US 3106609 A
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Oct. 8, 1963 A. E. DUSEY AUTOMOBILE SPEAKER SYSTEM Filed June 16, 1960 L5 in? MW M T 5 MM 0 4 WE United States Patent Ofifi e 3,196,609 Patented Oct. 8, 1963 3,106,609 AUTOMOBILE SPEAKER SYSTEM Alfred E. Dusey, North Riverside, Ill., assignor to Motorola, Inc., Chicago, IlL, a corporation of Illinois Filed June 16, 1960, Ser. No. 36,573 3 Claims. (Cl. 179-1 This invention relates to radio receivers, and more particularly to a loudspeaker system particularly useful in automobile radios.
It has become quite common in automotive radio installations to connect two speakers to the output stage of the auto radio receiver, one speaker being mounted in the dash and the other under the rear window ledge. However, with the addition of a rear seat speaker to known systems the total audio power produced in the car is generally somewhat less because of the power loss in the conventional balance potentiometer, or speaker fader control, used to adjust the relative volume as between front and rear speakers. In spite of such loss in total audio power, a two speaker system is recognized as giving better and more uniform distribution of sound in the automobile than that of a one speaker system.
In the output circuits of an auto radio, it has also been found to be practical to directly couple a loudspeaker to the power amplifier stage of a radio receiver without employing the customary transformer coupling therebetween. This has been made possible by the use of transistors in the power amplifier stage. Due to their low output impedance, transistors are much better suited from an impedance matching standpoint for direct coupling to the characteristically low input impedance of the speaker voice coil than are vacuum tubes with their characteristically high output impedance. Of course, the elimination of the output coupling transformer represents a substantial saving in weight and cost in radio receiver systems.
It is an object of the present invention to provide a dual speaker system for a radio receiver which system is adapted for operation with one speaker but which gives improved operation when two speakers are used.
Another object is to provide a radio receiving system which eliminates an output coupling transformer when used with one speaker to thereby reduce the receiver cost, and which system provides increased power output and efficiency when used with a simply connected additional speaker and control therefor.
A further object of the invention is to provide an improved radio receiver =and loudspeaker system for use in vehicles which is easily converted from a single speaker installation to a duel speaker installation, with the latter installation utilizing the single speaker therein.
A feature of the present invention is the provision of an improved radio receiver having a transistorized output stage directly connectable either to a single speaker or to dual speakers by means of simple plug-type connectors.
Another feature is the provision of an automobile radio receiver having a transistorized push-pull power amplifier directly connect-able to either a single speaker or to a dual speaker system interchangeable therewith, the dual speaker system having an audio choke in shunt with the speakers and a control to thereby improve the coupling efiiciency so that the dual speaker system delivers greater audio power than the single speaker without increasing the volume control setting of the radio receiver.
In the accompanying drawing:
FIG. 1 is a block and schematic diagram of a radio receiver wired for direct connection to a single or a double speaker system in accordance with this invention; and
FIG. 2 is a schematic diagram of a dual speaker systern adapted for connection to the radio receiver of FIG. 1 in accordance with this invention.
This invention providesa radio receiver and loudspeaker system which permits quick, convenient and reliable interchangeability between single and dual speaker operation. It finds particular use in automobile radio receiver systems to provide a front seat speaker as standard equipment, and a rear seat speaker as an optional accessory. This system includes a radio receiver having a transistorized power amplifier stage which, in a preferred form, includes two power transistors connected in push-pull relation with their output electrodes directly connected to a polarized plug. A single speaker is provided with a center tapped voice coil connected to a plug to be connected to the receiver plug, this connection causing the speaker to be driven directly by the transistors. For dual speaker operation, a harness assembly is furnished which includes a connector plug adapted To connect with the output plug of the receiver and further polarized connectors to be coupled to the two speakers. A choke included in the assembly is connected in shunt with the two speakers and across the output leads of the receiver. The harness also includes a speaker fader control for adjusting the relative volumes of the two speakers. Thus, conversion to dual speaker operation is quickly made by plug-in connections and, due to the choke, greater power is coupled to the dual speaker system under conditions in which the power is particularly desired.
