More than 120 million people in the world have a disabling hearing impairment –World Health Organization. Our ability to hear is a gift to be treasured. As we age, though, our hearing progressively diminishes.
Modern society, with the many and varied sounds and noises it generates, seems to have accelerated this process. A senior scientist at the Central Institute for the Deaf, in st. Louis, Missouri, U.S.A., noted: “About 75 percent of hearing loss in the typical American is caused not by the aging process alone but by what you’ve done to your ears throughout your lifetime.”
Intense, brief exposure to loud sounds can be harmful to the sensitive structures in the inner ear. More often, though, hearing loss is a result of “the cumulative effect of noisy jobs, noisy hobbies, noisy recreational activities,” said hearing specialist Dr. Margaret Cheesman. What can you do to protect your hearing? To find the answer, it is helpful to know something about how your sense of hearing functions.
THE SOUNDS WE HEAR
Our living environment seems to be getting louder. Daily many are battered by sounds of varying intensities ranging from the noise of cars, buses, and trucks in the street to the racket of power tools in the workplace.
Sometimes we add to the problem by turning up the volume. One particular way of listening to music is through headphones attached to a portable CD or cassette player. According to Marshall Chasin, cofounder of the Musicians’ Clinics of Canada, surveys conducted in Canada and in the United States indicate that youths are increasingly suffering loss of hearing caused by the use of headphones with the volume turned up.
But what is too loud? Sound is characterized in three ways –by duration, by frequency, and by amplitude. Duration simply refers to the length of time a sound is heard. A sound’s frequency, or pitch, is described in cycles per second, or hertz. The range of audible frequency for normal, healthy hearing is from 20 to 20,000 cycles per second.
A sound’s amplitude, or strength, is measured in units called DECIBELS [Db]. Normal conversation has a sound level of approximately 60 decibels. Audiologists say that the longer you are exposed to anything louder than 85 decibels, the greater will be the eventual loss of hearing. The louder the sound, the faster the damage to hearing.
A Newsweek magazine report noted: “Your ear can safely handle two hours with a power drill [100 dB], but not more than 30 minutes in a noisy video arcade [110 dB]. Every 10-decibe increase on the sound scale represents 10 times more ear-battering noise.” Tests confirm that sound becomes painful at approximately 120 decibels. Incredibly, some home stereo equipment can produce sound at more than 140 decibels.
To help you understand why loud sounds can damage your hearing, let us consider what happens when sound waves reach your ears.
APPROXIMATE DECIBEL LEVEL OF SOME COMMON SOUNDS
.BREATHING -10 DECIBELS
.WHISPERING -20 DECIBELS
.CONVERSATION -60 DECIBELS
.RUSH-HOUR TRAFFIC -80 DECIBELS
.FOOD BLENDER -90 DECIBELS
.PASSING TRAIN -100 DECIBELS
.CHAIN SAW -110 DECIBELS
.PASSING JET PLANE -120 DECIBELS
.SHOTGUN BLAST -140 DECIBELS
HOW OUR HEARING FUNCTIONS
The shape of the fleshy part of the outer ear, called the AURICLE, or PINNA, is designed to collect sound waves and direct them into the ear canal, where they soon reach the eardrum. At this point the sound waves cause the eardrum to vibrate, and the eardrum in turn, causes the three bones in the middle ear to vibrate.
Next, the vibrations are transmitted into the inner ear, a fluid-filled sac encased in bone. Here the vibrations move through the fluid in the cochlea, the snail-shaped hearing part of the inner ear that contains the hair cells. The fluid in the cochlea triggers the top portion of the hair cells to produce readable nerve impulses. These impulses are then transmitted to the brain, where they are decoded and interpreted as sound.
The limbic system helps the brain decide which sounds to pay attention to and which to dismiss, for instance, a mother may not consciously hear the normal sounds of a child at play, but she will respond instantly to a cry of alarm.
Hearing with two ears enables us to hear in stereo, which is very useful. It allows us to identify where the sounds are coming from. Yet, when a sound consists of speech, the brain can only understand one message at a time. “This is why,” says the book The Senses, “When listening to someone while talking on the telephone, people cannot readily take in what the person next to them is saying.”
HOW NOISE DAMAGES OUR HEARING
To visualize how loud sounds can damage our hearing, consider the following analogy. One occupational safety report compares the hair membranes in the inner ear to wheat in a field and the sound entering the ear to the wind. A gentle breeze, like a low level sound, will move the tops of the wheat, but the wheat is not damaged.
Increased wind velocity, however, will increase the stress on the wheat stalk. A sudden, extremely high wind or continuous exposure to lower winds over a long period of time may damage the stalk beyond repair and cause it to die.
It is similar with noise and the tiny, delicate hair cells in the inner ear. An instant loud blast can tear the tissues of the inner ear and leave scars that cause permanent hearing loss. In addition, prolonged dangerous noise levels can permanently damaged the delicate hair cells. Once damaged, they cannot regenerate. The accompanying result may be tinnitus –a buzzing, ringing, or roaring in the ears or head.
PROTECT AND PROLONG YOUR HEARING
Although heredity or some unforeseen accident may result in hearing loss, we can take precautions to protect and prolong our precious sense of hearing. It is good to learn in advance about potential hearing hazards. As one audiologist said, “waiting for a problem to arise before taking action is like applying the suntan lotion after you’ve been burned.
Often it is a matter of how we listen and not so much what we listen to. For example, if you use stereo headphones, you may want to set the volume at a level low enough for you to be able to hear sounds around you. If your car or home stereo is set loud enough to drown out ordinary conversation, this may well be a signal that it is also loud enough to damage your damage your hearing. Experts caution that two to three hours of exposure to 90 decibels can damage your ears. Earplugs or other hearing protection devices are recommended whenever you are in a noisy environment.
Parents do well to remember that children are more susceptible to hearing damage than are adults. Keep in mind the potential danger of noisy playthings. Why, a toy rattle can reach 110 decibels! Our ears are delicate, small, and wonderful mechanisms. With them we can hear all the varied and beautiful sounds of the world around us. Surely, this precious gift of hearing deserves to be protected.
YOU MAY BE LOSING YOUR HEARING IF YOU
1. Increase the volume on the radio or TV but others find it uncomfortably loud
2. Continually ask others to repeat themselves
3. Often frown, lean forward, and turn your head in order to hear the one speaking to you
4. Have difficulty hearing at public gatherings or when there is noise in the background, such as at a social gathering or in a busy store.
5. Often depend on others to tell you what was said.