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

Introduction to NVH (Noise Vibration and Harshness):

NVH stands for Noise vibration and harshness is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. NVH “noise, vibration, harshness” plays a role in many different areas, from washing machines and lawnmowers to motor vehicles, aircraft, wind turbines, etc. Every object that moves or is put into motion can cause potentially critical noise and vibration problems.

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NVH (Noise Vibration and Harshness) Basics:

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.

Altair NVH software, NVH test result of a car

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NVH (Noise Vibration and Harshness) Tests:

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.

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NVH Analysis:

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 the 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.

Noise vibration control in automobile bodies, Vehicle noise, vibration and sound quality

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.)

Recent NVH Test Equipment’s:

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

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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:

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