An Anechoic Chamber for SPCR

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THE SOLUTION: AN ANECHOIC CHAMBER

An anechoic chamber is a room specially treated to eliminate internal sonic reflections, or echoes. The etymology is obvious: An, meaning no, and echo: No Echo. A corollary is that it should be resistant to noise interference from external sources; ie, soundproof. I'd fantasized about building one like an underground bomb shelter beneath the garage and back yard, but that could only remain a fantasy for all kinds of reasons — not least of which was a guaranteed divorce! Last winter, it occurred to me that a more realistic approach is to convert an existing room in the house. Was this feasible? The question deserved some exploration.


The 12'x10' (with 8' ceiling) target room was SPCR's busiest and quietest lab room: Hard drives, fans, heatsinks and video cards were all recorded and measured acoustically here, with typical ambient levels of 18~20 dBA.


The other side of the room is also completely packed.

Since starting SPCR, I visited several anechoic chambers, two of which I've written about. The first is a full anechoic chamber at the University of British Columbia right here in Vancouver. This is one in which all internal surfaces of the room are treated to eliminate reverberation completely. In late 2002, I sought out the assistance of Professor Murray Hodgson at the Acoustics and Noise Research Group of the University of British Columbia; the man in charge of the UBC anechoic chamber. I was able to corroborate with Dr. Hodgson for a while, engaging some of his students in projects for SPCR. The close proximity made it seem possible for SPCR to establish a long term working relationship to access the anechoic chamber; alas, it is always busy with student projects, which take precedence over any non-UBC activities. Interestingly, it was not ideal for SPCR because the chamber is housed in a building that has a massive HVAC fan that's going almost all the time. Only when that fan is turned off does the ambient noise level drop low enough to measure the quietest computing products accurately.


The small UBC anechoic chamber is local; alas, too busy for regular access by SPCR.

The second anechoic chamber I wrote about is some 30~50' underground, at Gigabyte's headquarters in Taipei. Gigabyte's anechoic chamber is a pretty serious affair. It is a fairly large 5.5m x 4.8m x 3.1m hemi-anechoic room, which means the floor is deliberately left reflective, and the other five boundary planes are treated to be completely sound absorbent. This is the type of design most commonly stipulated in recent acoustics-related testing standards. The chamber was constructed at the end of 2002, and its sonic qualities are checked every two years by an independent consultant, Industrial Technology Research Institute. The residual ambient noise level in the chamber is reportedly 15 dB, unweighted, which is extremely low.


The residual noise in the Gigabyte chamber is an extremely low 15 dB, unweighted.

Like most anechoic chambers, both of the above have an outer skin of thick steel... just one of the umpteen technical features used in anechoic chamber construction. Discussions with various personnel in the acoustics industry revealed that typical anechoic chambers start at about $125,000. Over $200,000 is not unusual for a chamber of the size of Gigabyte's.



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