US1929928A - Sound reproducing system - Google Patents

Description

Oct. 10, 1933.

B. E. G. MITTELL SOUND REPRODUCING SYSTEM 2 Sheets-Sheet 1 Original Filed Nov. 18 1925 Oct. 10, 1933. B; E. e. MITTELL scum) REPRODUCING SYSTEM brigiual File Nov. '1 1925 2 Sheets-Sheet 2 IIIIII,II'IIIIII'III'I'IIIIIII'IIIIIII(IIIIIIIIII'III'IIIIIIIJI Patented Oct. 10, 1933 UNITED STATES I -i, 929,92s

scum) REPRODUCING, SYSTEM Brenchley Ernest George Mittell, Iver, England, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a. corporation of Delaware Application November 18, 1925, Serial No. 69,849,

and in Great Britain December 5, 1924. Renewed February 25, 1931 Claims. (01.177-1) This invention relates to sound reproducing systems such as talking machines or wireless receivers. I It is often desirable that the generator of 5 audio-frequency currents should be at a distance from the sound producing device, such a s-tele phone or loud-speaker. For instance in the case of a wireless receiver, with an outside aerial, the receiver is preferably placed in the neighbouro hood of the point at which the aerial and earth connections are led in; whilst it may not be convenient for the sound producing device to be operated in the same room. When a loudspeaker is used, moreover, it is preferable that it should be placed at a distance from the listeners and it is also desirable that the tone quality and the volume of the sounds produced should be regulable from the position of a listener.

According to the present invention, therefore, a sound reproducing system, comprising a unit in which audio-frequency electric currents are generated, such as a radioreceiver or talk ing machine record co-operating with a microphone circuit, or an electro-mechanical device operated directly by the record groove, a sound producing unit and a controlling unit, which permits of the control of the other two units independently of one another, has the said three units independently movable with regard to one another but interconnected electrically. The

control of the generating unit may be accom-' the valve filament circuit and the relay or relays may be energized from the battery which is used for heating the valve filaments.

One embodiment of the invention, in which the generator of audio-frequency currents is a single valve radio receiver, will be described by way of example, with reference to the accompanying drawings in which Fig. 1 shows diagrammatically the arrangement of the electrical circuit. Fig. 2 shows a convenient form of wall plug and socket connector.

Fig. 3 illustrates in more detail the relay in Fig. 1.

Fig. 4 shows the control .unit. Fig. 5 is a sectional view on the Fig. 6 is a part sectional end view of the control unit.

Fig. 7 shows diagrammatically the arrange- 65 ment of a modification of the electrical circuit.

e AA of nected to earth.

Referring more particularly to Fig. 1 the thermionic valve 1 is connected in the usualmanner to act as a detector and the output is connected through the primary circuit of an output transformer 2. The audio-frequency currents generated in the secondary circuit of this transformer are led through the connecting leads d and e. The valve filament is heated by current from the battery 3 through the right hand contact 4 of the relay 5. The left hand relay contact 6 is connected to the aerial and when contact is made on this side the aerialis con- The relay is actuated by two solenoids 7 and 8 one terminalof the two solenoid windings being connected together to contacts 27 and 28 on therelay arm and to one terminal of the battery 3 whilst the other terminals of the solenoid windings are connected to leads a and 0 respectively. The other terminal of the battery is connected to lead b. The control unit 9 and the loudspeaker 10 are connected as shown .with the receiving set by the leads ae. When, bypressing the left hand or on button of the switch 11, the leads a and b are connected together, the left hand solenoid 7 is energized and the connections of the receiving set are then as shown in Fig. 1. In this case the filament circuit of the valve is closed and the set is consequently in action. When the left hand button is released the contact is maintained by the spring catch 12. If now the right hand button be pressed the leads b and c are connected together and the solenoid 8 pulls down the relay arm, breaks contact 4 and makes contact 6. The filament circuit is thus opened and the aerial is connected to earth. This contact is likewise maintained, after the button has been released, by the spring catch 12.

