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Let’s talk about where to place absorption and diffusion technology. I don’t think in this video we’ll go through what absorption and diffusion technologies are but let’s look at mainly where we put them in general categories and for general usages so you can get a feel for all this craziness that we go through in room acoustics.

Usage, usage, usage. I can’t say that enough, I can’t repeat it often enough. The usage determines treatment. Usage determines room size. Just like in real estate, it’s location, location, location, in acoustics if you’re going to obtain a room sound quality level you must match it to usage. You must match size and volume, you must match treatment. So let’s walk through some usages and look at the absorption and diffusion treatment possibilities on the walls and ceilings. We’re not going to talk about floor right now, let’s just talk about walls and ceiling.

Voice. Most voice rooms that we’re hearing today, most vocals have that boxy effect that we hear from close proximity to wall surfaces. So absorption is the key treatment that they use in those. However, we’ve introduced a new process using diffusion in vocal rooms. And you’re going to start seeing some of that up here in the slider on our home page in January. You’re going to see an actual build of a voice room with diffusion and absorption. You’re actually going to hear audio tapes of the recordings using diffusion and absorption and I think you’re going to be very impressed.

I think we have a process here that adds new life and energy to our voice. And voice to me is very important. Vocals in a recording are the emotional connecting source. No matter who you are. If you’re a guitar player, you’re trying to get your guitar to sing. So the singing and the voice is really, really important. So we have a combination of diffusion and absorption in our vocal rooms and we have some videos on that that you can view.

Live rooms, when you’re recording an instrument in a room. Diffusion and absorption combinations. Diffusion on the sidewalls, if it’s a small volume room and if it’s a larger room then we have some more possibilities. So we can use portable diffusion. In small and large rooms we can use absorption on the sidewalls. It all depends on the usage, it all depends on is it going to be a live room for drums, is it going to be a live room for a choir, is it going to be a live room for a bunch of stringed instruments, is it going to be a live room for acoustic guitar. Usage, usage, usage.

Okay, listening. One of my favorites. Front and rear wall diffusion. Absolute, no argument, no discussion needed. Front and rear wall diffusion working together, not the same sequence, not the same frequency response but you get a match based on size and volume. Speaker size, very important here also.
So in our listening room we have front and rear wall diffusion and then our sides are going to be absorption. Now, our ceiling can be a combination of diffusion and absorption and just go to our Sacred Ground Studios in Los Angeles and you’ll see how all that works. Okay?

So mix and mastering. The rear wall is really a problem with mixing and mastering because that rear wall reflection comes back at the mixing and monitoring position. And then it interferes a time-delayed signal from the rear wall, interferes with the direct energy from the speakers in the front of the room.

So we use absorption or diffusion on the rear wall. Diffusion is a real popular choice these days. Vertical diffusion, so a diffusion sound in a horizontal domain. I have seen some two dimensional diffusion in studios but I think the most popular one is the vertical diffuser, diffusing sound in the horizontal domain. Remember, there’s an inverse relationship there. So in mixing and mastering side and front walls, always absorption. Because we’re after definition. We want to hear everything that’s in the mix. We don’t want to hear any room sound. We don’t want to hear anything other than the music and the voice. So we know what to do with a mix. Okay? Especially in mastering where spectral balance is so critical.

Home theater. Some possibilities here depending on your room size and volume. Rear wall is a good place for diffusion. Ceiling, a balancing act between absorption and diffusion. And then the front part of the room, obviously behind the projector, we have to have absorption and then the sidewalls are absorption for definition in the same vein as we use in our mixing room because we want to hear everything.

When we put diffusion on a ceiling – one of the functions of diffusion is to psycho-acoustically trick your brain so it can’t localize distance. And diffusers do that. They take a strong reflection and minimize it so your brain then can’t really localize how far the surface area away is. And the most rooms we work in the ceilings are so low that we want to make sure the brain can’t hear that distance. So diffusion is a popular area there.

So usage, usage, usage. Voice, live, listening, mix, mastering, home theater. Some possibilities here on treatment that we found through the years of doing this that takes into effect the problems of each particular usage.

This is an unedited transcript from our video series from Acoustic Fields. There will be some errors in grammar and sentence structure that occur during this translation process.

For complete understanding and comprehension, please view the video which is included in this text. For any additional information regarding this topic or others relating to room acoustics, please contact us directly at:

P: 520 – 392 – 9486

Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.


  • Karl says:

    Hi Dennis

    Just a quick email to say how much I enjoy your video clips …

    Sound is a fascinating science and as an engineering physicist, I am always leaning something new and your forums are the best place to so do. O to have your knowledge in this discipline.

    Anyway, I look forward to your next newsletter post…

    Kind regards and best wishes

    Karl G. Dodds
    Msc, Bsc

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