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Thursday, March 29, 2018
The human ear is not built for listening to music
Your ears cannot protect themselves from even relatively loud music.
Although the ear has reflexes which protects it against certain types of noise, there is not much it can do when the noise level goes above 120 dB.
The reaction time - 30 to 40 milliseconds - is a limitation in itself, as that is far too little to protect the ear from noise created by human beings.
The combination of three different factors could result in hearing impairment after listening to music:
The duration of time listening
Closeness to the source of the sound
How loud the music is played
No matter how loud the music is turned up when you listen to it, the basic rule is that the longer you listen, the more you stress the muscles in the inner ear. Fatigue of the ear may result in a temporary threshold shift, limiting the amount of quiet sounds that you can hear.
And the more you subject your ears to fatigue, the more likely it is that you will be permanently hearing-impaired.
The middle ear
What is the middle ear? The middle ear is the part of the ear between the eardrum and the oval window. The middle ear transmits sound from the outer ear to the inner ear. The middle ear consists of three bones: the hammer (malleus), the anvil (incus) and the stirrup (stapes), the oval window, the round window and the Eustrachian tube.
The bones of the middle ear
The eardrum is very thin, measures approximately 8-10 mm in diameter and is stretched by means of small muscles. The pressure from sound waves makes the eardrum vibrate. The vibrations are transmitted further into the ear via three bones in the middle ear: the hammer (malleus), the anvil (incus) and the stirrup (stapes). These three bones form a kind of bridge, and the stirrup, which is the last bone that sounds reach, is connected to the oval window.
The oval window
What is the oval window? The oval window is a membrane covering the entrance to the cochlea in the inner ear. When the eardrum vibrates, the sound waves travel via the hammer and anvil to the stirrup and then on to the oval window. When the sound waves are transmitted from the eardrum to the oval window, the middle ear is functioning as an acoustic transformer amplifying the sound waves before they move on into the inner ear. The pressure of the sound waves on the oval window is some 20 times higher than on the eardrum.
The pressure is increased due to the difference in size between the relatively large surface of the eardrum and the smaller surface of the oval window. The same principle applies when a person wearing a shoe with a sharp stiletto heel steps on your foot: The small surface of the heel causes much more pain than a flat shoe with a larger surface would.
The round window
The round window in the middle ear vibrates in opposite phase to vibrations entering the inner ear through the oval window. In doing so, it allows fluid in the cochlea to move.
The Eustachian tube
What is the Eustachian tube? The Eustachian tube is also found in the middle ear, and connects the ear with the rearmost part of the palate. The Eustachian tube’s function is to equalise the air pressure on both sides of the eardrum, ensuring that pressure does not build up in the ear. The tube opens when you swallow, thus equalising the air pressure inside and outside the ear. In most cases the pressure is equalised automatically, but if this does not occur, it can be brought about by making an energetic swallowing action. The swallowing action will force the tube connecting the palate with the ear to open, thus equalising the pressure.
Built-up pressure in the ear may occur in situations where the pressure on the inside of the eardrum is different from that on the outside of the eardrum. If the pressure is not equalised, a pressure will build up on the eardrum, preventing it from vibrating properly. The limited vibration results in a slight reduction in hearing ability. A large difference in pressure will cause discomfort and even slight pain. Built-up pressure in the ear will often occur in situations where the pressure keeps changing, for example when flying or driving in mountainous areas.
Noise and Hearing
Protection Fact
Sheet
One in ten Citizens has a hearing loss that affects his or her ability to understand normal speech. Excessive noise exposure is the most common cause of hearing loss. Some workers with long-term hearing loss have developed ways of adapting to the gradual onset of the disease. The effect of noise is real and can be devastating. Workers who also develop tinnitus (constant ringing in the ears) can find this to be unbearable. The important thing is that no matter what your present level of hearing loss, it is never too late or too hard to prevent further damage. Workers who already have serious hearing loss have even greater reason for saving the hearing they have left. The following information should provide reasons for eliminating noise hazards at work and in everyday life.
