By Evans Brasfield January 10, 2014 45 http://www.motorcycle.com/features/motorcycles-hearing-loss.html
In terms of rider education and injury prevention, a great deal of attention is paid to motorcycle safety by the government, motorcycle industry, and media. However, the subject of hearing loss among motorcyclists is rarely discussed. Yes, riders sometimes make passing remarks about ear fatigue after a long day in the saddle, and recent years have (in my subjective opinion) shown an increase in earplug use among riders. Still, the subject and the use of actual, provable scientific numbers have been relatively overlooked when compared to safety items like body armor and helmets.
Roughly one out of every 10 Americans suffer from hearing loss that affects their ability to understand normal conversation. The most common kind of hearing loss is the exposure to excessive noise, and the simple act of riding a motorcycle puts riders at risk for becoming part of those statistics. The wind noise at highway speeds can expose motorcyclists to sound levels in excess of 100 dB – that’s the equivalent of using a chain saw or standing in the middle of a dance club. Helmetless riders can experience noise 10 times greater than that, resulting in potential hearing loss in as little as 30 minutes. Hopefully your rides last longer than a half-hour.
According to the National Institute on Deafness and Other Communication Disorders, approximately 15 percent (26 million) of Americans between the ages of 20 and 69 have high frequency hearing loss due to exposure to loud sounds or noise at work or in leisure activities.
When we consider hearing loss, we need to keep two things in mind. First, noise-induced hearing loss (NIHL) is preventable. Second, NIHL is permanent. Once that hearing is gone, it’s gone forever.
NIHL in the workplace has been well documented, and OSHA has made rules regarding what is an acceptable duration of exposure to various levels of noise. Using these standards as a baseline, riders can learn what the relative intensity of noise they’re facing when they ride and make educated decisions on how to minimize their long-term risk for hearing loss. However, before we delve in to motorcycle-specific causes of NIHL, we should look at the physical causes of hearing loss so that we understand how noise damages our hearing.
Hear Ye, Hear Ye!
The human ear is an incredibly compact and complex structure, providing riders with vital information. (Credit: Bruce Blaus)
In the ear, the air pressure waves that are the physical embodiment of sounds are converted by the ear into the electrochemical impulses that the brain can understand. Sound waves travel through the outer ear (the pinna, the part that looks like a funnel) into the auditory canal. At the end of the canal, the eardrum (tympanic membrane) converts the air pressure waves into vibrations that are, in turn, transmitted via three tiny bones (ossicles – commonly referred to as the hammer, anvil and stirrup). Finally, the vibrations reach the cochlea (a fluid-filled bone structure consisting of a tapered tube that wraps around itself similar to a snail’s shell) where the vibrations are converted to a form that can be sent to the brain via the auditory nerve. This is where the magic – and damage – takes place.
The basilar membrane is one of the membranes dividing the cochlea’s tapered tube lengthwise into three parallel, fluid-filled tubes. The sound vibrations run down the basilar membrane causing hair cells (cilia) in the organ of Corti to vibrate. These delicate hair cells are responsible for making the connection to the auditory nerve by converting the physical vibrations into electrochemical signals. We’re born with about 15,000–20,000 of these cilia, and since we don’t grow new ones when they are damaged, we need to make the cilia last a lifetime.
Noises that are too loud damage and ultimately can kill the hair cells. The amount of damage that occurs is time dependent and related to the intensity of the sound. While an extremely loud noise, like an explosion, can cause immediate, permanent damage, extended exposure to less loud but still damaging noise can also lead to permanent damage. Our goal, as motorcycle riders, is to determine the sound threshold that will allow us to take the long rides we enjoy and still be able to talk to our friends and family when we get home.
In the Wind
Head forms like this are used in testing for wind noise in helmets.
We’re all aware that motorcycles have an image problem with the non-riding public. When they think about motorcycles, they generally think about loud pipes echoing through their neighborhood. However, loud pipes aren’t the primary culprit when it comes to NIHL among motorcyclists. At a stop and at low speeds, we can cause our own hearing loss – I’m looking at you unbaffled V-Twin riders – but once the speed approaches 40 mph, wind noise becomes the dominant sound, especially so for unhelmeted riders.
The noise that motorcyclists hear at highway speed is largely a function of turbulence. Recent studies have shown that the primary source of helmet turbulence – and noise – is in the chin bar of a full-face helmet. When these results were initially announced, the anti-helmet lobby latched on to the idea, saying it proved that helmets were bad for riders. However, if one considers the relative aerodynamics of the human head with its ears flapping out in the breeze versus the smoother, more aerodynamic shape of a modern full-face helmet, the fallacy of this argument is readily apparent.
An aside: Some studies have shown that certain helmet shapes and construction may amplify sounds of certain frequencies, which is not a good thing and may contribute to hearing loss. However, when compared to the full-on auditory assault of riding helmetless, using this factor as an excuse for not wearing a helmet is nothing more than a straw-man argument.