7. What are the characteristics of personal music players
For a given volume setting, ear-buds tend to lead to a greater sound exposure
Personal music players are portable devices that play audio files, such as MP3 files, using earphones or speakers. In addition, many of these devices can store videos and pictures, and podcast radio and TV programmes. Personal music players are used widely for leisure activities or work purposes, and some children use them as toys.
To identify the risk of exposure to sound from personal music players, it is useful to understand how music is recorded and reproduced as this influences the level and quality of sound output delivered by the personal music player.
- First, sounds are recorded through a microphone that perceives the pressure changes. The recorded information can be stored in different formats (digital or analogue) and compression levels using a variety of procedures.
- Then, when playing the audio file, the player reproduces the recorded sound signal. Manufacturers usually specify the electronic characteristics of the personal music players that determine for instance the maximum sound output level.
- Finally, to produce sound the personal music players are connected to loudspeakers, either headphones or external speakers of many different types. Some headphones have large pads that cover the ears and others sit directly above the ear. Earphones or ear-buds are smaller in size and are placed inside the ear, just outside or in the ear canal.
These headphones transform the electronic output of the player into sound energy. In that perspective, two aspects may influence the sound output: the way the headphones are plugged into the player and the characteristics of the headphones.
The volume of the sound emitted by personal music players varies from manufacturer to manufacturer, and is difficult to estimate. The amount of sound energy that reaches the eardrum also depends on the type of music, on the type of headphone used, and in the case of ear-buds on how deeply they are inserted in the ear canal. In general, the smaller the headphone, the greater the amount of sound energy transmitted for a given volume setting. A study showed that for a given volume setting of the player, ear-bud type headphones produce a sound output that is 7-9 dB(A) higher than that of standard headphones.
So, sound levels from personal music players depend on a series of factors. With the digital formats of sound recording and reproduction currently available, such as MP3, it is possible to reach high levels of sound output without distortion. At the maximum volume setting, sound pressure levels reaching the eardrum can range from 91 to about 121 dB(A) for different player-headphone combinations. More...