PNVF.COM Psychoacoustic Noise, Vibration Free, also known as Noise and Vibration,
abbreviated to PNVF and N&V respectively, is the name given to the field of
measuring, and modifying, the noise and vibration characteristics of vehicles,
particularly cars and trucks. Harshness is a bit of a historical misnomer.
Noise, and vibration, can be measured. There is a psychoacoustic measurement called harshness but it does
not correlate very well with many harshness issues.
Acronym Definition
PNV Park 'n View (trucker's term for park in view at truckstops)
PNV Partido Nacionalista Vasco (Basque Political Party)
PNV Potential Network Value
PNV Prenatal Vitamins
Psychoacoustic Noise, Vibration, and Harshness
Acoustical measurements and instrumentation
Acoustics
Digital signal processing
Resonance
Sound pressure level
Vibration
Vibration isolation
Psychoacoustic Noise, Vibration, and Harshness, also known as Noise and Vibration,
abbreviated to NVH and N&V respectively, is the name given to the field of
measuring, and modifying, the noise and vibration characteristics of vehicles,
particularly cars and trucks. Harshness is a bit of a historical misnomer.
Noise, and vibration, can be measured, but harshness is more of a subjective
assessment. There is a psychoacoustic measurement called harshness but it does
not correlate very well with many harshness issues.
Interior NVH is the noises and vibration experienced by the occupants of the
cabin, while exterior NVH is largely concerned with the noise radiated by the
vehicle, and includes drive-by noise testing.
NVH is mostly engineering, but often objective measurements fail to predict or
correlate well with the subjective impression on human observers. This is partly
because the human body has its own frequency response, eg the ear's response is
approximated by A weighting, but this does not mean that two noises with the
same A-weighted level are equally disturbing. The field of psychoacoustics is
partly concerned with this correlation.
In some cases the NVH engineer is asked to change the sound quality, ie adding
or subtracting particular harmonics, rather than making the car quieter.
Sources of NVH
The sources of noise in a vehicle are many, including the engine, driveline,
tire contact patch and road surface, brakes, and wind. Noise from cooling fans,
or the HVAC, and alternators, is also fairly common. Many problems are generated
as vibrations, transmitted via a variety of paths, and then radiated
acoustically into the cabin. Others are generated acoustically, and this is then
attenuated via various barriers until it excites the cabin. Vibrations are
sensed at the steering wheel, the seat or the floor and pedals. Some problems
are sensed visually - such as the vibration of the header rail or rear view
mirror on open topped cars.
Tonal vs Broadband
NVH can be tonal, such as engine noise, or broadband, such as road noise or wind
noise, normally. Some resonant systems respond at characteristic frequencies,
but in response to random excitation. Therefore, although they look like tonal
problems on any one spectrum, their amplitude varies considerably. Other
problems are self resonant, such as whistles from antennas.
Tonal noises often have harmonics. Here is the noise spectrum of Michael
Schumacher's Ferrari at 16680 rpm, showing the various harmonics. The x axis is
given in terms of multiples of engine speed. The y axis is logarithmic, and
uncalibrated.
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