US 2983795 A
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Description (OCR text may contain errors)
y 1961 A. K. TATEISHI ETAL 2,983,795
COMBINATION HIGH FIDELITY SYSTEM 2 Sheets-Sheet 2 Filed Nov. 18, 1957 FM on #28 aux o 955 D 9 F200 58 mg mzo: Jo 222 k Avk hm mm on INVENTORS ARTHUR KTATEISHI JOHN STAFFORD United States Patent:
COMBINATION men FIDELITY SYSTEM Arthur K. Tateishi and John E. Stafford, Toronto, On-
tario, Canada, assignors to Seabreeze Manufacturing Limited I Filed Nov. 18, 1957, Ser. No. 697,274
17 Claims. (Cl. 179-10011) This invention relates to improvements in sound reproduction and recording systems, and more particularly to high fidelity or hi-fi systems.
In an effort to meet the demand for increased functions and versatility of high fidelity systems, such systems have become extremely complex and expensive, putting them beyond the reach of all but a few, Moreover, as functions have been added to the systems they have not only grown electrically complex, but very bulky, requiring either custom installation or at best forming a bulky piece of furniture which is awkward to arrange. Even in their most elaborate forms, such present hi-fi systems do not afford the listener all of the versatility of functioning which 'may be desired.
It is the object of this invention to provide a complete high fidelity system, includingin' particular a stereophonic sound system, which will be extremely simple to operate and which will be more versatile and flexible than even the present most elaborate custom built system, yet which can be economically produced, and sold at a price within the means of purchasers of the ordinary better quality .radio phonograph sets. V r
In this connection, it is an important object to provide --a system as aforesaid which can be broken down into :component units that'can simply be plugged together in a simple manner in assembling the system, whereby the system may be purchased unit by unit'and built up into its ultimate versatility and flexibility over a period of time according to the means of the purchaser.
-Still another important object is to provide a system as aforesaid in which the units can be physically separated and can be operated as two independent high fidelity systems if enjoyment of high fidelity reproduction in two =diiferent rooms or locations is desired.
While simple sound reproduction systems have been built up using separately purchased units, such systems have necessarily been very limited in their functions due 'to the problems of interconnection, even to persons skilled in electronics. Where more versatile systems are desired, the interconnections previously required have been so complex that it has not previously been feasible to mermhandise the separate components.
These dilficulties of the past have been overcome in the present invention by the provision of two, preferably "matched, independent high fidelity sound reproduction systems or units adapted to be connected on opposite sides of two switches preferably having corresponding function -selecting positions and having simple connection means therebetween adapted to carry signals in either direction between the units, the arrangement being such that the :flexibilityof the system is achieved in the complexity of the switch connections and notin the complexity of connections between the units.
More particularly according to the invention, the con -nection between the pair of switches may c mprise a single connection which any purchaser may make, and .the switch connections comprise permanent factory made vconnections in the individual units, the switching being 2,983,795 Patented May 9, 1961 'ice such that the simple setting of the two switches to the particular function desiredautomatically makes the necessary connections to deliver the signal in the respective direction over the single interconnection between the switches to produce the system function set by the switches.
Inasmuch as stereophonic sound, which is now an essential to the hi-fi enthusiast, requires the provision of two sound channels or systems, the present invention, in providing the two sound systems located electrically on the opposite sides of the pair of corresponding switches, is not in any way unnecessarily increasing the cost of the system, yet by virtue of this arrangement and the simple interconnection, the two sound reproduction systems or units can be divorced from each other and utilized separately.
In this latter connection, in the preferred form of the invention one of the sound units or systems is incorporated in an independently operable tape recording and playing unit incorporating one of the switch pair and having -a main head and a stereo head, the main head being connected so that its output signal will play through the incorporated sound system and the stereo head being connected so that its output signal will be delivered to the switch, the sound system also being connected to the switch so that signals to be delivered to or received from the external sound system may be fed to and received from the switch.
Further according to the preferred form of the invention, the second sound system is arranged to incorporate the other switch and is connected therewith to receive signals from and deliver signals to the switch, the second sound system incorporating plug-in facilities for a radio frequency tuner and record player which selectively may be operated through the second sound unit as an independent hi-fi combination radio phonograph system or upon setting of the switch pair with the connections therebe tween may utilize the sound system of the tape recording and playing unit for dual channel output, or the selected signal from the effectively independent radio phonograph system involving the second sound unit may be recorded by the tape recorder.
