An Anechoic Chamber for SPCR

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ACOUSTIC RECORDING REPORT

For consistency, and also because it's very revealing, I made an acoustic recording that begins in the converted kitchen lab just outside the anechoic chamber, then finishes in the anechoic chamber. It's a downloadable MP3. There are some loud handclaps, so don't set the volume too loud.

* Acoustic report, SPCR anechoic chamber, Oct 2008 - MP3.

* The earlier acoustic interim report MP3 made in the bare room after the window was sealed up, before it saw any of the blue fill.

* Ambient noise in "kitchen" lab room vs. anechoic chamber - short MP3: 18 dBA in a live room vs. 11 dBA in the dead room. The much lower white noise (random noise that sounds like hiss) is due large to the absence of echoes in that frequency range.


CONCLUSIONS

The new anechoic chamber meets most of the initial objectives established for this project. It provides a much quieter space for accurate testing of ever quieter gear, and much higher freedom from external noise. There's both breakthrough and echoes at low frequencies, but the cost and complexity of eliminating these is daunting, and it may just be impossible to achieve in a room of this size in a conventional house. There is room for improvement, however, so don't rule out further changes in the future.

The chamber and the new gear acquired to take full advantage of it has been in use for three months. The improved low SPL accuracy and range has improved the resolution of acoustic analysis in our reviews, and the broad capabilities of the audio spectrum analyzer are only just beginning to be utilized. In time, as the number of reviews in the new chamber with the new equipment grows, the SPCR database of computer noise should become even more comprehensive, detailed and accurate than it is today. It's probably safe to say that SPCR is unique among computer technology web sites in owning an anechoic chamber, the acoustic equipment to make use of it... and hopefully, enough know-how to pull it all together in informative, entertaining articles that do more than promote the latest passing computer gadget.

FUNDING THE PROJECT

In April 2008, I asked the SPCR community for help to fund this project. Corporate sponsors were also contacted. Both readers and corporate sponsors responded generously, with cash donations from readers, and product gifts, randomly awarded to the individual donators, from the corporate sponsors. It was a successful fundraiser; some $11,000 was raised for the project in about one month. The progress of the fundraiser was documented as it unfolded in this lengthy forum thread.

There are too many individual contributors to name them all (some 300), and most want to keep their privacy. To all of you: My heartfelt thanks! Without you, this project would not have gone forward.

The corporate sponsors also deserve recognition, thanks and praise for their part in offering giveaway prizes for individual contributors. Their support is much appreciated by everyone involved with SPCR!

-- digg this article! --

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Other SPCR articles of related interest:

New Audio Test Gear, SPCR 2008
Exclusive Tour: Gigabyte's Anechoic & Thermal Test Chambers
Audio Recording Methods Revised
SPCR's Test / Sound Lab: A Short Tour
University of BC Fan Noise & Airflow Research Project

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Discuss this article in the SPCR forums.

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REFERENCE SOURCES

Selected Web Sources on Soundproofing, Anechoic Chambers and Acoustics

  • Brüel Acoustics - Web site of Italian acoustic consulting company with many useful articles about testing, chambers, etc.
  • Canadian Building Digests - Canada National Research Council's publication includes many informative articles about noise and buildings.
  • Magical Floating Floor and Sound Proof Walls - Article on Building a Home Recording Studio by Revolution Audio, a Canadian store for home recording studio products and services.
  • Sound and hearing - Highly informative section in HyperPhysics, an exploration environment for concepts in physics maintained by Carl R. (Rod) Nave, Department of Physics and Astronomy at Georgia State University in Atlanta.
  • Sound Transmission Class (in the Acoustic Info section) - Good summary of STC by State of the Art Acoustik, a Canadian architectural acoustic design company.
  • Eckel Industries - Major designer / builder of anechoic chambers.
  • Anechoic Chamber - description of Meyer Sound's chamber.
  • Orfield Laboratories - It's anechoic chamber is officially the quietest place on earth... better described by Ode Magazine and Audio Junkies.

Web Links for Selected Audio Measurement / Sound Control Products (Many of these sites also provide extensive sound control information)

  • Green Glue - A unique damping material applied between sheets of drywall that can dramatically decrease sound transmission. Lots of info and data on applications, along with suggestions for effective use.
  • UltraTouch - Replacement for fiberglass batting insulation made almost entirely of recycled and recyclable natural denim and cotton fibers.
  • Mason Industries - Maker of vibration and noise control products offers damping pucks made of neoprene or steel springs for resilient floors. The section on architectural engineering has many detailed applications for their products.
  • LinearX Systems - Manufacturer of numerous professional computer-based acoustics design and analysis tools.
  • Brüel & Kjær - Still the biggest name in acoustics instrumentation such as sound level meters and spectrum analyzers.
  • DPA - Mic division spun off from Brüel & Kjær in 1992, now a major quality microphone manufacturer with a huge product range.
  • Quiet Solution - Makers of QuietRock, one of the most popular drywall substitutes for improved acoustic isolation. Huge range of other soundproofing products. Plenty of interesting documentation.


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