Soundproofing Small, Loud Machines

The reality of it is, Acoustical Solutions focuses on correcting noise problems for whole rooms, large industrial equipment, or broader scopes in general. But what if you have a small thing in your garage like an Air Compressor, Electrical Generator, or whatever, and it’s just obnoxiously loud to you? We really don’t have a specific soundproof box to sell you, because there are so many small, loud machines in the world, with so many different sound requirements and air/exhaust requirements that it’s just not efficient to have a cookie cutter solution for that problem from a manufacturer’s point of view. Nothing personal. It’s just business.

However, I can tell you how to make one for yourself, and for not a whole lot of money, utilizing typical building materials and a few of our products.

Disclaimer: Don’t hurt yourself. Please use good common sense about your own abilities before trying any of this. Also, certain items require adequate ventilation which I will cover, but I can’t be all inclusive to every device on the planet. Most electrical powered machines require adequate ventilation to keep them from overheating. Anything that burns fossil fuels of any kind will create carbon monoxide and must be ventilated. I don’t recommend covering those items unless you are an experienced Do-it-Yourselfer.

Okay, with that out of the way, if you are still interested in taking any and all associated risks into your own very capable hands, let’s begin.

Quick answer: To make a soundproof box, build a heavy five-sided enclosure that fits over the machine. Use two layers of 5/8 inch particle board with Green Glue between them, line the inside with mass-loaded vinyl composite foam, and seal every seam and penetration airtight. Two things matter: mass to block the sound, and a complete seal, since a 1% gap leaks about 50% of the noise. Anything that needs cooling air, and anything that burns fuel, must be ventilated with a silenced duct. Built well, a box like this cuts the noise by roughly 75%.

If you would rather buy than build, or the machine is large or industrial, see our booths and enclosures or our guide to quieting a generator.

Step 1. Measure the machine and plan a box with a few inches of clearance on every side for airflow.

Step 2. Cut two layers of 5/8 inch particle board for all five sides and bond them together with Green Glue.

Step 3. Screw the panels to a simple 1x1 internal frame to make a five-sided box with an open bottom.

Step 4. Line the inside with 1-3/8 inch mass-loaded vinyl composite foam.

Step 5. Seal it airtight: acoustical caulk on every outside seam, and self-adhesive gasketing along the bottom edge.

Step 6. Add ventilation, an inline duct silencer or a baffled vent, and seal every wire or pipe penetration with firestop putty pads.

Step 7. Set the machine on vibration isolation pads, then lower the box over it.

Heavy things stop sound. Particle board is pretty heavy stuff. Basically, you want to build a 5-sided box with an open bottom to go over the widget. Use two layers of 5/8" particle board with Green Glue in between and screw them to a simple 1×1 frame inside the box. Line the inside of the box with 1-3/8" thick mass loaded vinyl composite foam. Along the bottom edge (that is resting on the floor) apply self-adhesive gasketing (special order; call us, reference part #5881-S) to the bottom. On the outside, caulk all the seams where one wall meets another with acoustical caulk.

That’s it, that’s the sound barrier. It will, at the very least, cut the sound by about 75%.

Now the trick is to get things in an out of the box like wires, tubing, or air intakes and exhaust, without ruining the soundproof box. Remember: A one percent gap will transmit fifty percent of the sound!

All by themselves they stop 50 dB, which is huge. Any hole you drill into this box needs to have fire stop putty on the inside and outside of the box perfectly sealing against whatever it is that is penetrating through the box.

This is the part most DIY boxes get wrong. A running motor needs air, but an open hole lets sound pour straight out, so the goal is to move air in and out while forcing the sound to fight through a silencer or a baffle.

If at all possible, run these to outside air, especially if there is carbon monoxide in your exhaust from your “widget.” Acoustical Solutions has probably some of the coolest air flow silencers I have ever seen and am happy to recommend them. Sound VAC inline duct silencers act kind of like a gun silencer in that they allow air to pass through the center completely unimpeded, and yet bleeds off as much as 33 dB of sound over the 5′ distance. I recommend the 6″ diameter version, it stops the most sound and is the cheapest.

If you know electronics fairly well, and all you have on your widget is a simple on/off switch, you could very easily run some wires up to a toggle switch you mount on top of “The Box” and operate it from the outside. You can also add a digital thermometer, so you can precisely see what the temp is inside. This will help you gauge whether or not it’s within tolerance for your widget.

One other thing, if your widget is vibrating in some way, concrete is actually much more elastic than you think. Your best bet is to get some heavy-duty isolation pads for underneath it.

So, if you have any questions or suggestions for improving this setup, I’d love to hear about it. Thanks!