These and other objects and features will become ape parent from the following detailed description taken in conjunction with the acompanying drawings, in which:
Figure l is a block diagrammatic view illustrating a tape recording and reproducing unit provided with a function selecting switch in accordance with the invention;
Figure 2 is a block diagrammatic view illustrating an independent audio amplifying and speaker unit provided with a function selecting switch having selecting positions corresponding to the switch of the unit of Figure 1, the figure showing in perspective form radio tuner and record player units arranged for plug-in connection with the audio amplifying and speaker unit;
Figure 3 is a block diagram showing the units of Figures 1 and 2 interconnected bya single connection between the function selecting switches in accordance with the invention, the switches being positioned to obtainstereophonic sound;
Figure 4 is a view similar to Figure 3, 'but showing the switches positioned to obtain tape reproduction;
Figure 5 is a view similar to Figures 3 and 4, but showing the switches positioned to play and record the output from the radio tuner unit;
Figure 6 is a view similar to Figures 3, 4 and 5, with the switches positioned to play and record the output from the record player unit;
Figure 7 is a view similar to Figures 3 to 6, but showing an alternative switch arrangement whereby the sound output from a television set is connected to be played through the two units-of-Figures 1 and 2.
With reference to Figure L'a tape recording and re producing or play-back unit is shown in very much simplified and block diagrammatic form, as comprising a tape 1 fedbetween reels 2. Associated with the tape is a main playing head3, which feeds an audio amplifier shown in block form as comprising a main preamplifier circuit 4, a volume control circuit 5, a tone control circuit 6, a voltage amplifier 7, and a power output 8, feeding through aplay-record switch 9 to a speaker unit, generally designated at 10. As shown, the speaker unit comprises a speaker 11 and associated with the speaker 11 is a socket 12 providing for plug-in connection through plug 13 of a more elaborate speaker assembly designated at 14. The speaker assembly 14 may comprise separate accurate response speakers in the form of a suitable cabinet unit.
The play record switch 9 provides for the delivery of an output signal from the power output of the audio amplifier to be delivered through an equalizing network 15 to a record head which is shown as comprising the head 3. The unit shown in Figure 1 is adapted for stereophonic play-back, and in this connection it is provided with an auxiliary or stereo head 16, the output of which is connected to a stereo preamplifier 17 connected to a volume control 18. In stereophonic sound, it will be understood that two separate recordings which may be, for instance, on the same tape if desired, are played simultaneously through two sound systems so that a third dimension in the sound is achieved. In the present case, the main playing head 3 may be energized by one recording on the tape 1, and played through the sound system comprising the audio amplifier 4, 5, 6, 7 and 8, and speaker unit 10, while the second recording is adaptedto be played through the stereo head 16 and through the sound system of the unit of Figure 2, as hereinafter more fully described.
According to the invention, the tape recording and play-back unit of Figure 1 is provided with a function selecting switch designated at 19. The actual form of this switch may vary as desired, and the switch illustrated is merely an example of a workable switch arrangement to carry out the invention. The switch is shown as having a contact 20 for external conn ction, preferably through a plug-in connection 21. A further contact 22 is connected to an input point of the audio amplifier indicated at 23, electrically in advance of the 'volume control circuit 5. Another contact 24 is connected tothe output of the stereo volume control 18. Another contact 25 is connected to an output point of the audio amplifier of the unit of Figure 1, indicated at 26, electrically immediately ahead of the power output circuit 8.- Another contact 27 is connected to an input jack 28 to which, if desired, a radio frequency tuner unit may be plugged.
A further contact 29 is shown connected to a further input jack 30, into which, for instance, the output of a record playing instrumentality may be plugged.
A rotor unit 31, operated by a suitable handle or knob 32, is provided to selectively connect the contacts 22, 24, 25, 27 and 29 to the externally connected contact 20, according to the function desired, and to connect the contacts 27 and 29 to the input contact 22 when the sound system of Figure 1 is to be utilized in the re production of signals delivered to the unit through the input jacks 28 and 30. a
Figure 2 illustrates a sound system comprising an audio amplifier broken up into block form and shown as a volumec'ontrol circuit 33, feeding a tone control circuit-34, feeding a voltage amplifier 35, feeding a power output amplifier 36 connected to a speaker unit 37. The circuits 33, 34, 35 and '36 ofthe unit or Figure 2 preferably have substantially identical characteristics,with the circuits 5, 6, 7 and'8 of the unit of Figure 1.
