A question I frequently hear from parents and grandparents is what MP3 player should I get my kids. Most people in the baby boomer generation are aware that too much music is not a good idea- they have been inundated with media reports since the early 1980s. Yet, there are advantages to having portable music, especially on long car trips. The earphones can couple to a car DVD player just as easily as anything else, so how do we keep the kids entertained on long trips while maintaining some sort of quiet in the car?
A quick review of what we know:
1. Earphones themselves are not a problem. We will always adjust to a comfortable listening level and the ear doesn’t know whether the sound is coming from 20 feet away or 20 mm away. It is just set to a comfort level.
2. The problem with MP3 players is that they are portable, allowing us to bring them into noisy areas where the volume is turned up over the background noise. (This is known as the cocktail party or Lombard effect).
3. The same MP3 player, same music being played, and same volume setting may have outputs that extend over a 20-dB range, and it all depends on the earphone that is being used. So, specifying the maximum volume setting is a good idea, but only a good first step. The end point (the part in the person’s ear) is the earphone.
So, why don’t we just make an earphone for our MP3 players that clips or limits all sounds over a certain level (e.g., 95 dB)? Well, we have these but they sound awful. Like all peak clippers there is a series of odd-numbered distortion products that are created. For those who like science, peak clippers turn an otherwise sinusoidal waveform into a square wave (i.e., the top has been clipped off). And the spectrum of a square wave is a series of every decreasing odd-numbered multiple distortion products of the offending clipped signal.
Actually this is easy to do. Obtain any of these “safe for kids” earphones and couple them to your hearing aid test box and an HA1 coupler. Put in an intense 1000-Hz signal and not only do you get the 1000-Hz signal out, but also 3000 Hz, 5000 Hz, 7000 Hz, and so on…. odd-numbered harmonics that are characteristic of a peak-clipped signal.
This is a very safe earphone for anyone, because you can limit the output, but more importantly it will completely stop any music-induced hearing loss. The reason?. The kid will throw the earphones in the garbage can. This peak clipping, although probably well-intentioned, causes the sound to be rough and anything but musical.
Another approach that has recently been introduced, an example of which is ETY Kids from www.etymotic.com (no, I am not a shareholder), uses an earphone that has reduced sensitivity. The output will never exceed a predetermined level, but at the same time the output is crystal clear with none of the problems of peak clipping.
I am not in the habit of naming products for the sake of naming products, but this reduced sensitivity earphone should be standard with all gifts of MP3 players or car DVD players.
So, my suggestion to parents who want to buy an MP3 player for their kids is to also get a pair of reduced-sensitivity earphones that the kids will actually wear.
