Patent Publication Number: US-2010119078-A1

Title: Audio distribution system

Description:
RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 10/145,225, filed May 13, 2002, which is a continuation-in-part of U.S. application Ser. No. 08/972,868, filed on Nov. 8, 1997. The entire teachings of the above application(s) are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an audio signal amplification and distribution system for multiple speaker applications, and, in particular, to a new and improved wall-mounted “powered” volume control having an integrated audio power amplifier for connecting between a signal source and one or more remote speakers. 
     Broadcasting audio or music, such as background music, within a facility is generally desirable to provide a relaxing or entertaining atmosphere or to enhance a desired theme or mood. In particular, buildings such as houses, hotels, restaurants, casinos, shopping malls, and other indoor or outdoor areas often are equipped with sound distribution systems to provide music and paging capability to different locations in or around the building or area. 
     One simple way to provide a distributed audio sound system is to provide a number of individual signal sources and amplifiers throughout the building or area. While such a sound system may be acceptable for distributing AM or FM radio broadcasts, it would typically not be suitable for rebroadcast of an audio recording or public address message since the music or sound may not be synchronized from room to room. Also, such sound systems necessitate multiple signal sources which can increase the costs of the system significantly, particularly if high fidelity sound reproduction is desired. For these reasons, it is generally preferable to use a single high-fidelity signal source. 
     A typical commercial high-fidelity sound distribution system provides for a single signal source and amplifier to provide a signal to a plurality of speakers distributed throughout a building or area. Systems of this nature advantageously provide synchronized music or paging capability to multiple areas of a building or facility. However, such systems have certain undesirable limitations or disadvantages. One disadvantage is the reduced impedance to the amplifier created by having a plurality of speakers connected to a single amplifier. Connecting too low an impedance (i.e., too many speakers) to an amplifier can overload and possibly damage the amplifier. Another disadvantage is that in large buildings a number of the speakers may be located great distances (e.g., over 100 feet) from the amplifier. Speaker wire has electrical properties of resistance, capacitance and reactance, all of which can impede or alter the transmitted audio signal, thereby causing poor audio output. This is especially true when low voltage or high-current signals are transmitted over great distances of wire. 
     Another limitation of traditional single amplifier systems is that the amplifier must be able to produce adequate power to operate a plurality of speakers. For large installations, the required high power amplifiers can be particularly expensive because larger and more expensive components must be used to produce the significant amounts of electrical power required. Also, the number of speakers available will be limited by the maximum power output of the central amplifier, making further expansion of the system difficult. 
     Another disadvantage of traditional single amplifier systems is that each speaker will produce music or a page at approximately the same volume. This may be undesirable in many applications where different audio levels may be required for different areas of a building or facility. For example, a lounge or bar area in a hotel may require music at a higher volume than in the lobby or dining areas. Thus, in such systems it is desirable to provide a means for independently adjusting the volume in each area to compensate for ambient background noise or to set a particular mood or tone suitable for each particular area. 
     Over the years, various devices have been proposed to provide for localized volume control. One early proposed solution was to provide a multichannel amplifier. A multichannel amplifier has a number of different channels, each having a separate volume control, and which may be used to individually control or adjust the signal strength or power provided to each speaker pair or each speaker in a single channel system. However, multichannel amplifiers are quite costly and the installer or owner is still limited in the number of speakers that the system may operate by the number of channels available on the amplifier and the maximum power output for each channel. Also, the volume control is usually located on the amplifier itself, making localized adjustment of remote speakers inconvenient. Furthermore, using a multi-channel amplifier necessitates running wire between each speaker and the amplifier. 
     A more widely accepted solution is to provide an adjustable autoformer in series with each local speaker pair to selectively attenuate the audio signal provided to the local speakers. For example, U.S. Pat. No. 4,809,339 to Shin et al. describes one type of autoformer suitable for localized audio signal attenuation. Such autoformers typically comprise a plurality of user selectable transformer coils connected between the central amplifier and the local speaker pair. Depending upon the position of a switch or selector knob, more or less reactance and/or resistance is placed in series with the speaker pair to limit or attenuate the amount of power delivered, accordingly. 
     Although such autoformers provide limited localized volume adjustment of remote speakers, they suffer from a number of disadvantages which have yet to be overcome by any known prior art systems. In particular, autoformer volume controls are often inconvenient in that volume control is not continuous. In other words, the volume may only be set at one of several (usually 8 to 12) discrete levels. Thus, a desired volume level located between two autoformer steps may not be achieved. Such volume controls are also undesirable where high-quality or high-fidelity audio sound output is desired. Autoformers have significant reactance to diminish the power delivered to the speakers. Passing an audio signal through an autoformer undesirably distorts the audio signal by introducing capacitance, resistance, and phase distortion at various frequencies in the audio range. In particular, the high and low frequencies of the audio signal are lost or greatly diminished when the signal passes through a transformer. Also, when several autoformers are connected together on a given output channel, the adjustment of one volume control will often result in a change of volume in an adjacent area due to the change in overall load reactance. Thus, such volume controls are not completely independently adjustable. 
     Other volume controls are known which suffer from similar or other drawbacks. For example, various resistive ladders, also commonly known as an “L-pad” or rheostat, have also been used to control the volume of the audio from one or more local speaker pairs. The resistive ladder allows the user to selectively increase or decrease the resistance in the line between the speaker and the amplifier to attenuate the audio signal. However, variable resistive ladders suffer from the additional drawback of undesirably generating significant heat and, thus, are not efficient and require extensive cooling or other heat dissipating means. 
     It is also known to incorporate amplifier/power boosters in a speaker itself. For example, U.S. Pat. No. 4,991,221 to Rush describes an amplifier and a speaker in a single enclosure. However, these types of systems are not well-suited for retrofit installations because the amplifier circuit requires a separate power supply line in addition to the speaker signal lines. Also, the signal quality for speaker/amplifier pairs located at extended distances from the original audio source will still suffer significant degradation due to the resistance, capacitance and inductance of the speaker wire and the relatively low signal input impedance of the amplifier/booster circuit (typically on the order of 100 Ohms). Furthermore, the gain control for such amplifier/booster circuits is typically located behind the speaker housing. This is undesirable for the vast majority of commercial and residential applications in which the speakers are typically located in inaccessible places such as on ceilings or walls out of reach. 
     A need exists, therefore, for a high-quality audio system for remote, multi-speaker operation which provides the capability for local continuous volume adjustment without significant signal degradation in a convenient inexpensive retrofittable system. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a simple, cost efficient, high-fidelity audio distribution system and method for providing a high-quality audio signal to numerous areas or rooms within a building or other facility. The present invention further provides the capability for users to make localized and continuous volume adjustment of remote speakers without significant noise or signal distortion. The system generally comprises one or more amplifiers and/or signal conditioners located at or near the audio source for receiving a signal from the audio source and generating an amplified audio signal which is transmitted over extended distances to one or more “powered” volume controls. Each volume control receives the amplified (low current, low resistance) signal from the amplifier and/or signal conditioner using a high-impedance input/attenuator. Desirably, this avoids unduly loading the amplifier and/or signal conditioner. Each volume control then amplifies the attenuated signal to a level determined by a user controlled adjustment device such as a variable resistor or potentiometer. Speakers are connected to the signal outputs of each volume control and receive the amplified audio signal to reproduce the music or page at the desired amplified volume level. 
