The Science of Sound: Why V8s Excite Us, Four-Cylinders Don't, and EVs Need to Make Some Noise
There's plenty of engineering that goes into making a car sound the way it does.
There are many reasons a classically trained violinist doesn’t serve as the opening act for a bass-thumping, guitar-thrashing heavy metal band. That’s because what’s beautiful music to some people can be migraine-inducing noise to others.
From the moan of an economical inline-four-cylinder to the banshee-like wail of a powerful V12, the sound a vehicle’s engine emits plays to your senses, both literally and figuratively. But for many car fans, the sound of a snarling V8 engine holds a special appeal.
The blueprint of the V8 engine goes back more than 100 years. A luxury for the wealthy at first, by the 1930s, both Ford and Chevrolet were selling affordable V8 vehicles to the masses. The muscle car era of the 1960s cemented the V8 as the engine to beat when it came to power, price, speed, and—of course—sound. Cars from that time, like the Ford Mustang, Chevrolet Camaro, and Dodge Challenger, continue that tradition today with V8 engine notes that leave you (and anyone else within earshot) in no doubt that these machines are as ferociously fast as they are fearsomely loud.
So why does a V8 engine sound so good?
Think of a Car Engine like a Musical Orchestra
For approximately 30 years, Gabriella Cerrato has been expertly tuning the sound a vehicle creates to meet the expectations of not only the car companies that hire her, but also the customers most likely to purchase a given make or model. That’s no easy task, and no single solution applies to all types of cars, SUVs or trucks when it comes to creating a specific mechanical sound.
“You can say the engine is really like an orchestra to some extent,” says Cerrato, the director of engineering services for HBK, a consultancy firm that assists car manufacturers with managing the noise, vibration, and harshness (NVH) of their vehicles.
Whether it’s an inline-four, a flat-six, or a V8, all internal-combustion engines produce a sound that can be described by the same basic formula. Cerrato explains that an engine creates a resonance or sound frequency, which raises or lowers, corresponding to engine speed.
So how does the number of cylinders in an engine affect the sound it makes?
By using an engine's revolutions per minute (RPM) and cylinder count to calculate how often the engine fires in Hertz (a unit of measurement that represents the number of cycles per second), you can find the engine’s frequency. In four-stroke engines, a cylinder fires once for every two turns of the crankshaft, so engine speed is halved in the calculation. “The higher you go with [the number of] cylinders, the higher you go with frequency,” Cerrato explains.
Too low a frequency can be unpleasant, says Cerrato, adding this is a common problem with the “booming” noise of many four-cylinder engines. Because they have twice the cylinder count, a V8 engine’s frequency is in a higher and generally more pleasing acoustic range. On the other hand, very high frequencies—potentially caused by a loud alternator, a whining transmission, or the whistle of wind noise around side mirrors—tend to be irritating and need to be minimized.
The Importance of Listening to Car Shoppers’ Preferences
Cerrato says a vital step in developing the right engine sound is to find “the sound that matches the DNA of a vehicle.”
It’s a sentiment echoed by Kyle Roche, senior global marketing manager for Harman International’s automotive division, who emphasizes the need to balance his company’s audio systems to both what’s under the hood with owner expectations. “We are at a period of time where there are so many powertrain options, hybrid, electric, gas…and each presents its own unique challenges,” says Roche.
“The engine is typically the highest decibel object in proximity to the car’s audio system,” he adds while emphasizing that overpowering engine noise with larger speakers and amps isn’t a suitable quick fix.
“Driving a Toyota Corolla versus driving an Aston Martin Vanquish, people are paying to hear the engine in that Aston Martin. You have to work closely with a manufacturer to define expectations with that given brand and vehicle.”
Not All V8 Sounds Are Created Equal
While Roche's point of view is from the perspective of tuning a vehicle's audio system to suit the vehicle's image and clientele, this way of thinking lends itself to the engine's sound.
For example, a Chevrolet Corvette customer likely expects the guttural roar of a V8 when they stomp on the gas pedal. Too little noise, and the owner could feel cheated out of the visceral driving experience. On the other hand, a Mercedes-Benz S-Class luxury sedan owner might prefer their machine's available twin-turbo V8 to operate in near silence while cruising on the highway. Both are engines with eight cylinders in a "vee" formation, but each powertrain presents vastly different engineering and marketing challenges.
According to Cerrato, getting a car’s engine note correct requires examining and understanding every aspect of a car’s design from a technical perspective. This includes its exterior shape and design, the layout of the engine bay, the amount of sound-deadening insulation used, and the plumbing of the exhaust.
“Engine noise is modulated by the entire powertrain,” says Cerrato. “Because [the engine] generates all these fundamental frequencies and noises…the vehicle’s manufacturer spends a lot of time designing how all these harmonic and non-harmonic noises combine to give the most pleasant sound.”
Cerrato says the difference between harmonic and non-harmonic frequencies is best explained by imagining the precise pitch of a tuning fork versus, say, the broader sound created by something like a fan. "Harmonic sound is the sound generated by any machine/device that moves periodically, as an example an engine, a pump, or a fan," While it may not be noticeable to the average ear, this sound consistently repeats over and over.
"On the other hand," she adds, "the same device, say a fan, also produces what we call broadband noise where the frequency content is broader. This is the 'ssshhhhh' type of fan noise, or another example is the persistent wind noise that you hear when you drive your car at 70 to 80 mph on the highway."
Silence Is Not Always Golden
While automakers have had more than a century to fine-tune the sounds of a V8 engine, ironically, considering their lack of pistons and silent-running nature, Cerrato says the latest electric vehicles are just as challenging to tune for noise levels.
“Before, you could maybe afford to have something like a noisy compressor or some tire noise. Now [with EVs] there are new targets for so many vehicle components.” Cerrato says that without the competing sound of an internal-combustion engine, something like the sound of tires crunching over asphalt becomes a new problem to solve.
And, of course, the human element comes into play. “A lot of people do not like a very quiet car,” says Cerrato, who counts herself among them. “Road noise is boring; studies find people like some sound [in their vehicle].”
May we suggest the beautiful music of a V8?