Abstract:
An apparatus and method for providing a centralized speaker system that allows multiple speakers connected to a central amplifier speaker line to be monitored and controlled from a central location via a master/slave protocol. The centralized speaker system comprises a central station for selectively communicating at least one of a command and an information signal to a destination device. A tone generator is adapted to communicate an activation tone to the destination device. An amplifier, which is colocated with the central station, is adapted to amplify the signals to the destination device.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   This application claims benefit under 35 U.S.C. § 119(e) from U.S. Provisional Patent Application Ser. No. 60/325,167 filed on Sep. 28, 2001, the entire contents of said application being expressly incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The invention relates to a method and apparatus for controlling audio speakers and, more particularly, to a method and apparatus for controlling a plurality of remote audio speakers from a central station via centralized amplifiers. 
   BACKGROUND OF THE INVENTION 
   Public address systems have been configured traditionally with multiple speakers that are connected together and driven with a common signal, or combined together as multiple networks or zones with a common signal per zone. The common signal originates from one or more sources of audio signal selected for transmission to all speakers, or to all speakers in a zone. 
   Typically, a public address system is configured as a system in which the amplifiers are colocated with the speakers, that is, the amplifiers are located in the same enclosure as the speakers. A user can adjust the volume of the speakers at the amplifier. The design is simple. A signal from the same source is transmitted to each amplifier. If the amplifiers are distributed throughout the building, different listeners can adjust the volume of the speakers to suit the environment they are in. For example, a listener in a noisy machine shop can adjust the volume to a higher level than a listener receiving the same signal in an office. 
   U.S. Pat. No. 4,922,536 discloses frequency division (FDM) and/or time division multiplexing (TDM) to digitally transmit audio signals from multiple microphones to a control booth, and to digitally transmit audio signals from the control booth to speakers. At each end of the digital transmission, the digital signals are converted to analog signals for processing. The control booth provides the control for all of the speakers. In another example, use of a microprocessor in a computing system to control routing of audio signals on a computer bus is shown in U.S. Pat. No. 4,862,159. In both of these audio systems, the speakers are dumb devices, that is, there is no digital audio processing at the speakers themselves. 
   Another example of a distributed speaker system is disclosed in U.K. Patent Application GB 2,123,193A which discloses a speaker system having a master station and remote speakers. Each of the remote speakers has a unique address, and the volume of each speaker can be individually adjusted. However, each speaker requires a respective amplifier that is integrated with the speaker. The amplifier also acts as a switching device to turn the speakers on and off 
   Thus, it is desirable to provide more flexibility in a speaker system network by using separate audio signals at each speaker in the network. For example, an operator at a central point may wish to transmit a message to only selected speakers in a network, or in multiple networks or zones, rather than to all speakers in a network or zone. Further, it is desirable to maintain amplifiers for each of the speakers in a speaker system network in a central location. Thus, the remote units are less expensive and simpler to maintain. 
   It is also desirable to provide separate volume control for each speaker, and to selectively broadcast the audio signal to selected speakers in the network system. For example, it is desirable for a public address system to remotely adjust the volume at selected speakers and selectively broadcast to the speakers. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a speaker system is provided having distributed speakers and amplifiers and centralized speaker monitoring and command control. 
   In accordance with an aspect of the present invention, an intelligent speaker unit is provided for use in the speaker system. In such a system, remote speakers can be selected. The volume for the selected speakers can be adjusted for its corresponding environment, and all of these tasks can be accomplished from a master station. In addition, the volume of the remote speakers can be adjusted locally or remotely using a field programmable device. A central amplifier is colocated with the master station and can serve a plurality of speakers. 
   In accordance with another aspect of the present invention, power is provided to the remote speaker units using an inaudible signal that is controlled from the master station via a tone generator. 
