Category Archives: Noise Vibration and Harshness

What Is NVH | NVH Noise | NVH Vibration | NVH Harshness | Noise And Vibration Theory | NVH Basics


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


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


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

01-types of Noise of car-NVH noise-wind noise-road noise-engine noise-exhaust noise-acoustic waves

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.

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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.

NVH | Noise Vibration And Harshness | NVH Basics | NVH Analysis | Noise Vibration And Harshness Introduction

2009  chevrolet  traversels

NVH stands for noise, vibration, and harshness.

Noise is unwanted sound; vibration is the oscillation that is typically felt rather than heard. Harshness is generally used to describe the severity and discomfort associated with unwanted sound and/or vibration, especially from short duration events.

01-altair-NVH software-NVH test result of a car

The automotive industry is currently spending millions of dollars on NVH work to develop new materials and damping techniques. The new design methods are starting to consider NVH issues throughout the whole design process. This involves integrating extensive modeling, simulation, evaluation, and optimization techniques into the design process to insure both noise and vibration comfort.  New materials and techniques are also being developed so that the damping treatments are lighter, cheaper, and more effective.

Some of the methods used to control noise, vibration, and harshness include the use of different carpeting treatments, the addition of rubber or asphalt material to car panels, gap sealant, and the injection of expandable foam into body panels.  The carpeting treatments include varying types of foam padding combined with different weights of rubber-backed carpet. 

The overall result of this technique is a mass-spring system that acts as a vibration absorber.  The rubber or asphalt materials are attached to various car panels to add damping and mass loading to reduce vibration levels and the rattling sounds from the panels.   Sealant is applied to close gaps in order to increase the transmission loss from the engine, wind, and road noise sources to the vehicle interior.  Expandable foam injected between panels, such as the dashboard and firewall, helps to add stiffness and vibration absorption.

All of these current methods are effective at reducing sound and vibration levels in a vehicle at higher frequencies.  However, some of the treatments become almost ineffective at lower frequencies below 200 Hz.  The treatments also add a substantial amount of weight to the vehicle, thus affecting its fuel economy, as well as adding cost.

NVH Test Equipment’s:

  • Analyzers,
  • Shakers and controllers,
  • Accelerometers,
  • Noise dosimeters,
  • Octave band filters,
  • Transducers for vibration and acoustics,
  • Dynamometers,
  • Sound level meters,
  • Microphones, and
  • Analysis software (Ricardo, Altair NVH Director, LMS Virtual Lab etc.)

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Recent NVH Test Equipment’s:

  • PC based analyzers,
  • Multichannel NVH data acquisition systems,
  • Acoustic holography devices,
  • Laser vibrometer’s, and
  • Anechoic test cells.

NVH Applications:

  • Engine noise vibration testing
  • Acoustic performance testing
  • Sound power testing
  • Pass by noise testing
  • Telephone testing
  • Environmental noise measurements and noise field mapping
  • Structural dynamics and vibration testing
  • Occupational health and safety

Advantages of NVH Test Equipment:

2010 Buick LaCrosse CXS HiPer Strut Front Suspension

  • Real-time multi-analysis is possible in one test run
  • Results obtained are accurate and precise
  • Report generation is made easy
  • Shorter lead times, and hence improved productivity