WO2013186812A1 - Public address system - Google Patents

Public address system Download PDF

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Publication number
WO2013186812A1
WO2013186812A1 PCT/JP2012/003870 JP2012003870W WO2013186812A1 WO 2013186812 A1 WO2013186812 A1 WO 2013186812A1 JP 2012003870 W JP2012003870 W JP 2012003870W WO 2013186812 A1 WO2013186812 A1 WO 2013186812A1
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WO
WIPO (PCT)
Prior art keywords
communication signal
receiver
communication
signal
transmitter
Prior art date
Application number
PCT/JP2012/003870
Other languages
French (fr)
Inventor
Tomohiro JONAN
Original Assignee
Toa Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toa Corporation filed Critical Toa Corporation
Priority to PCT/JP2012/003870 priority Critical patent/WO2013186812A1/en
Publication of WO2013186812A1 publication Critical patent/WO2013186812A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R27/00—Public address systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R29/00—Monitoring arrangements; Testing arrangements
    • H04R29/007—Monitoring arrangements; Testing arrangements for public address systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2227/00—Details of public address [PA] systems covered by H04R27/00 but not provided for in any of its subgroups
    • H04R2227/003—Digital PA systems using, e.g. LAN or internet
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/007—Protection circuits for transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/12—Circuits for transducers, loudspeakers or microphones for distributing signals to two or more loudspeakers

Definitions

  • the invention relates to a public address system having a number of loudspeakers.
  • Public address systems are known as sound broadcasting systems for informing and entertaining the public in buildings or facilities.
  • a typical public address system includes loudspeakers and amplifiers connected with lines, as disclosed in Patent Literature 1 (US2003/0063755A).
  • Patent Literature 1 US2003/0063755A
  • a public address system warns the public in buildings or facilities.
  • the EN 60849 specifies performance requirements for sound reinforcement systems that are used indoors or outdoors to broadcast information for the protection of lives within specified areas in the event of emergency.
  • the monitoring of a speaker line to comply with the EN 60849 is performed, for example, by sending intermittently or continuously predetermined signals (e.g. pilot signals) through the speaker line to an endpoint of the speaker line.
  • Other examples include impedance measurement or monitoring with use of extra wiring.
  • FIG. 10 shows one example of a known public address system 900.
  • the public address system 900 comprises an amplifier 902, a number of loudspeakers 903, a two-wire speaker line 904, and a number of monitoring devices 910 associated with the loudspeakers 903 respectively.
  • the output of the amplifier 902 is connected to the loudspeakers 903 via the speaker line 904.
  • the monitoring devices 910 are used to monitor the respective loudspeakers 903 according to signals sent from a central control device (not shown), which controls the communications, along the speaker line 904 of the public address system.
  • the loudspeakers 903 and the monitoring devices 910 are connected in parallel to the speaker line 904.
  • the system When a public address system is used in a large-scale facility or a large-scale building, the system includes one amplifier and a large number of loudspeakers each associated with a monitoring device. If such a large number of loudspeakers and their associated monitoring devices are connected to a single speaker line in parallel, the speaker line needs to be elongated so as to connect with all the loudspeakers and monitoring devices. If the impedance of each loudspeaker is low, high current passes through the speaker line, which could cause overload of the public address system.
  • a central control device connected to the speaker line of such a large-scale public address system needs to communicate with a great number of monitoring devices. This elongates a communication distance and thus could impair the stability of communication. This also requires great power. More specifically, a longer speaker line and more loudspeakers connected in parallel could increase electric resistance in the public address system and divide voltage to a greater extent. This causes attenuation of high frequency signals such as communication signals transmitted through the speaker line, thereby aggravating the communication quality.
  • One object of the invention as disclosed herein is to achieve the stability of signal transmission and less power for a public address system.
  • a public address system comprising a transmission medium configured to transmit a communication signal, a plurality of loudspeakers, and a plurality of communication controllers arranged in parallel on the transmission medium so as to correspond to the loudspeakers respectively.
  • Each of the communication controllers includes a first filter unit configured to prevent passage of the communication signal, a receiver arranged so as to receive the communication signal before the first filter unit, a controlling unit configured to determine whether to transfer the communication signal received by the receiver onto the transmission medium, and a transmitter configured to transfer the communication signal received by the controlling unit onto the transmission medium according to the determination by the controlling unit.
  • the stability of signal transmission can be achieved with less power.
  • Fig. 1 is a schematic diagram of a public address system according to Embodiment 1;
  • Fig. 2 is a schematic diagram of a central control device for the public address system according to Embodiment 1;
  • Fig. 3 is a schematic diagram of a monitoring device for the public address system according to Embodiment 1;
  • Fig. 4 is a schematic diagram of a filter unit used in the monitoring device according to Embodiment 1;
  • Fig. 5 is a flow chart of an operation performed mainly by the monitoring device according to Embodiment 1;
  • Fig. 6 is a schematic diagram of a public address system according to a modified example of Embodiment 1;
  • Fig. 7 is a schematic diagram of a public address system according to Embodiment 2;
  • FIG. 8 is a schematic diagram of a speaker controller for the public address system according to Embodiment 2;
  • Fig. 9 is a flow chart of an operation performed by the speaker unit according to Embodiment 2;
  • Fig. 10 schematically shows a conventional public address system.
  • FIG. 1 schematically shows a public address system 1 (one example of a public address system) according to one embodiment of the invention.
  • the public address system 1 is configured to be used in a large-scale facility or building.
  • the public address system 1 includes an amplifier 2, a number of loudspeakers 3, a speaker line 4 (one example of a transmission medium), a central control device 5, and a number of monitoring devices 10 (one example of a communication controller) associated with the loudspeakers 3 respectively.
  • the output of the amplifier 2 is connected to the loudspeakers 3 via the speaker line 4.
  • the amplifier 2 is connected to the speaker line 4 via a transformer.
  • the amplifier 2 has a DC power supply 25 that supplies DC current to the public address system 1.
  • the monitoring devices 10 are connected to the speaker line 4 in series.
  • the speaker line 4 may be a wire or a cable in a 2-wire form as shown in FIG. 1.
  • the speaker line 4 may be also a power line for the loudspeakers 3.
  • the public address system 1 includes a number of loudspeakers 3 connected to one amplifier 2 via the speaker line 4.
  • the amplifier 2 outputs an audio signal to broadcast.
  • the audio signal may have a frequency not greater than 20 kHz.
  • the audio signal is superimposed on DC power supplied from a power source (not shown) and transmitted through the speaker line 4.
  • the central control device 5 produces and outputs a communication signal.
  • the communication signal may have a frequency not less than 60 kHz.
  • the communication signal is then superimposed on the audio signal and DC power transmitted through the speaker line 4.
  • the superimposed signals are filtered by the monitoring devices 10, so that only the communication signal is processed by the monitoring devices 10, as will be described later.
  • the monitoring devices 10 are polled by the central control device 5 intermittently or continuously.
  • the polling signal which is one example of the communication signal, is relayed from one monitoring device to another until the polling signal reaches its designated monitoring device 10.
  • the designated monitoring device 10 that has received the polling signal then produces and sends a reply signal back to the central control device 5 through the relay between the monitoring devices 10 along the speaker line 4. If no reply signal is sent back, it is assumed that at least one of the connected monitoring devices 10 is not responding, and it may be concluded that there is some fault in the public address system 1 due to short-circuiting and/or open circuit occurred in the speaker line 4.
  • FIG. 2 schematically shows a structure of the central control device 5.
  • the central control device 5 controls communications via the speaker line 4 according to a predetermined communication protocol.
  • the central control device 5 polls each of the monitoring devices 10 to check if there is any fault occurred in the public address system 1.
  • the polling is an automatic, sequential testing of the monitoring devices 10, the loudspeakers 3, and the speaker line 4 for checking their operational statuses.
  • the central control device 5 includes filter units 51, 52, a CPU (Central Processor Unit) 53, a receiver 55, and a transmitter 56.
  • a CPU Central Processor Unit
  • the filter unit 51or 52 includes a band-pass filter that is designed so as to attenuate signals other than a communication signal including a reply signal.
  • the filter unit 51 or 52 thus allows passage of a communication signal only.
  • the CPU 53 controls the reception and transmission of a communication signal.
  • the CPU 53 produces a polling signal (one example of a communication signal) directed to one of the monitoring devices 10.
  • the polling signal produced by the CPU 53 is initially sent to an initial monitoring device 10i, which is connected to the speaker line 4 next to the central control device 5, as shown in FIG. 1.
  • the polling signal includes address data of any of the monitoring devices 10.
  • the CPU 53 also receives a reply signal, which is also an example of a communication signal, from the initial monitoring device 10i.
  • the CPU 53 identifies the status of the public address system 1 according to the communication signal received from the initial monitoring device 10i and outputs information on the status of the public address system 1. For example, the CPU 53 outputs error data or some other information on the public address system 1 to an external management system that monitors and controls operations of the public address system 1 via a network.
