Controlling noise, vibration, and harshness

Vehicle manufacturers and their suppliers are finding ways to deliver greater passenger comfort in the early stages of design.

NVH (noise, vibration, and harshness) is the industry term used to cover the subject of vibration and sounds. Unwanted sound is regarded as noise. Vibration is typically felt rather than heard, and tends to be low-frequency. Harshness usually means sudden events of short duration at higher frequencies. The 3M Automotive Glossary offers a list that illustrates the range of NVH terms: boom, buzz, chatter, chuckle, chirp, click, clunk, grind, groan, growl, hiss, howl, hum, knock, moan, ping, rattle, roar, rumble, squeak, squeal, tap, thump, whine, whir, and whistle. All of these produce negative sensations for people in a vehicle who either want quiet or the option of listening to the entertainment system without distortion. Low-frequency noise in particular has been linked to increased driver fatigue even if the volume is as quiet as 40 dBA.

Recent studies, some of which were presented at the SAE Noise and Vibration Conference in May, have shown that from 1980 to 2000, the noise level inside a vehicle has been decreased by an average of 0.3 dBA per year. As a vehicle gets quieter, the objective becomes one of tuning and balancing the sound rather than eliminating it, and new sources of noise become significant. For instance, a study conducted by Siemens VDO Automotive, during development of an active noise control system, indicated that people prefer different sounds during daytime driving than at night or in bad weather.