US2841654A - Record actuated sound system - Google Patents

Description

Unite RECORD ACTUATED SOUND SYSTEM Application Qctoher 14, 15-954, Serial No. 462,196

4 Claims. (Cl. 179-4001) This invention relates to a record-actuated sound reproducing system in which the actuation or nonactuation of the sound reproducers is determined by recorded signals. More particularly the invention relates to a sound reproducing system incorporating an electrical switching circuit interposed between the soundhead and the reproducer, the switching circuit being motivated by one or more signals recorded on the sound record so that the reproducer or reproducers are selectively connected to the sound channel or made inoperative.

The invention is particularly adapted for. use with motion picture multiple sound track systems although not limited thereto. In such systems, the motion picture film is provided with or synchronized with a multiple sound track record, one sound track record of which is used only at certain times to provide special effects, such as a large volume of widely distributed sound emanating from loudspeakers distributed throughout the auditorium. It has been found, however, that if these speakers be left in circuit during their unactuated periods they are subject to electrical noise such as crosstalkfrorn the other sound channels and switching clicks, and to background noise, and these noises are clearly audible to the theatre audience. In the instant invention, in order to eliminate the annoyance of this interference the speakers are automatically disconnected from the circuit and grounded during unactuated periods.

In general the invention accomplishes the actuation and deactivation of the special eiiects or auditorium spakers through the medium of selected tone signals which are recorded on the special effects sound track along with the signal which is to be reproduced, the signals being so recorded as to be ideally merely additive or intermixed without intermodulation. The selected tone signals are abstracted from the circuit and utilized to operate various relays having alternate positions of operation. In one position of operation of a selected relay the special eifects speakers associated therewith are connected in circuit with the soundhead actuated by the special effects soundtrack while in the other position of operation the speakers are disconnected from this circuit and grounded.

In one embodiment of the invention one selected tone signal and the sound signal to be reproduced are recorded simultaneously on the same sound track and the selected signal operates the relay to connect the special effects speakers to the reproducing circuit only during the periods of occurrence of the selected signal.

In an alternative embodiment of the invention the selected tone signal is recorded only during those periods in which there is no signal to be reproduced. In this instance the relay is actuated by the selected tone signal to disconnect the speakers or otherwise to make them inoperative.

In still another embodiment a plurality of selected tone signals are recorded simultaneously with the sound effects signal on the same sound track. The presence of any one of the tone signals causes a switching circuit to operate to one condition and the absence of the signal causes the circuit to operate to another condition. The several switching circuits switch various reproducing cirtes Patent Q 2,841,654 Patented July 1, 1958 r ai cuits in or out in accordance with the presence or absence of individual tone signals.

One purpose of this invention is to quiet a sound reproducing system during intervals of absence of the sound signal.

Another purpose of this invention is to provide a circuit for switching an electrical channel in obedience to the presence or absence of electrical energy of a selected frequency in that channel.

Another purpose of this invention is to provide a circuit for making an electrical channel conductive when the channel carries a current of a selected frequency While filtering that frequency from the output.

Another purpose of this invention is to provide a circuit for making an electrical channel non-conductive when the channel carries a current of a selected frequency.

Still another purpose of this invention is to provide a circuit for switching a plurality of reproducing circuits in or out of an audio circuit in accordance with the presence or absence respectively of selected ones of a plurality of different frequency tone signals in the audio circuit.

Further'understanding of this invention may be secured from the description and drawings in which:

Figure 1 is a block diagram illustrating use of the invention in a sound reproducing circuit.

Figure 2 is a circuit diagram of a switching and translating circuit used to accomplish the purpose of the invention.

Figure 3 is a circuit diagram of a modification of part of the circuit of Fig. 2.

Figure 4 is a block diagram illustrating the individual control of a plurality of reproducing circuits by separate and distinct tone signals.

Referring now to Fig. l, a strip of motion picture film 11 is provided with four magnetic sound tracks, one of which is utilized for special sound effects and which will be referred to hereafter as the sound track. Each of the four tracks has its own pickup or magnetic sound head, the pickup 12 for the special sound effect track only being shown in Fig. 1 since the other three are not pertinent to this description. The magnetic record constituting the sound track under consideration unavoidably contains noise or extraneous cross talk, switching clicks and burns. It also contains the special effects signal alternating with time periods during which the signal is absent. During these periods the noise of course persists.

