Shop Vac Enclosure

Shop vac’s are famous for fantastic suction – and a ton of noise.  When I was single and living alone, running the shop vac for a half-hour at a time while sandblasting was a non-issue: I just put earplugs in and went to work.  But in January ’07, when I was getting ready to sandblast the first batch of Mojolevers since moving in with my wife in our new house, I realized that it was just too damn noisy.  If I was going to run this thing for extended periods on a regular basis, I had to not just muffle it, but silence it.  I sketched out a design for a noise abatement enclosure, and paid yet another visit to Home Depot for some plywood and 2x4’s. 

My idea was for a plywood box lined with noise-absorbing foam in which the shop vac would sit.  The hose would pass through a fitting in one wall of the enclosure, and exhaust air would leave the enclosure via a serpentine exit duct, also lined with nose-absorbing foam.  Two views shot of the box in progress:

The foam is held in place with a generous application of 3M’s “Super 77” adhesive spray.  Once applied, the bond is so good that the foam itself tears before the glue gives up. 

The exhausted air leaves the box through that tall vertical slot on the side of the cabinet.

The finished enclosure, with the access door open:

The door seals tightly against a soft foam-rubber gasket, and is held shut by four buckles:

The enclosure sits on four caster wheels and has a couple of handles on top that make it easy to drag around the shop. 

So how well does it work?  Far better than I ever expected:

	Noise level of shop vac in open air at six feet:  85 dB.  This is as loud as my lawn mower, and happens to be OSHA's eight-hour exposure limit; workers exposed to these sound levels are required to wear hearing protection.
	Noise level of shop vac contained inside enclosure at six feet: 63 dB.  I couldn't find a description of what sort of common noise level this represents. A couple of charts list 70 dB as the level of a car at 45 feet, a toilet flushing, or a clothes dryer. Suffice it to say, then, that the noise emanating from my shop vac silencer is very close to the level of a normal conversation.
	Noise level of typical conversation in quiet room: 60 dB. Decibel charts consistently describe this as the sound level for "normal conversation," but I think my el cheapo SPL meter was reading high. 60 is the lowest reading it can measure, and the display dithered between "60" and "LO." The basement was essentially whisper-quiet for this reading.