Noise, Vibration and Harshness Make a Big Difference

Have you noticed how some cars “drive better” than others? Noise, vibration and harshness are the most likely reason. Here, we are going to present them to you

Talking about the technical specifications of a car often leads us to acceleration time, braking distance, energy consumption, and top speed. While those parameters are clearly important, we also have to admit that they are only relevant all the time in video games. In everyday use, there are other priorities.

Noise, vibration and harshness are important in prolonged use. They concern sources of energy which the occupants continuously absorb. Studying and controlling them is not only a matter of building a premium feeling for the car. They have direct impact on the occupants’ well-being and health over years of use.

Enthusiasts compare engine noise to
Enthusiasts compare engine noise to “music”, especially in sports cars such as the 1974 Lamborghini Countach (source: WheelsAge)

Noise

The most obvious source is the car’s engine. We are talking about cylinders executing small explosions at the rate of thousands per minute. Enthusiasts enjoy it to the point of identifying an engine from the noise it makes. However, even they agree that it is only pleasant when sent to the cabin within a certain level.

Japanese cars, like the 2002 Honda S2000, have a distinctive noise because they work at high RPM (source: WheelsAge)
Japanese cars, like the 2002 Honda S2000, have a distinctive noise because they work at high RPM (source: WheelsAge)

Other sources of noise come from the very movement. The car continuously pierces air and drags it over its body. Its tires roll over asphalt (or sand, gravel, mud etc.) at high speeds. And there are countless small parts physically interacting with one another. Some sources are louder than others, but they are many.

At first, noise bothers people by not letting them chat in the cabin. However, it can also affect the driver’s focus on the road. In some cases, they even develop symptoms of anxiety over time. That stems from the fact that the body is continuously receiving sound energy. At some point, it just cannot take it anymore.

Suppressing engine noise is a signature trait of luxury cars like the 1969 Imperial LeBaron (source: WheelsAge)
Suppressing engine noise is a signature trait of luxury cars like the 1969 Imperial LeBaron (source: WheelsAge)

Noise control

The best tool is to limit the number of sources. Simple mechanical chains and refined external design play a major role in this. Sometimes, design tweaks like adding side spoilers redirect the air flow in a way that minimizes turbulence and, as a result, noise. Systems with fewer movable parts are often more silent, too.

Old pickup trucks, like the 1970 Mitsubishi L200, have diesel engines with low sound deadening (source: WheelsAge)
Old pickup trucks, like the 1970 Mitsubishi L200, have diesel engines with low sound deadening (source: WheelsAge)

One can also isolate noise from the source. Using hydro-pneumatic links between suspension and chassis, mounting components on polymer bushes, and using double-pane windows are only some of the devices which companies may use. Sound-deadening materials like foam and rubber are usually the last resort.

While suppressing noise is often desirable, it comes at a cost. Applying those resources increases the cost and, in many cases, the weight. They tend to be more common in high-end cars because their powertrain is strong enough to withstand such additional loads. Besides that, their profit margins are more flexible.

Decades ago, Jaguar would extol the vibration smoothness of its 12-cylinder engine (source: WheelsAge)
Decades ago, Jaguar would extol the vibration smoothness of its 12-cylinder engine (source: WheelsAge)

Vibration

While you hear noise, you physically feel vibration. It is an oscillating movement that, in theory, emanates from whatever object that leaves its position of equilibrium. In a car, the main source is the engine and its explosions. Isolating them is one of the biggest challenges an automaker faces when designing engines.

Three-cylinder engines are common in compact cars, like the 2021 Volkswagen Polo, despite their high vibration (source: Volkswagen)
Three-cylinder engines are common in compact cars like the 2021 Volkswagen Polo (source: Volkswagen)

Parallel to that, vibration appears every time the car bumps against something rigid on the road. The only reason we feel only one bump, instead of a vibrating effect, is the heavy action of its tires and suspension. That quick and smooth dissipation comes from a complex chain of several different mechanical parts.

Just like noise, too much vibration causes discomfort from the very first moment. Over time, it may cause headaches and much more serious issues. As if that was not enough, loose components set on a vibrating surface create rattling. Vibration can generate additional noise and accelerate wear on some components.

The Ford Galaxie was the first luxury car made in Brazil and built a reputation for its minimal harshness (source: WheelsAge)
The Ford Galaxie was the first luxury car made in Brazil and built a reputation for its smooth ride (source: WheelsAge)

Vibration control

With the exception of aerodynamic drag, we are working with the same sources as in the previous topic. Vibration in cars comes from the physical interaction of parts, so dampening that interaction goes a long way. Hydraulic and pneumatic links between components, flexible materials for bushes… all that helps.

