The Polyfusor

An open source diffusor, made of polystyrene with 420 cells. That’s lots of cells :)


The Polyfusor is a 60x60 cm (2x2 feet) diffusor made of polystyrene. It has 420 cells with a width of 3 cm and a depth of 15 cm. It works great in recording or control rooms, and it has a modular design, so you can move it around or change it for an absorbent panel if needed. Frequencies from 565Hz (diffraction limit) to 6000Hz are affected.

If you want to build some Polyfusors you will need to make an initial investment for tools, but after that, producing them it’s quite cheap. Polystyrene is widely available at very low prices and you can make one of these diffusors in less than an hour.

Isn’t that sweet? Then let’s start!

Tools and Materials

The tools you will need to make diffusors. Polystyrene sheets and wood bases not shown.

For this tutorial, we are going to make 4 diffusors at a time because with our hot-wire machine can cut 4 rectangles together and save some time. If you have a different machine or you have built your own, adapt it to your needs.

Step 0: Create the column guides (only the first time)

If you have access to a laser machine, you can cut the column guides in MDF or plywood. You can download this CAD file which contains the 10 column guides. They fit in two 60x90cm boards.

Column guides (1 to 5) prepared to be cut by a laser machine.

The CAD file contains numbers so you can raster them with the laser. If you don’t, just write down the same number you see in the file. Use always the same corners, like in the file.

Column guides (1 to 5) prepared to be cut by a laser machine.

Once you have finished you will get 20 pieces divided in 10 blocks. Each block contains one positive (from 1 to 10) and one negative (from 11 to 20). You need all positives or all negatives, it doesn’t really matter. You can give the negatives away to a friend.

If you don’t have access to a laser machine you can still print and cut the guides in cardboard using a cutter. Download this zip file which contains all the guides ready to be printed in A4. Check that you are printing them at the real size (so you don’t end up with bigger or smaller guides). Then use a tape to stick the three A4’s of each guide together, and put them over cardboard. Then cut it with a cutter.

Column guide made of cardboard.

Now we are ready to start building our first diffusors.

Step 1: Cut rectangles with the hot-knife

Use the rectangular guide and the hot-knife to make rectangles. You will need 40 rectangles to make 4 diffusors.

You can use four nails in the corners of the guide so it won’t move while you cut.

We recommend working with ecologic polystyrene. If you don't, just work in a ventilated area, If the hot-knife is producing a lot of fume, reduce its temperature until less fume is produced but you can still cut it with ease. More info about hot-wire cutters safety can be found here.

You can cut the rectangles with the hot-wire machine as well, but it’s much slower.

Step 2: Mark the rectangles with the numeric guides

You have to mark 10 rectangles with the 10 column guides. You don’t need to mark all 40 rectangles because we are going to make blocks of 4 rectangles in the next step.

In this design, both the positive and the negative parts of the polystyrene are used. When you cut the first rectangle, the positive is column 1 and the negative is column 11. When you cut the second rectangle, the positive is the column 2 and the negative is the column 12. And so on :)

After marking each rectangle don’t forget to put the correct numbers so you don’t mess them up later. Mark both the positive and the negative in the bottom, and use always the same corner like in the video.

Step 3: Make blocks of rectangles

Now we need to make 10 blocks of 4 rectangles each one because we will cut them together with the hot-wire machine. Use tape to hold them together. The first rectangle of each block must be one of the marked ones.

It doesn’t matter where you put the tape but be careful not to cover any guide line because the hot-wire machine doesn’t cut tape. 

When you finish you must write additional numbers in the new rectangles so you don’t mess them up later. Remember to mark both the positive and negative sides on the same corners.

Step 4: Cut blocks with the hot-wire machine

Grab the hot-wire guide with your left hand and the polystyrene block with the right hand.
Whenever you need to push it up, use your right hand.
Whenever you need to push it down, use your left hand.
Whenever you need to push it right, use your right hand.

It may seem difficult at first, but it’s quite easy actually. Just like using a sewing machine but much easier.

Step 5: Group all the columns together

Just disassemble the blocks.

Then make groups of  20 columns, aligning all the numbers in the same corner.

10 positives + 10 negatives = 1 Polyfusor!

Step 6: Glue the columns to the wood base

Finally, we are going to use the glue gun to glue the parts to the wood base.

Do not put the glue directly on the polystyrene. Put it in the wood base first and the gently press the polystyrene until it doesn’t move anymore.

Put the first column in the border of the base and then glue the other ones together pressing them together to avoid any gaps. The last one should fit in fine with the last part of the base.

If any of the columns broke now it’s a good time to fix it with some glue gun as well.

If you are going to move it a lot, it’s a good idea to glue some of the cells together to give it additional strength.

The finished Polyfusors

Now you should have in your hands your very first 4 diffusors. Don’t worry too much about imperfections, they are going to work just fine :)

A Polyfusor, ready to be used.