Ericsson DIALOG - Transmission Unit Components and Function

Fig, 9
The bell
unit in
parts
The gongs (4) are of sheet brass and the fixing holes are eccentric
to permit easy adjustment for maximum sound intensity . Two
pillars are riveted to the ringer-plate in order to support the
gongs and the resonator cups (5).
The ringer produces a pleasant sound , penetrating even to people
with impaired hearing (limitation of hearing generally starts at
high frequencies). These important properties are obtained as
a result of the gongs having different pitches, and the subharmoni cs
of the signal being amplified by Helmholtz resonators (5).
The Ringer Output Spectrum is shown in fig. 10.
The ringer can be equipped with sound regulation if required. By
reducing the movement of the bar by means of a tag under the in-
strument. the sound intensity of the ringer can easily be altered -
continuous regulation from full output (74 dBa) to the soft signal of
a buzzer (45 dBa).
The impedance at 25 Hz (c/ s). with a 1 µ F capacitor in series
with the bell, is 4 500 Ohm. and at 800 Hz (c/ s) 36 000 Ohm.
9
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