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Anechoic and Free Field Chambers

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Ant Miller Ant Miller | 09:02 UK time, Thursday, 7 January 2010

Welcome back from the Christmas and New Year break- we took a little time out here in R&D to recharge batteries, fuel cells and exotic energy systems, as we have a tremendously exciting few months ahead of us.  We'll post about that soon, but lets kick off the new year with another great video from Quentin Cooper's further exploration of R&D.

In today's film Quentin meets with Chris Chambers and Ranulph Poole, two of R&D's most experienced engineers, and explores the peculiar spaces that are our 'controlled environments'.

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[Ed:- we've finally managed to get a corrected version of this film up- apologies for the delay in the corrections]


  • Comment number 1.

    This Quentin's commentary is so poor. It's an anechoic chamber, meaning an acoustical free field. So you don't get reflections. Hugely unnatural, he says. Wrong. Can't hear my footsteps! Wrong again.
    The acoustical environment is so "unnatural", you'd have to, for instance, walk as far as your nearest park to get the same effect. The difference between an anechoic chamber and a park, is that in the park there would be other disturbing noises. So you build thick walls to block all that out, but walls make reflections so then you load the inside with all the wedges, to get back to where you were, but no outside noise. If the presenter felt anything unnatural, it wasn't the lack of reflections -- it was the overall low noise level. Science reporting at it's golly-gee worst.

  • Comment number 2.

    In Quentin's defence, I think these comments are a little unfair, though I agree that the commentary could have been a little more accurate (unless he actually does have training in acoustics, in which case, I think he needs a good talking to).

    I would say that the extremely low noise level is about as unnatural as the lack of reflections i.e very unnatural, especially when they happen (or rather, don't happen) together. As you point out, an anechoic chamber implies an acoustic free-field. However, to take the example of a park- even in the very unlikely event of there being no background noise, this would not really be free-field conditions; in the video we could see that the floor was also acoustically treated and only partly covered by grids, so pretty close to free-field simulation. To find a naturally occurring effect such as this (forgetting the noise issue for a moment), you could go to your nearest park, but you'd also have to levitate quite a way off the ground. (However, had the chamber been semi-anechoic, i.e. hard floor, absorbent walls, then the original park example would hold).

    I would be interested to see the data showing that chamber to be anechoic down to 40Hz though! Doesn't seem big enough.

  • Comment number 3.

    Tonkatonks asked for data on the chamber. I did some quick measurements before the site was closed. To be precise, I was told by someone involved in it's design that the room was anechoic down to a little over 40 Hz in the horizontal width only and is higher in the other planes. However, this was more detail than was wanted for this short video.
    The key dimensions are. Internal width slab to slab, 30 feet 6 inches. Internal depth slab to slab, 26 feet 5 inches. Height slab to slab, 20 feet 6 inches.
    The clear internal working space (within the room treatment) is 20 feet 6 inches wide, 16 feet 5 inches deep and 10 feet 6 inches high.
    In the video, more floor grid panels were installed to provide practical working space for filming. Under normal test conditions, only sufficient floor support posts and grid panels would be in place to support test items and provide access.
    I hope this is useful in answering your questions.

  • Comment number 4.

    All this user's posts have been removed.Why?


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