How to Make Your Own Audio Diffusers

This article explains how to build audio diffusers for your room acoustics, based on Dr. Floyd Toole's book, Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms. Diffusers reflect sound in many different directions in a room to give your home audio system's sound a greater sense of spaciousness.

The Plan

The image below shows a simplified room layout according to Dr. Toole's principles. The blue areas represent diffusers. The red areas represent foam absorbers. The diffusers and absorbers are all mounted on the wall, about 18 inches off the floor and 4 feet high. These sizes are only examples and not critical measurements for creating diffusers.

The diffusers are made with concrete form tubes, cardboard tubes with walls typically about 3/8-inch thick. Home Depot sells them in sizes up to 14 inches in diameter and 4 feet in length. Construction supply stores sell them in sizes up to 2 or 3 feet in diameter, in lengths up to about 20 feet, but they'll be happy to cut them to your preferred length.

To make the diffusers, you'll need to split the tubes in half, then attach supports to mount the diffusers on the wall.

Choosing the Diffuser's Diameter

The diameter you choose for your diffusers is important. The thicker the diffusers and the farther they stand away from the wall, the lower the frequencies they can affect. According to Toole, a geometric diffuser like the ones in this article must be 1-foot thick to be effective through the entire midrange and treble frequency range. However, 1-foot thick diffusers are bulky, and the 24-inch diameter concrete forming tubes required to make 1-foot thick diffusers are expensive.

If you want to make your listening room great, build 1-foot thick diffusers. If you want your room nice-looking and more affordable, use 14-inch diameter tubes available at Home Depot. The 14-inch tubes will give you 7-inch thick diffusers, still better than many of the too-thin commercially available diffusers sold by pro-audio stores.

This tutorial builds 8-inch thick diffusers for a back wall and 7-inch thick diffusers for sidewalls.

Diffuser Positioning

It's a good idea to place a couple of diffusers at the "point of first reflection" on each sidewall. The point of first reflection is the place where, if you put a mirror flat on the wall, you can see the reflection of the speaker nearest that wall while you're sitting in your favorite listening chair.

You can also place a couple more diffusers farther back along the sidewall. Definitely put a few along the back wall, which will minimize flutter echo.

Measuring for the Cut

Once you have your tubes, you'll need to split them in half. Make the cuts straight and precise so your diffusers will be flush against the wall and appear professionally made.

We used a jigsaw with a fine-tooth blade consisting of 24 teeth per inch—the finer the teeth, the smoother the cut. You can split the tube in half with a hand saw, but your cut probably won't be as smooth or precise as with a powered jigsaw.

To make your cuts, measure the actual diameter of the tube. In this tutorial, the diameter is 14-1/4 inches.

Next, measure half of the diameter of the tube, and mark that height on each tube. Mark the halfway point on the tube on both sides, on each end.

Before you make height marks, put something heavy inside the tube to ensure it won't roll. We used an anvil—you know, like the one Wile E. Coyote used to try to drop on the Road Runner.

Making the Cut

To make a smooth, straight cut, clamp a 1x2 stripboard on the side of the tube. Make sure to align the 1x2 stripboard with the marks you just made.

Now, carefully cut the tube by using the 1x2 stripboard as a guide for the jigsaw. The blade is in the center of the saw, so your cut will be offset from your marks, but this is fine because you'll have a matching offset on the other side of the tube. In this tutorial, the offset is 1-1/2 inches.

Go nice and slow, and you'll be rewarded with a straighter and smoother cut.

With one side done, unclamp the 1x2 and move it over to the other side of the tube. Now clamp it along the other marks you made, making sure to clamp it so you'll get two even halves when you cut. If you cut the wrong side, you'll end up with one diffuser that's thicker than the other.

To make sure your line is straight, mark the distance on both sides of the half-tube, then stretch a wide strip of something like a wide fabric belt around the tube to serve as a guide to make your cut line. Then make a slow, steady, and precise cut along the mark with the jigsaw, or a hand saw.

Nailing in the Brackets

The mounting brackets are part of the 1x2 strip boards you used for measuring. To make the mounting brackets, cut the boards to the same measurement as the original inside diameter of the tube. Use a miter box to ensure a straight, square cut.

Nail the mounting brackets as shown below. You can use two brackets on each diffuser to make the diffusers less likely to warp. Then place one bracket about one foot from each end of each diffuser.

We also used 1-1/2-inch wire brads (nails) with flat heads of 1/8-inch diameter, with two brads per side, per bracket. Be gentle with the hammer because the cardboard tubes can dent easily. Just make sure the brad heads are flush with the tube.

Now mark the center point in one of the brackets and drill a 3/8-inch hole there. You need to put a hole in only one of the brackets.

Finishing Touches

Here's where you bring your creativity to the process: decorating your diffusers.

You could paint the diffusers, but keep in mind they're made like giant toilet paper tubes, with a continuous seam wrapping around the tube. You're better off covering the tubes with some fabric, wallpaper, or almost whatever you want. Perhaps whimsical paisley fabric? Or a favorite cartoon character? It's up to you. Just make sure the store has enough of it because you'll be using several yards' worth. 

Adding Fabric to Diffusers

To apply fabric, use a spray adhesive like Loctite 200, then:

1. Cut the fabric with about 6 inches to spare on every side.
   

2. Spray the surfaces of the tubes and give the adhesive half an hour to set.
   

3. Trim the fabric, leaving about 2-1/2 inches excess all around.
   

4. Spray the insides of the tubes on their long sides.

5. Fold the fabric in, making a couple of quick cuts with scissors to accommodate the mounting brackets.
   

6. Let the adhesive set for another half hour, then blast the inside ends of the tubes with a generous amount of adhesive.
   

7. Fold in the rest of the fabric.
   

Mounting the Diffusers

If you're OK with an amateurish but effective mounting system, hang each diffuser from a single drywall screw. The diffusers barely weigh anything, so you don't need to worry about hitting a stud with the screw. Instead, mark where you want to mount the diffuser, put the screw in so it sticks out about 1 inch, then hang each diffuser from the hole you drilled in the back bracket.

The downside of this technique is that drywall is not very sturdy, so the diffusers can easily be torn off the wall by accidental impacts. If you need more strength, use molly anchors or toggle bolts to mount.

Creating Legs for Diffusers

If you happen to have no place to screw in any mount, you can add legs to each of the diffusers so they can stand on their own. We used the 1x2 boards to create three legs, each 24 inches long.

We attached the legs to the diffusers with two 1/4-inch bolts per leg so that 18 inches of leg sticks out below the diffuser.

Other Mounting Options

Suppose you don't want to mount the diffusers on the wall or add legs to the diffusers. In that case, you can use some monofilament fishing line to hang them from the ceiling or make the diffusers 6 feet high and just let them stand on their own. There are all sorts of possibilities, and whichever way you go, you'll have better sound with diffusions.