   In accordance with still another aspect of the present invention, the remote speakers can be addressed individually or as part of a group. Thus, each remote speaker and each group are capable of receiving unique content specific, respectively, to the individual remote speaker address and group address. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram of a public address (PA) speaker system constructed in accordance with an embodiment of the present invention; 
       FIG. 2  is a block diagram of a master unit for the speaker system of  FIG. 1  that is constructed in accordance with an embodiment of the present invention; 
       FIG. 3  is a block diagram of a remote unit for the speaker system of  FIG. 1  that is constructed in accordance with an embodiment of the present invention; 
       FIG. 4  is a flow chart depicting a sequence of operations for configuring a speaker in accordance with an embodiment of the present invention; 
       FIG. 5  is a flow chart depicting a sequence of operations for initiating a group page in accordance with an embodiment of the present invention; 
       FIG. 6  is a flow chart depicting a sequence of operations for overriding a group page with an all call page in accordance with an embodiment of the present invention; and 
       FIG. 7  is a flow chart depicting a sequence of operations for changing a group identifier (ID) and/or a tap setting from a computer in accordance with an embodiment of the present invention. 
   

   To facilitate understanding, identical reference numerals have been used to designate identical elements that are common to the figures. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Although the present invention is described for use in an industrial environment, the present invention can also be used in other types of environments. For example, the present invention can also find application in a residential environment and a commercial environment. One such commercial environment can be a department store. For instance, sales announcements can be targeted to specific departments or floors.It will be appreciated by those skilled in the art that, although the present invention is described in the context of a public address system, the invention can be modified to be used in speaker systems in general. 
     FIG. 1  depicts a public address speaker system  100  in accordance with a first embodiment of the present invention. In the illustrated embodiment, four master control units  102 A,  102 B,  102 C and  102 D are used to monitor and control respective sets of speakers connected thereto. By way of an example, connected to master control unit  102 A are a Generator/Mixer  122   1 , a first amplifier  124   1 , second amplifier  124   2 , third amplifier  124   3  and fourth amplifier  124   4  hereinafter referred to plurality of amplifiers  124 ), a first RS-485 bus  126 , a second RS-485 bus  128 , a plurality of remote units  130  depicted as a first remote unit  130   1 , a second remote unit  130   2 , a third remote unit  130   3 , a fourth remote unit  130   4 , a fifth remote unit  130   5  and a sixth remote unit  130   6 , and a plurality of speakers  152  depicted as a first speaker  152   1 , a second speaker  152   2 , a third speaker  152   3  and a fourth speaker  152   4 , a fifth speaker  152   5  and sixth speaker  152   6 . The other master control units have similar configurations, that is, they are each connected to a tone generator/mixer  122 , a plurality of amplifiers  124 , remote units and corresponding speakers. Each master control unit  102  is connected to a computer  154 . The generator mixer  122  preferably supplies a 35 Hz or similar tone that is not audible as the power signal for the speakers  152 . 
   The operation of the speaker system  100  will now be described in general. Speaker system  100  provides the ability to address each of the plurality of speakers  152  individually or as a group. Depending on how the master control units  102  and remote units  130  are configured, a plurality of speakers can be organized into groups allowing the speakers to receive the same program material where the program material can be music and/or speech, for example. Alternatively, the plurality of speakers can be configured wherein each speaker is separate from the other speakers and must be addressed individually. Although each speaker  152  is connected to a particular master control unit  102 , speakers connected to respective ones of the master control units (e.g., master control unit  102 A and  102 D) can be assigned to the same group via the computer  154 . 
   Each of the plurality of speakers  152  preferably has a unique 16-bit address. Each of the plurality of speakers  152  can further be assigned up to four group identifiers (IDs), allowing as many as 255 possible group assignments for the plurality of speakers  152  for each of the four groups. The group identifier allows specific speakers to be assigned to a group and receive the same program signal. For example, with regard to the speakers connected to master control unit  102 A, first speaker  152   1  and second speaker  152   2  can be assigned to group A. Third speaker  152   3  and fourth speaker  152   4  can be assigned to group B. Fifth speaker  152   5  can be assigned to group C, and sixth speaker  152   6  can be assigned to group D. This allows each group to be assigned to a specific area and receive addressed program material with respect to other groups, if desired. As a further example, first speaker  152 , can be assigned to more than one group. 
   The master control unit  102  is preferably assigned a 4-bit address, allowing up to  16  master control units  102  to be used in the speaker system  100 . In a second embodiment of the invention, the computer  154  can be connected to the master control unit  102  via the first RS-485 bus  126 . In this manner, up to 16 master controls units  102  can be controlled individually and/or simultaneously via the computer  154  using the master control unit  102  addresses. 
