US2255517A

US2255517A - Talk-back communication system

Info

Publication number: US2255517A
Application number: US301546A
Authority: US
Inventors: Fred W Nickerson; William C Moore; Barnett Herbert
Original assignee: GUIDED RADIO CORP
Current assignee: GUIDED RADIO Corp
Priority date: 1939-10-27
Filing date: 1939-10-27
Publication date: 1941-09-09
Anticipated expiration: 1958-09-09

Description

Sept. 9, 1941. F. w. NICKERSON ETAL TALK-BACK COMMUNICATION SYSTEM Filed Oct. 27, 1959' 6 Sheets-Sheet l lvlcke son 2m 0- Moore Sept. 9, 1941. F. w. NICKERSON ETAL 2,255,517

TALK-BACK COMMUNICATION SYSTEM Filed 001;. 2'7, 1939 Sheets-Sheet 2 ATTORNEY.

%/+erbe f rneH- Sept. 9, 1941. F. w. NICKERS ON ET AL TALK-BACK COMMUNICATION v SYSTEM Filed Oct. 27, 1939 6 Sheets-Sheet 3 Sept, 19430 F. w. NICKERSON ETAL. 2,255,517

TALK-BACK COMMUNICATION SYSTEM Filed Oct. 27, 1939 6 Sheets-Sheet 4 f in w/sec.

Fr ed Sept. 9, 1941. w NlCKERSON HAL 2,255,517

TALK-BACK COMMUNICATION SYSTEM Filed Oct. 21 19.39 6 Sheets-Sheet 5 a M. 3 .234 mucv uwsw w 3 d 1. 2 vzoio i m I A 7' TORNE Y5 Se t. 9; 1941.

F. 'w. NICKERSON ETAL TALK-BACK COMMUNICATION SYSTEM 6 Sheets-Sheet 6 Filed Oct, 27, 1939 02? x. Zin -i view ENTOR..

5 n mm w mwmw N C r w m wm T dmw T A Fre Wi l $5 ?aiented Sept. 9, 1941 TALK-BACK COMMUNICATION SYSTEM Fred W. Nickerson and William C. Moore, Brooklyn, and Herbert Barnett, Jackson Heights, N. Y., assignors to Guided Radio Corporation, New York, N. Y., a corporation of :New York Application October 27, 1939, Serial No. 301,546

16 claims ,(01. 119-1) This invention comprises a combination of instrumentalities associated to form an audio-frequency communication system capable of sound transmission in either direction.

In a broad sense, the inventionrconsists of a combination of electrical instrumentalities of such characteristics'and so associated that,at

one end of the system there is provided a transmitter or microphone and a receiver or loudspeaker, while at the other end of the system there are provided a plurality of spatially distributed combined microphones and loudspeakers or transmitters and receivers so that at the latter end talk-out as well as talk-backcan be accomplished..

An important object of this invention is to provide a system of the above, nature having characteristics such that the combined loudspeaker and microphone, which hereinafter may be termed transducers, are capable of picking up and transmitting intelligible sounds from substantial distances. Another object of this invention is to provide a system of the above type which may be turned on from either end so that speech may be transmitted from either end to the other under controls at one end.

These and many other objects which will become apparent from the following detailed de-. scription of several forms of the invention are successfully secured.

This invention resides substantially in the combination, construction, arrangement and relative location of parts, all in accordance with this disclosure.

- In the accompanying drawings,

Figures 1 and 2 together comprise a diagrammatic illustration of one form of system in accordance with the objects and principles of this invention;

Figure 3 is a diagrammatic view of a modified form of system likewise in accordance with the objects and principles of this invention;

Figure 4 is a graph illustrating the response curve of the transducers 'showing'a rising response with increasing frequency;

Figure 5 is another chart illustrating the directional characteristics'of the transducers;

Figure 6 is a chart of the response of the electrical transmission network and transducer in combination illustrating its non-linear response;

Figure '7 is a chart illustrating the response of the transducers as loudspeakers, upper curve, and microphones, lower curve; and

Figure 8 is a chart illustrating the sensitivity of the human car at various frequencies.

In order to fully appreciate the nature of this invention and the manner in which the objects thereof are accomplished, a brief discussion of the principles thereof is desirable before describing examples of the forms which the complete system may take. The system herein described will effect two-way longdistance audio communication with intelligible signal pickup over'distance's heretofore unattained: the same electro-acoustic device as a microphone for speech pickup as is used for reproducing-;speech as a loudspeaker. .In this .twg way'j'ailidio frequency communication system,"amplifiergunits are employed which are controlled from one end of the system so that when the transducer is acting as -'a microphone it is connected tdthein'put of'the amplifying systemandwlien it isac ting 'as a "20 "loudspeakeritis connected.tothe oi1tput or the amplifier.

The system ofthisinventionlutilises acombination of acoustic transdu'ce'rs;transmissionnetworks and amplifiers having elctricaland acoustical characteristics that would The normally commonly known in that each is intentionally 'made to have a non-linear amplitude-frequency response and a limited frequency'range.1 In addition, there is provided in the system a so-called talk-back volume control to permit reduction of volume to increase the effectiveness of sound pickup at long distances.

