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.
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 [1
The subjective effects of free-hanging units are:
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 shielding the diffuse background noise as much as possible. The free-hanging units should cover the working area, preferably with a slight overlap.
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 [2
]. This will increase the sensation of control and create a less stress-induced environment.
 Sound Propagation in open-plan offices – influence of free hanging units. MONet 5 – acoustics workshop/010510, SP, Borås.
 Stellan Dahlstedt, Staffan Alm. Jämförelser av ljudabsorption i fabrikslokaler med dämpning av bullerkällor (Comparisons of sound absorption in factory premises with dampening down of noise sources). Lecture at the Swedish Acoustical Society’s meeting on 31 January 1978.