   The master control unit  102  is also connected to the 35 Hz generator/mixer  122  via the second RS-485 bus  128 . The RS-485 interface standard, which is hereby incorporated by reference in its entirety, is used in multipoint applications where at least one master control unit  102  and/or computer  154  controls many different devices. Although the present invention is depicted as using the RS-485 interface, the invention may be modified to include other types of interfaces and still fall within the scope of the present invention. In accordance with a preffered embodiment of the present invention, 35 Hz generator/mixer  122  can be connected to as many as four amplifiers. In  FIG. 1 , the 35 Hz generator/mixer  122  is, illustratively, connected to first amplifier  124   1 , second amplifier  124   2 , third amplifier  124   3 and fourth amplifier  124   4 . Each amplifier  124  can be connected to as many as thirty remote units  130 , and each remote unit controls a respective speaker  152 . Specifically, with regard to master control unit  102 A, first amplifier  124   1  is connected to first remote unit  130   1  and to second remote unit  130   2 . First remote unit  130   1  is connected to first speaker  152   1 . Second remote unit  130   2  is connected to second speaker  152   2 . Second amplifier  124   2  is connected to third remote unit  130   3  and fourth remote unit  130   4 . Third remote unit  130   3  is connected to third speaker  152   3 , and fourth remote unit  130   4  is connected to fourth speaker  152   4 . Third amplifier  124   3  is connected to fifth remote unit  130   5  which is in turn connected to fifth speaker  152   5 . Fourth amplifier  124   4  is connected to sixth remote unit  130   6  which is in turn connected to sixth speaker  152   6 . 
   Referring to the operation of speaker system  100 , an Enter Command Mode command is communicated to a particular master control unit  102  via the computer  154  and/or a master console with a memory and input devices (not shown). This command causes the master control unit  102  to enable a corresponding 35 Hz generator/mixer  122  to generate a 35 Hz power signal. As stated previously, the 35 Hz signal is inaudible and powers the corresponding remote units  130 . Specifically, the 35 Hz signal powers each of the remote units  130  via the colocated amplifier  124 . The remote units  130  each monitor the incoming message from the master unit  102  to determine whether it is being addressed either as an individual unit or as part of a group. Remote units  130  that are not being addressed power themselves off. If any of the remote units  130  are being addressed, the units remain powered on and communicate an acknowledgement to the master control unit  102 . 
   More particularly, the master control unit  102  communicates a command, along with data, wherein the two signal components comprise a message. The data portion of the message can comprise an address field, group identifier (ID) field, speaker status field and/or a tap setting field, as described below. The commands can comprise a command such as, but not limited to, an Idle/All-Page, Group Page, Speaker Page, Speaker Poll, Speaker Group A configure, Speaker Group B configure, Speaker Group C configure, Speaker Group D configure, Idle/All Page Tap Configure, Retrieve Configuration, Acknowledge Response, Config Response  1 , and Config Response  2 . 
   The tap setting is a predetermined audio setting and can comprise the following settings: off, low, mid, high and full. Each audio setting has a specific volume setting. The present invention can be modified by those skilled in the art to utilize numerical or other incremental or graduated settings to achieve specific volume levels and still fall within the scope of the present invention. 
   The Idle/All Page Tap Configure command is communicated to all remote units  130  and resets all tap settings to a default value. The Group Page command is communicated to remote units  130  that are assigned to a selected group. Rather than determining whether the command is addressed to the remote unit&#39;s  130  individual address, the remote unit  130  determines whether it is assigned to the group that is contained in the incoming message. 
   The Speaker Page command is communicated from a master control unit  102  to a specific speaker. All of the remote units  130  compare the address of the incoming message to their own address to determine whether the message is addressed to them. If the message is addressed to them, the unit remains powered on, executes the command, and/or communicate a response message to the master control unit  102 . 
