Potential health risks of exposure to noise from personal music ...

Health risks from exposure to noise from personal music players3.5.8. ConclusionsExposure to excessive noise is one major cause of hearing disorders worldwide. Somedata suggest an increased risk due to increase in use of audio leisure activities. Thereseems to be a trend for increased risk due to PMPs, as their qualities improved and theyhave become used by a largely increasing proportion of the population. The noiseinducedhearing impairments have received much attention in the past decades mostlybecause of hazards of industrial noise exposures. Based upon many scientific studies theInternational Standard Organization has published recommendations for health safety. Amost used ISO reference for risk assessment is that an exposure to a sound level of 85dB (A) for 8 hours a day, 5 days per week will induce in 5% of the exposed population ahearing loss of about 4 dB after 3 years and 9 dB after 45 years. These losses beingconsidered as quasi negligible this sound level-duration was considered as a safe limitabove which preventive actions should be taken. The ISO recommendations also expressthat, as shown by many studies, the noise-induced hearing loss is the product of soundlevel by duration of exposure, and follows the equal energy principle stating that adecrease of sound level if associated with a proportional increase in duration (forexample a halving in sound level associated with a doubling of exposure duration) inducesimilar risks. All data indicate a large inter-individual variability in vulnerability toexcessive sound exposures, some subjects being affected while others are not; up to nowthe factors underlying this variability are very poorly known.In the last decade many new and promising data were obtained concerning the biology ofpathological processes responsible for hearing impairments due to excessive soundexposures. Excessive noise can induce damage to most cell types in the inner ear, butpresently the sequence of these pathological events and their cause/effect relationshipsremain poorly known. Several environmental factors can have detrimental effects, suchas exposure to several chemicals and lowered levels of breathed oxygen which werefound to increase NIHL. The study on involvement of genetic factors has only recentlystarted and first evidences point to some possible genes and seem to exclude others.Following the development of molecular biology many new drugs were found to haveprotective effects against NIHL in fundamental experiments, these constitute new andvery promising perspectives to prevent and cure NIHL in the future in humans. Althoughsome few studies have started to assess some new drug treatments in humans muchfurther research is needed over coming years before definite clinical applications can beconsidered.3.6. Technical aspects of personal music players3.6.1. General characteristicsPersonal music players have a very wide field of application ranging from professionaltools at the workplace to the leisurely consumer and to children who use these devices astoys. They are portable digital music players that play music as audio files, such as MP3.In addition, most of these devices allow to store video, pictures, and to receive radio andTV programs (podcasting). Earphones and external speakers are the typical outputdevices delivering sound to the listener. Personal music players (PMPs) are widely used inconjunction with several headphones of different styles (insert, supra-aural, vertical, andcircumaural).To identify the risk levels of PMPs one has to realize that the chain of music reproductionis organised in stages which are more or less independent of each other but togetheraffect the output signal level. Personal music players reproduce music from a recording.The sound of a signal has usually been recorded through a microphone and theoscillations resulting from the pressure changes are stored as a sampled wave form.Different procedures and algorithms are used for storing of analogue or digital40