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Personal Music Players & Hearing

1. Why do personal music players raise health concerns?

  • 1.1 When are we exposed to noise and sound?
  • 1.2 What are noise and sound?

1.1 When are we exposed to noise and sound?

The SCENIHR opinion states:

3. SCIENTIFIC RATIONALE

3.1. Introduction

In a recent report WHO states (WHO 2002, Nelson 2005) “Worldwide, 16% of the disabling hearing loss in adults is attributed to occupational noise, ranging from 7% to 21% in the various subregions”. For almost two decades, the level of 85 dB(A) was regarded as the critical intensity for the workplace; at exposures below 85 dB(A) the probability of hearing losses occurring with long-term exposure was then considered sufficiently limited (Welleschik 1979). Therefore, international standards recommended the equivalent sound pressure level (Lequ, 8h) of 85 dB(A) (A filter-weighted, 8-hour working day-weighted average) as the exposure limit for occupational noise (ISO 1999:1990; NIOSH revised criteria 1974). However, more recent studies showed that this standard did not guarantee the safety for the human auditory system. Therefore, the new EC Directive Noise at Work Regulations on the minimum health and safety requirements regarding exposure of workers to the risks arising from physical agents (noise) introduces lower exposure action value at Lequ, 8h = 80 dB(A) (Directive 2003/10/EC).

Although early reviews (eg MRC 1986) concluded that leisure noise was unlikely to be a significant threat to hearing compared to occupational noise, they noted a need for more good data and research. Since then there have been huge changes in patterns of noise exposure. Smith et al. (2000) found that the numbers of young people with social noise exposure had tripled (to around 19%) since the early 1980s, whilst occupational noise had decreased.

There is a number of studies which documented that noise from environmental sources like traffic, aircraft, construction or neighbourhood, although sometimes very annoying, do not reach the equivalent levels that can be harmful to hearing. On the other hand, they can cause non-auditory effects. In the last years a pattern of environmental noise exposures has changed substantially; the leisure noise sources became of a main public concern as it was found that they can generate sounds across a broad frequency range and from high to low sound pressure levels. The equivalent sound levels in discos may range between 104.3 and 112.4 dB(A), and between 75 and 105 dB(A) from personal music players (Serra et al. 2005). The noise dose measures over 4 hours showed an Laeq of 104.3 dB. The nightclubs' average sound level ranged between 93.2 to 109.7 dB(A). Therefore it may be concluded that sounds such as music can, at high acoustic levels, be as dangerous for hearing as industrial noise.

In the last decade, PMPs with improved qualities and suitable for playback at high sound levels became available and have been used by an increasing proportion of the population. Data shows that for the MP3 players and equivalent devices the unit sales in Europe, between 2004-2007, were estimated as about 124 million but could be as large as 165 million and for all portable audio could be in the range 184-246 million. On top of this there were about 161 million handset mobile phones sold in EU countries in 2007 only. It is estimated that today about 10-20% of these phones include a MP3 playback function. This results in an estimated additional number of 16 to 32 million PMP devices. It is expected that the fraction of mobile phones containing the PMP function will rapidly increase such that up to 75% of all phones sold by 2011 may provide this function. Notably, data are not very precise at present and it is not clear whether people who have access to PMP function actually use them on a regular basis.

The personal music players (PMPs) which now play not only music, but provide podcasts of various broadcasts or lecture material, which is delivered largely through ear-bud type insert ear phones producing a range of maximum levels around 88-113 dB(A) across different devices. In the worst case scenario, it is possible to obtain level of about 120 dB(A).

Taking into consideration the above mentioned data, the Commission requested the Scientific Committee on Emerging and Newly Identified Health Risks to assess whether the health of citizens is appropriately protected by current requirements of Community directives and European standards by formulating terms of reference.

3.2. Methodology

The Working Group has considered evidence derived from a wide variety of sources, including peer-reviewed scientific literature and published reports of institutional, professional, governmental and non-governmental organisations. In common with the usual practice of SCENIHR Working Groups, no reliance has been made on unpublished work or publicly available opinions that are not science based.

During the course of the deliberations of the Working Group, a Call for Information was issued by the Commission and the replies have all been considered.

