Bass traps

Discussion in 'Room Acoustics, System Layout & Setup' started by Chipbyrd, May 25, 2012.

  1. Chipbyrd Audioholic Intern

    Chipbyrd
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    I am putting in some DIY bass traps.* I have 4x24x48 rigid fiber glass.* From what I have seen, it won’t be hard to make the trap.* I can make a frame, upholster it, and stick it in the corner.* But here’s where I have a couple questions.* First, what if I put another 16” piece behind the 24”?* Is that overkill? *It seems like more would be better, as shape of my room is odd and I actually have five corners.* *Would the extra piece likely make a significant difference in that configuration?* And second, I was thinking about making a decorative shelf to set on the trap.* If it is closed on top will it decrease its effectiveness?
    *
    Thanks you in advance for your help.
    *
    Chip****
  2. Gordonj Full Audioholic

    Gordonj
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    Chip did you ever make your bass trap? Either way comment back and I might be able to give some advice. Sorry for not looking sooner....

    Gordon
  3. Chipbyrd Audioholic Intern

    Chipbyrd
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    Thanks. I did put them in. I decided to use superchunks with a 24" face up to 4'. In the ceiling corners I made solid pyramids out of the 703. I also put up absorption at all first reflection points, except the ceiling. Haven't had the time to get to them. My wife is in the process of finishing all the upholstering.

    As soon as we are all finished with this stage, I want to build some diffusers for my back wall nad perhaps a couple other areas. At that point, I will undoubtedly have many questions.

    Thanks again.
  4. Gordonj Full Audioholic

    Gordonj
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    Let us know. I would enjoy rolling the sleeves up ;):D
  5. ctciatti Enthusiast

    ctciatti
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    I would like to do this too. Can't wait to see how they turn out.
  6. Chipbyrd Audioholic Intern

    Chipbyrd
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    I can't get my pictures to upload
  7. jbrown15 Audioholic Intern

    jbrown15
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    Would it be better to build bass traps out of OC703 or Roxel safe and sound?
  8. Gordonj Full Audioholic

    Gordonj
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    That is a good question. If you do a comparison of the Owens Corning 703 boards vs. the Roxul Safe-n-Sound vs standard mineral wool you can see some things.

    You would need to compare the Sound Absorption Coeffiecnts of each of the products for a direct comparison. Since in a DIY project it would be impossible to find the Coeffiecents of that specific build we can then only use the test data we have avaiable. Since most data does not go beyond 4" thickness we would need to compare the 4" thickness numbers. Also, we need to make sure that the test data are considered equal. In this case we would need to make sure that we verify that the product is all tested in a Type A mounting (meaning flat on a solid backing surface).

    Just looking at the 125 and 250 Sound Absorption Coefficents we can see what product performs the best at the given thickness.

    703 - 125hz = .17 250hz = .86 (2" max given)
    Safe - 125h = .52 250Hz = .96 (3" thickness only given)
    Wool - 125h = .35 250Hz = .65 (3" thickness)
    Wool - 125h = .45 250Hz = .90 (4"thickness)

    Based on that little bit of information it would seem that the Safe-n-Sound would perform better then the others. However, that only shows absorption down to 125Hz. With products such as this the numbers drop off very quickly below 125Hz. This is due to the fact that most porous materials are laid out in layers. For this reason the acoustic properties vary depending on if the sound incident is parallel or perpendicular to the fibers making up the porous material and that porous material in these thicknesses can not absorb the energy levels suffcicent to reduce LF.

    For fun here are numbers from a standard 3" and 4" thick absorber panel not specifcally a bass trap.

    RPG 3" Absorber Panel - 125Hz = .56 250Hz = 1.09
    RPG 4" Absorber Panel - 125Hz = .76 250Hz = 1.12

    Due to the limited ability to test LF panels in labs it becomes tricky to get good absorption numbers for products in the lower regions (below 125Hz) but here are some good products from a well respected manufacture company that we utilize all of the time.

    RPG "Modex Braodband" 4" thick -

    63Hz = .50 100Hz = 1.00 160Hz = .82 250Hz = 1.01

    RPG also has another product called "Modex Edge" that looks great. A stackable bass trap that can be for the corner or on a flat wall. It comes ready to place and can be stacked. Therefore, a easy way to tune the LF in a room with pre-made bass traps.

    And hopefully I answered the question...

    Gordon

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