NVH Testing (Noise, Vibration, and Harshness)

What is NVH?

Noise, vibration, and harshness (NVH), also known as noise and vibration, is the study and modification of the noise and vibration characteristics of vehicles such as cars and trucks. While we can measure noise and vibration, harshness is a more subjective quality and is measured either via jury evaluations or with analytical tools that can provide results reflecting human subjective impressions (psychoacoustics).

NVH can be tonal such as engine noise (or powertrain noise), or broadband, such as road noise or wind noise. Basically, it is everything that drivers or passengers can either hear and feel from a vehicle while driving. A few such examples are wind noise, road noise, bumps from the suspension, or vibrations from the engine.

What is noise?

Noise is unwanted sound or unwanted disturbance in an electronic signal. Acoustic noise is energy transmitted to the air that causes an audible disturbance. Tools such as acoustic intensity mapping and combustion/mechanical noise separation can be used to identify the best method of noise reduction.

What is vibration?

Vibration is an oscillation that causes noise and disturbance. Vibration is generally of concern due to its physical effects which can cause disturbance to people, disruption in electrical systems, and failure or breakdown in mechanical systems. Shakers and controllers are techniques used to test vibration issues.

What is harshness?

Harshness is generally used to describe the severity and discomfort associated with both vibration and noise. It is a qualitative system based on desired characteristics rather than on quantifiable measurements.

NVH testing

NVH testing is widely used in the automotive industry for the reduction, design, and quality assurance of interior and exterior vehicle noise and vibration. The process usually takes place during vehicle development mainly in passenger cars, trucks, and other similar vehicles. 

NVH testing involves subjecting a full vehicle, component, or subassembly to vibrations at different frequencies, as a means of determining mode shapes and isolating buzzes, squeaks, and rattles. Typical instrumentation used to measure NVH includes microphones, accelerometers, force gauges, and load cells. Component and subassembly NVH tests are most commonly performed using a vibration shaker, while entire vehicles are usually tested on proving grounds or road simulator testbeds. 

Many NVH facilities have semi-anechoic chambers and rolling road dynamometers. Typically, signals are recorded by a data acquisition system directly to a hard disk via sensors and an ADC converter (analog-to-digital converter), and a suitable signal conditioner.

Improving NVH can be achieved by reducing the source strength, interrupting the noise or vibration path, or by absorption of the noise or vibration energy. Techniques used to help identify NVH include part substitution, modal analysis, rig squeak and rattle tests (complete vehicle or component/system tests), lead cladding, acoustic intensity, transfer path analysis, and partial coherence.