Applications of Anechoic and Hemi Anechoic Chambers
Our society is far more environmentally aware than it was a generation or two back. While that is largely a good thing, it does present industry with a lot of problems. In most areas of Australia, development and expansion plans are now subjected to ever more rigorous noise-control assessments. The success of many proposals depends on being able to provide both accurate figures for the noise that appliances, tools, machinery and traffic will generate and detailed proposals for controlling it within limits acceptable to neighbours, workers and wildlife.
Before a new vehicle can be released to market for example, it should be tested and brought into compliance with state and national planning standards. The companies that produce noise control products and test facilities also have to ensure facilities meet these standards, creating tightly controlled acoustic environments.
Building Sound Suppression Chambers
An insulated test environment is essential before accurate noise analysis can be assessed. Typically developing the test environment is a bigger challenge than either the measuring devices or the software that analyses their output. They are not simply sound-proofed from outside noise but have to be able to provide a cut-off frequency whereby all sound above the frequency is removed, in order to effectively measure sound within. Measurement is not simply about volume, but has to plot what kinds of noise occur where and under what circumstances
Chambers can be either of an anechoic chamber or hemi-anechoic design detail. An anechoic chamber is insulated on all six sides of the chamber, using sound-absorbent materials with precise shapes and sizes (anechoic wedges) to control frequency cut-off. In comparison, a hemi-anechoic chamber utilises a solid floor, with anechoic wedges on five sides only. Solid floors are obviously important for practical access and load-bearing, but they also provide opportunities to examine how sound will be affected by real-world roads and floors. In an anechoic chamber, the only flooring provided will be a light mesh suspended floor above the anechoic wedges, just sufficient to position and retrieve equipment. Even those are sometimes retracted during testing.
Both types of chamber are usually designed for a particular testing scope and frequency requirement, or full ISO standard. Their size is mostly determined by the equipment being tested, but it can also be chosen to eliminate particular sound frequencies. Chambers will vary from the extremely large (for automotive testing) to the very small, perhaps the size of a small fridge, used to test small components like mobile phones or an electric toothbrush.
Hemi-anechoic Chamber Testing
The solid floor in a hemi-anechoic chamber can allow you to reproduce the intended operating conditions. It is not unusual for mechanical appliances to generate unexpected noises in service because they readily interact with the flooring they are stood on. The chamber therefore provides insight into the product development phase and requirements for anti-vibration control for products such as washing machines for example.
The development of some products is completely dependent upon being able to introduce a mix of absorbent, resonant and reflective materials: hi-fi speakers, amplifiers and musical instruments are obvious examples. Chambers are also frequently used to replicate concert hall conditions before a construction project.
Anechoic chambers often need to exclude more than just sound; they need to prevent the penetration of electromagnetic interference such as radio waves that would otherwise interfere with the product or sensitive measuring instruments.
Most soundproof chambers are effective down to about 10-20 dBA, but they can be made effective down to as little as -20 dBA if needed. IAC Acoustics offers a range of configurations for professional testing in areas such as NVH automotive test, psycho-acoustics, sensory deprivation, acoustic science and product development and calibration – perfect for scientists and engineers who need incredibly accurate measurements in a free-field acoustic environment to ISO standards.
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