     In accordance with one preferred embodiment, the present invention comprises a powered volume control for connecting between an audio source and one or more remote speakers. An input circuit receives an audio signal from the audio source and provides a preamplified signal output. This signal is amplified by an amplifier circuit to provide an amplified signal output which is a substantial replication of the preamplified signal and the audio signal from the audio source. For the purposes of the present application, the term “replication” means a generally identical version (notwithstanding distortion introduced from the circuitry) of the original signal but which may be scaled up or down in amplitude due to the attenuator or amplifier. Accordingly, the replication may be identical to, of greater magnitude, or of lesser magnitude than the original signal. It is further contemplated that the replicated signal may comprise a digitized version of the original signal. 
     The amplified signal output is then used to drive one or more remote speakers. To allow volume control of the remote speakers, a variable adjustment device is provided. The adjustment device may be a knob, a slider bar, a push button, etc. or the adjustment device may be a graphical user interface type control surface. The adjustment control may be accessed remotely, e.g., using wireless or infrared technologies. This can be adjusted by a user to change the magnitude of the preamplified signal and/or the gain or bias of the amplifier circuit such that the amplified signal output can be continuously adjusted over a predetermined range to adjust the volume of the one or more remote speakers. Advantageously, the circuitry is configured to eliminate interference, particularly in the low frequency range, from adjacent AC power sources or other sources of interference by grounding the output terminal or connector. 
     In accordance with another preferred embodiment, the present invention comprises a wall-mounted volume control for connecting between an amplified audio signal source and one or more remote speakers. An input circuit having a relatively high input signal impedance is adapted to receive a first amplified audio signal from the amplified audio signal source to produce an attenuated audio signal having a predetermined magnitude or range of magnitudes. An amplifier circuit receives the attenuated signal and provides a second amplified signal output which is a substantial replication of the attenuated signal and the first amplified signal from the amplified audio signal source. The amplified signal is then used to drive one or more remote speakers. To adjust the volume of the speakers, a variable adjustment device is provided which allows a user to adjust the magnitude of the second amplified signal such that speaker volume can be adjusted over a predetermined range. 
     In accordance with another preferred embodiment, the present invention comprises an audio distribution system for distributing an audio signal from one or more audio sources to one or more speakers located remotely from the audio sources. A first amplifier is provided and is adapted to be located at or near the one or more audio signal sources for receiving an audio signal input from said one or more audio signal sources. The first amplifier provides a first amplified signal output which is substantially a replication of the audio signal input. A second amplifier is also provided and is adapted to be located in an accessible location on a wall remotely from the one or more audio signal sources and electrically connected between the first amplifier and the remote speakers. The second amplifier has a relatively high input signal impedance and a relatively low output signal impedance and is adapted to receive the first amplified audio signal from the first amplifier and to provide an intermediate attenuated audio signal having a predetermined magnitude or range of magnitudes. The second amplifier is further adapted to amplify the attenuated audio signal to provide a second amplified signal to drive the one or more remote speakers. The second amplified signal is a substantial replication of the attenuated audio signal and the first amplified signal. A variable adjustment device is further provided for allowing a user to adjust the magnitude of the second amplified signal whereby the volume of the one or more remote speakers can be adjusted over a predetermined range. 
     In accordance with another preferred embodiment, the present invention comprises a method for distributing an audio signal from one or more audio sources to one or more speakers located remotely from the audio sources. According to the method, the audio signal input from one or more audio signal sources is amplified to provide a first amplified signal output which is substantially a replication of the audio signal input. The first amplified signal has an amplitude or magnitude such that it is relatively impervious to spurious noise. The first amplified signal is then transmitted through an elongated electrical conductor to one or more remote locations near one or more remote speakers. The first amplified signal is then passed through a variable resistor to produce an attenuated audio signal having a desired amplitude or magnitude as determined by a user variable adjustment device. The attenuated signal is then amplified to provide a second amplified signal which is transmitting along one or more electrical conductors to drive the one or more remote speakers. The method allows for localized speaker volume control of remote speakers with less noise interference and distortion than methods utilizing conventional autoformer volume controls. 
     The audio signal may be an analog signal or a digital signal. There may be multiple digital audio signals which may be multiplexed or time shared at the input device of the audio amplifier. Demultiplexing may be controlled by means of isochronous timing. The signal may be streaming digital audio data such as is used in TCP/IP networking. The digital audio may be transmitted to the volume control using optical technology or spread spectrum wireless technology. 
     The volume control may provide local source input switching which may consist of automatic or manual engagement of the local source. The local source may send or share music with other volume controls. 
     A power supply may be located proximate the input circuit. Alternatively, a power supply co-located with the amplifier circuit(s). 
     Four-conductor wire may be used to transmit the audio signal ground and power. Category 5 (CAT-5) wiring may be used instead of four-conductor speaker wire. 
     The amplifier design may be an analog linear amplifier, pulse width modulated or may use direct digital technology. 
     The volume control may be implemented as a component part of an audio distribution system for communicating audio signals between one or more audio sources and a plurality of remote speakers. The system includes at least one audio source for generating an audio signal, and a plurality of amplified volume controls, each disposable remote from the audio source. The volume controls are operative to receive and amplify the audio signal to power associated speakers. A power supply is disposable remote from one or more of the volume controls, for generating a power supply to power all volume controls. An audio/power distribution network is connectable to the audio source, power supply and volume controls, for communicating the audio signal and power supply signal throughout the network. A plurality of audio/power distribution nodes are connected to the audio/power distribution network for interfacing the audio source, power supply and volume controls to the distribution network. The power supply and audio source may be connected to any of the distribution nodes to provide audio signal and power to each of the volume controls. 
     In one embodiment, the audio/power distribution network comprises a multiconductor connector for communicating the audio signal(s) and power signal to each of the volume controls. A plurality of audio sources may be connected to the audio/power distribution network via the distribution nodes. 
     The audio signal may also be implemented as a multichannel signal, wherein the audio/power distribution nodes may be operative to selectively extract and communicate one of the audio signal channels to an associated volume control. 
     These and other embodiments of the present invention will be readily apparent to those skilled in the art having reference to the detailed description and drawings which follow, the invention not being limited, however, to any particular embodiments disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
       These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
         FIG. 1  is a schematic illustration of one preferred embodiment of a distributed audio system having features of the present invention; 
         FIG. 2  is an exploded perspective view of a powered volume control having features of the present invention; 
         FIG. 3  is an electrical schematic diagram of an optional signal conditioner having features of the present invention; 
         FIG. 4A  is a diagram of a powered volume control configured for stereo operation and having features of the present invention; 
         FIG. 4B  is a diagram of a powered volume control configured for bridged high-power stereo operation and having features of the present invention; 
         FIG. 4C  is an electrical schematic diagram of a 7.5 watt per-channel powered volume control having features of the present invention; 
         FIG. 5A  is a block diagram of a multiple speaker audio system incorporating a signal conditioner and a volume control and having features of the present invention; 
         FIG. 5B  is a graph illustrating relative signal amplitude in relation to the block diagram of  FIG. 5A ; 
         FIG. 6A  is an electrical schematic diagram of a master circuit card of a powered volume control having 15 watts of power amplification per channel; 
         FIG. 6B  is an electrical schematic diagram of a slave circuit card of a powered volume control having 15 watts of power per channel; 
         FIG. 7  is a schematic illustration of an audio system incorporating multiple powered volume controls arranged in a daisy chain configuration and having features of the present invention; 
         FIG. 8  is a simplified block drawing of a plurality of volume controls connected to a common power supply and audio source; 
         FIG. 9  is a block diagram illustrating the use of a node to interface one or more audio signals and power signal to a plurality of volume controls; 
         FIG. 10  is a signal diagram of a digital signal including a plurality of multiplexed audio signals therein; and 
         FIG. 11  is a block diagram illustrating use of a conventional token ring to communicate and selectively extract audio signals from a signal stream including multiple channels of audio signals. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of example embodiments of the invention follows. 
