Acoustical rafts


Acoustical design with free-hanging units

The use of free-hanging units provides flexibility and a multitude of acoustical solutions to problems related to acoustical design. Where free-hanging units are used to improve poor acoustics, solitary units give the benefit of diffraction effects, with a larger area of the absorbing patches being exposed to the sound field. Both effects can be used to increase sound absorbing properties.

In large, noisy environments such as open-plan areas, restaurants, shopping centres etc., free-hanging units can be installed close to working areas or other locations where acoustical treatment is needed in order to achieve suitable conditions for communication, concentration or recovery. Such areas can be, for instance, reception and information counters or refreshment areas, included in larger, noisy spaces.

In premises where, for various reasons, an overall ceiling cannot be used, e.g. where temperature is regulated via the joists (concrete core activation) or where there are large areas of glass, absorbent islands is one way of creating acceptable acoustic environments. The absorbent islands can be designed as baffles or horizontally suspended units.

Absorbing islands can also be used in environments where absorbing ceilings do not provide sufficient absorption. By supplementing with suspended horizontal absorbers or baffles, the acoustic environment can be improved with a reduction of the sound level and a diminishing of sound as distance increases.

Around an free-hanging unit, the acoustical effect is manifested as:

  • Noise reduction in the vicinity of Free-hanging units
  • Increased speech intelligibility and C50
  • Shorter early decay time (EDT)
  • Increased directional hearing

In open-plan spaces, free-hanging units can be used as a complement to wall-to-wall acoustical ceilings. Installing free-hanging units above workplaces will, in addition to the effects listed above, reduce sound propagation across large distances and contribute to increased privacy between working groups.

The subjective effects of free-hanging units are:

  • Increased speech and listening comfort
  • Reduced stress and stress-related symptoms
  • Less vocal effort
  • Easier to concentrate

In cases where the free-hanging units are used as solitary islands above workplaces, the absorbers should be installed as close to the workplace as possible, thus increasing the shielding effect. The free-hanging units should cover the working area, preferably with a slight overlap.

High installation


Low installation


When using free-hanging units as a complement to wall-to-wall acoustical ceiling, it is often better to split the free-hanging units into smaller patches and distribute these over the total ceiling area than to use larger free-hanging units irregularly over the ceiling. Division into smaller patches will enhance the diffraction effect and contribute to a more diffuse sound field.

If a workplace is near reflecting walls, the recommendation is to use wall absorbers as a complement to the free-hanging units.

Free-hanging units increase the ability to localise sound sources in the vicinity of a workplace. This will increase the sensation of control and create a less stress-induced environment.