Noise

Acoustic specialists from our Helsby-based consultants have completed a full noise assessment to decide if the proposed scheme falls within the relevant noise regulations. The team has followed the recommended procedures, which require a survey of background noise levels and wind speeds, and computer predictions of the noise from the turbines. The noise survey was conducted over four weeks and involved measurements at four locations agreed with the council’s environmental health department. Measurements were also taken at 14 other locations in the surrounding area.

The team has computer modelled the highest noise level generated by the proposed turbines, accounting for the flat terrain of the marsh area and the surrounding hills. The noise contour map below represents the potential impact of the operating wind farm assuming no other noise sources, such as traffic noise along local roads and the M56.

It clearly demonstrates that even if all existing sources of noise were suddenly absent the proposed wind farm would hardly be audible from the settlements of Frodsham and Helsby where levels are predicted at or below 45dB(A) (a noise level equivalent to the ambient level in an unnoccupied open plan office).

Facts about sound

• The measurement of environmental noise takes into account the characteristics of human hearing. It is expressed as dB(A). Its scale is logarithmic to base 10. A 10-dB(A) increase in sound level is generally perceived as a doubling of loudness.

• An average living room typically has a noise level of about 40dB(A), whereas busy road traffic generates about 70–80dB(A) measured on the pavement (approximately 3m from the vehicles). An average bedroom at night has a noise level around 30dB(A).

• Sound energy dissipates over distance. For example, a police siren has a noise level of 100dB when you are standing next to it, but if you were to stand 1 km away it would only rate at 40dB.

• Two machines emitting exactly the same sound level, say 60dB(A), produce a total noise level of 63dB(A), not 120dB(A). It would take 10 machines to increase the noise by 10dB(A), and many more to double the level to 120dB(A). Where two sources with noise levels differing by more than 10dB(A) are combined, the combined level will be just slightly higher than the highest individual value.