These apparently low fidelity? components referred to are combined in a system in ways which will be hereinafter described to efiect unusually long distance pickup of voice and. other sound signals by the electro-acoustic transducers which are so designedjas to operate eficiently as high power loudspeakers. By high power is meant in this disclosure the capability of handling energy in amounts of the order of ten watts or more of electrical power input. 1 To illustrate the effectiveness of systems inaccord- 'ance with this invention, itis noted that the 55" much as 2500 feet, that is to'say," the speaker -the best operation as a pickup device.

may stand that far from the transducer and talk with a person at the other end of the sys tern. that no system heretofore known has been capable of such operation, it being necessary es pecially where the loudspeakers are also used as microphones, to stand directly in front of them in order to transmit intelligible, speech. The result is that systems of this type may be installed, for example, on shipboard with the main station on the bridge of the ship and the over the ship. An oflicer on the bridge may with such a system communicate with any member of the crew, who need not be anywhere near the transducers in order to reply. This result is the more remarkable because intelligible speech can be transmitted through a substantial background of undesired sounds.

As will appear as the disclosure proceeds, the

combination into a communication system of the audio-frequency type of components having non-linear response and limited frequency range would be intentionally avoided by skilled designers of conventional loudspeaker communication systems for the reason that a result exactly contrary to applicant's is normally striven'for, that is, high fidelity of sound transmission and reproduction.

It is, of course, recognized that a loudspeaker as a talk-back microphone is in itself not new, such use thereof having been heretofore suggest-ed. When used, however, as a microphone such loudspeakers are only capable of reproducing intelligibly sounds picked up in the immediate vicinity thereof. The practical distinguishing feature in over-all result of applicant's system is its ability to intelligibly reproduce sounds from unusually long distances.

Referring more in detail to the components of applicants system, reference is firstmade to the talk-back loudspeaker, i. e., the transducer. In accordance with this invention, the transducer must have inherent low frequency discrimination and high sensitivity in the region of optimum ear sensitivity. To obtain such results the average trend of the frequency response curve of this device must rise with increasing frequency, and between, for example, 200 and 2500 cycles the rate of rise must not be less than three decibels per octave. Such a-response curve is illustrated in Figure 4. The straight line of this curve indicates the minimum average rising trend required for effective operation while the other curve is a sample loudspeaker curve that meets this limit. Such a device when used as a loudspeaker permits efficient reproduction of sound and when used as a microphone provides As illustrated in Figure 4, the frequencies below the important speech region, that is, below about 200 cycles, are rapidly attenuated. This is desirable because the low frequencies apparently produce a secondary effect which has a tendency to mask the higher and more important speech frequencies and thus operate to reduce the intelligibility.

This device in accordance with this invention is also designed tohave strong spatial discrimination. In other words, the device when used both as a talk-out and a long distance talk-back unit must have a sharp directional effect in a dimensional sense.

Figure 5. The transducers should have a -di-' It will, of course, be recognized at once- The directional discrimina-- tion of a suitable transducer is illustrated in I rectional characteristic greater than that illustrated in Figure 5 at a frequency of 1000 cycles and'should be so designed so as to have i an increasing directionaheffect up'to at least a 5 frequency of 3000 cycles. Such-a device when operating either as a talk-out' or a talk-back unit permits the collection of sound in a' narrow cone along the axis in which the horn thereof is directed with a much greater sensitivity to sounds within that region than to' sounds] and various transducer stations distributed at desired points noises outside of it. i v

The transmission circuits which receive the. electrical currents generated by the pickup devices feed into an amplifier.

cally discriminate so as to attenuate the low and other undesirable frequencies while increasing or emphasizing those frequencies which include the vowel sounds, voiced consonants and such sibi- 1am; sounds as are desired for good intelligibility of speech. 'Like the transducers, the frequency response of transmission circuits and amplifiers must have a trend which rises with increasing frequency between the lowest frequency trans- 5 mitted by the talk-back speaker and a frequency obtain the proper emphasis when the talk-back unit is used as a loudspeaker, the circuits are arranged so that the response curve of the electrical system may be automatically changed in any predetermined manner but preferably so that frequencies below 200 cycles per second are rapidly attenuated.

The sounds that the talk-back loudspeaker or transducer pick up are fed through the amplifier and reproduced by a receiving loudspeaker. This loudspeaker, which would be the one on the bridge in the case of ship installation, is not used in the'system shown, as a microphone. It must,

,however, be so designed that its. response is greatest in the higher vowel voiced cojnsonant and sibilant regions, thereby .having its greatest efficiency in a band of frequencies starting not higher than 1000 cycles up to not lower than 4000 cycles, and so constructed that frequencies below 500 cycles are markedly attenuated. The

response curve of such a loudspeaker is illustrated in Figure 6. When desired, a receiving loudspeaker of the conventional type may be employed if used in conjunction with an electrical network having transmission characteristics such that the response curve of the combieration as against talk-out operation. The earis more sensitive in the higher vowel, voiced consonant, and sibilant regions at low intensities so that it is important to keep the total volume of speech and noise low enough so that the car operates at a maximum sensitivity, as is illustrated as being necessary by the chart of Figure 8.

It is a well known fact that the sensitivity of the ear varies with the amplitude of the sound 0 impinging thereupon, and such a marked decrease in the ear sensitivity occurs if the volume is too greatly increased, as when an appreciable amount of extraneous noise is amplified, that "the effectiveness of the talk-back reception is seriously impaired. This result is normally un- The circuits just 5 ahead of the amplifier are designed to electrl-f 'lieved, hasnot heretofore been possible.

. 2,255Tsi7 derstood to be just opposite to what would be bridge those transducers which are to be operated. The transducers are indicated by the 'ref erence numerals l2, there being one illustrated for each switch l2. While, of course, only three transducers are shown it is apparent that any desired number as required may be employed.

