The Science Of Motorcycle Sound

Sounds from motorcycles affect riders in surprising ways. Janelle Kaz February 26, 2020

There is more going on with the sounds from a motorcycle and how it affects the human body than you might expect. Kevin Pak

The roar of a wide-open throttle, the robust, throaty growl of a big V-twin, the thrumpy exhaust notes of a vintage classic—just some of the motorcycle sounds that have entertained petrol heads all around the world for as long as motorcycles have existed. Whether it’s the engine noise, the gears shifting, the tire-pavement interactions, body vibrations, or maybe even some familiar rattling, motorcycles produce sound when they move. Even the pitch and volume of an electric bike’s gear set makes a faint mechanical whine which escalates with speed.

Combustion engine design and fine-tuned exhausts are huge components of the sound and feeling of riding a motorcycle. Janelle Kaz

The particular sound of a bike is very important to riders and motorcycle enthusiasts alike. Anyone who rides knows there’s no comparison for the suite of senses that makes up the experience of riding a motorcycle, including sound. Motorcycle brands know the value of a well-crafted sound and how it affects potential buyers. Entire departments are devoted to precisely tuning engine and exhaust design in order to appeal to an innate emotional response resulting from sound.

Just consider how different watching a motorcycle race on a screen is as opposed to actually being there, simply because it lacks the auditory bombardment of a racetrack. Imagine being at the racetrack, but in total silence. It doesn’t seem fathomable because we’re so used to the immersive sound that comes along with the intensity and speed of racing.

The sensory immersion of actually being on a racetrack is unlike anything else. Super Hooligans race at sunset in Huntington Beach, California. Janelle Kaz

Different engines sing different songs as they release compressed gas from the cylinders, then through the exhaust valves and exhaust system, crafting their own unique sound signatures. Some designs make such distinctive sounds that they are instantly recognizable long before the bike comes into sight. Whatever your preference may be, whether it is the balanced drone of a horizontally opposed engine or the uneven interval firing of a V-twin, the sound signature is a strong characteristic of our ride.

Even without a combustion engine, some electric bike makers have added a digital exhaust, allowing you to choose a different sound for your otherwise quiet bike by using an app on your phone.

It is clear that sound isn’t just something that we hear, it is something we feel. Sound is essentially touch at a distance. There is something unmistakable about the powerful auditory and visceral sensation produced by motorcycles which never gets old and enriches our lives every time one fires up.

Cam Brewer with the RSD 750cc two-stroke named the “water buffalo,” with its steep “ring-ding” sound waves resulting from rapidly released exhaust. Janelle Kaz

We are sensorial creatures, moving about the earth in response to our environment. Human senses have been shaped over time by evolution. Yet we do not see with our eyes nor hear with our ears—we accomplish these things with our brain. The eyes and the ears are simply the receptors of stimuli which are then transported to our brain to be interpreted as a sight or a sound.

However, the outer ear you see is not the only receptor of sound. Our entire bodies are conductors of sound, including our bones. One of the first examples of sound conduction through bone was from Beethoven, who began losing his hearing at the age of 26. He continued composing music by resting his skull on the piano in order to “hear” the vibrations of the piano strings. He also attached a thin rod to the piano and would clench the rod between his teeth, experiencing the vibrations through his jaw.

You can easily test this out by completely blocking your ear canals (or just covering your ears) and using your voice. You can still hear yourself because the vibrations coming from your vocal chords are vibrating your jaw, your skull, and your sensitive inner ear. This form of sound perception is known as bone conduction. It is with this same technology that bone conduction headphones have been created.

Sending vibrations through the skull via bone conduction bypasses the eardrum going straight to the cochlea. The translated signal then travels from the auditory nerve to the brain where it is perceived. Janelle Kaz

Rather than sending sound through the auditory canal, bone conduction headphones bypass the eardrum entirely, sending vibrations through the bones in your head to the cochlea, the sensory organ which translates them into nerve impulses for the brain to interpret.

This leaves your ears available to listen for important sounds while on the road—auditory cues which could save your life, such as oncoming traffic, squealing tires, or emergency sirens.

This technology has already proved helpful for soldiers in war zones, so that the person on the ground can hear communication through bone conduction while still listening to what is happening around them through their ears.

