Sound Damping Panels

Sound is an issue with any workshop, power tools are cool but make lots of noise.  My workshop has the added benefits of being in a garage, close to neighbors and harboring a CNC table. My primary concerns are the air compressor, shop vacuum and the CNC router table since it will run patterns that could easily run 30 minutes, an hour or more. Luckily, I am designing a cabinet to hold the vacuum, compressor and most importantly the CNC table for both dust and sound control.  The empty pockets created in my 2x4 frame design will create great places for sound damping panels.

Even though I am using these panels to sound dampen my CNC machine, the concept could easily be modified for more generic shop purposes to deaden the amount of sound in a cement basement or the sound that travels through walls from your table saw. One of my old friends could really have used these in his barn shop as his carpentry schedule often conflicted with his neighbors' TV and sleep schedules.

STEP 1: Cut the Backer Board
The first step is to cut a heavy backer board with adequate gap not to touch the edges of the cabinet, mine has a 1/2" gap. One of the features of sound transfer we are trying to avoid is vibration, sound that will actually shake the cabinet.  By reducing the amount of contact that sound has with the outside of the cabinet we reduce the amount of direct transfer.  This backer board I am using is thick 3/4" plywood, it has to be heavy to absorb the physical force of the sound waves being thrown at it.  The heaver the board, the more force it takes to move it.  For even better sound deadening capability I contemplated using cement board for even more heft but since I am also cladding the outside of the cabinet with another layer of 3/4" plywood I figured it would be overkill and an unnecessary expense.

You can see below that the sound panel is simply hung on eye hooks and wire strung through a hole in the plywood.  This will create an extremely small area for vibratory forces to transfer sound.

STEP 2: Shred and Soak Paper
Time to recycle! Fill your bucket with shredded paper from the office, packing paper, newspaper or even cardboard.  Do your best not to put any pieces with tape or plastic in the mix as they obviously won't break down in water. It's best to fill the bucket pretty full as this will compact greatly when wet.

 

Fill the bucket with water, making sure to cover your material.  Let is soak for 15 to 30 minutes to soften up. If you are using harder material such as cardboard, look forward to longer soaking times.

Use a power drill with a paint mixer attachment to blend and shred the paper to a mushy pulp.

Pour out the pulp into a cloth sack or old pillow case to drain most, but not all, of the water. It is important, that you not wring out the pulp as we still need some of that moisture.  Just reduce it to an oatmeal texture. You will need enough moisture to mix more ingredients.

After draining you will notice the volume has been reduced by 90% or more.  Dump the mushy paper back into the bucket. Add some wood glue to act as a bonding agent so our finished product won't fall apart.  Don't add so much it will be a stiff piece of plastic, just enough to stick together.  I added about 1/4 cup of glue as well as some coloring.  The coloring will not only make the finished product look cool but will also help you know when the glue is mixed in.  Get the drill and paint mixer and mix until the color is nice and even.  A simple and cheap colorant is dried drink mix, I used tropical punch flavored Kool Aid (don't add the sugar obviously).

  
STEP 3: Prep Backer Board
Take the backer board you cut in step 1 and line the edges with tape or cardboard to help hold the material in place.

Drizzle some wood glue across the surface of the backer board and with a wet brush spread it around.  This glue will help adhere the mix to the backer board when it dries.

 
STEP 4: Apply Backer Texture
Scoop the well-mixed mush onto your prepped backer board.  Try not to squeeze the moisture out, it should still be fairly wet and sloppy.  You will want this to remain puffy as much as possible so it will dry with a less dense makeup.  The lower density material will help absorb high pitch noises.

Spread out the mixture across your backer board as evenly as possible without compressing it.  I find a chopping motion using a large tooth tiling trowel works well.  You will want about 1/2 an inch or so of material covering the surface.  Be sure not to smooth the top of the mix, you will want a very irregular surface as this will cause diffusion of the sound that is not absorbed by the panel.  If sound is split and reflected in different directions it will reduce the energy of the individual sound waves and reduce their effectiveness.

After you have spread out the mix evenly, let it setup for 10 or 15 minutes then remove the tape. Removing the tape will allow you to inspect the edges of the board to insure coverage as well as help the mix dry by letting water drip away. Point a fan on the board and give it a day or two to dry.

STEP 5: Re-Hang and Make Some Noise

Multiple panels are hung on each wall, ceiling and doors of the cabinet to trap as much noise as possible.

Here is a video of the panels in action!



-Have Fun!