The Two Types of Noise Generated By Cars



When reading about quiet and noisy cars, there are often misunderstandings when it comes to the different types of noise that come into play. I would therefore like to briefly explain the two main dimensions to consider.

External Noise

The external noise is about the noise that is generated outside a vehicle, which affects the noise pollution impacting pedestrians, cyclists and near-by residents.

The noise mainly stems from the tires/tyres rolling on the road surface but also from the engine. The noise from the wind hitting the chassis of the car is primarily heard inside the car and less so outside.

At low speeds, hybrid and electric vehicles generate very little external noise, which has become an issue in urban environments where pedestrians have a hard time hearing the cars. But at higher speeds, also hybrids and electric cars generate a lot of external noise; primarily road noise. Which means that it is a misconception that an electric car would automatically be a quiet car. Electric cars will also generate a lot of road noise at higher speeds.

Some ways to combat external noise is cars driving at lower speeds, smoother and less noisy road surfaces, smaller wheels and narrower, thicker and quieter tires/tyres and quieter engines (the quietest being an electricity-powered engine).

Internal Noise

The internal noise deals with the interior noise experienced by the driver and passengers inside the cabin of the car.

When people talk about cars and noise pollution, they very often reference to the external noise – the external noise is indeed a very serious source of noise pollution that severely damages the health of people living close to busy roads.

The issue of internal noise and how it negatively affects drivers and passengers is something which is seldom talked about in the media – but it is nevertheless a very big issue with millions of drivers across the world wishing that the interior driving environment was substantially less noisy and more comfortable and relaxing. A lot of people suffer from headaches and pain in the ears. Considering the huge number of people with tinnitus globally, one can assume that a sizable amount of tinnitus sufferers also have issues with too much noise inside cars.

Furthermore, recent research has concluded that the constant low-pitch road noise felt in the cabin of the car makes drivers tired and sometimes puts them to sleep which leads to accidents; some with a fatal outcome.

Key sources of interior noise are engine noise, road noise, wind noise as well as noise from miscellaneous rattles and squeaks in the interior. Some ways to combat internal noise is general application of sound-absorbing materials throughout the vehicle, laminated and/or thicker noise-reducing glass, less noisy engines (and better sound-proofing between the engine and the cabin, in the so-called firewall), softer suspensions with smaller wheels and narrower, thicker and quieter tires/tyres etc.

Again, it is a misconception that a hybrid or electric car would automatically mean that it is a quiet car in terms of the interior cabin noise. One prime example is the Toyota Prius hybrid car, which despite its hybrid engine is to be seen as a noisy car due to poor soundproofing and loud road noise being generated inside the vehicle.

I hope this provides some clarification in order to mitigate potential misconceptions about external vs. internal noise so that a discussion about quiet and noisy cars will be focusing on what’s most relevant in any given context and situation.

To learn more about cars and sound/noise, get your copy of the Quiet Cars eBook – Your Guide to a Quieter Ride – plus join the Quiet Cars online community.

Image: Danielle Scott

Quiet Cars - An Introductory Guide to a Quieter Ride (eBook and online community)