GB447971A - Loudspeaking telephone system - Google Patents

Abstract

447,971. Intercommunication systems; loud-speakers; supporting telephone instruments. LEWIS, T. K., and BALLER, W. G., Baldow, Clapton - in - Gordano, Somerset. Nov. 21, 1936, No. 7837/36. [Class 40 (iv)] In an intercommunication system, connections between a loud-speaking master station Mas and one of the substations A, B employ two speaking circuits each including the transmitter of one station and the receiver of the other, whilst connections between two substations employ only a single speaking circuit including the transmitter and receiver at each station. For a call from A to B, receiver hook H is raised and selector contact LS2 is closed operating at the same time ringing key R to close a calling circuit from battery DC through buzzer Z at station B. When pressure on key R is relaxed, contacts R2, R3 remain closed under the control of the hook-switch and when the called party has removed his receiver, a single series circuit for receiver Rr and transmitter T at each station is completed over contact LS2. For a call from A to Mas selector contact LS1 is closed causing also the operation of key M as well as R. The master station has a key SA for each sub-station, each such key having three positions with contacts closed as shown in Figs. 1a ... 1c. The calling circuit includes identifying lamp SLA and buzzer Z at Mas. In reply, switch SA is moved from normal to speaking position, completing two speaking circuits one including sub-station transmitter T, contacts LS1, SA4, SA2, and loud-speaker Rr, and the other including master-station transmitter T, contacts SA1, SA3, M6 and sub-station receiver Rr. For a call from Mas to A, lamp SL is lit to indicate a call from the master-station and selector contact LS1 must then be closed, operating also M to complete talking circuits as before. The loud-speaker preferably employed, Fig. 2, is of moving-coil type with a permanent magnet 14, and the microphone 18 is mounted by means of a metal strap 19 in the centre of the same aperture in the panel 13, preferably with its mouth pointed slightly upwards and with a cowl 20 to avoid feed-back. Dimensions of transmitters and receivers giving satisfactory results are given in the Specification.