Do You Hear What I Hear?

The quietest helmet in McCombe's test, a tight-fitting BMW System II, measured 108.4 dB(A) at 100 mph. The OSHA standards would allow you only about 40 minutes of that, assuming you didn't need to stop for a chat with Officer Friendly. At the more realistic US speed of 65 mph, wind noise around the typical helmet would be about 100 dB(A), which OSHA says you could tolerate for a maximum of 2 hours per day. Every helmet in the study exceeded 100 dB(A) at 70 mph, something to think about if your riding style leans more toward warp speeds. These sound levels are verified by the Cornell study, which reported 101-107 dB(A) at wind tunnel speeds of 61 mph. Back in 1987, David Marr did some sound level readings for Road Rider, and came up with dB levels of 11032-116 at speeds from 35 mph to "highway." The differences are probably due more to measuring techniques than ambient levels, but we're still talking about a lot of noise.

Currently, MCN is working on its own wind tunnel tests, and will share the results as soon as they are available.

Frequency

McCombe's crew not only measured wind noise levels, but also looked at the frequency of noise, measured at a speed of 78 mph (typical motorway speed in England). The highest dB(A) levels are in the low frequencies up to about 300 Hz., and sound level of wind noise drops off rapidly above 1000 Hz. (Figure 6). This may seem like useless information, but frequency is important, for reasons that might surprise you.

Doesn't My Helmet
Reduce The Noise?

Obviously, riding without a helmet exposes the rider's ear canals to noise. A nice cushy helmet with sound-deadening foam inside should reduce noise, right?

Yep, a typical helmet reduces ("attenuates") noise. But even with all that fiberglass and foam, a helmet attenuates noise only in the higher frequencies - noises above 1000 Hz_ or so. The attenuation of 2000 Hz. noises is almost 14 dBs, and above 4000 Hz. a helmet can strangle a whopping 25 dBs.

But wait a minute! Remember the frequency of helmet wind noise? It's down in the low-frequency range-under 1000 Hz. That means a helmet might reduce the noise of singing tires and revving engines, but won't reduce much of the wind noise. With or without a helmet, you'll still be listening to about 100 dB(A) of wind noise at 65 mph, whether you are plodding along on a quiet Gold Wing or twisting up the wick on a ZX- 11. Hey, What's The Big Deal?

Okay, I've waded through the statistics that say I'm probably going deaf. But I've been riding for 30 years and can still hear fairly well, so what's the big deal about hearing loss? And even if I have lost some hearing, why start wearing earplugs now, after the damage has been done?

Well, the big deal is that I've probably lost a lot of my hearing acuity without even realizing it. When those high frequency receptors break off, we can't hear consonants as well, and that makes it hard to hear words like "trucker."

We can evaluate hearing loss in a couple of different ways. One way is to get in a soundproof booth and measure hearing with accurate devices. I'm not sure I really want to know how much I've damaged my hearing already. The other way is just to be aware of what happens to your own hearing after a ride. Hey, I can do that!

McCombe's team accomplished some serious testing of actual hearing loss in motorcyclists, both to determine temporary hearing loss during a ride, and to see if motorcyclists had greater hearing loss than other people. In one study, they had carefully selected riders do a standard test run, with their hearing measured before and immediately after the ride. The standard ride was 1 hour at 80 mph. To make sure the data was absolutely accurate, riders were screened for ear diseases and occupational noise exposure, and candidates were clinically examined. They didn't want people who had already gone half deaf from working in a foundry. Only riders whose significant noise exposure was motorcycling were selected to participate. Some 400 volunteers were weeded down to 18 riders. To measure the temporary hearing loss, riders were tested at a nearby clinic, or in a special portable booth brought to the site.

The Results?

Some temporary hearing loss occurred in every rider after one hour of fast riding. The audiologists describe this as a "threshold shift," or what you might think of as not being able to hear quite as well after the ride as before. Comparisons of motorcyclist's hearing to averages also showed that riders with longer motorcycling experience had permanently lost more hearing.