A measure of noise absorption
The energy of the sound incidence is the sum of the reflection, transmission and absorption.
If A is the fraction of the sound energy that is absorbed, T is the fraction which passes through the fabric and R is the fraction which is reflected (by reflection or diffusion), then A + T + R = 1. The absorption value aw represents the part of the sound energy that is not reflected: aw = 1 - R. The absorption value is also the sum of the absorption and transmission: aw = A + T. The greater the aw value, the more energy the material absorbs. An aw value only applies for a certain frequency. The NEN ISO 11654 Acoustics standard is a standard for converting the aw values of all frequencies into a single number. Human hearing is most sensitive to the frequency range of speech. Therefore, the acoustic values for the range 250 - 2,000 Hz are very important.
The tested De Ploeg fabrics have an aw value between 0.4 and 0.75. That means that they absorb 40-75% of the noise. The position of the fabric is also important for the acoustic effect:
- The greater the distance from the wall to the fabric (up to a maximum of 30 cm), the more noise the fabric absorbs.
- The larger the pleats, the more noise the fabric absorbs.
Aw values only give a general indication of a fabric’s noise-absorbing properties. For acoustic calculations, it is necessary to look at the reverberation times at different frequencies.
Variable sound absorption with curtains
Compared to acoustic panels, curtains have the advantage that they are more versatile; they can be used either open or closed for more or less sound absorption. This way, the reverberation time can be adapted to the activity taking place in the room at that time, such as a lecture, a meeting, group work or a music or singing performance.
Guidelines for the correct reverberation time
- Office or classroom 0.5 seconds
- Theatre 1 second
- Church 3 seconds
We will be pleased to provide you with further information on the possibilities and properties of our noise-absorbing fabrics and wall panels, or for acoustic advice.