As in the case of the'unitof Figure l, the sound sys= tem of the unit of Figure --2 is shown as employing as the speaker unit 37 a speaker 38 which may form a permanent part of the unit, and an associated socket 39 into which a more elaborate speaker assembly, indicated at 40, may be connected by a plug 41. The speaker assembly 40 may comprise ,asuitagble cabinet unit as desired.
The audio amplifier comprised by the circuits 33 to 3 6 is shown as being energized from a power supply 42 in connection with an A.-C. source connecting plug 43 through a power transformer 44. The power supply input through plug 43 is shown connected to a socket 45 into which an automatic record changer and pick-up unit indicated at.j46 is adapted to be plugged through corresponding plug-in member 47.
The record changer 46, of course, incorporates a driving motor which is illustrated by a field winding 48 and a control switch 49 associated with the socket 45 is provided to connect power through the socket, in the position shown, to energize the record changing motor.
It will be understood that this unit may, if desired, be a stereo or two-channel record player unit.
Also connected to the power supply 42 is a socket 50, into which a radio tuner ,51 comprising, as will be understood in the art, a radio frequency amplifier and detector, either of the A.M. or F.M. type, with or without intermediate frequency stages, is adapted to be plugged by means of the plug 52. Thus, the automatic record changer 46 and radio tuner 51 comprise separate units from the sound system of Figure 2, which separate units may be quickly connected to the sound system of Figure 2 by plug-in connection.
In accordance-with the invention, the unit comprising the sound system of Figure 2 is provided with a function selecting switch 53 corresponding to the switch 19 of the unit of Figure 1, though not shown as of identical construction.
The switch 53 has a contact 54 for external connection througha plug-inconnector 55. The plug-in connectors 21 and 55 of the function selecting switches of the unitsof Figures 1 and 2am adapted to be connected by a single plug-in connectorindicated at 56 in Figures 1 and 2, which may comprise the usual cable connector having an outer grounding sleeve or conductor to connect the chassis of the two systems ofFigures l and 2 to a common ground and an inner signal carrying conductor 56'. The switch 53 has a further contact 57 in connection with an output point of the audio amplifier of the unit of Figure, 2 indicated at 58 between the voltage amplifier circuit and the power output circuit. A further contact 59 is connected to the input of the volume control circuit 33. A further contact 60 isconnected to the socket 50 of the radio tuner 51 and another contact 61 is adapted to be connected -to the output of the record changer unit 46 through a plugein connection 62.
The switch 53 is provided witha rotor 63 operated by a handle or position, selector element 64, the arrangement of the rotor and the stationary contacts 54,57, 59, 60 and 61 being such that the externally connected contact 54 is selectively connectedto the input and the output connected switchcontacts 59 and 57 respectively, according to the selected functioning of the unit of Figure 2, and the contacts 60 and 61 are selectively connected to the input connected'contact '59 while the output connected contact 57 -is connected .to the externally connected contact 54 when the switch rotor 63 is turned to select radio or record reproduction.
The interfunctioning of the tape recording and reproduction unit of Figure 1 and the sound system comprising the unit of-Figufe '2 and plug-inassociatedunits 'comto 6; In Figure 3,"the two functionselecting switches Hand 53 are shown connected by the single plug-in connector 56, and with the rotors of the switches set correspondingly to a stereo position. In this position it will be seen that the output from the main playing head 3 of the tape recording and reproducing unit is connected to play through the first sound system comprised by the audio amplifier circuits 5, 6, 7 and 8 to produce an audio output from the speaker unit 10. At the same time, the output from the stereo head 16 as delivered from the stereo volume control circuit 18, is delivered to the stereo contact 24 of the first function selecting switch 19, and this latter contact is in connection through the rotor with the externally connected contact 20 to deliver a signal to the externally connected contact 2; of the corresponding or second function selecting switch From the contact 54 the signal is delivered through the input connected contact 59 to the audio amplifier of the second sound system comprised by the circuits 33, 34, 35 and 36 and the speaker unit 37 to produce an audio output from the speaker. Thus, with the switches set in the position of Figure 3, two recordings on the tape 1 are played through two separate sound systems to pro- 'vide stereophonic sound.
