Thread: A misadventure into sound damping enclosures for loud workshop machinery

Hi everyone,

A couple of years ago, my shop vac died, so I did what anyone who doesn't have a full-sized dust extraction system would do. I bought another.

I bought a DeWalt DWV-900L vacuum... a device I would not wish on my worst enemy. I wrote a scathing review on it found here:

https://www.productreview.com.au/lis...dewalt-dwv900l

So, one of the (many) things that bothered me about this shop vac, is it's almost exactly as loud as your typical circular saw, or indeed DeWalt table saw (which I own, and love.. just so you know I'm not brand bashing). Living in close proximity to other households, that wasn't going to be tolerated long... So I designed and built an enclosure for it, with the express purpose of silencing the beast.

Doing a little online meandering through the wilderness of YouTube and other multimedia sites capable of demonstrating the difference between the shop vac in open air and in whatever design of box they were showing off.... was an enlightening experience. One guy had a box made of chip board, and lined it with those blankets your typical removalist will use to stop any scratches on furniture. It worked pretty well. So I had that ever so humble thought:

"Pfff, I can make that so much better!"

The three things I learned:

1. The more mass surrounding the box, the better the sound was contained. So I opted for a cabinet shell of two layers of 17mm ply I had laying about, then for fun (and smoother gloss finish) I surrounded that with another 15/17mm layer of MDF that I had laying about. I read somewhere in a home-theatre site that using a thick layer of rubbery glue to stick gyprock to joists reduced noise transmission, so I used.... a lot of tubes of liquid nails dotted with silicone sealant to stop resonance while providing some reduction in noise transmission.
2. You want the joins to be air tight, so I used silicone caulking in all the crevices/joins. I used typical door draft seals for the door edges.
3. Noise is managed in two ways:
   
   1. Diffusion (scattering around oddly-shaped, hard objects) I figured the shop vac would do that to any reflections, however, the interactions with it's own noise, create both additive and destructive waves to add/cancel out previous noise.
   2. Absorption (line the inside of the box with sound-absorbing material). In my case, I used some automotive sound deadening materials (a self-adhesive roll of foam rubber, which is good since it also has some thermal resistance. Since I had to buy a roll, I actually doubled up, and occasionally tripled up the layering. I was also told to try out a foam adhesive made by my better half's workplace. So I went "why not", and glued those recording studio tiles to the inside of my lining for added over-engineering insanity. (Note: I had to ensure adequate airflow, and this required a little thought to my placement of said acoustic tiles.
   
   

So how do you get power in and air both in and out.. all while keeping the noise contained?

That's a great question. You see, you definitely do NOT want a direct line of sight from your vacuum out of your box.The noise will escape there. So I took the concept of a transmission line speaker system to create a somewhat meandering path, where all sides are covered in sound deadening/damping material.

However, speakers intentionally create drag on their airflow because it's beneficial. That's not so great if you want continuous circulation of air flow. If you place the vacuum on a recessed (and padded) shelf, and line both the top side, AND underside of the shelf, (and the door to the cabinet as well) you can use the recess in the shelf to pass pipe/cords down in front of the shelf and out the air/power inlets and outlets. Remember your holes have to be big enough to pass your hose through, but also your power plug. So I drilled two 60mm holes (one for the vacuum hose inlet) and the other for the cord and exhaust.

Here's a rendered 3D model image showing the recessed shelf, lined top and bottom like the rest of the enclosure.
VacuumSilencingBox_ShowingRecessedShelf&Lining.jpg

Here's rendered image of the lower section, showing the inlet/outlet holes
VacuumBox1ShowingInlet&Outlet.jpg


Here's a real-world photo of it, showing the door seals, and added studio tiles. I've half pulled one off because the glue came unstuck after a while, being wrapped around the front edge of the shelf. The vacuum died before the glue, and the airflow was fine.

IMG_2037_DxO.jpg

You might be wondering, Just how much quieter was the vacuum?

In short, all I could hear was the faintest hum of the motor, that was largely drowned out by the sound of air rushing through the hose. It was crazy... I went from barely hear myself yell... to hearing the embarrassing bodily eruptions of a neighbour across the lane way.

A FEW KEY NOTES:

• I was running this with a cyclonic separator. I would NOT recommend using a vacuum in an enclosure like this without one. You can't hear the sound change when the bag fills up or the pipe gets clogged, so you could, in theory burn the motor out.
• I originally intended to mount a switch onto the cabinet to turn the vac on/off... but the vac died several times before that happened (only once inside the box), and by then, I was ready to cut my losses. While it was running, I simply used the power point switch. Obviously, an enclosure inhibits using the vacuum's power switch and any power "off take" you may have.
• You do not have to build it as excessively as this. Even a box with a blanket made a difference.

So with the vacuum well and truly dead, now I had a custom built enclosure, but no vacuum. So I did what any space-starved workshop denizen would do.... after copious amounts of procrastination..

Cut the door into the face boards for 8 drawers, rip out all the lining and shelf, then shamelessly use whatever scrounged ply, MDF, scrap at hand (in several thicknesses) to build drawers for my clamps and screws... which seem to be everywhere in my little workshop. I swear they're multiplying.

Here's some pics of the finished chest of drawers:

IMG_2057_DxO.jpg IMG_2058_DxO.jpg

So now this box stores stuff in the drawers. I have my mitre saw on top... thinking about mounting some fold-down wings to support the timber I'm cutting and add stop blocks/rails.... but that's for another day.

Ah the workshop, it's a never-ending battle, isn't it!

Merry Christmas, and may all your workshop wish lists, holiday goals, and new-years resolutions be filled by friends, family, or in a pinch, scantily clad beauties. Whatever you prefer.

Hamish.