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I've just tested the frequency response of some fabrics. The results are interesting.

Discussion in 'Home Theater Projects' started by Jones_Rush, Oct 23, 2003.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Since I live outside of the U.S (and not even in a country which its main language is english), I knew I could never find the right word for "Burlap". Also, the PartsExpress.com transparent fabric is too expensive for me (with shipping and taxes...).

    This is why I've decided to go on a hunt for a cheap and good looking fabric which will attenuate as little as possible, up to 20khz.

    I've gone to a certain street in my country, where there are dozens of fabric stores one next to the other. I've showed them the PartsExpress fabric (I have a sample of it), and told them I need a similar fabric, which will not stop the sound waves.

    The sellers all used the same technique: they blew air from their lung, right into the PartsExpress fabric. Then, they searched for a fabric, which will be as easy to blow to, as the PartsExpress fabric was.

    All of the fabrics they found, where kind of transparent. I've taken a few samples of the fabrics (all black) which were the most non-transparent, and when placed right against an object, could cover it completely with black.

    I've went back home, and used the following method to check out the fabrics:
    I've put my RS SPL meter about 50cm from my nOrh 9.0 speaker (which should be flat to 20khz). Then, I've created (using the computer) a 16khz, 18khz, and 20khz sine sweeps. I played each sine sweep one time with the fabric on the speaker (tightened with sticky paper), and one time without it. I've written the changes in SPLs.

    These are the conclusions:
    Unless my method of testing is faulty, the conclusion is simple: people were selling you lies for years. Acoustically Transparent fabrics are easy to find, can look very good, and are dirt cheap. With most of the fabrics I've tested, there was no SPL deviation between the time when the fabric was on the speaker, to the time it was off, up to 20khz.

    Just to be sure I didn't mess the experiment, I've also taken some fabrics which it's very hard to see through (but are still pretty thin). They were definitely NOT acoustically transparent. I've measured deviations of 4-5 dB SPL, already at 16khz.

    I can't believe that so many of you were suckers for the ugly Burlap, or the expensive commercial "acoustically transparent" fabrics. The sad truth is that if I had a choice to get Burlap, or the PE fabric for a lower price, I would have probably gone with it, without thinking twice.

    Oh, and by the way, the PE fabric isn't totally acoustically transparent. It is about -1.5 dB at 20khz. Not that it matters that much, but still, If someone decides to pay so much for a fabric, he should at least get good performace out of it, don't you think ?.
     
  2. ThomasW

    ThomasW Cinematographer

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    Interesting.....

    FWIW the RS meter isn't the least bit accurate at anything above ~8Khz

    Obviously there are no fabrics that are totally 'acoustically transparent' at all frequencies. Even the best ones will absorb some high frquency info. This is why hardcore audiophiles never use grill cloths.

    For sound absorbing panels, acoustical transparency isn't an important issue. The reason burlap is recommended for the sound absorbing panels (and not speaker grills) is that it is a natural fiber (less reflective than synthetics) with a loose open weave, that absorbs sound fairly well, and it's usually cheap.
     
  3. Jones_Rush

    Jones_Rush Stunt Coordinator

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  4. TimForman

    TimForman Supporting Actor

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  5. MichaelDDD

    MichaelDDD Supporting Actor

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    That is interesting stuff, Jones_Rush. [​IMG] Lots of research on your part. Thanks for sharing the results with us.
     

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