Curtains / Drapes

What are acoustic curtains?

Acoustic curtains are used to flexibly provide sound absorption in spaces (i.e. make them less ‘echoey’).

They can either be:

hung and extended along hard vertical surfaces ( walls, windows, etc) to absorb sound and reduce the sound reverberation (i.e. ‘deaden’) in spaces, or;
folded away, sometimes in dedicated cupboards, to increase the sound reverberation in spaces.

Acoustic curtains extended (reduced reverberation)

Acoustic curtains stored (increased sound reverberation)

What materials are acoustic curtains made from?

Acoustic curtains are usually made with porous textiles such as:

Velvet velour
Velvet alicante
Wool serge

The weight of the fabric used to absorb sound ranges from approximately 0.3 kg/m² to 0.6 kg/m².

Some fabrics can also be made flame retardant.

What are the sound absorption characteristics of acoustic curtains?

Acoustic curtain systems achieve sound absorption performances that range from Class C to Class B absorption. Also, with fabric being a porous material, acoustic curtains are better at absorbing sound at mid and high frequencies (from 500 Hz) than at low frequencies (below 250 Hz).

The sound absorption characteristics mainly depend on:

the weight of the fabric.
the fullness of the curtains.
the distance between the curtains and the hard backing behind (if applicable).
the airflow resistance of the fabric.

The paragraphs below show the influence of each characteristic on the sound absorption performance of the curtain system.

Influence of the WEIGHT of the fabric on the sound absorption

The heavier the fabric, the higher the sound absorption. This is especially the case at mid frequencies (500 Hz and 1000 Hz).

The graph below shows the sound absorption coefficients, in octave bands, for different fabric weights.

Sound absorption coefficients of acoustic curtains with fabrics of different weights [1] [2]

Influence of the FULLNESS of the curtains on the sound absorption

What is the fullness? It is measured in percentage (%) and corresponds to the quantity of fabric used to cover the length of the tracking system. The fullness equals to:

0% when the curtains are flat;
50% when the total length of the curtains corresponds to 3/2 of the tracking system’s length;
100% when the total length of the curtains corresponds to twice the length of the tracking system;
and so on…

Explanation of curtain fullness – tracking system’s length

Because more material and deeper folds come with a higher fullness, the sound absorption of curtain systems increases with the fullness of the fabric.

The graph below shows the sound absorption coefficients, in each octave band, depending on the fullness of the same fabric.

Sound absorption coefficients of acoustic curtains with different fullness [1] [2]

Influence on the sound absorption of the DISTANCE between the curtains and the hard surface behind

Curtains are better at absorbing sound when they are positioned in front of and away from a hard surface.

The distance, between the curtains and the hard surface, generally ranges from 100 to 300 mm.

Ideal configurations of acoustic curtains

The graph below shows the sound absorption coefficients, in each octave band, depending on the distance between the curtains and the hard surface behind.

Sound absorption coefficients of acoustic curtains with different distance between the curtains and the hard surface behind [1] [2]

What about the sustainability of acoustic curtains?

See the Environmental Product Declarations for some product examples.

Note: the above information is drawn from review of product information and the following documents:

[1] Acoustic Absorbers and Diffusers – Theory, Design and Application (Third Edition) – T.J. Cox and P. D’Antonio
[2] Sound Materials – A Compendium of Sound Absorbing Materials for Architecture and Design – Tyler Adams

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