| 摘要 |
927,545. Magnets. PHILIPS ELECTRICAL INDUSTRIES Ltd. Oct. 12, 1959 [Oct. 15, 1958], No. 34507/59. Class 35. [Also in Group XXXIX] The stray field of an annular permanent magnet assembly, e.g. for a loud-speaker, is opposed by flux from a second permanent magnet. The assembly comprises a core 1 with end-plates 2 and 4 of soft magnetic material, and an annular permanent magnet 3, preferably of anisotropic ferrite. A thin-walled easing 6 of soft magnetic material defines an air gap 7, with the rim of the end-plate 4 larger than the working air gap 7a. Flux opposing that of the main magnet 3 in the gap 7 and in the housing 6 is provided by a disc-shaped or annular second permanent magnet 5. This magnet, the housing and the gap 7 are proportioned so as not to provide any of the flux in the working gap 7a. The gap 7 may be filled with a non- magnetic material and the housing may not contact the main magnet 3 as shown, but a layer of synthetic resin may be interposed. The main magnet may be magnetized after assembly in a loud-speaker but before the housing and second magnet are fitted. |
