The Ultrafusor is a 60×60 cm (2×2 feet) diffuser 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 Ultrafusors you will need to make an initial investment in 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 diffusers in less than an hour.

Isn’t that awesome? Then let’s start!

Tools and Materials

The tools you will need to make diffusers. Polystyrene sheets and wood bases are not shown.
  • Hot-wire machine: we recommend the Proxxon Hot Wire machine (Amazon US | UKES | FR | ITA | DE | CA ). It costs approximately 100€. Any hot-wire machine which can handle 60x15cm should work.
  • Hot Knife: we recommend a ~200W Hot Knife for DIFOs  (Amazon US | UK | ES | FR | ITA | DE ) which costs approximately 75€. And a 15W one if you are going to make less than 20 Ultrafusors for yourself.
  • Glue Gun: any cheap glue gun is valid. It costs 10€ approx. 
  • Rectangular guide: better if made of wood. Dimensions are 60x15cm.
  • Column guides: you can cut them with a laser machine or make them with cardboard. More on that in step 0.
  • Marker pen: you need a pen which can write on the polystyrene. Permanent pens usually work.
  • Polystyrene sheets: they come in different dimensions, like 2x1m for example. What is really important is the width: it has to be 3cm. 
  • Wood bases: you will need a wood base to glue the final polystyrene columns. MDF of 3mm works great, but you can use any other flat wood like plywood. Dimensions are 60x60cm.

For this tutorial, we are going to make 4 diffusers at a time because 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.

Safety tips

  • It’s important to have a ventilated space when cutting the polystyrene.
  • Remember to use a mask as well as safety gloves when cutting the polystyrene.
  • Remember that hot glue guns and hot knives are very hot!

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

There are two ways to create your column guides: you can make them with cardboard and scissors, or with a laser cutter. Keep reading to find instructions on both options.

If you have access to a laser machine, you can cut the column guides in MDF or plywood. You can download this CAD file (v1.1) 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.

Laser Cut – Column guides

Once you have finished, you will get 20 pieces divided into 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.

Don’t have access to a laser machine?

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 pdf (v1.1) 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 diffusers.

Step 1: Cut rectangles with the hot-knife

Use the rectangular guide (dimensions are 60x15cm) and the hot knife to make rectangles. You will need 40 rectangles to make 4 diffusers.

You can use four nails in the corners of the guide so it won’t move while you cut. But be careful with them!

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 fumes, reduce its temperature until less fume is produced but you can still cut it with ease. More info about hot knife cutters’ safety can be found here.

You can cut the rectangles with the hot-wire machine as well, but it’s obviously 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 column 2, and the negative is 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 at the bottom, and always use the same corner as in the video.

Step 3: Make blocks of rectangles

Now we need to make 10 blocks of 4 rectangles each 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 guidelines 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.

All your guides in the same corner

Step 4: Cut blocks with the hot-wire machine

Grab the hot-wire guide with your left hand and the polystyrene block with your 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. Just like using a sewing machine.

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 Ultrafusor!

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 then 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 using the 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 Utrafusors

Voila! Now you should have in your hands your very first 4 diffusers. Don’t worry too much about imperfections, they are going to work just fine 🙂

An Ultrafusor, ready to be used.
Laboratorio sonoro – Serrería digital @ Medialab Prado