• Noise Level Exposure before Hearing Damage Occurs
• Noise Levels Inside Helmets

I've collected information that will give you some facts on why we should always wear ear plugs when riding motorcycles. Those of you who scoff at ear plugs, read on.

US Department of Labor regulations list the following noise levels with the maximum exposure before hearing damage occurs time intervals.

Loud rock music weighs in at 110dB average on an A weighted scale. We're talking permanent hearing damage in a half an hour or less. Hearing damage due to noise exposure is cumulative and irreversible. You can see that from these figures you wouldn't need much of a cut in dB to save your ears while playing music. I only use 15dB earplugs most of the time I play. Mine are custom and expensive.

Noise Levels Inside Helmets

An 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 2035 dB below 1000 Hz and 2540 dB at higher frequencies. In practice, you can achieve about 15 dB of noise attenuation in the low frequencies and 2530 dB above 1000 Hz, so by using ear plugs Doreen can reduce her exposure down to the 7590 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: http://www.mcnews.com/articles/helmet.htm

From Various Mailing Lists

(I used to think the cylindrical foam plugs were good, until I tried the ProTech Sof-Foam plugs, the neon orange, contoured ones. I ran out of them this week and had to use some cylindrical ones, and felt like I was being tortured! A testimonial, dear friends. I paid $0.83/pair for the ProTechs)

--

-Alex Matthews (matthews at ajsh dot colorado dot edu)

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Date: Tue, 15 Jul 1997 19:57:59 -0700
From: Alex Benn <bennah at mail dot cooley dot com>
Subject: Touring Suggestions (REALLLY LONG)
Message-ID: <#008>

EAR PLUGS

I've followed the washing ear plugs thread, but didn't chime in. So here's my chime. After HOURS of extensive testing, I think the Spark Plugs from Northern Safety (800.631.1246) (http://www.northernsafety.com/) were the best combination of comfort and sound insulation. For ~$20 for a box of 200 earplugs, I don't see any great need to ever wash them. They're comfortable and durable, although there is some significant manufacturing variance in terms of foam hardness.

The Laser Lites (available from the same source) are more effective at sound insulation, but had too much pressure for my ears. I wished at times that I had had Silicone inserts custom-made for my particular ears, but since I never did, I can't really evaluate them. The standard "Safety-Ear" foam plugs from Wal-Mart work fine too, but are not as sound insulating as the Spark Plugs. If you do buy them at Wal-Mart, you can save ~$2 by buying them in the hunting section rather than the pharmacy. I also tried the Silicon ear-covering type, but they are barely worth using at all.

One problem -- if you're going to be wearing ear plugs for ~10 hours/day for weeks on end, you need to make sure you pull them out every hour or so, cuz you're really interfering with your body's natural cleaning mechanism (I'm alluding to ear wax, but I refuse to get too graphic), and eventually you'll chafe the heck out of a real sensitive part of your body. After about a month I was bleeding a little in the canal, and seeping interstitial fluid, so I had to give the canal a bit of a rest. Some earwax cleaning and vitamin/oil lotion helped regrow the skin, and frequent breaks prevented recurrence of the (REALLY) painful problem.

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Howard Leight Disposable Foam Earplugs

http://www.howardleight.com/

http://www.howardleight.com/Industrial/Products/max.html

MAX-LITE (NRR 33) pre-shaped foam earplugs feature a smooth outer skin for maximum user comfort. The NRR 33 rating makes the MAX the highest rated disposable earplug in the U.S. The smooth, soil-resistant skin helps prevent dirt from penetrating the surface prior to insertion. Attenuation tested in accordance with ANSI S3.19-1974. Coral color, packed in poly bags.

http://www.howardleight.com/Industrial/education/FrequentlyAskedQuestions.html