Acoustic behaviour of periodically arranged absorbers in concrete structures subject to thermal constraints

Thermally activated concrete ceilings are often used in office buildings, since they improve the thermal comfort. They are, however, sound reflecting and hence need an acoustic treatment, which usually consists of suspended absorbers. These are neither attractive nor are they cost efficient. An alternative way of adding sound absorption to concrete ceilings consists of introducing periodically flush-mounted sound absorbing materials. For appearance reasons these materials need to be covered by plaster layers or perforated sheets. Both, the sound absorbing materials and the covers affect the thermal efficiency. In order to find a suitable compromise for acoustic and thermal efficiency as well as architectural appearance a theoretical model for calculating the sound field in the absorber-filled cavities of the ceiling, the plaster layers and the adjacent half-space is introduced. It is validated experimentally at normal and field incidence. Using this model an acoustic optimisation process is performed subject to practical and thermal constraints. This optimisation is complemented by a thermal investigation. Finally, design guidelines for thermally activated concrete ceilings are given.