Low-Frequency Noise (LFN) Disturbance

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Low Frequency Noise

A member of Finch Consulting’s (Finch) Noise and Vibration Team was recently appointed to advise the County Court at Central London in relation to an ongoing case relating to disturbance, allegedly due to noise from building services plant in a block of flats.

The issue first materialised around 2009 when refurbishment works were undertaken. The Environmental Health Department of the Local Authority, alongside several independent acoustic consultants, had investigated the issue over the years with no resolution in sight. A Finch expert was appointed following the Court’s order for the parties to appoint acoustic experts.

Our expert, following an extensive investigation, in contrast with all previous practitioners, concluded that the issue at hand relates to low-frequency noise annoyance.

Heath v Brighton Corporation (1908) is an early case which highlights the effects of low-frequency noise on a sufferer and the law’s unwillingness to protect over-sensitive or unique sufferers of nuisance.

Our expert was able to provide a comprehensive report to assist the Court in understanding the issue at hand, the technical complexities involved and the remedies that could be considered.

Low-Frequency Noise (LFN)

Low-frequency noise, in the frequency range from about 10Hz to 200Hz, has been recognised as a special environmental noise problem, particularly to sensitive people in their homes. Health care systems around the world, are facing the prospect of nearly 40% of their population being over 65 by 2051. This population dynamic may represent an important influencing variable for care agencies responsible for solving LFN problems, and related annoyance, as the largest population of LFN sufferers is in the 50+ age group. An approximate estimate is that about 2.5% of the population[1] may have a low-frequency threshold which is at least 12 dB below the average threshold, corresponding to nearly 1,000,000 persons in the 50–59-year-old age group in the EU-15.

low noise frequency graph

Figure 1 Demographics: 65+ as Predicted for Selected Countries

Conventional methods of assessing annoyance, typically based on A-weighted equivalent level, are inadequate for low-frequency noise and often lead to inappropriate decisions by regulatory authorities.

The Low-Frequency Noise Sufferers Association was formed in the UK in November 1989, following a conference of people affected by low-frequency noise.

Leventhall [2] review in 1989 suggested that local authorities in the UK might receive over 500 complaints of low-frequency noise a year for which nearly 90% of the noises are identified. Work in 2004 on a small sample of complaints, indicated that only about a third of complaints were resolved by technical means, whilst for the remainder, the noise source could not be found, the noise could not be measured, or measurements of noise did not correlate with the complainant’s perception of it.

In a different publication, Leventhall et al[3] say that low-frequency noise causes severe problems to the small number of people who are sensitive to its effects. Complainants tend to be middle-aged and older, although a small number of younger people may be affected. Perception of any continuous noise, at any audible frequency, will cause distress, but legislation and control action is, in practice, more effective at solving higher frequency noise problems.

A result of the difficulties in assessment and control is that there are a number of people in the community, mainly older people, whose quality of life is affected by their perception of low-frequency noise. Their complaints should be taken seriously, and the demand upon resources will intensify with current demographic trends towards an ageing population.

Locating and controlling the source of the noise ought to be the priority, but this is not always possible. In the recent case in which Finch was involved, practitioners did not make the correct diagnosis of the situation for almost 10 years, and the judge involved in the case appeared to take a hostile view towards the complainant. In a lot of these cases, complainants are left to endure the problem, continuing to suffer without further complaints to external authorities. A very small number of complainants are known to have improved their situation by changing and controlling their attitude to the noise, in a form of self-help.

Equipping individuals with the requisite skills to re-establish control over their lives is consistent with the need to address a core symptom recorded by low-frequency noise sufferers, namely “loss of control over their personal space“[4].

Guidance on the assessment of low-frequency noise

Regulatory authorities must accept that annoyance due to low-frequency noise presents a real problem which is not addressed by the commonly used assessment methods for environmental noise. The A-weighted sound pressure level is inadequate, as is the NR and NC criterion curves.

Complaints of low-frequency noise are investigated under the Environmental Protection Act 1990 and enforcement action is only viable if a local authority is satisfied that a statutory nuisance exists. Consequently, a decision of ‘Not a nuisance’ is often made.

Low-frequency noise is not effectively legislated for and investigations can produce controversial, contradictory and inconclusive results. In a study by Moorhouse et al[5] a total of 11 LFN complainants were referred by environmental health officers with 3 self-referrals. The officers in this study investigated the complaint in all referred cases and generally made sound level measurements in the complainants’ properties. In some cases, investigations were also carried out in neighbouring properties or by the utility companies[6]. In half of the cases, measurable LFN was recorded but was not considered actionable by the EHO (‘No Nuisance’ cases). Other cases were assessed as ‘No Noise Found’.

Criteria for assessing low-frequency noise levels vary from country to country.

Defra put in place a five-year research programme, Commitment 4, which looks at low-frequency noise problems. This includes the document Procedure for the assessment of low-frequency noise disturbance[7] produced by the University of Salford and published in 2005. Revision 1, dated December 2011, provides a comprehensive procedure for the assessment of low-frequency noise. This procedure is quoted in BS4142:2014[8]  in relation to the assessment of low-frequency noise.

