Noise can be defined as loud or unpleasant sound, especially when it causes disturbance. However, amongst individuals there can be a distinctly subjective response to noise which is potentially influenced by a wide range of factors. In extreme cases some people may be diagnosed with hyperacusis, but more commonly people may just have less tolerance for a particular type of noise.

Some people simply abhor the sound of chalk on a blackboard, for example, whilst others might react more severely to mechanical noise such as electric drills. Maybe there is an association with the dentist’s drill that explains the latter.

Noise sensitivity refers to the ‘internal states (be they physiological, psychological [including attitudinal], or related to lifestyle or activities conducted) of any individual which increases their degree of reactivity to noise in general’ (Job, 1999). In the investigation of noise complaints it may be possible that a complainant is very sensitive to noise. Thus the adage: ‘whereas to the lay person anything that annoys him is a nuisance, the legal test for noise/nuisance is objective’ (Malcolm and Pointing, 2011).

The law of nuisance has been regarded as imprecise due to it being ancient, complex and part of the common law. However, in most jurisdictions there is a clear recognition that everyday activities generate noise and the principles of ‘give and take’, ‘reasonableness’ and ‘an average person’ are all important.

In order to assess whether there are reasonable grounds for complaint and/or whether some intervention is required to prevent or control a noise, we must follow recognised procedures and standards to objectively measure and evaluate the situation. The measurements should quantify and evaluate the likely potential impact of the noise as opposed to describing it subjectively. This raises the importance of standardisation and good acoustical practice.

If a noise is measured with an instrument in accordance with ‘the standards’, the result should be substantially the same as that which would be obtained with any other similarly designed instrument. The current standard for sound level meters, IEC 61672, is published in three parts. Before and after each series of measurements, all sound level meters should be calibrated in the field with appropriate acoustic calibrators. In addition, the performance of the instrumentation (both the calibrator and the sound level meter) should be verified at specified intervals by an accredited laboratory (meters at least every two years and calibrators annually).

Frequency and hearing

The frequency of a sound (measured in Hertz, Hz) is the rate at which pressure fluctuations are produced per second. The response of the human hearing mechanism to noise depends on the sound frequency and the sound pressure level.

In theory, the human ear can detect sounds with frequencies from 20 Hz to 20,000 Hz, however, the human ear is not equally sensitive to sound at different frequencies. To adequately evaluate human exposure to noise, the instrumentation must account for this difference in sensitivities over the audible range. For this purpose, frequency weighting networks have been developed. These are “frequency weighting filters” and they allow us to measure noise over a specified range of frequencies while filtering or blocking out all other frequencies.

Frequency weighting networks “weight” the contributions of the different frequencies to the over-all sound level, so that sound pressure levels are reduced or increased as a function of frequency, before being combined to give an overall level. The two internationally standardised weighting networks in common use are the ‘A’ and ‘C’, which have been designed to correlate to the frequency response of the human ear for different sound levels.

At the threshold of hearing, a noise is just “loud” enough to be detected by the human ear. Above that threshold, the degree of loudness is a subjective interpretation of sound pressure level or intensity of the sound. Practically all sounds contain a mixture of frequencies and this mix will affect the perceived loudness. A highfrequency sound (e.g., a squealing loose fan belt) at the same acoustic pressure as a low-frequency sound (e.g., a rumbling compressor) will be perceived to be louder. This is because the human ear is most sensitive to mid-range and high frequencies and is less sensitive to the lower frequencies.

Tones are noises with a narrow sound frequency composition (e.g., a whine, hiss, screech, or hum etc.) and when these are clearly audible they have the potential to be more annoying than a broadband noise and to consequently give rise to a greater impact.

Environmental noise criteria

Environmental noise (often referred to as ‘community noise’ or ‘neighbourhood noise’) can potentially affect people in their homes, properties and in public areas. Typically the term applies to the cumulative effect of noise emitted from many sources. In many monitoring scenarios, however, we are concerned about the noise from a specific or individual source, such as a factory emitting fan noise, and its potential effect on local residents.

