About 23 million headset radios and tape players are sold in the United States every year, and a look at toy store racks confirms that there's a new target audience for them: the grade-school crowd.
Painted in bold primary colors or cute pinks and purples, the personal stereos range from sturdily built $50 models to bare-basics versions obtainable for less than $10. What they all have in common is the ability to create sound so loud it can cause an insidious, cumulative hearing loss.
Studies have shown sound levels from the machines can reach 115 decibels or more. At that level, permanent hearing damage could occur after just 15 minutes.
"I think that there are a lot of kids who get an awful lot of hearing damage because I'm sure that they never use the headset at 15 minutes a day, but a great deal more than that," said Dr. Jack Vernon, otolaryngology professor at Oregon Health Sciences University in Portland.
Noise-induced hearing loss is cumulative and is a function of sound intensity and duration. So listening to even moderately loud music for longer than 15 minutes or listening day after day can cause permanent damage.
And the earlier a child begins using a headset to listen to loud music, the more years over which damage can accumulate.
Consequently, parents need to be careful about supervising their children's use of these powerful little sound machines, hearing experts say.
But that is easier said than done because, unlike other situations where young people encounter loud music, headset use is less likely to provide clues that the sound is too loud.
For example, a teen-ager who has just attended a rock concert may experience muffled hearing or ringing in the ears, clear signals that the sound was too loud. Such symptoms--although they often disappear after a few days--mean some permanent hearing loss has occurred at high sound frequencies, many experts agree.
And a child who turns up the volume on his bedroom stereo too high will soon have angry parents at his door, which can guard against damage.
But a headphone-wearing child is difficult for a parent to monitor. As a rule of thumb, experts say, headset sound that is loud enough to be heard by passers-by can cause damage if used more than two hours a day. However, individuals can be more sensitive than that to damage.
Record producer Jeff Baxter is serving as a celebrity spokesman for the "Hearing Is Priceless" education campaign of the House Ear Institute of Los Angeles. When talking to teen-agers about saving their hearing, he uses analogies he thinks young people will understand.
"You like to swim . . . you like to be in the water, but you're not interested in drowning," he tells them. "So why would you fill your ears with debilitating sound when what you really want to do is feel the music with your body?"
Baxter was noted for blocking out the booming sound of on-stage amplifiers with an earmuff-style headset when he was a guitarist in the 1970s with the rock groups Steely Dan and the Doobie Brothers. He credits this with maintaining his hearing so that he is able to produce records today.
He says young people can enjoy the experience of being surrounded by sound at a very loud concert but still protect their hearing by wearing foam earplugs. These let sound pass through but cut down on the volume.
At clinics such as the one associated with the House Ear Institute, it is common to see young men in their 30s who have constant ringing in their ears, called tinnitus, or who are having trouble understanding speech because of hearing damage from rock concerts two decades earlier.
If a similar phenomenon occurs with headset use--which has enjoyed its boom only since the early '80s--hearing specialists don't expect it to emerge for another decade.
One of the early studies on headset effects was conducted in 1984 at the University of Iowa. Researchers asked 16 headset-stereo owners to listen to music for three hours at the loudness setting they normally used.
The study found that the nine volunteers who listened to music at an average of 90 decibels--equivalent to noise from a vacuum cleaner--showed little or no hearing loss.
But the seven subjects who listened at 94 to 104 decibels--roughly equivalent to the noise from a blender at the low end and a chain saw at the high end--temporarily lost an average of 10 decibels of hearing at high frequencies.
With a permanent hearing loss of this degree, conversational speech would have to be 10 decibels louder for the person to hear the difference between "feet" and "heat." That is because consonant sounds are of higher audio frequency than vowels, and high-frequency hearing is the first to be damaged by noise. (A voice in normal conversation is about 60 decibels.)
Further, the study found that the person who listened to 104-decibel music lost 25 decibels of hearing in one ear and 35 decibels in the other.