  • the receiver 55 receives a communication signal that has passed through the filter unit 51 and sends it to the CPU 53.
  • the transmitter 56 sends a communication signal from the CPU 53 to the speaker line 4 via the filter unit 52.
  • the CPU 53 may perform the above operations according to a program read from a memory (not shown).
  • FIG. 3 schematically shows a structure of the monitoring device 10.
  • the left side of the monitoring device 10 as shown in FIG. 3 is referred to as an "upstream side", which is nearer to the central control device 5 along the speaker line 4.
  • the right side of the monitoring device 10 as shown in FIG. 3 is referred to as a "downstream side", which is nearer to an end point (not shown) of the speaker line 4.
  • the monitoring device 10 has its own unique address (e.g. IP address) or identification information for identifying the monitoring device 10.
  • IP address e.g. IP address
  • the monitoring device 10 includes a filter unit 11 (one example of a first filter unit) connected to the speaker line 4, a filter unit 12a (one example of a second filter unit), a filter unit 12b (one example of a third filter unit), a CPU 13 (one example of a controlling unit), a switch 14a, a switch 14b, a receiver 15a (one example of a receiver or a first receiver ), a receiver 16a (one example of a second receiver), a transmitter 15b (one example of a transmitter or a first transmitter), a transmitter 16b (one example of a second transmitter), a switch 17, an A/D converter 18, and a D/A converter 19.
  • the filter unit 11 is provided on the speaker line 4.
  • the filter unit 11 is a band-pass filter that is so designed as to attenuate at least the frequency band of a communication signal.
  • the filter unit 11 allows passage of an audio signal and a DC signal.
  • FIG. 4 shows one example of a structure of the filter unit 11.
  • the example includes parallel LC circuits serving as a band-pass filter.
  • the filter units 12a and 12b are connected to the switches 14a, 14b respectively via transformers.
  • the filter units 12a and 12b include band-pass filters that are so designed as to attenuate as least the frequency band of an audio signal and a DC signal. In other words, the filter units 12a and 12b allow passage of a communication signal.
  • the switch 14a is connected to the filter unit 12a via a transformer.
  • the switch 14a switches between the receiver 15a and the transmitter 15b to receive and send signals from and to the speaker line 4 according to a command from the CPU 13. Initially, the switch 14a is being switched to the receiver 15a, as will be described later.
  • the switch 14b switches between the receiver 16a and the transmitter 16b to receive and send signals from and to the speaker line 4 according to a command from the CPU 13. Initially, the switch 14b is being switched to the transmitter 16b, as will be described later.
  • the receiver 15a receives a communication signal from a monitoring device 10 on the upstream side via the filter unit 12a and the transformer. The receiver 15a then sends the communication signal to the CPU 13 via the A/D converter 18. The transmitter 15b sends a communication signal received from the CPU 13 via the D/A converter 19 to the monitoring device 10 on the upstream side. The receiver 16a receives a communication signal from a monitoring device 10 on the downstream side via the filter unit 12b. The receiver 16a then sends the communication signal to the CPU13 via the A/D converter 18. The transmitter 16b sends a communication signal received from the CPU 13 via the D/A converter 19 to the monitoring device 10 on the downstream side.
  • the switch 17 switches between the A/D converter 18 and the D/A converter 19 according to a command from the CPU 13.
  • the switch 17 is switched to the A/D converter 18 when the receivers 15a, 16a receive a communication signal, which is to be converted into a digital signal by the A/D converter 18 and then processed by the CPU 13.
  • the switch 17 is switched to the D/A converter 19 when the transmitters 15b, 16b send a communication signal, which has been processed by the CPU 13 and then converted into an analog signal by the D/A converter 19.
  • the A/D converter 18 converts an analog communication signal into a digital communication signal to be processed by the CPU 13.
  • the D/A converter 19 converts a digital communication signal that has been processed by the CPU 13 into an analog communication signal.
  • the CPU 13 is connected to the receivers 15a, 16a and the transmitters 15b, 16b via the A/D and D/A converters 18, 19.
  • the CPU 13 controls the switching of the switches 14a, 14b and 17 by producing and sending command signals to the switches 14a, 14b and 17.
  • the CPU 13 also performs relays between a monitoring device 10 on the downstream side and a monitoring device 10 on the upstream side (or the central control device 5 if the CPU 13 is of the initial monitoring device 10i connected to the speaker line 4 next to the central control device 5).
  • the CPU 13 determines whether the address data of the monitoring device 10 included in the received communication signal is of its own. If the address data is not of its own, the CPU 13 transmits the received communication signal to a monitoring device 10 on the downstream side. If the address data is of its own, the CPU 13 produces a reply signal and sends it to a monitoring device 10 on the upstream side or the central control device 5.
  • the CPU 13 also controls its associated loudspeaker 3.
  • the CPU 13 may perform these operations according to a program read from a memory (not shown).
  • the monitoring device 10 also includes a filter unit 61, a rectifier 62, and a DC power supply 63.
  • the filter unit 61 allows passage of a DC signal from the speaker line 4.
  • the rectifier 62 rectifies the DC signal.
  • the DC power supply 63 receives the rectified DC signal and power the monitoring device 10.
  • FIG. 5 shows a flow chart of processes performed by each monitoring device 10.
  • the monitoring device that performs the processes is referred to as a "monitoring device 10a”
  • the monitoring device connected on an upstream side of the monitoring device 10a is referred to as a “monitoring device 10-1”
  • the monitoring device connected on a downstream side of the monitoring device 10a is referred to as a “monitoring device 10-2”, as shown in FIG. 1.
  • the receiver 15a and the transmitter 16b of the monitoring device 10a are being activated by the switches 14a and 14b respectively so that the monitoring device 10a is able to receive superimposed signals from the monitoring device 10-1 on the upstream side.
  • Step S101 Superimposed signals are received from the speaker line 4 by the monitoring device 10a.
  • the superimposed signals include an audio signal originally sent from the amplifier 2, and a communication signal sent from the central control device 5.
  • the superimposed signals are filtered by the filter unit 11 on the speaker line 4 so that the communication signal is attenuated and only the audio signal and the DC signal are allowed to pass through the filter unit 11.
  • the audio signal is transmitted to each loudspeaker 3 through the speaker line 4.
  • the superimposed signals are also filtered by the filter unit 12a so that the audio signal is attenuated and only the communication signal is allowed to pass.
  • the communication signal from the filter unit 12a is then received by the receiver 15a that is being activated by the switch 14a at this stage and sent to the CPU 13.
  • Step S102 After the communication signal has been received, the CPU 13 commands the switch 14a to switch to the transmitter 15b.
  • Step S103 The CPU 13 determines whether the communication signal is directed to the monitoring device 10a itself by identifying the address data included in the communication signal. If the communication signal is directed to the monitoring device 10a itself, the process goes to step S108. If it is not, the process goes to step S104.
  • Step S104 The CPU 13 sends the communication signal, via the D/A converter 19, to the transmitter 16b that is being activated by the switch 14b at this stage. The communication signal is then sent to the monitoring device 10-2 on the downstream side through the speaker line 4.
  • Step S105 After the communication signal has been transmitted, the CPU 13 commands the switch 14b to switch to the receiver 16a.
  • the monitoring device 10a is now able to receive a reply signal from the monitoring device 10-2 on the downstream side.
  • Step S106 The CPU 13 then determines whether any reply signal has been received via the receiver 16a, which has been sent from the monitoring device 10-2 on the downstream side. If a reply signal has been received within a predetermined time, the process goes to step S107. If not, the process goes to step S110.
  • Step S107 The CPU 13 commands the switch 14b to switch to the transmitter 16b.
  • Step S108 If the communication signal is directed to the monitoring device 10a itself, the CPU 13 produces a reply signal.
  • Step S109 The CPU 13 sends out the reply signal, which has been received from the monitoring device 10-2 on the downstream side as determined in step S106 or has been produced by the monitoring device 10a itself in step S108, to the transmitter 15b and then to the monitoring device 10-1 on the upstream side via the speaker line 4.
  • Step S110 If no reply signal has been received within a predetermined time as determined in step S106, the CPU 13 commands the switch 14b to switch to the transmitter 16b.
  • Step S111 The CPU 13 commands the switch 14a to switch to the receiver 15a.
  • a reply signal is sent from the monitoring device 10 to which the polling signal is directed and then relayed through the monitoring devices 10 on the upstream side and eventually transmitted to the central control device 5.
  • the central control device 5 receives the reply signal, and then produces and outputs information including the status of the public address system 1 via network, as discussed above.
  • the central control device 5 identifies an error and outputs error information. For example, when the central control device 5 has received a reply signal from the monitoring device 10a (FIG. 1) but did not receive a reply signal from the monitoring device 10-2 on the downstream side (FIG. 1), the central control device 5 may determine that there is a fault in the speaker line 4 between the monitoring device 10a and the monitoring device 10-2.
  • the error information output by the central control device 5 may indicate that, for example, the speaker line 4 has short-circuiting and/or open circuit.