   Speaker system  100  also has an audio current monitoring system that monitors the current between the remote units  130  and the speakers  152 . A conventional current transformer is preferably provided in the tap control and speaker fault sense circuit  142  ( FIG. 3 ) to detect a drop in current between each of the speakers  152  and their corresponding remote units  130 . Additionally, the remote units  130  are polled via the Speaker Poll command. Specifically, each remote unit  130  is requested by the master control unit  102  to provide its status. If a current drop or no current is detected between the remote unit  130  and respective speaker  152 , the remote unit  130  communicates this information to the master control unit  102 . A repairman can then be dispatched to the identified remote unit  130  and/or speaker  152  and make the necessary repairs. If no faults are detected by the remote unit  130 , a positive indication is communicated to the master control unit  102 . 
   As stated previously, remote units  130  and their respective speakers  152  can be assigned, for example, to groups A, B, C and/or D. The Speaker Group A configure, Speaker Group B configure, Speaker Group C configure, and Speaker Group D configure commands are used to configure the remote unit  130 . The Idle/All Page Tap configure command is communicated from the master station  102  to the remote units  130 . The command establishes the default value for the Idle/All page command. 
   The Retrieve configuration command is communicated from the master station  102  to the remote stations  130  to determine the configuration of the remote settings. The remote units  130  respond with a Config Response  1  acknowledgement containing their address, the ID of the group, if any, that they belong to, and their status. The remote units can also respond with a Config Response  2  response containing their idle tap setting, the ID of the group, if any, that they belong to and their present tap setting. 
     FIG. 2  depicts components of the master control unit  102  for the speaker system in accordance with an embodiment of the present invention. Specifically, the master control unit  102  comprises a master microcontroller  110  which is connected to an RF transceiver  112 , a modem  116  (e.g., a 9600 baud RF modem), a power supply  114 , a system RS485 port  118 , and a tone generator RS485 port  120 . The modem  116  is also connected to the RF transceiver  112  which is connected to the RF channel &amp; control circuit  108 . A plurality of audio lines  104  illustratively depicted as  104   1 ,  104   2 ,  104   3  and  1044  are connected to the RF channel selection &amp; control circuit  108 . The power supply  114  is preferably connected to a 24V DC power connection  106 . 
   The microcontroller  110  controls the speakers and associated devices connected thereto, as well as serving as an interface between the computer  154  and the remote units  130 . The computer  154  and microcontroller  110  preferably communicate via the system RS485 port  118 . 
   As stated previously, each master control unit  102  has a unique 4-bit address that the computer  154  can use to address it. Upon receiving an indication from computer  154  that a command will be sent to a speaker, the microcontroller  110  of the addressed master control unit(s) enables its 35 Hz generator/mixer  122 . Specifically, the master microcontroller  110  communicates an activation signal to the 35 Hz generator/mixer  122  via the tone generator RS485 port  120 . The 35 Hz generator/mixer  122 , in turn, communicates a 35 Hz signal to the amplifier  124  which powers the remote unit(s)  130  connected to the speaker being addressed for the time period that the 35 Hz signal is being communicated. 
   The microcontroller  110  then communicates the command received from the computer  154  to the remote unit(s)  130 . The command is communicated to the modem  116  in a digital format. The modem  116  converts the received signal to an analog signal. The analog signal is then communicated to the RF transceiver which modulates the analog signal to an appropriate frequency. 
   The modulated analog signal is then communicated to the RF channel selection &amp; control circuit  108 . When the microcontroller  110  communicates a command to a remote unit  130 , the microcontroller  110  preferably operates without data concerning the audio line  104  to which the remote unit is connected. Therefore, all of the remote units  130  are preferably powered on and the command is communicated on all of the audio lines  104 . Each of the remote units then determines whether the received command is addressed to it. 
     FIG. 3  is a block diagram of a remote unit  130  for the speaker system of  FIG. 1  that is constructed in accordance with an embodiment of the present invention. The remote unit  130  preferably comprises a microcontroller  140  connected to a field configuration port  150 , a modem  148 , a transceiver  144 , an audio buffer  138 , a tap control &amp; speaker fault sense circuit  142 , and a power supply  132 . The power supply is also connected to the audio buffer  138 , an RF transformer  136  and speaker transformer  134 . 
   The audio line connection  104  interfaces with the speaker transformer  134 , the RF transformer  136  and audio buffer  138 . When a signal is received at the remote unit  130 , the signal is routed and processed according to its frequency. For example, when a 35 Hz signal is received at the remote unit  130  via the audio line  104 , the 35 Hz signal is routed to the audio buffer  138  which then communicates the signal to the microcontroller  140 . The remote unit  130  is then activated to receive commands from the master control unit  102 . 