It’s hard to imagine the engine and exhaust noises being absent from the racetrack and pits, but this silent speed may be our future. Andy DiBrino and his father getting ready to hit the track. Janelle Kaz

Additionally, this is how elephants communicate over such long distances. Bone is a solid structure and therefore a very fast conductor of vibrations. Elephants stomp on the ground, signaling to other elephants via low-frequency seismic vibrations. The vibrations travel along the earth and up through the bones of another elephant, reaching the cochlea and the brain. The males even touch their trunk to the earth as a way to triangulate the direction in which the female is sending the signal from.

Water also transmits these vibratory sound waves over great distances and some whale skulls and mandibles (jawbones) have acoustic properties which conduct low frequencies directly to the inner ears.

As you probably know, we’re made up of two-thirds water. However, you may not know that because the water molecule is so small, this quantity translates into 99 percent of our molecules. Water is a great conductor of sound.

You don’t just hear your motorcycle with your ears—our entire bodies are conductors of the vibrational energy of sound. EL3 Productions

Additionally, it has been found that humans also listen through the largest organ in the body, our skin. A type of sensory receptor covering our skin at varying densities known as mechanoreceptors are capable of sensing sound.

Therefore, depending on the bike you’re on, there is a very particular sound that emanates through you as you ride. Not just via the vibrating of your eardrum, but traveling through your entire body—your skin, your organs, and your bones.

Interestingly, there is promising research on the healing properties of certain vibrations, such as those discovered by Dr. Lee Bartel in his findings of how sound can stimulate cells in the body and brain to increase blood flow. So far, this treatment has shown significant positive effects for sufferers of Alzheimer’s, dementia, depression, and fibromyalgia.

Of course, there has yet to be any scientific studies done on the physiological ways in which the sounds and vibrations of a motorcycle affect the human body and mind, but if this research were to take place, I would be very intrigued to learn the results. Perhaps, like me, you consider your time on two wheels meditation in motion and feel a sense of relief while out on the road.

Clearly, there are other sensory stimuli at play which likely also attribute to an increase in overall well-being while riding, such as the movement of wind, the experience of velocity, the novelty—whether you’re riding somewhere new or simply noticing changes in your surroundings, perhaps the sun on your face, and/or the views that you travel through (hopefully beautiful land- or urban-scapes).

Drag racing at the Moto Beach Classic event in Huntington Beach, California. Kevin Pak

The majority of us are so used to sound being such a huge part of life that we never stop to wonder what, exactly, sound is. Sound is a pressure wave created by vibration through a medium. Sound is a form of energy, a force which sets surrounding particles in motion, thus transporting this energy through oscillations in air pressure—as a wave—through space and time.

These sound waves need a medium to travel through, such as a solid, liquid, or gas. It is true that there is no sound in a vacuum, however this does not entirely apply to outer space. The majority of space as we know it isn’t an empty void; particles still exist, but they might be so spread out that the sound traveling through them is at a low enough frequency that the human ear cannot detect it.

Ever since I started spending a lot of time out on the road, I’ve met at least a dozen older riders who have felt compelled to express the need for ear protection while riding. It isn’t the bombastic sounds from the exhaust, but rather the damaging effects from the turbulent airflow around your head—the wind.

Studies have shown that even a full-face helmet cannot completely protect your ears from the permanent damage caused by wind. Just a couple of years ago, research was conducted which revealed some pretty scary results. The studies showed that permanent hearing damage can be caused after only 15 minutes of riding at 62 mph (100 kph) without earplugs. Just as you might expect, the faster you go the less time it takes to cause irreparable harm.

Filtered earplugs are recommended in order to protect motorcyclists from the severe damage caused by the high-frequency wind, while still allowing them to hear lower-frequency sounds, such as their engine, human speech, and oncoming traffic.

A recent study tested a novel acoustic material designed to significantly reduce noise caused by the turbulent wind around the helmet. It is a porous, natural leather foam set inside the motorcycle helmet with a remarkable ability to decrease the noise caused by a wide range of high frequencies.

Mount Wilson, a peak located in the San Gabriel Mountains, with its Radio Ridge Antenna Farm receiving a barrage of radio waves serving the Los Angeles area. Sam Ray

Although sound is currently an inextricable feeling of riding motorcycles, we should respect the powerful force of wind regardless of what bike we’re on, and recognize the incredible nature of our sensitive eardrums. Wind, after all, carves canyons and shapes mountains. Losing the ability to hear our loved ones in old age is incredibly sad, especially if it can be prevented via a combination of bone conduction headphones and filtered earplugs while riding—which still applies for quiet electric bikes.

