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Thread: Sound attenuation

  1. #1 Sound attenuation 
    Forum Cosmic Wizard
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    I need a few suggestions.
    I bought a small oiless aircompressor (1/3 hp) almost a year ago. I thought it would be suitable for inflating tires, running an airbrush, and other similar small jobs.

    I recently got it out of the box to use it and discovered that it is very loud, about 110db loud. It makes as much noise as my skilsaw or an impact gun does.

    It is too late to just return the damn thing.
    I took the cover off and noticed the manufacturers had not even bothered to put a silencer on the intake. I found a way to attach a small stainless can to it and can use it to make a muffler. The can diameter is about 2.5 inches, SO I have the possibility of building a silencer for it.
    I know I could build a large box with sound foam and internal baffles to just set the compressor inside, but I want to keep this thing portable.

    Can anybody recomend a baffle arrangement and stuffing material that might reduce 110 or 120 db to a reasonable noise level without it being too large?
    (Preferably about 2.5 inch diameter and less than 16 inches long)


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  3. #2  
    Forum Radioactive Isotope cosmictraveler's Avatar
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    My Dewalt doesn't have that loud of a problem albeit it is rather annoying. Because of that I've put it into a small storage room and bought about 50 feet of hose so that I can use the machine and shut the door so as not to hear the racket. I don't use it that often so the noise really is inconsequential for the most part.


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  4. #3  
    Forum Cosmic Wizard
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    Thanks Cosmic, but like I said I want to keep it portable. If I just put it in the shed and use a long air hose I lose that.
    Also I have a heavier compressor that runs almost silently.
    It is a very small compressor. Only about 1scfm at 40psi or .7scfm at 90psi on a 3 gallon tank.

    I do not expect this thing to ever be as quiet as my little diaphram type compressor for the airbrushes, that one just sort of sits there and hums when it is running.

    The reason I gave the silencer diameter as 2.5 inches and the length as under 16 inches is that I just happen to have a piece of scrap thin wall aluminum tube that size sitting here and it makes a press fit to the can I attached to the compressor.
    However the plumbing supply is close enough that I can use ABS or PVC and adapt it to any diameter up to 6inches.

    I already tried stuffing the tube with pot scourers and sticking it on, and while it did quiet the noisy little bugger a bit the noise reduction was not nearly enough that you could run this compressor without disturbing everybody in a 1 block radius.

    (I never would have believed that such a small compressor could be so noisy. I was warned that cheap oilless compressors were loud, but this one is ridiculous)
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  5. #4  
    Forum Isotope
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    Quote Originally Posted by dan hunter View Post
    (I never would have believed that such a small compressor could be so noisy. I was warned that cheap oilless compressors were loud, but this one is ridiculous)
    They're amazingly loud, aren't they? If one were to set out to design a noise-producing weapon, I doubt one could do better.

    I don't know the details of your particular unit, but if it's like the one my neighbor threw away, the noise seems to come from the entire body of the unit. If yours is like that, there's likely no easy, compact solution. I suppose you could try wrapping several layers of acoustic blanket around the thing, but whether you could attenuate the noise enough to satisfy is an open question.

    In the meantime, be sure to wear good ear protection. Those noise levels are seriously harmful.
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  6. #5  
    Forum Cosmic Wizard
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    Thanks TK.
    Trying the tube moved most of the noise to the end of the tube so I will take my time and muddle through it a bit.
    I know I could build an isolation box for it but after buying plywood and acoustic foam I would likely just be cheaper to buy a new silent compressor.
    I don't intend to spend a lot on solving the problem since the unit only cost $60 to start with.

    I do appreciate the suggestion of just wrapping it in a sound blanket though.
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