The control unit 9 comprises,- in addition to the switching arrangement for putting the set into or out of action, means for controlling the volume and tone quality of the sounds produced by the loud speaker 10. The volume control is obtained by varying the amount of resistance in series or in parallel with the loud speaker and the control of quality is obtained by varying the electrdstatic capacity in series or in parallel with the loud speaker. The variable capacity and resistance employed for tone and volume control are preferably either both connected in-series or both in parallel with the loud speaker as by this means the number of leads required to the lea necessary when both resistance and capacconnections.

Referring now to Figs. 4. 5 and 6 which show and loud speaker to be placed in connection with the receiving set. The five leads a-e may conveniently be formed into a single five core cable with which the building, in which the system is to be used, is wired and the five leads may be connected at suitable points to wall sockets 13. This particular socket is adapted for use where the capacity and resistance used for controlling purposes are placed in series with the loud speaker and in which it is necessary that the loud speaker be connected to the same socket as that to which the control box is connected and the socket 14: for. the loud speaker connecting plug 15 is consequently provided integral with the main socket 13. The leads a-d are connected with four terminals of the main socket 13 as shown in Fig. 2 and lead 6 is connected with one terminal of the loud speaker socket 14, the other terminal of the loud speaker socket being connected to the fifth terminal of. the main socket. The control unit 9 is provided with a flexible cable 16 terminating in a five pin plug 17 adapted to engage with the main socket 13. The loud speaker 10 is likewise provided with a flexible cable 13 terminating in the two pin plug 15.

If the controlling resistance and capacity be provided in parallel with the loud speaker the leads Ze may be connected directly to the terminals of the sockets 13 which are adapted to connect with leads f and g of the control unit respectively and also with any desired number of separate sockets suitable to receive the loud speaker plug 15. In this case the control unit and loud speaker may each be plugged into any desired one of the corresponding sockets provided.

In Fig. 3 is shown in more detail the relay 5 of Fig.- 1. This consists of a T-shaped member 19 rotatably mounted upon a pin 20. Two soft iron plungers 21 and 22 are pivotally attached to the two upper ends of the member 19 and enter the solenoids 7 and 8 respectively. The solenoids are each provided with iron yokes 23 and iron cores 24. The lower end of the member 19 is provided with a roller 25 which engages with a cam 26 on thespring catch 12. A spring carrying two contacts 27 and 28 is fixed to the top of the member 19, the contacts being adapted to engage and make electrical contact with fixed contacts 6 and 4 respectively. One end of the winding of each of the solenoids "7 and '8 is connected tothe terminal 29 and to the contacts 27 and 28 whilst the other two ends of the windings are connected to terminals a and 0 respectively. a

When the winding of the solenoids is ener gized the plunger 22 is attracted downwards into the position shown in Fig. 3 and electrical connection is made between contacts 27 and 6. The spring catch 12 ensures that this contact is maintained when the current through the solenoid is interrupted and it is therefore only necessary for current to flow momentarily through the coil to eflect the desired change in along the resistance elements.

the control unit 9 of Fig. 1 in more detail, the switch, indicated by 11 in Fig. 1, comprises two bell crank levers 30 and 31 which are rotatably mounted on a pin 32. The levers are actuated by press buttons 33 and 34 respectively and are normally pressed against the press buttons by a spring35. The levers are adapted to make contactwith contacts 36 and 37 respectively which are insulated from one another and connected to leads 0 and,a respectively, the levers 30 and 31 being connected to the lead I). The upper arms of the levers 30 and 31 are adapted to engage with a pin 38 mounted on a slider 39 which carries upon its upper surface the inscriptions on" and "011; When the button 34 is pressed the slider 39 is moved to the right and when contact is made between the lever 31 and the contact 87 the word on is visible through an aperture 40 in the control unit casing. The slider is held in this position by friction until the button 33 is pressed and the lever 30 then moves the slider to the left and the word off 7 becomes visible through the aperture 40.

The variable resistance which provides volume control consists of a number of resistance elements 49 mounted upon a bobbin 41 and connected in series, the free terminal or the first element being connected to'the :left hand contact 50 and the lead 1 and the'remaining contacts 50 being connected to suitable tappings The contact arm 42 is fixed to a rotatably mounted hollow shaft 43, provided with a control knob 4.4, and is adapted to slide over the contacts 50 and make electrical contact therewith.

