When planning a new build or a renovation, there are many aspects that naturally receive attention: design, functionality, choice of materials and budget.
Unfortunately, acoustics are often only considered too late – and this can have major consequences. Poor acoustics affect comfort, productivity and wellbeing. That is why it is essential to take acoustics into account already during the design phase.
In this article, we share knowledge about how to calculate the acoustics of a room, why it is important, and what to do if reality does not match the calculation. We take Sabine’s formula as our point of departure, as it is the classic tool for estimating reverberation time.
Why should I calculate the acoustics?
Imagine an open-plan office where sounds from, for example, conversations, phone calls and typing on keyboards blend together. Or a classroom where the teacher has to raise their voice to be heard. These are situations that could have been avoided with a simple acoustic calculation early in the project phase.
A calculation provides an indication of how the room is expected to behave acoustically. This makes it possible to select the right solutions and avoid costly adjustments later on. It creates reassurance for the client, the architect and the users alike.
How do I calculate the acoustics?
The core of an acoustic calculation is the reverberation time. It describes how long it takes for the sound level in a room to decrease by 60 dB. The shorter the reverberation time, the more damped the sound in the room will be perceived.
To calculate the reverberation time, you need to go through a number of steps, each of which is crucial to the accuracy of the calculation.
We begin by reviewing the individual steps of the calculation, then take a closer look at Sabine’s formula and conclude with an example.
1. Define the room volume
The first step is to determine the size of the room. The volume is found by multiplying length, width and height. It is important to measure as accurately as possible and to remember that ceiling height may vary if, for example, there are sloping walls or installations.
V = L × W × H
The volume is essential, as it forms the foundation of the calculation.
2. Map the surfaces
Next, the room’s surfaces are assessed: ceilings, floors, walls, windows and doors.
Each surface has different acoustic properties. An acoustic ceiling absorbs sound, whereas a concrete ceiling reflects most of it. A large glass wall can have a significantly negative impact on acoustics, while soft elements such as curtains or carpets contribute additional absorption.
3. Find the absorption coefficients of the materials
All building materials have an absorption coefficient (α), which indicates how much sound is absorbed at different frequencies. These values can be found in databases or provided by manufacturers.
As a standard reference, the 500 Hz frequency band is often used. However, depending on the project, it may be relevant to consider several frequency bands, such as 250 Hz, 500 Hz and 1000 Hz. This is because materials can behave very differently at low and high frequencies.
Below is a brief overview of typical α-values at 500 Hz:
| Material / surface | Typical α-value (500 Hz) | Notes |
| Concrete / plastered wall | 0.02 – 0.05 | Very hard and reflective |
| Glass (window) | 0.03 – 0.07 | Large glass surfaces result in long reverberation |
| Wooden floor / parquet | 0.05 – 0.10 | Some absorption, but mainly reflective |
| Carpet (thick, with underlay) | 0.20 – 0.40 | Can vary significantly depending on thickness and quality |
| DAMPA acoustic ceiling | 0.60 – 0.95 | Value depends on perforation, cavity depth and backing materials |
| Light curtain | 0.10 – 0.20 | More effective at high frequencies |
| Heavy curtain | 0.35 – 0.60 | Particularly effective at mid and high frequencies |
| Person (seated) | approx. 0.5 m² sabin per person | Added as “equivalent absorption” |
You can find all our acoustic measurements under each product or in our download centre.
4. Calculate the total absorption area
Here, the area of each surface is multiplied by its absorption coefficient (α), and the results are added together. For elements such as people or furniture, an equivalent absorption area can be used. The sum is the total absorption area (A).
Example:
A ceiling of 50 m² with α = 0.8 provides 40 m² of absorption.
A wall of 30 m² with α = 0.1 provides 3 m².
Total A = 43 m².
5. Apply Sabine’s formula
With volume (V) and absorption (A), the reverberation time can be calculated:
Reverberation time = 0.161 · V / A
The result shows how long sound remains in the room and can be compared with recommended values for the relevant room type.
6. Evaluate the result and adjust
If the calculation shows that the reverberation time is too long, additional sound-absorbing materials must be added, such as an acoustic ceiling, wall panels, ceiling island or other acoustic elements. If it is too short, it may be worth retaining some harder surfaces to ensure that the room does not feel “dead”.
By carefully going through all steps, you gain a more realistic understanding of how the acoustics will perform in practice.
