Noise, Ears and Hearing
CAN NOISE BE DANGEROUS? CAN IT REALLY HURT MY EARS?
Yes - noise can be dangerous. If it is loud enough and lasts long enough, it can damage your hearing. Fortunately, this type of damage, called "noise-induced hearing loss," can be reduced or prevented altogether. Other causes of hearing loss include age, medications, trauma, illness, or heredity.
CAN I "TOUGHEN UP" MY EARS AGAINST LOUD NOISE IF I HEAR IT DAILY?
No. If you think you have grown used to a loud noise, it probably has damaged your ears, so that you do not hear as well as you once did. Surely, you don't want to toughen your ears by losing part of your hearing!
HOW DOES THE EAR WORK? HOW DOES NERVE LOSS OCCUR?
The ear has three parts: the outer, middle, and inner ear. The outer ear, or auricle, (the part you can see) opens into the ear canal. The eardrum separates the ear canal from the middle ear. Small bones in the middle ear, the malleus, incus, and stapes, transfer sound to the inner ear. The inner ear contains the auditory (hearing) nerve, which leads to the brain.
Any source of sound sends out vibrations or sound waves into the air. These funnel through the ear opening and down the ear canal and strike your eardrum, causing it to vibrate. The vibrations are passed to the small bones of the middle ear, which amplify and transmit them to the cochlea, a fluid-filled organ in the inner ear. The cochlea is divided horizontally by the basilar membrane. The vibrations cause a wave which travels along the basilar membrane, bending the hair cells on the membrane. Different hair cells detect different pitches (high or low). The stereocilia, bristly structures on the hair cells, bump an overlying membrane. As they move, channels on the surface of the stereocilia open up, allowing chemicals to flow in. These generate an electrical signal, which travels along the auditory nerve to the brain, which interprets the signal as a “sound”: music, a slamming door, a voice, etc.
Exposure to excessive noise leads to the production of “free radicals” which cause permanent damage to the hair cells as well as the auditory, or hearing, nerve. Exposure may be “impulse” or continuous. Exposure to a single, intense impulse noise, such as an explosion, can result in immediate, permanent hearing loss. Continuous exposure to loud noise can also damage hair cells, although the process occurs more gradually than for impulse noise. Hearing loss may be accompanied by tinnitus – a ringing, buzzing, or roaring in the ears. Impulse and continuous noise may also cause temporary hearing loss, which usually resolves 16 to 48 hours after exposure.
HOW CAN I TELL IF A NOISE IS DANGEROUS?
People differ in their sensitivity to noise. As a general rule, noise may damage your hearing if you have to shout over background noise to make yourself heard, the noise hurts your ears, it makes your ears ring, or you are slightly deaf for several hours after exposure to the noise.
We measure sound in two ways: Intensity, or loudness of sound, is measured in decibels. Pitch is measured in frequency of sound vibrations per second. A low pitch such as a deep voice or a tuba makes fewer vibrations per second than a high voice or a violin.
WHAT DOES FREQUENCY HAVE TO DO WITH HEARING LOSS?
Frequency is measured in cycles per second, or Hertz (Hz). Young children, who generally have the best hearing, can often distinguish sounds from about 20 Hz, such as the lowest note on a large pipe organ, to 20,000 Hz, such as a high, shrill dog whistle that many people would be unable to hear at all.
Human speech, which ranges from 300 to 4,000 Hz, sounds louder to most people than noises at very high or very low frequencies. When hearing impairment begins, the high frequencies are often lost first, which is why people with hearing loss often have difficulty hearing the higher-pitched voices of women and children.
Loss of high frequency hearing also can cause distortion of sound in the speech range. Someone whose hearing is impaired may confuse certain consonants, so that many words sound garbled. This is especially true of words that start with S, F, SH, CH, H, or a soft C, because the sounds of these consonants are in a much higher frequency range than vowels and other consonants.
Thus, words that rhyme and begin with higher frequency consonants (like "hill", "fill", and "sill") may sound exactly the same. You may need to have confusing words repeated or even spelled out, or guess at the meaning of whole sentences.
WHAT ABOUT DECIBELS?
Intensity of sound is measured in decibels (dB). The scale runs from the faintest sound the human ear can detect, which is labeled 0 dB, to over 180 dB, the noise at a rocket pad during launch. It is important to understand that decibels are not measured in the linear arithmetic that we normally use. For example, you know that a car going 60 mph is going twice as fast as one going 30 mph -- this is linear arithmetic. Decibels, on the other hand, are measured logarithmically. This means that as decibel intensity increases by units of 10, each increase is 10 times the lower figure. Thus, 20 decibels is 10 times the intensity of 10 decibels, and 30 decibels is 100 times as intense as 10 decibels.
HOW HIGH CAN THE DECIBELS GO WITHOUT AFFECTING MY HEARING?
Many experts agree that continual exposure to more than 80 decibels may become dangerous.
DOES THE LENGTH OF TIME I HEAR A NOISE HAVE ANYTHING TO DO WITH THE DANGER TO MY HEARING?
