Sound Absorption Coefficient Calculator

Created by Komal Rafay
Reviewed by Dominik Czernia, PhD, Jack Bowater and Adena Benn
Last updated: Oct 31, 2022

We have created this sound absorption coefficient calculator to help you determine the sound-absorbing property of a material. Measuring the sound absorption coefficient is significant for materials where the value is not already determined, and you might be looking to try combinations of new materials.

In this article, you will learn how to calculate the sound absorption coefficient for various materials using the sound absorption coefficient formula. If you don't know it already, you can find out the sound absorption coefficient and why knowing its value is significant for implementing soundproofing systems in any living or working area.

We have also provided the average sound absorption coefficient values for common materials.

What is sound absorption coefficient? Sound absorption coefficient definition

The sound absorption coefficient is the numeric value that signifies the sound-absorbing properties of any material. Its symbol is usually α\alpha.

When sound waves travel in a room and come in contact with a surface, three things could happen:

  1. Part of the sound is reflected;
  2. Part of the sound passes through; and
  3. Part of the sound is absorbed and converted to heat energy.

We consider the sound absorption coefficient as a measure for assessing the effective sound absorption by any material. Its value ranges from 0 to 1, with 1 being the perfect absorber.

We measure the total room sound absorption in sabins. It is the unit of measurement of sound absorption, representing the effective sound absorption inside a room.

💡 Did you know that sounds travel at different speeds through different mediums? You might visit our speed of sound in solids calculator to understand the phenomenon better.

And if you want to study the speed in all various mediums, we still got you covered with our speed of sound calculator.

Sound absorption coefficient calculator

The sound absorption coefficient calculator is an easy-to-use tool that will help you determine the sound absorption coefficient values of many materials.

Our tool provides three different formulas to perform the calculations:

  1. The first one calculates the sound absorption coefficient based on the absorbed sound intensity and the incident sound intensity.

  2. The second method is total room sound absorption.
    You have the option of entering the multiple surfaces present in the room in terms of their surface area and the absorption coefficient values of each surface. The calculator can take input for up to 10 different surfaces.

  3. The third method is the average sound absorption coefficient.
    The average sound absorption is calculated using the total absorption of the room and the total surface area in the room in square meters (m2m^2) .

Besides these various calculations, you can view α\alpha (sound absorption coefficient) for some common materials. All you need to do is select yes from the given options, and you will be able to see a list of different sound-absorbing materials and their coefficient values.

How to calculate sound absorption coefficient

The numeric value of the sound absorption coefficient helps understand how effectively any material can block out or absorb sound. The best sound absorbers are materials with sound absorption coefficients (α\alpha) close to one. As mentioned previously, our sound absorption coefficient calculator allows three different methods to calculate α\alpha values in different scenarios:

Sound absorption coefficient from sound intensities

The first is the sound absorption coefficient using absorbed and incident sound intensity. The formula for sound absorption coefficient is:

α=Ia/Ii\alpha = I_a/ I_i

where:

  • α\alpha - The sound absorption coefficient;
  • IaI_a - The absorbed sound intensity; and
  • IiI_i - The incident sound intensity.

The sound intensities are usually in W/m2 (watts per meter squared). Remember to measure them at the same frequencies!

For example, if you have 0.9 W/m2 and 0.3 W/m2 as your absorbed and incident sound intensities, then all you have to do is divide them, and the result would be α\alpha = 0.3. It means that the material is a relatively poor sound absorber.

Total absorption of a room formula

When you calculate the total sound absorption of a room, where you have multiple surfaces that you're using to soundproof that room, you need the surface area and the absorption coefficient for each material.

The formula for total sound absorption of a room is:

A=Siαi A= \sum{S_i\alpha_i}

where:

  • AA - The total sound absorption of the room;
  • αi\alpha_i - The absorption coefficient of the ithi^{th} material; and
  • SiS_i - The surface area of the ithi^{th} material.

Average sound absorption coefficient formula

When you are looking to determine the mean or average sound absorption coefficient, you need to input the total sound absorption of the room and the total surface area.

The formula is:

αm=A/S\alpha_m = A / S

where:
αm\alpha_m - The average sound absorption coefficient;
AA - The total sound absorption of the room in square feet sabins; and
SS - The surface area of the room.

So, you may divide the total sound absorption of the room by the room's surface area, and your result is the average sound absorption coefficient.

