The biggest risk to your hearing on a motorcycle is exhaust and engine noise, right? Wrong. It’s actually wind noise (and not the flatulent kind). Wind noise from turbulence can cause permanent hearing damage at speeds that are easily reached on the freeway. That is, speeds of around 60mp/h (approximately 100km/h) produce enough noise to permanently reduce your hearing within a few hours.
That’s bad. Because once you lose your hearing, it’s not like your house keys – you can’t get it back. So, what is a safe level of wind noise the average human ear can handle and for how long? And what preventative steps can you take to protect your ears?
Let’s take a quick lesson on how your ears work. Unlike your senses of sight, taste and smell which involve chemical reactions, hearing is a purely mechanical process. This obviously makes sense as sound passing through the air is the result of vibrations of air particles in the atmosphere which in turn affects air pressure. The journey then into our ears and to our brain goes like this:
- Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
- The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
- The bones in the middle ear couple the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
- Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave.
- As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cell, creating an electrical signal.
- The auditory nerve carries this electrical signal to the brain, which translates it into a sound that we recognize and understand.
(Above courtesy of https://www.nidcd.nih.gov/health/hearing/pages/noise.aspx).
Noise-Induced hearing loss comes in two forms – one-time exposure from an extremely intense ‘impulse’ sound (like an explosion) or exposure to loud sounds over a long period of time – such as motorcycle riding. The damage from high levels of noise usually effects the hair cells – which do not grow back. Once they are gone, they are gone forever.
Decibels Sound pressure (for our purposes, let’s think of it as volume) is measured in decibels, which is a logarithmic scale (not linear). That means that that a sound that is 20 decibels is not twice as ‘loud’ as something that is 10 decibels, but in fact 100 times as loud. A sound that is 100 decibels is 100,000 times louder than a sound that is 10 decibels. The chart below shows various types of sounds and the approximate volume, or decibels of those sounds:
Motorcycle Riding and Hearing Loss
There have been many studies related to hearing loss caused by motorcycle riding and as stated at the outset, it’s not the sound of engines or exhausts, but the wind. You can test this yourself. When you’re riding at around anything below 40mph, the main sound you will hear is that of the engine and exhaust. But as you go faster, it’s wind noise that takes over and almost completely masks engine noise at speeds of 60mph and above. The main source of this noise is turbulence that gets into the helmet via the gap between it and your neck. The air swirls around at high speed and the faster you go the more severe this sound is.
Most authorities indicate that it is safe to be exposed to levels of between 85-90dB for up to eight hours for a 24 hour time period. On a motorcycle, that sound level is experienced at a fairly sedate speed of between 30m/h and 45m/h (approximately 50km/h to 70km/h). So, for general suburban riding, your hearing is fairly safe. However, once your speed increases, two things occur – the ‘loudness’ increases exponentially and therefore reduces the length of time you can safely ride. At 60mph, decibels reach 96-101dB. At that range, any more than two hours can begin to cause permanent damage. At higher speeds that you would experience on a race track, it can sometimes mean that exposure has to be limited to less than an hour. Therefore anyone doing regular freeway stints or track days needs to find a solution to lessen the impact on their ears. In part 2 of this article, we’ll look at the ways to reduce hearing loss on a motorcycle.