During the periods in which sound eifects modulations in the sound track occur they are accompanied in the same sound track by a constant alternating current modulation of a selected frequency of, for example, 12,000 cycles. The total resulting current in the sound channel 13 constituted by the output conductors of pickup 12 represents intermixing during recording by methods which form no part of this invention but which produce a magnetic record containing both the sound and the tone without intentional modulation of either by the other. The recording of the constant alternating current of a selected frequency or tone starts at the beginning of recording of each sound signal portion, or perhaps a short distance before, and terminates at the end of the recording of the sound signal portion. This produces a current in the sound head which has an approximately constant value.

After amplification in amplifier M the composite sound and tone signal is applied to a tone switching circuit, represented by rectangle 16, which constitutes the circuit for carrying out the objects of this invention. The output conductors 17 of this circuit are connected to a final amplifier 15 which actuates, through condoctors 19, the speaker or speakers represented by the symbol 21.

One embodiment of switching circuit 16 is depicted in Fig. 2. The input conductors 1S and 15" are shunted by a series resonant circuit comprising inductance 22 and adjustable capacitance 23. The resonant frequency of this circuit is designedto equal the frequency of the tone, which in this case is 12 kc. The series resonant circuit at resonance generates a high voltage of the frequency of the tone at its common junction 34. The capacitor 23 is made adjustable to permit tuning for maximum capacitor voltage consistent with minimum interference with the sound efiects signal. ance of coil 22 is made fairly high, an inductance of 150 mh being found satisfactory for use at 12 kc. The Q of this coil should be moderate, for example, about 12 for usually-encountered input line impedances as, for example, a line impedance of 500 ohms. it is, however, necessary that the rejection of this series circuit be high for frequencies of 8 kc. or less.

A parallel resonant circuit consisting of inductance 24 and adjustable capacitance 26 is inserted in series with the conductor 15'. This circuit including coil 24 and condenser 26, being in the signal channel, should be rather sharply resonant so as to present little loss at frequencies of 8 kc. and below. For example a coil 24 of 30 mh. and a capacity 26 varying from .005 to .006 ,uf. is satisfactory when a tone frequency of 12 kc. is used. Output is derived from this circuit through a conductor 27 which is, in effect, a continuation of conductor 15. Conductor 27 is connected to the forward contact 28 of a single-pole double-throw relay contact assembly having an armature 29 connected to an output terminal 31. The terminal 31 is connected through the conductor 17, Fig. 1, to the input of amplifier 18. The other switch contact 32, Fig. 2, is connected to ground through resistor 33.

The shunt resonant circuit including inductance 24 and capacitance 26 is designed to resonate at the tone frequency, its adjustment being refined by use of the adjustable capacitor 26. Adjustment should be made so that the circuit presents a very high impedance to the 12 kc. tone while presenting low impedance to the signal frequencies of 8 kc. and below.

Actuation of the relay contact arm 29 is effected by coupling the junction 34 through condenser 36 to a voltage divider 37 which serves as an amplitude control. The voltage divider slider 38 is connected to the control grid 39 of a triode 41 having a shunt resonant circuit in its anode conductor 42. This shunt resonant circuit consists of inductance 43 and capacitor 44 and is designed to resonate at the tone frequency. The anode conductor 42 is connected to a source of positive potential represented by terminal 46. The anode 47 of triode 41 is coupled through capacitor 48 to a cascade voltage-doubling rectifier comprising diodes 49 and 51 and capacitor 52. The output of the rectifier is connected to the grid53 of directcoupled amplifier triode 54 having the winding 56 of a relay 55 in its anode circuit, the relay contact assembly comprising armature 29 and contacts 28 and 32. Positive anode potential is secured from the common junction 57 of a voltage divider containing resistors 58 and 59 energized from terminal 46.

If a system is employed in which the tone is on only when the sound signal is absent, then the relay contacts must be connected as illustrated in Fig. 3. When the relay coil 56 is deenergized the contact armature 29 is biased to engage the sound channel contact 28 as shown, but when direct current derived from the 12 kc. tone energizes coil 56 the armature is moved to engage contact32, breaking the sound channel circuit and grounding output terminal 31.

In the operation of the circuit of Fig. 2 a sound signal consisting of audible frequencies up to 8 kc., combined with a switch signal having a frequency of 12 kc., is ap plied across the input conductors 15 and 15". The series resonant circuit shunting these conductors is tuned by variable condenser 23 to secure maximum potential at The induct- 12 kc. at the junction 34. The shunt resonant circuit interposed in series in conductors 15 and 27 is tuned by variable condenser 26 for maximum rejection of the 12 kc. tone frequency with minimum effect on the special effects output signal. The combined effect of the series and shunt resonant circuits may be considered to be that of an L-section of a band rejection filter tuned to reject a band centered at 12 kc., and having a slope steep enough not to aifect frequencies of 8 kc. and below. The output at relay contact 28 is thus devoid of the 12 kc. tone frequency but contains substantially unattenuated all other signal frequencies between zero and 8 kc. which were applied to the input terminals 15' and 15".