The 2023 Cadillac Lyriq uses a special suspension with variable response to minimize vibration (source: GM)
The 2023 Cadillac Lyriq uses a special type of suspension with variable response (source: GM)

We no longer talk much about this topic because the industry has already done much. The very adoption of flexible suspensions proves that. You can easily simulate the difference by moving a shopping cart or a suitcase on a regular street. Their wheels use rigid axles and transmit every single bump to your hands.

Thermal engines bring another important source: the rod ratio. The figure comes from dividing the stroke by the length of the connecting rod. It is a geometric relationship between several parts of a cylinder that indicates how much side forces the piston exerts. The higher it is, the less smoothly the engine will run.

Pioneer SUVs, like the 1987 Isuzu Trooper, had a reputation of awful NVH (source: WheelsAge)
Pioneer SUVs, like the 1987 Isuzu Trooper, had a reputation of awful NVH (source: WheelsAge)

Harshness

While those other topics have clear sources and can be objectively measured, harshness is subjective. It is the global effect of noise, vibration and impacts on the car’s occupants, especially over time. That nature has made many authors change the name from NVH to N&V and consider harshness only conceptually.

Rolls-Royce cars, like the 2020 Ghost, are a reference in NVH quality (credit: Enes Kucevic)
Rolls-Royce cars, like the 2020 Ghost, are a reference in NVH quality (credit: Enes Kucevic)

As the name suggests, harsh cars are unpleasant. You cannot hold a conversation or even admire the view because there is always something to distract. Drivers have to force themselves to ignore that, in order to focus on the road, so that gives them additional stress. Mental and physical stress to the same extent.

Everyone can stuff comfort and entertainment items into a car. What truly distinguishes high-end ones is their overall smoothness; driving them is peaceful and predictable. You can focus on the road because the car will act as your extension, executing your commands without distracting or disturbing you in any way.

Mercedes-Benz, which builds the 2022 SL AMG, is one of the companies that invest in NVH excellence (source: Mercedes-Benz)

Latest advancements in NVH

As hard as it works, there is only so much the car industry can do. Noise and vibration come from the very existence of the car in the real world and its use of mechanical components. At some point, reducing its harshness demands solutions that make it heavier and more expensive, so it is necessary to find balance.

Generalist cars, like the 2022 Hyundai Ioniq 5, invest in high-quality materials to reduce harshness (source: WheelsAge)
Generalist cars, like the 2022 Hyundai Ioniq 5, invest in high-quality materials to reduce NVH (source: WheelsAge)

When it comes to noise, a newer solution has come from headphones: active noise cancellation. In other words, the car’s sound system identifies the noise’s sound waves and emits opposite ones, so they cancel one another. That trick has made cabins so silent that some occupants actually find it weird for a car.

Vibration is more difficult to counter because, as we have seen, it comes from the use of thermal engines. However, we happen to be living the rise of electrified cars. Their most noticeable difference is that their electric motors make virtually no noise or vibration. That change leads us to another part of this article.

Electric cars like the 2022 BMW i4 represent new standards in noise, vibration and harshness (source: BMW)
Electric cars like the 2022 BMW i4 represent new standards in noise, vibration and harshness (source: BMW)

NVH in electric cars

ICE engines are the main source of noise, vibration and harshness in a car, sure. But removing them does not mean the problem is magically solved. On the contrary, that just sheds light on the other sources we have mentioned. Those are the new challenges the industry is going to face in the age of electric cars.

The 2023 Toyota Prius is more aerodynamic than ever, which benefits noise (source: Toyota)

Aerodynamics and tires have become the new top targets. That is interesting because makers are already investing in them for energetic efficiency. Dedicated hybrid and electric cars like the Nissan Leaf and the latest Toyota Prius have several design modifications and use high-tech tires precisely because of that.

Other than that, any rattling noise becomes easier to notice. It is necessary to apply smooth materials and padded surfaces in the cabin to prevent dry noises like that. Besides, sound-deadening material is a norm to isolate components such as suspension and brakes. Fortunately, that turns out to reduce vibration too.

Fully electric cars like the 2023 Audi Q8 e-tron bring the best in terms of noise, vibration, and harshness reduction (source: Audi)
Fully electric cars like the 2023 Audi Q8 e-tron bring the best in terms of NVH reduction (source: Audi)

Now, you have read a lot about noise, vibration and harshness. We believe that this knowledge will help you identify the real differences between high-end and low-cost cars. More importantly, we hope you can apply that next time you shop for a car. Your body and the people traveling with you will appreciate it!

The Dodge Challenger managed to outsell younger rivals mostly by staying true to its pony-car roots. Check that out!
High-quality model cars are more impressive than they have the right to be. Check out our article on such a beautiful car-related gift!