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Why there’s no such thing as egg crate acoustic treatment

Dennis Foley September 11, 2014 No Comments
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A comment to my past video on why there’s no such thing as egg crate acoustic treatment really made me laugh. The guy called me an asshole and said it would be different if I was using a cardboard instead of styrofoam crate to make my point. So how much do I think the conclusions would I change in that video by using cardboard rather than styrofoam? Absolutely none.

The sound energy could care less what surface it strikes as the laws of physics come into play and they’re not that descrimitive, they don’t make those kind of selections. Now that said you get a different sound because sound takes on the characteristics of the surfaces that it strikes. We’ll probably do a video on that, the technical reasons why that is.

Sound takes on the sound of the surface it strikes

Glass and wood sound are good examples of that. The physics behind a cartons diffusion? Use your common sense. All the depths are the same so let’s give it the benefit of the doubt that it does act as a diffuser. What is it diffusing? All the depths, and quarter wavelength rule applies here, are the same so even if it is a diffuser it’s diffusing one group of frequencies. Is that what we wanted a diffuser to do? Absolutely not.

That’s called beaming. That’s taking a particular frequency range and shoving it at you constantly and only that frequency range. To cover a whole room surface with it you’re getting just that frequency range diffused. Well who wants that? That negates the performance of a diffuser. A diffuser is more of a broadband tool over a wide range of frequencies, with a quadratic diffuser is. Two, three hundred cycles to thirty five hundred cycles, well now we’ve got something to talk about.

The depths in the egg crate are all the same so that’s not diffusion, that’s sound redirection and sound annoyance. Well what’s our rule? Do no harm. Just because it looks like a diffuser, just because it has the appearance of a diffuser and it has depressions and stuff doesn’t make it a diffuser.

You can make the same argument for a sponge that you use to clean up in your kitchen, i.e. it must be a sound absorbing device because it has holes in it. Yes it has holes but it’s a half-inch thin. How much energy is that really going to absorb? Not much. So the material that it’s made of has nothing to do with the physics.

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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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