  • the superimposed signals containing an audio signal and a communication signal is filtered by the filter unit 11 so that the communication signal is prevented from passing through the speaker line 4.
  • a communication signal is always transferred between one transmission source and one destination.
  • the polling signal and the reply signal in response to the polling signal are transferred only between the central control device 5 and the monitoring device 10i, during which no communication signals are transferred between any other monitoring devices.
  • the polling signal is initially transferred from the central control device 5 to the initial monitoring device 10i. Then, the polling signal is transferred from the initial monitoring device 10i to its downstream side monitoring device 10-1. Next, the polling signal is transferred from the monitoring device 10-1 to its downstream side monitoring device 10a, where a reply signal in response to the polling signal is generated. The reply signal is then transferred from the monitoring device 10a to its upstream side monitoring device 10-1. Subsequently, the reply signal is transferred from the monitoring device 10-1 to its upstream side monitoring device 10i. Finally, the reply signal is transferred from the monitoring device 10i to the central control device 5, where information on the status of the public address system 1 is produced and output.
  • the communication signal is always transferred only between one transmission source and one destination and is prevented from passing all through the speaker line 4 to reach all the monitoring devices 10 connected to the speaker line 4.
  • great current can be prevented from passing through the speaker line 4 when a communication signal is sent from the central control device 5 or each monitoring device 10, even though one or more loudspeakers 3 with low impedance are connected to the speaker line 4 in parallel.
  • a plurality of monitoring devices 10 are arranged in parallel on the speaker line 4 so as to correspond to the loudspeakers 3 respectively, and each of the monitoring device 10 includes a first filter unit 11 configured to prevent passage of a communication signal, a receiver 15a arranged so as to receive the communication signal before the first filter unit 11, a CPU 13 configured to determine whether to transfer the communication signal received from the receiver 15a to the speaker line 4, and a transmitter 16b configured to transfer the communication signal received from the CPU 13 to the speaker line 4 according to the determination by the CPU.
  • the communication signal is much less affected by large impedance that is resulted from the speaker line 4 and a number of loudspeakers 3 connected in parallel.
  • each monitoring device 10 needs power only when receiving and sending a communication signal.
  • the other monitoring devices 10 that are not in operation for processing the communication signal can be set in a sleep mode with least power.
  • an increase of resistance and division of voltage on the speaker line 4 can be prevented even with an elongated speaker line with a number of loudspeakers 3 connected thereto. Therefore, the communication signal is prevented from being attenuated, so that the communication quality in the public address system 1 is enhanced and stability of communication is assured with less power.
  • the public address system 1 can be protected from electrical overload due to a large number of loudspeakers 3 and their associated monitoring devices 10.
  • FIG. 6 schematically shows a public address system 101 (one example of a public address system) according to one modified example of the invention.
  • the public address system 101 differs from the public address system 1 in Embodiment 1 (FIG. 1) in that the monitoring devices 10 are connected to the speaker line 4 separately from the loudspeakers 3. Those members having the same function as Embodiment 1 are numbered the same and thus are not discussed in detail here.
  • FIG. 7 schematically shows a public address system 201 (one example of a public address system) according to another embodiment of the invention. Those members having the same function as Embodiment 1 will be numbered the same and thus will not be described in detail.
  • the public address system 201 includes a central control device, a speaker line 4, and a number of speaker units 230 connected to the speaker line 4.
  • the output of the central control device 240 is connected to the speaker units 230 via the speaker line 4.
  • Each speaker unit 230 has its own unique address (e.g. IP address) or identification information for identifying the speaker unit 230.
  • the speaker unit 230 includes a speaker controller 210 (one example of a communication controller) and a loudspeaker 203.
  • the central control device 240 outputs a modulated audio signal superimposed on DC (Direct Current) for supplying power to the speaker units 230.
  • the central control device 240 includes a computer that includes a CPU and a memory (not shown).
  • the audio signal is converted from a digital signal into an analog signal, and modulated and imposed on DC on the speaker line 4.
  • the central control device 240 also includes a DC power supply 245.
  • the modulated audio signal has a relatively high frequency.
  • the audio signal includes address data of any of the speaker units 230 connected to the speaker line 4.
  • the superimposed signals are filtered by the speaker units 230 so that the modulated audio signal is prevented from passing through the speaker line 4, as will be described in detail later.
  • FIG. 8 schematically shows a structure of the speaker controller 210.
  • the speaker controller 210 includes a filter unit 211 (one example of a first filter unit), a filter unit 212a (one example of a second filter unit), a filter unit 212b (one example of a third filter unit), a CPU 213 (one example of a controlling unit), a switch 214a, a switch 214b, a receiver 215a (one example of a receiver or a first receiver), a receiver 216a (one example of a second receiver), a transmitter 215b (one example of a transmitter or a first transmitter), a transmitter 216b (one example of a second transmitter), a switch 217, an A/D converter 218, a D/A converter 219, a D/A converter 221, and an amplifier 222.
  • the filter unit 211 is provided on the speaker line 4.
  • the filter unit 211 is a band-pass filter that is so designed as to attenuate at least the frequency band of a modulated audio signal. In other words, the filter unit 211 prevents passage of the modulated audio signal through the speaker line 4.
  • the filter units 212a and 212b are connected to the switches 214a, 214b respectively via transformers.
  • the filter units 212a and 212b include high-pass filters that are so designed as to cut off DC and to output the audio signal.
  • the switch 214a is connected to the filter unit 212a via a transformer.
  • the switch 214a switches between the receiver 215a and the transmitter 215b to receive and send signals from and to the speaker line 4 according to a command from the CPU 213. Regularly, the switch 214a is being switched to the receiver 215a, as will be described later.
  • the switch 214b switches between the receiver 216a and the transmitter 216b to receive and send signals from and to the speaker line 4 according to a command from the CPU 213. Regularly, the switch 214b is being switched to the transmitter 216b, as will be described later.
  • the receiver 215a receives an audio signal from a speaker controller 210 on the upstream side via the filter unit 212a and the transformer. The receiver 215a then sends the audio signal to the CPU 213 via the A/D converter 218.
  • the transmitter 215b sends a communication signal, which is to be sent to the speaker controller 210 on the upstream side, if any.
  • the transmitter 216b sends an audio signal received from the CPU 213 via the D/A converter 219 to the speaker controller 210 on the downstream side.
  • the receiver 216a receives a communication signal from a speaker controller 210 on the downstream side via the filter unit 212b and the transformer, if any.
  • the switch 217 switches between the A/D converter 218 and the D/A converter 219 according to a command from the CPU 213.
  • the switch 217 is switched to the A/D converter 218 when the receiver 215a receives an audio signal.
  • the switch 217 is switched to the D/A converter 219 when the transmitter 216b is to send an audio signal.
  • the speaker controller 210 includes a modulator and a demodulator.
  • the demodulator demodulates a modulated audio signal received from the receiver 215a and sends the demodulated audio signal to the A/D converter 218.
  • the modulator modulates an analog audio signal received from the D/A converter 219 and sends the modulated audio signal to the transmitter 216b.
  • the A/D converter 218 converts an analog audio signal that has been demodulated by the demodulator into a digital audio signal to be processed by the CPU 213.
  • the D/A converter 219 converts a digital audio signal that has been processed by the CPU 13 into an analog audio signal.
  • the CPU 213 is connected to the receivers 215a, 216a and the transmitters 215b, 216b via the A/D and D/A converters 218, 219.
  • the CPU 213 controls the switching of the switches 214a, 214b and 217 by producing and sending command signals to the switches 214a, 214b and 217.
  • the CPU 213 also performs relays between a speaker controller 210 on the downstream side and a speaker controller 210 on the upstream side (or the central control device 240 if the CPU 213 is of the initial speaker controller 230-1 connected to the speaker line 4 next to the central control device 240 as shown in FIG. 7).
  • the CPU 213 receives the audio signal and determines whether the address data of the speaker controller 210 included in the received audio signal is of its own. If the address data is its own address data, the CPU 213 sends the audio signal to the amplifier 222 via the D/A converter 221. If the address data is not its own address data, the CPU 213 then transfers the audio signal to a speaker controller 210 on the downstream side.
  • the CPU 213 also controls its associated loudspeaker 203.
  • the CPU 213 may perform these operations according to a program read from a memory (not shown).
  • the D/A converter 221 converts a digital audio signal received from the CPU 213 into an analog audio signal.
  • the amplifier 222 is connected a loudspeaker 203.
  • the amplifier 222 amplifies the analog audio signal received from the D/A converter 221, and then outputs the amplified analog audio signal to the loudspeaker 203 as sound.
  • the speaker controller 210 also includes a filter unit 261, a rectifier 262, and a DC power supply 263.
  • the filter unit 261 allows passage of a DC signal from the speaker line 4.
  • the rectifier 262 rectifies the DC signal.
  • the DC power supply 263 receives the rectified DC signal and power the speaker controller 210.
  • FIG. 9 shows a flow chart of processes performed by each speaker controller 210.
