Have you ever heard a ringing in your ears after a loud concert? Did sounds seem muffled? These could be early signs of permanent hearing loss. Constant or even occasional loud noises can damage your hearing beyond repair. More than 35 percent of the 28 million cases of hearing loss in the United States are caused, at least in part, by exposure to hazardous noises. Hazardous noise can be anything from loud music to the sounds of a lawn mower. To find out how hazardous a sound is, we measure its loudness in decibels
, which tell us its power or intensity. The decibel scale is logarithmic - each 10-dB increase is a factor of 10. The normal human ear can hear sounds down to 0 dB. The roar of a rocket lifting off registers over 140 dB. Experts consider noise levels above 85 dB hazardous, particularly when you're exposed to them for long periods. The louder the noise, the less time it takes to damage your hearing. Many rock concerts are 110 dB or more. If you attend often, you can damage your hearing before you know you are in danger. The ear has three parts - the outer, the inner, and the middle ears. The outer ear includes the visible part outside our head and the ear canal, which ends at the eardrum
. The middle ear contains three tiny bones called ossicles
. The inner ear contains the cochlea
, housing thousands of hair cells and nerve endings. When sound waves travel down the ear canal and strike the eardrum, it vibrates. This causes the ossicles to vibrate. The sound is then transmitted to the inner ear. Vibrations set the fluid within the cochlea in motion, stimulating the hair cells. The movement of the hair cells stimulates the auditory nerve endings, which send the sound pattern to the part of the brain that interprets it. Hearing problems in the outer and middle ears can cause conductive hearing loss
. An example is otitis media, fluid in the middle ear caused by infection. These problems can often be corrected with medicine or surgery. Sensori-neural hearing loss is usually permanent and is caused by damage to hair cells in the inner ear. When hair cells or auditory nerves are destroyed, they cannot be repaired. Loud and persistent sounds can damage hair cells and cause permanent hearing loss and tinnitus
. Next time you listen to music, keep the volume low and rest your ears often. Use earplugs at concerts. Remember, once your hearing is damaged by loud noise, it's gone forever!
Identify the type and location of a sound without the help of your eyes.
How good are you at listening when you can't rely on your eyes for help? Test your skill at identifying odd sounds coming from different directions when you're blindfolded. Gain a new appreciation for the way those two little funnels on either side of your head work. Materials
- objects to make noise with, such as blocks, stones, coins, a glass, empty can, or pen
- scarf or handkerchief for a blindfold
- earplugs (available at most hardware, drug, music, or sporting-goods stores)
- Choose a classmate to sit blindfolded in the middle of a circle of students seated at various points around the room. Have this student place an earplug in one ear.
- Silently point to a student in the surrounding circle, who then makes a sound with one of the objects you've gathered. For instance, that person can use the object to clap, tap, click, snap, or rattle.
- Ask the blindfolded student to point back in the correct direction of the sound and identify it.
- Repeat this step with five other students in the circle, each of whom makes different sounds. Record how often the blindfolded student identifies the correct location and sound.
- Ask the blindfolded student to unplug her or his ear. Repeat the process. Is she or he better able to identify the location and source of the sounds?
- Select other students in the class and repeat the experiment. Are some students more accurate in distinguishing sounds and locations than others? Why do you think this is so? Questions 1. What sounds were easiest to identify? Which were hardest? Does this tell you anything about the way we hear and the sounds we expect to hear? 2. What are some things you can do to improve your hearing or listening ability?