       FIG. 1  illustrates the general arrangement and connection of a distributed audio system having features in accordance with one preferred embodiment of the present invention. The system generally comprises an audio source  6  having a right channel signal output line  8  and left channel signal output line  10 . Both the right channel  8  and the left channel  10  are referenced to a respective ground  12 . The audio source  6  provides an electrical signal representing an audio signal and may further generate a stereo signal representing a variance in the signal between the right channel  8  and the left channel  10 . The audio source may comprise any number of suitable audio sources, including, without limitation, a radio tuner/receiver, tape player, phonograph, compact disc player, microphone or similar device. Alternatively, or in addition, a public addressing system (not shown) may integrate with the audio source  6  to provide for the transmission of a paging signal through the audio system. 
     The output from the audio source  6  connects to an audio amplifier (or in this case an optional signal conditioner  14 ) through electrical connectors. Multiple digital audio signals may be multiplexed or time shared at the input device of the audio amplifier. Demultiplexing may be controlled by means of isochronous timing. The signal conditioner  14  may be located up to about 100 feet or more from the audio source  6 , but is preferably located within about 30 feet from the audio source and is most preferably located within about 10 feet from the audio source. The signal conditioner  14  amplifies the audio signal to a suitable level for components receiving the audio signal from the signal conditioner. The signal conditioner  14  generally comprises input terminals, internal amplifier circuitry, and signal output connectors, as shown. In an alternative embodiment, a balanced output from the audio source, and suitable conductors may allow for locating audio source  6  up to 500 feet from the signal conditioner  14 , if desired. 
     An external power supply  16  preferably provides 24 volts DC on a power supply line  18  referenced to a common ground line  19  to the signal conditioner  14 . Suitable power supplies providing voltage regulated DC current are known by those skilled in the art and, accordingly, they are not described in detail herein. A power line  22  connects to the signal conditioner  14  and extends through the system to a plurality of powered volume controls  20 . Those of ordinary skill in the art realize that the power supply  16  could alternatively be internal to the signal conditioner  14  and/or each powered volume control  20  or it could be configured to operate on other voltages. 
     Those of ordinary skill in the art will also appreciate that the system can be configured to work without the signal conditioner  14 , using a conventional amplifier or direct connection. For example, the volume control  20  could be connected to the output channel of a conventional amplifier or directly to the audio signal source  6 . The signal conditioner  14  is preferred, however, to amplify the signal to a desired predetermined level for transmission over significant distance and to provide a plurality of parallel output terminals, if desired. 
     The signal conditioner  14  provides the right channel line  24 , the left channel line  26 , a power line  22  and ground  12  to each of a plurality of volume controls  20 . The volume control  20  provides user adjustable amplification of the audio signal and provides the amplified signal to one or more speakers. Preferably, each volume control  20  powers two speakers. Each volume control  20  has a speaker output connector block  28 , an input connector block  30 , and an output connector block  32  and. as shown, each of which has four terminals. Each volume control amplifies the audio signal from the signal conditioner, and transmits the amplified signal to a pair of remote speakers. Each volume control is preferably located as near as possible to the speakers in a convenient, accessible place. Advantageously, the volume control has a high input impedance thereby enabling a plurality of volume controls to connect to a single signal conditioner without undesirably placing too low an impedance load on the signal conditioner  14  or other amplifier. 
     The speaker connector block  28  comprises a right channel terminal  34  and right ground terminal  36  and a left channel terminal  38  and left ground terminal  40 . A right speaker  42  connects via a right speaker line pair  46  to the right channel speaker terminal  34  and right channel ground terminal  36 . A left speaker  44  connects via a left speaker line pair  48  to the left channel speaker terminal  38  and left channel ground terminal  40 . 
     The input connector block  30  comprises a power input terminal  50  which connects to the power supply line  22 , a ground terminal  52  which connects to the ground  12 , a right channel input terminal  54  for receiving the right channel audio signal, and a left channel input terminal  56  for receiving the left channel audio signal. The audio signal received by the volume control  20  may be an analog signal or a digital signal. The signal may be streaming digital audio data such as is used in TCP/IP networking Digital audio may be transmitted to the volume control  20  using optical technology or spread spectrum wireless technology. The four lines from the signal conditioner  14  connect to the volume control  20  at the input connector block  30 . Alternatively, for mono-channel or monophonic applications a three conductor wire could be used to carry power, the audio signal and ground to the volume controls  20 . The output connector block  32  comprises a power output terminal  58  which provides power to other parallel connected volume control  20 , a ground terminal  60  which connects to the ground  12 , a right channel output terminal  62 , and a left channel output terminal  64 . 
     Internal to the volume control  20  and as described in more detail herein is circuitry which amplifies the incoming signal for right and left channel speakers  42 ,  44 . A user-adjustable variable adjustment device such as a voltage divider, variable resistor, potentiometer or similar device controls the magnitude of the signal provided to the amplifier  102  thereby providing for continuously variable volume level adjustment. The amplified signal is output to the speaker connector block  28  to which the right speaker line pair  46  and left speaker line pair  48  connect and thereby feed the signal to a right speaker  42  and a left speaker  44 , respectively. 
     The volume control  20  may provide local source input switching which may consist of automatic or manual engagement of the local source. The local source may send or share music with other volume controls  20 . This is similar to sharing files or printers in a networked computer system. [Not sure what you meant by item # 10 ] 
     Volume Control Housing 
       FIG. 2  illustrates one preferred configuration of a volume control  20  adapted to be installed in a wall  80 . Advantageously, the volume control  20  is configured to fit within an electrical wall box or other type enclosure placed in a wall, including, but not limited to, a single, double, or multi-gang wall box, a plaster ring, a face plate mount or a partially in-the-wall partially out-of-the-wall box. Alternatively, the entire control may be aesthetically located outside the wall in a box or control panel, if desired, or one or more remote hand-held units such as infrared controls may also be used. 
     The outer housing  79  of the volume control  20  is preferably constructed of an electrically nonconductive material. Alternatively, the housing  79  may be constructed of metal that is electrically isolated from the internal circuitry contained within. The speaker connector block  28 , input connector block  30 , and output connector block  32  are provided at the back of the volume control  20 , thereby providing terminals to connect the volume control  20  to the signal conditioner  14 , speakers  42 ,  44 , and/or other volume controls. The front of the volume control  20  has a mounting bracket or yoke  82  having pre-formed holes or openings  84  for securing the volume control to a wall box  81  via suitable screws or other fasteners. Advantageously, the entire volume control  20  is preferably sized to fit within a single gang wall box  81 . The mounting bracket holes  84  are located accordingly to mount the volume control in a standard single gang box, using screws or other attachment device. 
     The above construction provides significant advantages over prior art devices because in-wall mounted volume controls are more convenient to operate than centralized volume controls or volume controls integrated in a speaker booster circuit. Furthermore, integrating the high power amplification capability with high-quality audio signal reproduction in a wall box volume control is a significant advance over systems of the prior art, especially when considered in view of the added flexibility provided for installing such powered volume controls as a retrofit or replacement for existing autoformer attenuators. Suitable electrical boxes  81 , either single-gang or multi-gang, are common in both commercial and residential electrical wiring systems and are readily available. Alternatively, other in-wall mounting options exist, such as plaster mounting rings and the like, and are contemplated for use with this preferred embodiment of the present invention. 
