source: bhNEWS
TIME - July 28, 2008
Pictures, audio: http://tinyurl.com/57vjm6
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How Bad Are iPods for Your Hearing?
By Laura Blue
Hearing loss is more common than ever before. About 16% of American
adults have an impaired ability to hear speech, and more than 30% of
Americans over age 20 =97 an estimated 55 million people =97 have lost
some high-
frequency hearing, according to a new study published Monday in the
Archives of
Internal Medicine. The finding has got experts =97 and concerned
parents =97wondering anew: Does listening to loud music through
headphones lead
to long-term hearing loss? Brian Fligor, director of diagnostic
audiology at Children's Hospital Boston, explains how much damage your
headphone
habit might cause =97 and how to mitigate your risk.
Q: How much hearing loss does an iPod cause?
A: It depends on the person, it depends on how long you're listening,
and it depends on the level at which you're setting your iPod.
If you're using the earbuds that come with an iPod and you turn the
volume up to about 90% of maximum and you listen a total of two hours
a day,
five days a week, our best estimates are that the people who have
more
sensitive ears will develop a rather significant degree of hearing
loss =97 on
the order of 40 decibels (dB). That means the quietest sounds audible
are 40 dB
loud. Now, this is high-pitched hearing loss, so a person can still
hear
sounds and understand most speech. The impact is going to be most
clearly
noted when the background-noise level goes up, when you have to focus
on
what someone is saying. Then it can really start to impair your
ability to
communicate.
This would happen only after about 10 years or so or even more of
listening to a personal audio device. One patient I had used his
headphones
instead of earplugs when he was on his construction job. He thought as
long as
he could hear his music over the sound of his saws, he was protecting
his
ears =97because he liked the sound of his music but didn't like the
sound of
the construction noise. He had a good 50 dB to 55 dB of noise-induced
hearing loss at 28 years old. We asked a few pointed questions about
when he
was having difficulty understanding people, and his response was
classic. "When I'm sitting at home with the TV off, I can understand
just fine," he
said, "but when I go out for dinner, I have trouble."
There is huge variation in how people are affected by loud sound,
however, and this is an area where a number of researchers are
conducting
studies. Certainly a huge part of this is underlying genetics. We know
how
much sound causes how much hearing loss based on studies that were
conducted in
the late '60s and early '70s, before employers were required to
protect
workers' hearing in noisy work environments. What was found is that
when
people are exposed to a certain level of noise every day for a certain
duration,
they're going to have a certain degree of hearing loss on average.
But the amount of hearing loss might differ by as much as 30 dB
between
people who had the toughest ears and those with the most tender ones =97
a huge
variation. Unfortunately, we don't know who has the tougher ears and
who has the tender ones until after they've lost their hearing. So, as
a
clinician, I have to treat everyone as if they had tender ears.
Particularly with noise-induced hearing loss, the primary area where
the ear is damaged is not the eardrum, not the part of the ear that
you can
see and not the bones that are inside the middle ear =97 it is actually
deeper
inside. It's where the nerve that brings the sound message up to the
brain
connects with the inner ear, and it involves some very specialized
cells.
These are hair cells, and specifically we're looking at the outer hair
cells.
When they're overexposed or stimulated at too high a level for too
long a
duration, they end up being metabolically exhausted. They are
overworked. They tem****arily lose their function, so sound has to be
made louder
in order for you to hear it. These cells can recover after a single
exposure, but if you overexpose them often enough, they end up dying,
and you
lose that functional ability inside your inner ear. The cells that die
are
not replaceable.
As far as a rule of thumb goes, the figures we got in our studies
were that people using that standard earbud could listen at about 80%
of maximum
volume for 90 minutes per day or less without increasing their risk
for noise-induced hearing loss. But the louder the volume, the
shorter
your duration should be. At maximum volume, you should listen for
only
about 5 minutes a day.
I don't want to single out iPods. Any personal listening device out
there has the potential to be used in a way that will cause hearing
loss.
We've conducted studies of a few MP3 players and found very similar
results
across the MP3 manufacturers. Some in-the-ear earphones are capable
of
providing higher sound levels than some over-the-ear earphones. That
said,
studies we've done on behavior show that the type of earphones has
almost
nothing to do with the level at which people set their headphones.
It's all
dictated by the level of background noise in their listening
environment. When we
put people in different listening environments, like flying in an
airplane =97 we used noise we'd recorded while flying on a Boeing 757
commercial
flight, and we simulated that environment in our lab =97 80% of people
listened at
levels that would eventually put their hearing at risk. On the subway
system
here in Boston, the ambient noise levels are very comparable to the
level
on an airplane, although it sounds very different. The noise is
sufficiently high that it induces people to listen to their headphones
at excessively
loud volume.
I'm a self-professed loud-music listener. I use my iPod at the gym,
and I love it. I think it's one of the greatest inventions ever. I
even
advocate that people listen to music as loud as they want. But in
order to
listen as loud as you want, you need to be careful about how long
you're
listening. I would also strongly recommend that people invest in
better earphones
that block out background noise. Some of the research we did studied
earphones that completely seal up the ear canal. These are passive
sound-
isolating earphones, as opposed to the ones that are active noise
cancelers
that block out some of the noise. As far as I can tell, both would
allow people
to listen to their headphones at their chosen level =97 and more likely
at
a lower volume than if they were using the stock earbuds.
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