| 摘要 |
The flow passage 14 between an inlet 12 and an outlet 15 has a movable wall or walls 15, 16 to vary the flow cross section and sound absorbing means 19, 21 is arranged outwardly of the passage. The walls 15, 16 may be moved by bending or bodily (Fig. 6) or a circular plastics tube (160, Fig. 8) may be centrally constricted by a bellows (161). The material 21 may be replaced by baffles (Fig. 5). The walls 15, 16 may be formed by pairs of plates (17a, 17b, Fig. 7) variably compressing sound absorbing material there between. <IMAGE> |