As a general rule, scientific reports that are published in English language peer-reviewed scientific journals are considered primarily. This does not imply that all published articles are considered to be equally valid and relevant for health risk assessment. On the contrary, a main task is to evaluate and assess the articles and the scientific weight that is to be given to each of them. Only studies that are considered relevant for the task are commented upon in the opinion. Many more reports were considered than are cited in the reference list. However, only articles that contribute significantly to the update of the opinion are explicitly discussed, commented and cited. In some areas where the literature is particularly scarce, namely on market trends in sales of PMPs and mobile phones with MP3 function, data obtained from professional databases were obtained and analyzed for relevance and importance by experts.

Relevant research on the assessment of health risks related to listening to PMPs’ can be divided into broad sectors such as epidemiologic studies and experimental studies in humans. Other studies, used frequently in other risk assessment procedures, such as experimental studies in animals and cell culture studies were considered occasionally, only when necessary to understand the mechanisms of potential noise induced hearing loss.

A health risk assessment evaluates the evidence within each of these sectors and then weighs together the evidence across the sectors to a combined assessment. This combined assessment should address the question of whether or not a hazard exists i.e., if there exists a causal relationship between exposure and some adverse health effect. The answer to this question is not necessarily a definitive yes or no, but may express the weight of the evidence for the existence of a hazard. If such a hazard is judged to be present, the risk assessment also estimates the magnitude of the effect and the shape of the dose-response function, used for characterizing the magnitude of the risk for various exposure levels and exposure patterns. A full risk assessment also includes exposure assessment in the population and estimates of the impact of exposure on burden of disease. Epidemiological and experimental studies are subject to similar treatment in the evaluation process. It is of equal importance to evaluate positive and negative studies, i.e., studies indicating that the exposure to noise from devices like PMPs’ and mobile phones with this function have an effect and studies not indicating the existence of such an effect. In the case of positive studies the evaluation focuses on alternatives to causation as explanation of the positive result: with what is the degree of certainty for ruling out the possibility that the observed positive result is produced by bias, e.g. confounding or selection bias, or chance. In the case of negative studies one assesses the certainty with which it can be ruled out that the lack of an observed effect is the result of (masking) bias, e.g. because of too small exposure contrasts or too crude exposure measurements; one also has to evaluate the possibility that the lack of an observed effect is the result of chance, a possibility that is a particular problem in small studies with low statistical power.

Obviously, statistical significance is only one factor in this evaluation. Other characteristics of the study are also taken into account, such as the size of the database, the assessment of the participation rate, the level of exposure, and the quality of exposure assessment. The observed strength of association and the internal consistency of the results, including aspects such as dose-response relation are particularly important. Regarding experimental studies, additional important characteristics are the types of controls that have been used and the extent to which replication studies have been performed. It is worth noting that this process does not assess whether a specific study is unequivocally negative or positive or whether it is accepted or rejected. Rather, the assessment will result in a weight that is given to the findings of a study. In the final overall evaluation phase, the available evidence is integrated over various sectors of research.

Source & ©: SCENIHR,  Potential health risks of exposure to noise from personal music players and mobile phones including a music playing function (2008), Sections 3.1.Introduction & 3.2 Methodology

Note: The European Directive 2003/10/EC on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise) is available at:
 http://eur-lex.europa.eu/en/

The criteria issued by the U.S. National Institute for Occupational Safety and Health (NIOSH) are available at: www.cdc.gov/niosh/topics/noise/ 

1.2 What are noise and sound?

The SCENIHR opinion states:

3.3. Sound: Definitions and measurements

3.3.1.Definitions

In view of the clarity required for this document and as an aid to communications between disciplines and across national borders it is important to agree on definitions for scientific and technical purposes. It is also noted that the use of some words like e.g. ‘noise’ is not consistent between disciplines and therefore needs a definition.

Note that in the language of the electronic devices, noise is used for that part of the signal of statistical nature which is not carrying the intended information, as it is reflected for example in signal to noise ratios. Next to statistical noise there is non-statistical ‘hum’ on many signals to be tabulated. The signal on one line may actually contribute to the hum or noise on the other line specifying the ‘cross talk’.