Thev reference numeral I3 is used to indicate generally the control units, one of which is provided for eachtransducer and is controlled at this directional efl'ect increases markedly as the frequency increases. This property combined with the low frequency discrimination of the talk-back loudspeaker increases the effect ofhigher sensitivity in the region of best ear sensitivity over what would be obtained if the increased directional effect with frequency were not present.

Referring to Figures ,1 and 2, a description will be provided of a system in accordance with the objects and principles of this invention. These two figures are to be read together, representing a single complete system. It may be noted that one of the more suitable fields of use for this invention is on shipboard. The power supply for the system of the invention is from the 110 volt direct current circuit of the ship, represented by the reference numerals l and 2'. They are connected through a main switch 3 and a pair of choke coils 4.and 5 to the supply leads I and 2 for the apparatus of this invention. These leads are bridged by a pair of condensers 8 and l in series having their common tap grounded, as indicated at 8. The combination of choke coils and condensers provides a filter circuit for keeping out any undesired current fluctuations which may be present in the power circuit feeding the apparatus.

In the various figures the power supply leads i and 2 are not extended to all of the various instrumentalities receiving energy therefrom for purposes of simplifying the drawing. However.

thecorresponding leads of the various instrumentalities are provided with the same reference numerals l and 2, from which it will be apparent to those skilled in the art that all of the leads marked l are connected to the power lead 8 and all of the leads 2 are connected to the power lead 2.

' At 9 and H] are illustrated the loudspeaker and microphone, which in the case of a ship installation would normally be on the bridge of a shipunder the control of an officer. As noted in ing type. This switch is likewise on the bridge adjacent to the microphone it) so that when the bridge oflicer wishes to use the system to talkouthe closes this switch. At 12 are shown a plurality of switches which are preferably of a locking'type, that is, they remain closed'when operated until again operated for opening. There is one of these switches provided for each transducer station on the ship. As each is closed a corresponding transducer is placed in circuit so that the bridge ofllcer may control from the least 'in part by the respective switches l2. Each of these control units consists .of two relays 62 and 60. The reference numeral [4 indicates generally the control. unit under the influence of the switch II by means of which-the apparatus is controlled at the bridge for operation either for talk-out over the microphone to or for talkback over the transducers and the. loudspeaker 9. This control unit consists of three relays 43, M and 45. It may be noted that the apparatus within the square I3 for the middle transducer is the same as that illustrated directly above and below it and hasmerely been shown in this form to further simplify the drawing.

One terminal of the microphone I0 is connected by wire l5 to the grounded terminal of the volume control 20, which is illustrated as comprising variable resistors and is also connected by wire l8 to the input lead IQ of the amplifier 25. The other terminal of the microphone lil is connected by wire IE to the input terminal of the volume control 20 as shown. The output terminal of this volume control is connected by wire 2| to the normally open fixed take other forms.

push-pull circuit.

contact of switch 22, which is a part of relay 44. The leads l5 and I6 are bridged by a condenser li, for the purpose of properly equalizing the talk-out frequency characteristic of this particular circuit. The movable contact of switch 22 is connected by wire 23 to the other input terminal of the amplifier 25, through variable impedance network 24.

The amplifier 25 is illustrated as an ordinary audio-frequency vacuum tube amplifier, which, as those skilled in the art will appreciate, may Referring to the amplifier generally, it is'noted that the input transformer is indicated at IT. The lead from one terminal of the output of this transformer to the control grid of the vacuum tube 26 includes a condenser 69, which will be referred to later. The circuits of the first amplifier tube 26 are resistancecoupled to the circuits of the second amplifier tube Zl', the output of which tube is coupled by v a. transformer to a pair of

multi-electrode vacuum tubes

28 and 29 connected in the well known The reference numeral F in all cases indicates the filament or heater leads of the vacuum tubes which would be connected to the terminals F of the winding of the power pack transformer, all in accordance with well known practice. These connections have not been completed for sake of simplicity. The output of the amplifier is supplied to the output transformer OT, which is provided with the

leads

32 and 33. At.3l is indicated a full wave vacuum tube rectifier, which is used in conjunction with the usual power supply filter arrangements, etc., as is well known in the art.

' The leads 30 are to be connected to a suitable alternating current supply source which may be from an inverted rotary converter operating from the power line of a ship. For emphasis, it is again noted that this amplifier may take any one of a number of well known forms and is only to be difierentiated therefrom by the features which will be referred to later.

The output of the amplifier appears between ground (wire 33) and wire 32 which is connected to the normally open fixed contact of switch 36, which is a part of relay 43. This wire is also connected to the normally closed fixed contacts of switch 34 which is a part of relay 44 and switches 31 and 38 which are parts of relay 45. The movable contact of switch 34 is connected by wire 35' to one terminal of the receiving or bridge loudspeaker 9. The other terminal. of this loudspeaker is grounded by wire 33, which is also connected to both of the movable contacts of switches 31 and 38 (relay 45) and to the normally open fixed contact of switch 39 which is a part of relay 43. The movable contact of switch 39 (relay 43) is connected by a Y normally closed fixed contact of switch 36 (relay 43) is connected by wire 54 to the input terminal of the constant impedance volume control 53 shown as composed of variable resistors. The ground terminal of the volume control is connected to wire l9, and the output terminal 0f the volume control is connected through the condenser 52' by wire 52 to the normally closed fixed contact of switch 22 which is a part of relay 44. The normally open fixed contact of switch 42 (relay 44) is connected by wire'5D to the normally open fixed contacts of switch 40 which is a part of relay 43. The movable contact of switch 40 (relay 43) is connected to the lead I of the direct current power source. The movable contact of switch 42 (relay 44) is connected by wire 5| to one terminal of the winding of the relay 45, which includes switches 31 and 38. The other terminal of this winding is connected by wire 2 to the power source and wires 5| and 2 are bridged by a suitable current reducing resistor, as indicated at 5|. The normally closed contact of switch 42 (relay 44) is connected by wire 42' to each of the movable contacts of switches 65 which are apart of relays 60 in the control units l3. One of the fixed contacts of switch 40 (relay 43) is connected by wire 48' to each of the normally open fixed contacts of the switches 65 (relays 60). The normally open fixed contact of switch 4| (relay -44) is connected to the lead I of the power source and the movable contact is connected by wire 48 to one terminal ofthe winding of the relay 43, which includes

switches

36, 39 and 40. The other terminal of this winding connects to the positive lead 2 of the current source.

