If you walk into a room, clap you hands and hear “ta-da-da-da” after the initial clap, what you are hearing is the delayed reflections arriving from the surrounding surfaces. These sometimes tiny short reflections are called “flutter echos”. These reflections are problematic in that they often cause frequency specific phase shifting and colorations that are not sought after in recording or good listening spaces. These reflections can be tamed with absorption materials or diffusors.
Diffusion is the process if scattering. Sound diffusors are hard devices that diffuse or scatter reflections in a different direction or in a different time than if unaltered. Scattering into a different direction makes sense because it interrupts the ping-pong like reflections between parallel surfaces. Delaying the reflections is helpful because it smooths out the delays into more of a unperceived short reverb and analogous sound. These time variances are generally very minute, typically only a difference of nano or milli-seconds. Once again these come in various forms and sizes and can also be designed with a little bit of ingenuity. Here is a pro studio with some major diffusion in the control room.
A simple example of a diffusor is a book shelf stocked with books of varying depths. These varying depths allow an uneven surface that allows the sound hitting them to return not only in different directions but subtle time differences as well. Log cabin style walls are also diffusive due to their rounded shapes.
In my space I use absorption toward the back of my room to control reflections and diffusors at the front of my space, Specifically in the mix’s sweet spot. (The sweet spot is where you ears and the monitor speakers form to make a perfect, ear-height equilateral triangle.) Diffusors between the monitors and my ears help scatter any reflections away and out of time from the direct sound from the speakers themselves. You really cannot go wrong on placement of diffusers. A diffusive ceiling is great to help breakup the floor to ceiling reflections. The rear wall in a control room is another great place.
DO IT YOURSELF
The gray diffusors shown below were built with a 2 foot by 2 foot frame out of 1″ thick styrofoam. I used a yard stick to mark the various “depths” then cut them with a blade. Once cut, I used liquid nails to glue the pieces together and then fit them into the 1″ by 6″ wooden frame. I then used gobs of wall pain and a brush to make them look decent. Here they are hanging and alternating with absorption panels at a former location.
Behind my secondary monitor, you can see that there are two wooden diffusors. These were built with the help of my awesome father-in-law one day while “playing” in his shop. The idea behind the designs was to “confuse the heck out of any sound that hit them.” We had a great time joking about and designing them. Each 2 foot by 2 foot frame houses 10 narrow compartments. The bottom one is more of the varying depths idea and the top one is lots of wooden slats placed on angles with air gaps between them. I have them placed in front of my mix position to break up any reflections from the front wall and simply because they are just plain awesome. I love and miss you Kip Clark!