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  1. #11
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    Oct 2006
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    Mpls, MN
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    Sound walls are made by offset studs on double thick walls. The studs from one side don't transmit mechanically to the sheathing on the other (which acts like a drum). 1' of air space might even be excessive, but Ed's got the right idea.

    My solution for the shop here was to sheathe the entire outside with 1.5" pink high density foam as an underlayment to the insulated siding. Combined with the R19 and 5/8" sheetrock, it's very effective (and has an R value approaching 30). I can barely hear my air compressor on the other side of the wall from it. All seams were taped with house-wrap red tape.
    Syncrowave 250DX
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    Smith O/A rig
    And more machinery than you can shake a 7018 rod at

  2. #12
    Join Date
    Sep 2005
    Location
    Orlando / Daytona, FL
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    143

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    Some good thoughts here. I did use double stud construction in part of the building (since its overall 40x60 but the sound proof room is only 40x20). I know roll up doors are only good for 10db reduction (I have about 100db total, and would like to get that down to 60-70db), but if I did add another roll up door that was 8-10" from the existing garage door I may get 15 or 20db reduction, due to the air space and isolation effect. I bought some of those big blue foam sheets today to play with, I am going to stuff them into the door and do a before and after db test, and then also build a wall with them on the outside to see how much DB is reduced.
    Justin Starkey
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  3. #13
    Join Date
    Sep 2002
    Location
    Clark County, NV
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    2,696

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    Have you looked at the stuff commercially sold for sound studios, the precut foam that looks like a bunch of wedges so sound doesn't bounce?

  4. #14
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    Oct 2006
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    Mpls, MN
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    Actually, the wedges are designed to absorb and diffract the waves. When they reflect (which does happen, even off foam), they're sent a different direction than their source as to prevent echos from being picked up in recording (which can cause smearing or even phase cancellation).
    Syncrowave 250DX
    Invison 354MP
    XR Control and 30A

    Airco MED20 feeder
    Thermal Dynamics Cutmaster 81
    Smith O/A rig
    And more machinery than you can shake a 7018 rod at

  5. #15
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    Sep 2002
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    Clark County, NV
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    True, Jim; thanks for the clarification. In fact, the serious sound studios (I know you know this, I'm just rambling...) have no walls parallel to one another to further help. This includes floor and ceiling, too.

  6. #16
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    Oct 2006
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    Mpls, MN
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    Yep, but ironically, if you want ideal sound reproduction you need a rectangular room of the golden ratio (or so the really kooky audiophiles would have you believe).
    Syncrowave 250DX
    Invison 354MP
    XR Control and 30A

    Airco MED20 feeder
    Thermal Dynamics Cutmaster 81
    Smith O/A rig
    And more machinery than you can shake a 7018 rod at

  7. #17
    Join Date
    Feb 2008
    Posts
    873

    Default Add mass loaded vinyl

    I don't know if it would be economically feasible in your case, but do consider the use of mass loaded vinyl such as the product shown at http://www.acousticalsurfaces.com/no...ylbar.htm?d=14.

    You should consider building a smaller enclosure around your dyno setup inside the garage. It's easier and cheaper to address the source than the whole building. Also, the placement can greatly affect exterior sound transmission as certain locations couple sound to your walls (or in this case, thin garage doors) better.

    Keep in mind that R-value and STC ratings are completely different animals. Higher R value doesn't translate into higher STC rating (unless you're talking about the single case of greater thickness of the same material). Block wall=terrible R value but great sound attenuation, fiberglass insulation=great R value, not the best sound dampening material.

    I presume from the title of your post that you want to confine the obnoxious roaring sound of race car engines to your garage so the police don't show up and write you a citation for disturbing the peace, and you don't care much at all about heat transfer.

    Put some MLV on your doors and see what a sound meter tells you.

    80% of failures are from 20% of causes
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  8. #18
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    Mpls, MN
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    Real Time Analysis has never proven mass loaded films to be all that effective in my experience (certainly not cost effective). The only car I ever witnessed where mass loading was proven effective at engine frequencies, was also filled with several hundred pounds of sand loaded "bondo-crete". A 3db measured reduction is audibly "half" but we don't hear linearly, so in order to cut a perceived volume in half, you really need more like 9db of reduction.