Leads 48 and 2 are bridged by condensers 49 which act as time delay devices to delay the release of the relay 43. One terminal of the winding of the relay 44, which includes

switches

22, 34, 4| and 42 is connected to the positive terminal 2 of the current source, and the other terminal is connected by wire 41 to one terminal of push button switch The other terminal of switch H is connected to wire I of the direct current power source. One contact of each of the switches I2 is connected by wire 55 to wire' I of the direct current power source. The other contact of each of these switches is connected by wires 66 respectively to the movable contact of switch 63 which is a part of relay 62 and to the normally closed fixed contact of switch". The normally open fixed contact of switch 58 is connected to the direct current power source wire I, which is also connected to the movable contact of switch 64, which is a part of relay 62 and to the normally closed fixed contacts of switch 68 which is a part of relay 60. The power, lead 2 is connected to the commonterminal of two opposing windings of the relay 62 and by wire 6| to one terminal of the winding of the relay 60. The other terminal of the winding of the relay 60 is connected by wire 59 to the movable contact of switch 58 which is a part of relay 62. The normally open fixed contact of switch 63 (relay 62) is connected through a resistor as shown to the remaining terminal of the right hand winding of relay 62 while the remaining terminal of the left hand winding of this relay is connected through a resistor to the normally open fixed contact of switch 64 (relay 62) and to the'normally closed fixed contact of'switch 66 which is a part of relay 60. The movable contact of switch 66 (relay 66) is connected by wire 66' to one terminal of the transducer 12'. The movable contact of switch 68 (relay 60) is connected by wire 68 to the other terminal of the transducer I2 through a condenser |2b which acts as a blocking condenser for direct current; A push-button switch |2a is provided for connecting the leads 66' and 68' of the transducers together for turning the station on from the outside. It may be' noted .that the connections in each of the control units l3 are the same as those just described.

The network 24 connected in the lead 23 consisting of a condenser adjustable to three values of capacitance, shunted with a resistor, and the condenser 69, Figure 2, are provided so that the over-all response of the network and amplifier in combination with the transducers as previously described will be non-linear but having a rising trend with increasing frequency and rapid atten Q uation below about 200 cycles per second and an operating range up to about 3,000 cycles per second. It is to be noted that the volume controls 20 and 53 are used alternately, the volume control 20 being used for talk-out and the volume control 53 being used for talk-back. The circuit connections as' will be described in connection with the operation are such that the change over from one volume control to the other is accomplished automatically to provide the proper volume level or to accomplish good speech intelligibility whenthe transducers are used as talk-back units. The

talk-back volume control is adjustable to control the talk-back signal level in order to secure the proper signal strength for maximum ear sensitivity under the operating conditions likely to be encountered. The condenser 52' in series with the talk-back volume control 53 reduces the-low frequencies further for talk-back.

In describing the operation of this system, it is first to be noted that all switches and connections are shown in their normal positions, that is when the system is not in use, although the switch 3 is closed so that energy is available to put the system in use. If it be assumed that a bridge ofiicer wishes to talk-out through one or more of the transducer stations,.he first closes switch l2 corresponding to those stations he desires to operate. He then closes switch I, with the result that current flows from wire I through switch If wire 45, relay u, back to wire 2. The result is that relay 44 is operated and the movableconswitches I2 have been closed.

as is clear from Figure 1.

, t 2,255,617 tacts of

switches

22, 34, 4I and42 are moved over lead I9 is already connected to the other ter-.

minal of this microphone. The closing of switch 4I supplies current through wire I, switch 4|, wire 48, to relay 43, and from there through wire 2 back to the'direct current power source. Since there is very little resistance in series with the parallel circuit of relay coil 43 and condensers 43, the relay operates immediately and switches 40, 38 and 35 are operated. The operation of switch 34 disconnects wire 35 from wire 32 so that the bridge loudspeaker is out of circuit.

As soon as switch 43 is operated current flows.

from wire I, through the normally open contact of switch 40 (why 43), wire 50, normally open contact of switch 42 (relay 44), the movable contact wire 5|, relay 45, and back to direct current power source through the lead 2. The energiration of the winding of relay 45 opens switches 31 and 38, which are simply in parallel. The opening of these circuits removes a short-circuit across the

output terminals

32 and 33 of the amplifier. The operation of switch 36 which is a part of relay 43 connects the output lead 32 of the amplifier to wire 35' and switch 39 also a part 'of relay 43 connects the other output lead '33 to wire 39'. Wires-36' and 39' run respectively to the normally open contacts of the

switches

66 and 88 of each of the relays 60.

