1971 年 27 巻 10 号 p. 501-506
A theoretical and experimental study of the influence of air flow on the attenuation characteristics of a single expansion chamber filter is presented. The acoustic energy dissipation caused by air flow at the open end is counted for the equivalent resistance ρ_0cM which derived from Eqs. (1)-(4), where ρ_0c is the characteristic impedance of air and M is the Mach number of air flow. From Eqs. (6)-(8) and Eqs. (14)-(16), one gets the equations for the particle velocity at each area change in a tube with air flow, which was described by Eq. (9) and Eq. (17), and the effective cross-sections ratios σ_M and σ_(M') are obtained. Assuming that the area changes of a single expansion chamber filter can be expressed by these effective cross-section ratios, the attenuation characteristics of the filter with air flow for a reflection-free source and a constant-pressure source can be given by Eq. (28) and Eq. (31) respectively. The theoretical values of the sound attenuation for a constant pressure source are compared with the measured values over a range of mean-flow velocity U≤40m/sec. The results are shown in Fig. 7.