吸音壁内に組込まれた共鳴器の吸音特性

抄録

A resonator is used practically in an absorbing wall as well as in a rigid wall. In this paper the absorption characteristic of a resonator array in an absorbing wall is studied under the condition of a plane wave incidence normal to the wall. Kosten and Zwikker investigated the absorption characteristic of a resonator array in a rigid wall. Ingard showed the equivalent circuit of a resonator in free space. In these cases, the resonator array in an absorbing wall is assumed to be represent by the equivalent circuit as shown in Fig. 2. The total absorption coefficient, α_&lttotal&gt, of a wall and a resonator can be calculated by the equivalent circuit as shown in Eq. (4) or Fig. 3. Fig. 3. (a) is the case when μ_2&gt1. 0 and Fig. 3. (b) is the case when μ_2≦1. 0, where μ_2 is the normalized resistance of the resonator. It is of particular interest that, in Region III of Fig. 3. (b), α_&lttotal&gt becomes smaller than α_&ltwall&gt. The experimental results by the tube method are shown in Figs. 5 and 6 by dashed lines. Fig. 5 is an experimental example in Region I and Fig. 6. is in Region III. Solid line is the calculated absorption characteristic of a resonator array by Eq. (4), where μ_2 is calculated by the experimental equation of Ingard on the resistance of turbulence. This calculated curve agrees well with the experimental result. Consequently, it is found that Eq. (4) expresses well the absorption characteristic of resonator array in an absorbing wall.