| 摘要 |
Sound attenuating ducting has an inner, helical wire 1 supporting an inner and outer layer 2 and 7 formed by strips 3 and 8 of a foamed thermoplastic rubber material. Axial and helical reinforcing yarns 5 and 6 extend along the ducting between the layers 2 and 7. The two strips 3 and 8 are applied from extruders, the extrusion rate of the inner strip being set to be less than that of the outer strip so that the inner strip is stretched to produce a more porous structure than in the outer strip. In this way, the inner layer 2 is efficient in absorbing orifice noise within the ducting and the outer layer 7 contains radiated noise. <IMAGE> |
