What is NVH & How It Affects Passenger Comfort?

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What is NVH?

NVH stands for Noise, Vibrations & Harshness – particularly in the context of automobiles, especially passenger vehicles. Occupants of a moving vehicle often experience noise, vibrations & harshness, or NVH. NVH is very unpleasant at varying motor speeds and also causes fatigue on both the vehicle and occupants. Hence, it is necessary to have a proper NVH design of an automobile as it is critical for the safety and comfort of the occupants.

Some buyers prefer a silent/quiet passenger vehicle, while others like a particular/unique exhaust note of a car or a bike. In some cases, manufacturers ask the NVH engineer to change the sound quality by adding or subtracting particular harmonics rather than making the vehicle quieter. You can readily measure the noise and vibrations, while harshness is a subjective quality. It is either measured via jury assessments or with the help of analytical tools. These tools provide results that reflect human subjective impressions. These analytical tools belong to the branch of physics called psychoacoustics.

Noise, Vibrations & Harshness: Definition

Noise means the sound emanated from a moving object. Vibrations mean the rapid swinging of an elastic solid or fluid. Harshness is the severity of the sound or noise emitted by the vehicle or its components. Just like aerodynamics, NVH is an advanced subject of automotive engineering that needs specialized testing facilities. These days, NVH engineering is a major part of the overall care package. Automotive manufacturers use special hemi-anechoic chambers and extremely sophisticated listening devices to analyze and tune the sound characteristics of new vehicles.

Anechoic Chamber (Courtesy: http://acoustafoam.com)

NVH is typically an engineering field. An interior NVH assessment considers the noise and vibration experienced by the occupants of the cabin. However, exterior NVH mainly deals with the noise emitted by the vehicle, which includes the drive-by noise. Most often, objective measurements of NVH do not correlate well with the subjective assessment of human observation.

NVT: Types of Noises & Vibrations in An Automobile

The sources of noise in a vehicle can be classified as

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