Walk outside on a cold winter day just after the first big snowfall and you can hear the hush in the air. Everything sounds different because that hush in the air is the snow absorbing sound. Now, compare that to walking into a gym where the sound bounces around and lingers in the room.

When sound hits a material, three things can happen. First, the sound can be reflected; like in the gymnasium where it bounces off the hard walls and is redirected. Second, some of the sound can be transmitted through lightweight materials, like thin office walls. Finally, the sound can be absorbed. What happens to the sound when it is absorbed? It gets trapped in the material and converted into an extremely small amount of heat. Don’t count on it as a replacement for your heating system.

Materials that absorb sound are porous, like the snow. The air gets trapped in between the little snow crystals (or fibers in other materials) and turned into heat. One of the most common materials used to absorb sound is fiberglass. Closed-cell spray foam, on the other hand, acts as a good thermal insulator, but is a very poor acoustical absorber.

Just as not all materials are porous enough to absorb sound, not all materials absorb sound in the same way. Acoustical absorption is frequency dependent. That means two materials may look the same, but one might absorb high frequencies or high pitch sounds, and another may absorb mid or low frequencies. Typically, as the thickness of the material increases, so will the absorption of low frequency sound.

At ABD Engineering & Design, it’s our job to engineer acoustical solutions that control how the sound is reflected, transmitted, or absorbed based on the type of space. If maximum absorption were the goal, we’d treat every project like a movie theater or even like an anechoic chamber. But in the real world, different spaces have different acoustical needs, and our job is to develop acoustical solutions that are custom fit to meet those needs.

Melinda Miller

Melinda Miller

Melinda Miller, PE, LEED AP BD+C, EDAC, INCE. Bd.Cert., Melinda is the Principal Engineer, stationed in Portland, Oregon. Melinda has been working in acoustical engineering since 2001. Her expertise includes diagnosing and preventing noise problems, as well as designing acoustically optimized environments using 3D computer modeling, and evidence-based design practices. Melinda earned her Bachelor's Degree in Mechanical Engineering from the University of Idaho in 1998, and Master's from the University of Illinois, Chicago, in 2003. Melinda has presented technical papers and speeches for the Acoustical Society of America, the American Institute of Architects, the Chicago Chapter of the Audio Engineering Society, Columbia College, 
and The University of Illinois at Chicago.

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