EP2862369B1

EP2862369B1 - Public address system and control device for public address system

Info

Publication number: EP2862369B1
Application number: EP12731186.8A
Authority: EP
Inventors: Tomohiro JONAN; Tsuneo Ikoma
Original assignee: Toa Corp
Current assignee: Toa Corp
Priority date: 2012-06-15
Filing date: 2012-06-15
Publication date: 2016-05-25
Anticipated expiration: 2032-06-15
Also published as: JP5908616B2; WO2013186823A1; JP2015523744A; EP2862369A1

Description

Technical Field

The invention relates to a public address system having a number of loudspeakers. The invention also relates to a control device applied to a public address system.

Background Art

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 a plurality of loudspeakers connected to an amplifier via a speaker line, and respective controllers for monitoring connection in the speaker line; an example being disclosed in Patent Literature 1 ( US2003/0063755A ). In the event of an emergency a public address system warns the public in buildings or facilities.
Public address systems used in Europe must meet the EN (European Norm) 60849 which requires monitoring the connection and accuracy of a speaker line extending from an amplifier to an end point of the speaker line. EN 60849 specifies performance requirements for sound reinforcement systems that are used indoors or outdoors to broadcast information to protect those located within specified areas in the event of an emergency. The EN 60849 standard requires a redundant system that assures the maintenance of its alarm function even when a disconnection in the line is present.
EP 2 017 803 A1 discloses a public address system comprising: a transmission medium having a loop shape and configured to transmit a transmission signal therethrough in a first direction and in a second direction opposite to the first direction, the transmission signal including a communication signal having a predetermined frequency range and an audio signal having a different frequency range than the communication signal; a plurality of loudspeakers connected to the transmission medium.
DE 33 47 609 A1 discloses a communication and monitoring system for traffic control in which communication around the loop occurs in one direction with coupling loops between each sub-station. Each sub-station and the central station contain amplifier stages.
GB 2 471 860 A discloses a voice enhanced fire alarm system which comprises a detector control apparatus connected to a data bus network of detector apparatuses linked by fire proof electric cabling.

Summary of Invention

Technical Problem

The public address system needs to maintain its ability to broadcast even when a disconnection occurs in any part of the speaker line.
One object of the invention disclosed herein is to achieve a public address system that is more reliable and secure.

Solution to Problem

According to one aspect of the invention, a public address system is provided comprising a transmission medium having a loop shape, a plurality of loudspeakers connected to the transmission medium, and a first filter unit connected to the transmission medium. The transmission medium is configured to transmit a transmission signal in a first direction and in a second direction opposite to the first direction. The transmission signal includes a first signal having a predetermined range of frequency and a second signal having a different range of frequency than the first signal. The first filter unit is configured to filter the transmission signal so as to attenuate the first signal and output the second signal. The first filter unit is connected to the transmission medium such that the first signal is prevented from being transmitted in the first direction while the first signal and the second signal are transmitted in the second direction. Advantageous Effects of Invention
According to the one aspect of the invention, it is possible to achieve a public address system that is more reliable and secure.

Brief Description of Drawings

[Fig. 1]
FIG. 1 is a schematic diagram of a public address system according to one embodiment;
[Fig. 2]
FIG. 2 is a schematic diagram of a control device for the public address system shown in FIG. 1;
[Fig. 3]
FIG. 3 is a schematic diagram of a filter unit used in the control device shown in FIG. 2;
[Fig. 4]
FIG. 4 is a schematic diagram of a monitoring device for the public address system shown in FIG. 1;
[Fig. 5]
FIG. 5 is a schematic diagram of an isolating unit of the monitoring device shown in FIG. 4;
[Fig. 6]
FIG. 6 is a flow chart of an operation performed by the control device shown in FIG. 2; and
[Fig. 7]
FIG. 7 is a schematic diagram of a monitoring device according to another embodiment.

