Introduction to good acoustics
Acoustics in a room can be described as the reverberation time, i.e. how long it takes for a sound to fade out in a room.
Reverberation time depends heavily on the room’s surface structure. Hard, smooth surfaces such as concrete and plaster result in long reverberation times, while materials with an open surface structure, such as Troldtekt acoustic ceilings, result in short reverberation times and thus excellent acoustics.
- Troldtekt's open structure absorbs sound
- A high level of sound absorption yields a short reverberation time
- A short reverberation time makes it easier to hear what is being said
- Acoustic interference is minimised
A brief outline of some of the most important room acoustics concepts: sound and noise, frequency, sound pressure, reverberation time, sound absorption and speech intelligibility.
See also what the most commonly used structure of a Troldtekt ceiling looks like.
Introduction to acoustics
In this video, you will be introduced to the most important basic concepts of room acoustics.
Good acoustics are a prerequisite for a good indoor climate. If the acoustics are poor, sound becomes noise, and you are unable to hear what is being said.
Good acoustics are important for everyone’s sense of well-being at home, work and school, as well as at institutions, swimming pools, cinemas or theatres. In other words, in any room where people spend time together.
Sound and noise
Sound is compression waves that travel through the air. We normally distinguish between sound and noise. We call pleasant, ordered waves sound, but categorise chaotic obtrusive waves as noise.
Scientifically, sound is:
"Elastic molecular oscillations in the air or other media that create a chain reaction by setting the nearest particles in motion. The sound will then spread at a certain propagation velocity which is called the speed of sound in the medium in question.”
Frequency
Frequency is an expression of how many times a sound wave oscillates per second. Frequency is measured in Hertz (Hz). 100 Hz corresponds to 100 oscillations per second. The frequency of bass sounds is low, while that of treble sounds is high.
Low-frequency bass sounds have long, soft sound waves with few vibrations per second, while a treble sound has many vibrations per second.
For instance, the wavelength in air for a sound wave with a frequency of 20 Hz is 17 metres, while the wavelength for a high-frequency treble sound wave with a frequency of 20 kHz is only 1.7 centimetres.
This means that the sound wave is inversely proportional to the frequency.
Reverberation time
Reverberation time is the time it takes for a sound in a room to fade out. In scientific terms, it is the time in seconds it takes for the sound level to drop by 60 dB after the sound source has ceased.
If the surfaces are hard and reflective (1), it will take a long time for the sound to fade out because the sound is reflected many times before it disappears. On the other hand, if the surfaces in the room are made of absorbent materials (2), the sound will quickly fade out.
Sound absorption
Short reverberation times can be achieved by using materials which are good at absorbing sound. This property can be described using an absorption coefficient – specified using the Greek letter a (alpha).
Hard and rigid materials with a smooth surface (1) often have a low sound absorption coefficient, while materials with a soft, uneven or porous surface (2) typically have a high sound absorption coefficient.
The higher the proportion of the room’s total surface area that absorbs the sound, the less reverberation the room will have. It is therefore important to select a material with a high sound absorption coefficient for large surfaces.
In this way, it is possible to regulate and reduce the reverberation time to achieve a good acoustic environment with a clear acoustic image.
The ceiling will usually be the easiest surface to regulate acoustically, since it is both large and accessible.
Speech intelligibility
If a room has a long reverberation time, spoken words will not fade out before the next words reach the listener. The result is poor speech intelligibility, and it becomes difficult for the listener to understand what is being said. However, if the sound is absorbed, there is a short reverberation time, good acoustics and a high level of speech intelligibility.
Troldtekt® & acoustics
In a villa, holiday home or apartment, you will typically choose a so-called directly installed ceiling: in other words, a ceiling panel fastened with screws or brackets directly onto battens in the ceiling.
One usually chooses to insulate with mineral wool behind the ceiling panels, which also provides by far the best sound absorption.
The structure of a Troldtekt ceiling can look like this:
The curve to the right shows how this structure with a Troldtekt ceiling absorbs sound in the room. And as the curve shows, sound is absorbed across the entire frequency range for normal speech (250 - 2,000 Hz) between 0.75 and 1.00 - or between 75 and 100%.
Sound is 100 per cent absorbed when sound absorption is equal to 1.
Acoustics calculator
With Troldtekt’s acoustics calculator you can get a quick overview of the acoustics in a room.
Enter the dimensions and material selection of your room, and the acoustics calculator generates a straightforward report showing reverberation times, absorption area and other useful information about acoustics.