It will be recalled that one or more of the Assuming that the uppermost switch I2 has been closed, current flows from lead I, through lead 55, upper switch I2, wire 56, switch 58 (relay 53) the winding of relay 60, and back to the lead 2 through wire 6|. This operates relay 60, closing switch 65 and

operating switches

65 and 68. The operation of switches 86 and 68 connects the corresponding transducer I2 to the leads 36 and 39', The same operation occurs in each control unit I3 for which the corresponding switch I2 has been closed.

The system is now set up for operation for talk-out, that is, the bridge ofiicer speaking over the microphone I supplies speech energy to the amplifier, the output of which is supplied to the transducers I2 whose switches I2 are closed. During all the time the bridge oificr talks he holds switch II closed. In order to be talked to, that is, in order for talk-back operation to occur, as soon as he finishes. speaking or issuing a command, he releases switch II. The opening of switch I I breaks the, circuit to relay 44 with the result that all the switches controlled by it move to the position shown in Figure 1. Thus the bridge loud-speaker 9 is connected throughswitch 34 which is a part of relay 44 to output lead 32 and, since it is always connected to output lead 33, it is ready to be operated, except that the release of relay 44 also caused relay 45 to release and short-circuit the output of the amplifier temporarily.

Input lead I9 is connected through switch 39 (relay 43) to lead 39 and input lead 23 is connected through

switches

22 and 36 to lead 36'. At this time the network 53 is in circuit and netn at switch 4:. Thus switches 31 and as of relay 45. close and momentarily short-circuit the loudspeaker 3, preventing the emission from the loudspeaker of the various noises incident to the change-over, which has been found important in that the elimination of these noises is desirable. It has been found that if these noises are permitted to reach the loudspeaker 9 the person thereat is initially distracted as the speech comes over the loudspeaker. Practice indicates that the elimination of this distraction serves for more accurate communication. The across the speaker only exists momentarily, as will be explained later.

The release of relay 43 sufliciently to .permit the switches controlled thereby to move back from operated position to the position shown in Figure 1 is momentarily delayed by reason of the time required vfor the condensers 49 to discharge through the relay winding and it is during this period that the short-circuit on the bridge loudspeaker at switches 3'I and 38 of relay 45 occurs.

However, as soon as switch 40 moves back to the position shown, current flows from wire I, through wire 40', through closed switch 65, wire 42',,the normally closed contacts of switch 42, wire 5|, relay 45, and back to the direct current This causes switches, 31 and 38 of relay 45 to open and break the short-circuit. Relay 63 remains operated, holding switch 55 closed and the transducer connected to the leads 35 and 39'.

In addition to connecting the loudspeaker 9 to the output leads of the amplifier, the release of the relay 44 causes the transducers to be connected to the input of the amplifier at switches 36 and 39 of relay 43. The system is now ready for talk-back in a manner which it is believed will be apparent. This change in connections substitutes the talk-back volume control 53 for the talk-out volume control 20 so that the gain of the amplifier system ischangedfor talkback in accordance with the description previously provided. The condensers I2b in addition to acting as blocking condensers assist in providing the proper amount of equalization for the transducers for maximum speech intelligibility both for talk-out and talk-back." These con-' densers, if desired, may be variable as may be the other modifying elements of the circuits to adapt them for operation under varying conditions. I r

The operation of the system will now be described for a case where talk-back is desired to the bridge, the conversation to initiate at the talk-back end. Assuming switchesI2 are open,

work 20 is out of circuit, switch 22 being in the pos tion shown.

The release of relay 44 also'breaks the circuit to relay 45 at switch 42 and the circuit to relay as they would normally be, the person desiring "to talk-back to the bridge, at one of the trans- The closing oi switch I2a, say for the upper transducer station in Figure 1, causes current to flow from wire I, through the normally closed contacts of switch 63 which is a part of relay 50, switch I2a, back through the normally closed contacts of switch 56, also 'of relay 60, to and through the left hand winding of relay 62 and back to lead 2. The energization of the left short-circuit hand winding of relay 62 is sufllcient to cause operation of the three

switches

68, 63 and 64 controlled thereby. Current fiows through lead I, the normally open contacts of switch 58, wire 59, relay 60, and wire 51. back to wire 2. The closing of switch 64 completes a holding circuit for this winding from wire I, through switch 64 to the left hand winding of magnet 62 and back to the direct current power lead 2 so that even though switch I2a is immediately opened the left hand winding of relay 62 remains energized.

The operation relay 60 connects the transducer with the wires 36' and 39' as before'through the normally open contacts of

switches

66 and 68. The closing of switch 65 causes current to flow from lead I through the normally closed contact of switch 40, which is a part of relay 43, wire 40, switch 65 (relay 60), wire'42', normally closed contacts of switch 42, wire relay 45, and back to the lead 2. Thus the short-circuit is taken oiT the bridge loudspeaker at'switches 31 and 38 of relay 45.

The system is now ready for talk-back. The bridge oflicer, in order to talk-out, closes the corresponding station switch I2 and as he talks holds switch II closed, which of course operates the control unit I4, as previously described. The closing of switch II also supplies current from the lead I, wire 55, switch I2, wire 55, closed switch 63 of relay 62 and the right hand winding of relay 62, back to the power lead 2. Thus the right hand winding of the relay 62 is energized in the opposite direction to the other winding so that the relay releases and switches 58, 63 and 64 assume their normal positions. Relay 60 remains operated as long as switch I2 is closed however as previously described. It is therefore obvious to those skilled in the art that when the system has been put in operation by pressing the outside push button I2a, it may be shut ofi by the bridge oflicer by operating and then releasing his switch I2.

