Techreport,
Proposed criteria for the assessment of low frequency noise disturbance
Acoustics Research Centre, Salford University, (2005)
Abstract
The aim of this study is to recommend a method for assessing low frequency
noise (LFN), suitable for use by Environmental Health Officers (EHOs)
in the UK. A general introduction to LFN is given, in which it is
argued that a method of assessment is needed both from the sufferer’s
point of view, because there is currently not much to protect them
against LFN, and from the Environmental Health Officer’s point of
view, where guidance is needed in determining whether a nuisance
exists.
Criteria already in use in Germany, Sweden, Denmark, the Netherlands
and Poland were reviewed and compared. Experience from these countries
in applying the criteria was also reviewed, and was found to be generally
positive.
A complementary set of field and laboratory studies was conducted
in order to establish the best form for an assessment method. In
the field studies, eleven cases of reported LFN were investigated,
as well as five control cases where no complaints about LFN had been
received. Analysis of recordings made over three to five days at
each location distinguished three groupings: positively identified
LFN, unidentified, and marginal. Three cases were positively identified,
meaning that the various national criteria were exceeded and there
was correlation between the resident’s logged comments and the LFN
level. Five cases were unidentified: the criteria were generally
not exceeded, (except perhaps by traffic noise), and there was a
lack of correlation between comments and noise levels. Three cases
were marginal in that the LFN was marginal with respect to the criteria
and did not correlate with comments. It was concluded that the criteria
were successful at distinguishing cases where an engineering solution
could be applied from those where no such solution could be
found.
In the laboratory tests, a set of ‘thresholds of acceptability’ were
established by asking 18 subjects to set the level of various low
frequency sounds to a just-acceptable level for imagined day and
night situations. The sounds presented consisted of a set of tones
across the low frequency range, ‘real’ LFN extracted from field test
recordings, and synthesised beating tones with varying degrees of
fluctuation. LFN sufferers were found to be the least sensitive group
in absolute terms, contrary to the common image of ultra-sensitive
individuals. In relative terms however, they were the most sensitive
group in that they set acceptability thresholds closer to their threshold
of hearing. From the existing national reference curves, the Swedish
curve showed the best agreement with the results. It was also demonstrated
that fluctuating sounds are less acceptable than steady sounds for
the same average acoustic energy and should be penalised. Furthermore,
it was shown that 5dB is an appropriate penalty almost irrespective
of the degree of fluctuation above a limiting value.
A method for assessing LFN suitable for use by EHOs is proposed. This
consists of a reference curve based on 5dB below the ISO 226 (2003)
average threshold of audibility for steady sounds, plus a means to
establish whether a 5dB relaxation for steady sounds should be applied.
It is expected that this will benefit EHOs by helping to identify
cases where they are able to improve the situation by enforcing noise
control measures. It is also expected that in a significant proportion
of LFN cases it will not be possible to identify a ‘hardware’ solution.
Consequently, it is suggested that further research be conducted
into alternative solutions.
