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    How to Silence Your Shop Vac

    by Thomas R. Schrunk

    Sanding used to give me the choice of two evils: I could use the sander’s onboard dust bag and let my lungs be the final filter, or I could attach a shop vacuum and replace dust pollution with noise pollution. To solve both problems, I built a particleboard box and lined it with acoustic padding. With the vacuum inside, the noise reduction was so great that I had it tested by a sound engineer. He registered an amazing 25-decibel reduction (see chart) to a level below that of an average conversation.

    The vacuum can be switched on and off from outside the box, it will work with tool-activated vacuums, and I can now sand at will without creating either air or noise pollution.

    Make the box in a morning
    The concept and the design are simple. Acoustic panels absorb 50% or more of the sound that strikes them; the sound not absorbed is bounced into other parts of the box, gradually reducing the noise. The internal surfaces of the walls and top are lined with acoustic padding, and the exhaust from the vacuum passes through a baffle to extend its contact with the padding before exiting at the rear of the box.

    Noise-containment box. The dimensions shown give an internal space of 20 in. deep by 20 in. wide by 24 in. tall.

    The box shown here holds a 5-hp Ridgid vacuum, but the size can be adjusted to fit any machine. You’ll need the internal dimensions of the box to be at least 4 in. greater than the dimensions of the vacuum to allow space for the padding and for easy removal of the vacuum for emptying. For this size box, you’ll need a sheet and a half of 3/4-in.-thick particleboard or medium-density fiberboard (MDF). The greater density of MDF gives it slightly better sound-dampening properties, but it weighs and costs more.

    Use a router to cut 1/8-in.-deep rabbets and dadoes to help align the sections. Use yellow glue and a 16-ga. nail gun to assemble the back, sides, and shelf. Then use construction adhesive to apply padding to the underside of the shelf and the thin strips at the bottom of the sides.

    Apply the padding.

    Apply the padding to the bottom before you attach it to the box. Apply padding to the rest of the inside, including the door. For extra noise suppression, use 2-in.-thick padding on the inside of the top, right above where the noisy exhaust exits the vacuum. Next, cut out the hole for the hose inlet.

    Mark the hose inlet. Use the vacuum in the box to mark where the hose will enter the box.

    Sacrificial board. For a cleaner cut through the padding, clamp a piece of plywood or Masonite to the inside.

    Then attach the door hinge and latch, and screw on the casters. Feed the vacuum’s electrical cord through the exhaust outlet, but don’t plug it in. Turn on the vacuum’s switch, place the vacuum in the box, and close the door. Plug the vacuum into an extension cord with a switch. Throw the switch on the extension cord and enter a whole new world of peaceful vacuuming.

    Measuring the Noise Reduction

    A sound engineer measured the noise reduction after putting the vacuum in the noise-containment box. 83 decibels (db.) is on the threshold of needing hearing protection, while 58 db. is quieter than the average conversation.

    Sources of Supply

    Acoustic padding
    Acoustical Surfaces Inc. (www.acousticalsurfaces.com; 800-527-6253) sells 2-ft. by 4-ft. batts of 1-in.-thick acoustic padding with a noise-reduction coefficient (NRC) of 0.80 for $18, and 2-in.-thick pads (NRC 1.15) for $32.

    Ceiling tiles
    You also can use ceiling tile from home centers. Many have labels giving the NRC. Look for an NRC of at least 0.50, which absorbs 50% of the sound.

    From Fine Woodworking #195

    Photos: Mark Schofield; drawings: Vince Babak


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    sean mao writes: He came up with the final patterns and dimensions for the example detailed here. |
    Bob Schram writes: Sean, all that came through on your post was your router IP address. Can you try again? Thanks.
    Bob Schram writes: I have the same question as when I first saw this project posted. Which Acoustic panels were used? The source listed has dozens of different types of materials/products shown. I could spend a week just wading through all their products to try and find the most suitable. I still haven't found any that match the NRC ratings listed in this article.
    Judy Wavers writes:

    I have the same concern as expressed in other posts.  What keeps the vac from over heating and what about the pressures of the exhaust inside the cabinet?

    Gra Relf writes: The exhaust port in the rear of the case is sized to give ample exhaust capacity whilst also keeping the noise level down so that it won't build up pressure. The vacuum is cooled via the air that is sucked through the suction hose and exhausted out of the machine exhaust. Being inside the case with the rear exhaust port sized as per the drawing will not advesley effect the cooling of the vacuum. It may even enhance the cooling as the exhausted air is forced around the body of the vaccum before exiting.
    n/a n/a writes: There IS an exhaust outlet cut into the back of the case. 2" wide by 27" long. 1 1/2" from the lower edge.
    Wayne Ross writes:

    This sounds great for my small shop, but how long can you leave it running before the heat builds up with no exhaust.  Would it help to cut an exhaust hole in the back to allow the heat to escape

    project success writes: I have my project due tomorrow and I had absolutely no information on this topic. sell
    Clint M writes: Exactly what l need, but l can't help wandering, if enough air is available for the vac to function properly, and as a previous poster asked, what about the heat that is generated?
    Clint M writes: This is exactly what l would like too. Besides the obvious heat build up, my other concern , is with the vac being in a box, surrounded by acoustic panels, how much air iis coming into the box, to supply the vac?
    williama willis writes: You should have your web designer make the adjustments.(Remember he is the professional in this field. my response
    Ken Guenther writes:

    Looks like a very good way to reduce the noise level in the workshop, however I can not help but wonder about the heat build up inside causing the vacuum to go up in a puff of smoke or at least shortening the life of the shop vac.

    P Alley writes:

    This is almost exactly what I need for the blower I use to groom animals!  (MOF I know a lot of groomers I'm going to pass this on to...)  But...how do you ensure that the air going out is quiet?  The blowers tends to shriek as the air enters as well as exits if you are using it as a vacuum, and it's just deafening.  I don't want it building up pressure inside the box, though.  How to avoid?
    Thanks all!

    Joe Swetz writes: I built a similar cart for my 5 gal. air compressor...really helps reduce the noise. Add'l Tip...if you build the cart to the same height as your bench or table saw you can use it to extend your workbench surface or use as support/outfeed table for your table saw .
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