In the world of sound, however, noise has also a slightly different meaning in that it is any sound which is not desired by a certain observer. Therefore, in the context of the current mandate, the use of the word noise has to be carefully explained: While, on the basis of the above definitions, the use of the word ‘noise’ is reserved for those cases where the potentially affected person is not intentionally listening, this is not conclusive for the users of personal music players and the like. Because the sound pressure levels of earphone devices to an outside observer remain far below the limits of physiological effects, it is the sound of personal music players which is of concern to this mandate. This outside observer may nevertheless be distracted and annoyed and may rightfully, in the lexicographic meaning of the word call noise what is sound in his neighbours ears.

For the historic importance of noise protection in work environments like factories or the transportation industry the word ‘noise protection’ and ‘noise-induced hearing loss and impairment’ have been coined while a number of such terms e.g. in the context of professional musicians and their job do not really qualify the use of the word ‘noise’. Therefore, and for the scope of comparability between the scientific literature in both cases, that of noise exposure and of sound exposure (which leads to very similar physiological effects at comparable levels) it has been decided for the purpose of this mandate to keep up with the established wording and to use the word ‘noise’ irrespective of whether the ‘noise’ exposure is wanted (e.g. when playing a personal music player) or not (e.g. in the typical workplace setting). Thus, ‘noise’ is used consistently in the context of all disease and malfunction patterns, while the word ‘sound’ is used consequently throughout this opinion to clarify that the concern is the voluntary listener of personal music players and not the observer of the listening situation.

3.3.2.Sound: Physical and technical background

Sound or Sound waves comprise a wave phenomenon. Sound waves are ‘longitudinal’ waves because sound waves consist of areas of higher and lower local pressure. The propagation of sound waves occurs in all media, i.e. in gases, liquids and solids as well as in more complex fluids like e.g. organisms and tissues.

Fundamentally, sound waves are characterized by their spectrum. A spectrum is the summation of individual frequencies (f) and amplitudes a certain signal has in the surrounding medium. In daily acoustic settings sound is a complex summation of many different sounds from different sources. Sound will not propagate through vacuum and its propagation is influenced by material properties like density and compression / shear strengths. Characteristic parameters of sound waves in a given situation derive from the fundamental wave equation which may be to challenging to evaluate for a given complex scenario.

The exposure to sound in a typical setting is determined by many factors which are not always easy to assess. For sound propagation, the geometry of the room, the surface materials and furnishings as well as its occupation, the materials and media surrounding the source and the listener play a determining role. Like for any other wave, the sound wave at a specific location depends on interference from different sources which depends on the relative phase reaching the location from different sources or after travelling different pathways. Thus, the distribution of energy and the energy absorption in sound exposure scenarios is not necessarily straightforward which leads to the many flavours of acoustics as subfields of physics and engineering, medicine and architecture. Well-known examples are the different acoustical characteristics of a furnished and unfurnished room, the sound-design of commercial products like cars and the engineering of anti-sound-reflection surfaces to be used in the prevention of sound propagation next to highways, railway lines, but also within sound-studios and in other architectural settings. Notably also details of the anatomy of the ear, the hair dress and clothing specific to one listener may affect the sound distribution before the sound reaches the sound sensitive cells in the inner ear of a specific observer.

To assess the exposure from different sources in a specific point, it is common use to analyse the different contributions by their frequency and to provide certain measurements related to sound (like power, amplitude etc) by their densities in the frequency spectrum. Depending on whether sound waves are harmonic (‘tones’, ‘hum’) or relate to uncorrelated events. Sound with an equal energy distribution across frequencies is called ‘white noise’, while most sources of sound exhibit dominating frequency bands originating from resonance phenomena. Typically, the above described complex interaction of sound waves with the particular environment and media (absorption, refraction, reflection and interference) leads to a changing spectrum of sound waves with progressing propagation or the modified position of an observer.

Source & ©: SCENIHR,  Potential health risks of exposure to noise from personal music players and mobile phones including a music playing function (2008), Sections 3.3.1 Definitions & 3.3.2 Sound: Physical and technical background


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