| 摘要 |
822,098. Acoustic apparatus. WESTERN ELECTRIC CO. Inc. June 4, 1957 [June 7, 1956], No. 17707/57. Class 13. [Also in Group XXXIX] An acoustic signalling device comprises a transducer 32, driven by a single-frequency input and harmonics thereof, which is coupled to a first tubular resonator 36, resonating at a first predetermined frequency above the resonant frequency of the transducer, which is in turn coupled to a second tubular resonator 37 which is of such length that the two resonators together resonate at a second predetermined frequency below the resonant frequency of the transducer, all three resonant frequencies lying within the range from 1000 to 2000 c.p.s. Specification 754,338, [Group XXXIX], is referred to. |
