相関法による吸音材料の吸音特性の測定法

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A Method of Measuring the Absorption characteristics (Absorption Coefficient and Acoustic Impedance) of Acoustic panels by the Correlate method is studied in this paper. The principles of the Method of Measuring as are follows. Absorption characteristics are derived from the frequency characteristics of Acoustic panels calculated from the relation between the reflected sound wave of Hard board. The reflection coefficient of which is quite near 1, and the reflected sound wave of Acoustic panel, which is regarded as the input signal and the output signal of Acoustic panel function, respectively (Fig. 5), and which are equivalent pulsive sound waves measured by the Correlate method using M-sequence signals (Fig. 1, Fig. 2). The forms of the reflected sound waves depend mainly upon shift pulse time T_m of M-sequence signals and frequency Characteristics of Acoustic panels. In this method, the influence of edge phenomenon (Fig. 4) compounded in the reflected sound waves is taken into consideration so that the measurement may be possible even if the Acoustic panel is not wide enough (Fig. 6). It is derived from the fact that the reflected sound wave measured by the Correlate method contains the influence of edge phenomenon but that the reflected sound wave calculated by Kirchhoff's equation does not contain it. Also, the suitable values of shift pulse time T_m in the measurement of Absorption characteristics are decided by approximating the frequency characteristics by the Correlate method (Fig. 1) to that by the Multi-filter method (Fig. 1, Fig. 7, Fig. 8). This method is to be considered useful for the measurement of Absorption characteristics (α_0, Z_0) of Acoustic panels by comparison between Normal incidence Absorption characteristics of Acoustic panel (Uletan Foam) measured by this method and the Tube method (Fig. 9〜Fig. 14), and by comparison between Statistical incidence Absorption coefficient α_start derived from Oblique incidence Absorption coefficient α_θ (Fig. 15) measured by this method and Reverberation Absorption coefficient α_rev (Fig. 17). Thus, we measured Normal incidence and Oblique incidence Absorption characteristics of Acoustic panel under performance (Wall of unechoic room for high frequence), and it is shown that this method is useful as one of the methods of measuring the Absorption characteristics of Acoustic panels of the spot (Fig. 18, Fig. 19).
社団法人日本音響学会の論文
1972-08-01

相関法による吸音材料の吸音特性の測定法

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