Abstract:
In a home or business where there is a central sound source for a stereo and one or more sets of loudspeakers which are located remote as in different rooms from the sound source. A volume control switch is mounted in conjunction with each set of loudspeakers. Within the transmission line between the sound source and each set of loudspeakers there is included a sense signal which is located at a high frequency which is beyond the range of human hearing therefore not to be heard by any human. This sense signal is compared to the audio signal from which the position of the volume control for each set of loudspeakers can be ascertained. Upon initial activation of the sound source, sound is not emitted from the remote loudspeakers upon making a memory change in the volume control for a set of loudspeakers, sound will be immediately emitted from that set of loudspeakers and only that set.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The field of this invention relates to sound systems and specifically to a sound system that is installed within a home or business where the sound system operates multiple sets of loudspeakers which are located in different rooms of the home or business. 
     2) Description of the Prior Art 
     There is a trend of people longing to have music enjoyed in multiple rooms of their home or place of business. The conventional way to install such a stereo system or a radio within a home or business is to have one sound source (receiver, amplifier, CD player, tape deck, and so forth) in a central location of a house or place of business. Wires are then run to different sets of loudspeakers located within each room. A problem then occurs that the amplifier from the sound source cannot safely power all of the loudspeakers simultaneously unless such are connected in a certain pattern which changes depending upon the number of loudspeakers used. A manual loudspeaker selector can solve the problem with this being located at the central source which provides on and off selection for the loudspeakers within the rooms desired. For example, if the user wants the bedroom in an off position but the family room speakers on, such can be selected at the central source. The drawback to this type of an arrangement is that the selector is located at the central equipment location thus forcing the user to leave the room in which the operation or deactivation of the loudspeakers is desired. 
     Another problem is that if the loudspeakers are too loud in one room and not loud enough in another room, there is no way to change the volume levels in each room independently. A product exists similar to a manual speaker selector with this product again being located at the central location. This product adds volume control for each set of loudspeakers. This, too, has a disadvantage in that the user needs to make the change at the central location to adjust the volume of a particular set of speakers within a particular room. Also, the user has to speculate as to exactly what level the speakers are to be turned on to in a particular room since the user is not located within that room. Frequently, a user will turn on the speakers thinking that the desired level has been obtained. When the user then goes into the specific room the user now knows that the loudspeakers are either too loud or they are too low which requires the user to go back and readjust the volume at the central location. 
     The most commonly used method an apparatus to solve the volume problem with different sets of loudspeakers within different rooms is installation of volume controls within each room which are wired in line with the loudspeaker wires that run into that room. Now, volume control is independent, but there is no way to turn on the equipment, choose between sound sources, or make changes to the sound source (such as a CD player, radio station or tape player) without returning to the central sound source location. There are ways to solve this problem of controls within each room. However, these ways are exceedingly expensive and also require a significant amount of added equipment plus the running of additional wiring to each room from the central source to provide the control functions. 
     SUMMARY OF THE INVENTION 
     The structure of the present invention relates to a circuit installed between remote sets of loudspeakers and a central sound source. This circuit constantly monitors the position of the volume control of each set of loudspeakers in each room, and when a change is noted, it activates appropriate switches and safely turns on the appropriate set of loudspeakers. The primary advantage of the present invention is that it uses existing wiring. Only the equipment at the central source and at the loudspeaker sets needs to change. A track or station selection can be added with only equipment changes at the central source and the remote sets of loudspeakers not requiring the addition of any wiring. The added circuit utilizes a high frequency (out of the range of human hearing) sense signal that is added to the audio that feeds the volume control of each loudspeaker set. Using a sense resistor to create a voltage divider with the volume control, the amplitude of the sense signal can be measured and from that deduce the position of the volume control for each particular set of loudspeakers. High pass and low pass filter circuits are used to isolate the audio amplifier and the sense signal generator from each other. The low pass filter circuit is designed to be able to handle the same power level as the volume control from the central sound source. There is utilized a peak detector circuit which will convert the high frequency sense signal to a DC signal. This DC signal can be amplified. A processor will determine if a level change has occurred which indicates the volume control for a particular set of loudspeakers has been moved. By measuring the level, we can determine the switch position relative to a maximum and a minimum position. This determining of the switch position can be accomplished by digital or analog means. A digital processor has the advantage of easy calibrating the levels so the loads of different sets of loudspeakers can be compensated accordingly. A digital processor can also cause activation or deactivation of the audio to the particular set of loudspeakers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a diagrammatic view of a typical stereo system as a sound source that might be installed within a home or building; 