Description of Embodiments

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 only for illustration and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

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 control device 5 (one example of a control device), and a number of monitoring devices 10 (one example of a communication controller) associated with the loudspeakers 3 respectively.
The amplifier 2 is connected to the speaker line 4. Though not shown, the amplifier 2 is connected to the speaker line 4 via a transformer.
The monitoring devices 10 are connected to the speaker line 4 in series. The loudspeakers 3 are connected in parallel to the speaker line 4. The control device 5 is connected to the speaker line 4.
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 is arranged in a loop such that signals from the amplifier 2 or produced by the control device 5 are transmitted to the speaker line 4 bi-directionally. The speaker line 4 may be a power line for the loudspeakers 3. The power supply in this embodiment is DC (Direct Current).
In the public address system 1, the amplifier 2 outputs an audio signal (one example of a second signal) to be broadcast by the public address system 1. The audio signal may have a frequency lower than or equal to 20 kHz. The audio signal is superimposed on DC supplied from a power source (not shown) and transmitted through the speaker line 4. The control device 5 produces and outputs a communication signal (one example of a first signal). The communication signal may have a frequency greater than 60 kHz. The communication signal is then superimposed on the audio signal and DC transmitted through the speaker line 4. The superimposed signal (one example of a transmission signal) is then sent to the speaker line 4.
The communication signal is prevented from being transmitted in a first direction of the speaker line 4 when both the audio and the communication signals, as a superimposed signal, are transmitted in a second direction through the speaker line 4, as will be described later. The second direction is opposite to the first direction.
The monitoring devices 10 are intermittently or continuously polled by the control device 5. The control device 5 produces and sends the polling signal (an example of a communication signal) to a designated one of the monitoring devices 10. The designated monitoring device 10 that receives the polling signal then produces and sends a reply signal back to the control device 5 along the speaker line 4. If no reply signal is received, 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; possibly due to short-circuiting and/or open-circuiting having 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.

< Control Device 5>

FIG. 2 schematically shows a possible structure of the control device 5. The control device 5 controls communications via the speaker line 4 according to a predetermined communication protocol. For example, the control device 5 polls all monitoring devices 10 to check if a fault or disconnection has occurred in the public address system 1. The polling is an automatic, sequential test to check the operational statuses of the monitoring devices 10, the loudspeakers 3, and the speaker line 4.
The control device 5 includes a first filter unit 51 (an example of a first filter unit), a second filter unit 52 (an example of a second filter unit), a switch 53, a receiver 54a, a transmitter 54b, a CPU (Central Processor Unit) 55 (one example of a processor), an A/D converter 57, and a D/A converter 58.
The first filter unit 51 includes a band-pass filter that is designed to allow an audio signal and a DC signal to pass, and to attenuate any other signal. FIG. 3 shows an example of a structure of the first filter unit 51. The example includes parallel LC circuits serving as a band-pass filter. The filter design is not limited to this configuration, and may utilize any other known band-pass filters or high-pass filters.
The second filter unit 52 is connected to the speaker line 4. The second filter unit 52 includes a band-pass filter that is designed to allow a communication signal including a reply signal to pass, and to attenuate any other signal.
The switch 53 is connected to the second filter unit 52 via a transformer. The switch 53 switches between the receiver 54a and the transmitter 54b to receive and send signals from and to the speaker line 4 according to a command from the CPU 55.
The receiver 54a receives a communication signal, a reply signal for example, from the monitoring devices 10 connected to the speaker line 4 via the second filter unit 52. The receiver 54a then sends the communication signal to the CPU 55 via the A/D converter 57. The transmitter 54b sends a communication signal received from the CPU 55 via the D/A converter 58, a polling signal for example, to the monitoring devices 10 via the speaker line 4.
The A/D converter 57 converts an analog communication signal into a digital communication signal to be processed by the CPU 55. The D/A converter 58 converts a digital communication signal that has been processed by the CPU 55 into an analog communication signal.
The CPU 55 controls the reception and transmission of the communication signal. The CPU 55 produces a polling signal and sends the polling signal to a designated monitoring device 10 connected to the speaker line 4. The polling signal includes address data of the designated monitoring device 10. The CPU 55 also receives a reply signal from the designated monitoring device 10. Accordingly, the CPU 55 sends a polling signal to each of the designated monitoring devices 10 and determines whether a reply signal from each of the designated monitoring devices 10 has been received. Thus, the CPU 55 detects the status of the public address system 1. The CPU 55 then outputs information regarding the status of the public address system 1. For example, the CPU 55 outputs fault data or 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 CPU 55 may perform the above operations of the public address system 1 according to a program read from a memory (not shown).

