Do You Hear What I Hear?

hearing degradation, particularly at frequencies of 3000 to 6000 cycles per second (Hz) (Figure 2).

Another of McCombe's studies showed measurable hearing loss by recreational motorcyclists and professional police officers. McCombe's work points to one conclusion: Every motorcyclist is exposed to noises that will eventually damage hearing. Racers might go deaf sooner, but the rest of us are next in line.

Most of us with normal hearing would consider noise levels of 80 dB(A) to be reasonably quiet, 110 dB A) to be loud, and 115 dB(A) to be uncomfortable. A jackhammer 3' away at 120 dB(A) is about as much as most of us can take without sticking our fingers in our ears. The sound output of a Boeing 727 engine can exceed 130 dB(A) 100 off to one side, which is three times as loud as a jackhammer, and about two pages off the chart!

Time

But, remember that hearing damage is determined by duration as well as loudness. We seem to be able to tolerate loud noises for brief periods of time, or modest noises fur extended periods, without hearing damage. The federal OSHA noise exposure standards might serve as a convenient guideline for motorcyclists. We've created a graphic version for you (Figure 4).

According to the OSHA chart, you could operate your 85 dB(A) motorcycle all day and all night without exceeding the limits. Even if you are in 90 dB(A) traffic, you could ride for 8 hours per day. But if you are riding in a 100 dB(A) environment, your time limit is reduced to 2 hours per day. And the safe exposure for 115 dB(A) is 15 Minutes per day. Rest breaks don't zero the clock, either; you add together all the riding time within 24 hours.

Helmet Wind Noise

While your neighbors might think of engine exhaust as the loudest motorcycling sound, wind noise is often more of a problem for the rider. Air buffeting and swirling around the rider's head generates noise, with or without a helmet. It's fair to ask the question: "Does a helmet increase or reduce wind noise?" More importantly, "Is wind noise around the rider's head likely to damage his hearing?"

According to McCombe's research, both motorcycle noise (exhaust, valves, tires and wind noise increase with speed. But wind noise gets louder than vehicle noise as speeds climb above 40 mph. Averaging the results from 10 helmets, wind noise exceeded 110 dB(A) at 100 mph (Figure 5). We might also note that adding texture to the outside of a helmet doesn't cut down noise, so buffalo horns or fur won't help.

It's really just a clever little generator that turns sound waves unto electrical zits. The translation of vibrations to nerve impulses is accomplished by nerve endings that you can think of as tiny hairs lining the inside of the cochlea.

Going Deaf

The cochlea is filled with hydraulic fluid to help damp the nerve hairs from big noise shocks. But when sound vibrations are too great, the hairs get yanked back and forth so they eventually break off, similar to what happens if you continue to bend a paperclip back and forth quickly. If it isn't obvious, a broken nerve stump is about as useful as a loose spark plug wire.

You probably suspected we'd be bouncing over a few whoop-de-doos on this ride, but stay with us here. The location of the little hairs in the cochlea determines what sound frequency they detect. And the ones closest to the eardrum get the best chance to get snapped off. That's why most people lose hearing at the higher frequencies first. The hearing system does have some emergency tactics to help avoid nerve damage. For example, there are some tiny muscles in the inner ear that can tighten up to cushion the little bones (ossicles). But those muscles get tired pretty quickly, and then the damage can continue.

The important thing to remember about hearing is that big, burley guys may have hairy chests, but no one has big, burley cochlea hairs. Everyone has the same shot at going deaf. But do motorcyclists really lose hearing more than the average Joe?

One of McCombe's studies documented noise-induced hearing loss in grand prix motorcycle racers. About a third of the 44 riders in this study used earplugs regularly. Almost half of the racers showed significant

What's LOUD?

How long it takes for your nervy little cochlea hairs to snap off is a function of how loud the noise is, plus how long you listen to it. Let's look at some typical sound levels, and see if we can figure out where a noise gets loud enough to damage hearing. According to the Environmental Protection Agency, a refrigerator generates about 50-65 dB(A). That's pretty quiet. The typical automobile generates perhaps 70 or 80 dB(A). Really noisy power tools such as planers and maters generate sound levels of about 100 dB(A) as the cutting edges bite into wood. A gas chainsaw can generate about 110 dB(A), mostly exhaust noise. It is important to note that 110 dBs is a lot louder than 100 dBs because the dB scale isn't linear, it's logarithmic. Every 3 dB's doubles the level. According to the EPA, motorcycles generate between 80 and 110 dB(A), measured at the bike (Figure 3).