Sabine’s formula – the classic tool
Sabine’s formula is the most widely used method for estimating the reverberation time of a room. It was developed by the American physicist Wallace Clement Sabine around 1900, when he investigated why some auditoriums had poor speech intelligibility.
His research showed that the relationship between room volume, the properties of sound-absorbing materials and the time sound persists could be described mathematically.
Sabine’s formula is simple and effective:
Reverberation time = 0.161 · V / A
Where V is the room volume in m³ and A is the total absorption area in m² sabins.
Calculation in practice
Imagine an open-plan office measuring 12 × 10 × 3 metres. This gives a volume of 360 m³. The room has a ceiling of 120 m², a floor of 120 m² and walls totalling 132 m².
If all surfaces are hard and absorb very little sound (α ≈ 0.05), the total absorption area will be very low:
- Ceiling: 120 × 0.05 = 6.0 m²
- Floor: 120 × 0.05 = 6.0 m²
- Walls: 132 × 0.05 = 6.6 m²
Total A = 18.6 m²
Inserting the values into Sabine’s formula gives:
Reverberation time = 0.161 × 360 / 18.6 ≈ 3.1 seconds
This means that sound remains in the room for more than three seconds – far too long for an office environment.
We choose to add an acoustic ceiling (α ≈ 0.85) and carpet on the floor (α ≈ 0.25). The calculation then looks different:
- Ceiling: 120 × 0.85 = 102.0 m²
- Floor: 120 × 0.25 = 30.0 m²
- Walls: 132 × 0.05 = 6.6 m²
Total A = 138.6 m²
Recalculating:
Reverberation time = 0.161 × 360 / 138.6 ≈ 0.42 seconds
This is now a level that is very well suited to an open-plan office. Sound is absorbed quickly, and the room feels far more comfortable and calm to work in.
Is the calculation always accurate?
A calculation is a model – not a guarantee.
In practice, several factors can influence acoustics: frequency dependency of materials, furniture layout, the number of people in the room, or complex room geometries. Therefore, it is wise to treat the calculation as a guideline that should be followed up with validation once the room is completed.
At DAMPA, we recommend planning with a degree of flexibility. This allows for adjustments using additional panels or modified coverage if initial measurements show deviations.
What should I do if the acoustics do not meet expectations?
Even with thorough calculations, differences between theory and practice can occur. The room may be used differently than planned, the furniture layout may change, or material performance may vary.
In such cases, it is possible to fine-tune the acoustics. This can be done, for example, by adding more sound-absorbing elements such as ceilings islands, wall panels, ceilings or other acoustic solutions.
At DAMPA, we advise on which solutions provide the best balance for the specific room and requirements. In this way, acoustics can be brought into line – even if the conditions change along the way.
Next steps
Good acoustics are not created by chance. They require knowledge, calculation and planning from the very beginning of a project. Sabine’s formula is a simple and effective tool that provides an initial insight into how a room will sound. However, the greatest certainty is achieved by combining calculations with experience-based advice and a plan for adjustment if reality does not fully match the numbers.
At DAMPA, we are ready to help you with your next project. Contact us by email: dampa@dampa.dk or by phone: +45 63 76 13 00
Frequently asked questions
- Why is it important to calculate acoustics already during the design phase?
Because poor acoustics can have major consequences for comfort, productivity and wellbeing. A calculation early in the process provides insight into how the room will behave acoustically and can save costly adjustments later. - What is reverberation time?
Reverberation time describes how long it takes for the sound level in a room to decrease by 60 dB. A short reverberation time results in a more damped room, while a long reverberation time causes sound to linger and interfere with conversations and work. - How do you calculate the acoustics of a room?
You start by finding the room volume (length × width × height), mapping the surfaces and their materials, finding the absorption coefficients of the materials and calculating the total absorption area. Finally, Sabine’s formula is used to determine the reverberation time. - What is Sabine’s formula, and why is it relevant?
Sabine’s formula was developed around 1900 by Wallace Clement Sabine and is used to calculate reverberation time. It shows the relationship between room volume and total absorption and is still the most widely used method today because it provides a simple and effective estimate. - What should you do if the acoustics do not meet the target?
Even with thorough calculations, differences between theory and practice can arise. In such cases, it is possible to fine-tune the acoustics, for example by adding more acoustic elements such as baffles, wall panels or screens. In this way, acoustics can be brought into balance, even if the room changes over time.