  • the speaker controller that performs the processes is referred to as a "speaker controller 210a”
  • the speaker controller connected on an upstream side of the speaker controller 210a is referred to as a “speaker controller 210-1”
  • the speaker controller connected on a downstream side of the speaker controller 210a is referred to as a “speaker controller 210-2”, as shown in FIG. 7.
  • the receiver 215a and the transmitter 216b of the speaker controller 210a are usually activated by the switches 214a and 214b respectively so that the speaker controller 210a is able to receive a modulated audio signal superimposed on DC from the speaker controller 210-1 on the upstream side.
  • the transmitter 215b and the receiver 216a are not activated unless any signal is transmitted from the downstream side to the downstream side (for example, a reply signal from a downstream side speaker controller 210-2, likewise Embodiment 1).
  • the explanation is focused on the signal being transmitted from the upstream side to the downstream side. Therefore, the operation described below leaves out the explanation of the switching between the receiver 215a and the transmitter 215b or between the transmitter 216b and the receiver 216a.
  • Step S201 A modulated audio signal superimposed on DC is received from the speaker controller 210-1.
  • the audio signal superimposed on DC is filtered by the filter unit 211 so that the audio signal is prevented from passing through the speaker line 4. Meanwhile, the audio signal passes through the filter unit 212a which prevents DC from passing through the filter unit 212a.
  • the audio signal from the filter unit 212a is then received by the receiver 215a that is being activated by the switch 214a and sent to the CPU 213.
  • the audio signal is then demodulated by the demodulator and converted into a digital audio signal by the A/D converter 218.
  • the digital audio signal is then received by the CPU 213.
  • Step S202 The CPU 213 determines whether the received audio signal is directed to the speaker controller 210a based on the address data included in the audio signal. If it is determined that the audio signal is directed to the speaker controller 210a itself, the process goes to step S203. If not, the process goes to step S 204.
  • Step S203 The audio signal is converted into an analog signal by the D/A converter 221 and is output to the loudspeaker 203 via the amplifier 222 as sound.
  • Step S204 The CPU 213 determines whether the audio signal is directed to any other speaker controller 210. If it is determined that the audio signal is directed to any other speaker controller 210, the process goes to step S205.
  • Step S205 The audio signal is converted into an analog signal by the D/A converter 219, modulated by the modulator, and then transmitted to the speaker controller 210-2 on the downstream side via the transmitter 216b.
  • the modulated audio signal is filtered by the filter unit 211 so that the audio signal is prevented from passing through the speaker line 4.
  • a modulated audio signal is always transferred between one transmission source and one destination.
  • the modulated audio signal is initially transferred from the central control device 240 to the speaker controller 210-1. Then, the modulated audio signal is transferred from the speaker controller 210-1 to its downstream side speaker controller 210a, to which the modulated audio signal is directed. When the modulated audio signal includes any other address, the modulated audio signal is further transferred from the speaker controller 210a to its downstream side speaker controller 210-2. In this manner, the modulated audio signal is relayed between the speaker controllers 210 from the upstream side to the downstream side of the speaker line 4.
  • the audio signal is always transferred only between one transmission source and one destination and is prevented from passing all through the speaker line 4 to reach all the speaker units 230 connected to the speaker line 4.
  • great current can be prevented from passing through the speaker line 4 when the modulated audio signal is sent from the central control device 240, even though one or more loudspeakers 203 with low impedance are connected to the speaker line 4 in parallel.
  • Embodiment 2 ⁇ Advantageous Effects of Embodiment 2>
  • the audio signal is prevented from being attenuated while being transmitted along an elongated speaker line. Therefore, the audio signal can be transmitted to the end point of the speaker line 4 in a stable condition, and less power is required.
  • the audio signal can be output by only designated speaker units 230.
  • the audio signal may further include the address data for designating some groups of loudspeakers 203 connected to the speaker line 4, so that audio information can be broadcasted locally.
  • the central control device 240 generates and sends out a modulated audio signal containing addresses designated to two or more speaker units 230 among the speaker units 230 connected to the speaker line 4.
  • each speaker unit 230 When the speaker controller 210 of each speaker unit 230 has received the modulated audio signal, the CPU 213 copies the modulated audio signal, and then the transmitter 216b transmits a copied audio signal to a downstream side speaker controller 210 on the speaker line 4. If the CPU 213 determines that the received modulated audio signal contains the address of the speaker unit 230 corresponding to the CPU 213 itself (hereinafter called "self-address") but does not contain any other addresses for other speaker units 230, the CPU 213 just sends the modulated audio signal to the D/A converter 221 so that the audio signal is output from the loudspeaker 203 as sound.
  • self-address the address of the speaker unit 230 corresponding to the CPU 213 itself
  • the CPU 213 determines that the received modulated audio signal contains the self-address and also contains one or more addresses of other speaker units 230, the CPU 213 then copies the modulated audio signal and sends the copied audio signal to the transmitter 216b, as well as sending the modulated audio signal to the D/A converter 221. In copying the modulated audio signal, the CPU 213 may also erase the self-address out of the modulated audio signal.
  • the modulated audio signal is relayed from one speaker unit 230 to another until the modulated audio signal is received by all of the designated speaker units 230, which output the audio signal through loudspeakers 203 as sound.
  • the filter design is not limited to the above described, and may have any other known band-pass filters or high-pass filters.
  • the invention may be utilized as a public address system used in a large-scale facility or building.
  • 1 Public address system (one example of a public address system) 2 Amplifier 3 Loudspeaker 4 Speaker line (one example of a transmission medium) 5 Central control device 10 Monitoring device (one example of a communication controller) 11 Filter unit (one example of a first filter unit) 12 Switch 13 CPU (one example of a controlling unit), 12a Filter unit (one example of a second filter unit) 12b Filter unit (one example of a third filter unit) 15a Receiver (one example of a receiver or a first receiver) 15b Transmitter (one example of a transmitter or a first transmitter) 16a Receiver (one example of a second receiver) 16b Transmitter (one example of a second transmitter) 51 Filter unit 53 CPU 55 Receiver 56 Transmitter 201 Public address system (one example of a public address system) 203 Loudspeaker 210 Speaker controller (one example of a communication controller) 211 Filter unit (one example of a first filter unit) 212a Filter unit (one example of a second filter unit) 212b

Abstract

The public address system (1) comprises a transmission medium (4) configured to transmit a communication signal, a plurality of loudspeakers (3), and a plurality of communication controllers (10) arranged in parallel on the transmission medium (4) so as to correspond to the loudspeakers (3) respectively. Each of the communication controllers (10) includes a first filter unit (11) configured to prevent passage of the communication signal, a receiver (15a) arranged so as to receive the communication signal before the first filter unit (11), a controlling unit (13) configured to determine whether to transfer the communication signal received by the receiver (15a) onto the transmission medium (4), and a transmitter (16b) configured to transfer the communication signal received by the controlling unit (13) onto the transmission medium (4) according to the determination by the controlling unit (13).

Description

PUBLIC ADDRESS SYSTEM
The invention relates to a public address system having a number of loudspeakers.
Public address systems are known as sound broadcasting systems for informing and entertaining the public in buildings or facilities. A typical public address system includes loudspeakers and amplifiers connected with lines, as disclosed in Patent Literature 1 (US2003/0063755A). In the event of emergency, a public address system warns the public in buildings or facilities.
For public address systems used in Europe, monitoring the connection and correctness of a speaker line extending from an amplifier to one end point of the speaker line is required to meet the EN (European Norm) 60849. The EN 60849 specifies performance requirements for sound reinforcement systems that are used indoors or outdoors to broadcast information for the protection of lives within specified areas in the event of emergency. The monitoring of a speaker line to comply with the EN 60849 is performed, for example, by sending intermittently or continuously predetermined signals (e.g. pilot signals) through the speaker line to an endpoint of the speaker line. Other examples include impedance measurement or monitoring with use of extra wiring.
FIG. 10 shows one example of a known public address system 900. The public address system 900 comprises an amplifier 902, a number of loudspeakers 903, a two-wire speaker line 904, and a number of monitoring devices 910 associated with the loudspeakers 903 respectively. The output of the amplifier 902 is connected to the loudspeakers 903 via the speaker line 904. The monitoring devices 910 are used to monitor the respective loudspeakers 903 according to signals sent from a central control device (not shown), which controls the communications, along the speaker line 904 of the public address system. The loudspeakers 903 and the monitoring devices 910 are connected in parallel to the speaker line 904.
[PTL 1] US2003/0063755A
When a public address system is used in a large-scale facility or a large-scale building, the system includes one amplifier and a large number of loudspeakers each associated with a monitoring device. If such a large number of loudspeakers and their associated monitoring devices are connected to a single speaker line in parallel, the speaker line needs to be elongated so as to connect with all the loudspeakers and monitoring devices. If the impedance of each loudspeaker is low, high current passes through the speaker line, which could cause overload of the public address system.
