Amplitude modulation and impulse noise
Modern IWTs routinely produce audible amplitude
modulation. Leventhall reports that “a timevarying
sound is more annoying than a steady sound
of the same average level and this is accounted for
by reducing the permitted level of wind turbine
noise.” Pedersen and van den Berg state that
“from various studies it follows that this modulation
is equivalent in annoyance to the un-modulated
sound at an approximately 5 dB higher level.”
Ontario noise guidelines require a 5 dBA adjustment
for industrial noise that has amplitude modulation
but not for IWTs. Industrial wind turbines also
produce impulsive sound, which can be unexpected
and disturbing to residents.
Audible LFN