   It is conventional to use human speech to power up the remote unit  130 ; however, human speech fluctuates and can cause a circuit board to repeatedly power on and off. By having a 35 Hz signal, that is, a continuous inaudible signal as a power signal, no interference will occur between an audible page and the 35 Hz signal. 
   The received signal can also be a command from a corresponding master control unit  102 . The command is routed to the RF transformer  136  and communicated to the RF transceiver  144  where it is then demodulated and communicated via the RF transceiver  144  to the modem  148  (e.g., a 9600 baud RF modem) for conversion to a digital signal. The microcontroller  140  receives the digital signal from the modem  148  and executes the command. 
   For example, if the command required that a tap setting be made, the microcontroller  140  communicates the settings to the tap control &amp; speaker fault sense circuit  142  which adjusts relays (not shown) that changes the transformer settings on the speaker transformer  134 . The tap control &amp; speaker fault sense circuit  142  also monitors the current between the speaker  152  and the remote unit  130  (e.g., via a current transformer (not shown)). If a drop in current or no current is detected, the remote unit  130  informs the master control station  102  when a command for its status is received. 
   The field configuration port  150  allows on-site programming of the remote unit  130 . When the remote unit is first installed, its address needs to be stored on the remote unit  130  so that it can respond to messages addressed to it from the master control unit  102 . Any type of computer-related device can be used to program the remote unit  130 . 
     FIG. 4  is a flow chart depicting a sequence of operations for configuring a speaker in accordance with an embodiment of the present invention. The method  400  proceeds to step  402  where a field programming device (not shown) is connected to the field configuration port  150  (e.g., serial port). The field programming device can be a computer, processor, terminal and the like. 
   At step  404 , the field programming device communicates a Speaker Address Configure command which allows the field programming device to assign a 16-bit address to the remote unit  130 . 
   At step  406 , the field programming device communicates the Speaker Group A configure command to the remote unit  130 . The remote unit&#39;s address, Group (ID), and tap settings are provided as inputs, for example, to the microcontroller  140  and associated memory. These settings apply to Group A. Additionally, each group can comprise subgroups numbered from 1 to 255 (i.e., each speaker can belong to any of the 255 subgroups). 
   At step  408 , the remote unit  130  communicates an acknowledgement message to the field programming device. This indicates that the remote unit accepted the inputted information and serves as a confirmation. 
   At step  410 , the field programming device communicates the Speaker Group B configure command to the remote unit  130 . The remote unit&#39;s address, Group ID, and tap settings are provided as inputs to the microcontroller  140 . These settings apply to Group B. Additionally, each group can be numbered from 1 to 255, allowing 255 subgroups to be assigned to Group B. 
   At step  412 , the remote unit  130  communicates an acknowledgement message to the field programming device. This indicates that the remote unit  130  accepted the Group B configuration information and serves as a confirmation. 
   At step  414 , the field programming device communicates the Speaker Group C configure command to the remote unit  130 . The remote unit&#39;s address, Group ID, and tap settings are provided as inputs to the microcontroller  140 . These settings apply to Group C. Additionally, each group can be numbered from 1 to 255 allowing 255 subgroups to be assigned to Group C. 
   At step  416 , the remote unit  130  communicates an acknowledgement message to the field programming device. This indicates that the remote unit accepted the Group C configuration information and serves as a confirmation. 
   At step  418 , the field programming device communicates the Speaker Group D configure command to the remote unit  130 . The remote unit&#39;s address, Group ID, and tap settings are provided as inputs to the microcontroller  140 . These settings apply to Group D. Additionally, each group can be numbered from 1 to 255, allowing 255 subgroups to be assigned to Group D. 
   At step  420 , the remote unit  130  communicates an acknowledgement message to the field programming device. This indicates that the remote unit accepted the Group D configuration information and serves as a confirmation. 
   Although the method  400  depicts all four groups being inputted to a speaker, it is possible to practice the invention with no groups, or more or less than the use of four groups. 