The Salford report states that:

  • in some cases a source of LFN is found and can be dealt with; however, in many cases, the cause of the disturbance remains a mystery;
  • 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 the hearing threshold, which varies from one individual to the next;
  • 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;
  • the guidance provides a procedure to determine whether low-frequency sound that might be expected to cause disturbance is present in a complainant’s premises;
  • this document does not specifically provide guidance in locating the source of the LFN;
  • the procedure is intended to assist in the evaluation of existing problems;
  • levels of sound above criteria based on the average threshold of hearing are frequently found to be acceptable and levels falling marginally below can occasionally cause a disturbance, so no generic approach to the prediction of disturbance appears to be possible;
  • typically, complainants tend to be female and over 55 years of age;
  • there are theories that people who have been exposed to LFN may have become sensitised to it;
  • it is important to establish whether the complainants may have been at risk of noise-induced hearing damage which is often associated with hearing problems such as tinnitus, recruitment etc;
  • the most common sources of LFN disturbance are rotating machinery of one sort or another; this may range from large industrial equipment, at distances up to several kilometres away (low-frequency sounds travel with far less attenuation than higher frequency sounds), to small domestic items (fridges, fish tank pumps, central heating pumps), perhaps in a neighbouring property;
  • this document is not intended to provide a prescriptive indicator of a nuisance since there are other factors that may need to be considered in reaching this decision.

In Section 4.1 the document presents the criterion curve shown in the table below:

Proposed Reference Curve for Assessment of Low-Frequency Noise (fluctuating sounds)

Leq Sound Pressure Level (dB) at third-octave band centre frequencies (Hz)
10 12.5 16 20 25 31.5 40 50 63 80 100 125 160
92 87 83 74 64 56 49 43 42 40 38 36 34

 

NB: If the noise occurs only during the day then 5 dB relaxation may be applied to all third-octave bands

Fluctuating sounds are known to be more disturbing than steady sounds. The report, therefore, states that the criterion curve should be relaxed by 5 dB for steady sounds to take account of this. If the sound is audible, then a subjective judgement may be made as to whether it should be considered fluctuating.

Unidentified Source

The Salford Procedure says that 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.

A paper by Moorhouse et al[9] reviews a protocol to support LFN sufferers in the UK, in cases where the source of the disturbance was not found. The paper also says that “anecdotal evidence also suggests that there are further categories where a LFN was present but has disappeared by the time of the investigation although the disturbance continues. A likely mechanism for the delayed responses in such cases is a cycle of increased auditory gain and anxiety“.

For cases where the source of the disturbance remains a mystery, and therefore there is no prospect of external control of the perceived LFN, Moorhouse et al proposed and tested an alternative means of mitigating the disturbance to the sufferer. The proposed therapeutic approach draws on an understanding of the mechanisms involved in troublesome tinnitus and hyperacusis (there is no implication that LFN complaints are necessarily caused by tinnitus).

The general impression from the results of the work by Moorhouse et al is that some of the subjects benefitted from the intervention, with others showing little change; the factors likely to influence success are the quality of the referral by the EHO, the quality of the audiology input and the attitude of the complainant.

In addition, Leventhall et al[10] in 2009 developed a Defra-funded course in computerised Cognitive Behavioural Therapy aimed at relieving the problems of those suffering from noise exposure, in particular, exposure to low-frequency noise. The course enabled participants to learn methods of coping with the noise, by guiding them through a course of CBT which had been specially prepared for sufferers from noise.

In 2005, under the same Defra funding, Leventhall et al also produced the document Coping strategies for low-frequency noise. A small group of people, whose complaints of low-frequency noise had not been resolved, were invited to attend a series of relaxation sessions led by a psychotherapist. The aims of the sessions were to improve the participants’ coping strategies and their quality of life and to relieve them of some of the distress which the noise caused. A general reduction in the subjects’ stress levels was shown, suggesting positive effects of psychotherapy upon symptoms that had, in this group’s case, proved resistant to improvement by the conventional local authority and specialist interventions. This ‘therapeutic’ approach to LFN interventions could lead to improved health and effectiveness and fewer demands on local services. Although the techniques of tinnitus management were informative, the analogy between the problems of low-frequency noise sufferers and those of tinnitus sufferers fails at the point where low-frequency noise sufferers believe that an external agency is the cause of their problems.

For any more information on low-frequency noise disturbance, please contact [email protected].

[1] HG Leventhall, “low-frequency noise and annoyance”, Noise &Health Journal, 2004, vol 6, issue 23, Pages 59-72

[2] Leventhall et all Coping Strategies for Low-frequency Noise, June 2005, NANR 125

[3] Leventhall et al Development of a course in computerised Cognitive Behavioural Therapy aimed at relieving the problems of those suffering from noise exposure, in particular, exposure to low-frequency noise (NANR 237) June 2009

[4] Leventhall, H. G., Benton, S., and Pelmear, P. A review of published research on low-frequency noise and its effects. Prepared for Defra, 2003

[5] A Moorhouse et al: Trials of a protocol to support LFN sufferers in the UK, (2015), Euro noise 2015

[6] Since mechanical services associated with the utility companies was suspected as being the source of the low-frequency noise disturbance

[7] Procedure for the assessment of low-frequency noise disturbance, Moorhouse, AT, Waddington, DC and Adams, MD,  Revision 1 December 2011, Contract no NANR45

[8] BS 4142:2014+A1:2019 Methods for rating and assessing industrial and commercial sound

[9] A Moorhouse et al: Trials of a protocol to support LFN sufferers in the UK, (2015), Euro noise 2015

[10] Leventhall et al Development of a course in computerised Cognitive Behavioural Therapy aimed at relieving the problems of those suffering from noise exposure, in particular, exposure to low-frequency noise (NANR 237) June 2009

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