This reverb time calculator is a tool that allows you to estimate the amount of time it will take for a sound to decay in a given space. Calculating the reverb time (aka RT60) is necessary for determining the acoustics of a room and can be used to optimize the sound quality for various applications.
To use the calculator, you will need to know the following:
- The room dimensions;
- The size and number of doors and windows; and
- Optionally, the absorption coefficient of the materials through which the sound travels (advanced mode)
If you want to know how we use the above three elements to calculate RT60, keep reading this article. We'll learn the reverberation time formula used by this RT60 calculator.
What is the reverberation time?
Reverberation time indicates how long it takes for sound to decay in a room. By definition, it is the time required for the sound level in a room to reduce by 60 dB after the direct sound from the source has ceased (to know what we mean by "sound level" and dB, visit our dB calculator).
The longer the reverberation time, the more live the sound in the room will be. On the other hand, a short reverberation time is desirable in rooms where clarity of speech is paramount, such as lecture halls.
The reverberation time of a room depends on its size, shape, and absorption properties, as we'll see in the reverberation time formula. Generally, large rooms with hard surfaces will have long reverberation times, while small rooms with soft surfaces will have short reverberation times.
Now, let's look at how to calculate the reverberation time.
Reverberation time formula
To calculate the reverb time, we use the following empirical formula:
RT60 = 0.163 × V/A
- RT60 — Reverberation time (reverb time), calculated in seconds (s);
- V — Total volume of the room, in cubic meters (m³); and
- A — Effective absorbing area of the room, in square meters (m²);
A room is no more than a giant rectangular prism. From our rectangular prism volume calculator, we know that V equals the product of the length, width, and height of the room:
V = Length × Width × Height
Effective absorbing area
The effective absorbing area is the tricky part of the RT60 calculation. It is not simply the surface area of a rectangular prism but the surface area of each element (walls, doors, windows, etc.) multiplied by its corresponding absorption coefficient:
A = α₁S₁ + α₂S₂ + ... + αₙSₙ
- Sᵢ — Area of a specific element of the room's surface, in m²; and
- αᵢ — Absorption coefficient of that element surface (unitless).
The absorption coefficient indicates how well a material absorbs sound. The higher the absorption coefficient, the less time it will take for the sound to decay.
This calculator considers five types of elements:
- Doors; and
🙋 In the advanced mode of the reverberation time calculator, you can look at the absorption coefficients of the elements and modify them.
Ceilings, floors, doors, and windows have rectangular shapes. Therefore, their surface area (S) is the area of a rectangle (height×width or length×width) multiplied by the number of elements. On the other hand, the area of the walls is the area of a rectangular prism (2 × (Length + Width) × Height) minus the surface area of the remaining elements.
And that's it. Now you know how to calculate reverberation time using the math behind this calculator.