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Last week I was asked about ideal acoustic panels placement and whether they should be side walls or ceiling, or elsewhere. Okay, well let’s look at what we need. So all the energy in your room must operate in the three standard dimensions of length, width and height but its different depending on room usage.

With a home theater you’ve got to move the energy through those length, width and height dimensions and achieve some kind of sound field at the listening position that mimics with the filmmaker and the audio people on the DVD or whatever your source is trying to accomplish.

If it’s two channel then almost ninety percent of the time you’re going to use absorption on the side walls. Why? Because it is the time signature of the reflections at the listening position that you must manage. You can manage that time signature through the use of diffusion or you can manage it through the use of absorption. Those are your two choices.

You have absorption and diffusion and you don’t want any reflection in this issue as you already have that, it’s there by definition.

So what do you get with absorption?

You get a reduction in amplitude or strength, so that’s the easiest way to reduce the time signature at the listening position. Just take some of its strength away, okay. Diffusion doesn’t do that but it spreads the reflection out into a series of smaller reflections so no change in time signature or amplitude but the spreading out helps with non localization of the reflection.

So that said in critical listening rooms, absorption for me is best because it’s the easiest way to control the reflection. Yes you do lose a little energy but the trade off is worth it. Adding diffusion to the rear and the front walls boost it back up to normal, a nice diffused, defined sound stage. So I like to get my definition using the side walls and I like to get my air spaciousness and separation using the front and rear. Its a design philosophy that seems to really work well.

Other options

Now you can do other things too. Right now in the studio we are doing really high frequency diffusion in the horizontal dimension all around the edge of the studio above listening level and what we’re finding is it adds a lot of air and openness to the top of your room. If you stand up out of your chair and listen you’ll find that the sound field in your two channel system is pretty much just a little above the speakers to the floor. You stand up, you can’t hear that much as you would if you were sitting in the chair with the axis of radiation of the speakers set correctly to the room.

You just get more definition and its easier and here’s another thing about it. it’s easier to control and get right at the beginning. Diffusion takes a lot of testing. So I would say in two channel just stay with absorption for the side walls but watch the rate and level that’s critical. Go down into the hundred cycles and make sure that you absorb up through five hundred. We don’t care past that because it going to be a hundred percent in any foam past five hundred and that’s the law of physics on thickness.

So it’s not acoustic company’s doing it, it’s just the materials that we all work with which are defined by the laws of physics to perform in certain thickness domain. But look at one hundred to five hundred, that’s the critical part. I never liked the way, the curves were in existing foams when I developed ours, and that’s why it has a different curve as explained in the following video. When you hear it you’ll understand why. You can check it out here.

In Summary

So I hope that helps you. If you have any questions at any time I am always on hand to help answer them. Leave them in the comments section or email me at If you would like to learn more about room acoustics please sign up for my free videos and ebook by joining the mailing list here. I send room tuning tips and things for you to test in your room every Wednesday. They are easy to follow and really help you enjoy more of your music. And if you would like your room acoustic issues analysed for free by me then please fill in the form here and I will be happy to take a look for you.

Thanks and speak soon

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.


  • enrique pantaleon says:

    H Dennisi, i intend to put wall acoustic panels and add led strip light behind the frame of the panel. To achieve the lighting effect, the panel needs to be hoisted 2 inches off the wall
    My first question is does this defeat the purpose of sound absorption as there will be a gap between the wall and the panel? My other question is my room is rectangular, the tv will be placed at the back of the rooms smaller wall (in size – its rectangular) and infront of the tv will be all the sound equipment then speakers. Where should I place the panels?
    Thank you in advance.

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