FIG. 4 schematically shows a possible structure of the monitoring device 10. In this embodiment, the left side of the monitoring device 10 as shown in FIG. 4 is referred to as an "upstream side", and is nearer to the control device 5 along the speaker line 4. The right side of the monitoring device 10 as shown in FIG. 4 is referred to as a "downstream side", and is nearer to an end loop of the speaker line 4.
The monitoring device 10 has its own unique address (for example, an IP address) or identification information for identifying the monitoring device 10. The monitoring device 10 includes an isolating unit 11 (one example of an isolating unit) connected to the speaker line 4, a filter unit 12, a switch 13, a receiver 14a, a transmitter 14b, a CPU (Central Processor Unit) 15 (one example of a control unit), an A/D converter 17, and a D/A converter 18. The monitoring device 10 also includes a filter unit 61, a rectifier 62, and a DC power supply 63.
The isolating unit 11 is provided on the speaker line 4. As shown in FIG. 5, the isolating unit 11 includes a switch 111, a comparator 112, and a relay control 113. In a normal state, the speaker line 4 continuously carries direct current. The comparator 112 compares the voltages at both ends of the switch 111 and outputs a result of the comparison to the relay control 113. When a disconnection occurs between the monitoring devices 10 on the speaker line 4, current is stopped and the voltages at both ends of the switch 111 become different. The relay control 113 monitors and detects the difference of the voltages to determine whether disconnection in the speaker line 4 occurs. When the relay control 113 determines that disconnection in the speaker line 4 occurs, the relay control 113 opens the switch 111, so that the monitoring device 10 is isolated from the speaker line 4. The isolated monitoring device 10 is no longer able to send a communication signal; subsequently, the control device 5 can determine that a disconnection occurred around the monitoring device 10 from which no reply signal is received.
The filter unit 12 shown in FIG. 4 is connected to the speaker line 4. The filter unit 12 includes a band-pass filter that is designed to allow passage of a communication signal and attenuate any other signal.
The switch 13 is connected to the filter unit 12 via a transformer. The switch 13 switches between the receiver 14a to receive signals from the speaker line 4, and the transmitter 14b to send signals to the speaker line 4 according to a command from the CPU 15.
The receiver 14a receives a communication signal, a polling signal for example, from the control device 5. The receiver 14a then sends the communication signal to the CPU 15 via the A/D converter 17. The transmitter 14b sends a communication signal received from the CPU 15 via the D/A converter 18, a reply signal for example, to the control device 5.
The A/D converter 17 converts an analog communication signal into a digital communication signal to be processed by the CPU 15. The D/A converter 18 converts a digital communication signal that has been processed by the CPU 15 into an analog communication signal. The A/D converter 17 and the D/A converter 18 are switched according to a command from the CPU 15.
The CPU 15 is connected to the receiver 14a and the transmitter 14b via the A/D converter 17 and D/A converter, 18. The CPU 15 controls the switching of the switch 13 by producing and sending command signals to the switch 13. The CPU 15 determines whether the received communication signal is directed to the monitoring device 10, or whether the address data of the monitoring device 10 included in the received communication signal is its own. If the address data is its own, the CPU 15 produces a reply signal and sends it to the control device 5.
The CPU 15 also controls its associated loudspeaker 3. The CPU 15 may perform these operations according to a program read from a memory (not shown).
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 receives the rectified DC signal and power the monitoring device 10.

FIG. 6 shows a flow chart of processes performed by the control device 5.

Step S101: A communication signal is produced by the control device 5 for polling. The communication signal includes address data of a designated monitoring device 10.
Step S102: The communication signal is sent out to the speaker line 4, where the communication signal is superimposed onto an audio signal transmitted from the amplifier 2.
Step S103: The communication signal superimposed onto the audio signal is transmitted in the first direction and the second direction of the speaker line 4. For the first direction, the process goes to step S104, and for the second direction, the process goes to step S105.
Step S104: The communication signal superimposed on the audio signal, which is transmitted in the first direction of the speaker line 4, is filtered by the first filter unit 51 such that the communication signal is attenuated and the audio signal is transmitted through the speaker line 4.
Step S105: The communication signal superimposed on the audio signal is transmitted in the second direction of the speaker line 4.
Step S106: The CPU 55 of the control device 5 determines whether a reply signal from the designated monitoring device 10 has been received within a predetermined time.
Step S107: If a reply signal is not received within a predetermined time, the control device 5 determines that there is a fault in the speaker line 4 around the designated monitoring device 10.
Step S108: The CPU 55 of the control device 5 determines whether the polling is finished. If not, the process goes back to step S101 and the control device 5 produces a communication signal for another designated monitoring device 10. By repeating steps S101 to S108, the control device 5 transmits a communication signal to each of the monitoring devices 10 to receive a reply signal from each monitoring device 10.
Step S109: The CPU 55 of the control device 5 produces and outputs the status of the speaker line 4 based on the results of steps S101 to S108. The status of the speaker line 4 may include whether there is a fault in the public address system 1 due to short-circuiting and/or open-circuiting having occurred in the speaker line 4. The status of the speaker line 4 may further include a location where disconnection occurs. For example, if the control device 5 has received a reply signal from one monitoring device 10 but has not received a reply signal from a next monitoring device 10 on the downstream side, the control device 5 then may determine that the disconnection occurs between the two monitoring devices 10.

