| 摘要 |
The diaphragm 1 comprises a member 2 having a thickness that varies from a first thickness at a first location at the periphery 5 to a second thickness at a second location which is nearer to the centre 4 than the first location. The member 2 has a third thickness t at a third location which is between the first location and the second location, the third thickness being both thicker than the first thickness and the second thickness. The thickness varies for the majority of the radial distance between the first location and the second location. The member 2 may be in the form of a lightweight rigid foam body 9 coated with thin laminar stiffening layers 10, 11 glued to its front and rear surfaces 7, 8. Various suitable materials for the foam body 9 and the layers 10, 11 are listed in the description. |