The series resonant circuit consisting of inductance 22 and capacitance 23 has low impedance for the 12 kc., frequency signal accompanied by high potential at junction 34, with higher impedance for all other frequencies. A fraction of the potential of junction 34 is selected by use of voltage divider 37 to control relay opa oration. Voltage divider 37 should have high resistance, for example, 1 megohm. It is desirable to amplify and rectify the 12 kc. tone signal in order to secure enough power to operate a relay and it has been found preferable to employ two stages of amplification to insure ample power under all conditions. of inductance 43 and capacitance 44 improves the selectivity of the first stage of amplification. Crystal diode rectification is employed between the first capacity-coupled stage of amplification and the second direct-coupled stage. Tests have shown that this circuit provides ample power for operating a high impedance relay in the anode circuit of triode 54.

The circuit of Fig. 4 depicts a system in which a plurality of tones additively combined with sound on a single sound effects track are employed to switch the sound to one or more sound reproducers, alternatively or in concert and in any desired combination. As a specific example let it be supposed that the sound is to come at one time from a speaker on a stage, at another later time from a speaker at the left of the auditorium, at another still later time from a speaker at the right of the auditorium, and at still another succeeding time from all three speakers together.

To accomplish these results the sound effects are mixed in the sound track as before described, being mixed at one time with a 12 kc. signal or tone, at another time with a 15 kc. tone, at another time with an 18 kc. tone, and at still another time with all three tones of 12, 15 and 18 kc. When the sound effects are absent all tones are also absent from the track. The film 11 carrying the sound track is moved past the pickup 12 so that the single sound channel composed of the pickup output conductors 13 contains electrical energy representing these signals and sound added together as described. This energy is voltage-amplified in amplifier 14. The output conductors 15 of amplifier 14 are connected to three switching and translating circuits 61, 62 and 63, the inputs of which are connected in parallel. The switching and translating circuit 61 is substantially the same as circuit 16 of Fig. 1, described in connection with Fig. 2, and its various resonant circuits are tuned to 12 kc. as described. The switching and translating circuits 62 and 63 are similar to circuit 61 except that their resonant circuits are tuned to 15 kc. and 18 kc. respectively,;

The output conductors 17, 64 and 66 are connected through amplifiers 18, 67, and 68 to speakers 21, 69 and 71. Speaker 21 is installed on the stage, speaker 69 is installed at the left side of the auditorium, and speaker 71 is installed'at the right side of the auditorium.

In only one respect does the circuit 61 of Fig. 4 dif-' fer from the circuit of Fig. 2, namely, in the design of the resnonant circuit designated in Fig. 2 as composed of inductance 24 and capacitance 26 in parallel. In circuit 61 this resonant circuit must take the form of a broader band filter or of a low-pass filter, so that all frequencies- The anode trap consisting below 8 kc. are transmitted while the tone frequencies of 12, and 18 kc. are very highly attenuated. Filters having the same requirements must he used in circuits 62 and 63.

In the operation of the circuit of Fig. 4, when the film 11 containing no sound effect signal or tones of any frequency is run past the pickup 12, all relays in the three switching and translating circuits 61, 62 and 63 remain unoperated and normal, short-circuiting their respective speakers 21, 69 and 71. When the sound track contain; sound effects admixed with only the 12 kc. tone, the relays in circuit 62 and 63 remain normal, deactivating the auditorium speakers 69 and 71. However, the relay 55, Fig. 2, in circuit 61, Fig. 4, is operated by tr e 12 kc. tone, and the relay connects speaker 21 into circuit, so that the sound effects are heard from the stage. in the neXt part of the film the sound effects are admixed only with 15 kc. tone. The speakers 21 and 71 are then shortcircuited while the relay in circuit 62 is operated, causing the sound to emanate only from the left auditorium speaker 69. In the next part of the film only the right speaker 71 is connected, and in the final part of the film all three relays are simultaneously operated and the sound is heard from all three speakers at the same time.