It certainly does. The longer you are exposed to a loud noise, the more damaging it may be. Also, the closer you are to the source of intense noise, the more damaging it is. Every gunshot produces a noise that could damage the ears of anyone in close hearing range. Large-bore guns and artillery are the worst, because they are the loudest. But even cap guns and firecrackers can damage your hearing if the explosion is close to your ear, and pistols are worse than rifles because the end of the barrel is closer to the ears. Anyone who uses firearms without some form of ear protection risks hearing loss.
IF I CAN'T AVOID NOISE, WHAT ARE THE BEST WAYS OF PROTECTING MY HEARING?
If you must be exposed to intense noise (even moderate noise for long periods), you should wear some kind of air-tight ear protector. There are two types: earplugs and earmuffs.
CAN'T I JUST STUFF MY EARS WITH COTTON?
No. Ordinary cotton is much too porous to provide any protection at all. Professional earplugs are made of various materials: rubber, foam, wax-impregnated cotton, and plastic. Most sporting goods stores sell them at a modest price. They should be fitted separately for each ear, because each ear canal might be a different size. If both plugs fit snugly, they can provide about 15 dB of noise protection.
Well-fitted protective earmuffs screen out more noise than earplugs - up to 25 dB. (However, you cannot wear muffs over glasses without a sound-leak occurring). Hearing specialists recommend muffs for anyone who works in construction, mining, lumber, or any other noisy jobs. Muffs can also provide protection for target shooters, hunters or anyone who uses firearms, power tools or noisy yard equipment. A combination of earplugs and earmuffs will give you the most protection.
WON'T EARMUFFS OR EARPLUGS KEEP ME FROM HEARING THE DOORBELL OR CONVERSATION?
Not at all. You will be able to hear a telephone, conversation or the doorbell. What you will notice is a reduction in background noise. In fact, some people in high-pressure situations wear ear protectors just because the quieter atmosphere helps them concentrate.
WHAT IF MY HEARING IS ALREADY DAMAGED? HOW CAN I TELL?
Hearing loss usually develops over a period of several years. Since it is painless and gradual, you might not notice it. What you might notice is a ringing or other sound in your ear(s) although there are other causes of “tinnitus,” including medications, or trouble understanding what people say; they may seem to be mumbling. This could be the beginning of high-frequency loss.
If you have any of these symptoms, you may have nothing more serious than impacted wax or an ear infection which can be easily treated, or it may be hearing loss.
Research with antioxidants and stem cells offers promise for treating hearing loss, but for now it must be considered a permanent condition.
If you suspect hearing loss, have a medical examination by an otolaryngologist (a physician who specializes in diseases of the ears, nose, throat, head, and neck) and a hearing test by an audiologist (a health professional trained to measure and help individuals deal with hearing loss).
| Typical Level (Decibels) | Example | Dangerous Time Exposure |
|---|---|---|
| 0 | Lowest sound audible to human ear | -- |
| 30 | Quiet library, soft whisper | -- |
| 40 | Quiet office, living room, bedroom away from traffic | -- |
| 50 | Light traffic at a distance, refrigerator, gentle breeze | -- |
| 60 | Air conditioner at 20 feet, conversation, sewing machine | -- |
| 70 | Busy traffic, office tabulator, noisy restaurant. At this decibel level, noise may begin to affect hearing if you are constantly exposed | Critical level begins |
| 80 | Subway, heavy city traffic, alarm clock at 2 feet, factory noise. | More than 8 hrs. |
| 90 | Truck traffic, noisy home appliances, shop tools, lawn mower. As loudness increases, safe time exposure decreases. | Less than 8 hrs. |
| 100 | Chain saw, boiler shop, pneumatic drill Exposure may be dangerous at 100 dB, and with every 5 dB increase, the "safe time" is cut in half. | 2 hours |
| 120 | Rock band concert in front of speakers, sandblasting, thunderclap. At 120 dB, exposure can injure the ear. | Immediate danger |
| 140 | Gunshot blast, jet plane. Noise at 140 dB may cause actual pain in the ear. | Any length of exposure time is dangerous |
| 180 | Rocket launching pad. Without ear protection, noise at this level causes irreversible damage. | Hearing loss inevitable |
Permission to reprint by: American Academy of Otolaryngology - Head and Neck Surgery, Inc. 1101 Vermont Avenue, NW, Suite 302, Washington, D.C. 20005
References
Mayo Clinic staff. (2009, Aug. 22). Risk factors. In Hearing loss. Retrieved from http://www.mayoclinic.com/health/hearing-loss/DS00172/DSECTION=risk-factorsNational Institute on Deafness and Other Communication Disorders (NIDCD). (2008, October). Noise-induced hearing loss. Retrieved from http://www.nidcd.nih.gov/health/hearing/noise.asp
National Institute on Deafness and Other Communication Disorders (NIDCD). (2009, May 18). Directory of Organizations. Retrieved from http://www.nidcd.nih.gov/directory/keyword.asp?keyword=52
NIDCD Information Clearinghouse, http://www.nidcd.nih.gov/health/misc/clearinghouse.html