Definition of Noise, Vibration, and Harshness

NOISE, VIBRATION AND HARSHNESS (NVH)

Definitions
Noise is any unwanted sound, usually unpleasant in nature. Possible sources of noise are:

- engine
- engine accessories
- intake and exhaust systems
- driveline
- electric motors and pumps
- wind
- mechanical pumps
- road surface (components reacting to road surface-induced forces)

Vibration is an unwanted periodic motion of a body or medium. It may be felt, heard, or seen. Possible sources of vibration include the:
- tires
- engine
- engine accessories
- suspension
- driveline
- exhaust system
- road irregularities (wave pattern, corrugated).
- rigid body motion (bounce, pitch, yaw).

Harshness refers to the ride quality and is very subjective. Reference to the previous conditions is usually the only way to identify harshness as a symptom.

All internal combustion engines and drivelines produce some noise and vibration; operating in a real world environment adds noise and vibration that are not subject to control. Vibration isolators, mufflers and dampers are used to reduce these to acceptable levels.

A driver who is unfamiliar with a vehicle may think that some sounds are abnormal when actually the sounds are normal for the vehicle type.

As a technician, it is very important to be familiar with vehicle features and know how they relate to NVH concerns and their diagnosis. If, for example, the vehicle has automatic overdrive, it is important to test drive in and out of overdrive mode.