Measurement of Absorption Coefficients to ISO354 using Tall Sources and Microphones

ISO 354:2003 specifies a method of measuring the sound absorption coefficient of material samples used as wall or ceiling treatments, or the equivalent sound absorption area of objects, such as furniture, persons or space absorbers, in a reverberation room. The standard specifies the dimensions of the room and the room volume, with a desired volume of approximately 200m3. To achieve this volume more proportional dimensions than found in normal rooms are necessary. This means ceiling heights of reverberation rooms are higher than typically found in buildings. However, the same sound source and microphone heights are specified as used in room acoustics standards such as ISO 3382 that of 1.2-1.5m. Material samples are typically laid on the floor of a reverberation room and hence the direct distance to the sample is short. This paper reports on measuring the same samples using standard source and receiver heights as well as doubling those heights. This additional height should allow more time for sound mixing which is needed to achieve a diffuse sound field.