Furthermore, a central control device connected to the speaker line of such a large-scale public address system needs to communicate with a great number of monitoring devices. This elongates a communication distance and thus could impair the stability of communication. This also requires great power. More specifically, a longer speaker line and more loudspeakers connected in parallel could increase electric resistance in the public address system and divide voltage to a greater extent. This causes attenuation of high frequency signals such as communication signals transmitted through the speaker line, thereby aggravating the communication quality.
One object of the invention as disclosed herein is to achieve the stability of signal transmission and less power for a public address system.
According to one aspect of the invention, there is provided a public address system comprising a transmission medium configured to transmit a communication signal, a plurality of loudspeakers, and a plurality of communication controllers arranged in parallel on the transmission medium so as to correspond to the loudspeakers respectively. Each of the communication controllers includes a first filter unit configured to prevent passage of the communication signal, a receiver arranged so as to receive the communication signal before the first filter unit, a controlling unit configured to determine whether to transfer the communication signal received by the receiver onto the transmission medium, and a transmitter configured to transfer the communication signal received by the controlling unit onto the transmission medium according to the determination by the controlling unit.
With the public address system according to one aspect of the invention, the stability of signal transmission can be achieved with less power.
Fig. 1 is a schematic diagram of a public address system according to Embodiment 1; Fig. 2 is a schematic diagram of a central control device for the public address system according to Embodiment 1; Fig. 3 is a schematic diagram of a monitoring device for the public address system according to Embodiment 1; Fig. 4 is a schematic diagram of a filter unit used in the monitoring device according to Embodiment 1; Fig. 5 is a flow chart of an operation performed mainly by the monitoring device according to Embodiment 1; Fig. 6 is a schematic diagram of a public address system according to a modified example of Embodiment 1; Fig. 7 is a schematic diagram of a public address system according to Embodiment 2; Fig. 8 is a schematic diagram of a speaker controller for the public address system according to Embodiment 2; Fig. 9 is a flow chart of an operation performed by the speaker unit according to Embodiment 2; and Fig. 10 schematically shows a conventional public address system.
Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
<Embodiment 1>
<Public Address system 1>
FIG. 1 schematically shows a public address system 1 (one example of a public address system) according to one embodiment of the invention. The public address system 1 is configured to be used in a large-scale facility or building.
The public address system 1 includes an amplifier 2, a number of loudspeakers 3, a speaker line 4 (one example of a transmission medium), a central control device 5, and a number of monitoring devices 10 (one example of a communication controller) associated with the loudspeakers 3 respectively. The output of the amplifier 2 is connected to the loudspeakers 3 via the speaker line 4. Though not shown, the amplifier 2 is connected to the speaker line 4 via a transformer. The amplifier 2 has a DC power supply 25 that supplies DC current to the public address system 1.
The monitoring devices 10 are connected to the speaker line 4 in series.
The speaker line 4 may be a wire or a cable in a 2-wire form as shown in FIG. 1. The speaker line 4 may be also a power line for the loudspeakers 3.
The public address system 1 includes a number of loudspeakers 3 connected to one amplifier 2 via the speaker line 4.
In the public address system 1, the amplifier 2 outputs an audio signal to broadcast. The audio signal may have a frequency not greater than 20 kHz. The audio signal is superimposed on DC power supplied from a power source (not shown) and transmitted through the speaker line 4. The central control device 5 produces and outputs a communication signal. The communication signal may have a frequency not less than 60 kHz. The communication signal is then superimposed on the audio signal and DC power transmitted through the speaker line 4. The superimposed signals (one example of a transmission signal) are filtered by the monitoring devices 10, so that only the communication signal is processed by the monitoring devices 10, as will be described later.
The monitoring devices 10 are polled by the central control device 5 intermittently or continuously. The polling signal, which is one example of the communication signal, is relayed from one monitoring device to another until the polling signal reaches its designated monitoring device 10. The designated monitoring device 10 that has received the polling signal then produces and sends a reply signal back to the central control device 5 through the relay between the monitoring devices 10 along the speaker line 4. If no reply signal is sent back, it is assumed that at least one of the connected monitoring devices 10 is not responding, and it may be concluded that there is some fault in the public address system 1 due to short-circuiting and/or open circuit occurred in the speaker line 4.
The detailed description on each device connected to the speaker line 4 in the public address system 1 will now be described in detail.
<Central Control Device 5>
FIG. 2 schematically shows a structure of the central control device 5. The central control device 5 controls communications via the speaker line 4 according to a predetermined communication protocol. In particular, the central control device 5 polls each of the monitoring devices 10 to check if there is any fault occurred in the public address system 1. The polling is an automatic, sequential testing of the monitoring devices 10, the loudspeakers 3, and the speaker line 4 for checking their operational statuses.
The central control device 5 includes filter units 51, 52, a CPU (Central Processor Unit) 53, a receiver 55, and a transmitter 56.
The filter unit 51or 52 includes a band-pass filter that is designed so as to attenuate signals other than a communication signal including a reply signal. The filter unit 51 or 52 thus allows passage of a communication signal only.
The CPU 53 controls the reception and transmission of a communication signal. The CPU 53 produces a polling signal (one example of a communication signal) directed to one of the monitoring devices 10. The polling signal produced by the CPU 53 is initially sent to an initial monitoring device 10i, which is connected to the speaker line 4 next to the central control device 5, as shown in FIG. 1. The polling signal includes address data of any of the monitoring devices 10. The CPU 53 also receives a reply signal, which is also an example of a communication signal, from the initial monitoring device 10i. The CPU 53 identifies the status of the public address system 1 according to the communication signal received from the initial monitoring device 10i and outputs information on the status of the public address system 1. For example, the CPU 53 outputs error data or some other information on the public address system 1 to an external management system that monitors and controls operations of the public address system 1 via a network.
The receiver 55 receives a communication signal that has passed through the filter unit 51 and sends it to the CPU 53. The transmitter 56 sends a communication signal from the CPU 53 to the speaker line 4 via the filter unit 52.
The CPU 53 may perform the above operations according to a program read from a memory (not shown).
<Monitoring Device 10>
FIG. 3 schematically shows a structure of the monitoring device 10. In this embodiment, the left side of the monitoring device 10 as shown in FIG. 3 is referred to as an "upstream side", which is nearer to the central control device 5 along the speaker line 4. The right side of the monitoring device 10 as shown in FIG. 3 is referred to as a "downstream side", which is nearer to an end point (not shown) of the speaker line 4.
The monitoring device 10 has its own unique address (e.g. IP address) or identification information for identifying the monitoring device 10.
The monitoring device 10 includes a filter unit 11 (one example of a first filter unit) connected to the speaker line 4, a filter unit 12a (one example of a second filter unit), a filter unit 12b (one example of a third filter unit), a CPU 13 (one example of a controlling unit), a switch 14a, a switch 14b, a receiver 15a (one example of a receiver or a first receiver ), a receiver 16a (one example of a second receiver), a transmitter 15b (one example of a transmitter or a first transmitter), a transmitter 16b (one example of a second transmitter), a switch 17, an A/D converter 18, and a D/A converter 19.
The filter unit 11 is provided on the speaker line 4. The filter unit 11 is a band-pass filter that is so designed as to attenuate at least the frequency band of a communication signal. In other words, the filter unit 11 allows passage of an audio signal and a DC signal. FIG. 4 shows one example of a structure of the filter unit 11. The example includes parallel LC circuits serving as a band-pass filter.
The filter units 12a and 12b are connected to the switches 14a, 14b respectively via transformers. The filter units 12a and 12b include band-pass filters that are so designed as to attenuate as least the frequency band of an audio signal and a DC signal. In other words, the filter units 12a and 12b allow passage of a communication signal.
The switch 14a is connected to the filter unit 12a via a transformer. The switch 14a switches between the receiver 15a and the transmitter 15b to receive and send signals from and to the speaker line 4 according to a command from the CPU 13. Initially, the switch 14a is being switched to the receiver 15a, as will be described later. The switch 14b switches between the receiver 16a and the transmitter 16b to receive and send signals from and to the speaker line 4 according to a command from the CPU 13. Initially, the switch 14b is being switched to the transmitter 16b, as will be described later.
The receiver 15a receives a communication signal from a monitoring device 10 on the upstream side via the filter unit 12a and the transformer. The receiver 15a then sends the communication signal to the CPU 13 via the A/D converter 18. The transmitter 15b sends a communication signal received from the CPU 13 via the D/A converter 19 to the monitoring device 10 on the upstream side. The receiver 16a receives a communication signal from a monitoring device 10 on the downstream side via the filter unit 12b. The receiver 16a then sends the communication signal to the CPU13 via the A/D converter 18. The transmitter 16b sends a communication signal received from the CPU 13 via the D/A converter 19 to the monitoring device 10 on the downstream side.
The switch 17 switches between the A/D converter 18 and the D/A converter 19 according to a command from the CPU 13. The switch 17 is switched to the A/D converter 18 when the receivers 15a, 16a receive a communication signal, which is to be converted into a digital signal by the A/D converter 18 and then processed by the CPU 13. The switch 17 is switched to the D/A converter 19 when the transmitters 15b, 16b send a communication signal, which has been processed by the CPU 13 and then converted into an analog signal by the D/A converter 19.
