SE318611B - - Google Patents

Abstract

1,133,049. Microphones. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 23 March, 1967 [26 March, 1966], No. 13661/67. Heading H4J. In an electrodynamic microphone, a sleeve may be moved, from a first position in which it seals the rear of a microphone capsule and inhibits entry of sound at the rear, to a second position in which sound can enter at the rear. In the first position the microphone has an omnidirectional characteristic while in the second position it has a cardioid characteristic. A housing 1 (Fig. 1), comprises a soundpermeable cap 2 fitted to a tubular metal casing 3. The diaphragm 5 of a microphone capsule 4 communicates with outside air through a protective member 6 and, in one position of a sleeve 8, through ducts (not shown) at the rear 7 of the capsule 4. The sleeve 8 is urged by a spring 9 against a rubber ring 10 at the capsule rear 7. The casing 3 is encircled by a rotatable collar 11 (Fig. 2) in which is a plastics sleeve 12. A recess 13 in the sleeve 12 receives a lug 14 inside the collar 11. An inclined surface 15a of the sleeve 12 bears on a pin 15b disposed in a longitudinal slot 16 in the casing 3 and screwed to the sleeve 8. Rotation of members 11, 12 forces the pin 15b to move forwards or backwards over the cam surface 15a, whereby the sleeve 8 engages or disengages the ring 10 to close or open the capsule rear 7. Alternatively, the casing (3), Fig. 3 (not shown), encloses a tightly fitting rotatable sleeve (8). A pin (15) secured to the sleeve (8) is movable in a transverse slot in the casing (8). The end of the sleeve (8) facing the capsule (4) has eccentric apertures (18) covered with gauze (19) and which in one position co-operate with apertures in the front of the casing (3) which in turn communicate with the rear of the diaphragm (5). The sleeve wall has apertures (20), which may contain acoustic resistance, and which in one position co-operate with apertures (21) in the wall of the casing (3). In one position of the sleeve (8) the apertures (18, 20, 21) are such that sound can reach the rear of the diaphragm (5).