Category: Noise Vibration and Harshness

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

NVH Noise, Vibration and Harshness

NVH Noisevibration and harshness, also known as noise and vibration, abbreviated to NVH and N&V respectively, is the name given to the field of measuring and modifying the noise and vibration characteristics of vehicles, particularly cars and trucks.

Noise:

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

noise and its types - NVH Harshness - NVH Noise car
Noise and its types – NVH Harshness – NVH Noise car

Vibration:

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

NVH noise vibration - NVH vehicle - noise and sound
NVH noise vibration – NVH vehicle – Noise and sound

Harshness:

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

types-of-noise-of-car-nvh-noise-wind-noise-road-noise-engine-noise-exhaust-noise-acoustic-wav
Types-of-noise-of-car-NVH-Noise-wind-noise-road-noise-engine-noise-exhaust-noise-acoustic-wav

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 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 a transmission of the amplified vibration.

audible-range-of-sound-pitch-intensity-sound-soundwaves-nvh-noise-level
Audible-range-of-sound-pitch-intensity-sound-sound-waves-NVH-noise-level

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’s noises are not in the audible range.

What causes NVH?

The NVH’s key sources in a car are its engine, drive trains and tires, and also airflow (aerodynamic effect) in its body. Tires seem to be a major noise source because of the vibration generated by their movement, which then passes into the cabin on the suspension mounts.

How can you lower your NVH?

The cancellation of NVH (Noise, Vibration and Harshness) is based on three fundamental principles –

1. Reduce the source of noise and vibration,
2. Isolation from the frame body of the car and
3. Absorption of NVH before entering the cabin as far as possible.

The first approach to minimise the NVH has never been the simplest. For example, aerodynamics play a major role in noise. As air flows through the car’s body, any disruption in its direction causes vibrations of air molecules that transmit the sound.

Car manufacturers work to make more accurate and balanced engines, and to minimise vibration by drive train components. Likewise, tire manufacturers have used various treading patterns and substances to minimise undesirable harshness.

The second and possibly challenging way to minimise NVH is to separate the core frame of the car from the source of vibration. Intensive and costly suspension technology, such as stand-alone, multi-link and hydro-pneumatic systems, isolates the chassis frames and steering column from road surfaces, eliminating vibration and shock.

The Car engine, suspension and exhaust parts are assembled more on rubber and polyurethane bushes than on solid metals to even further eliminate the sources of noise. The softer materials try to avoid vibration transmission.

The Third and  final way to reduce the noise and vibrations as much as possible seems to be the last choice in the NVH battle. In mechanical terms, this refers to steering dampers that absorb the worst shocks caused by poor road surfaces.

With in the cabin, passive sounds can be absorbed through rubber-filled column and double-glazed windows to isolate sound by isolating material fastened on different points in the cabin.

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.

noise-vibration-and-harshness-free-interior-space-lower-level-noise-vibration-and-harshness
noise-vibration-and-harshness-free-interior-space-lower-level-noise-vibration-and-harshness

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
Altair NVH software, NVH test result of a car
types-of-noise-of-car-nvh-noise-wind-noise-road-noise-engine-noise-exhaust-noise-acoustic-wav
types-of-noise-of-car-nvh-noise-wind-noise-road-noise-engine-noise-exhaust-noise-acoustic-wav

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.

safety-analysis-of-noise-vibration-and-harshness-nvh-component-displacement-frequency-respons
safety-analysis-of-noise-vibration-and-harshness-nvh-component-displacement-frequency-response

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.

01-Noise vibration control in automobile bodies, Vehicle noise, vibration and sound quality
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.
hiper-strut-front-suspension-reduce-vibration-and-harshness-from-tyres-and-axial-shifting
hiper-strut-front-suspension-reduce-vibration-and-harshness-from-tyres-and-axial-shifting

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