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LOUDSPEAKER INTERCOMMUNICATION TELEPHONE
The ordinary telephone limits the movements of the user by necessitating the use of one hand at least. In order to obviate this in the case of persons holding important executive positions, the loudspeaking telephones have been developed. By operating a key it is possible to move about in an average size office and carry on a conversation with any desired extension on the system. In a quiet office the external loudspeaker can be heard 30 to 40 feet away and the microphone will readily respond at that distance. This is accomplished by very careful design of the circuit and components, and without resort to the use of valve amplifiers, which are costly both initially and for future maintenance. Three systems are standardized:-
In the case of (c) while ordinary conversations may be carried on between the two master stations it is not practicable to provide for dual loudspeaker communications. The master station consists of a polished mahogany casework equipped with lamps to indicate when a side station calls, and associated keys for answering or calling the side stations. A low pitched buzzer is fitted internally to attract attention when any station calls. A sensitive microphone is mounted in the top left-hand corner and in the right-hand corner there is a warning lamp which remains lit during a conversation and thereby guards against the leaving of a key in the operated position after a conversation is completed. Connections are made to a terminal box. N1745 is shown pictured above. Mahogany casework For side stations see N1720 and N1590.
Taken from the Ericsson (ETL) Telephone Catalogue No. 55 Introduced circa 1934. A Loud Speaker Intercommunication Telephone System incorporating all the notable features of our standard intercommunication system with the addition of loud speaker facilities for one or two Master Stations. 
Present day progress demands that persons holding important executive positions
should not be required to waste time doing needless operations, and at all times
they should have full access to records, files and important papers.
Unfortunately, however, the use of the ordinary telephone limits the movements
of the user it necessitates the use of one hand at least and thus prevents quick
and easy access to papers and at the same time the making of notes.In order to improve such conditions, the Loud Speaker Telephones have been developed, by means of which a person is not required to engage either hand while telephoning, incoming speech being received on a loud speaker and outgoing speech picked up by means of a sensitive microphone. This means that after a single operation of a key it is possible to move about in any average size office and carry on a complete conversation with any desired extension.
In case (c) an extra condition which must be catered for is that of communication between the two master stations. There are many ways of doing this but the particular requirements of each installation have to be carefully considered, as it is not possible to give good loud speaker reception at one station when speaking at a distance from the microphone at the other station. When a side Station calls up, a lamp associated with it lights and indicates the number of the station calling. The lever key mounted immediately below this lamp is then operated and the speaking circuit is completed. An audible call is also given by a low pitched buzzer in order to attract attention. A sensitive microphone is mounted in the top left-hand corner and a warning lamp in the right-hand corner. To guard against the leaving of a key in the operated position after the completion of a conversation, the warning lamp remains lit during the time that any key is in the operated position. A side station is called by depressing the appropriate key to its full extent or ringing position. On release the key takes up a middle or speaking position. For those who desire a really neat and inconspicuous arrangement, a three-unit master station has been designed with the microphone and warning lamp fitted into a neat and pleasing inkstand (N7699B shown to the right). The casework is of polished mahogany or finished in oxidized-silver or bronze. The key box may then be fitted in any convenient position within reach.
Conference facilities may be obtained by the master station throwing the appropriate keys. The stations thus selected can then speak and also hear what the other stations are saying. From the point of view of initial cost and future maintenance it is not desirable to use any type of valve amplifier, and the Ericsson system requires only the usual type of dry batteries for the signalling part of the system, and either a 6-volt accumulator or high capacity dry cells for the speaking part. MICROPHONE INKSTANDS
Taken from Ericsson (ETL) Intercommunication Telephone Booklet No. 4G |
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Last revised: September 24, 2022FM2 |
Table telephone for use as master station on loudspeaking telephone systems.
The side station instruments with intercommunication facilities are similar to our standard intercommunication telephones with the addition of one or two press buttons
and lamps. When a call is received from the master station, the buzzer is operated in the usual way and a lamp is also lit in order to indicate that it is the master station calling. The removal of the hand-micro and pressing the master station button establishes the connection.