DIY acoustic panel help/advice

Discussion in 'Home Theater Projects' started by BrianKR, Aug 31, 2003.

  1. BrianKR

    BrianKR Second Unit

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    I read everything I could find on building my own acoustic panels and I think I am ready to go? .

    Which way is better for acoustic panels;
    build frame, place the unfaced side outward, cover with fabric than hang the completed board firmly against the wall;
    or
    cut 2 pieces of rigid FB (ex: 2 - 24" x 60") and place both faced sides against each other, making a sandwich with the faced sides in the middle,
    then place it in a frame, cover with fabric and place it 1" off/away from the wall?

    Is there any 'acoustical' benefit to using batting over the rigid fiber board before covering with fabric?

    Last question; should the sides of the panel (framing) be perforated?
     
  2. Pete Mazz

    Pete Mazz Supporting Actor

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    What are you trying to accomplish with the treatments?

    Pete
     
  3. Greg Monfort

    Greg Monfort Supporting Actor

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    I didn't quite follow all that, but the object is to either make a diaphramatic, helmholtz, or aperiodic absorber. In each case there's a cavity of some calculated depth, so this cavity is sealed. The front panel will either be a flexible panel, a ported one, or a perforated one. Stuffing the cavity lowers the Q of the absorber, making it effective over a wider BW. Covering the face of it lowers its reflectivity to frequencies higher than it's designed for and increases SAF.

    Does this answer your questions?

    GM
     
  4. BrianKR

    BrianKR Second Unit

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    >What are you trying to accomplish with the treatments?<

    Asorption for high and mid frequency mostly.


    >Does this answer your questions?<

    Some of them yes
     
  5. ThomasW

    ThomasW Cinematographer

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  6. BrianKR

    BrianKR Second Unit

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    Why use pegboard for backing if the panel is to be placed against the wall? What acoustic purpose does it serve? Reason for asking; hardboard is cheaper and even a little stronger.
     
  7. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Those acoustic panels actually perform well when they are slightly away from the wall. My panels have 4" of space between them and the wall which use pegboard, 2x4s, and a fiberglass/polyester sandwich.

    I found the pegboard had a few advantages over hardboard. One side of the pegboard is very coarse and fuzzy, this grips the polyester or fiberglass and prevents it from sliding around. It also has holes that can act as marks, or you can use them to put screws into. I think the main purpose of this backpanel is to add strength. I built mine a while ago and there is still no sign of sag, just some discoloration to a panel's fabric that was left near a window. I guess burlap isn't very colorfast.

    I think pegboard will also breath easier which probably doesn't really help it that much.

    I believe thick soft batting has better absorption over thin rigid fiberglass (Especially in high frequencies). I would use the rigid fiberglass as a backing or just by itself. You could always use the compressed fiberglass or sound board as a backing with the batting exposed for best performance. Either that, you can just use fiberglass batting backed with your hardboard.

    If you put rigid fiberglass in front of the batting, then some high frequencies may be reflected from the compressed fiberglass that would have been absorbed by the soft batting.

    The goal is you want the cover cloth to let as much sound pass through. Burlap is probably the most acoustic transparent material out there but it may not fit your decor. Using single knit polyester will also perform very well. When you start to use tight or thicker fabrics, the absorption will begin to suffer. Muslim is cheaper than burlap but looks pretty nice when it's pressed onto a rigid panel.

    I also don't think there's any benefit to be had by perforating the side braces.
     
  8. Pete Mazz

    Pete Mazz Supporting Actor

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    Rigid fiberglass of 3 lbs density, like Owens Corning 703, is a much better absorber than regular fiberglass or batting, for a given thickness. At 4" thick, it pretty well absorbs all but the lowest freqs.

    For a mid/high absorber, a 2" thick panel made with 703 would be all you need. May be a little tougher to find, tho. Contact drywall/insulation suppliers.