Figure 3 showsdiagrammatically a modified circuit which differs in the main from that of the circuit of Figures 1 and 2 in that part of the equalization or control means by which good intelligibility of speech is secured and the volume thereof controlled is shown inserted in the receiving speaker circuit in place of the input circuit of the amplifier, as in the former circuit.

In Figure 3 some of the reference numerals used in the previous figures are employed to designate the same or substantially similar parts for the purpose of aiding in interpreting the disclosure. ln this case the direct current power supply circuit is represented by the negative lead I. and the positive lead 2 and controlled by the main switch 3. The negative side of the circuit is connected by wire through a choke coil 1| to one side of the push button switch H. The other side is connected by wire 12 to the winding of relay 13, the other terminal of which is connected by wire 14, back through the choke coil 14' to the other side of the-main switch 3. Thus when switch II is closed, relay 13 is operated and the

switches

6, 80, 84 and 88 move from their positions shown to their other positions.

At this point it may be noted that the heaters or filaments FI to F-6, inclusive, for the rectifier tube 11 and amplifier tubes I22 and I26 are in series across the line through the tapped resistor I I9 when switch 3 is closed. Thus current flows from wire I0 through wire 125, the whole of resistor H9, filaments FI to F6, and wire 14 to the other side of the line. Thus when the system is in operation the heaters of all the tubes are at operating temperatures and floating across the line. Here it may be noted that the rectifier 11 is a half wave vacuum tube rectifier with a resistance-capacitance filter and vacuum tubes I22 and I26 are the usual amplifying tubes with their associated circuits coupled to form a cascade amplifier with which the tubes I22 are associated in a push-pull circuit. The choke coils '1I and 14' are simply for filtering purposes to keep the variations in screen and plate potential of the output tubes from reacting on the input. The filaments F--I to F6 are all shown associatedtogether to simplify the circuit but they will, of course, occupy their respective positions in the vacuum tubes as represented by the same symbols and reference numerals with respect to each tube. The reference numeral I00 represents generally the audio-frequency amplifier employed in this system, which includes the input transformer IT and the output transformer OT.

The high impedanc primary terminal of the input transformer is connected by wire 18 to the normally open fixed contact of switch 60 which is a part of relay 13. The movable contact of this switch is connected by wire 19 to the movable contact of switch 84, also on relay 13. The normally open fixed contact of switch 84 (relay 13) is connected by wire 81 to one terminal of the bridge microphone IO. The other terminal of this microphone is connected by wire 82 to ground, as shown at 83, as is one terminal oi the bridgeloudspeaker 9. The other terminal of this loudspeaker is connected through an adjustable impedance network shown comprising inductance, resistance and capacity, and a volume control II'I comprising variable resistance with wires 83 and H6. Wire 6 is connected to the normally closed fixed contact of switch 6 which, is a part of relay 13. The movable contact of this switch is connected by wire 85 to one of the terminals of the output transformer OT of the amplifier. The other terminal of this transformer is grounded as is the other terminal of the input transformer as shown. The normally closed terminal of switch 80 (relay 13) is connected by wire I M to the low impedance taps on the input transformer IT. The normally open fixed contact of switch 6 (relay 13) is connected, by wire 81 to the normally open fixed contact of switch 88 which is also a part of relay 13. The normally closed fixed contacts of switches 88 and 84 on relay 13 are connected together. The movable contact of switch 89 (relay 13) is connected by wires 94 and 69 to the normally open fixed contacts of switches 95 and 93 on relays I05 and I06. The movable contacts of switches 93 and 95 of the relays I06 and I05 are connected respectively by the wires 90 to one terminal of each of the transducers I2. The other terminal of each of the transducers is con nected back through the normally closed switches 12a by wires M to the movable contacts of switches 96 and 91 of the same relays.

The normally open fixed contacts of switches 96 and 91 on relays I05 and I06 are connected by wires 82 and 92 to ground 83. The normally closed fixed contacts of switches 93 and 95 on relays I06 and I05 and one end of the tapped resistors I09 and H0 are all connected by the wire II4 to the negative side of. the power supply through main switch 3. The movable contacts of switches I04 and98 on relay I06 and switches 69 and IN of relay I05 are connected by wire I24 to one end of the tapped resistor H9. The

total current. flows through this circuit. so that normally open fixed contacts'of each of the switches I04 and 08 on relay I08 are connected by wire I03 to the normally open fixed contacts of each of the switches MI and I02 on relay I05, and by wires I23 and I23 to the tap on resistor H9. One terminal of the wlndingof relay I06 is the relay I06 is-normally not operated. However,

connected by wire III to the movable contact of the lower station switch I2. The normally engaged contact of this switch is connected to wire Ill. The normally disengaged contact of this switch and the other switch I2 are connected to gether, and tothe positive terminal of the power supply through wires I4, choke I4, and main switch 3. upper switch I2 is also connected to wire I0. The other end of resistance I09 is connected by wire III to the normally disengaged contacts'of the switches I2. Wire III is connected as shown to wire I4. A tap connection from resistance I09 is'connected by wire I08 to the other terminal of the magnet I06. Wire III is also connected to a resistance II 0,.the other terminal of which is connected by wire H3 to wire'II4 which is connected to one of the fixed contacts of switch 95. The other fixed contact of this switch is connected by wire 94 with the movable contact of switch 88. The movable. contact of the upper switch I2 is connected bywire II to one terminal of the magnet I05. The other terminal of this magnet is connected to wire II2 which comprises a tap on resistance H0 and to one of the fixed contacts of switch 96.

if a person at the transducer station pushes the button I2'a momentarily, this will force the current to flow through the relay coil I06 causing the operation of the relay.

