1959 - History of Ericsson - History of Ericsson

Fig. 7
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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.
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