   At step  422 , the field programming device communicates a Speaker Page configure command to the remote unit  130 . The address of the remote unit(s)  130  is inputted, along with tap settings. The remote unit(s)  130  store the received tap settings which are the volume levels each corresponding speaker will output when it receives a page to its individual address and not to its group address. As discussed above, each group has its own tap settings. 
   At step  424 , the remote unit  130  communicates an acknowledgement to the field programming device indicting that the inputted information is accepted. 
   At step  426 , the field programming device communicates an Idle/All Page configure command to the remote unit  130 . Tap settings and the remote unit&#39;s address are also inputted. The tap setting inputted is the default tap setting. All of the speakers are preferably set at the same default volume. 
   At step  428 , the remote unit  130  communicates an acknowledgement to the field programming device indicating that the settings inputted were accepted. 
   Computer  154  stores tables of which speaker is connected to which master control unit  102  and the settings of groups and individual speakers  152 . A user options the speaker system  100  via the computer  154  and/or the field programming device. 
     FIG. 5  is a flow chart depicting a sequence of operations for initiating a group page in accordance with an embodiment of the present invention. The method  500  is initiated at step  502  where a user selects a particular group to page from a master control unit. 
   At step  504 , the computer  154  alerts the master control unit(s)  102  corresponding to the speakers in the selected group that a command will soon be issued. In response to this indication, each master control unit  102 , at step  506 , enables its corresponding 35 Hz generator/mixer  122 , which communicates a power signal to all of the remote units  130  associated with that master control unit to provide power to the remote units  130 . 
   At step  508 , each master control unit  102  associated with the selected group communicates to the computer  154  a confirmation that the remote units are powered. 
   At step  510 , the computer  154  communicates to the master control unit(s)  102  that a group page has been requested, along with the group Id. 
   At step  512 , the master control unit(s)  102  communicate a Group Page command to the remote units  130 , along with the group IDs. Each speaker loop receives the command. 
   At step  514 , the remote units  130  compare the received group IDs to the group IDs that they were assigned. If the group IDs do not match, the remote units set their tap settings to off. However, if the group IDs do match, then the remote units set their tap settings to the assigned group setting. 
   At step  516 , the master control unit(s)  102  communicate to the computer  154  that the Group Page command has been configured. 
   At step  518 , the master control unit(s)  102  communicate to their corresponding remote units that there are no more commands to be carried out. 
   At step  520 , the master control unit(s)  102  disable their corresponding 35 Hz generator/mixers  122 . Specifically, an End Command Mode command is communicated to the 35 Hz generator/mixers  122 . The master control unit(s)  102  also communicate a confirmation message to the computer  154  that the 35 Hz generator/mixer is no longer powering the remote units  130 . 
   At step  522 , an audio signal is broadcast by the speaker system  100  via respective speakers  152  in the selected group. The remote unit(s)  130  and respective speakers  152  that were not part of the group page previously sent, set their tap settings to zero. Therefore, audio will not be broadcast from those speakers but rather only from the speakers that were identified as being in the selected group. 
   At step  524 , the computer  154  communicates to the master control unit(s)  102  that a command will be issued. In response to this communication, the master control unit(s)  102 , at step  526 , enable their corresponding 35 Hz generator/mixers  122  to power the remote units  130  and place the remote units  130  into the idle/default state. The master control unit(s)  102  communicate to the computer  154  that their remote units  130  are powered. 
   At optional step  528 , the master control unit(s)  102  can communicate the Idle/All Page command to the remote units  130  and set the tap settings for the remote units to a default setting. As indicated at step  528 , the paging type can go from a group page to an idle/all page without having to turn the 35 Hz generator/mixer off and then back on again. That means that the remote unit(s)  130  that are in the selected group remain powered while the remote unit(s)  130  that are not in the selected group become powered at step  526 . 
   At step  530 , the computer  154  communicates to the master control unit(s)  102  that there are no more commands expected. In response to the communication, the master control unit(s)  102  disable their corresponding 35 Hz generator/mixers  122  and send a confirmation to the computer  154 . 
     FIG. 6  is a flow chart depicting a sequence of operations for overriding a group page with an all-call page in accordance with an embodiment of the present invention. The method  600  is initiated at step  602  where a user selects particular group(s) to page from a master control unit(s)  102  from the computer  154 . 