Can Noise Really Hurt My Ears?
Yes, noise can be dangerous. If it is loud enough and lasts long enough, it can damage your hearing. Hearing damage can be caused by several factors other than noise, but noise-induced hearing loss is different in one important way, it can be reduced or prevented altogether.
Can I “Toughen Up” My Ears?
No. If you think you have grown used to a loud noise, it probably has damaged your ears, and there is no treatment—no medicine, no surgery, not even a hearing aid—that completely restores your hearing once it is damaged by noise.
How Does the Ear Work?
The ear has three main parts: the outer, middle, and inner ear. The outer ear (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 help transfer sound to the inner ear. The inner ear contains the auditory (hearing) nerve, which leads to the brain.
Any source of sound sends vibrations or sound waves into the air. These funnel through the ear opening, 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 transmit them to the hearing nerve in the inner ear. Here, the vibrations become nerve impulses and go directly to the brain, which interprets the impulses as sound: music, a slamming door, a voice, etc. When noise is too loud, it begins to kill the nerve endings in the inner ear. As the exposure time to loud noise increases, more and more nerve endings are destroyed. As the number of nerve endings decreases, so does your hearing. There is no way to restore life to dead nerve endings; the damage is permanent.
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 have difficulty hearing for several hours after exposure to the noise. Sound can be measured scientifically 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 violin.
What Does Frequency of Sound Vibration Have to Do with Hearing Loss?
Frequency is measured in cycles per second, or Hertz (Hz). The higher the pitch of the sound, the higher the frequency. 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 the high shrill of a dog whistle that many people are unable to hear.
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 usually lost first, which is why people with hearing loss often have difficulty hearing the high pitched voices of women and children. Loss of high frequency hearing also can distort sound, so that speech is difficult to understand even though it can be heard. People with hearing loss often have difficulty detecting differences between certain words that sound alike, especially words that contain S, F, SH, CH, H, or soft C sounds because the sound of these consonants is in a much higher frequency range than vowels and other consonants.
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. Decibels 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 85 decibels is 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 is 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. Anyone who uses firearms without some form of ear protection risks the potential for hearing loss. Recent studies show an alarming increase in hearing loss in youngsters. Evidence suggests that loud music along with increased use of portable radios with earphones may be responsible for this phenomenon.
Can Noise Affect More Than My Hearing?
A ringing in the ears, called tinnitus, commonly occurs after noise exposure, and it often becomes permanent. Some people react to loud noise with anxiety and irritability, an increase in pulse rate and blood pressure, or an increase in stomach acid. Very loud noise can reduce efficiency in performing difficult tasks by diverting attention from the job.
Who Should Wear Hearing Protectors?
If you must work in an excessively noisy environment, you should wear protectors. You should also wear them when using power tools, noisy yard equipment, firearms, or riding a motorcycle or snowmobile.
What Are the Laws for On-the-Job Exposure?
• Habitual exposure to noise above 85 dB will cause a gradual hearing loss in a significant number of individuals, and louder noises will accelerate this damage.
• For unprotected ears, the allowed exposure time decreases by one-half for each 5 dB increase in the average noise level. For instance, exposure is limited to 8 hours at 90 dB, 4 hours at 95 dB, and 2 hours at 100 dB.
• The highest permissible noise exposure for the unprotected ear is 115 dB for 15 minutes/day. Any noise above 140 dB is not permitted.
The Occupational Safety and Health Administration (OSHA), Standards 29 Code of Federal Regulations (CFR) 1910.095 (General Industry) and 29 CFR 1926.52 (Construction Industry) states that each employer will implement and maintain a written Hearing Conservation Program for their respective industries. In order to determine if a hearing conservation program is needed, a site noise evaluation must be done. This can be accomplished by conducting a noise evaluation, noise monitoring, or Job Hazard Analysis (JHA). If during these tests a noise is found to be 85 dB or higher, a written conservation program will need to be written. OSHA requires a yearly hearing test for the approximately five million workers exposed to an average of 85 dB or more of noise during an 8-hour workday. If noise is found to be greater than 95 dB, hazard controls must be used.
