Sound Absorption Coefficient – What is it and Why Do I Care?

The Role of the Sound Absorption Coefficient in the DIY Recording Studio

Looking to outfit your recording studio with broadband absorbers, bass traps, or any other types of acoustical treatment? Are you disgusted with the high prices of professional acoustic products and planning to make your own DIY absorbers or bass traps? Well, if the answer to either question is “yes,” then you should have interest in the sound absorption coefficient’s role in recording studio design. Simply stated, the sound absorption coefficient is an indicator of how much sound a material absorbs. This number ranges from 0 – 1.0 and is assigned to ranges of frequencies. Materials have a different sound absorption coefficient for each range, because the material is not going to behave the same for the entire frequency spectrum. For example, broadband absorbers that tame high-end frequency reflections may not be appropriate as bass traps. Also, be aware that soundproofing and acoustic treatment are not necessarily the same thing and may require different materials to achieve each result.

It is nice to know the sound absorption coefficient of the professional products, as you may plan to shop around and compare specs. However, knowing the sound absorption coefficient is essential if your plan is to construct DIY broadband absorbers or bass traps. The heart of your DIY creations will be the materials you purchase to construct them. Acoustic treatment products tend to be dense, so it may be tempting to use this as your guide for choosing materials. However, this is not the only consideration. A material may be dense, but if it is highly reflective, this will subtract from its sound absorption coefficient. Also, if you are planning to create acoustic treatment that is covered in fabric, then the fabric should also be non-reflective. There is really no reason to delve too deeply into the technical side of this, unless you have no other plans for the next few months and have no desire to actually record. But to get a better understanding of what the sound absorption coefficient means, check out the examples below. They represent two sound-absorption extremes.

Image of Speak Emitting Sound Waves - Sound Absorption Coefficient Page

Photo by OpenClipartVectors / CC0 1.0

Sound Absorption Coefficient of a Basic Brick – Ranges from about .03 to .07 throughout the entire frequency spectrum.

Sound Absorption Coefficient of Unrestricted Air – About 1.0 throughout the entire frequency spectrum.

Many people believe that Owens Corning 703 rigid fiberglass is the way to go. I chose to use fluffy fiberglass and compress it into an appropriate density. Either way works effectively. Find the way that works best for you.

Check out the sound coefficient list at BobGolds.com. It helped me tremendously while I was formulating my acoustic treatment plan. You may even have some items already in your possession that have good sound absorption. Be creative. The recording studio does not have to look great to be effective. After all, audio recordings are made for listening, not watching.

Check out the following link for a good acoustic treatment material.
Wel-Bilt Oversize Moving Blanket

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