Referring in more detail to FIG. 1 of the accompanying drawing, an amplitude modulation radio receiver is shown with the conventional stages thereof illustrated in block form. The receiver includes a radio frequency amplifier stage 10 to which the received signals are applied from antenna 11. Amplifier stage 10 selects and amplifies the received signal which is applied to a converter stage 12 where the signal is heterodyned with a signal from an oscillator thereof and the resultant out put applied to an intermediate frequency amplifier stage 13. The amplified intermediate frequency signal is then applied to a combined detector-automatic gain controlaudio frequency amplifier stage 14 where the amplitude modulation intelligence is recovered and further amplified and then applied to a driver stage 16. Amplified audio frequency signals from driver stage 16 are coupled to a power amplifier stage 17' by means of a coupling transformer 18. The secondary winding of transformer 18 provides a balanced input for a pair of power transistors 21 and 22 of the power amplifier stage 17. Transisters 21 and 2.2 are connected in push-pull relation, with their respective emitter electrodes 23 and 24 connected in common to a source -of.B+ potential, such as the radio receiver power supply connected to the electrical system of the automobile.
The operation of the receiver as briefly described thus far is known in the art and may be seen to be that of a superheterodyne amplitude modulation radio receiver with a transistorized push-pull output stage, although the invention may be used in other types of equipment as is apparent from the following description.
In accordance with the invention the respective collector electrodes 26 and 27 of transistors 21 and 22 serve as the output electrodes of the power amplifier stage and are directly connected to a pair of output leads 28 and 2 9; there being no output coupling transformer provided between the transistors and the output terminals. These output leads, together with a common lead 31 connected to a reference potential such as ground, extend from the receiver and terminate in a one-way or polarized connector 32.
A single loudspeaker 41 is provided with the radio receiver. Since the customary output transformer hitherto provided for matching impedance is eliminated, the impedance of the voice coil 42 of loudspeaker 41 is selected to be as close as possible to the output impedance of power amplifier stage 17. However, since the direct current resistance of a voice coil of the necessary matching impedance may be relatively high, the impedance of the voice coil is compromised at the point where the power lost from an increase in DC. resistance would offset the power gained by improving the impedance match. Nevertheless, it has been found that speaker 41 renders quite satisfactory single speaker performance, the advantages of eliminating the output transformer more than offsetting any less efficient power transfer.
The ends of coil 42 are connected by leads 43 and 44 to a socket 46 and male plug 47 respectively of a oneway or polarized connector 48. A center tap 49 of coil 42 is connected by a lead 51 to another socket terminal 52 of connector 48. One-way connector 48 is thus adapted to mate with connector 32 for connecting coil 42 across output leads 29 and 28 and to connect the center of the coil to common lead 31.
When it is desired to connect two speakers to the output stage 17 of the receiver, connector 48 is disconnected from connector 32 and speaker 41 is connected into a dual speaker system as shown in FIG. 2. The dual speaker system utilizes a connector harness assembly generally indicated at 61 which includes an input connector 62 which is again a polarized plug-type connector identical in form to connector 48 so as to mate with the output connector 32. A socket terminal 63 of connector 62 is connected to a harness lead 64, and a plug terminal thereof 66 is connected to another harness lead 67. Another socket terminal 68 is connected by means of a lead 69 to a center tap 71 of an audio frequency choke 72, the end terminals of which are connected to leads 64 and 67. A one-way output connector 74 has a plug terminal 76 connected to lead 64 and a socket terminal 77 connected to a lead 78. A rear seat speaker 81 is connectable to the harness assembly 61 by means of an input connector 82 adapted to mate with connector 74. The ends of a voice coil 83 of speaker 81 are connected to a socket terminal 84 and a plug terminal 85 of connector 82.
The other one-way output connector 73 of the harness assembly 61 is identical to the receiver output connector 32 but a middle terminal plug 92 thereof is not connected in the circuit. Lead 78 from connector 74 is connected to a plug 93 thereof and the other harness lead 67 is connected to a socket 91 thereof. Hence, when speaker 41 is connected in the dual speaker harness circuit 61 by plugging connector 48 into connector 73, all of voice coil 42 is connected in series with voice coil 83 of the rear seat speaker 81. The circuit relationship between the front seat speaker 41 and the rear seat speaker 81 is thus established by keying the one-way connectors to one another as described so that there can be no accidental mismatch in the phase of the two speakers.