    Pete
     
  9. TimForman

    TimForman Supporting Actor

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  10. BrianKR

    BrianKR Second Unit

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    This is what I came up with.
    Pretty easy to build and they compliment the room.
    1 x 2's
    5 panels 60" x 24"
    1" Rigid Knauf
    build a frame open front and back
    place the Knauf in
    add batting to the front and back of the RFB
    then cover with transparent 'black' fabric
    I am hanging them 1 1/2" off the wall

    I also built 2 corner bass traps with regular unfaced R19 insulation and 8oz batting and 4 panels 6' X 2' with 2 x 3's and pegboard for behind my stage/false wall

    I am still building and covering them. I will hang them tomorrow. Thx for the input and I will let you know how I make out with them.
     
  11. ThomasW

    ThomasW Cinematographer

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    2"X6"s filled with R-19 aren't bass traps.

    Fiberglass bass traps need to be at least 12"-24" thick depending on the frequencies involved. Other effective bass traps are as GM stated resonators tuned to the desired frequency.
     
  12. BrianKR

    BrianKR Second Unit

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    Sorry Thomas.
    I guess I am not very good at describing what I am trying to build. I meant I am building 4 panels behind the stage made out of R19 and 2 x 3's 6'H by 2'W.

    The bass traps I am building from the floor to ceiling in the corners stuff with unfaced owens R38 insulation. I will try to take some pictures of what I am building tomorrow and post them.
     
  13. TimForman

    TimForman Supporting Actor

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    Sounds like the corner traps the guys at PS Audio made for their listening room. I like this idea.
     
  14. Chris Carswell

    Chris Carswell Supporting Actor

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    Anyone else try the Knauf fiberglass duct board?
     
  15. ThomasW

    ThomasW Cinematographer

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  16. Chris Carswell

    Chris Carswell Supporting Actor

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    Thanks Thomas but that's who I originally got the idea from. I just wanted to see if anyone has used it compared to other designs.
    I finally got my A.EXP mag (address change really makes it snail mail [​IMG] ). Great write up so far. Did you help any with that or was Jon the sole author?

    BTW, on your site, what is used for "FrontView1.jpg" ? Is that a RD-75, a carver, or ??? What is used for the low end? How do they sound? I had a set of Spectra II & now regret selling them [​IMG]
     
  17. ThomasW

    ThomasW Cinematographer

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    Hi Chris

    Jon's the author, my job was proof reader :wink:

    That pic's part of Victor B's amazing RD-75 hybrid array.

    [​IMG]

    Here's a link to more info
     
  18. BrianKR

    BrianKR Second Unit

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    TomW, those speakers are insane!

    I finished building and installing my rigid FB panels lastnight. They more than did the trick with the hard echo/hand clap problem I had in the room.

    I am just getting started on a bass trap design and I should have it completed and installed by Saturday. My room is still a little on the boomy side. If the traps do the trick my HT room will finally be completed. All I will need to add is a FP and upgrades in time.
     
  19. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I like how the picture was taken from down low, it makes the speakers appear monumental. Wait, they are monumental...
     
  20. Jones_Rush

    Jones_Rush Stunt Coordinator

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    I looked at Keith Kidder's website, and noticed that at the and he admited that the room makes the speakers sounds a bit soft on the high frequencies.

    I was wondering if the reason for this could be that he used only a 1" fiber glass absorber, plus, he gave no space from the wall. I think this sould mean that his absorbers will only make a good job starting from about 1khz. Leaving the entire bass and mid range reverbration higher in SPL, and uneven to the upper frequencies.

    He did used some bass traps, but maybe they are not enough, or simply does not do the job well. I never seen such construction of bass trap before. To me it seems like a regular panel placed at the corner, and if this pannel is again that 1" fiber glass "kanuf", then even with the relatively large distance from the wall, it still shouldn't do too much work at the lower end.

    Imo, if he used 4" thick fiberglass for all his panels, and put a 4" distnace from the wall, for all panels, he should have gotten a much more ballanced sound, because it doesn't seem like he has too many panels in his room.

    One last thing, isn't his HUGE untreated window between the speakers is a very bad thing, and kind of an anti thesis to everything he is trying to accomplish ?.
     

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