The A/D converter 18 converts an analog communication signal into a digital communication signal to be processed by the CPU 13. The D/A converter 19 converts a digital communication signal that has been processed by the CPU 13 into an analog communication signal.
The CPU 13 is connected to the receivers 15a, 16a and the transmitters 15b, 16b via the A/D and D/ A converters 18, 19. The CPU 13 controls the switching of the switches 14a, 14b and 17 by producing and sending command signals to the switches 14a, 14b and 17. The CPU 13 also performs relays between a monitoring device 10 on the downstream side and a monitoring device 10 on the upstream side (or the central control device 5 if the CPU 13 is of the initial monitoring device 10i connected to the speaker line 4 next to the central control device 5). In particular, the CPU 13 determines whether the address data of the monitoring device 10 included in the received communication signal is of its own. If the address data is not of its own, the CPU 13 transmits the received communication signal to a monitoring device 10 on the downstream side. If the address data is of its own, the CPU 13 produces a reply signal and sends it to a monitoring device 10 on the upstream side or the central control device 5. The CPU 13 also controls its associated loudspeaker 3.
The CPU 13 may perform these operations according to a program read from a memory (not shown).
The monitoring device 10 also includes a filter unit 61, a rectifier 62, and a DC power supply 63. The filter unit 61 allows passage of a DC signal from the speaker line 4. The rectifier 62 rectifies the DC signal. The DC power supply 63 receives the rectified DC signal and power the monitoring device 10.
<Operation of Monitoring Device 10>
FIG. 5 shows a flow chart of processes performed by each monitoring device 10. Here, the monitoring device that performs the processes is referred to as a "monitoring device 10a", while the monitoring device connected on an upstream side of the monitoring device 10a is referred to as a "monitoring device 10-1", and the monitoring device connected on a downstream side of the monitoring device 10a is referred to as a "monitoring device 10-2", as shown in FIG. 1.
At the start, the receiver 15a and the transmitter 16b of the monitoring device 10a are being activated by the switches 14a and 14b respectively so that the monitoring device 10a is able to receive superimposed signals from the monitoring device 10-1 on the upstream side.
Step S101: Superimposed signals are received from the speaker line 4 by the monitoring device 10a. The superimposed signals include an audio signal originally sent from the amplifier 2, and a communication signal sent from the central control device 5. The superimposed signals are filtered by the filter unit 11 on the speaker line 4 so that the communication signal is attenuated and only the audio signal and the DC signal are allowed to pass through the filter unit 11. The audio signal is transmitted to each loudspeaker 3 through the speaker line 4. The superimposed signals are also filtered by the filter unit 12a so that the audio signal is attenuated and only the communication signal is allowed to pass. The communication signal from the filter unit 12a is then received by the receiver 15a that is being activated by the switch 14a at this stage and sent to the CPU 13.
Step S102: After the communication signal has been received, the CPU 13 commands the switch 14a to switch to the transmitter 15b.
Step S103: The CPU 13 determines whether the communication signal is directed to the monitoring device 10a itself by identifying the address data included in the communication signal. If the communication signal is directed to the monitoring device 10a itself, the process goes to step S108. If it is not, the process goes to step S104.
Step S104: The CPU 13 sends the communication signal, via the D/A converter 19, to the transmitter 16b that is being activated by the switch 14b at this stage. The communication signal is then sent to the monitoring device 10-2 on the downstream side through the speaker line 4.
Step S105: After the communication signal has been transmitted, the CPU 13 commands the switch 14b to switch to the receiver 16a.
At this stage, since the transmitter 15b and the receiver 16a are being activated, the monitoring device 10a is now able to receive a reply signal from the monitoring device 10-2 on the downstream side.
Step S106: The CPU 13 then determines whether any reply signal has been received via the receiver 16a, which has been sent from the monitoring device 10-2 on the downstream side. If a reply signal has been received within a predetermined time, the process goes to step S107. If not, the process goes to step S110.
Step S107: The CPU 13 commands the switch 14b to switch to the transmitter 16b.
Step S108: If the communication signal is directed to the monitoring device 10a itself, the CPU 13 produces a reply signal.
Step S109: The CPU 13 sends out the reply signal, which has been received from the monitoring device 10-2 on the downstream side as determined in step S106 or has been produced by the monitoring device 10a itself in step S108, to the transmitter 15b and then to the monitoring device 10-1 on the upstream side via the speaker line 4.
Step S110: If no reply signal has been received within a predetermined time as determined in step S106, the CPU 13 commands the switch 14b to switch to the transmitter 16b.
Step S111: The CPU 13 commands the switch 14a to switch to the receiver 15a.
According to the above operation performed by each monitoring device 10, a reply signal is sent from the monitoring device 10 to which the polling signal is directed and then relayed through the monitoring devices 10 on the upstream side and eventually transmitted to the central control device 5. The central control device 5 receives the reply signal, and then produces and outputs information including the status of the public address system 1 via network, as discussed above. When the central control device 5 has not received a reply signal from the monitoring device 10 to which the polling signal is directed, the central control device 5 then identifies an error and outputs error information. For example, when the central control device 5 has received a reply signal from the monitoring device 10a (FIG. 1) but did not receive a reply signal from the monitoring device 10-2 on the downstream side (FIG. 1), the central control device 5 may determine that there is a fault in the speaker line 4 between the monitoring device 10a and the monitoring device 10-2.
The error information output by the central control device 5 may indicate that, for example, the speaker line 4 has short-circuiting and/or open circuit.
<Operation of Public Address System 1>
According to the public address system 1 of this embodiment, the superimposed signals containing an audio signal and a communication signal (a polling signal and a reply signal) is filtered by the filter unit 11 so that the communication signal is prevented from passing through the speaker line 4. In other words, a communication signal is always transferred between one transmission source and one destination. For example, when the central control device 5 polls the nearest monitoring device 10i (FIG. 1), the polling signal and the reply signal in response to the polling signal are transferred only between the central control device 5 and the monitoring device 10i, during which no communication signals are transferred between any other monitoring devices.
Particularly, when the central control device 5 sends out a polling signal directed to the monitoring device 10a, the polling signal is initially transferred from the central control device 5 to the initial monitoring device 10i. Then, the polling signal is transferred from the initial monitoring device 10i to its downstream side monitoring device 10-1. Next, the polling signal is transferred from the monitoring device 10-1 to its downstream side monitoring device 10a, where a reply signal in response to the polling signal is generated. The reply signal is then transferred from the monitoring device 10a to its upstream side monitoring device 10-1. Subsequently, the reply signal is transferred from the monitoring device 10-1 to its upstream side monitoring device 10i. Finally, the reply signal is transferred from the monitoring device 10i to the central control device 5, where information on the status of the public address system 1 is produced and output.
According to the public address system 1, therefore, the communication signal is always transferred only between one transmission source and one destination and is prevented from passing all through the speaker line 4 to reach all the monitoring devices 10 connected to the speaker line 4. As a result, great current can be prevented from passing through the speaker line 4 when a communication signal is sent from the central control device 5 or each monitoring device 10, even though one or more loudspeakers 3 with low impedance are connected to the speaker line 4 in parallel.
<Advantageous Effects of Embodiment 1>
According to the public address system 1 of the above-described embodiment, a plurality of monitoring devices 10 are arranged in parallel on the speaker line 4 so as to correspond to the loudspeakers 3 respectively, and each of the monitoring device 10 includes a first filter unit 11 configured to prevent passage of a communication signal, a receiver 15a arranged so as to receive the communication signal before the first filter unit 11, a CPU 13 configured to determine whether to transfer the communication signal received from the receiver 15a to the speaker line 4, and a transmitter 16b configured to transfer the communication signal received from the CPU 13 to the speaker line 4 according to the determination by the CPU. With such a public address system 1, the communication signal is much less affected by large impedance that is resulted from the speaker line 4 and a number of loudspeakers 3 connected in parallel. Furthermore, each monitoring device 10 needs power only when receiving and sending a communication signal. Thus, the other monitoring devices 10 that are not in operation for processing the communication signal can be set in a sleep mode with least power. As a result, an increase of resistance and division of voltage on the speaker line 4 can be prevented even with an elongated speaker line with a number of loudspeakers 3 connected thereto. Therefore, the communication signal is prevented from being attenuated, so that the communication quality in the public address system 1 is enhanced and stability of communication is assured with less power.
Furthermore, the public address system 1 can be protected from electrical overload due to a large number of loudspeakers 3 and their associated monitoring devices 10.
<Modified Example of Embodiment 1>
<Modified Example 1>
FIG. 6 schematically shows a public address system 101 (one example of a public address system) according to one modified example of the invention.
The public address system 101 differs from the public address system 1 in Embodiment 1 (FIG. 1) in that the monitoring devices 10 are connected to the speaker line 4 separately from the loudspeakers 3. Those members having the same function as Embodiment 1 are numbered the same and thus are not discussed in detail here.