For as long as humans have recognized that sound helps or alters mood and mind states, we’ve been using technology to induce some desirable state of mind. Perhaps this will someday be applied to electric bikes—just imagine restorative binaural beats emanating from your running motorcycle, mechanical vibrations designed to improve brain and other organ functioning or even bone density as you ride. Only time will tell where the unseen waves of sound carry us.

Do you have any experience with filtered earplugs or bone conduction headphones while out on two wheels?

As we transition away from non-renewable fossil fuel sources, do you imagine a quiet future for motorcycles and racing?

28 February, 2020

The lack of combustion engine intake and exhaust sounds in electric motorcycles is a major impediment to my acceptance of the breed. I know there's some sound in an EV, but not what I'm looking for.

· 28 February, 2020

There's nothing more surreal (and pleasurable) than the odd moment when a 60 mph tailwind makes my ride dead silent, and I throttle down significantly such that the bike sounds like it's idling in the driveway, and you watch the gorgeous desert landscape peel away before you as you pierce it on a thin ribbon of highway at breakneck speeds. Bicycling silently in an urban environment presents a similar thrill, improved by endless details you don't see, hear, feel or smell when driving, or even motorcycling. (We all know how motorcycling provides ten times the aroma of nature than driving does. Bicycling gives about twice that of motorcycling.) Ah, but road racing. That where the sound and vibration of the engine tells you how fast you are going, what rpm your engine is at, and even what gear you are in. You find yourself ignoring the tachometer, yet shifting just before the rev limiter kicks in. You discover that the proper amount of braking and downshifting is determined by "muscle memory", which is where your subconscious brain automatically decides what to do, based on sound and feel as much as sight. You achieve the same level of skill when training for a pilot's license. You can ignore all the instruments, because your ears and buttocks tell you what the speed, roll, altitude and vertical speed indicators are saying. Yes, I do believe the blind could be taught to ride and fly. Drive a car? Nope.

28 February, 2020

"You achieve the same level of skill when training for a pilot's license. You can ignore all the instruments, because your ears and buttocks tell you what the speed, roll, altitude and vertical speed indicators are saying." Umm... no. In fact, the exact, complete opposite is true - as JFK Jr. and many, many other deceased pilots and their families would strongly concur. Google "spatial disorientation" - an all-too-common killer in aviation - where relying on your physical senses "based on sound and feel as much as sight" will all but guarantee your demise.

28 February, 2020

We alter exhaust systems to get sound we like. We alter the volume and/or the tone. Same thing can be accomplished with an electric bike by simply adding a computerized synthesizer that could produce any tone or volume we want. No more synthetic than altering the sound with different tubes and mufflers. But with the added ability to change the tone or volume in an instant instead of being fixed. The thing that turns me off on electric bikes - no gear box. There is something about changing gears while accelerating that is exhilarating to me. Oddly enough, from what I've understood, some Hondas that are running CVTs have "shift points" designed in to give the feeling of shifting. People associate it with acceleration. Honda did a similar thing on their hydrostatic ATVs, having either a constant variable swash plate operation or a manual five position set up that "shifted". I want an electric bike that can make the noise I want, be it XR750 or H2 with chambers, that has a gear box to get the rush of the sound and the shifting.

· Sp 12 January, 2024

Within the past few years Ive been using the foam earplugs on every ride. Inserting them deeper practically eliminates all wind and exhaust noises. It's a satisfying quiet which makes me focus more on what I see on the roadside and feel with the bike. Shifting according to vibrations.

· 29 December, 2023

It's always been (as an engineer) my understanding that sound, especially sub-audible and very low bass sounds, also set up resonances in the cavities of the body - stomach, chest, etc. These are different for all people and, along with all the effects mentioned in the article, account for tastes

4 March, 2020

I think the coolest thing about electric bikes is the quiet; to stand up on the pegs so you can't see it either is for me, magical. Like flying in a dream. That said, I've [mostly] used ear plugs, especially while touring, since I started riding 50 yrs ago and today at 63 I still hear well. Also, earplugs make a long day in the saddle WAY less tiring

2 March, 2020

Riding is a different experience when you can hear sounds like the tires or clutch chatter instead of exhaust noise. Spectators like the noise more. Kaz, which sounds better: a scout 60 on the open highway or an enduro on a dirt road? Or the scout on a winding forest road?