at the pre-construction phase. For example modulation may only
be evident when the operation of multiple turbines causes a periodic variation in level due
synchronous operation of some of the turbines and remedial actions (such as varying
operational speeds to avoid synchronous operation of turbines) would be directed to
eliminate such effects.
Low-Frequency Noise and Infrasound – There have been concerns raised about possible
health impacts associated with low frequency noise (rumbling, thumping) and infrasound
(noise below the normal frequency range of human hearing) from wind farms. Low
frequency noise and infrasound levels generated by wind farms are normally at levels that
are well below the high levels required to cause any health effects. An assessment of lowfrequency
noise or infrasound is therefore not required as part of the pre-construction
phase or the post-construction monitoring phase. An assessment of these characteristics
can be required by the relevant authority where such components are reported as being
Draft National Wind Farm Development Guidelines – 2 July 2010 Page 39