When you reach a certain age, your hearing often starts to go. Unfortunately, that age is becoming younger and younger.
Blame it on the music.
For my generation, the downhill slide began with the first wave of high-octane, 1960s rock concerts - gatherings that brought thousands together for hours to hear music at volumes that rivaled a 747 pulling away from an airport gate.
For boomers' children, there were plenty of noisy concerts, plus the Walkman, then the Discman and now the iPod and its cousins - portable music players that make it easy to spend too much time assaulting the ears with noise so loud that it can and does cause permanent damage.
This is known as Noise Induced Hearing Loss. It happens when continuous exposure to loud noise damages the tiny hair cells inside the ear that trigger sound signals to the brain. Eventually they die, and with them, a part of our ability to hear dies, too.
The process is stealthy, cumulative and irreversible. It might not make itself known for a decade or more. But it's definitely not your grandpa's problem.
The American Speech-Language-Hearing Association (ASHA) estimates that nearly 10 million Americans - including 13 percent of schoolchildren - suffer from some degree of NIHL.
The Canadian Hearing Society found that a quarter of those who suffer hearing loss are younger than 40, while 70 percent are under 60.
I ran into these startling numbers when I got an offer to try out a pair of Guardian HA-31 wired headphones from Hamilton Electronics, a New Jersey company that specializes in audiovisual products for schools and professionals.
These $40, earmuff-style headphones are designed for the children of adults who are willing to look in on the kids while they're listening to music on their iPods, computers or stereo systems.
The right earpiece of the Guardian headset has small red and green lights on the side. When the volume of whatever's playing is within safe levels, the green light glows. When the sound gets too loud (90 decibels), the red light starts to glow.
"If someone's always listening in the red zone, it might be a good idea for the parent to talk to the child and see if he needs his hearing tested," said Sheldon Goldstein, Hamilton president - and a boomer who recently discovered that his hearing had been damaged by loud rock concerts in the 1960s and 1970s.
The headphones run for 125 hours on internal rechargeable batteries, which make them a bit heavier than normal headphones. They produced a sound that was warm and pleasant, if a bit heavy in the bass and weak in the treble ranges. The quality was about what you'd expect for a headset in this range.
You might wonder why the makers of music players don't limit the sound output of their gadgets to nondangerous levels.
"When these were originally designed, I don't think too many people were even thinking about noise level or possible hearing damage," Goldstein said.
It is also possible to find true volume-limiting headphones, such as such as iHearSafe earbuds, which max out at 80 decibels ($20 at ingemicorp.com), but the gadgets that generate the noise certainly don't make safe listening a priority.
The Apple iPod, whose incarnations account for more than 70 percent of the market for portable digital music players (more than 100 million sold), does have a setting that can limit noise to a particular output level, but it can be changed via normal settings. And Apple's Web site is curiously vague about figuring out just how loud is too loud.
Unfortunately, there hasn't been a lot of hard research on this problem, because it's relatively new. But here's what I've been able to learn.
First, there's general agreement that prolonged exposure to sound levels of 85 decibels or more can be damaging over the long term.
Second, digital players that now store hundreds of hours of music and play 10 to 20 hours on a charge encourage users to listen longer than they did a decade ago with players that held a single CD (74 minutes) or tape (90 minutes).
A 2006 study of five digital music players by researchers at Children's Hospital Boston and the University of Colorado found that they were all remarkably similar in sound output at comparable volume levels - maxing out at 100 decibels or more. A hundred decibels is the noise you'll perceive standing next to a lawnmower, a pneumatic chipper or passing subway train.
At their highest volume settings, the study concluded, the maximum recommended exposure under government standards is only five minutes a day with earbuds - which pump more sound directly into the ear - and 18 minutes a day with earmuff-style phones.
Another study, this one involving 100 doctoral students at Harvard, found that most listened to music at the same volume level when there was little outside noise. But many cranked up the volume to dangerous levels when ambient noise increased. This was particularly true of males and earbud users.
Yet another study, by Australia's Hearing Cooperative Research Centre, showed that a third of teens routinely listen to music at 85 decibels or more.
The bottom line: Even though they're bulkier and not as cool looking as earbuds, earmuff-style phones like the Guardian model I tried block more outside noise, so listeners aren't as likely to crank up the volume to harmful levels. Custom in-ear models designed to reduce outside noise also may help.
An even better bet, according to some experts, is a noise-canceling earmuff headphone, which reduces low-frequency rumble with electronic "counter-noise." I've tried these with an iPod and books-on-CD in planes and in the car, and I've been amazed at how much lower I can set the volume on the player. The downside - noise canceling headphones start at $50 and quickly head to the stratosphere.
Meanwhile, experts offer a few simple rules for protecting your kids' hearing and your own. Dean Garstecki, a Northwestern University audiologist, pushes the 60/60 rule: Limit your earbud listening to 60 minutes a day at 60 percent volume. That's likely to be a bit draconian for most young people (and even adults).
The American Speech-Language-Hearing Association's rule is that if you can hear music coming from a listener's earphones from 3 feet away, the volume is too high. Likewise if the volume is so loud that the listener is oblivious to normal conversation around him.
I recommend the ASHA's safe-listening education site, which includes cartoons and games for the kids as well as information for parents and teachers. Surf to www.listentoyourbuds.org
You can find out more about the Guardian headphones at www.hamiltonelectronics.com, or you can order them from www.projectorscreenstore.com.
For a plain-English version of the Children's Hospital/University of Colorado music player study - including a table of recommended maximum exposure times with different types of headphones at various volume levels - visit www.hearing conservation.org/docs/virtual- PressRoom/portnuff.htm.