    Air is one of the best attenuators we know of (a vacuum chamber would be better). Keeping that air from bumping into more air is how we stop propagation of the waves. Fiberglass, poly fill, and a number of other foam mediums are all employed to convert acoustic energy into heat energy as the sound turns into motion in a heavier substance and thus is consumed. The denser the material, the faster sound travels through it, but the faster it's consumed with the conversion to mechanical energy (and thus heat). But longer waves (lower frequency) are able to travel much farther than higher frequencies so to mass load against them becomes extremely difficult. What range are you trying to isolate most?

    Isolating the air masses, and separating them with more isolated air masses is a very cheap and effective means of sound control. Adding mass to panels to try and increase the amount of energy needed to penetrate the panel is a very inefficient method as your point of diminishing returns is quickly met with the inability to use the door as it was intended.

    I second the idea to isolate the dyno inside the building. This adds your shop as the isolated air space around the dyno box.
    Syncrowave 250DX
    Invison 354MP
    XR Control and 30A

    Airco MED20 feeder
    Thermal Dynamics Cutmaster 81
    Smith O/A rig
    And more machinery than you can shake a 7018 rod at

  9. #19
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    Sep 2002
    Location
    Clark County, NV
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    Quote Originally Posted by Fishy Jim View Post
    Yep, but ironically, if you want ideal sound reproduction you need a rectangular room of the golden ratio (or so the really kooky audiophiles would have you believe).
    Now that is some interesting stuff! The Golden Ratio pops up all over the place! That might require some bedtime reading just to satisfy the piqued curiosity; thanks! So does the sound source go in the middle or is there another formula to find a focus, oh nevermind; now I've got homework; great...

  10. #20
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    Oct 2006
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    Mpls, MN
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    It's probably been 5 years since I paid any attention to the audiophile crowd's theories and practices.

    What I know in my experience, is that you want about 5' behind your speakers to the wall, and you want about the same to either side of them or a little less (depending how big your room is, and how big your speakers are). Then you want exactly the same distance from either speaker to your nose, and you want them at exactly the same angle (but not necessarily pointed directly at you - that takes some experimenting). Distance to the speakers should be at least 12' with this arrangement (so you're already talking about a 25' long room). The goal is to end up with an acute triangle that points at the listening position. The result when you get it right is a sound stage that's wider and deeper than your room.

    The other fun thing to do is make a near-field effect listening environment where your speakers are about 3-4' from your listening position. It's like giant headphones only with better staging (still not as good as the room-effect staging). The room acoustics are mitigated and you can drown out nuisance noises better (sorry, the wife doesn't work very well with this one because she just gets annoyed and louder when she's inadvertently ignored). I still have my video/audio editing suit set up at my desk and those speakers are set up near-field.

    Now if you want a really kooky read, check out Steve Deckert (he's in IL, I forget the name of his company, but he's got a forum - or did). This guy is very smart, and very nuts at the same time (he's a proponent of golden ratio rooms). I've heard his single ended triode amps on some good speakers with a way over priced sound source and they were pretty phenomenal. I don't think they're worth the price he asks for them though (and you need very efficient speakers to get much volume out of them - mine being 92db/1w/1m don't quite cut it and need around 5 watts to have a good dynamic range). I've also built a quad 12" woofer clam-shelled double band pass box he designed called the "house wrecker" and can affirm that it will shake an entire 3 story apartment building with under 500 watts (my crown amp puts out 440). However, it severely lacked in transient response or delicacy - it was about the equivalent to an off beat drummer. My push-pull double 12" will disgrace that enclosure, and occupies about 1/3 the space as well as being so transparent you can do blind tests and get mixed results as to whether the subject thinks its powered or not (unless listening to rap, and then you know somethings missing because the house isn't rattling anymore).

    I'm pretty much out of the audio scene these days. My good stuff is all in storage till kiddo is old enough to not endanger it, and I got to the point after spending a grand on an amp that there's too much money involved to go the next step up. My KRK v8's are the best listening I get for a while. I don't even have the SACD player in my equipment rack.
    Syncrowave 250DX
    Invison 354MP
    XR Control and 30A

    Airco MED20 feeder
    Thermal Dynamics Cutmaster 81
    Smith O/A rig
    And more machinery than you can shake a 7018 rod at

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