     A stem  86  of a variable adjustment device, such as a potentiometer or trim pot, extends from a hole formed in the yoke  82  of the volume control  20  providing means to control the level of amplification of the audio signal, i.e., the volume for each the right channel and the left channel. It is contemplated that connected to the stem  86  may be a potentiometer control knob  88  which may be of the slider bar, rotating knob, or digital push button type, as desired. The potentiometer control may also be provided in a graphical user interface (GUI) type control surface for volume adjustment and other control features. A decorative face plate  87  preferably covers the exposed front of the mounting bracket  82  to provide an aesthetic installation. While a wall mounted volume control is disclosed, those skilled in the art will readily appreciate that additional controls could also be incorporated, as desired, such as balance, treble, and/or bass adjustment. The volume control and additional controls could be controlled remotely using wireless or infrared technologies. 
     Signal Conditioner Circuitry 
       FIG. 3  more fully illustrates the internal componentry of the signal conditioner  14  shown in  FIG. 1 . Note that preferred component values and device specifications are given for illustrative purposes only and should not be construed as limiting the invention herein disclosed. 
     The signal conditioner  14  generally comprises a two channel amplifier each having gain determined by a variable resistor potentiometer, and a plurality of signal conditioner output connector blocks  100 . Advantageously, the signal conditioner  14  appears as a very high impedance to the signal source thereby preventing the signal conditioner from distorting or overloading the signal source. The signal conditioner  14  is preferably powered by a 24-volt regulated power supply which also powers each volume control connected thereto. A voltage of 24 VDC is preferred in order to maintain the “low voltage” status of the product. 
     The signal conditioner  14  amplifies the audio signal for transmission to a plurality of volume controls  20 . A continuously variable master adjustment device such as a resistor or potentiometer RP 1 , RP 2  allows adjustment of the level of amplification on each channel. The variable master adjustment device provides the user the advantage of being able to preset the maximum voltage presented to the input of the volume controls. This prevents an inexperienced volume control operator from driving the remote amplifier or the speakers into distortion or damaging the volume control or speakers. The variable master adjustment device also allows the volume control and speaker to be grounded, i.e., shut off, if desired. 
     The signal conditioner&#39;s output has four conductors which advantageously enable the system of this preferred embodiment to connect to most existing wiring systems thereby providing a system ideal for retrofitting existing outdated or inadequate systems. The four lines carry the following signals: 24 volts DC power  22 , ground  12 , right channel  24  in reference to ground, and left channel  26  in reference to ground. Alternatively, for mono-channel applications three conductors may be utilized to carry power, ground, and the audio signal. 
     For ease of manufacturing, design and operation the left channel amplification circuitry mirrors the right channel amplification circuitry and, accordingly, only the right channel amplification circuitry is described in detail herein. Furthermore, the audio amplifier of this preferred embodiment is of the type commonly used for audio signal amplification. The circuit is built around a LM1875 20 watt power audio amplifier built by National Semiconductor and is described on page 1-154 to 1-159 of the National Semiconductor application book. Advantageously, the LM1875 amplifier is a monolithic power amplifier which offers low distortion and high quality signal performance at temperatures up to 170° C. while thermal protection limits return operation to 150° C. The LM1875 offers up to 30 watts of power output with distortion levels of generally less than 0.015% total harmonic distortion (THD) at 1 Khz at 20 watts and is extremely stable at gains of 5 or greater. The gain of the amplifier is preferably between about 5 and 20 and most preferably between about 7 and 13. Of course, other semiconductor amplifiers may be used in place of the LM1875, including, but not limited to, integrated circuit known as the TDA2040, TDA7262, or TDA2614 available from Thomson Electronics. 
     While the amplifier design shown and described herein is analog linear amplification, it will be appreciated that other amplifier designs may be used. For example, the amplifier may be pulse width modulated or may use direct digital technologies. 
     As known by those of ordinary skill in the art, adequate heat dissipation helps maintain amplifier longevity and performance. The National Semiconductor application book provides detailed information regarding heat dissipation and proper heat sinking of the amplifier components. 
     The right channel audio signal from the audio source  6  enters the signal conditioner  14  at the right channel connector  8  having reference to ground  12 . Preferably the connector is a standard RCA plug which is commonly used in audio applications. Of course, a plethora of suitable electrical and optical connectors exist and may be used to enjoy the advantages of the invention herein disclosed. Although RCA connectors are mentioned explicitly the invention should in no way be limited to connectors of any one type. Thus, it is contemplated that the use of any suitable audio-quality connectors, such as spade terminals, are within the inventive scope of this application. 
     It is also envisioned that the signal from the audio source could be configured as a balanced output, if desired. Balanced output eliminates undesirable noise in the audio signal. A typical balanced output comprises three lines, consisting of a positive terminal, a negative terminal and ground. A balanced signal is often carried over a three conductor cable comprising a twisted pair and ground for each channel. Three pin connectors are used to connect a balanced output to an input circuit. Thus, in a mono-channel application, the balanced output would require four conductors and a stereo application would require six conductors (two for right channel, two for left channel, ground and power). Those of ordinary skill in the art are familiar with balanced outputs and, accordingly, they are not discussed in great detail herein. Other electrical connectors exist and can easily be adapted for use with the present invention, as desired, such as pin connectors, terminal strips and the like. 
     Other types of wiring may be substituted for four-conductor speaker wire. For example, Category 5 (CAT-5) wiring may be used. The use of CAT-5 wiring allows additional control signals or data to be transmitted separately with audio signal and power conductors. 
     Use of CAT-5 wiring allows for high-speed transmission of audio information by twisted pair. Such high-speed transmission is especially beneficial when the transmission is a digital audio bit stream as opposed to an audio signal. 
     Connected to the right channel connector  8  is a 1 k.Ω. resistor R 2  which feeds into a 50 k.Ω. variable resistor potentiometer RP 2 . As is known by those of ordinary skill in the art, the variable resistor is preferably configured as a voltage divider in both the signal conditioner  14  and the volume control  20  (described later). The variable resistor RP 2  is user variable between a series resistance of about 0 to 1000 k.Ω.s, more preferably between about 0 and 100 k.Ω.s and most preferably between about 0 and 50 k.Ω.s and provides for adjustment of the signal voltage level to an input A 1  of the amplifier  102 . The signal is applied to the terminal of amplifier  102  through a series connected 1 k.Ω. resistor R 4  and a 1.0 uF capacitor C 2 . 
     The positive side of the capacitor C 2  connects in parallel with the positive side of a 100 pF capacitor C 4 , a 22 k.Ω. resistor R 6  and the positive input A 1  of the amplifier  102 . The negative side of the capacitor C 4  connects to ground. The capacitor C 4  and the capacitor C 2  work in unison to form a band-pass filter for the amplifier  102  thereby allowing only a certain range of frequencies to the amplifier. The capacitor C 2  blocks any low frequency or direct current (DC) from entering the amplifier  102 . Capacitor C 4  provides a short circuit path for high frequency noise or signals. The 22 k.Ω. resistor R 6  in turn connects in parallel with a 1.5 k.Ω. resistor R 15 , a 10 uF capacitor C 13  and a 1N52429 zener diode D 2 . The zener diode D 2  biases the amplifier  102  so that the output voltage may swing from +12 volts to −12 volts. A resistor R 15 , preferably 1.5 K.Ω., is connected to power supply node  104 . Current flow is controlled by a 1N4004 diode D 1  connected to a one-half (½) amp fuse  106 . The fuse prevents greater than a predetermined current flow from entering the circuitry of the signal conditioner  14  and causing damage thereto. The fuse  106  connects to a terminal accepting power via the power line  18  from the power supply  16  (see  FIG. 1 ). The diode D 1  protects the circuitry by preventing current from flowing backwards through the circuit should the power input inadvertently be hooked up positive input to ground. 
