GB1225098A - - Google Patents

Abstract

1,225,098. Electro-acoustic transducers; magnifying sound. COMPAGNIE DES COMPTEURS. 27 Feb. 1969 [27 Feb., 1968], No. 10496/69. Headings H4J and H4X. Acoustic generating apparatus comprises a transducer 10 (e.g. magnetostrictive or electrostrictive) presenting a face 12 which vibrates in operation to propagate acoustic waves in air or other fluid medium in contact with the face 12. A screen 13 has a regular array of apertures 14 and elastic mechanical connection is established between the screen 13 and face 12 to position the screen 13 parallel and closely adjacent the face 12. The apertures 14 may be slots. Preferably the ratio R between the area of the material of the screen 13 and the area of the openings alone is between 3 and 5. During vibratory movement of the face 12, gas between this face 12 and regions of the screen 13 remote from an opening 14 is alternately compressed and expanded in, effectively, an array of compression chambers (15), Fig. 2 (not shown). These "compression chambers" maintain the face 12 and screen 13 spaced. The gas escaping through the openings radiates in phase. Acoustic power radiated by the face 12 is greater than the power which would be radiated by the face 12 without the screen 13 under the same conditions of electrical supply to the transducer. The screen 13 and face 12 are strictly parallel, the distance D being maintained by suspending the screen 13 from a vertical frame 16 by coiled springs 17. At equilibrium the springs 17 are compliant in the horizontal direction compared to the stiffness presented by the repulsive force due to air in the "compression chambers". In order to position the screen 13 properly the transducer 10 is approached towards the screen 13 and the assembly is displaced horizontally. The distance D between screen and face 12 varies slowly with the distance A of the screen 13 from the frame 16 (fixed) and the optimum positioning is easily obtained. The force F 1 , being large compared with the gravitational force on the screen 13, permits location of the assembly in any desired attitude, vertical or otherwise.