What is claimed is:

1. A record-actuated sound reproducing system comprising, a record medium having a selected tone signal and signals to be reproduced recorded on a single sound track thereof, pickup means positioned to convert the signals recorded on said sound track into corresponding electrical signals, a signal translating channel having its input connected to said pickup means, said signal translating channel including a filter network connected in series therein offering a high impedance to a signal frequency corresponding to that of said selected tone signal and low impedance to signal frequencies corresponding to the signals to be reproduced, a resonant network connected in shunt to the input of said signal translating channel having a low impedance to signal frequencies corresponding to that of said selected tone signal and high impedance to signal frequencies corresponding to the signals to be produced, loudspeaker means, switch means connecting said loudspeaker means to the output of said signal translating channel in one condition of operation and disconnecting said loudspeaker means from said signal translating channel and grounding said loudspeaker means through a resistor in a second condition of operation, and means for deriving a potential from said resonant network for determining the condition of operation of said switch means.

2. A record-actuated sound reproducing system comprising, a record medium having recorded on a single sound track thereof a selected tone signal intermixed with signals to be reproduced, pickup means positioned to convert the signals recorded on said sound track into corresponding electrical signals, a signal translating channel having its input connected to said pickup means, said signal translating channel including a filter network connected in series therein offering high impedance to a frequency corresponding to that of said selected tone signal but low impedance to signal frequencies corresponding to those of said signals to be reproduced, a resonant network connected in shunt to the input of said signal translating channel having a low impedance to a frequency corresponding to that of said selected tone signal but high impedance to signal frequencies corresponding to those of said signals to be reproduced, loudspeaker means, switch means connecting said loudspeaker means to the output of said signal translating channel in a first condition of operation and disconnecting said loudspeaker means from said signal translating channel and grounding the loudspeaker means through a resistor in a second condition of operation, means for deriving from said resonant network a potential representative of said selected tone signal, and means operated by said potential to place said switch means in said first condition of operation, said switch means being in said second condition of operation in the absence of said potential.

3. A record-actuated sound reproducing system comprising, a record medium having recorded on a single sound track thereof a selected tone signal alternating with signals to be reproduced, pickup means positioned to convert the signals recorded on said sound track into corresponding electrical signals, a signal translating channel having its input connected to said pickup means, said signal translating channel including a filter network connected in series therein offering high impedance to a frequency corresponding to that of said selected tone signal but offering low impedance to frequencies corresponding to those of said signals to be reproduced, a resonant network connected in shunt to the input of said signal translating channel having a low impedance to a frequency corresponding to that of said selected tone signal but high impedance to frequencies corresponding to those of said signalsto be reproduced, loudspeaker means, switch means connecting said loudspeaker means to the output of said signal translating channel in a first condition of operation and disconnecting said loudspeaker means from said signal translating channel and grounding the loudspeaker means through a resistor in a second condition of operation, means for deriving from said resonant network a potential representative of said selected tone signal, and means operated by said potential to place said switch means in said second condition of operation, said switch means being in said first condition of operation in the absence of said potential.

4. A record-actuated sound reproducing system comprising, a record medium having recorded on a single sound track thereof a plurality of selected tone signals intermixed with signals to be reproduced, pickup means positioned to convert the signals recorded on said sound track into corresponding electrical signals, a plurality of signal translating channels having their inputs connected to said pickup means, each signal translating channel including a low-pass filter connected in series therein offering high impedance to all frequencies corresponding to those of said plurality of selected tone signals but offering low impedance to signal frequencies corresponding to those of said signals to be reproduced, each of said signal translating channels including a resonant network connected in shunt to the input thereof, each of said resonant networks having a low impedance to a respective frequency corresponding to that of one of said plurality of selected tone signals but high impedance to all other frequencies, a plurality of loudspeaker means, each of said plurality of signal translating channels including an associated switch means connecting one of said plurality of loudspeaker means to the output of the signal translatmg channel in a first condition of operation and disconnecting and grounding said one of the plurality of loudspeaker means through a resistor in a second condition of operation, means for deriving from each said second mentioned resonant network a potential representative of said respective frequency of a tone signal, and means operated by said potential to place said associated switch means in said first condition of operation, said switch means being in said second condition of operation in the absence of said potential.

References Cited in the file of this patent UNITED STATES PATENTS 2,075,861 Mueller Apr. 6, 1937 2,101,121 Wixon Dec. 7, 1937 2,298,618 Garity et al Oct. 13, 1942 2,313,867 Garity et al Mar. 16, 1943 2,361,490 Mueller Oct. 31, 1944 2,427,850 Gehman Sept. 23, 1947 2,499,587 Kellogg Mar. 7, 1950 2,714,633 Fine Aug. 2, 1955

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