acoustics Article The Effect on Room Acoustical Parameters Using a Combination of Absorbers and Diffusers—An Experimental Study in a Classroom Emma Arvidsson 1,* , Erling Nilsson 2, Delphine Bard Hagberg 1 and Ola J. I. Karlsson 2 1 Engineering Acoustics, Lund University, John Ericssons väg 1, 221 00 Lund, Sweden;
[email protected] 2 Saint-Gobain Ecophon AB, Yttervägen 1, 265 75 Hyllinge, Sweden;
[email protected] (E.N.);
[email protected] (O.J.I.K.) * Correspondence:
[email protected] Received: 9 June 2020; Accepted: 2 July 2020; Published: 4 July 2020 Abstract: Several room acoustic parameters have to be considered in ordinary public rooms, such as offices and classrooms, in order to present the actual conditions, thus increasing demands on the acoustic treatment. The most common acoustical treatment in ordinary rooms is a suspended absorbent ceiling. Due to the non-uniform distribution of the absorbent material, the classical diffuse field assumption is not fulfilled in such cases. Further, the sound scattering effect of non-absorbing objects such as furniture are considerable in these types of rooms. Even the directional characteristic of the sound scattering objects are of importance. The sound decay curve in rooms with absorbent ceilings often demonstrate a double slope. Thus, it is not possible to use reverberation time as room parameter as a representative standalone acoustic measure. An evaluation that captures the true room acoustical conditions therefore needs supplementary parameters. The aim of this experimental study is to show how various acoustical treatments affect reverberation time T20, speech clarity C50 and sound strength G.