     Preferably, a 1000 uF capacitor C 14  is connected between the supply rail  104  and ground  12 . As is known by the those skilled in the art, the capacitor C 14  will act as an open circuit to DC current but allow AC signals to pass freely. Thus this design further reduces noise in the system of the present invention by allowing high frequency signals on the power supply node  104  to freely flow to ground  12 . Furthermore, the capacitor C 14  acts as a power storage device should the power at node  104  momentarily sag. 
     The signal at the positive amplifier input A 1  is reproduced or replicated at the amplifier output A 4  having gain determined by the user controlled variable resistor RP 2  and is inverted in relation to the signal of the amplifier input A 1 . The negative amplifier input A 2  connects in parallel with a 22 k.Ω. resistor R 10  which in turn feeds back to the amplifier output A 4  through resistor R 10 . This connection provides negative feedback to reduce the gain and increase the fidelity of the amplifier. The negative amplifier input A 2  also connects to ground through a 1 k.Ω. resistor R 8  in series with a 47 uF capacitor C 6 . The amplifier  102  also has DC power supply voltages applied across terminals A 3  and A 5 . These are known by those of ordinary skill in the art as “rail voltages” and are constant power supply voltages needed to operate the amplifier  102 . The output voltage at the amplifier output A 4  must remain between the voltage at the terminals A 3  and A 5 . Terminal A 5  is connected to the power supply rail  104  and is also referenced to ground through a 0.1 uF capacitor C 8 . The capacitor C 8  shorts high frequency noise to prevent it from interfering with the operation of the amplifier  102 . Amplifier terminal A 3  connects directly to ground. 
     The amplifier output A 4  connects to a resistor-capacitor network comprising a 0.1 uF capacitor C 10 , 4.7.Ω. resistor R 12 , and 1000 uF capacitor C 12 , and resistor R 14 . The resistor-capacitor network provides high frequency stability and prevents parasitic oscillation. The capacitor C 12  blocks any DC signal from the output while the capacitor C 10  acts as a short to ground for high frequencies. The opposite side of the capacitor C 12  connects in parallel with a 1 k.Ω. resistor R 14  and the output terminal for the right channel output  24 . Terminating the audio signal line  24  through a connection to ground through R 14  provides DC residual bleed off of voltage produced by the output of the amplifier  102 . 
     The amplifier output A 4 , provides the right channel signal to the signal output terminal  24  and to a plurality of output connector blocks  100 , as shown in  FIG. 1 . One or more output blocks  100  may be connected to one or more volume controls  20  ( FIG. 1 ) as desired. Each connector block  100  also provides a power terminal  22 , left channel signal terminal  26 , and a ground terminal  12  as shown. A four conductor line connects to each connector block  100  to carry the audio signal, and power, to each volume control  20 . Advantageously, four conductors are utilized to power traditional speaker pairs, i.e. two conductors for each speaker, thereby making the four conductor configuration of the system of the present invention ideal for retrofit applications. Other wiring, such as CAT-5 wiring, may also be used. In particular, CAT-5 wiring is ideally suited when high speeds are required, for example, when a digital audio bit stream is used. 
     As noted above, the system of the present invention may also be configured to operate without the signal conditioner  14  or other amplifier by connecting the audio source  6  ( FIG. 1 ) and power supply  16  ( FIG. 1 ) directly to the volume control  20  ( FIG. 1 ). 
     The operation and connections for the left channel amplifier circuitry essentially mirrors the operation and connections for the right channel amplifier described herein and, therefore, this description will not be repeated. 
     Volume Control Circuitry 
     As noted above in connection with  FIG. 1 , the output terminals of the signal conditioner  14  connect via wires or some other form of signal conductor to the input connector block  30  of one or more volume controls  20 .  FIG. 4A  illustrates a basic block diagram of one possible embodiment of the circuitry for a volume control  20 . The signal enters the volume control  20  through the input connector block  30  which in turn connects to an input attenuator  120 . The attenuator decreases the voltage swing of the input signal. The signal is then further divided by a variable resistor RP 4 . Accordingly, the left channel signal is also divided by a variable resistor RP 3 . The voltage divided right channel signal then enters the volume control amplifier  103 , which preferably has a constant gain. Thus, the variable resistor RP 4  determines the magnitude of the signal presented to the constant gain amplifier  103 . The resistance of the variable resistor RP 4  is between about 0 to 1000 k.Ω.s, more preferably between about 0 and 100 k.Ω. and most preferably between about 0 and 50 k.Ω.s. The amplified signal is then provided to the left speaker  44  through the speaker connector block  28 . 
     Power to the circuit is provided through the input connector block  30 . A power line from the connector block  30  connects to a fuse  108  and then to a diode D 1  before connecting to the volume control amplifiers  103 ,  203 . The supply rail is referenced to ground through a capacitor C 14 , thereby shorting any high frequency noise on the supply rail. The capacitor C 14  also acts as a power storage device should the power at node  104  momentarily sag. The volume control also comprises an output connector block  32  connected electrically to the input connector block  30  so that a plurality of volume controls may be configured in a daisy chain arrangement, as will be explained in more detail later. 
     The circuitry of the volume control  20  may be configured to operate in a bridged or single channel mode.  FIG. 4B  illustrates a volume control  20  configured in bridged mode. In bridged mode, the volume control  20  supplies power to left and right speakers  42 ,  44 , ( FIG. 1 ). The connections to the input connector block  30  and to the speaker connector block  28  may be varied, as desired, to achieve other stereo-power output and mono-channel output configurations. 
       FIG. 4C  illustrates the internal componentry of one preferred embodiment of a volume control  20 , configured for stereo audio amplification. The circuitry of the volume control  14  generally resembles the circuitry of the signal conditioner  14 . The four conductor wires from the signal conditioner  14  connect at the input connector block  30 . The terminals of the input connector block  30  are each daisy chained directly to the corresponding terminals of the output connector block  32  to facilitate connection of additional volume controls  20  in a daisy chain fashion, as described below in more detail. 
     The power terminal  22  also connects to a ½ amp fuse  108  as in the circuitry of the signal conditioner  14 . Power is supplied to the circuit in the same fashion described above for the signal conditioner  14 . The ground terminal  52  also connects to a circuit ground  12 . The left channel amplification circuitry also mirrors the right channel amplification circuitry in the volume control  20 . Thus, in the interest of brevity only the differences in the right channel circuitry of the volume control  20  in comparison to the right channel circuitry of the signal conditioner  14  are described herein. 
