 |
 |
 |
|
 |
||||||||||
|
ResearchIT STARTED WITH THE RESEARCH...Pollution is a major problem for motorcycles, all terrain vehicles, and snowmobiles.
ARTICLE BELOW WAS WRITTEN BY DAVID HOUGH BEFORE THERE WERE ANY EAR NOISE REDUCTION MUFFS AVAILABLE TO INSTALL IN HELMETS. Noise Levels Inside HelmetsAn article by David Hough in the June issue of MCN discussed the long-term effects of wind noise on the hearing of motorcyclists. Since we already had the wind tunnel reserved for drag testing, another Cal Poly student volunteered to make noise measurements. A microphone was placed in each helmet between Doreen's ear and the inner helmet liner. We measured the total "A-weighted" sound pressure level at 60 and 80 mph. (Noise is "A-weighted" to more accurately model how you perceive the "loudness" of a noise.) Although the total noise levels measured in the wind tunnel are comparable to those reported by David Hough for helmet wind noise, the noise environment generated in the wind tunnel is different in detail from what you experience when riding your motorcycle. What we are really comparing is the performance of the helmets relative to one another when exposed to the same noise environment.Again, as with drag, the full-face helmets performed better than the open-face ones. No surprise here, since we expect objects which have more aerodynamic drag to generate more wind noise. For the full-face helmets, the Shoei X-9 at 103 dBA was the most effective in reducing noise. The Arai RX-7RRIII at 106 dBA at 80 mph was the least effective. Does this mean that Doreen should sneak out of the lab with the X-9 and feel SECURE that she has the best helmet for noise protection? No. What it means is that motorcycle helmets are designed to protect your head, not your hearing. Doreen's hearing is at risk regardless of which brand or model helmet she chooses. How much risk? That's hard to tell exactly, because HEARING DAMAGE risk criteria were developed for the workplace, not the playplace. To give you an idea, OSHA says you cannot be exposed without hearing protection to 100 dBA for more than two hours per day in the occupational environment and recommends half that for a recreational environment. That is, regardless of which helmet you choose, if you ride your motorcycle on a daily basis, (like commuting, for example) for two hours, the probability is one in four that after 30 years you will have serious hearing damage. Remember too, that if you already work in a noisy environment, the riding time is added to your exposure time at work. "Ha, I'll never do that much riding." laughs Doreen. But Doreen shouldn't be so hasty to scoff. Remember the criteria are based on probabilities. Doreen will actually sustain hearing damage at much lower exposure levels. Additionally, what the government defines as hearing damage and what Doreen thinks it means are probably two different things. The government standard means that Doreen can have up to a 25-dB loss in response in the 500-2000 Hz range. That's the frequency range in which good response is required for voice recognition. Unfortunately, this is the same frequency range in which most of the wind noise occurs. What does that mean to Doreen? With a 25-dB loss, Doreen is on the verge of having trouble understanding telephone conversations, hearing movies or television, or carrying on conversations with friends because speech information falls into those critical frequencies. Also, you lose hearing ability in the higher frequencies before the low ones, so Doreen has lost the ability to hear some music and other higher-pitched sounds long before she begins to have difficulty following conversations. In addition, some INVESTIGATORS believe that OSHA has erred on the side of industry. That is, instead of the 90 dBA allowed for an eight-hour work day, 80 dBA is considered best to minimize hearing loss. To prevent hearing loss, noise levels should not exceed 75 dBA according to these folks. Because the consequences of HEARING DAMAGE are too serious to ignore, what can Doreen do besides giving up her motorcycle? Unlike with the aerodynamic drag, riding slower won't help very much. At 60 mph, Doreen was still exposed to between 97 and 101 dBA. The only practical alternative is to wear additional hearing protection. The best to date, are formable, slow-recovery foam ear plugs. Not only are they cheap, but they provide the best overall noise protection of any single device. Under laboratory conditions, they can attenuate noise by 20-35 dB below 1000 Hz and 25-40 dB at higher frequencies. In practice, you can achieve about 15 dB of noise attenuation in the low frequencies and 25-30 dB above 1000 Hz, so by using Earplugs Doreen can reduce her exposure down to the 75-90 dBA noise levels which will substantially reduce her risk of hearing loss. -- Dr. E.M. Gates Product Comparison Premium Helmets: Seven High-End Lids Hit the Racetrack, Interstate, and Wind-Tunnel From: www.mcnews.com/articles/helmet.htm |
| Back to the top Copyright © Quiet Ride Ear Muffs. All rights reserved. | Designed and maintained by Designett Web Design |