Humans are born with 15,000 hair cells per ear. When large quantities of these cells become damaged hearing loss occurs. There has been an increase in hearing loss within the population. It is estimated that one in three adults over the age of 65 has a hearing loss condition due to irreversible damage to sensory cells. (Heller S, Oshima K, 2005).
There are two types of Noise Induced Hearing Loss (NIHL): sensineural hearing loss and tinnitus. Sensorineural hearing loss occurs when sound waves oscillate through the inner fluid of the cochlea and over stimulate and kill the hair cells. This damage is due to exposure to harmful sounds. Two types of noise cause this to occur: a loud impulse noise, such as canon, and loud continuous noise, such as music from headphones.
Sound is measured in decibels. Exposure to sounds greater than 85 decibels may cause hearing loss. People with noise-induced hearing losses typically have reduced hearing of high pitch sounds (that is, for frequencies between 3000 and 6000 Hz). In general, the louder the noise and the longer you are exposed to it, the greater the amount of hearing loss you may suffer. OSHA suggest that the louder the sound the less time it takes for damage to occur. Sounds of less than 80 dB, even after long exposure, are unlikely to cause hearing loss.
A loud impulse sound can result in permanent hearing loss from the time of exposure. This will cause a condition called Tinnitus. Tinnitus is a slight ringing in one or both ears, however some cases, if severe enough will cause a buzzing or even a roaring sound. These symptoms may subside over time but often times the condition will prevail throughout a lifetime. Continuous exposure to a loud noise will also damage the structure of the inner ear hair cells.
As hair cells from a certain frequency range are damaged those frequencies are no longer heard. The most sensitive cells are those that pick up high frequency sounds. So often when a person has contracted NIHL they are unable to hear sounds with high frequencies. Vowel sounds are unique because they are high frequency sounds. Those that have NIHL often acknowledge that they cannot hear vowel sounds. When tinnitus occurs the damaged cells will continuously send signals to the auditory nerve cell even though there is no real sound. This sound is described as a persistent buzz in the head at the frequency of the hearing damage. That means if the sound that caused the damage was 100 dB then the perceived Tinnitus buzz will equal that value. This condition will compromise the quality of life and ruining all ability to hear the same (www.nidcd.nih.gov).
Activity 6 Measurements of Headphones and Noise Induced Hearing Loss
When listening to music through earphones at mid level the sound generated reaches levels of 100 dB this is loud enough to cause permanent damage after just 15 minutes a day. Students will conduct a survey with a digital sound level meter. Each group of students will set their portable listening device to their normal listening volume. Students will be asked to estimate the total amount of time that they listen to their music during the day. The device will then be measured to determine the average decibel (dB) output. Students will then compile the data and determine the average amount of time and decibel reading for a typical high school student. They will then compare this data to the
OSHA Regulation 1910.95 Occupational Noise Exposure
scale to determine if the average student may be causing damage to their hair cells (Table 3).
Activity 7 Persuasive Essay on Noise Induced Hearing Loss
Students will be given three news articles about iPod use and hearing loss. Students will then write a persuasive essay that takes a stance for or against passing new laws on headphone technology. The Articles that I have chosen are; Behind the Music: IPods and Hearing Loss, More Headphone Use Leading To Hearing Loss, Ipod Trend Brings Spike in Noise Induced Hearing Loss and Walkmans and Hearing Loss (See references for sources).