Environmental Talk At UGPulse: Turn Down That Noise
How fast are you losing your sense of hearing?
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First published: October 5, 2006
If you don't listen to this advice now, you may not be able to hear it later.
Several years ago in a flat in a Kampala suburb my father knocked hard on my room's door. I opened and as usual he was shouting, "Turn down that music or we will all lose our hearing". I had to do something about this. I loved rock 'n' roll and Rick Dees and his American Top 40 was my favourite personal treat on Sundays. As far as I knew and believed, rock was never played with the volume down. My satisfaction only came when the stereo was playing loudest. So I saved and bought a pair of headphones akin to those used by discotheque D.J.s. And it was rock and roll as loud as I wanted direct into my ears. Now I could listen to my player in peace, day and night.
My father knew better. "Those headphones will harm you even more," said he. I was just a teenager and rebellious like most others of my age. Since my infancy my hearing had been quite poor. I wasn't good at picking whispers and the whole family was cross that I hadn't realized how delicate my hearing is.
Some years down the road, I regret my "rebellion". My hearing has never been worse than it is now. The music did really do harm. Sometimes these days I even fail to register greetings directed towards me. It is now that my father's argument is making sense. I learnt that sensory cells in my inner ear designed to convert sound waves into nerve signals had been damaged or even destroyed.
A healthy human ear responds to a wide range of frequencies, from the rumble of thunder at 20 hertz (cycles per second) to overtones of a piccolo at nearly 20000Hz roughly the pitch of a piano's highest notes. Sounds like 't', 'th' and 'sh' become hard to distinguish. Children's and women's voices may become difficult to understand, especially against background noise. People often say they can hear well enough, they just can't understand what others are saying.
Another common symptom of hearing loss, I learned, was the ringing in one's ears, which audiologists call tinnitus. Researchers don't know why, but damaged ears often relay faulty messages to the brain, percieved as ringing, buzzing or whistling. Specialists say it is usually temporary. Given a rest, ears can recover. But if you go on exposing yourself to loud, the ringing becomes permanent. You cannot recover the hearing you've lost either. Once sensory cells are gone, they are gone.
Some loss of hearing is normal with age at least among people in industrialised areas. In the 1950's, audiologist Samuel Rosen tested an African tribe tucked away in quiet isolation on the Sudanese-Ethiopian border. Men well into their seventies, he found, could routinely hear faint murmurs across a distance more than the length of a football field. Few of us in this modern life will be so lucky by the age we are 55.
An audiologist tested the hearing of freshers at one American university. At 18, they should have had consistently sharp ears. But nearly a third showed signs of hearing loss. Most audiologists suspected pop music was to blame. Live concerts commonly reach sound levels above 120 decibels louder than a pneumatic drill. Then another New York professor of audiology grabbed a meter and set off into the streets. Stopping anyone carrying a Walkman-style stereo tape player, he measured sounds of 115dB and higher pouring out of tiny ear-pieces directly into vulnerable ears.
A hundred and ten decibels have ten times the intensity of a hundred decibels and 120 dB is a hundred times more intense. That is enough to do permanent damage. Customised car stereos can have sound levels reaching 130 dB or more roughly as loud as a jet at take off.
The sound energy reaching our ears when a pin drops may equal no more than quadrillionth of a watt of power enough to move the eardrums less than the diameter of a hydrogen molecule. Yet if our ears are sharp we hear it, can identify it and its precise location.
By the time the sound has passed through the tiny trio of bones in the middle ear, it has been intensified 30 times. Then in the inner ear's fluid filled spiral chamber, the cochlea, sound waves surge across a springy membrane, like ripples across a pond. The membrane is lined with rows of sensory cells, called hair cells, that respond to different wave frequencies. The outer row of hair cells is specially vulnerable. Exposing them to excessive sound energy is like exposing young trees to a gale force wind. The energy shakes them apart. Eventually the cells die and the result is gradual irreversible hearing loss.
What is the best way to ensure that you don't suffer from hearing loss? Avoid loud noises it is that simple. If you have to shout to converse over background noise, it is too loud. The volume is probably high if someone sitting next to you can hear the music coming from your stereo headset. I bought a mobile handset that has a noise meter. If a concert gets too loud, either I change my position relative to the speakers or quit.
Noise becomes more damaging the longer it lasts. A food processor spins out about 90 dB nothing to worry about for about a minute or two. But experts say exposure to 90 dB eight hours a day five days a week will eventually cause permanent damage. And each time you add three decibels, the time it takes to cause lasting injury drops by half. At frequent exposure to 120 dB discotheque levels, damage can start in less than a minute.
The ear can protect itself against some loud sounds by tightening a membrane in the inner ear, thereby dampening sound. But bursts of noise, like a firework, can take the ear by surprise, causing damage. Unfortunately avoiding noise is not always easy. The sound of a cheering football crowd can reach 120 dB.
When you can't get away from noise, ear muffs or earplugs are your best bet. Earmuffs, which cover the ears completely, offer full protection. But let us face it, they don't go with many outfits. Earplugs are almost as effective as earmuffs in blocking sound. Although they are difficult to use correctly, they fit conveniently in a pocket or handbag.
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First published: October 5, 2006