PAGE No. 14

Loud Speaking Intercom, Telephones
July 1933

Present day progress demands that persons holding important executive positions should not be required to waste valuable time doing needless operations, and at all times they should have full access to records, flies or important papers. The inter-departmental type of telephone has done much to improve the administration of a business and has proved itself an indispensable item in an up-to-date office. Unfortunately, however, the use of the ordinary telephone limits the movements of the user. It necessitates the use of one hand at least and so prevents quick and easy access to papers and at the same time the making of notes.

In order to improve such conditions, the Ericsson Company has placed on the market loud speaking telephones 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 the single operation of a key it is possible to move about in any average sized office and carry on a complete conversation with any desired extension. The essential qualities of such a scheme are, that the received speech shall be both loud and clear, and the microphone shall be capable of picking up normal conversation from any part of the office. By very careful design of the circuits and components this has been made possible to a degree which is considered superior to any similar system on the market. In a quiet office the cone type speaker (noted for its clearness) can be heard 30 to 40 feet away, and the microphone will pick up at this distance without difficulty.

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.

The following three systems are standardised:-

  1. A system consisting of a master station and a number of side stations with communication only between master and side stations.
  2. A system consisting of a master station and a number of side stations with full inter-communication facilities between the side stations.
  3. A system consisting of two or more master stations and a number of side stations with full intercommunication facilities between the side stations.

It should be noted that 'master station' denotes a station with a loud speaker and microphone, and 'side station' one with a standard bakelite micro-telephone.

System (a) consists of a master station similar to those shown in the illustration above and may be equipped up to 20 lines. A side station consists of an Ericsson Bakelite table telephone fitted with a neat push button for calling up the master station. A small cable is run from the master station to each of the side stations.

In system (b), which is the most popular arrangement, the master station is the same as for (a) but the side stations are equipped with instruments of the types illustrated for 5 and 15 lines. These are similar in appearance to the standard Ericsson intercommunication telephones but are fitted with a press button and lamp for working in conjunction with the master station. Direct communication is given between all the side stations by means of the local intercom buttons. The operation of a master station button gives direct communication with that master station, and other side stations cannot overhear.

In system (c) the same remarks apply as for system (b) but, each side station must have a button and lamp fitted for each master station, as in the right hand illustration of side-station telephones with intercommunication facilities which shows an instrument having 15 local buttons and two master-station buttons.

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.

The following facilities are therefore provided:-

  1. One master station is equipped with a hand-micro which can be used when speaking to the other master station.
  2. All master stations are fitted with handmicro's, and arrangements being made that in all cases the station originating the call shall use the hand micro.
  3. Arrange that when 'master' communicates with 'master' each shall use the small watch receiver attached to the master station key-box.


The master station consists of a polished mahogany case-work, as shown in the illustration, the front of which is equipped with the necessary number of keys and lamps.

When a side station calls up, the 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.

The 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. If necessary, repeat rings can be given by further pressure on the key. When required, the loud speaker can be cut off by using the watch receiver provided.

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, which is finished in oxidised-silver and is both useful and ornamental. The key box may then be fitted in any convenient position within reach.

In all cases the loud speaker may be placed in any position in the room, the volume being such that it will be audible from all positions.

The intercommunication part of the side station instruments follows the standard practise which has been described in a previous issue of the bulletin. 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. Similarly, to call the master station the hand-micro is removed and the master station button depressed to its fullest extent. Should a side station be engaged when called by the master station the lamp at the side station will light and attract the attention of the user.

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.

As illustrated, two sizes of master stations are made, with a capacity of 11 and 20 keys respectively.

The side stations will generally be equipped with:-

5 side & 1 master station
10 side & 1 master station
15 side & 1 master station

with provision for extending to two master stations on each size.

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Last revised: October 13, 2019