     The right channel input terminal  54  connects to attenuator circuitry shown as  120 . The attenuator comprises a 100 k.Ω. resistor R 50  in series in with the input signal. Alternatively, an attenuator bypass switch  122 , in parallel with the resistor R 50 , provides means for bypassing the attenuator to maintain the signal at its fullest magnitude. Thus, depending on the position of the switch  122 , the 100 k.Ω. resistor R 50  may be bypassed with a short or placed in series with the input signal. For example, if the volume control  20  were to be directly connected to a line level source (unamplified), the resistor R 50  may be bypassed via switch  122  so as to not decrease the signal strength to too low a level. 
     A jumper  124  connects opposite the attenuator  120  to a ribbon wire  126 . The ribbon wire connects at the front of the board to an input jumper  128 . The input jumper  128  connects to a 10 k.Ω. variable resistor RP 4 . The 10 k.Ω. resistor RP 4  adjusts the magnitude of the signal presented to the right channel amplifier circuitry, thereby controlling the magnitude of the signal exiting the volume control  20  and the volume of the sound at the right speaker  42 . The variable resistor RP 4  is controlled by a user adjustable device such as the rotatable stem  86  shown on  FIG. 2 . Moving to  FIG. 6B , the same circuitry described above for the signal conditioner  14  connects to resistor RP 4 . It is an advantage of the present invention that both the variable resistors which control right and left channel power amplification, i.e. volume, are located on the master board  141 , as shown in  FIG. 6A , which decreases manufacturing costs and increases reliability. As shown in  FIG. 4C , a single control, dual track potentiometer controls the right channel variable resistor and the left channel variable resistor in unison. Alternatively, separate controls for each of the right and left channel could be provided to achieve balance control between the right and left channel. 
     The left channel output connects to the speaker connector block  28  through 1000 uF capacitor C 12 . The right channel line connects to the right channel speaker output terminal  34 . Ground  12  connects to the right channel ground terminal  36 . The right speaker  42  connects to the output connector block  28  via a two conductor right speaker line  48  as shown in  FIG. 1 . 
     System Operation 
       FIG. 5A  is a schematic block diagram of the powered volume control described above.  FIG. 5B  shows corresponding relative signal voltage levels which occur during typical operation of this preferred embodiment. To operate the system, the audio source  6  (in this case a tape output) and the power supply  16  must first be energized, thereby enabling the power supply to provide current to the signal conditioner  14  and the volume control  20 . The audio source  6  provides an audio signal at a voltage level commonly known as “tape out” level. The tape out level is a common output voltage level in the audio industry and most audio equipment is capable of producing a signal at a tape out level. The level of the signal from the audio source  6  is approximately 1 volt AC as shown at section  182  of the signal voltage graph  180 . Note that the graph  180  shows the relative, not actual voltage level, of the audio signal at each section within the system. 
     From the audio signal source  6 , the signal travels via a right channel line  8  and a left channel line  10  to the input of the signal conditioner  14 . Alternatively, the system could be configured in a mono-channel configuration thereby providing an identical audio signal on both the right and left channel or a single channel having greater power. Advantageously, the input of the signal conditioner  14  presents a high input impedance, generally greater than about 1 k.Ω.s, which prevents the signal conditioner from distorting the output of the audio source  6  and excessively loading the audio source output voltage. More preferably, the input impedance of the signal conditioner  14  is between about 1 k.Ω. and 100 k.Ω.s and most preferably greater than about 1000 k.Ω. Upon entering the signal conditioner  14 , the signal passes through the variable resistor RP 2  ( FIG. 3 ) which generally creates a voltage drop in the signal to about 0.5 VDC as shown at section  184 . The variable resistor RP 2  is selectably controllable to alter the degree of attenuation in the signal shown at section  184 . Adjusting the resistance of RP 2  adjusts the amplitude of the signal. Thus, an operator may adjust the level of the audio signal at node  184  controlling the right and left channel variable resistors or other adjustment device, such as a potentiometer, variable resistor, rheostat, trimpot, or digital resistor network. Such control advantageously provides means to prevent the volume control  20  from receiving a signal from the signal conditioner  14  which would damage the volume control or the speakers. 
     The signal next enters the amplifier  102 . The gain of the amplifiers of the signal conditioner  14  and the volume control  20  are generally constant and thus the power of the signal exiting the amplifier is determined by the magnitude of the signal entering the amplifier. 
     The amplified audio signal is shown in  FIG. 5B  as an amplified signal at section  186 . Upon exiting the amplifier, the amplified signal is provided at terminal  24  on the signal output block  100 . The signal exiting the signal conditioner  14  is fairly robust and advantageously is prepared for transmission at the higher voltage amplitude which aids the signal in resisting interference and provides sufficient magnitude for transmission to a distant volume control  20 . Preferably, the amplitude of the output signal from the amplifier  102  swings in the range from about plus/minus 4 to 5 volts in reference to ground, although other biasing ranges may be suitable such as .+/−.1-3 volts or up to .+/−.30-50 volts or more. Because the output voltage of the signal conditioner at section  186  is fairly robust, the millivoltage noise it may pick up creates less overall distortion than a signal at a tape out voltage level which may swing less than about .+/−.1 volt. Thus, the present invention creates a conditioned audio input signal which, because of its increased magnitude, is more resistant to the effects of noise and provides a more robust signal to facilitate transmission over extended distances. Further, the low output impedance of the signal conditioner  14  allows for more voltage to be dropped across devices connected thereto, such as the volume control  20 . The signal conditioner has output impedance of less than about 100.Ω., more preferably less than about 1.Ω., even more preferably less than about 0.01.Ω., and most preferably less than about 0.001.Ω. Four conductors or wires, which carry the right and left channel signals, ground, and power, link the signal conditioner  14  to each of one or more volume controls  20 . The amplitude of the amplified audio signal between the signal conditioner  14  and the volume control  20  is shown at section  188  on the relative signal graph  180 . 
     The volume control  20  connects to each conductor from the signal conditioner  14 . The volume control  20  displays a high input impedance which thereby allows a plurality of volume controls to be connected to a single signal conditioner  14  without overloading. The input impedance of the volume control  20  is preferably greater than about 1 k.Ω., more preferably between about 1 k.Ω. and 1000 k.Ω. and most preferably greater than about 1000 k.Ω. The input impedance of the particular preferred embodiment described herein is about 100 k.Ω. This is a significant advantage over prior art systems which are limited in the number of additional speakers that can be connected to a single amplifier because each additional speaker, having an impedance of anywhere from 4 to 8 .Ω.s, would combine in parallel thereby incrementally loading the amplifier with a lower and lower impedance. Advantageously, a single signal conditioner  14 , in conjunction with adequate power from one or more power supplies  16 , can serve up to a hundred or more powered volume controls  20 . Additional power sources may be provided as needed, to supply additional volume controls. Such power sources may be separated or may be incorporated in the powered volume control(s), as desired. 
     The signal at section  188  enters the volume control  20  through terminals  50 ,  52 ,  54 ,  56  at section  190 . This signal is attenuated by attenuator  120  which decreases the amplitude of the incoming signal at section  192  to about 1 volt thereby insuring that the amplifier  103  of the volume control  20  is not driven into clipping mode or does not suffer permanent damage. The attenuated signal at section  192  is provided across the variable resistor RP 4  having resistance selectably controlled by the user of the volume control  20 . The operation of the volume control allows the operator to adjust the position of variable resistor RP 4  to alter the resistance presented to the incoming signal which in turn controls the signal presented to the volume control amplifiers at section  194  and the sound volume provided by the speakers  42 ,  44 . 