This relay is also operated when the lower station switch I2 is turned on. The circuit in this case is as before through the choke coil I4, wire III, the normalfy open contact of switch I2, the movable contact of the same switch, wire I01,

. the winding of relay I06, wire I08, back to the The normally engaged contact of the In describing the operation of this circuit it will be assumed that all the switches are in their ofi" position as shown, except switch 3 which must necessarily be on. Current flows through lead 2 from the power source through switch 3,wire 14, the heaters F6, F5, F4, F3, F2, PI of the amplifier and rectifier .tubes, one section of resistor N9, the other two sections of resistor H9 in parallel, wire I25, and back through switch 3 and wire I to the negative terminal of the power source. This heats the filaments or heaters of the vacuum tubes sufiiciently so that they are ready for operation. It will be noted that the voltage drop across one section of resistor H9 is connected in series with the grid bias for the output tubes I22. The value of this voltage drop is sufiicient to bias these tubes to cut-ofi so that no plate current flows; this is the normal or standby condition for this'amplifier. Current also fiows from the positive terminal of the power source through wire 2, switch 3, wire I4, choke coil I4, rectifier tube 'I'I, to the first two stages of the amplifier comprised in the double tube I26; Current also flows as described above to and through the choke coil I4, then through wire II I to one end of eachof the tapped resistors I08 and H0. The current passing through resistor I09 flows through the normally closed contact of switch 91, which is a part of relay I06, to the movable contact of the same switch, through wire 9 I, normally closed push button switch I2a, transducer I2, wire 90, the movable contact of switch 1 93 on the same relay, the normally closed fixed contact of the same switch, and back through wire H4 and switch 3 to the negative terminal of the power supply I. the transducer circuit through wire I08, the winding of relay I06, the movable arm of switch I2, the normally closed contact of the same switch, choke coil 1I, wire I0, and back through switch 3, to the negative terminal of the power supply I. The resistance of the winding of the relay is so much higher than the resistance of the transducer circuit that only a negligible portion of the There is a parallel path around" tap on resistor I09. It will, of course, be apparent to those skilled in the art that relay I05 may be operated in the same way'as relay I06. The

operation of either or both of these relays short circuits one part of resistor II9 through wires I23, I23, switches MI and I02 in parallel or I04 and 98 in parallel, wires 89 and I24. The short circuiting of this part of resistor II9 removes the cut-off bias from the grid circuitof the power amplifier tubes I22 and simultaneously increases the filament current to the normal value, this,

by wire I2I, the normally closed fixed contact of q witch 80, the movable contact of the same switch. wire IS, the movable contact of switch 84, the normally, closed fixed contact of the same switch, the normally closed fixed contact of switch 88,

the movable contact of switch 88, and wire 89,

to whichever of the transducers I2 is connected as described above. The output transformer of the amplifier I00 is connected through the movable contact of the switch 6, the normally closed fix'ed contact of the same switch, wire I I6, volume control and adjustable impedance network II! to the bridge loudspeaker 9.

As will be seen from the diagram, one end each of the input transformer IT, the output transformer OT, the transducer I2, and the bridge speaker 9 is grounded. Thus the necessary circuits for talk-back operation are set up. I

When th push button II associated with the microphone I0 is operated, current flows as above described, to and through the choke coil I4, wire III, the winding of relay I3, wire I2, the contacts of switch II, choke coil II, wire I0, and back to the negative side of the power supply through switch 3 and wire I. This causes relay I3 to operate and the

switches

6, 80, 84, and 68 to move to the positions opposite frorn'those shown in the diagram. The circuits for talking out are now set up as follows: The microphone I0 is connected by wire 8|, the normally open fixed contact of switch 84, the movable contact of the same switch, wire I9, the movable contact of switch 80, the normally open fixed contact of The condenser it has its positive side con nected through rectifier H and wire Hi to one side of the relay coil 33, and its negative side connected directly to the other side of said relay coil. This condenser has a value of capacity sufficiently large to delay the release of the relay 13 when the push button ii is released. This slowing up of the release of relay l3 minimizes undesired clicks or thumps in the bridge loudspeaker which would otherwise have a distract ing effect.

The. condenserv 520 in combination with the volume control shown connected to the tube. I26, attenuates the undesired low frequency components of speech and extraneous noises in ord'er. to increase the emphasis in the higher vowel, voiced consonants and sibilant regions. In the talkback circuit, additional control over the irequency response of the amplifier, as well as its gain, is provided by the volume control and adjustable impedance network iii, the controls of which are mounted on the bridge so that the bridge officer may adjust the talk-back gain and frequency response to suit operating conditions.

What We seek to secure by United States Letters Patent is:

1. An audio-frequency signaling system including a microphone, a loudspeaker, a transducer, a multi-tube vacuum tube amplifier, means for alternately connecting the microphone to the input of the amplifier and the transducer to the output thereof, or the transducer to the input of the amplifier and the loudspeaker to the output of the amplifier, and control means adjacent the microphone and the transducer whereby twoway audio-frequency communication mat be initiated from either point.

2. In an audio-frequency communication system the combination including a microphone and a loudspeaker at a central station, a transducer at a receiving station, an amplifier, and means controlled from either the central station or the receiving station for connecting the microphone to the input of the amplifier and the transducerto the output of the amplifier, or the transducer to the input of the amplifier and the loudspeaker to the output of the amplifier.

