New ratings in ISO 11654 of plane sound absorbers made for speech communication in classrooms and meeting rooms

摘要

A computer-based study of a typical furnished classroom has been made, where reverberation times, sound pressure levels, signal-to-noise ratios, speech intelligibilities and auralization files have been computed for five common types of ceiling. The sound absorption of those ceilings vary significantly in the octave bands 125-4000 Hz, of which one is an almost completely reflecting surface and the other four represent common tile products intended for suspended ceilings. The results show that the speech intelligibility indices (STI) are almost the same for the four absorptive materials applied in this analysis, the STI:s range from 0,77-0,80 with realistic background noise. The reflecting ceiling has a lower value. It seems most important to absorb mid frequency energy. These findings support a proposal for a voice weighted average sound absorption coefficient 'α_v'. It differs from the 'α_w' defined in ISO 11654, where the rating curve puts more weight on the absorption at higher frequencies. The voice weighted α_v stresses the mid frequency absorption and rates resonator types of products more equally to porous types, which can be justified by similar STI results in the classroom. This new α_v should be relatively easy to explain to architects, contractors and occupants of work premises.