The condensers 51, which provide control of quality, each, have one of their terminals. connected to common bars 45 and to lead g, their other terminals 52 being connected respectively to contacts 53. A contact arm 46 is fixed to a shaft 47, provided with a knob 48, which is rotatable within the shaft 43 and in electrical connection therewith. This connection is the one common to the resistance and capacity which can be seen in Fig. 1.

The contact arm 46 may bereplaced by. a broad contact arm which is adapted to make contact with any desired number of the contacts 53 at one time. By this means there are no drops in the value of the capacity as the arm is rotated over the contacts but as it is rotated to make contact with an additional contact the value of the capacity connected to that contact is added to that previously in circuit. The values of the individual capacities required for a given total capacity is. less with this arrangement than with that shown in the drawings. I

The values of the capacities used will vary with the loud speaker employed and with the inherent capacity of the house wiring and of the output transformer. The value of the inherent capacity can, however, always be adjusted to a' definite fixed amount to,suit the'control unit by the insertion of suitable capacity in series or in parallel with the wiring. If, for example, the loud speaker requires a parallel capacity of between 0.005 and 0.01 microfarads and the inherent capacity is 0.02 microi'arads whilst the control unit gives a series capacity of from zero to 0.01, a permanent series capacity of 0.02 microiarads, must be inserted and the control unit will then cover the desired range.

The knobs 44 and 48 maybe provided with suitable indexes adapted to register with scales carried upon the upper surface of the control unit. This is, however, not shown in the drawings.

It must be noted that alteration or the pure resistance in series or parallel with the reproducer will alter the frequency characteristic, and therefore the quality, in addition to the volume.

In some cases, particularly where reproducers of low impedance are used and consequently the capacity of the line becomes of less importance,

it is sufiicient to" provide only one 01 the two forms of control mentioned for example the volume control.

When the invention is applied to a talking machine, an electrical pick-up device or micro phone is substituted for the usual sound box and the audio-frequency currents may then be amplified by a thermionic amplifier which may be controlled from a distance by a control unit. The control unit may also actuate electrically any of the various controls which have been proposed for use in magazine talking machines.

The number of wires which run between the unit in which audio-frequency currents are generated and the control unit and reproducer may of course be varied as desired. It has been found possible, in the arrangement described, to reduce the wires from me to four, for example .by making the receiver earth connections through a condenser of large capacity and using line at in place of lines a, b, or c.

I claim:

1. A sound reproducing system comprising radio receiving unit, a sound producing unit and a single controlling unit having means for controlling the other two units independently of one another, and having the said three units independently movable with regard to one another but interconnected electrically, and wherein said radio receiving unit comprises a thermionic valve and wherein said single controlling unit comprises means for making and breaking the file.- ment circuit of said thermionic valve and means adapted to connect the aerial of said radio receiver to ground when the filament circuit of trical condensers, a plurality of contact studs 'operatively connected to said condensers, and a rotary switch arm adapted to make electrical contact with successive studs while still maintaining contact with those studs with which it has already made contact to vary the capacity of said sound producing unit.

8. In a sound producing system wherein a unit in which audio-frequency electric currents are generated is associated with a sound producing unit, the combination with said units of a controlling unit for independently controlling the same, said controlling unit comprising a plurality of electrical condensers operatively connected with said sound producing unit, a plurality of resistance elements electrically connected to said sound producing unit, a plurality of contacts associated with said-condensers and resistance elements, and a pair or coaxially mounted and electrically connected switch arms adapted to be moved independently and selectively into engagement with said contacts.

4. In a sound reproducing system wherein a unit in which audio-frequency electric currents are generated is associated with a sound producing unit, the combination with said units or a controlling unit for independently controlling said two first named units, said controlling unit including a plin'allty 0! press button switches, a relay embodying a plurality or exciting coils and an armature associated with said switches, the actuation or one or said switches being adapted to close the circuit oi one of said exciting coils and actuate said armature,'and means for maintaining said armature in the position into which it has been moved by the actuation of said 5. In a sound reproducing system wherein the unit for generating audio-frequency electric currents is associated with a sound producing unit, the combination with said units or a controlling unit comprising a plurality of press button switches, means actuated by said button switches toindicate the button which was last pressed, a relay embodying a plurality or exciting coils and an armature operatively connected with said button switches, and means for maintaining said

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