     After the magnitude of the incoming signal is adjusted to a relative voltage of about 0.5 volts (depending on the desired voltage output level) at section  194 , the signal enters the amplification circuitry of the volume control  20 , shown in  FIG. 4C . The volume control  20  has an amplifier  103  to increase the magnitude and/or power of the signal provided to the right channel output terminal  54 . From the right channel output terminal  54  the right channel signal travels to the right speaker  42 . From the left channel output terminal  56  the left channel signal travels to the left speaker  44 . As shown in the circuitry ( FIG. 5A ) and the shaded section  196  ( FIG. 5B ), the power of the signal at the output terminal  54  may be adjusted using the variable resistor knob  88  ( FIG. 2 ) to control the volume at the speaker  42 . Since the volume is user adjustable, the signal voltage may swing from 0 volts to about +/−11 volts, referenced to ground. Of course, using different circuitry and biasing voltages, the output voltage may range from 0 volts to +/−50 volts. Further, as known by those of ordinary skill in the art, the voltage output of the volume control  20  is also a function of the resistance of the load attached thereto. 
     Advantageously, the volume control  20  displays a low output impedance thereby making the volume control  20  appear as a substantially ideal power source to each speaker. The volume control  20  preferably has an output impedance of less than about 100.Ω., more preferably less than about 1.Ω. and even more preferably less than about 0.01.Ω. and most preferably less than 0.001.Ω. It is contemplated that a number of various speaker types could be used with this system and although this preferred embodiment discloses connecting a single pair, modifications could easily be made to the circuitry disclosed herein to facilitate connecting additional speakers, if desired. 
     The amplification levels of the signal conditioner  14  and the volume control  20 , determined by the variable resistors RP 2 , RP 4 , are preferably adjusted by a user so that the signal conditioner provides the volume control with a signal magnitude such that when the volume control variable resistor RP 4  is set for maximum amplification (volume) the volume control amplifier  103  is safely below power levels which could result in clipping and distortion or damage to the volume control or speakers. The signal conditioner  14  thus sets the maximum level and prevents the volume control from being improperly adjusted to provide distorted audio output or causing damaging electrical or mechanical overload. 
     Preferably, the volume control  20  provides 7.5 watts per channel RMS at 0.2% THD with a frequency response of 20 Hz-20 KHz. The volume control  20  may accept a signal input at line level, at the adjustable level from the signal conditioner  14 , or at a higher magnitude, if an attenuator is incorporated, from the output of a power amplifier. 
     Optional High Power Volume Control 
     In an alternative embodiment, the volume control  20  can be configured to output 15 watts per channel. Although the overall configuration and operation of this alternative preferred embodiment are generally the same as for the lower power version of the volume control described above, some salient differences exist and are described herein. 
     Two primary electrical hardware differences exist between the low power 7.5 watt version described above and the 15 watt high power version. To achieve 15 watts of power amplification, another circuit board, called a slave board, is utilized having generally similar circuitry as in the main board. When the slave board is added to the system of the low power volume control, it may be necessary to fit the system within a double gang or multi-gang box instead of a single gang box. Alternatively, the high power version or the low power version could be configured to fit within enclosures of various sizes and shapes, including single gang wall boxes. Again, while the preferred embodiment described herein may be contained within or mounted to a wall, other mounting configurations and locations exist and may be used while still enjoying the benefits and advantages at the present invention as herein disclosed. 
     As shown in  FIG. 6A , the connector blocks  28 ,  30 ,  32  are identical to the 15 watt embodiment shown in  FIG. 4C . Connected to the input terminal  54  is the attenuator  120  which in turn connects to the jumper  124  having ribbon cable  126  leading to the input jumper  128 . The 10 k.Ω. variable resistor RP 4  connects to the input jumper  128 . However, the output of the variable resistor RP 4  in the high power embodiment is different from the circuitry of the 7.5 watt low power embodiment in that it links to a master board to slave board jumper  140 . A ribbon wire connects to the jumper  140  thereby carrying the signal via ribbon cable to the slave board input  144  on the slave board  142  ( FIG. 6B ). 
       FIG. 6B  illustrates the preferred componentry and configuration of the slave board  142 . From the slave board input  144  the signal enters circuitry that is generally identical to the circuitry of the 7.5 watt embodiment and the circuitry of the main board. To accomplish the additional power amplification, two LM 1875 amplifiers are utilized per channel instead of one. Thus the slave board contains two LM 1875 amplifiers and the master board contains two LM 1875 amplifiers. To further achieve increased amplification, the output of the first slave amplifier  150  is fed into the negative input A 2  of the second slave amplifier  152  through a 22 k.Ω. resistor R 54 . In addition, the positive input terminal A 1  of the second slave amplifier  152  is simply connected to ground through a 0.1 uF capacitor C 15 . The output of the second slave amplifier  152  eventually connects to the negative terminal  156  of the slave board signal output  154 . Conversely, the output of the first slave amplifier  150  eventually leads to the slave board positive output terminal. The slave board  142  achieves double amplification by operating the second slave amplifier  152  as an inverting amplifier whereby the output of the second slave amplifier is amplified and inverted in relation to the amplified output of the first slave amplifier  150 . 
     The slave board receives power via the ribbon cable at the slave board power terminal  160 . Further, ground is provided via the ribbon cable at the slave board ground terminal  162  to facilitate slave board operation. The slave board output terminal block  154  connects via ribbon cable to the slave master jumper  170  located on the master board  141 . This connection provides the right channel output from the slave board  142  to the speaker connector block  28 . Also provided to the speaker connector block is the output from the left channel amplifier pair located on the master board  141 . As shown in  FIG. 6A , the master board  141  is generally identical in operation to the slave board  142 . The output of the first and second master board amplifiers connect to the speaker connector block. The signal to the speakers  42 ,  44  is not referenced to ground, but between an amplified input signal and an amplified inverted input signal. The volume control  20  provides 7.5 watts per channel RMS at 0.2% THD with frequency response of 20-20 KHz. The volume control  20  may accept signal input at line level or at speaker level. 
     In yet another embodiment, the 7.5 watt configuration and the higher power 15 watt configuration may selectively be configured in a single or mono-channel bridged amplifier configuration, thereby providing increased power amplification to a single channel. The mono-channel amplifier is configured by connecting the positive lead on the signal input to one channel of the amplifier and the negative lead on the signal input to the other channel of the amplifier. Thus the output is the amplified difference between the negative input and the positive input. 
     Series/Daisy Chain Configuration 
     As shown in  FIG. 7 , the output connector block  30  of each volume control  20  preferably provides terminals to connect an additional volume control in an alternative embodiment known as a daisy chain arrangement. Advantageously, each volume control  20  provides an output connector block  30  thereby facilitating connection to the input of another volume control  20  via a four conductor line  70 . Connecting the system in this manner aids installation by reducing the number of four conductor wires which must be installed in areas away from the audio source  6 . In essence, a single four conductor connector line  70  links each volume control  20 . The connector line  70  connects the output connector block  32  of one volume control to the input connector block  30  on the next volume control. 
     In the preferred embodiment, the power supply  16  is able to power from about 1 to 6 volume controls  20 , and more preferably, about four. Consequently, in this preferred embodiment, a supplemental power supply  16   a  may be used to supply additional volume controls with power. The supplemental power supply  16   a  connects at the power input of every fifth volume control  20 . Of course, those persons skilled in the art will realize that other configurations are possible wherein greater or less than four volume controls may be powered by a single power supply  16 . Alternatively, each volume control may contain its own power supply circuitry connected, for example, to a suitable 120 voltage AC source. 
