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Noise Vibration and Harshness usually abbreviated to NVH is the study of how much external sounds, vibrations or anything that
reduces the overall refinement reaches inside a vehicle. Whenever noise vibration and harshness is discussed, it is usually the methods to reduce these issues or to make the vehicle more refined that is being discussed. One of the characteristics of a luxury vehicle especially flagships and other full size sedans is interior silence and refinement, the ability to be isolated from the outside by your vehicle. Usual NVH issues are low frequency sounds (tire noise), high frequency sounds (wind noise, rattles, squeaks), engine noise, vibrations and the feeling from driving over rough pavement or potholes. The way the chassis and/or suspension is engineered will impact on how much vibration and harshness will enter the passenger compartment. Using exceptional build quality especially in the interior to prevent parts from squeaking and rattling as measures to keep out exterior noise are almost useless if there are unwanted interior sounds. Properly seal the vehicle by using more than adequate rubber sealing around the doors so when they are closed (with windows up) they help to keep out noises from the exterior. Using acoustic laminated glass for the windshield and windows which is very effective at keeping out wind noise and other high frequency noises. Using noise cancellation by means of measuring engine noise and then generating a low frequency sound from speakers to cancel unwanted frequencies. Using average to high amounts of sound damping material which either absorb or block sound. Various sound damping materials can be used in one vehicle and numerous paragraphs are needed for sound damping material alone. One common material is bitumen which is a dense tar like substance which is good at damping high frequency sounds. It is often mixed with other materials like sand or asbestos. Another material is needle felt which is a non woven thick cloth substance made by condensing and pressing woollen fibres and can be made into various shapes and sizes. High density foam insulation is also used as a sound damper and is good at damping low frequency sounds. Clay filled polyvinyl acetate is another sound damper that is more than twice as effective at damping sound as bitumen but is also very expensive. These sound dampers are usually placed on the interior floor, behind the firewall, maybe even in the pillars among other places in various quantities and combinations. Sound damping material adds alot of weight to the vehicles and are usually added to the body before interior or mechanical parts are mounted. Some of these NVH measures (mostly sound damping materials) can also be applied as aftermarket additions to some regular vehicles. Materials like bitumen, rubber and polymer wax can be placed along various parts of a vehicle's body by experts to increase the NVH capabilities. Rolls Royce vehicles, The Lexus LS and the Mercedes Benz S-Class are some of the vehicles that are well known for their quietness and isolation because of their continued research in noise vibration and harshness. |
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