Formula used
Absorbed intensity: Ia = Ii × α
Transmitted intensity: It = Ii × τ
Reflected intensity: Ir = Ii × max(0, 1 − α − τ)
Total absorption: A = Σ(S × n × α)
Average absorption coefficient: ᾱ = A ÷ ΣS
Required treatment area: Srequired = [(Atarget − Acurrent) ÷ αtreatment] × safety factor
Panel count: N = ceiling(Srequired ÷ panel area)
How to use this calculator
- Select metric or imperial units and your desired precision.
- Add every important room surface, material, area, and quantity.
- Choose whether each row belongs to the existing or proposed design.
- Review or replace the frequency-dependent absorption coefficients.
- Enter a target absorption and panel size for treatment sizing.
- Complete the SAA fields only when twelve-band data is available.
- Calculate, compare the chart, then export CSV or print a PDF.
Worked example
A room has 40 m² of painted concrete and eight fiberglass panels. Each panel covers 0.72 m². The calculator multiplies every area by its frequency coefficient.
The untreated condition uses only the concrete row. The proposed condition includes both concrete and panels. Their difference shows added absorption at every octave band.
| Input | Example value | Purpose |
|---|---|---|
| Existing wall area | 40 m² | Baseline room absorption |
| Panel area | 0.72 m² | Area of one absorber |
| Panel quantity | 8 | Total proposed treatment |
| Target frequency | 1,000 Hz | Treatment sizing band |
| Safety factor | 1.10 | Planning allowance |
Frequency-band guide
| Band | Typical concern | Common treatment focus |
|---|---|---|
| 63–125 Hz | Deep bass and room modes | Thick porous absorbers and tuned traps |
| 250–500 Hz | Low-mid buildup and muddiness | Broadband panels with useful depth |
| 1,000–2,000 Hz | Speech clarity and reflections | Wall or ceiling absorbers |
| 4,000–8,000 Hz | Brightness, flutter, and hiss | Fabric, foam, carpet, or curtains |
About sabins, NRC, and SAA
A sabin represents one unit of perfectly absorbing area. One metric sabin equals one square metre with an absorption coefficient of one. Imperial sabins use square feet instead.
NRC is the rounded average of absorption coefficients at 250, 500, 1,000, and 2,000 Hz. It is useful for quick product comparison. It does not describe low-frequency behavior.
SAA averages twelve one-third-octave coefficients from 200 through 2,500 Hz. It provides a broader single-number summary. Complete laboratory data is needed for meaningful reporting.
Limitations and measurement notice
Preset coefficients are planning values, not product certifications. Mounting, thickness, air gaps, edge exposure, humidity, and laboratory methods can change measured performance.
The calculator adds absorption arithmetically by frequency. It does not model modal decay, scattering, diffusion, transmission loss, impedance, panel resonance, or spatial sound-field variation.
Use manufacturer test reports for procurement and compliance decisions. Commission an acoustician for critical studios, auditoriums, healthcare spaces, classrooms, factories, or regulated projects.
Frequently asked questions
What does an absorption coefficient of 0.80 mean?
It means the tested surface absorbs about 80 percent of incident sound energy under the stated measurement conditions. The remaining energy is reflected or transmitted.
Can one material use a single coefficient?
A single value is convenient but incomplete. Real materials absorb differently across frequency, so octave-band data gives a more useful design picture.
Why can an opening have an absorption coefficient of one?
Sound leaving through an opening does not return to the room. Room-acoustics calculations therefore treat that lost energy as complete absorption.
Is NRC enough for bass treatment?
No. NRC excludes 63 Hz and 125 Hz, where bass problems often occur. Review low-frequency coefficients separately before choosing treatment.
What is the difference between absorption and transmission loss?
Absorption describes energy removed from a room sound field. Transmission loss describes how strongly a partition blocks sound passing into another space.
Should I include people and furniture?
Include them when estimating occupied conditions. Seating, people, curtains, books, and soft furnishings can meaningfully increase total absorption.
Why does an air gap improve some panels?
An air gap changes particle velocity near the absorber. It can improve low-frequency performance, but the exact gain depends on construction and mounting.
Can this calculator predict reverberation time?
It provides the total absorption needed by reverberation formulas. A dedicated reverberation-time calculator should also consider room volume and method limits.
Why might laboratory coefficients exceed one?
Edge effects and the test method can produce reported values slightly above one. This calculator caps coefficients at one for conservative energy accounting.