What About Diffusion?

The other half of the acoustic treatment plan

Diffusion doesn't impact RT60 time a lot. Some diffusers have absorption properties (minor) and the scattering can mean more sound finds its way to existing absorption sooner. But diffusion and scatting are not big parts of managing RT60 times (or reflected decay times) in domestic rooms.

But it is still very useful for opening up the sound in a room, effectively hiding the size of the room from our ears/brains.... letting the recording (rather than the room's walls) define the size of the acoustic space.

If you can, adding diffusion in a similar quantity to your absorption is often a winning recipe in dedicated rooms. But what kind? Depth and shape matter. Depth because that largely determines the frequency at which it is effective, and shape because that largely determines how effectively it works to diffuse audio without artifacts.


Reflection Point Diffusion and Areas Ahead of the Seating Positions

Diffusion or scatting in two dimensions in the areas in front of the seating area makes the most sense.

The Auralex Hemisphere Sound Diffusors would be a good example. The 7" thickness can be an issue but it is also their chief strength (in the sense that the depth means they work over a larger ranger of frequencies).

The Auralex Geofuser is probably better/more universally accessible/place-able in many rooms. In fact if I was going to buy a commercial product, that would be on my short list to consider. It doesn't do as much as the deeper units but it might be all one can fit. It's also available in 1'x1' panels which can open up more possibilities.

Sonitus does something similar with their Dimension 4 product:

Or their bargain priced FourFuser:

In my own room I made some 20"x20"x3.5" deep diffusion with plywood bent from one side to the other kind of like it was chopped out of a large cylinder.....and I used it on the side walls intermixed with twice as many absorbers. (So, very similar to the Auralex Geofuser in form factor and range.)

And maybe the GIK polyfusor/cylindrical Evolution PolyFusor © – Sound Diffuser / Absorber Combination will come back into production.

Diffusion or Scattering Behind the Seating Position

At or behind the seating, diffusion that scatters in all directions is more fitting. DO NOT put them at first reflection points. That means that putting these produces on the back wall behind you is not ideal. But the back wall near the corners, the side wall to the rear of the seating position, or on the ceiling above or behind the seats, makes a lot of sense.

Skyline diffusers are excellent -- but require significant distance to work properly. Otherwise, they create phase shifts that sound worse than not having them in place. So in most normal sized home theaters, it can be challenging to get enough distance for them to work correctly.

So something like the Sonitus Dimension 4 is often more practical. It can work at shorter distances. Dimension4 DR6 (1 Pack).

Acoustic Frontiers has one that also seems less likely to introduce phase issues at most domestic room distances. Wave Diffusers like this:

are based on this Aeolian Diffuser concept but in a smaller footprint.