UPDATE 10/3/2012 - This muffler worked well, but check out this one made from foam and duct tape! Much cheaper and lighter weight!
Shop Vacs are great, as are their Rigid equivalent, but they’re quite loud. I don’t really like having to wear ear protection every time I’m working on my CNC router in the shop (see my CNC Shop-Vac nozzle mount), so I decided to do something about it.
The three possible solutions I came up with were to: A – put noise absorbing foam on the surfaces around it, B – enclose the vac, or C – make some sort of muffler for it. After some experimentation, I put a custom-made muffler on my Shop-Vac and put as much foam around it as I had. This material came from shipping material, but it was porous and seemed to have the correct shape, so I used it.
Here’s the results of my experiments:
- 4ft side no protection – 82.8
- 4ft back no protection – 84.1
- 4ft side – box 83.4db
- 4ft back – box 81.0db
- 4ft side – absorber only – 84.1
- 4ft back – absorber only – 83.7
- 4 ft side – muffler and absorber – 78.4
- 4 ft back – muffler and absorber – 77.2
Noise wasn’t measured in the front (where the suction hose comes out) of it, and the sound meter was actually a few feet below, but I tried to keep things consistent. I’m moderately pleased with the results. Averaging the sides and back, the overall noise reduction was 5.65 decibels. According to GCAudio.com, or the first site I that Google came up with for this subject, a change in 5 dB is a “clearly noticeable change.” According to NIOSH, one can be exposed to 85 dB for 8 hours/day, so this should be a relatively safe noise level.
That being said, I’m still planning on wearing my earplugs when exposed for more than a couple of minutes, but since a dial tone is around 80 dB, I’m not as concerned as I was before.
As for the nuts and bolts of things, the panels were laid out after the muffler was installed, measuring where there was a high sound level. I could have experimented more, but on top of where the Shop Vac is mounted, there’s a shelf where I thought noise could bounce off of easily. It measured well over 90 dB, so insulation was placed there. Also, it was placed in front of it on the wall, which seemed to make a difference in the level at a distance.
From Amazon: Pyle PSPL01 Mini Digital Sound Level Meter (used for measurements in this post)