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Anechoic Chambers

 

What is an Anechoic Chamber?

IAC Acoustics offers both Anechoic and Hemi-anechoic chambers.  Anechoic rooms are fully lined with anechoic wedges, including the floor, to create a specific controlled test environment for professional acoustical testing.  Hemi-anechoic rooms are of the same design and configuration, however they are equipped with a sold floor, to facilitate the testing of large and heavy objects whose typical application would be on a reflective pane. Both test facilities allow for precision acoustic testing to benchmark research and product development to ISO measurement standards.

An anechoic chamber can be considered similar to a precision acoustical measurement instrument, providing a free-field environment without noise interference or sound reflection. In an ideal free-field environment, the inverse square law would function perfectly. This means that the sound level from a spherically radiating sound source decreases by 6dB for each doubling of distance from the source. For a free field to exist with perfect inverse square law characteristics, room boundaries must have a sound absorption coefficient of unity at all angles of incidence. In practice this is usually not quite perfect and deviations from the inverse square law are to be expected.

IAC Acoustics has installed hundreds of hemi-anechoic facilities to universities, research laboratories and test houses. Our range of single and double wall construction rooms allow for high precision measurements to be carried out in a hemi-anechoic environment.

The IAC Acoustics fully anechoic room is designed for the research physicist or engineer who must make precise sound measurements in a free-field acoustic environment. rooms provide high sound transmission loss (TL) characteristics and have a completely anechoic wedge lined interior to meet these requirements.

Construction of Anechoic Rooms

For anechoic rooms to function well, a number of acoustic, mechanical, electrical and aerodynamic considerations apply. These will include some, or all, of the following:

 

  • Anechoic treatment selection
  • Cut-off frequency
  • Internal acoustic ambient noise level
  • Noise reduction
  • Vibration isolation
  • Silenced ventilation systems
  • Acoustic doors – operation and sizing
  • Interior floors – suspended cable floors
  • Lighting and electrical systems
  • Overall structural design considerations
  • RF shielding requirements

Anechoic Wedges

One practical well proven method to achieve a free-field is to shape sound absorbing material into wedge configurations for mounting on to the interior surfaces. The wedge shaped geometry ensures a gradual change in the acoustic impedance of the transmission media, ensuring that sound waves are absorbed by the material, rather than reflected at an interface. The effectiveness of the absorption depends on the geometry and materials used. The lowest frequency at which the absorption is effective (cut-off frequency) is inversely proportional to the depth of the wedge. IAC’s own impedance tube is used for critical adjustment of wedge dimensions before finalising each design. Due to variations in material characteristics, statistical quality control measures are employed during wedge production to ensure specified acoustic performance.

Talk to us today

Please contact us for advice relating to your new project.

Scott Simmons

+44 (0) 1962 873018
+44 (0) 7803 234084

 

National Physical Laboratory - NPL

 

  • Fully anechoic facility
  • 125Hz cut-off frequency
  • ISO 3745 compliant for pure-tone anechoic chambers
  • Unique twisting basket door arrangement
  • Fire retardant foam wedges
  • Integrated microphone positioning system

“Since its commissioning, the NPL freefield chamber has been used extensively, delivering world-class measurement results in a number of research projects, for example in characterising novel transducers, as well as reliable calibration data for our clients. In a recent international project to evaluate methods for determining the free-field performance of sound level meters, results determined in the NPL chamber were found to be comparable with data from other laboratories where post-processing had been applied and were significantly better than others where such techniques were not used.”

Richard Barham, Principal Research Scientist, NPL

Anechoic Chamber Applications

  • Microphone Calibration
  • Sound Level Meter Calibration
  • Psycho-acoustic Testing
  • Sensory Deprivation Testing
  • Speaker Research & Development
  • Acoustic Science
  • CE Marking & Certification
  • Hearing Research

Solent University - Southampton

 

IAC was approached by Solent Acoustics, part of Southampton Solent University, to build and commission a single-walled hemi-anechoic chamber, to enable teaching and research for its students.

  • 100Hz cut-off rating
  • Very high performance for a single wall construction
  • Chamber used for practical laboratory testing
  • Microdyne foam anechoic wedges used

“I am more than happy with the level of performance of the hemi-anechoic chamber installed by IAC Acoustics. Having specified a cut off frequency of 170Hz we were very impressed when the chamber achieved 100Hz, enabling us to take a wider range of measurements at lower frequency. Overall the project ran smoothly and it was a pleasure to work with IAC.”

Christopher Barlow, Associate Professor of Acoustics

Satra Technology

Formed in 1919 SATRA helps manufacturers and suppliers to evolve by providing technical knowledge, research and testing. Currently commissioned for testing various PPE items such as high visibility clothing, footwear and protective eyewear, SATRA wanted to be able to offer testing of hearing protection to their portfolio. In order to certify, test and develop products such as ear defenders for various manufacturers, an anechoic chamber was required.  You can view a time lapse of the chamber build here:

“The new hemi-anechoic chamber will help to widen the range of services SATRA is able to provide, not only for hearing protectors, but hopefully other products in the future. Overall the project ran very smoothly and the new chamber performs very well.”

Andy Todd, SATRA Acoustic Engineer

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