NVH engineering these days forms a major part of the overall car shape package. Automotive giants like Mercedes – Benz make use of special hemi – anechoic chambers together with ultra – sophisticated listening devices used to analyze and tune the sound character of the fresh vehicles. Noise and vibration can readily be measured whereas harshness is a subjective quality and is either measured via jury evaluations or with the help of analytical tools which provide results that reflects human subjective impressions. These analytical tools belong to a field known as psychoacoustics.
An interior NVH deal with noise and vibration experienced by the occupants of the cabin, while exterior NVH is largely concerned with the noise radiated by the vehicle, and includes a drive – by noise testing. Most often objective measurements of NVH fail to foresee or correlate well with the subjective impression on human observers rather NVH is mostly engineering. Let’s say, although the ear's response at intermediate noise levels is approximated by A – weighting, two distinct noises with the same A – weighted noise level may not necessarily be equally disturbing.
The vehicles have many sources of noise namely the brakes, tyre’s contact patch with road surface, engine, driveline, brakes, and even, wind. Further, these noises from cooling fans or other engine accessories are fairly common. Many problems occur either as vibration or noise, transmitted through a variety of paths, and then emitted acoustically into the cabin. These are known as structure – borne noise. Others are produced acoustically and travel through airborne paths. Structure – borne noises are attenuated by isolation whereas airborne noises are reduced by their absorption or via. the use of barrier materials. Vibrations are sensed at the seat, the floor, the pedals, the armrests or the steering wheel. Some of the problems occurring from vibrations can be sensed visually like the vibration of the rear – view mirror or header rail on the convertibles.