In Figure 4, the rotors of the switches 19 and 53 have been turned to corresponding tape positions. In this case, the output from the main playing head 3 of the tape unit is delivered through the first sound system to produce an output sound from its speaker unit 10. At the same time, a signal from the output point 26 of the first sound system is delivered to the contact 25 of the first function selecting switch 19, through the rotor of the switch to the externally connected contact 20, and through the single plug-in connector 56 to the externally connected contact 54 of the second function selecting switch 53.
The signal is then delivered through the rotor 63 of switch 53 to the contact 59 which is connected to the input of the second sound system comprised by the circuits 33 to 36 and speaker unit 37. Thus, with switches 19 and 53 in the tape position, the signal output from the tape will be simultaneously played through the two sound systems. It is to be noted that the signal taken from the tape unit and delivered through the first function selecting switch 19 and to the second function selecting switch 53, and from the latter switch to the input of the second sound system, is taken from an output point 26 located electrically after the volume and tone control circuits 5 and 6 so that the settings of the volume and tone control circuits in the tape unit will govern the volume and tone in the electrically similar second sound system with which the second function selecting switch 53 is associated. Thus, the first sound system of the tape forms the master system, and the second sound system is a slave thereto.
Figure 5 illustrates the relationship of the contacts and rotors of the function selecting switches 19 and 53 when they are moved to corresponding radio positions. In this case, the output from the radio tuner is connected through contact 60 to contact 59 which delivers the signal to the input of the second sound system comprised by the circuits 33 to 36 and speaker unit 37. At the same time, the output point 58 of the second sound system is connected through contact 57 to the externally connected contact 54 to deliver a signal in a direction reverse from that of Figures 3 and 4 to the externally connected contact 20 of the first function selecting switch 19, and the signal is delivered from this latter contact 54 to input connected contact 22 to deliver the signal to the input point 23 of the first sound system.
Thus, with the function selecting switches in the radio position, the signal from the radio tuner 51 will be amplified simultaneously in the two sound systems, and the listener will have the benefit of the output from the 6 speaker units 10 and 37 of both systems. Alternatively, if desired, the switch 9 may be operated to arrange for recording of the radio program on the tape 1.
In the case of the switch relations of Figure 5, the second sound system now becomes the master and the first sound system of the tape unit becomes the slave, the reverse of that described in connection with Figure 4.
In Figure 6, the switches are shown as moved to the phono position, and in this case, the signal from the automatic record changer is delivered by the second function selecting switch 53 to the input of the second sound system, and is also delivered by the switch 53 from the output point 58 to the first function selecting switch 19 and from this latter switch to the input point 23 of the first sound system.
In the selecting of the operation of the two sound systems to play and/ or record signals from the record changer 46, there is the additional operation of energizing the changer motor indicated by the field winding 48 and for this purpose, the control switch 49 is shown ganged to the second function selecting switch 53 in Figure 2, the arrangement being such that the motor is energized when the switch 53 is moved to the phone position.
With the relationship of the switches as shown in Figure 6, it will be understood that both sound systems will play the signal from the record changer and, if desired, by operation of the record switch 9, the signal from the record may be recorded on the tape 1. Where the unit of Figure l is divorced from the unit of Figure 2, it will be understood that signals from a radio tuner or a record player may be played through the sound system of the tape unit by plugging the radio tuner or the record player into the input jacks 28 and 30, and the signals therefrom may be recorded, if desired, on the tape 1.
It will be understood that the operation of the switches to set them at the various function selecting positions may, of course, be manual, or may, if desired, be eifected through a suitable servo-mechanism so that the operation of one of the switches 19 or 53 will eifect desired operation of the other. Also, while the switches 19 and 53 have been shown as rotary type switches, they may obviously be constructed in the form of push-button switches.
It will also be understood that the system as a whole and the individual components or units making up the system are shown in simple form for purposes of illustrating the combinations which may be achieved according to the invention by the use of the double function selecting switches and the simple connection 56 therebetween, and that the individual units may be as complicated as desired, and further units may be added in the system. For instance, in Figure 7, an alternative system embodying the invention is disclosed, but again the system employs a pair of function selecting switches 19' and 53 which, in conjunction with a single connector 56, provide for a highly versatile high fidelity system. In this case, the switch 19' has additional contacts 65 and 66 to provide for the delivery of an audio frequency signal from a television set 67 through the function selecting switches 19' and 53 to both sound systems comprised by the circuits 5 to 8 and speaker unit 10, and circuits 33 to 36 and speaker unit 37 respectively.