     Optional Embodiments and Modifications 
     Many optional embodiments and modifications are possible to provide enhanced operation or functionality in a powered volume control or distributed audio system as disclosed herein. For example, in one optional embodiment (not shown) an additional component, known as an attenuator, may be integrated in the path of the right and left channel between a power amplifier and the signal conditioner  14  or a volume control  20 . Including an attenuator facilitates connection to a power amplifier (not shown) whereby the high power signal from the power amplifier is reduced by about 30 dB. The additional attenuator, such as an OP-3 available from Sonance, Inc. of San Clemente, Calif. provides a 30 dB reduction in signal strength thereby preventing overloading signal conditioner  14  or volume control  20 . Attenuators of this nature are known to those skilled in the art and, accordingly, the internal circuitry thereof are not described in detail herein. 
     It is also contemplated that the signal conditioner  14  or volume control  20  could connect to a powered speaker. The powered speaker contains additional amplification circuitry to further increase the amount of power provided to a speaker. 
     It is also contemplated that the conductors of any of the preferred embodiments described above may comprise fiber optic cable or a combination of optical and electrical conductors. Optical transmission has the advantage of immunity to electrical interference and decreased power loss as compared to common electrical conductors. Alternatively, the audio signal could be transmitted to each volume control  20  via radio or other EMF waves thereby further aiding installation. 
     The various embodiments described herein are also not limited to rotary or slide controls for volume of one of many associated speakers. A wide variety of other controls may also be used, such as up/down push buttons operating an electronic control, infrared control via a hand held remote infrared transmitter, digital resistive network, or an electronic capacitive touch panel. The rotary or slide potentiometer could also easily be replaced with a digital push button or numeric keypad which could be linked to a digital display to provide a visual volume level display. Such a system would have the advantage of presetting the volume to a certain level prior to an event or period. Mastering of multiple “slave” volume controls may also be accomplished using circuit techniques to provide mastered control of numerous volume controls, as desired. 
     Optionally, the powered volume controls for multi-speaker systems described herein may be configured to provide individual treble, bass and balance adjustments. These may be provided by simple filter networks which modify the frequency characteristics of the signal presented to the speakers. Balance adjustment may be provided by a dual variable resistor or a single variable resistor configured to distribute power between a right and left channel. Treble, bass and balance controls are known by those of ordinary skill in the art and accordingly are not discussed in great detail herein. 
     In yet another optional embodiment the volume control  20  may be configured to provide for integral source selection control thereby allowing an operator in a remote location to choose between a number of different audio sources. For example, a remote tuner could preferably be used to select a number of modulated or digitally multiplexed signals provided on one of the four lines presented to the volume control  20 . Thus, based on the selection, various music channels could be selected, or in the case of a building wide announcement, the entire sound system could be used to provide alternate audio output to each different speaker or speaker pair in the building or area. It is also envisioned that an on/off switch could be utilized on the signal conditioner  14 , or the volume control  20 . 
     Similarly, it is contemplated that the electronics of the embodiment disclosed herein could be controlled by a computer from a central or remote location. Such a system would integrate with software which automatically controls system operation including the volume level of each volume control  20  and corresponding speaker or speakers. For example, in the quiet of morning outside entry speakers could have a low volume, but during the midday business the computer could automatically increase the volume to a louder preprogrammed volume level. To achieve such control, data ports would be provided on the signal conditioners  14  or the volume controls  20 . Connecting to the data port is a data control line from the computer or electronic control. Advantageously, the data port could comprise a serial RS-232 data port to facilitate interface with personal computers. Alternatively, the data port could comprise an infrared or RF receiver or other type of data communication equipment. Internal to the signal conditioner  14  and the volume control  20  are electronics which are integrated with the amplifier electronics to control the system as desired. 
     Alternatively, any of the above preferred embodiments and others deriving therefrom may be installed as a mono-channel application. Mono-channel applications are well suited for shopping centers, airports, convention centers and the like. Advantageously, a paging system incorporating the claimed invention provides for selective volume control depending upon the area, the activity in the area and the ambient noise level during a particular time. For example, a convention center may need greater paging volume in certain, more noisy areas. However, in other areas or at different times in that same area lower paging volumes may be required due to reduced noise levels. The preferred embodiments described herein provide this capability. 
     Referring to  FIGS. 8 ,  9 ,  10  and  11 , an audio distribution system is illustrated that may incorporate a plurality of volume controls  20  within an audio distribution system. Referring to  FIG. 8 , a plurality of volume controls  20  are illustrated, each connected to receive signals from the power supply  16  and the audio source  6 . For simplicity, the signal conditioner  14  is not illustrated. In this simplified view, the audio signal conductor is shown as a single line, as may be suitable for distribution of a single audio signal. However, as noted above, a plurality of audio signals may be communicated to each of the volume controls. 
       FIG. 9  illustrates an embodiment wherein a plurality of audio signals are communicated through the audio distribution network. Each volume control  20  is provided with an associated node  21  operative to selectively communicate audio signals from the audio signal conductors to the volume controls. As will be apparent to those of ordinary skill in the art, the node  21  may operate under the control of volume control  20  to communicate signals on either of the audio signal conductors  23   a ,  23   b , to the associated volume control. The power supply signal may be communicated to the volume control in the same manner as described in connection with  FIG. 8 . 
     As shown in  FIG. 9 , the power supply and/or audio source may be disposed proximate the volume control(s) as most convenient to access the audio distribution network. As such, a computer derived audio signal can be input into a node in the same room as the computer, while a CD player may be connected to the network in another room, where the CD player may be more conveniently located. 
       FIG. 10  illustrates a digital signal format of a frame of digital data that may be communicated on one or more audio signal conductors. The frame  25  comprises a plurality of segments, including signals audio.sub. 1 , audio.sub. 2 , audio.sub. 3 , audio.sub. 4 , . . . audio.sub.N. Each of the signals, e.g. audio.sub. 1 , may be a separate channel of audio signal that may be selectively extracted by the node, and communicated to the associated volume control. As such, multi-channel selection may be effected at the volume control location, without the need to communicate control signals to a remote channel selector. 
       FIG. 11  illustrates use of the present invention in relation to a conventional token ring arrangement. A simplified illustration of a token ring  27  is provided, including a plurality of nodes  21 . Each node  21  is operative to extract the selected audio signal from the token ring and communicate the selected signal to the associated volume control  20 . Each node  21  may also function as an input device to communicate power and/or audio input through the token ring, for communication to other nodes on the token ring, and their associated volume controls. Where the audio signal is a time multiplexed signal, as shown at  FIG. 10 , the node  21  includes demultiplexing circuitry to selectively extract the particular channel audio signal desired to be communicated to the associated volume control. The node  21  may also include multiplexing circuitry for communicating an input audio signal to token ring, for transport to other nodes. The token ring may be implemented as a multiconductor cable, or a plurality of multiconductor cables, some of which may communicate multiplexed audio signals, and others of which may communicate power supply signals. 
     As will be apparent to those of ordinary skill in the art, the audio/power distribution network described herein allows the power source and/or audio source(s) to be connected to any convenient node, without having to be located at a particular base area. As such, new homes may be wired for such network usage, and the location of the power supply and audio components may be later located as convenient, at one or more node locations throughout the network. 
     It will be understood that the above described arrangements of apparatus and the method therefrom are merely illustrative of applications of the preferred embodiment and it is not intended to limit the scope of the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by a fair reading of the claims which follow. 
     The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety. 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.