< Embodiment 2>
FIG. 7 schematically shows a public address system 201 (one example of a public address system) according to another embodiment of the invention. Those members having the same function as Embodiment 1 will be numbered the same and thus will not be described in detail.
The public address system 201 includes a central control device, a speaker line 4, and a number of speaker units 230 connected to the speaker line 4. The output of the central control device 240 is connected to the speaker units 230 via the speaker line 4. Each speaker unit 230 has its own unique address (e.g. IP address) or identification information for identifying the speaker unit 230. The speaker unit 230 includes a speaker controller 210 (one example of a communication controller) and a loudspeaker 203.
The central control device 240 outputs a modulated audio signal superimposed on DC (Direct Current) for supplying power to the speaker units 230. The central control device 240 includes a computer that includes a CPU and a memory (not shown). In the central control device 240, the audio signal is converted from a digital signal into an analog signal, and modulated and imposed on DC on the speaker line 4. The central control device 240 also includes a DC power supply 245.
The modulated audio signal has a relatively high frequency. The audio signal includes address data of any of the speaker units 230 connected to the speaker line 4. The superimposed signals are filtered by the speaker units 230 so that the modulated audio signal is prevented from passing through the speaker line 4, as will be described in detail later.
<Speaker controller 210>
FIG. 8 schematically shows a structure of the speaker controller 210. The speaker controller 210 includes a filter unit 211 (one example of a first filter unit), a filter unit 212a (one example of a second filter unit), a filter unit 212b (one example of a third filter unit), a CPU 213 (one example of a controlling unit), a switch 214a, a switch 214b, a receiver 215a (one example of a receiver or a first receiver), a receiver 216a (one example of a second receiver), a transmitter 215b (one example of a transmitter or a first transmitter), a transmitter 216b (one example of a second transmitter), a switch 217, an A/D converter 218, a D/A converter 219, a D/A converter 221, and an amplifier 222.
The filter unit 211 is provided on the speaker line 4. The filter unit 211 is a band-pass filter that is so designed as to attenuate at least the frequency band of a modulated audio signal. In other words, the filter unit 211 prevents passage of the modulated audio signal through the speaker line 4.
The filter units 212a and 212b are connected to the switches 214a, 214b respectively via transformers. The filter units 212a and 212b include high-pass filters that are so designed as to cut off DC and to output the audio signal.
The switch 214a is connected to the filter unit 212a via a transformer. The switch 214a switches between the receiver 215a and the transmitter 215b to receive and send signals from and to the speaker line 4 according to a command from the CPU 213. Regularly, the switch 214a is being switched to the receiver 215a, as will be described later. The switch 214b switches between the receiver 216a and the transmitter 216b to receive and send signals from and to the speaker line 4 according to a command from the CPU 213. Regularly, the switch 214b is being switched to the transmitter 216b, as will be described later.
The receiver 215a receives an audio signal from a speaker controller 210 on the upstream side via the filter unit 212a and the transformer. The receiver 215a then sends the audio signal to the CPU 213 via the A/D converter 218. The transmitter 215b sends a communication signal, which is to be sent to the speaker controller 210 on the upstream side, if any. The transmitter 216b sends an audio signal received from the CPU 213 via the D/A converter 219 to the speaker controller 210 on the downstream side. The receiver 216a receives a communication signal from a speaker controller 210 on the downstream side via the filter unit 212b and the transformer, if any.
The switch 217 switches between the A/D converter 218 and the D/A converter 219 according to a command from the CPU 213. The switch 217 is switched to the A/D converter 218 when the receiver 215a receives an audio signal. The switch 217 is switched to the D/A converter 219 when the transmitter 216b is to send an audio signal.
Although not shown, the speaker controller 210 includes a modulator and a demodulator. The demodulator demodulates a modulated audio signal received from the receiver 215a and sends the demodulated audio signal to the A/D converter 218. The modulator modulates an analog audio signal received from the D/A converter 219 and sends the modulated audio signal to the transmitter 216b.
The A/D converter 218 converts an analog audio signal that has been demodulated by the demodulator into a digital audio signal to be processed by the CPU 213. The D/A converter 219 converts a digital audio signal that has been processed by the CPU 13 into an analog audio signal.
The CPU 213 is connected to the receivers 215a, 216a and the transmitters 215b, 216b via the A/D and D/ A converters 218, 219. The CPU 213 controls the switching of the switches 214a, 214b and 217 by producing and sending command signals to the switches 214a, 214b and 217. The CPU 213 also performs relays between a speaker controller 210 on the downstream side and a speaker controller 210 on the upstream side (or the central control device 240 if the CPU 213 is of the initial speaker controller 230-1 connected to the speaker line 4 next to the central control device 240 as shown in FIG. 7). In particular, the CPU 213 receives the audio signal and determines whether the address data of the speaker controller 210 included in the received audio signal is of its own. If the address data is its own address data, the CPU 213 sends the audio signal to the amplifier 222 via the D/A converter 221. If the address data is not its own address data, the CPU 213 then transfers the audio signal to a speaker controller 210 on the downstream side. The CPU 213 also controls its associated loudspeaker 203.
The CPU 213 may perform these operations according to a program read from a memory (not shown).
The D/A converter 221 converts a digital audio signal received from the CPU 213 into an analog audio signal.
The amplifier 222 is connected a loudspeaker 203. The amplifier 222 amplifies the analog audio signal received from the D/A converter 221, and then outputs the amplified analog audio signal to the loudspeaker 203 as sound.
The speaker controller 210 also includes a filter unit 261, a rectifier 262, and a DC power supply 263. The filter unit 261 allows passage of a DC signal from the speaker line 4. The rectifier 262 rectifies the DC signal. The DC power supply 263 receives the rectified DC signal and power the speaker controller 210.
<Operation of Speaker Controller 210>
FIG. 9 shows a flow chart of processes performed by each speaker controller 210. Here, the speaker controller that performs the processes is referred to as a "speaker controller 210a", while the speaker controller connected on an upstream side of the speaker controller 210a is referred to as a "speaker controller 210-1", and the speaker controller connected on a downstream side of the speaker controller 210a is referred to as a "speaker controller 210-2", as shown in FIG. 7.
The receiver 215a and the transmitter 216b of the speaker controller 210a are usually activated by the switches 214a and 214b respectively so that the speaker controller 210a is able to receive a modulated audio signal superimposed on DC from the speaker controller 210-1 on the upstream side. The transmitter 215b and the receiver 216a are not activated unless any signal is transmitted from the downstream side to the downstream side (for example, a reply signal from a downstream side speaker controller 210-2, likewise Embodiment 1). Here, the explanation is focused on the signal being transmitted from the upstream side to the downstream side. Therefore, the operation described below leaves out the explanation of the switching between the receiver 215a and the transmitter 215b or between the transmitter 216b and the receiver 216a.
Step S201: A modulated audio signal superimposed on DC is received from the speaker controller 210-1. The audio signal superimposed on DC is filtered by the filter unit 211 so that the audio signal is prevented from passing through the speaker line 4. Meanwhile, the audio signal passes through the filter unit 212a which prevents DC from passing through the filter unit 212a. The audio signal from the filter unit 212a is then received by the receiver 215a that is being activated by the switch 214a and sent to the CPU 213. The audio signal is then demodulated by the demodulator and converted into a digital audio signal by the A/D converter 218. The digital audio signal is then received by the CPU 213.
Step S202: The CPU 213 determines whether the received audio signal is directed to the speaker controller 210a based on the address data included in the audio signal. If it is determined that the audio signal is directed to the speaker controller 210a itself, the process goes to step S203. If not, the process goes to step S 204.
Step S203: The audio signal is converted into an analog signal by the D/A converter 221 and is output to the loudspeaker 203 via the amplifier 222 as sound.
Step S204: The CPU 213 determines whether the audio signal is directed to any other speaker controller 210. If it is determined that the audio signal is directed to any other speaker controller 210, the process goes to step S205.
Step S205: The audio signal is converted into an analog signal by the D/A converter 219, modulated by the modulator, and then transmitted to the speaker controller 210-2 on the downstream side via the transmitter 216b.
<Operation of Public Address System 201>
According to the public address system 201 of this embodiment, the modulated audio signal is filtered by the filter unit 211 so that the audio signal is prevented from passing through the speaker line 4. In other words, a modulated audio signal is always transferred between one transmission source and one destination.
Particularly, when the central control device 240 sends out a modulated audio signal to the speaker line 4 on the downstream side of the central control device 240, the modulated audio signal is initially transferred from the central control device 240 to the speaker controller 210-1. Then, the modulated audio signal is transferred from the speaker controller 210-1 to its downstream side speaker controller 210a, to which the modulated audio signal is directed. When the modulated audio signal includes any other address, the modulated audio signal is further transferred from the speaker controller 210a to its downstream side speaker controller 210-2. In this manner, the modulated audio signal is relayed between the speaker controllers 210 from the upstream side to the downstream side of the speaker line 4.
