O.K. Please help! Add sound absorption panels or not add them??

Discussion in 'Home Theater Projects' started by Curt Luther, Oct 14, 2003.

  1. Curt Luther

    Curt Luther Stunt Coordinator

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    I have my top half of my dedicated home theater room drywalled now and I am wondering if I should be using sound absorption or not on the bottom half. I planned on installing 1/2" fiber board over top of the drywall half way up the wall and then cover it with a light duty carpet. All of my walls are filled with R13 insulation and then a layer of 30lb roofing felt and then the drywall. If I should use the 1/2" fiber board for sound absorption then I will, I want to do it the right way, but I look at alot of pictures of members rooms and I don't see that they used anything half way up the walls. Please help before I install the bottom row of drywall. If I don't need to spend the extra $$$ then I won't.

    Thank you,
    Curt
     
  2. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Fiberboard is not an effective sound absorber! It has some utility for sound isolation (= noise blocking = "soundproofing"). Thin carpet will have some modest sound absorption effect, particularly at high frequencies.

    Most people use a MINIMUM of 1/2 inch of rigid or semi-rigid fiberglass for sound treatment, covering a substantial area of home theater walls. Thicker (up to several inches) will reach into the bass frequencies. Commercial movie theaters typically use a 1 1/2 inch layer. Untreated drywall is pretty reverberent, and will seriously compromise the quality of your home theater sound.

    How much treatment is necessary? This depends on the particular room and construction. Thorough acoustical testing provides the answers. This is just starting to catch on in the industry.

    Regards,
    Terry
     
  3. Curt Luther

    Curt Luther Stunt Coordinator

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    Thanks Terry,

    Would the rigid fiberglass board go under or over the drywall. It sounds like it would not be as resistant to damage as drywall. If it goes over the top of drywall, what do most people cover it with? Do you buy it at home improvement stores? Any help would be great.

    Thanks,
    Curt
     
  4. Tab Nichols

    Tab Nichols Stunt Coordinator

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    Here is a good look at building sound absorbing panels... most people agree that a thin burlap is the best cloth for covering them, as it is somewhat "acoustically transparant."

    Three of them is a good start, at the most important reflection points in the room. These points are where the first sound reflections bounce off the left and right walls, and the cieling, between the speaker and the listening point.

    To find this point, sit in the listening position, and have someone hold a mirror on the left wall. When you can see the speaker in the reflection in the mirror, that is where the panel should go. Do the same for the left wall, then the ceiling.

    This covers your most important reflection points, and will help stop the room from being so reverberent. It will increase audibility, and improve stereo (and surround) imaging.

    Some will disagree with doing a panel on the ceiling, but I think it is just as important.
    Good luck!
     
  5. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Another very popular covering is fabric specifically manufactured to be acoustically transparent. Guilford of Maine's FR701 series is the "standard" for this. The advantage over burlap is aesthetic - these fabrics come in a wide range of colors and styles.
     
  6. patrick korn

    patrick korn Auditioning

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    i have bought my self a apartment and y want to decorate my home theater room but wat is the best way that?the neighbores won,t hear the big noise thats coming out of my appartment.
     
  7. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Hello Patrick,

    There are two parts to home theater acoustics: "sound treatment" and "sound isolation". They are very different. Sound treatment is what makes the movie soundtrack sound accurate and realistic inside your home theater. Sound isolation is what blocks the sound from passing through walls and anoying your neighbors.

    Sound treatment is most often done by adding soft, thick surfaces on walls, ceiling, and floor. These absorb sound waves at a wide range of frequencies, reducing reflections so that the room has much less reverberation. High reverberation creates bad distortion and makes dialog hard to understand. Hard walls, ceilings, and floors will usually limit home theater sound to being no better than poor to fair.

    Sound isolation means using heavy walls and other structures to help block the transmission of sound. The room also has to be very well sealed so that sound doesn't leak through any cracks.

    Sound isolation is done when the room is built. Sound treatment can be done afterwards. So unless you are prepared to do some significant construction, it may be too late to have an ideal home theater and spare your neighbors from the noise.

    I can think of two easy and inexpensive things to do which may help:

    1. Seal any cracks in walls, ceiling, around electrical boxes, etc. using non-hardening acoustical caulk.

    2. Lower the sound in your home theater. Use "night listening" mode on your receiver. This lowers the dynamic range so that you can still hear the dialog with the volume turned down. This does compromise the sound quality, but it may be your only option at this point.

    Regards,
    Terry
     
  8. Curt Luther

    Curt Luther Stunt Coordinator

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    O.K. I found two different rigid boards at Home Depot, they are as follows:

    Super Tuff- R Polyisocyanurate foam board made by Dow.
    It has a tough black backing on both sides and has a foam type material in the middle and is 1 inch thick and is a 4'x8' sheet. $12 a sheet.

    the other:

    Insulation sheathing and is made by Owens Corning and is Pink and is not as sturdy and comes in 3/4" and 1" thickness $9 a sheet

    Will either of these work and which one would be better? Also, I assume it goes over the top of the drywall???

    Thank you,
    Curt
     
  9. Terry Montlick

    Terry Montlick Stunt Coordinator

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    I don't know the specific acoustical properties of either of these types of foam board, but in general, foam board does not have very high sound absorption. It is not open celled and porous, and is far inferior to unfaced fiberglass.

    You won't find rigid or semi-rigid fiberglass at Home Depot, I'm afraid. It's primarily for industrial use, for heat and sound insulation of HVAC ducts. I'm most familiar with the Owens Corning 700 series, but Johns Manville Linacoustic duct liner is pretty much equivalent. Check the yellow pages for industrial insulation suppliers.
     
  10. Sonnie Parker

    Sonnie Parker Second Unit

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    The John Mansville Linacoustic Permacoate is what I have researched and found several professionals are using. It works great for the bottom half of the room. This can be purchased in rolls. The 1/2" X 4' X 100' roll should cost around $150. You can also get it in 1" thickness if you so desire.
     

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