相関法による吸音材料の吸音特性の現場測定法

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This is a study on the field measurement method of absorption characteristics of acoustic panels by the correlation method using M-sequence signal. Particularly, the principle of the measuring apparatus is detailedly described. In this method, the absorption characteristics, i. e. the complex reflection coefficient is obtained from the correlated wave forms measured in the presence and absence of acoustic panel. The measuring apparatus, by which the equivalent incident and reflected sound waves can be measured, is composed of two parts; one is a M-sequence signal generator (Fig. 1), that gives a basic M-sequence signal and a delay signal, and the delay time can be set manually and swept according to the measuring time (Fig. 3). The other is field measurement apparatus mainly composed of multiple and time average circuits using the two signals mentioned above (Fig. 2). By a long enough delay time range and a unit step delay time accuracy of 2. 5μs, not depending upon the frequency, it is possible to measure the equivalent sound wave even in a high-audio frequency. Error of measurement of the correlation method and effects of the oblique incident absorption characteristics of panel and the cubic incident wave corresponding to the measuring condition of this method, on the measured values of normal incident absorption characteristics are discussed (Fig. 4, Fig. 5). Propagation sound waves for the reverse-square law (Fig. 6), incident and reflected sound wave s (Fig. 7), and absorption characteristics of lawn, soil and absorbent fence by this apparatus are shown (Fig. 8, Fig. 9).
社団法人日本音響学会の論文
1974-09-01

相関法による吸音材料の吸音特性の現場測定法

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