     FIG. 2 is an electrical schematic diagram of a “peak detector circuit” and an “on comparators with latch circuit” that is used in producing the sense signal of the present invention; 
     FIG. 3 is an electrical schematic of the “100 kilohertz fourth order band pass circuit” that is utilized within the overall circuit of the sense signal of the present invention; 
     FIG. 4 is an electrical schematic of the “100 kilohertz generator circuit” that is utilized within the overall circuit of the sense signal of the present invention; 
     FIG. 5 is an electrical schematic for an “amp load protection circuit” that is included within the overall sense circuit of the present invention; and 
     FIG. 6 is an electrical schematic of a “power supply circuit” that is included within the overall sense signal of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring particularly to the drawings, there is shown a sound source  10  in the form of a conventional stereo system. The sound source  10  includes a receiver  12  and a pair of loudspeakers  14  and  16 . Sound source  10  is to be located at a central location  18  such as within a family room of a house. Let it be assumed that this house has other rooms such as rooms  20 ,  22  and  24 . Mounted within the room  20  is a loudspeaker  26  which is operated through a button control  28 . Access into the room  20  is accomplished by means of a door  30 . In a similar manner, the room  22  has a loudspeaker  32  which is operated by means of a button control  34 . Access into the room  22  is provided by means of a door  36 . Still in a similar manner, the room  24  has a loudspeaker  38  which is operated through a button control  40 . A door  42  provides access to the interior of the room  24 . A transmission line in the form of an electrical wire assembly  44  connects between the receiver  12  and the button control  28 . A separate electrical wire assembly  46  connects between the button control  28  and the loudspeaker  26 . A transmission line in the form of an electrical wire assembly  48  connects between the receiver  12  and the button control  34 . A separate electrical wire  50  connects between the button control  34  and the loudspeaker  32 . A transmission line in the form of an electrical wire assembly  52  connects between the receiver  12  and the button control  40 . A separate electrical wire  54  connects between the button control  40  and the loudspeaker  38 . Manual turning of a button control  28  will cause the sound volume of loudspeaker  26  to change. Manual turning of button control  34  will cause change in the sound volume to loudspeaker  32 . Manual turning of button control  40  will cause the sound volume to change to loudspeaker  38 . It is to be understood that normally the loudspeakers  26 ,  32  and  38  will each comprise a set of speakers, not just one. 
     Typically, prior to the present invention, the user would turn on the receiver  12  producing a sound from the loudspeakers  14  and  16 . The sound would be set by the user to the desired level by listening to the sound that is produced from the loudspeakers  14  and  16 . This same level of sound would then be transmitted to each of the loudspeakers  26 ,  32 , and  38 . If a volume control button, such as buttons  28 ,  34  and  40 , were included within each of the rooms  20 ,  22  and  24 , the sound level within each of the rooms could be varied and could be different from that which is produced from loudspeakers  14  and  16 . However, there would be no way to ever turn off completely the sound that is being supplied to the loudspeakers  26 ,  32  and  38  unless the receiver  12  was actually turned to an off position. The circuit of the sense signal shown in FIGS. 2-6 will actually be mounted in conjunction with the receiver  12  and also in conjunction with the control buttons  28 ,  34  and  40 . This sense signal is to be conducted through the transmission lines  44 ,  48  and  52 . 
     Let is be assumed the receiver  12  is activated but sound is not being emitted from any of the loudspeakers  14 ,  16 ,  32  or  38 . Let it further be assumed that a person desires to have sound within room  24 . The person only needs to move button control  40  which will cause sound to be emitted from loudspeaker  38 . The volume level of the sound can be adjusted in the normal manner by varying the position of button control  40 . 
     Referring particularly to FIG. 6, there is shown a “power supply circuit” where an external AC (alternating current) source is supplied to an AC wall transformer  56 . This AC wall transformer  56  steps down the 120 V AC voltage RMS (root means squared) from a conventional wall socket of a house or building to 13 V AC RMS that is applied a line  58 . Diode  60  halfwave rectifies the AC to provide a positive DC voltage. The diode  62 , mounted in line  64  which connects to line  68 , halfwave rectifies the AC to provide a negative DC voltage within line  64 . Capacitors  66  and  68  filter out any residual AC voltage from the positive DC supplied to diode  60 . Capacitors  70  and  72  filter out any residual AC voltage from the negative DC voltage supplied to diode  62 . Regulator  74  regulates the positive DC voltage to a constant positive 15 volts DC. Capacitors  76  and  78  further filter out any AC voltage from the regulated positive 15 V DC. Regulator  80  regulates the negative DC voltage to a constant negative 15 V DC. Capacitors  82  and  84  further filter out any AC voltage from the negative 15 V DC. The positive 15 V DC at junction  86  and the negative 15 V DC at junction  88  are used to power the rest of the sense circuit shown in FIGS. 2-5. Typically, the capacitors  66 ,  76 ,  70  and  82  could have a value of 0.1 μf (microfarad). Capacitors  68  and  72  could each have a value of 1000 μf. The capacitors  78  and  84  could each have a value of 220 μf. 