Ideally, noisy machinery and work places should be engineered to be more quiet or the worker’s time in the noise should be reduced; however, the cost of these actions is often prohibitive. As an alternative, individual hearing protectors are required when noise averages more than 90 dB during an 8-hour day. When noise measurements indicate that hearing protectors are needed, the employer must offer at least one type of earplug and one type of earmuff without cost to employees. If the yearly hearing tests reveal hearing loss of 10 dB or more in higher pitches in either ear, the worker must be informed and must wear hearing protectors when noise averages more than 85 dB for an 8-hour day. Larger losses of hearing and/or the possibility of ear disease should result in referral to an ear, nose and throat physician (otolaryngologist).
What Are Hearing Protectors? How Effective Are They?
Hearing protection devices decrease the intensity of sound that reaches the eardrum. Hearing Protectors come in two forms: earplugs and earmuffs. Earplugs are small inserts that fit into the outer ear canal. They must be snugly sealed so the entire circumference of the ear canal is blocked. An improperly fitted, dirty or worn-out plug may not seal and can irritate the ear canal. They are available in a variety of shapes and sizes to fit individual ear canals and can be custom made. For people who have trouble keeping them in their ears, they can be fitted to a headband.
Earmuffs fit over the entire outer ear to form an air seal so the entire circumference of the ear canal is blocked, and they are held in place by an adjustable band. Earmuffs will not seal around eyeglasses or long hair, and the adjustable headband tension must be sufficient to hold earmuffs firmly around the ear.
Properly fitted earplugs or muffs reduce noise 15 to 30 dB. The better earplugs and muffs are approximately equal in sound reductions, although earplugs are better for low frequency noise, and earmuffs for high frequency noise. Simultaneous use of earplugs and muffs usually adds 10 to 15 dB more protection than either used alone. Combined use should be considered when noise exceeds 105 dB.
Why Can’t I Just Stuff My Ears with Cotton?
Ordinary cotton balls or tissue paper wads stuffed into the ear canals are very poor protectors; they reduce noise only by approximately 7 dB and are not considered as adequate protection.
What Are the Common Problems of Hearing Protectors?
Studies have shown that one-half of the workers wearing hearing protectors receive one-half or less of the noise reduction potential of their protectors because these devices are not worn continuously while in noise or because they do not fit properly. A hearing protector that gives an average of 30 dB of noise reduction if worn continuously during an 8-hour workday becomes equivalent to only 9 dB of protection if taken off for one hour in the noise. This is because decibels are measured on a logarithmic scale, and there is a 10-fold increase in noise energy for each 10 dB increase.
During the hour with unprotected ears, the worker is exposed to 1,000 times more sound energy than if earplugs or muffs had been worn. In addition, noise exposure is cumulative. So the noise at home or at play must be counted in the total exposure during any one day. A maximum allowable while on-the-job exposure followed by an exposure to noisy lawnmower or loud music will definitely exceed the safe daily limits. Even if earplugs and/or muffs are worn continuously while in noise, they do little good if there is an incomplete air seal between the hearing protector and the skin. When using hearing protectors, you will hear your own voice as louder and deeper. This is a useful sign that the hearing protectors are properly positioned.
Can I Hear Other People and Machine Problems If I Wear Hearing Protectors?
Just as sunglasses help vision in very bright light, so do hearing protectors enhance speech understanding in very noisy places. Even in a quiet setting, a person with normal-hearing who is wearing hearing protectors should be able to understand a regular conversation. Hearing protectors do slightly reduce the ability of those with damaged hearing or poor comprehension of language to understand normal conversation. However, it is essential that persons with impaired hearing wear earplugs or muffs to prevent further inner ear damage. It has been argued that hearing protectors might reduce a worker’s ability to hear the noises that signify an improperly functioning machine. However, most workers readily adjust to the quieter sounds and can still detect such problems.
