The latest issue of the Journal of the Acoustical Society of America (colloquially and affectionately referred to by its acronym, as JASA) had an article called “MP3 Player Listening Sound Pressure Levels Among 10 to 17 Year Old Students” (November, 2011). This was written by Dr. Stephen Keith and his colleagues in Canada’s national capital… for those who don’t know Canada, its Ottawa- a place where it snows 11 months of the year.
Many factors can affect the sound level that reaches the ear such as the output voltage of the MP3 player, earphone, and the recorded level of the music. Depending on these factors, the level can reach 125 dBA. More typically the sound level is far less, and this is the subject of this article.
Couple this with the fact that it’s not just the sound level generated but also the duration of exposure. And then add the fact that we don’t really know what we are talking about when it comes to a signal like music where there are intense and even silent portions in the same musical bar. Many of the noise models are well,… based on noise, and not music.
And let’s not forget the issue of how well the earphone fits into the person’s ear. This is a highly variable variable. A well-fit earphone seals the low frequency sound into a person’s ear canal but even a small slit leak (especially if a person’s mouth is continually opening and closing) will reduce the level of sound that a person is actually exposed to.
So, the level that reaches the ear of a listener depends on a myriad of factors including how long a person listens to the music, and on the type of music which can have periods of quiet.
It turns out that depending on the person, and all of the stuff above, as little as 3.2% of teenagers are at risk to an MP3 player induced hearing loss, and as much as 22% may be at risk in a worst case situation. Quite a range, but then again there are many factors and we don’t really know the contribution of each one as well as perhaps we could.
It’s actually a well written and very thorough article. If you are planning to read only one JASA article this year, this is probably it. It covers almost every aspect and every variable that needs to be examined in the study of the effects of music induced hearing loss.
Even though the contribution of music exposure to one’s maximum noise or music dose may be as little as 3.2% we all live in noisy environments. Add this 3.2% to mowing the lawn (not that any teenagers actually mow the lawn anymore), to the sound emanating from a video game though high tech 5.1 surround speakers, driving on the highway with the windows open, and even the occasional motorcycle ride, then this 3.2% may be a significant factor.
Looking at it backwards, it’s only 3.2%, so if your favorite song comes on, go ahead and turn up the volume; just turn it down to a more reasonable level after, and if you are a teenager reading this, make sure that you get someone else to mow the lawn for you.