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One of the questions from last weeks Google Hangout stated “I’m researching which home theater acoustic ceiling tiles I need and want some guidance. I want a mixture of absorption and diffusion on the ceiling. So what kind of ceiling tiles are going to be appropriate? Foam panels?”

Alright so let’s back up a little bit. What is our usage? The ceiling treatment for a control room versus a home theater room versus a listening room are different, not drastically and sometimes only subtly, but it still has to be dealt with. The ceiling and the floor reflection reaches your listening position first. It’s usually the shortest distance between you and the direct energy. The floor is especially, because you’re sitting on it, so the floor treatment and the ceiling treatment have to work together and the usage of the room has to work together.

Now let’s go back to diffusion and absorption which this person would like to use. Diffusion and absorption are good for home theater, good for personal listening environment maybe not so good for a control room. Once again what are we doing in the control room? How are we doing things? So we’ve got to always get back to usage. I’m always going to harp and preach about usage because don’t put the cart before the horse, don’t put the room treatment ahead of the usage.

Usage first, room treatment second.

Alright, so if this is a home theater room then a good balance of absorption and diffusion is good because what are we trying to do with the sound fields creating by all these multiple sources, all these speakers? What are we trying to accomplish? When we want to make our room sound realistic we want the sounds that move left to right across our video screen to move left to right across our audio screen in our room if you will, or sound stage.

We want the rear channels to imitate the ambient noise and levels that are going on behind us but also be able to move the sound from the front of the room to the rear of the room and sometimes move the sound from the rear of the room to the front of the room. Now that’s a great trick if it can be done on video although I have not seen that, I have not seen a video where they have a video of something going on behind the listener and the sound translating, I’m still waiting for that. They’re not doing that yet. They’re doing a lot of sound in front of the room like explosions and stuff moving across you, front to rear but not too much rear to front.

So diffusion and absorption is good for home theater and listening rooms. Now that said, what kind of ceiling panels and what kind of diffusion sequences? Completely unknown. I can’t really tell you what to use in this particular situation because I don’t know enough about the issues in your room. There is no one-size-that-fits-all.

You see a lot of home theater companies that just use a hundred percent absorption. Why? It’s cheap, it’s easy to install, it’s easy to make look pretty and consistent but it’s horrible for performance. Absolutely horrible to have all the surfaces in your room all sound absorptive treatment, it’s not good. So it’s not realistic and diffusion needs to be brought in there.

So what is the best ceiling tile for absorption?

What is the best treatment for diffusion in ceiling areas? I will tell you that diffusion in ceiling systems is not easy because diffusers by definition are a little bit heavy to build, they’re expensive to build and you have to have the support structure to support them.

We’re doing a home theater room for one of our customers in Australia. He’s using our 2-inch foam for absorption. We’re doing 2-foot by 2-foot but he’s also building diffusers based on prime 11 sequence. Two by two foot for the diffusers and then he’s going to alternate them through a room that’s 15 by 16. So he’s going to have 150 to 175 square feet of these diffusers and absorbers.

So there’s a good example to work with. Now here’s the next question, where do you put the absorption and where do you put the diffusion? All that has to be analyzed. Do I start with absorption in the corners and on the side walls? Do I alternate diffuser, absorber, diffuser, absorber across the horizontal plane or do I do it on the vertical plane? Once again we have to look at the configuration. What are our sources? Where’s our energy coming from in the room? What part of that energy needs to be diffused? How much diffusion we put where in the room? Depends on usage.

In Summary

I hope this explanation helped. 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.


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.

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