Noise:

Noise is defined as any unpleasant or unexpected sound created by a vibrating object.

Vibration:

Vibration is defined as any objectionable repetitive motion of an object, back-and-forth or up-and-down.

Harshness:

Harshness is defined as an aggressive suspension feel or lack of “give” in response to a single input.

Noise and Vibration Theory:

A vibrating object normally produces sound, and that sound may be an annoying noise. In the case where a vibrating body is the direct source of noise (such as combustion causing the engine to vibrate), the vibrating body or source is easy to find. In other cases, the vibrating body may generate a small vibration only.This small vibration may cause a larger vibration or noise due to the vibrating body’s contact with other parts. When this happens, attention focuses on where the large vibration or noise occurs while the real source often escapes notice. An understanding of noise and vibration generation assists with the troubleshooting process. The development of a small noise into a larger noise begins when a vibration source (compelling force) generates a vibration. Resonance amplifies the vibration with other vehicle parts. The vibrating body (sound generating body) then receives transmission of the amplified vibration.

A sound wave’s cycle, period, frequency, and amplitude determine the physical qualities of the sound wave.

The physical qualities of sound are:

• Audible range of sound
• Pitch
• Intensity

For sound to be heard, the resulting acoustic wave must have a range of 20 to 20,000 Hz, which is the audible range of sound for humans. While many vehicle noises are capable of being heard, some NVH noises are not in the audible range.