In other respects, the system of Figure 7 corresponds to the systems of Figures 3 to 6, with the switch rotor units 31 and 63 performing the same function as the rotors 31 and 63 of switches 19 and 5 3, and with the contacts 20', 22, 24, 25, 27' and 29' being connected in the same manner as contacts 20, 22, 24, 25, 27 and 29 of switch 19, and contacts 54, 57', 59, 60' and 61 of switch 53 being connected in the same manner as contacts 54, 57, 59, 60 and 61 of switch 53.
It will be understood that various modifications and arrangements in grouping of units, the circuits of the assa'aes units themselves and the nuinber of units involved may be varied as desired in accordance with, and withoutdeparting from the scope of the invention as set forth in the appended claims. For instance, the tape recording and play-back unit may bearranged to record two tracks at the same time from sounds originating from a stereo record player comprising a record playing device to replace the conventionalrecord player 46, in which case it will beunderstood that a, second signal carrying conductor corresponding to the conductor 56 will be required but, of course, this conductor could be incorporated in the same cable 56 as the signal carrying condoctor 56' not shown,
Further, of course, simultaneous broadcast of A.M.,
and TV could be recorded Where the tape recorded was arranged for two track recording.
What we claim as our invention is:
1. A high fidelity system comprising a first sound sys: tern comprising an audio amplifier and speaker means, means for creating a signal to be fed to said sound system, a first multi-position switch associated with said sound system, connections between said switch and a point of input and a point of output from the audio amplifier of said sound system, said switch having a contact arranged for external connection selectively connectable with one or other of the aforesaid switch connections dependent, on the setting of said switch, a second sound system comprising an audio amplifier and speaker means corresponding to said first sound system, a second multiposition switch corresponding to said first switch associated with said second sound system, connections between said secondswitch and a point of input to and a point of output from the audio amplifier of said second sound system, said second switch having a contact arranged for external connection selectively connectable with one or other of the aforesaid second switch connections dependent on the setting of the said second switch, and means for' connecting the contacts arranged for external connectioniof said switches to connect the output of the amplifier of said first sound system to the input of the amplifier of saidsecond sound system serially through said switches and vice versa.
2. A high fidelity system comprising two independently complete sound amplifying systems, each comprising signal generating means, an audio amplifier and speaker means and each incorporating function selecting switch means with said switch means having function selecting positions and each switch means having a contact arranged for external connection selectively connectable to a point of input and a point of output of the respective system, and conductor means connecting said switch contacts thereby coupling said systems together serially through said, switcheswhereby to conduct a signal in either direction, serially through said switch means between said systems dependent on energization of said signal generating means and on the function selecting positions of said switch means.
3. A system as claimed in claim 2 in which said switch contacts connecting means comprises a single plug-in con nection.
4. A highvfidelity system comprising a first sound amplifying system, signal generating means for energizing said sound system, a first switch having function selecting switch positionsprovided with a contact arranged for external connection selectively connectable through said first switch man input and an output point of said sound system, a second independent sound amplifying system, signal generating means for energizing said second soundsystem, a second switch having function selecting switch positions corresponding to said first switch and provided with a contact arranged for external connection selectively connectable through said second switch to'an input and an output point of said second sound system, signal generating means, for energizing said second sound system, and means serially connecting the contacts of: said switches arranged for external con; nect on whereby to conduct a signal in either direction serially through said switch means between said systems dependent'on energization of said signal generating means.
and on the function selecting positions of said switches;
5 A system as claimed in claim 4 in which said signal generating means for energizing said first sound system comprises a tape reproduction and recording instrumcii tality having a main playing head in connection withth e, input of said-first sound system, a recording head inconnection with the output of said first sound system and a stereo head in output connection with said first function selecting switch for' delivering a signal therethrough to said second function selecting switch for one first switch position, andsaid second function selecting switch has a corresponding switch position for delivering s aid latter signal to the input of said second sound system.
6. A system as clairn'ed'in claim 4 in which-said signal generating meansfor energizing said first sound system comprises a tape reproduction and recording instrumentality connected for reproduction to the input and for recording to the output of said first sound system.