According to the public address system 1 of the above-described embodiment, the first filter unit 51 is connected to the speaker line 4 such that the communication signal is prevented from being transmitted in the first direction of the speaker line 4 while a communication signal and an audio signal are transmitted in the second direction of the speaker line 4. Therefore, audio signals can be transmitted bi-directionally through the speaker line 4 at any time, and the public address system 1 is able to keep its broadcasting function alive even when disconnection occurs at any point of the speaker line 4.
Furthermore, a communication signal is filtered so as not to pass in the first direction of the speaker line 4. If the communication signal is transmitted through the speaker line 4 bi-directionally in the same way as the audio signal, the communication signal can be transmitted to a designated monitoring device 10 even when disconnection occurs on an upstream side or a downstream side of the designated monitoring device 10. In this case, a fault might not be detected properly since a reply signal from the designated monitoring device 10 could be sent back to the control device 5 in either one of the first or second direction of the speaker line. In the above Embodiment 1, however, the communication signal is allowed to be transmitted only in one direction of the speaker line 4. Therefore, while performing secure broadcasting, the public address system 1 is still able to reliably detect faults in the speaker line 4.

< Embodiment 2>

FIG. 7 schematically shows a structure of a monitoring device 210 according to Embodiment 2. Members having the same functions as in Embodiment 1 will be numbered the same and will not be described in further detail. In this example, each monitoring device 210 transmits a communication signal from one to another in a relay.
The monitoring device 210 includes an isolating unit 211 (an example of an isolating unit) connected to the speaker line 4, a filter unit 221 connected to the speaker line 4, filter units 212a, 212b, a CPU 213, switches 214a, 214b, receivers 215a, 216a, transmitters 215b, 216b, a switch 217, an A/D converter 218, and a D/A converter 219.
The isolating unit 211 is provided on the speaker line 4. The isolating unit 211 has the same structure and functions as the isolating unit 11 (FIG. 5) according to Embodiment 1. Similarly to Embodiment 1, when the relay control 113 determines that disconnection in the speaker line 4 occurs, the relay control 113 controls the switch 111 to open, so that the monitoring device 210 is isolated from the speaker line 4. Accordingly, the isolated monitoring device 210 is no longer able to send a communication signal, and therefore the control device 5 can determine that disconnection occurs around the monitoring device 210 from which no reply signal was received.
The filter unit 221 is provided on the speaker line 4. The filter unit 221 is a band-pass filter that is designed to pass only an audio signal and a DC signal and to attenuate any other signal.
The filter units 212a and 212b are connected to the switches 214a, 214b respectively via transformers. The filter units 212a and 212b include band-pass filters that are designed to allow a communication signal to pass and to attenuate any other signal.
The switch 214a is connected to the filter unit 212a via a transformer. The switch 214a switches between the receiver 215a to receive signals from the speaker line 4, and the transmitter 215b to send signals to the speaker line 4 according to a command from the CPU 213. Initially, the switch 214a is switched to the receiver 215a and stands ready to receive a signal from the upstream side of the speaker line 4. After the signal has been received from the upstream side, the switch 214a is then switched to the transmitter 215b to send a signal to the upstream side of the speaker line 4.
The switch 214b switches between the receiver 216a to receive signals from the speaker line 4, and the transmitter 216b to send signals to the speaker line 4 according to a command from the CPU 213. Initially, the switch 214b is switched to the transmitter 216b that is ready to send a signal to the downstream side of the speaker line 4. After the signal has been sent to the downstream side, the switch 214b is then switched to the receiver 216a to receive a signal from the downstream side of the speaker line 4.
The receiver 215a receives a communication signal from a monitoring device 10 on the upstream side via the filter unit 212a. The receiver 215a then sends the communication signal to the CPU 213 via the A/D converter 218. The transmitter 215b sends a communication signal received from the CPU 213 to the monitoring device 210 on the upstream side via the D/A converter 219. The receiver 216a receives a communication signal from a monitoring device 210 on the downstream side via the filter unit 212b. The receiver 216a then sends the communication signal to the CPU 213 via the A/D converter 218. The transmitter 216b sends a communication signal received from the CPU 213 to the monitoring device 210 on the downstream side via the D/A converter 219.
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 an analog communication signal received by receivers 215a and 216a is converted into a digital communication signal. The switch 217 is switched to the D/A converter 219 when a digital communication signal is converted into an analog communication signal.