Further, in accordance with the invention, the harness assembly 61 includes a variable resistance or potentiometer 96, the end terminals of which are connected to harness leads 64 and 67. A variable tap 97 of potentiometer 96 is connected to lead 78 between the speaker voice coils 42 and 83 so that the potentiometer functions as a speaker fader control for adjusting the output of speakers 41 and 81 with respect to one another by shunting the voice coils to a greater or lesser extent. Preferably, potentiometer 96 is mounted on a suitable bracket by means of a bushing concentric with the rotatable control shaft connected to variable tap 97. The bushing may then be inserted through a hole provided in an automobile dashboard and a fastening nut and speaker control fader knob assembled thereto. The choke 72 is also mounted on the bracket and together with the speaker control provides the control assembly 101 indicated schematically in FIG. 2.
In operation, the amplified signals from the push-pull power amplifier stage 17 are conducted by leads 28 and 29 thereof to the single speaker 41 when it is connected to connector 32. The oppositely phased signals are fed to the opposite ends of coil 42 and returned to ground by the connection of center tap 49 to the common output lead 31. Thus, the effect of the push-pull signal in coil 42 is cumulative.
For dual speaker operation, speaker 41 is disconnected and the harness assembly 61 is connected to output connector 32 by means of mating connector 62. Speakers 81 and 41 are plugged into the circuit of the harness assembly as described above, which insures an in-phase, series connection of the two speakers across the output leads 29 and 28. Iron core choke 72 is now in shunt with the speakers across the output, thereby providing the ground return, properly divided by means of its center tap connection to lead 31, to the collectors 26 and 27. Due to the low direct current resistance and relatively high A.C. impedance of choke 72, an improved impedance 'match with the transistors is provided since the choke increases the total impedance of dual speaker system over that of the single speaker system. This in turn increases the collector-to-emitter voltage and thus the amount of power coupled from power amplifier stage 17 to the dual speaker system, automatically providing a power improvement for the two speakers without altering the volume control setting or modifying the output stage of the receiver. The impedance of potentiometer 96 may be selected in the range from about to about 400 ohms. A higher impedance of the speaker control increases the power delivered to the voice coils 42 and 83 of the speakers. Also, when tap 97 is adjusted from a single speaker emphasis position (front or rear) to the balanced mid-position (dual speakers), the power dissipation across the control is less severe. Although greater power is thus developed to the speakers, the combined power consumption of the two speakers remains relatively constant in all positions of tap 97 since, as it approaches the mid position, a greater portion of the power gained by increasing the output load is absorbed by potentiometer 96. Even more power output is obtainable from the dual speaker system if the variable control potentiometer 96 is switched out, leaving just the center tapped choke 72 in shunt with the dual speakers.
In a commercial receiver and loudspeaker system con structed in accordance with the above described invention, the following components and values have been found to provide satisfactory operation:
Transistors 21 and 22 2N176.
B+ potential 13.8 volts nominal.
Front seat speaker 41 6" x 9" permanent magnet with 20 ohm center tapped voice coil.
Speaker 81 6" x 9'' RM. type with a 20 ohm' voice coil.
Choke 72 Approx. 100 ohms impedance at a frequency of 400 cycles.
Potentiometer 96 100 ohms.
It is to be understood that the foregoing components and values are listed for purposes of completeness and not by way of limitation. With such components it was found that the total power developed by both speakers exceeded that of the single speaker for all settings of the control potentiometer. In other words, the improved power gain resulting from the choke load more than offsets the power loss across the potentiometer.
