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Building a sound proof door

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  • #16
    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).


    • #17
      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

      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.


      • #18
        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.


        • #19
          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...


          • #20
            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.


            • #21

              There's a company called SoundDown (located in FL I think) that specializes in reducing noise levels from boat engine rooms. They sell a lead shield, foam backed product that does a tremendous job. Seems the real trick is to search out and eliminate all free air flow. They actually showed me with their equipment how much noise will travel through a 1/4" dia. hole.

              I used them to insulate the engine room on a 72' Bertram Convertible I sold to a European client. Good people to deal with.

              I'd do an internet search and contact them with your information.


              • #22
                Are you sure you want to sound proof a dyno room? Can you imagine how lowd it will be when you open the door and all that sound comes out at once?


                • #23
                  Sound Room

                  Ive done a few radio stations, Many Moons ago,and we used sheet lead, almost what a good mason uses for flashing,,Light enoung to roll out,and staples it to the doors,that we insulated the inside!!!!!!!!! worked great,couldnt here the cop cars go buy all day,as the studio was close to the main drag!!Just my 2 cents!:


                  • #24
                    The sound of door can be reduces in number of ways. Such as use of carpet
                    piece on the bottom of door reduce its resistance, which reduce the sound.


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