     The +15 V and −15 V are supplied to an op amplifier  90  of the “100 KHz sense signal generator circuit” that is shown in FIG.  4 . The circuit used to provide the 100 KHz sense signal is of a Wien-bridge oscillator design. Resistors  92 ,  94  and capacitors  96  and  98  provide a positive feedback path for the op amp  90  causing the op amp  90  to oscillate at 100 KHz. Resistors  100  and  102  provide negative feedback to set the amplitude of 100 KHz oscillations of the op amp  90 . Variable resistor  104  is used to adjust the amplitude of the 100 KHz oscillations. Diodes  106  and  108  provide automatic gain control to maintain the oscillations at the desired amplitude. Op amp  110  is a unity gain voltage follower used to buffer the 100 KHz oscillations of op amp  90  from change due to circuit loading. The output of the 100 KHz sense signal generator is at junction  112  of the op amp  110 . Capacitors  114  and  116  comprise filtering capacitors. Resistor  118  protects the output of the op amp  110  from excessive current and supplies 100 KHz sense signal to the loudspeaker output connector  120 . Typical values for the capacitors  92  and  94  would be 370 Pf (picofarads). Typical values for the capacitors  114  and  116  would be 0.1 μf. Typical values for the resistors  100  and  102  would be 4.99 KΩ (kilo-ohm). Typical value for the variable resistor  104  would be 3.68 KΩ, and typical value for the resistor  118  would 4.75 KΩ. 
     The output from junction  112  is supplied to a fourth order bandpass filter circuit which is of a multiple-feedback bandpass design and, as shown in FIG. 3, is to provide a second order filter response. Two identical second order filters are cascaded to provide an overall fourth order filter response. The output of the generator from junction  112  is supplied into line  122  of FIG.  3 . Capacitor  124  and resistor  126  provide negative feedback to op amp  128  for the low pass response. Capacitor  130  and resistor  132  provide negative feedback to the op amp  128  for the high pass response. Resistor  134  sets the gain in the pass-band for the op amp  128 . Resistor  136  provides compensation to minimize the DC offset generated by op amp  128 . Resistors  137 ,  138 ,  140  and  142  along with capacitors  144  and  146  form an identical circuit to that described previously in this paragraph. The input to the fourth order bandpass filter is applied to resistor  126  from the loudspeaker output connector  120 . The output from the fourth order bandpass filter is at junction  148  of op amp  150 . Capacitors  152  and  154  are filtering capacitors for the op amp  128 . 
     The input to the “peak detector circuit” shown in FIG. 2 is supplied to line  156 . Line  156  connects to op amp  158 . Op amp  158  charges capacitor  160  through diode  164  to the peak voltage seen in line  156 . Diode  164  prevents capacitor  160  from discharging through op amp  158  when the input voltage in line  156  is lower than the voltage on capacitor  160 . Resistor  162  provides a slow discharge path for capacitor  160 . Op amp  166  is a unity gain follower to buffer the voltage on capacitor  160  from circuit loading. Diode  168  provides a negative feedback path for op amp  158  when the voltage in line  170  is less than the input voltage in line  156  to prevent saturation of op amp  158 . Resistor  172  is a filtering resistor for line  170 . Capacitors  174  and  176  are filtering capacitors for the op amp  158 . The output for the peak detector, previously described, is supplied to junction  178 . Typical values for capacitors  174  and  76  would be 0.1 μf. Typical value for resistor  172  would be 100 KΩ. Typical value for resistor  162  would be 31.1 KΩ. Typical value for capacitor  160  would be 10 μf. 