From the foregoing description it is evident that the radio receiver and loudspeaker system of the invention provides a simple and efficient means for converting from i gle Speaker operation to dual speaker operation in an tomobile. The complete radio receiver may be sold as a standard model with front seat speaker 41 regularly included in the package. A rear 5631i. speaker kit, consisting of the harness assembly 61 and the rear seat speaker 81 with its connector, may then be stocked and sold as a separate unit which converts the standard radio receiver for dual speaker operation either at a later date or when it is sold as a deluxe version of the receiver. The harness assembly includes its own mounting bracket and is easily mounted on the dashboard beneath the receiver or at any other convenient location, and, due to the provision of keyed connectors, the installation may be performed by the average customer Without danger of misconnections.
1. A dual speaker system for an automobile radio receiver which includes a transistorized push-pull output stage having first, second and common output leads directly connected to the terminals of a polarized output connector, said dual speaker system including in combination a harness assembly including a first connector polarized to mate with said output connector and having first, second and third harness leads connected thereto for respective interconnection with said first, second and common output leads, an audio frequency choke having first and second terminals connected between said first and second harness leads and an intermediate terminal connected to said third harness lead for balanced shunt loading of said push-pull output stage, potentiometer means connected between said first and second harness leads and having a variable intermediate tap, a second polarized connector having a terminal connected to said first harness lead and another terminal connected to said tap, a third polarized connector identical with said output connector and having a terminal connected to said second harness lead and another terminal connected to said tap; a rear seat speaker having a voice coil and a fourth connector including terminals connected across said voice coil of said rear seat speaker and being polarized to mate one-way with said second connector; a front seat speaker having a voice coil With end terminals and a center tap and further having "a fifth connector polarized to mate with said output and third connectors and including terminals connected to said end terminals and center tap of said front seat speaker voice coil for selectively connecting the front seat speaker directly to the output stage of said receiver to provide single speaker operation therewith and in series with said rear seat speaker for operation as the second speaker of said dual speaker system, the loading of said output stage by said harness assembly being such that the total power delivered .by said speakers when connected to said receiver by said harness assembly exceeds that of said first speaker when connected by itself to the receiver.
2. A dual speaker system for an automobile radio receiver which includes a transistorized push-pull output stage having first, second and common output leads, said system including in combination, first and second speaker means having voice coils therein, said voice coil of said first speaker means having a center tap, a control circuit for coupling said speaker means to said output stage including an audio frequency choke having an intermediate tap and a potentiometer having a variable intermediate tap, first connector means having detachable output and input portions for connecting said choke and said potentiorneter across the first and second output leads of the output stage and for connecting said intermediate tap of said choke to the common output lead of th e output stage, and second and third connector means each having Idetachable output and input portions for omnecting said voice coils of said first and second speaker means respectively in series across said choke and said potentiometer and for connecting the common junction of said voice coils to said variable intermediate tap of slid potentiometer, said input portion of said second connector means being engageable with said output portion of said first connector means for connecting said voice coil of said first speaker means across the first and second output leads of the output stage and 'for connecting said center tap of said voice coil of said first speaker means to the common output lead of the output stage.
3. A dual speaker system for an automobile radio receiver, said system including a transistorized push-pull output stage having first, second and common output leads, first and second speaker means having voice coils therein, a control device for coupling said speaker means to said output stage including an audio frequency choke having an intermediate tap, said device also including a potentiometer having a variable intermediate tap, first connector means for connecting said choke and said potentiometer across said first and second output leads of said output stage and for connecting said intermediate tap of said choke to said common output lead of said output stage, second and third connector means for connecting said voice coils of said speaker means in series across said choke and said potentiometer, and for connecting the common junction of said voice coils to said variable intermediate tap of said potentiometer.
References Cited in the file of this patent UNITED STATES PATENTS 1,760,821 Douglass May 27, 1930 1,780,899 Bradshaw et al. NOV. 11, 1930 2,109,602 Weiss Mar. 1, 1938 2,481,576 DeBoer Sept. 13, 1949 2,521,129 Sampson et al Sept. 5, 1950 2,655,565 Thompson Oct. 13, 1953 2,787,672 Crossby Apr. 2, 1957 2,950,356 Stott Aug. 23, 1960 2,959,640 Schultz Nov. 8, 1960 OTHER REFERENCES Popular Mechanics magazine, February 1959, pp. 157- 160, 236, 238, and 240,