Up to this point we have discussed reflected sound off flat surfaces. There are three things that can happen when sound hits a wall. It can be reflected, absorbed, or diffused. If you have a multifaceted surface such as a rock wall the sound reflected will be diffused. Diffusion spreads the reverberant sound evenly throughout a room, which not only prevents standing waves but also eliminates dead spots, i.e. places where components of the sound are missing through phase cancellation as discussed in standing waves. Flat surfaces can be broken up by placing diffusers on studio walls.
Diffusion in the Control Room
I must say at this point that I have a problem with diffusion in a control room. Sure the diffuser does disperse the sound evenly within the room and it sounds impressive but I've found that when working in a diffuse control room you get a distortion of the amount of "life" in a sound. The diffusion makes everything sound airy and open but what's on tape might not have that factor.
A control room is a working environment, not a listening room
In a control room you are wanting to hear exactly what is on tape and you want to be able to analyse it completely so that you can add the necessary components such as EQ,reverberation, compression etc. Direct sound from the speaker is the aim in a control room and I feel diffusion clouds that image. I realise I'm about to be criticised for such a view soI leave it up to you.
The shapes chosen for diffusers are really a matter of taste and cost. Avoid concave curves, which focus sound instead of dispersing it, but otherwise pyramids, lattices, or computer designed random surfaces all work well. The depth of a diffuser determines the lowest frequency that will be affected. A diffuser one foot deep will scatter sound down to 160 Hz. Diffusers can be built by the home studio owner quite simply by creating a multi surface plane. The typical one is lots of blocks of wood of various sizes glued onto a backing sheet. Go to a house construction site and ask for all the 100mm x 100mm (4" x 4") offcuts. Glue the blocks of irregular lengths onto a backing sheet of plywood, spray it with paint and stick it on the wall. You will now be the owner of a new trendy studio with a diffuser on the back wall of your control room.
Diffusion In the studio
Diffusion in the studio is a great idea and one of the best way to add it is to have stone walls in your studio. Not flat stone but round and irregular stones that create a rigid random diffuse surface. The reverberation created in such a room will be rich and diffuse which is what you want in a good reverb unit. (Note here that some effects units have a control over diffusion in their reverb programs)The greater the "depth" of the diffuser the lower the frequencies affected. I recommend such a wall in a drum room if you want live drum sounds. Otherwise try the wooden block system, it works really well also
VARIOUS TYPES OF DIFFUSERS
I have called the angled - curved - pyramid shapes absorbers/diffusers because they can be built as low frequency absorbers yet will also act as diffusers. See the section on low frequency absorbers. Today various companies manufacture pre - built diffusers that can be purchased and installed in your studio.
I must say here that the last three diffuser types are pure diffusers and perform no other function whereas the the first three types can act a low frequency absorbers. In the home studio your room sizes are usually small and low and low-mid frequency coloration is your main problem so to waste treatable wall space with just a diffuser to me is a waste of wall space. Slat resonators also act as diffusers because the slats with the gaps break up the surface and I would advise you to use them instead. The best place to use diffusers is in a live room if you have the space to dedicate a room specifically for that.