   At step  604 , the computer  154  alerts the master control unit(s)  102  corresponding to the speakers in the selected groups that a command will soon be issued. In response to this indication, the master control unit(s)  102 , at step  606 , enable their corresponding 35 Hz generator/mixers which provide s a power signal that powers the remote units  130  associated with the selected groups. 
   At step  608 , the master control unit(s)  102  associated with the selected groups communicate to the computer  154  a confirmation message that the remote units  130  are powered. 
   At step  610 , the computer  154  communicates to the master control unit(s)  102  that a group page has been requested, along with the group ID. 
   At step  612 , the master control unit(s)  102  communicate a Group Page command to their corresponding remote units  130 , along with the group IDs. Each speaker loop receives the command. 
   At step  614 , the remote units  130  compare the received group IDs to the group IDs that they were assigned. If the group IDs do not match, the remote units  130  set their tap settings to off. However, if the group ID&#39;s do match, then the remote units  130  set their tap settings to the assigned group setting. The method  600  then proceeds to step  616 . 
   At step  616 , the master control unit(s)  102  communicate to the computer  154  that the Group Page command has been configured. 
   At step  618 , the master control unit(s)  102  communicate to their corresponding remote units that there are no more commands to be carried out. 
   At step  620 , a user over-rides the group page with an emergency All Call page via the master console. In response to the emergency All Call page, the computer  154 , at step  622 , communicates to the master control unit(s)  102  that an All Call page has been requested by a user. 
   At step  624 , the master control unit(s)  102  communicate an Idle/All Page command to their respective remote units  130 . Upon receiving the Idle/All Page command, the remote units  130  apply their default tap settings at step  626 . 
   At step  628 , the master control unit(s)  102  communicate to the computer  154  that the All Page command has been executed by the remote units  130 . 
   At step  630 , the computer  154  communicates to the master control unit  102  that no more commands are expected. In response, the master control unit(s)  102  disable their 35 Hz generator/mixers  122  and communicate the disablement of the generator/mixers  122  to the computer  154 . 
   At step  632 , the page is placed and the announcement goes to all the speakers  152 . 
     FIG. 7  is a flow chart depicting a sequence of operations for changing a group ID and/or a tap setting from a computer (e.g., computer  154  or a field programming device) in accordance with an embodiment of the present invention. The method  700  is initiated at step  702  where a user requests the change of a group ID or tap setting for a specific speaker(s)  152 . 
   At step  704 , the computer  154  communicates to the master control unit(s)  102  that a speaker command is about to be communicated. In response, the master control unit(s)  102  enable their respective 35 Hz generator/mixers  122  to power the remote units  130  and sends a confirmation to the computer  154  that the remote units  130  associated with the master control unit(s)  102  are powered and ready to receive the next command. 
   At step  706 , the computer  154  communicates to the master control unit(s)  102  that a group configuration is required. For purposes of illustration, the Group A configuration is selected. The address of the remote units  130 , group ID and desired tap settings are also communicated to the master control unit(s)  102 . 
   At step  708 , the master control unit(s)  102  communicate a Group A Configure command, along with the remote unit&#39;s  130  addresses, group ID and tap setting to their respective remote units  130 . 
   At step  710 , the remote units  130  compare the received addresses to their assigned address. If there is a match, the received configuration will be saved and an acknowledgement message is communicated to their respective master control unit(s)  102 . If there is no match, the remote units  130  will ignore the command and power off. 
   At step  712 , the master control unit(s)  102  wait for an acknowledgement from their respective remote units  130 . If the waiting period expires, the master control unit(s)  102  resends the command as many as three times before a fault is declared. 
   At step  714 , when an acknowledgement message is received or has timed out after three attempts to communicate with the remote units  130 , their respective master control unit(s) inform the computer  154  of the success or failure of the requested configuration. 
   At step  716 , the computer  154  repeats steps  706  to  714  if necessary and communicates to the master control unit(s)  102  that no additional commands will be sent. 
   At step  718 , the master control unit(s)  102  disable their respective 35 Hz generator/mixers  122  and send a confirmation to the computer  154 . 
   Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention can be described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and the following claims.