1959 - History of Ericsson - History of Ericsson

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Fig. 5 x 8163 The Ericovox, L M Ericsson's Hands-Free Telephone Fig. 6 x 8160 The loudspeaking telephone, side \iew L loudspeaker M microphone c sound-insulating plate between loudspeaker and microphone 104 from opening the sender circuit and causing singing. The bias current through A j is at the same time reduced, which increases the attenuation in A^ to the same extent as that in A., diminishes. The received signal from L via M and G1 is therefore effectively attenuated both at Ai and A... The very high attenuations offered by the solution described has made possible a unique location of microphone and loudspeaker, namely within the same housing. In view of the extremely small size of the transistors, it has also been possible to place the entire amplifier unit within the housing. Accordingly the complete loudspeaking telephone consists of a single unit (fig. 5). The electromagnetic microphone is placed below the slots behind the buttons. The microphone is directed upwards, which means that its sensitivity is equal in all directions in the horizontal plane. Through the slots around the base of the instrument the sound of the loudspeaker is equally distributed in all directions. This makes the Ericovox the ideal conference telephone with equally good facilities for all persons in the room to join in a conversa-
Fig. 7 X 8162 x 8161 The Ericovox viewed from different angles The photographs show the compact structure and the location of the components tion. Its omnidirectional character has been made possible by the unusual location of the loudspeaker. Fig. 6 shows a side view of the instrument with the plastic cover removed. As seen from the figure, the loudspeaker (L) is directed downwards. This unusual location of the ioudspeaker has several advantages. By making use of the sound which radiates out from the rear of the cone, the sound field from the instrument is symmetrical in all directions in the horizontal plane. In front of the cone is an acoustic load which defines the radiated power of the loudspeaker at low frequencies and determines the bass cut. This ensures that the received signal is comparatively free from low frequency disturbances, e.g. from the electric power supply. The shape of the response curve in the treble region is also determined by the location of the loudspeaker. At higher frequencies the width of the beam becomes smaller and smaller, so that, as the frequency rises, a decreasing part of the beam will pass out through the slots in the casing. With this position of the loudspeaker, moreover, it has been possible to use a large loudspeaker of good quality within a telephone of neat proportions. In fact, it is on the placing of the loudspeaker that the appearance and proportions of the Ericovox have been based. An acoustically insulating plate (c) has been placed between the microphone (M) and loudspeaker (L), as shown in fig. 6. The majority of the components are mounted on this plate. Moreover, since the main axes of the microphone and loudspeaker are in opposite directions (180°), Aa is the most favourable possible. Fig. 7 shows the compact structure of the instrument and the placing of the components. The Ericovox is entirely transistorized, so that there is no risk of its becoming overheated. Moreover, the circuit is temperature-stabilized for the range 0° C to + 50° C (+ 32° F to + 122° F). This means that the Ericovox can be used in practically any climate provided, of course, that it is not placed in the direct rays of the sun. The current supply comes from the telephone line, so that no separate power unit or power mains are required. The reason for this is that the transistors consume extremely little power and work at a low voltage. The maximum length of line to which the Ericovox can be connected, counted in ohms, is shown in table 1, which is based on the d.c. supply. As regards the transmission of speech and dial impulses, the usual local regulations governing high efficiency telephone instruments naturally apply also to the Ericovox. 105
Page 1: 4 1959
Page 4 and 5: Ericovox, the One-Piece Loudspeakin
Page 6 and 7: Fig. 3 X 8156 Block schematic of co
Page 10 and 11: Fig. 8 X 2443 Sending frequency res
Page 12 and 13: 108 The Ericovox meets the requirem
Page 14 and 15: Fig. 3 Grouping of components in wi
Page 16 and 17: Fig. 9 X 8132 Case with pyramid-sha
Page 18 and 19: Fig. 12 X8134 Instrument with base
Page 20 and 21: Fig. 18 X8135 The locations of the
Page 22 and 23: Gothenburg Automatic Transit Exchan
Page 24 and 25: Fig. 3 x 8181 Block schematic of gr
Page 26 and 27: Fig. 6 122 x 8180 Block schematic o
Page 28 and 29: Fig. 8 X 2472 Link circuits for ori
Page 30 and 31: Fig. 10 X8182 Traffic supervisor's
Page 32 and 33: Fig. 2 X8167 Relay switchboard AMD
Page 34 and 35: 130 Priority The switchboard is des
Page 36 and 37: Crossbar Exchange Installed on Larg
Page 38 and 39: L M Ericsson to Undertake First C.T
Page 40: The Ericsson Group Associated and c

1959 - History of Ericsson - History of Ericsson

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