7. A system as claimed in claim 6 in'which said signal generating means for energizing said second'sound sys tem comprises a radio tuner instrumentality in plug in connection with the input of said. second sound system.
8. A system as claimed in claim 6 in which said signal generating means for energizing said second sound system comprises a record playing instrumentality in plug in connection with the input of said second sound system.
9. A system as claimed in claim 8 in which said record playing instrument hasv a motor -eleme nt having a power input plug in connection with a power outlet of said second system, and a switch for'saidmotor gangedto said second function selecting switch.
10. A sound reproduction and recording system comprising a first unit in the form of a tape recording and play-back unit having a main playing head connected to provide asignal input to a first audio amplifying and speaker system-and a second playing head adapted to provide a separate signal to a second audio amplifying system for producing stereophonic sound, said unit having a first multi-contact function selecting switch having a contact for'external connection, a contact in connection with an input point and a contact in connection with an output point of said audio amplifying system, and a contact in connection with an output point from said second playing headfand a function selecting switchelement having a plurality of function selecting positions for selectively connectingsaid three last-mentioned contacts to said first-mentioned contact, and a second unit in the form of a second independent audio amplifying and speaker system having electrical characteristics substantially similar to said first audiosystem, said second unit having a second multi-contact function selecting switch corresponding to said first switch and having a contact for external connection, ,a contact in connection with an input. point and a contact in connection with an output point of said second audio amplifying system, and a function selecting switch. element having a plurality of function selecting positions corresponding to the positions of the aforesaid selecting switch element to connect the external contactor" said second switch to said second switch input connected contact when the external contact of said first switchis connected to an output connected contact of said first switch and vice versa, said units being connected by a plug-in connector extending between and serially connecting the external contacts of said switches.
ll. A sound reproduction and recording system as claimed in claim 10, in which said external switch con tacts are detachably connected by a ping-in connector comprising a single signal carrying conductor.
12: A sound reproduction and recording systernas claimed in claim 1 1 in which a third unit in the form of a"radio'fr'equency amplifying and detecting'unitis in plug-in connection with said second unit to deliver an audio frequency signal to a further contact on said second switch, said first switch having a further contact corresponding to said latter contact, said function selecting switch elements being adapted, on being correspondingly moved to connect said respective further contacts to said respective external contacts, to connect a signal from said third unit to the input of said second audio amplifying system and the output of said second audio amplifying system to the input of said first audio amplifying system.
13. A sound reproduction and recording system as claimed in claim 11 in which a third unit in the form of an automatic record changer and pick-up unit is in plugin connection with said second unit to deliver an audio frequency signal to a further contact on said second switch, said first switch having a further contact corresponding to said latter contact, said function selecting switch elements being adapted, on being correspondingly moved to connect said respective further contacts-to said respective external contacts, to connect a signal from said third unit to the input of said second audio amplifying system and the output of said second audio amplifying system to the input of said first audio amplifying system.
14. A sound reproduction and recording system as claimed in claim 13 in which said third unit incorporates a motor in plug-in connection with a source of power common to said motor and said second audio amplifying system, the power circuit of said motor having a control switch ganged to said second switch to effect energization of said motor when said second switch function selecting element is moved to connect the signal from said record i0 changer and pick-up unit to the input of said second audio amplifying system.
15. A sound recording and reproducing system as claimed in claim 10 in which each of said audio frequency amplifying systems is provided with a volume control.
circuit and a tone control circuit and the connections between the respective switch contacts and the inputs of said audio amplifying systems is electrically in advance of said volume and tone control circuits and the connections between the respective switch contacts and the outputs of said audio amplifying systems are electrically beyond said volume and tone control circuits whereby the one audio amplifying system is adapted to be a master and a slave to the other audio amplifying system according to the settings of said function selecting switch elements.
16. A sound reproducing and recording system as claimed in claim 10 in which switch means are provided to selectively connect an output point of said first audio amplifying system to a tape recording element.
17. A sound reproducing and recording system as claimed in claim 10 in which each of said audio amplifying and speaker systems has a first speaker member and a separate plug-in speaker unit.
References Cited in the file of this patent UNITED STATES PATENTS 2,611,618 Camras Sept. 23, 1952 2,620,405 Shickel Dec. 2, 1952 2,732,429 Wolfe Jan. 24, 1956 2,778,874 Mueller Jan. 22, 1957 2,792,449 Bottini May 14, 1957