Diffusion Vs. Absorption

[joemintz]

I'm going to be setting up a live room across from my current control room (bedroom) soon and I was wondering what the advantages of absorption (foam/fiberglass) are as opposed to diffusion (ala the rpg skyline and other products). It's a relatively small room, maybe 15' by 12', and I'm going to be tracking vocals, drums, electric and acoustic guitar, and acoustic bass. Any help with regards to materials and placement is much appreciated.

 

[Mind Riot]

Typically most folks go with absorption instead of diffusion for small rooms, but I don't know exactly where the cut off is between a small room and a large room. It's not really set in stone.

What do you want the room to be like as a recording environment? Do you want it to be live and add it's own imprint to whatever you record in it? That can be good, but not necessarily for all things. If you want to record an intimate acoustic guitar or vocal it may be tough without building a vocal booth. A live room can sound really awesome though.

On the other hand, a more dead, absorptive room gives you the choice of how much ambience you want to be added later artificially. From dead and tight to however much you want it's up to you, but it will be artificial ambience.

Another thing to consider is that even if you want a live, diffuse room ANY room is going to need bass trapping no matter what.

For bass traps, which you'll need either way, getting some rigid fiberglass panels and placing them so they straddle the room corners works well and is about the cheapest option. Owens Corning 703 is the standard, if you can find it. It's a commercial insulation, so don't go to Lowes or Home Depot, they'll just give you a blank look. Check in your local yellow pages under Insulation Suppliers. An HVAC contractor may have some, and they may take pity on you and sell you some. Mineral wool equivalents work just as well and may be cheaper if you can find some.

 

[RICK FITZPATRICK]

but I don't know exactly where the cut off is between a small room and a large room. It's not really set in stone.

My understanding is, when a rooms dimensions are wavelength proportions, then the room modes dominate the acoustics. That means the wavelengths the size of the rooms dimensions cannot be diffused as it would take geometric obstructions wavelenth size. Therefore, all diffusion must occur in higher frequencys. However, diffusion in small rooms, even by RPG(mid and hiZ) devices is still debated. For one, it is recommended that a room with diffusers on a rear wall, should be 3 times the lowest wavelength to be diffused, from the diffuser to the engineering position. At a 1000hz, this would be only about 3.1 feet. But at a 100hz, you would need a whopping 31 ft On the other hand,
absorbers can contribute somewhat to diffusion by placing small patches on walls and ceilings in such a way as there is reflective surfaces between the patches, such as a checkerboard illustrates. No that this pattern is necessary. Only that this reflective area should approximate the area of the absorber between and around patches.
Also, because of the "edge effect", a given square footage of absorbant material will give a HIGHER total ROOM absorption coefficient if cut into smaller pieces and distrubuted around the room on walls and ceilling. So, it sounds to me like using a patchwork of absorption material such as OC 703 will not only give better absorption results, but diffuse to a degree as well.
But then again, I've also been told that the one thing no one EVER talks about with diffusers such a quadratic residue type, is the wells act as 1/4 wavelength silencers(absorption) too!!! Go figure. The deeper you go into the rabbit hole, the darker it gets
fitZ