The Electrical Engineer, September 10, 1897, pages 343-344:
BY J. WRIGHT.
This modern application of the telephonic principle as a means of establishing communication between a popular theatre or opera house and one's private drawing-room is only growing in public favour. By its means one can sit comfortably at home in all weathers and listen to the latest comedy, opera, or tragedy, as the case may be, by the payment of a purely nominal rental. Such being the case, a few words as to the apparatus employed, as well as the modus operandi, may prove of interest.
The electrophone in its simplest form is an application of that familiar and wonderful invention the telephone, and like it, has a system of transmitters and receivers, the one being stationed at the theatre and connected by a line (overhead or underground, as the case may be) with the other, which is situate in the subscriber's house. I will primarily, therefore, proceed with a description of the transmitters. These are of the well-known Ader pattern, consisting of a series of carbon rods, A (Fig. 1), smaller in diameter at their extremities than at the centre, loosely supported in a horizontal position by the carbon blocks, B, which are provided with cavities in the sides for their reception. These carbon blocks are mounted by means of screws on the under side of a thin wooden diaphragm of pine or other resonant wood, C, and the whole is supported by a massive rectangular framework of cast lead, D. The connections to this transmitter are made by pieces of flexible cord, having thin copper tabs soldered to their extremities and clamped under the small nuts or screws which hold the carbon blocks, B, in position. These substantial transmitters are susceptible to the softest strains of an orchestra, and are equally as efficient when subjected to a full chorus. They are, therefore, admirably adapted to the purpose, and very seldom get out of order. They are as a rule arranged in what is known theatrically as the "float"--i.e., the part of the stage just in front of or behind the footlights--and are, on an average, from 12 to 24 in number, but this, of course, depends a great deal on the size of the stage. They are mounted in cavities of such a size as to allow a certain amount of side and end play for freedom of vibration, and the upper surfaces of their diaphragms are flush with the stage. The mounting consists of a rubber ring suspension on stationary wire hooks, this form of fixing having been found advantageous as offering immunity from actual stage vibrations, and allowing them plenty of freedom on all sides for their own individual action, which is maintained uniform and steady by the weight of the leaden frame.
It is necessary, in order prevent loss of battery power over the transmitters while idle during the day, to have a means of cutting them out of circuit until required. This is effected by a species of automatic switch, a diagrammatic representation of which is shown in Fig. 2, where A is the active electromagnet, B is a species of horizontal pivoted lever, provided at one end with a counterweight, and at the opposite, or working extremity, with a loosely-hinged pawl, C. The latter when depressed by the lever, B, under the influence of the armature of the electromagnet to which it is attached, actuates a compound ratchet wheel, D, composed of two discs--one of brass and the other of ebonite. These two discs are clamped together in such a relative position that their teeth alternate. Contact is thus made and broken with a small vertical brass spring, E, which acts as a contact brush. These switches are as a rule connected on the first line--viz., that in connection with the first transmitter, and are actuated by a current from a battery of E.C.C. dry cells, situated at the central exchange or switch-room.
The accessories, comprising induction coils, batteries, automatic switches, and so forth, are contained in an accessible cupboard in a suitable portion of the wings, or under the stage. The coils, which are the same in principle as an ordinary telephone induction coil, need no description. The battery power for each theatre is supplied by a couple of E.P.S. accumulators in teak boxes, provided with handles and portable in form. Now as regards the switching arrangements.
From the cupboard containing the accessories the wires from the various transmitters are led to jacks similar to those used on telephone switchboards, to which in general construction, in fact, the central distributing board bears a close resemblance. The connection between subscriber and theatre jack is made by means of a two-way cord and plug in the usual manner.
Now as to that part of the apparatus situate at the subscriber's house, to wit, the receivers. These are also of the Ader pattern, and have double poles, being very similar, in fact, to the small receivers attached to the instruments of the National Telephone Company. There are two of these to each person, and they are conveniently arranged on a light metal frame, A (Fig. 3), semi-circular in form and of a convenient width to fit over the ears. The receivers are indicated in Fig. 3 by the letter B, and they are attached to the frame by the medium of a swivel joint behind, which allows of a certain lateral motion in order that they may be comfortably adjusted to the ears. A metal rod, C, attached to the frame ends in a leather-covered handle, D, by which the instrument is held when in use. The connections to the receivers are made by means of a flexible cord, which runs up through the centre of the handle and rod and subdivides to the receivers. A small flat table of polished wood is provided to carry the contact jacks. This can be stood on a convenient table and connected with the system by a wall socket and plug and a length of twin cord. The receivers are for an ordinary subscriber four in number, but extra ones can be fitted if desired. The connections from the receivers to the line are, as shown in Fig. 4, divided into two loops supplying respectively the right or left receivers of each set.
I may here state that the Electrophone Company, whose chairman is Lord Loftus, are working in unison with the National Telephone Company, so that it is necessary for a subscriber to be connected with the telephone system in order that he may be able to communicate with the switch-room. The electrophone is generally fitted as an extension to the telephone apparatus, being put in circuit by means of a switch after having obtained a connection with the required theatre.
The invention has also been adapted to a system of automatic boxes for use in restaurants and places of amusement. This modification takes the form of clock-work mechanism, which controls the contacts by means of levers attached to the driven spindle. The action of the apparatus is as follows: On the insertion of a sixpenny piece in the slot provided for the purpose it slips down a shoot and forms a rigid link between a winding, spindle and the spring barrel. On turning a handle in front of the case, the clockwork is wound up, and the receivers, which are on separate handles, and are suspended on hooks at the side of the instrument when not in use, are brought into circuit, and remain in that condition until the mechanism has run down, which it does at the end of a few minutes; the hearing can then be prolonged by a repetition of the operation. Automatic boxes of this type are to be found at the Café Royal, Piccadilly Restaurant, and other similar resorts. A constant supply of popular music is maintained on these boxes during theatre hours, and is denoted by an indicating arrangement fixed over each box.
These indicators are a species of electromotor, consisting of armature and field magnets with a commutating device. The movable spindle carries an index finger, which indicates on a dial the particular entertainment that happens to be connected at the time. The indicators of several boxes are connected in one circuit, the remaining terminal of each one being earthed, and they are driven by a battery of some 50 accumulators from the central switch-room.
In conclusion, I may mention that the transmitters of this system have been fitted in popular churches so that subscribers may listen to their favourite preacher at home. In such cases they take the form of a dummy bible lying in a natural position on the pulpit desk, or a hassock under the lectern, and are also fitted in the galleries at points where they will readily collect the sound of the preacher's voice.
The company have reception-rooms at the Victorian Era Exhibition, Earl's Court, and also at their headquarters at Pelican House, Gerrard-street, Soho, where this invention may be tested.