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material to make acoustic cover

Discussion in 'Electronic Design' started by colin, Apr 1, 2007.

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  1. colin

    colin Guest

    Hi,
    I need to make a cover wich can block most of the noise from a 1M long shaft
    inside
    some equipment wich has little else in it beside the shaft and some bearing
    blocks.

    Idealy it would not be very heavy, easily fabricated and able to serve as a
    cover under its own strength.
    with unsuported areas of 200mm x 100mm.

    Ive used sound deadening pads before, even resorting to some spare roofing
    felt on the inside of
    washing machine wich was pretty effective, but I havnt got a cover as such
    to atatch it to.

    cardboard would be strong enough, but needs something rubbery to absorb the
    sound,
    can you get rubberised cardboard ?

    rubber sheet would be good for sound deadening but wouldnt take a shape and
    keep it,
    not sure plastic would be any good at absorbing the sound.

    best bet so far is to make a thin aluminium cover and atatch sound deadening
    pads to it,
    but I was wondering if there was anything better,
    although you can actually get aluminium sheet lamintaed to a layer of sound
    deadening wich is a bit expensive but might be worth it.

    Colin =^.^=
     
  2. MooseFET

    MooseFET Guest

    If you are trying to keep sound that is traveling through the air from
    getting through, it is one problem. If the whole assembly is
    vibrating it is a different problem.

    Two layers of material that only connect at the anchor points will
    work fairly well on sound traveling through the air. The inner layer
    should have a few small holes in it. When you tap on the cover it
    should go "thump" not "ding" or "clank". If it goes "ding" try
    putting a small bit of visco-foam between them.

    Sound traveling on the mechanical part, requires that you provide for
    a mass on the cover and a way for it to stay still while the other
    stuff moves. Some of this can be done with just how the cover is
    shaped. If it is mounted at its edges, running zig-zag bends in a
    band near the outsides will allow the cover to flex at that point.
    Running an "X" shaped bend through the middle will prevent the bulk of
    it from bending.
     
  3. jasen

    jasen Guest

    I've seen sponge rubber with a latex(-like) deadening layer in it.
    it was used to line printer cabinets (for noisy impact printers)

    It may be rigid enough as it is or you could glue it to some cardboard etc...

    Bye.
    Jasen
     
  4. colin

    colin Guest

    yeah that sort of thing but I havent come accros any.

    I tried cardboard on its own wich was a marginal improvement,
    although I think it might of cured a light dependant problem id overlooked !

    I think ive come to the conclusion that Il have to make a 2 part thing,
    Im thinking some 0.3mm tin steel sheet will make a support and outer shell,
    hopefully this is easy enough to bend into a simple U shape and strong
    enough to not unbend on its own,
    and line it with some sound absorbing 25mm foam from RS.

    not sure how effective this is, the foam will isolate the outer from the
    chassis too,
    and cover most of it exept for the underside,
    hopefully stop any sound geting past it and deaden the sound inside a bit so
    it doesnt try get out elsewhere.

    Is 1M long but only 4"x4",
    probably dont need to fix it,
    although the U section might try to unbend,
    maybe some velcro.

    Colin =^.^=
     
  5. Ben Bradley

    Ben Bradley Guest

    What is the frequency spectrum of the sound? High frequencies can
    be stopped by a fairly thin cover. Mids and lows are more problematic,
    and to be most effective the cover needs mass (a steel plate is good,
    but I wonder if the .3mm stuff you mentioned might be too thin) and
    especially for low frequencies, to be sealed airtight.
    I reread your OP, I imagine bearing noise would be mids and highs.
    While the foam may help (as in deadening out the resonances of the
    metal plate it's placed against), the majority of your sound reduction
    will come from the metal plate. The cover (actually the whole
    enclosure) would best be mounted in a way that is vibrationally
    isolated from the bearing blocks, else the mechanical vibrations will
    go directly through to the place which will then radiate the sound
    like a loudspeaker.
     
  6. colin

    colin Guest

    I think I might make a sandwich of the foam between two steel sheets,
    so the outer is completly isolated by the foam,
    just adhesive holding it together.

    Colin =^.^=
     
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