According to the public address system 201, therefore, the audio signal is always transferred only between one transmission source and one destination and is prevented from passing all through the speaker line 4 to reach all the speaker units 230 connected to the speaker line 4. As a result, great current can be prevented from passing through the speaker line 4 when the modulated audio signal is sent from the central control device 240, even though one or more loudspeakers 203 with low impedance are connected to the speaker line 4 in parallel.
<Advantageous Effects of Embodiment 2>
According to the public address system 201 of Embodiment 2, since each speaker unit 230 relays a modulated audio signal from one to another along the speaker line 4, the audio signal is prevented from being attenuated while being transmitted along an elongated speaker line. Therefore, the audio signal can be transmitted to the end point of the speaker line 4 in a stable condition, and less power is required.
<Modified Example of Embodiment 2>
In the public address system 201, the audio signal can be output by only designated speaker units 230. In particular, the audio signal may further include the address data for designating some groups of loudspeakers 203 connected to the speaker line 4, so that audio information can be broadcasted locally.
In this example, the central control device 240 generates and sends out a modulated audio signal containing addresses designated to two or more speaker units 230 among the speaker units 230 connected to the speaker line 4.
When the speaker controller 210 of each speaker unit 230 has received the modulated audio signal, the CPU 213 copies the modulated audio signal, and then the transmitter 216b transmits a copied audio signal to a downstream side speaker controller 210 on the speaker line 4. If the CPU 213 determines that the received modulated audio signal contains the address of the speaker unit 230 corresponding to the CPU 213 itself (hereinafter called "self-address") but does not contain any other addresses for other speaker units 230, the CPU 213 just sends the modulated audio signal to the D/A converter 221 so that the audio signal is output from the loudspeaker 203 as sound. If the CPU 213 determines that the received modulated audio signal contains the self-address and also contains one or more addresses of other speaker units 230, the CPU 213 then copies the modulated audio signal and sends the copied audio signal to the transmitter 216b, as well as sending the modulated audio signal to the D/A converter 221. In copying the modulated audio signal, the CPU 213 may also erase the self-address out of the modulated audio signal.
According to this modified example, therefore, the modulated audio signal is relayed from one speaker unit 230 to another until the modulated audio signal is received by all of the designated speaker units 230, which output the audio signal through loudspeakers 203 as sound.
<Other Embodiments>
In the public address system 1 or 201 according to Embodiment 1 or 2, the filter design is not limited to the above described, and may have any other known band-pass filters or high-pass filters.
<General Interpretation of Terms>
In understanding the scope of the present disclosure, the term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. Also, the terms "part," "section," "portion," "member" or "element" when used in the singular can have the dual meaning of a single part or a plurality of parts.
The term "configured" as used herein to describe a component, section, or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. Some of the steps in flowchart can be performed in a different order. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such features. Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
The invention may be utilized as a public address system used in a large-scale facility or building.
1 Public address system (one example of a public address system)
2 Amplifier
3 Loudspeaker
4 Speaker line (one example of a transmission medium)
5 Central control device
10 Monitoring device (one example of a communication controller)
11 Filter unit (one example of a first filter unit)
12 Switch
13 CPU (one example of a controlling unit),
12a Filter unit (one example of a second filter unit)
12b Filter unit (one example of a third filter unit)
15a Receiver (one example of a receiver or a first receiver)
15b Transmitter (one example of a transmitter or a first transmitter)
16a Receiver (one example of a second receiver)
16b Transmitter (one example of a second transmitter)
51 Filter unit
53 CPU
55 Receiver
56 Transmitter
201 Public address system (one example of a public address system)
203 Loudspeaker
210 Speaker controller (one example of a communication controller)
211 Filter unit (one example of a first filter unit)
212a Filter unit (one example of a second filter unit)
212b Filter unit (one example of a third filter unit)
213 CPU (one example of a controlling unit)
215a Receiver (one example of a receiver or a first receiver)
215b Transmitter (one example of a transmitter or a first transmitter)
216a Receiver (one example of a second receiver)
216b Transmitter (one example of a second transmitter)
217 D/A converter
218 Amplifier
230 Speaker unit
240 Central control device

Claims (7)

  1. A public address system, comprising:
    a transmission medium configured to transmit a communication signal;
    a plurality of loudspeakers; and
    a plurality of communication controllers arranged in parallel on the transmission medium so as to correspond to the loudspeakers respectively, wherein each of the communication controllers includes:
    a first filter unit configured to prevent passage of the communication signal;
    a receiver arranged so as to receive the communication signal before the first filter unit;
    a controlling unit configured to determine whether to transfer the communication signal received by the receiver onto the transmission medium; and
    a transmitter configured to transfer the communication signal received by the controlling unit onto the transmission medium according to the determination by the controlling unit.
  2. The public address system according to Claim 1, wherein
    the communication controllers are arranged so as to transfer the communication signal from an upstream side to a downstream of the transmission medium,
    the each of the communication controllers includes a first receiver, a first transmitter, a second receiver, and a second transmitter, the first receiver and the first transmitter being arranged upstream of the first filter unit, the second receiver and the second transmitter being arranged downstream of the first filter unit,
    the first receiver receives the communication signal and the second transmitter transfers the communication signal received by the first receiver to a downstream side of the communication controller, when the communication signal is transmitted from an upstream side of the communication controller, and
    the second receiver receives the communication signal and the first transmitter transfers the communication signal received by the second receiver to the upstream side, when the communication signal is transmitted from the downstream side.
  3. The public address system according to Claim 2, wherein
    the controlling unit switches the first receiver off and the first transmitter on, and switches the second transmitter off and the second receiver on, after the communication signal transmitted from the upstream side has been received by the first receiver and transferred to the downstream side by the second transmitter, and
    the controlling unit switches the second receiver off and the second transmitter on, and switches the first transmitter off and the first receiver on, after the communication signal transmitted from the downstream side has been received by the second receiver and transferred to the upstream side by the first transmitter.
  4. The public address system according to Claim 1, wherein
    the controlling unit is configured to determine (i) not to transfer the communication signal onto the transmission medium when the communication signal is directed to the communication controller of the controlling unit itself or (ii) to transfer the communication signal onto the transmission medium when the communication signal is not directed to the communication controller of the controlling unit itself.
  5. The public address system according to Claim 1 , further comprising a second filter unit and a third filter unit, the second filter unit being arranged so as to send the communication signal that has been received from the transmission medium to the receiver, the third filter unit being arranged so as to send the communication signal that has been received from the transmitter to the transmission medium,
    wherein an audio signal is transmitted with the communication signal on the transmission medium, the audio signal having a first frequency band and the communication signal having a second frequency band different from the first frequency band,
    the plurality of the loudspeakers receive and output the audio signal,
    the first filter unit is further configured to allow passage of the audio signal, and
    the second and third filter units are configured to prevent passage of the audio signal and allow passage of the communication signal.
  6. The public address according to Claim 1, wherein
    the communication signal includes a modulated audio signal,
    the each of the communication controllers is coupled to a corresponding loudspeaker of the plurality of loudspeakers, and
    the controlling unit is configured to output sound based on the modulated audio signal through the corresponding loudspeaker when the controlling unit has determined not to transfer the communication signal.
  7. The public address according to Claim 1, wherein
    the communication signal includes a modulated audio signal,
    the each of the communication controllers is coupled to a corresponding loudspeaker of the plurality of loudspeakers, and
    the controlling unit is configured to (i) output sound based on the modulated audio signal through the corresponding loudspeaker when the controlling unit has determined that the communication signal is directed to the communication controller of the controlling unit itself and (ii) transfer the communication signal onto the transmission medium when the controlling unit has determined that the communication signal is directed to any other communication controller.
PCT/JP2012/003870 2012-06-13 2012-06-13 Public address system WO2013186812A1 (en)

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Application Number Priority Date Filing Date Title
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Application Number Priority Date Filing Date Title
PCT/JP2012/003870 WO2013186812A1 (en) 2012-06-13 2012-06-13 Public address system

Publications (1)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5406634A (en) * 1993-03-16 1995-04-11 Peak Audio, Inc. Intelligent speaker unit for speaker system network
US20030063755A1 (en) 2001-09-28 2003-04-03 Nourse James D. System for controlling remote speakers using centralized amplifiers, centralized monitoring and master/slave communication protocol
WO2006050754A2 (en) * 2004-11-09 2006-05-18 Robert Bosch Gmbh Public address system
US20070035407A1 (en) * 1999-11-10 2007-02-15 Capowski Anthony J Alarm system with speaker

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5406634A (en) * 1993-03-16 1995-04-11 Peak Audio, Inc. Intelligent speaker unit for speaker system network
US20070035407A1 (en) * 1999-11-10 2007-02-15 Capowski Anthony J Alarm system with speaker
US20030063755A1 (en) 2001-09-28 2003-04-03 Nourse James D. System for controlling remote speakers using centralized amplifiers, centralized monitoring and master/slave communication protocol
WO2006050754A2 (en) * 2004-11-09 2006-05-18 Robert Bosch Gmbh Public address system

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