“rather than simply comparing measured noise levels against a single limit or guideline, the noise investigator will need to carefully monitor and assess the noise in accordance with a particular standard or code of practice”

In practice the potential impact of a noise emission is dependent on a wide range of factors, such as:

  • The time, duration and predictability of the emission
  • The amplitude and frequency of the noise emission
  • The nature of the source, e.g. equal levels of aircraft and industrial noise are likely to give rise to significantly different degrees of annoyance
  • The location of noise sensitive receptors
  • The sensitivity of any individuals affected
  • The ambient and background noise level
  • The nature and character of the locality
  • The presence of special acoustic characteristics such as tones, impulsive elements or modulation – where the noise level changes in its loudness, tone or character
  • The incongruity or familiarity of the noise – is it typical of noise which would be normally heard in the area?

Rather than simply comparing measured noise levels against a single limit or guideline, the noise specialist/investigator will need to carefully monitor and assess the noise in accordance with a particular standard or code of practice. When it comes to interpreting the data, the competent specialist will call on a wide range of criteria and guidance and form an opinion as to the likely effect of the noise.

“when it comes to interpreting the data, the competent specialist will call on a wide range of criteria and guidance and form an opinion as to the likely effect of the noise”

In considering this, he/she should form an opinion about some key issues, such as:

  • Whether the noise significantly disturbs normal daytime outdoor recreation and/or the enjoyment of a property
  • Whether the noise currently (or is likely to) adversely affect indoor activities at the receptor position – e.g., sleeping, conversation, reading or studying
  • Whether the noise is clearly audible within a residential property during evening time and/or typical sleeping hours (or likely to be clearly audible with the windows open)
  • Whether the noise affects the viability of a commercial operation or impacts upon people who need relatively quiet conditions to perform work activities (e.g., receptors in an office)

In practice, noise limits have been established for industrial and commercial activities having regard to local circumstances and the need for environmental protection. The World Health Organization (WHO, 2000) has published guideline values for community noise in specific environments and LAeq is generally the preferred index. LAeq is the equivalent continuous noise level for the measurement period, measured in A-weighted decibels (dBA). It is defined as the sound level of a steady sound, having the same energy as a fluctuating sound over the specified measuring period.

To protect the majority of people from being seriously annoyed during the daytime, the sound pressure level on balconies, terraces and outdoor living areas should not exceed 55 dBA LAeq for a steady continuous noise (this LAeq is assessed over a 16-hour daytime and evening period). The 2000 WHO guidelines also state: “For bedrooms the critical effect is sleep disturbance. Indoor guideline values for bedrooms are 30 dB LAeq for continuous noise and 45 dB LAmax for single sound events. At night-time, outside sound levels about one metre from facades of living spaces should not exceed 45 dB LAeq, so that people may sleep with bedroom windows open. This value was obtained by assuming that the noise reduction from outside to inside with the window open is 15 dB.”

Thus, the WHO (2000) indoor guideline values for bedrooms are 30 dBA (LAeq assessed over an 8-hour period), however, it is recognised by the WHO that lower noise levels may be disturbing, depending on the nature of the noise source.

The WHO defines health as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity, and recognises the enjoyment of the highest attainable standard of health as one of the fundamental rights of every human being.

The most recent WHO guidance (2009) recommends a ‘Night Noise Guideline (NNG) of 40 dBA outside a residential property or noise sensitive location, however, this is defined as a ‘long-term average sound level’ as opposed to a level measured during a limited period on one night. An interim target of 55 (Lnight, outside) has been set by the WHO in recognition of the very many situations in which the achievement of the NNG is not feasible.

It is noteworthy that the WHO 2000 quoted criteria are generally applied to industrial activities and the 2009 Night Noise Guideline is predominantly based on transportation noise and is used in policy and strategic considerations. Throughout Europe, there is a tendency for noise from industrial facilities to be regulated by way of planning permission limits, permits and/or by way of environmental licences (e.g., Integrated Pollution Prevention and Control (IPPC) Licences).

Rating environmental noise

Although it has known limitations, LAeq is universally recognised as a basis for assessing the impact of noise on humans. According to WHO guidance (2000) ‘there is a very complex multi-dimensional relationship between the various characteristics of the environmental noise and of the effects it has on people. Unfortunately, we do not completely understand all the complex links between noise characteristics and the resulting effects on people. Thus, current practice is to reduce the assessment of environmental noise to a small number of quite simple quantities that are known to be reasonably well related to the effects of noise on people.’

