Techreport,
Procedure for the assessment of low frequency noise complaints
Acoustics Research Centre, Salford University, (2005)
Abstract
Low frequency noise (LFN) is now a recognised problem in many countries
in the world. Experience of LFN complaints from the last 30 years
has built up a good picture of the typical situations in which disturbance
arises. While only a relatively small number of people are affected,
those who are tend to suffer severe distress. It is not unusual for
sufferers to sleep in a car or shed to avoid the sound, and they
may suffer various symptoms such as depression or even feel suicidal.
In some cases a source of LFN is found and can be dealt with. However,
in many cases (typically 50% to 80% of cases), no environmental sound
that could account for the sufferer’s reaction can be found, and
the cause of the disturbance remains a mystery.
This guidance leads on from previous reports published by Defra: Le03
and Mo05.
Most Local Authorities will receive complaints about LFN at some point,
and usually find them particularly difficult to deal with for several
reasons. Firstly, existing noise criteria are not appropriate for
evaluating LFN; in almost all other situations the established noise
descriptors are based on the A weighted sound level (dB(A)) which
effectively filters out low frequency sounds.
Secondly, LFN cannot be reliably evaluated on the basis of the investigator’s
experience; indeed, officers investigating a case of LFN may not
even be able to hear the LFN themselves. This is possible because
disturbance by LFN is known to occur at levels only slightly higher
than hearing threshold, which varies from one individual to the next.
Also, the rate of growth of perceived loudness with level is more
rapid at low frequencies so that a sound could appear loud to one
person whilst still inaudible to another. An additional factor is
that ‘sensitisation’ to low frequency sound appears to occur over
time, and therefore a brief visit may not give an accurate impression
of what it is like to live with the sound.
Thus, the investigator is left with no suitable criteria and without
even personal experience to guide them. Thirdly, the measurement
of low frequency sound can be technically difficult. Against this
background, criteria for determining acceptable levels of LFN have
been introduced in Germany, Denmark, Sweden, Poland and the Netherlands
since 1997; the guidance presented in this document has been requested
and funded by Defra with the aim of developing a method for the assessment
of low frequency noise suitable for use by Environmental Health practitioners
in the UK.