Convert sound absorption coefficient to dB

❗ Decibels measure sound volume, while sabin measures the sound absorption of any given surface. What's more, the value of sabin is greater than or equal to zero, while decibel is a logarithmic value (i.e., can take any real value).

Sound absorption coefficient chart

It's time we look at the α\alpha values for some common materials.

Materials

Sound absorption coefficient

Acoustic tiles

0.4 - 0.8

Brickwork, painted

0.01 - 0.02

Carpet, heavy on concrete

0.3 - 0.6

Concrete block, coarse

0.3 - 0.4

Cotton batts

0.79

Fiberboard on battens, 12 mm

0.3 - 0.4

Floor (concrete)

0.03

Floor (wood)

0.06 - 0.1

Hardwood

0.3

Glass, ordinary windows

0.1 - 0.2

Mineral wool, 100 mm

0.65

Polyurethane foam, flexible

0.95

Rubber sheet, 6 mm porous

0.1 - 0.2

Slag wool or glass silk 50 mm

0.8 - 0.9

Vinyl tile

0.04 - 0.07

The sound absorption coefficient chart shows the corresponding values of selected materials measured at the same frequencies. There are many other sound-absorbing materials with varying strengths in terms of soundproofing.

If you were wondering what fabric is suitable for sound absorption, there are many, like cotton batts, fabric acoustic panels, and any porous fabric. Depending on your need and how much sound has to be absorbed, you may use them.

Applications of sound absorption coefficient

Let's consider this, you are building your house, and you want to make some of the rooms soundproof. You might consider adding some sound-absorbing material to the flooring and roofing, and walls. A good sound-absorbing material reflects minimal sound and reduces the energy lost as heat. This is one of the applications of the sound absorption coefficient.

Some other examples include:

  • Soundproofing - as the name indicates, aims to reduce sound intensity between the source and receiver. You soundproof the rooms where you don't want the noise going out or the outside hustle coming in.

  • An anechoic chamber is a room that sops the reflection of sound and electromagnetic waves. Its design ensures the maximum absorption of sound. These chambers are effective in measuring the sound pressure level. If you want to find out how to measure sound absorption coefficient, this is the right place to, e.g. prepare a material sound absorption table.

  • Room acoustics is a concept that explains how sound behaves in a closed space based on different frequencies and types of rooms.

  • Noise barrier is usually an outdoor structure designed to reduce noise pollution in certain areas, which require little to no noise in their surroundings. The result from the sound absorption coefficient equation should be as close to one as possible.

✅ You may want to take a look at our roofing calculator if you plan on getting new soundproof roofing. And in case you decide to throw in new flooring, we also have a flooring calculator to help you figure out the costs and materials required.

FAQ

What is the sound absorption coefficient?

The sound absorption coefficient definition is a "measure of how much sound is absorbed by a material". Mathematically, the sound absorption coefficient definition is "the ratio of incident to absorbing sound".

The equation of sound absorption coefficient is:

α = Ia/ Ii

where:

  • α - The sound absorption coefficient;
  • Ia - The absorbed sound intensity; and
  • Ii - The incident sound intensity.

What is a good sound absorption coefficient?

A good and efficient sound absorber is a material with a sound absorption coefficient close to 1. The sound absorption value of materials ranges from 0 to 1, with 0 being poor and 1 being a perfect sound absorber.

These sound-absorbing materials are significant in constructing structures where the sound's controlled absorption and reflection are crucial. The commonly used materials are cotton batts, mineral wool, acoustic tiles, and various wooden panels.

How can I measure the sound absorption coefficient of a small room?

The formula to calculate the sound absorption of a room is:

A= ∑ ( Si × αi )

where:

  • A - The total sound absorption of the room;
  • α i - The absorption coefficient of the ith material; and
  • Si - The surface area of the ith material.

To calculate the sound absorption of a small room:

  1. Note the surface area and absorption coefficient of all sound-absorbing materials in the room.
  2. Multiply each surface area with its corresponding α.
  3. Sum all the products obtained in step 2.
  4. The result is the total sound absorption of the room.

What is the sound absorption coefficient of cotton?

The sound absorption coefficient of cotton batts is 0.79.

The value of the sound absorption coefficient ranges between 0-1, with 0 being poor and 1 being good at absorbing sound. The coefficient value of cotton is close to one and it is considered a good sound absorber. The more sound a material absorbs, the better it is at soundproofing.

Komal Rafay
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Sound absorption coefficient
Incident sound intensity
W/
ft²
Absorbed sound intensity
W/
ft²
Sound absorption coefficient
Material sound absorption table
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