小試料を使った遮音特性の一測定法

抄録

Usually, the sound transmission properties of wall partitions etc. are characterized by the transmission loss measured in the laboratory. In this case, it is now recommended that the area of test pieces should be at least 10m^2, in order to conform with the practical conditions. However, in the course of fundamental research of sound insulating constructions, it is often desirable to measure the transmission properties conveniently, which may not be necessarily the defined transmission loss. Recently, we have developed a new method suitable for these measurements using small-sized test materials. A small concrete chamber is used for the receiving chamber, which has an opening on upper surface to set the test materials. Interior surface of the chamber is lined with mineral wool absorbers. As the condition of sound source, the following two arrangements are usded: A. The receiving chamber is placed in the reverberation chamber and the reverberant sound is used as the source of sound. B. Absorbent-lined small chamber is placed upon the receiving chamber. Loudspeaker is mounted in this source chamber, directly opposite to the opening of the receiving chamber. Microphone is set in the receiving chamber, and the measurements of transmission are carried out by the following three steps. 1. Without test materials, sound pressure level L_o is measured. 2. After setting the test meterials to the opening, sound pressure level L_c is measured at the same position of microphone. 3. Sound pressure level difference L_o-L_c is calculated, which is used as the measure of transmission characteristics. Position of the microphone is chosen near the sample surface for the source condition A, and apart form sample surface more than 100 mm for the condition B. For single partitions, measured level difference L_o-L_c coincides fairly well with usual transmission loss for the source condition A and with normal incidence mass law for the condition B, at the frequencies higher than the fundamental resonant frequency of the panel.