1985 年 41 巻 12 号 p. 864-869
The slow-tube waveguide, a new type of the acoustic slow waveguide radiator, is described. In this radiator, a thin-walled slow-tube waveguide is used as the basic element in an end-fire radiator. By introducing the equivalent source function within the slow-tube, the determination of the sound radiation field is conveniently carried out from the volume integral, not the surface integral. It is ascertained that Hansen-Woodyard's condition giving the optimum length of the slow-rod waveguide radiator is also valid for the slow-tube waveguide radiator. The effects of the wall thickness for long tube on the directional pattern are investigated theoretically and the superiority of the thin-walled slow-tube is confirmed. The poor directional pattern of the thick-walled slow-tube is related to the wave number ratio (k_z)/k differing substantially from (k_z)/k=1, where k_z is the wave number along the slow-tube and k the wave number of the surrounding medium. At the same time, it is clarified that the large diameter slow-tube leads to increase in directivity, especially by lowering the side lobe level.