In NVH testing, the purpose of an anechoic chamber is not to create a space that is completely free of sound. What matters is effective control of background noise and sound reflections, so that the signal being measured is not masked by other sound sources.
That is why NVH test laboratories use anechoic chambers. When a sound source is placed in an environment with very low background noise and minimal sound reflections, engineers can more clearly identify where the sound originates, at which frequencies it occurs, and how it changes under different operating conditions.
For cars, motorcycles, and mechanical systems in general, this is particularly important. A subtle motor whine, brake squeal, or rattling noise inside the cabin can be difficult to detect during road testing. But when the vehicle is tested in a controlled environment, these signals become much easier to measure and analyze.
1. What is an Anechoic chamber
An anechoic chamber is a specially designed space intended to eliminate or minimize two major factors: external noise entering the chamber and sound reflections inside the chamber. Within an anechoic chamber, emitted sound is absorbed rather than reflected, resonated, or propagated along unwanted paths.
The walls, floor, and ceiling of the chamber are covered with wedge-shaped or pyramid-shaped sound-absorbing panels made from high-density porous materials. These panels can absorb more than 99% of incoming sound energy, significantly reducing reflections from different directions. The entire chamber is typically installed on a vibration isolation system to prevent vibrations from the ground, traffic, or surrounding equipment from being transmitted into the test environment.
In the automotive industry, NVH anechoic chambers are typically large enough to accommodate an entire vehicle and are equipped with roller systems, allowing the vehicle to operate at different speeds inside the chamber.
2. Why is NVH testing performed in an Anechoic chamber
When a vehicle is driven on the road, the microphone does not only pick up sounds from the vehicle under test. It also captures noise from other tires, wind, surrounding vehicles, construction sites, and many other sound sources.
This makes it more difficult to identify the actual source of noise. An anechoic chamber helps eliminate or significantly reduce these unwanted acoustic interferences.
When the vehicle operates inside an anechoic chamber, engineers can:
- - Accurately isolate individual sound sources.
- - Measure sound pressure levels with a high degree of reliability.
- - Compare data between different tests and vehicle models under the same standardized conditions.
- - Detect extremely low-level sounds that would normally be masked by background noise in a conventional environment.
This allows engineers not only to identify the sound source, frequency range, and sound transmission path, but also to consider component or vehicle redesign based on the measured parameters. As a result, the anechoic chamber provides significant value throughout the product development process.
3. NVH tests performed in an Anechoic chamber
3.1. Interior Noise Testing
This is one of the most common applications in automotive development.
Microphones are positioned at multiple locations inside the cabin, including the driver's ear position and the ear positions of front- and rear-seat passengers, to measure the noise levels actually perceived by occupants. The vehicle operates on a roller system at different speed ranges while engineers monitor the sound spectrum in real time. The objective is to determine which frequencies exceed the specified threshold and identify their corresponding noise sources.
3.2. Exterior Noise Testing
Microphones are positioned outside the vehicle to measure noise emitted from the exhaust system, engine, tires, and other external sources. The data is used to verify compliance with international standards such as ECE R51 in Europe, as well as the regulatory requirements of individual countries. This is a mandatory requirement for vehicle type approval and market access in many countries.
3.3. Powertrain NVH Testing
The engine or electric motor assembly is operated inside the anechoic chamber at different load levels and rotational speeds.
Engineers create an operating point map to precisely identify which combinations of RPM and load generate noise levels above the specified threshold. For electric vehicles, this testing is particularly important for controlling e-motor whine and inverter noise.
3.4. Wind Noise Testing
When combined with a wind tunnel or a wind-noise reproduction system, an anechoic chamber allows engineers to accurately analyze aerodynamic noise generated around the A-pillars, side mirrors, door seals, and gaps in the vehicle body.
This type of testing cannot be performed reliably on public roads because real-world wind speed and direction are constantly changing.
3.5. Squeak & Rattle Testing
The vehicle is subjected to vibration at different amplitudes and frequencies to simulate driving over rough roads.
Microphones installed inside the cabin record every sound generated during the test. In the controlled environment of an anechoic chamber, even a very slight squeak from a plastic clip inside the dashboard can be detected and located.
This is an extremely important test because squeaks and rattles are among the leading causes of customer complaints regarding perceived vehicle quality.
3.6. Brake NVH Testing
Brake squeal and brake judder are measured under controlled acoustic conditions to minimize environmental interference and obtain clean frequency-spectrum data.
Engineers can accurately identify resonance frequencies between the brake pads and brake discs, and then adjust the material properties or surface geometry to address the issue.
3.7. HVAC system testing
Fans, air ducts, and air-distribution mechanisms are tested independently inside the anechoic chamber.
The objective is to determine which fan speeds generate resonance, which locations within the duct system produce aerodynamic noise, and the overall noise level of the HVAC system under each operating mode.
4. Important notes
In NVH, measurement data is extremely important, but dB is not everything.
Two sounds may have the same sound pressure level, yet be perceived very differently by the listener due to differences in frequency, temporal variations, and the repetitive characteristics of the sound.
That is why vehicle development programs often combine objective data, obtained from sensors and microphone measurements, with subjective evaluation, in which engineers, evaluators, or test drivers sit inside the vehicle, listen to the sounds, and rate them according to a predefined evaluation scale.
Once a correlation is established between measured data and human perception, the development team has a stronger basis for making informed design decisions.
5. Commonly used standards
Depending on the purpose of the test, vehicle type, and target market, an NVH laboratory may apply a range of different standards.
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Standard |
Main content |
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Determination of sound power levels in acoustic test environment. |
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Measurement of interior noise in a running vehicles. |
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Requirements for exterior noise emissions form motor vehicles in Europe. |
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Measurement of interior noise in light vehicles. |
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Evaluation of human exposure to vibration. |
6. Where does the Anechoic chamber fit into the vehicle development process
The anechoic chamber is not the final step in the NVH testing process. Instead, it is used continuously throughout the vehicle development lifecycle:
- - Component development stage: Individual components such as motors, transmissions, and braking systems are tested before being integrated into the vehicle.
- - Prototype stage: The complete vehicle is tested and the results are compared with the NVH targets established at the beginning of the project.
- - Pre-production stage: Final verification is performed to ensure that the mass-produced vehicle meets all applicable internal and regulatory NVH requirements.
- - Production quality control stage: Random samples are taken from the production line to detect deviations from NVH targets caused by manufacturing variations.
For Vietnamese vehicle manufacturers expanding into international markets, data obtained from anechoic chamber testing is not only a basis for improving vehicle performance and acoustic comfort, but also provides technical evidence that the product meets the requirements and standards of individual export markets.
GPower Vietnam provides specialized NVH testing equipment and solutions, including acoustic microphone systems, accelerometers, and frequency spectrum analyzers for automotive testing laboratories. Contact us for detailed consultation.
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