Quantifying acoustic improvements

Discussion in 'Home Theater Projects' started by Josh~H, Jul 29, 2003.

  1. Josh~H

    Josh~H Stunt Coordinator

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    I'm trying to tame the acoustic "liveness" of my basement home theater: area rug, DIY wall treatments, etc.

    I wonder if there's some way to quantifiably measure the improvments I'm gaining by all this. i.e., some sort of relatively inexpensive instrumentation that will verify that I am indeed accomplishing the acoustic goals I set out to achieve. I know I should just be happy if "it sounds better," but I need some scientific evidence that my modifications are effective.

    Does anyone know if I can get what I think I'm looking for?
     
  2. Brian Corr

    Brian Corr Supporting Actor

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    The easiest/cheapest way is with a test tone cd and a Radio Shack SPL meter. (I suppose the clap test is the easiest and cheapest) [​IMG]
    By playing test tones and recording the SPL before and after, you can see how room nodes affect spl's at different frequencies before and after treatment.
    The next step would be to purchase software and a calibrated mic. That gets into the hundreds of dollars though.
     
  3. Josh~H

    Josh~H Stunt Coordinator

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    Well, as luck would have it, I just purchased the Radio Shack SPL meter this weekend. I used it to adjust the level of each channel to be uniform in dB where I'm listening.

    How would a test-tone CD/DVD help with this? Would I have to check out the dB level of various frequencies (at the same amp output) before/after changing part of the room? Wait, come to think of it, maybe the Avia disk I have has those test sounds. Is that a good one to use? Will the cheapie Radio Shack SPL be good enough to get the job done?
     
  4. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Hi Brian,

    Unfortunately, a sound-level meter with test tones won't give you any room "liveness" information. For this, you need to measure reverberation time. Test tones won't do this.

    The most popular method is to use a stimulus called a MLS (Maximal Length Sequence). You need some special software to process this, however, and this software tends to be expensive because it is designed for professional acousticians. However, I'm not a big fan of MLS because it is white noise (constant energy per frequency), rather than pink (constant energy per octave). This puts a lot of energy into the high frequencies, which could damage tweeters if you are not careful.

    Regards,
    Terry
     
  5. TimForman

    TimForman Supporting Actor

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    The only way I'm aware of short of buying MLS software and mics is the clap test. The first place to start is usually not where people think it would be and that's the ceiling. It doesn't take much to build a couple of acoustic panels and hang them from the ceiling. The biggest reason for starting with the ceiling is that many modern HT speakers are designed with reflective wall resonances in mind. If you dampen your walls without considering this you may be doing yourself and your speakers a disservice.
     

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