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 (called tinnitus), which could be the result of long-term exposure to noise that has damaged the hearing nerve. Or, you may have trouble understanding what people say; they may seem to be mumbling, especially when you are in a noisy place such as in a crowd or at a party. This could be the beginning of high-frequency hearing loss; a hearing test will detect it.
If you have any of these symptoms, you may have nothing more serious than impacted wax or an ear infection, which might be easily corrected. However, it might be hearing loss from noise. In any case, take no chances with noise—the hearing loss it causes is permanent. If you suspect a hearing loss, consult a physician with special training in ear care and hearing disorders (called an otolaryngologist or otologist). This doctor can diagnose your hearing problem and recommend the best way to manage it.
It is possible for you to enjoy an active lifestyle and protect your hearing from damage. While many everyday activities generate enough noise to cause hearing loss, with a little awareness and reasonable care, most people can expect to maintain their hearing throughout their life. Exposure to noise causes hearing damage and is almost always preventable.
Remember to practice safety. Don’t learn it by accident.
1. NRR Ratings The performance of earplugs and earmuffs varies between brands and styles. One way to choose a hearing protector is to compare Noise Reduction Ratings. The Noise Reduction Rating, or NRR, measures the muff's or plug's ability to block out noise or "attenuate"; sound. This measurement is stated in decibels; a plug with an NRR of 26 blocks out a maximum of 26 decibels of noise. The NRR listed is the maximum protection that could be achieved if the plug fit the wearer perfectly and was inserted correctly. In most work situations attenuation is half of the listed NRR. For example, if the NRR is 30 the hearing protector most likely blocks out 15 decibels of noise.
All of the earplugs and muffs we stock have been tested by an accredited laboratory that assigned an NRR rating. As you look through our selection, look for the NRR rating by each style of protection.
2. How damaging are your work activities? The chart below lists common sounds and their decibel ratings.
Tractor or combine idling, barn cleaner, conveyor, elevator: You can begin to lose your hearing at this dB if you're exposed to it for eight (8) hours or more per day.
90 dB
Blower compressor, pneumatic wrench, chopping silage (no cab), full-throttle mower: If you are exposed to noises at this level for four (4) hours or more per day, hearing loss can occur.
100 dB
Tractor at 80% load, squealing sows, power tools, hand-held metal grinder: One hour of exposure per day is the limit at this decibel level.
110 dB
Full-throttle combine, 10-HP vane-axial barn fan: Anything over 15 minutes exposure per day can cause damage.
120 dB
Thunderclap (near), sandblasting, bad muffler, old chain saw: The danger is immediate.
140 dB
Gunshot, engine back-fire, dynamite blast, jet engine. Any length of exposure time is dangerous and may actually cause ear pain.
As noise gets louder, damage can occur sooner. There is no "cure" for hearing loss. This chart is only a guideline. Anything over 85 dB can be damaging to your hearing. Chart provided courtesy of the National Farm Medicine Center
Tractor or combine idling, barn cleaner, conveyor, elevator: You can begin to lose your hearing at this dB if you're exposed to it for eight (8) hours or more per day.
90 dB
Blower compressor, pneumatic wrench, chopping silage (no cab), full-throttle mower: If you are exposed to noises at this level for four (4) hours or more per day, hearing loss can occur.
100 dB
Tractor at 80% load, squealing sows, power tools, hand-held metal grinder: One hour of exposure per day is the limit at this decibel level.
110 dB
Full-throttle combine, 10-HP vane-axial barn fan: Anything over 15 minutes exposure per day can cause damage.
120 dB
Thunderclap (near), sandblasting, bad muffler, old chain saw: The danger is immediate.
140 dB
Gunshot, engine back-fire, dynamite blast, jet engine. Any length of exposure time is dangerous and may actually cause ear pain.
3. How do you know if noise is damaging your hearing? You may have a problem if you:
Hear ringing, other noises or a fullness in your ears
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