Garage geeks love their Shop-Vacs (we’ll call them wet/dry vacs, since Shop-Vac is a specific brand), but boy are they noisy! Depending on many variables—room dynamics, how close you are to the unit, etc.—the typical decibel reading for a running wet/dry vacuum is anywhere between 85-95db. That’s pretty loud. For comparison, the average conversation is around 60-65db.
There are baffle attachments available for wet/dry vacs, but they’re really made to prevent dust from flying around, not so much for noise even though they’re marketed as-such.
A few YouTubers have built some clever wet/dry vac cabinets, complete with sound diffusion, exhaust ports and casters that are seemingly simple to make and, in some cases, lower the noise these machines put out by around 20-22db—a much more acceptable and tolerable level.
These videos aren’t all that new (and the first and last are two-parters), but the concepts are still very valid. Check them out and let us know if you’ve got a similar or better solution short of a central vacuum system where the machine is actually in another room.
There’s also a great write-up with detailed plans available from the folks at Start Woodworking.