Sound Absorption Coefficient Calculator

Calculate the sound absorption coefficient (α) of a material or room surface using measured incident SPL and reflected SPL, or find total room absorption using surface area and absorption coefficients. Enter your calculation mode, provide the relevant acoustic measurements, and get back the absorption coefficient (α), total absorption in sabins, and a breakdown of absorbed vs. reflected energy.

Choose what you want to calculate

dB

Sound pressure level of the incident wave striking the material

dB

Sound pressure level of the wave reflected from the material surface

m²

Total surface area of the absorbing material

Absorption coefficient of the material (0 = perfect reflector, 1 = perfect absorber)

sabins

The total absorption (in sabins) you need to achieve

Known absorption coefficient of the material you plan to use

Results

Primary Result

--

Energy Absorbed

--

Energy Reflected

--

Absorption Class (ISO 11654)

--

Absorbed vs. Reflected Energy

Frequently Asked Questions

What is the sound absorption coefficient?

The sound absorption coefficient (α) is a dimensionless value between 0 and 1 that describes how much sound energy a material absorbs rather than reflects. A value of 0 means the surface reflects all incident sound, while a value of 1 means it absorbs all of it. Most real-world architectural materials fall somewhere between 0.05 and 0.95 depending on frequency.

What is a good sound absorption coefficient?

It depends on the application. For recording studios and home theaters, materials with α ≥ 0.70 are considered highly absorptive. Acoustic foam and heavy curtains typically range from 0.50–0.90. Hard surfaces like concrete and glass have very low values (0.01–0.05). According to ISO 11654, Class A materials have a weighted absorption coefficient (αw) ≥ 0.90.

How is the sound absorption coefficient calculated from SPL measurements?

The coefficient is derived from the ratio of absorbed to incident sound intensity. Since intensity is proportional to the square of pressure, α = 1 − (10^((Reflected SPL − Incident SPL)/10)). This means a 10 dB drop between incident and reflected levels corresponds to 90% absorption (α = 0.90).

What is a sabin and how does it relate to the absorption coefficient?

A sabin is the unit of acoustic absorption. One sabin represents the equivalent absorption of one square metre of a perfectly absorbing surface (α = 1.0). Total room absorption (A) in sabins is calculated as A = α × S, where S is the surface area in m². Multiple surfaces are summed: A_total = Σ(αᵢ × Sᵢ).

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

The standard laboratory method uses a reverberation room (ISO 354): measure the room's reverberation time (RT60) with and without the material, then calculate the difference. For simpler in-situ measurements, you can use an impedance tube (ISO 10534-2) or measure the incident and reflected sound pressure levels with a microphone at known distances from the surface, as supported by this calculator.

What is the sound absorption coefficient of common materials?

Typical mid-frequency (500 Hz–1 kHz) values include: open-cell acoustic foam (0.70–0.95), heavy carpet on concrete (0.30–0.55), cotton fabric (0.40–0.75), plasterboard (0.05–0.15), bare concrete (0.01–0.04), glass (0.03–0.05), and wood panels (0.10–0.30). Always verify values at the specific frequency band relevant to your project.

What does ISO 11654 absorption class mean?

ISO 11654 classifies materials into five classes (A–E) based on their weighted sound absorption coefficient (αw). Class A (αw ≥ 0.90) is the most absorptive, used in critical listening environments. Class E (αw 0.15–0.25) provides minimal absorption. Materials with αw < 0.15 are not classified. This standard is widely used in Europe for specifying acoustic ceiling tiles and wall panels.

What is the difference between NRC and the sound absorption coefficient?

The Noise Reduction Coefficient (NRC) is a single-number rating equal to the arithmetic mean of absorption coefficients at 250, 500, 1000, and 2000 Hz, rounded to the nearest 0.05. The sound absorption coefficient (α) is a frequency-specific value. NRC is commonly used in North America for rating acoustic products, while ISO 11654's weighted αw is preferred in Europe.

More Physics Tools