For many years it has been recognised that the LAeq index alone does not provide an adequate assessment of tonal and/or impulsive noise due to them having the potential to be more annoying than broadband noise. In fact, adjustments for tonal or impulsive sound have been advocated in every version of the international standard for measuring environmental noise (ISO 1996) since it was first published in 1971.

Throughout the world, there is widespread acceptance that tonal and/ or impulsive noise needs to be penalised or adjusted to reflect its potential for annoyance. The latest version of ISO 1996-1 (2016) defines the basic quantities to be used for the description of noise in community environments and describes assessment procedures. It also specifies methods to assess environmental noise and gives guidance on predicting the potential annoyance response of a community to long-term exposure from various types of environmental noises. (The term “rating level” is used to describe sound measurements to which one or more adjustments have been added. On the basis of these rating levels, the long-term community response can be estimated).

There are a number of methods for the objective identification of tones to determine if an adjustment is required. The simplified methodology is based on the sound pressure level in a one-third octave band of interest exceeding the average sound pressure levels of both adjacent one-third octave bands by a specified level. However, in the event that there is a difficulty in identifying a tonal noise source using this method, or there is disagreement over the presence of tonal noise, then the recommended approach is to adopt the narrow-band methodology (engineering method) outlined in Annex J of ISO 1996-2:2017.

A noise source that attracts an impulsive characteristic will often be described as something with a thumping, banging or impact noise that is clearly audible above everything else. It is distinguished by a sharp rise in noise level. Typically, impulsive characteristics are obvious and discernible and many jurisdictions use simplified procedures to verify or assess the presence of impulsive noise. However, the latest version of British Standard BS 4142 (2014) does provide an objective method for measuring the prominence of impulsive sounds, which permits a graduated adjustment to the measured LAeq.

The root and rot of noise

Etymologists tell us that the word noise originated from the Latin nausea (sickness). While the linkage between noise, annoyance and sleep disturbance has been obvious, the scientific evidence for other health effects has been more elusive. However, annoyance can act as a trigger for more adverse responses and as previously mentioned, individual human sensitivity (and susceptibility) are pertinent factors. In recent decades, worldwide recognition of the significant burden of disease associated with environmental noise has developed.

It is now known that within exposed populations, stress reactions, sleep interference and other biological and biophysical effects occur as a result of environmental noise. Furthermore, chronic exposure affect ‘metabolism and the cardiovascular system, with increases in established cardiovascular disease risk factors such as blood pressure, blood lipid concentrations, blood viscosity, and blood glucose concentrations. These changes increase the risk of hypertension, arteriosclerosis, and are related to severe events, such as myocardial infarction and stroke’ (Lancet Review, 2014).

The environmental burden of disease has been addressed by recent publications and controversial findings were published by the WHO in 2012. The WHO study incorporated a review of the scientific evidence supporting exposure-response relationships and case studies in calculating the burden of disease were completed by a working group of international scientists. The study methodology, based on the exposure-response relationship, exposure distribution, background prevalence of disease and disability weights of the outcome, was applied to calculate the burden of disease in terms of disability adjusted life-years (DALYs). The WHO results indicate that “at least one million healthy life years are lost every year from traffic related noise in the western part of Europe alone.”

“programmes are emerging to reduce environmental noise exposure; however, noise pollution remains a major environmental health problem in Europe”

Policies and programmes are emerging to reduce environmental noise exposure; however, noise pollution remains a major environmental health problem in Europe, with the transport sector being a major cause. Based on 2017 data, approximately 100 million people are exposed to road traffic noise above 55 dB in the 33 member countries of the European Environment Agency (EEA). Of these, 32 million are exposed to very high noise levels (above 65 dB). Railway noise is the second largest source, with 19 million people exposed above 55 dB (EEA, 2017). These EEA data are expressed in terms of Lden (Dayevening- night level), which is a descriptor of noise levels based on energy equivalent noise level (Leq) over a whole day with a penalty of 10 dB(A) for night time noise (22.00-7.00) and an additional penalty of 5 dB(A) for evening noise (i.e. 19.00-23.00).

Summary

Given the varying response of humans to different sources and noise types, many different standards, guidelines and legislative codes have evolved. Therefore the way we assess road traffic noise differs from how we assess other types of industrial noise or wind-farm noise. In addition, the standards and methodology for assessing environmental noise are regularly updated and it is important that practitioners keep abreast of these developments.