Why do cars sound the way they do?
Over the past several weeks, we have discussed sound. I suppose that last week we also had a brief discussion about the lack of sound in certain cars like electric vehicles. It’s one of my favorite topics and one of the best parts about cars, but the question needs to be answered about why each car sounds different. Although we may have discussed briefly in the first article in our “Sound Series”, we didn’t really dive into it.
Why does a Hyundai Genesis coupe with a 3.8 liter, V-6 engine sound so different from a Ford Mustang with a 3.7 liter, V-6. At the same time, most family sedans with a six cylinder engine are going to sound different than a pickup with a six cylinder engine. You get the idea… While there is some similarity across the board with different engine layouts, each car is going to sound a little bit different from the next. Why is this?
The simplest answer is that each car is engineered differently to carry out a different purpose. Even the same kind of cars are going to be engineered a little differently. Mazda does not engineer cars to feel, look, and sound like Subaru. There are different design philosophies at work within each of the two manufacturers. While Mazda seeks to keep the fun in driving while providing a buyer with the best possible fuel economy and styling, Subaru is more focused on a safe, comfortable, driving experience for the person who isn’t afraid to get a little dirty. Both companies offer a small car, midsize sedan, and SUV options, but both manufacturer philosophies are going to dictate a different overall experience for each car, including the sound.
While this is a horizontal comparison across brands, we have to revisit the vertical comparison as well within a certain brand. Subaru is a great example of vertical comparison. The Subaru Legacy, Forester, and even the base model Impreza are going to be bought by people who generally want a quieter ride to and from the home and work. The Impreza WRX and Sti variants are going to be bought by those who are enthusiasts and who want more speed and handling… a sportier overall experience. Along with the sportier experience comes a little extra sound.
Ok great then… some cars are louder than others because of how and for whom they are engineered. But why can you hear a car when someone steps on the accelerator and speeds off into the distance? The simple answer was the way a car is engineered, but the deeper answer is because of all that engineering working together. You see, and engine has a lot of moving parts that contribute to the sound we hear. We all know that, but a lot of times we forget that an engine is not just a big chunk of metal with a few pistons. There is an actual explosion that happens within the engine that moves the pistons that ultimately powers the car. If you haven’t noticed, explosions are usually pretty loud. This is why there is an exhaust system fitted to the car with a muffler that helps dampen the sound produced.
An exhaust system is what most people think about when considering the sound of a car. That certainly contributes. The way an exhaust system is engineered can vary the sound of any car, even if two identical cars with the same engine are fitted with a different exhaust system. It seems simple, and it is. An exhaust system itself is not the only component that contributes to the sound of a car.
The firing order of the pistons in an engine also contribute to the sounds that an engine makes. The prime example of this is the sound of a Ferrari V8 versus the sound of an American V8. Most people recognize the sound of a bubbly and gruff American muscle car when it comes down the street. It growls and sputters. A Ferrari sounds less burly, and it doesn’t have the “potato-potato” sputter that a Dodge Challenger has. This is because of the firing order of the pistons in the two engines. In the Ferrari, the firing order is even, firing back and forth across the engine block. An American V-8 engine has an unequal firing order. This means that some of the pistons on one side of the engine block will fire consecutively rather than firing back and forth each time.
Think of it as a list of odd and even numbers on either side of a piece of paper. Odd numbers are on one side and even on the other. A Ferrari will start with one and will count from one to eight going back and forth across the page to hit every number in succession. The Challenger, might start by counting one and two, then it will skip to number four before traveling back across the page to hit number three.
When the gases inside the combustion chamber are ignited, they send an exhaust pulse out the manifold, headers, and through the exhaust system. Those pulses, or explosions, cause the sound that leave the vehicle through the exhaust. The unequal pulses are why we hear a burble in an American muscle car. See? Pretty simple… right?
Each engine layout produces what it called a root note. It is interesting to note that a four cylinder engine will actually have a similar base sound as an eight cylinder engine. A five cylinder engine will have a similar base sound as a ten cylinder. Six and twelve are also similar. This is more and more apparent as the engine is revved to higher RPMs. The reason for this is because of what is known as a dominant frequency. Frequency has to do the amount of times that a sound wave “vibrates” in one second. Because the eight cylinder engine has twice as many cylinders as the four cylinder engine, the frequency produced is going to be proportional and will cause the two engine types to have a similar tone. If you don’t believe me, and I know it is hard to believe that a four cylinder Civic engine sounds similar to a V-8 from a Ford Mustang, listen to it yourself! This is, of course, mainly before all the other components have been tuned to vary the organic sound produced by just the engine.
I could write an entire college course on the ins and outs of what affects the sound of a car. Companies spend millions tuning cars in their own sound labs to get a desired sound from an engine. It may seem like a trivial thing to many, but it is one of those things that we just don’t think about very much. Sound is crucial, and it comes from many different components. When all of those components work together, they produce what we hear as a car drives by.
–SWF