3. In an audio-frequency communication system, the combination including a microphone and a loudspeaker at a central station, a transducer at a receiving station, an amplifier, means controlledfrom either the central station or the receiving station for connecting the microphone to the input of the amplifier and the transducer to the output of the amplifier, or the transducer to the input of the amplifier and the loudspeaker to the output of the amplifier, and an impedance network connected in the input of the amplifier whereby the over-all response of the system is non-linear and has a rising frequency response with increasing frequency.

4. In a two-way audio-frequency communication system, the combination including a microphone and loudspeaker situated at a central station, a transducer situated at a receiving station, an amplifier, an impedance network connected to the input of the amplifier, and means at the central station for connecting the microphone to said network and the transducer to the output of the amplifienand means at the receiving station for connecting the transducer to the net work and th loudspeaker to the output of the amplifier, said network and amplifier in combination having a non-linear response and the respouse having a rising trend with increasing frequency.

5. In a two-way audio-frequency communication system the combination including a microphone and loud-speaker situated at a central station, a transducer situated at a receiving station, an amplifier, an impedance'rietwork connected to the input of the amplifier, means at the central station for connecting the microphone to said network and transducer to the input of the amplifier, means 'at the receiving station for connecting the transducer to the network and the loudspeaker to the output of the amplifier, said network and amplifier in combination having a non-linear response and the response having a rising trend with increasing frequency, and means for short-circuiting the transducers dur ing change-over.

6. In a two-way audio-frequency transmission system, the combination including a microphone and a loudspeaker, a transducer, an amplifier, a pair of volume controls, means for connecting the microphone to the input of the amplifier, the transducer to the output of the amplifier, and one of said volume controls in circuit for speech transmission in one direction, and means for connecting the transducer tothe input of the amplifier, the loudspeaker to the output of the amplifier, and the other volume control in circuit for speech transmission in the opposite direction.

7. In a two-way audio-frequency transmission system, the combination including a microphone and a loudspeaker, a transducer, an amplifier,

a pair of volume controls, means for connecting the microphone to the input of the amplifier, the transducer to the output of the amplifier, and one'of said volume controls in circuit for speech transmission in one direction, means for connecting the transducer to the input of the amplifier, the loudspeaker to the output of the amplifier, and the other volume control in circuit for speech transmission in the opposite direction, and means for short-circuiting the transducer during change-over.

8. A two-Way audio-frequency communication system including a central station having a microphone and a loudspeaker, a remote station having a transducer, an amplifier, input and output circuits for the amplifier, a volume control in the output of the amplifier, and means at the central and remote stations for connecting at will either the microphone or the transducer to the input of the amplifier and the transducer and loudspeaker to the output of the amplifier respectively.

9. A two-way audio-frequency communication system including a microphone and a loudspeaker, a transducer, an amplifier, input and output circuits for the amplifier, a volume control in .the output of the amplifier, means for connecting at will either the microphone or the transducer to the input of the amplifier and the transducer and loudspeaker to the output of the amplifier respectively, and impedance means in the amplifier circuit for imparting thereto a limited frequency range of non-linear characteristics. I

10. A two-way audio-frequency communication system including a microphone and a loudspeaker, a transducer, an amplifier, input and output circuits for said amplifier, means at one point for connecting either the microphone or the transducer to the input circuit of the amplifier and the loudspeaker or the transducer to the output of the amplifier, whereby two-way communication may be accomplished and controlled from one point, and means at the transducer station for initiating two-way conversation.

11. A two-way audio-frequency communication system including a microphone and a loudspeaker, a transducer, an amplifier, input and output circuits for said amplifier, and means at one point for connecting either the microphone or the transducer to the input circuit of the amplifier and the loudspeaker or the transducer to the output of the amplifier, whereby two-way communication may be accomplished and controlled from one point, and a pair of volume controls alternatively and automatically connected to the input circuit of the amplifier for either direction of communication.

12. A two-station long distance two-way audioirequency communication system including a microphone and an-amplifier, a transducer having directional characteristics in a dimensional sense, with an increasing response with increasing frequency, a non-linear amplifier and input and output circuits for the amplifier, and control means at each station for connecting either the microphone or the transducer to the input circuit of the amplifier and the transducer or loudspeaker respectively to the output circuit of the amplifier.

13. A long distance two-way audio-frequency communication system including a microphone and an amplifier, a transducer having directional characteristics in a dimensional sense with an increasing response with increasing frequency, an amplifier and input and output circuits for the amplifier and control means for connecting either the microphone or the transducer to the input circuit of the amplifier and the transducer or loudspeaker respectively to the output circuit of the amplifier, said amplifier and input circuit having a non-linear response and a limited frequency range.

14. A long distance two-way audio-frequency communication system having talk-out and talkback stations, a microphone and a loudspeaker at the talk-out station, a transducer at the talkback station, an amplifier, talk-out and talkback volume control networks, and means at speaker at the talk-out station, a transducer at the talk-back station, an amplifier, talk-out and talk-back volume control networks, and means at the talk-out station for connecting the microphone to the input of the amplifier through the talk-out network and transducer tothe output of the amplifier or the transducer to the input of the amplifier through the talk-back network and the loudspeaker to the output of the amplifier, and means for short-circuiting the transducer during changeever from talk-out to talkback or talk-back totalk-out.

16. A long distance two-way audio-frequency communication system including a talk-out station having a microphone and loudspeaker thereat, a plurality of talk-back stations each having a transducer thereat, an amplifier, means at the talk-out station for connecting the microphone to the input of the amplifier and one or more of the-transducers to the output of the amplifier, and means at each transducer station for connecting the transducer thereat to the input of the amplifier and the loudspeaker to the output thereof...

FRED W. NICKERSON. WILLIAM C. MOORE. HERBERT BARNEE,