     The “on comparators with latch circuit” utilizes resistor  180  which is to provide compensation for the DC offset of op amps  182  and  184 . Capacitor  186  charges through resistor  188  to the output voltage level at junction  178  of the peak detector circuit. The long time constant of resistor  180  and capacitor  186  provide a time delay to the inputs of the comparators on pin  190  of op amp  182  and pin  192  of op amp  184 . Op amp  182  compares the voltage that is on pin  194  of op amp  182  to the voltage that is on pin  190 . When pin  194  has a lower voltage than pin  190 , the output voltage within line  196  is −14 v DC. When pin  194  has a higher voltage than pin  190 , the output voltage in line  196  is +14 v DC. Op amp  182  provides a positive output voltage within line  196  when the voltage on pin  194  moves in the positive direction and a negative output voltage in line  196  when the voltage on pin  194  moves in a negative direction or when there is no change in voltage level on pin  194 . Op amp  184  provides a positive output voltage in line  198  when the voltage on pin  192  moves in a negative direction and a negative output voltage in line  198  when the voltage on pin  192  moves in the positive direction or there is no change in voltage level on pin  192 . Diode  200  blocks any negative voltage within line  196  from the op amp  182  and will pass any positive voltage within line  196  onto resistor  202 . Diode  204  will block any negative voltage within line  198  from the op amp  184  and pass any positive voltage within line  198  from op amp  184  to resistor  206 . Resistor  202  protects the base of transistor  208  from excessive current while providing for the saturation of transistor  208  when positive voltage is applied to resistor  202  from diode  200 . Transistor  210  will saturate when transistor  208  saturates and keeps transistor  208  saturated after the positive voltage is removed from resistor  202 . Resistor  212  protects transistor  210  from excessive current during saturation. Resistor  206  protects the base of transistor  214  from excessive current while providing for the saturation of transistor  214  when positive voltage is applied to resistor  206 . Transistor  216  will saturate when transistor  214  saturates and keeps transistor  214  saturated after positive voltage is removed resistor  206 . Resistor  218  protects transistor  216  from excessive current during saturation. Capacitors  220  and  222  are filtering capacitors for the op amp  182 . The switch  224 , when manually activated, causes 15 V to be applied to pin  194  of op amp  182  which resets the comparator. The resistor  226  is a pull up resistor. Typical values would be as follows: resistor  180 , 49.9 K; resistor  302 , 10 K; resistor  218 , 10 K; capacitors  220 ,  222  and  186 , 0.1 μf; and resistor  206 , 10 K. 
     Referring particularly to FIGS. 3 and 5, there is shown the speaker switch circuit. The speaker output connector  120  is connected to the in-house wiring that goes to the left channel remote speakers. The speaker output connector  228  is connected to the in-house wiring that goes to the right channel remote speakers. Audio amplifier input  230  is connected to the left channel output of the audio amplifier which is located at the receiver  12 . The audio amplifier input  232  is connected to the right channel output of the audio amplifier of the receiver  12 . Inductors  236  and  238  protect the audio amplifier outputs from the 100 Khz sense signal. Switch  240  connects the speaker outputs of connectors  120  and  228  to the audio amplifier inputs  230  and  232 . Switch  240  starts in the “off” state which has the speaker output disconnected from the amplifier inputs and connects inductors  236  and  238  to ground. When transistor  208  or transistor  214  saturates, current flows through the coil  242  of switch  240  which energizes the coil  242  causing the relay to close the switch  240  connecting the speaker outputs  120  and  228  to the audio amplifier inputs  230  and  232 . Resistor  244  protects coil  242  from excessive current. Light emitting diode  246  will light to indicate that the audio amplifier input is connected to the speaker output. Resistor  248  protects the light emitting diode  246  from excessive current. Typical values for inductors  236  and  238  are 33 μh. 
     There is included a “protection circuit” for the audio amplifier within the receiver  12 . This protection circuit comprises resistors  250  and  252  which protects the audio amplifier from low loads produced by multiple speaker zones being on at the same time. Switch  254 , when manually activated, either activates or deactivates the resistors  250  and  252 . Resistor  250  provides protection for the audio amplifier input  230  with resistor  252  providing protection for the audio amplifier input  232 . Resistors  250  and  252  have typical values of 3 ohms. 
     For the speaker arrangement shown in FIG. 1, there will be utilized one power supply circuit, one “100 KHz sense signal generator circuit”, four “100 KHz fourth order band pass filter circuits” (one for each speaker zone), four “peak detector circuits” (one for each speaker zone), four “on comparators with latch circuits” (one for each speaker zone), four “speaker switch circuits” (one for each speaker zone), and one “amplifier protection circuit”. It is to be understood that a greater or lesser number of loudspeakers could be used with corresponding changes in the circuitry.