The A/D converter 218 converts an analog communication signal into a digital communication signal for processing by the CPU 213. The D/A converter 219 converts a digital communication signal that has been processed by the CPU 213 into an analog communication 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 monitoring device 210 on the downstream side and a next monitoring device 210 on the upstream side, or the control device 5 if the CPU 213 is an initial monitoring device connected to the speaker line 4 next to the control device 5.
The CPU 213 determines whether the received communication signal is directed to the monitoring device 210, or whether the address data of the monitoring device 210 included in the received communication signal is its own. If the address data is not its own, the CPU 213 transmits the received communication signal to a next monitoring device 210 on the downstream side. If the address data is of its own, the CPU 213 produces a reply signal and sends it to a monitoring device 20 on the upstream side, or the control device 5.
Similarly to Embodiment 1, the monitoring device 210 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 receives the rectified DC signal and powers the monitoring device 210.
The reply signal may include the address data or identification information of the monitoring device 210 that has produced and transmitted the reply signal. The control device 5 that has received such a reply signal will then be able to identify which part of the speaker line is in trouble, based on the address data or identification information.
In this example the superimposed signal, containing an audio signal and a communication signal that includes a polling signal and a reply signal, is filtered by the filter unit 221 so that the communication signal is prevented from passing to the downstream side of the speaker line 4. Accordingly, a communication signal always passes between one transmission source and one destination. When the control device 5 polls one of the monitoring devices 210 connected to the speaker line 4, a polling signal sent from the control device 5 is first sent to a monitoring device 210 (hereinafter called a "first monitoring device 210") that is nearest to the control device 5. At the same time, the polling signal is filtered by the filter unit 221 of the first monitoring device 210 so as not to pass through the speaker line 4 to a monitoring device 210 (hereinafter called a "second monitoring device 210") on the downstream side of the first monitoring device 210.
If the polling signal is not designated for the first monitoring device 210, the CPU 213 of the first monitoring device 210 transfers the polling signal to the second monitoring device 210. Then the filter unit 221 of the second monitoring device 210 filters the polling signal so as stop the polling signal from passing through the speaker line 4 to a monitoring device 210 (hereinafter called a "third monitoring device 210") on the downstream side of the second monitoring device 210. This relay transmission of the communication signal is performed until the polling signal reaches a designated monitoring device 210.
When the designated monitoring device 210 receives the polling signal, it sends a reply signal. In a way similar to the transmission of a polling signal, a reply signal is transferred in a relay from one monitoring device to another, from the downstream side to the upstream side, until the reply signal is received by the control device 5.
In this example, a communication signal including a reply signal in response the polling signal passes only between two neighboring devices on the speaker line 4 while the communication signal is prevented from passing between any of other two neighboring devices on the speaker line 4. Accordingly, during polling, the communication signal always passes only between one transmission source and one destination, except for which the communication signal is not allowed to pass.
According to Embodiment 2, the following effects are achieved in addition to the effects described in Embodiment 1. In Embodiment 2, each monitoring device 210 needs power only when receiving and sending a communication signal. Thus, the other monitoring devices 210 that are not in operation for processing the communication signal can be set in a sleep mode with least power. As a result, the communication signal can be prevented from being attenuated and the communication quality in the public address system 1 is enhanced; further stable communication is assured with less power. Since high current can be prevented from passing through the speaker line 4, even a number of loudspeakers 3 with low impedance can be connected to the speaker line 4 in parallel.

< Other Embodiments>

The control device 5 may send a communication signal without a designated address. For example, the control device 5 can transmit a communication signal in the looped speaker line 4 and determine whether the communication signal has returned to the control device 5. In this case, the control device 5 is arranged such that the CPU 55 receives a return signal without filtering by the second filter unit 52 (FIG. 2).
The control device 5 may not include the second filter unit 52, but instead, the second filter unit 52 may be included in another device connected to the speaker line 4, or may be directly connected to the speaker line 4.
Frequencies of the signals described above are not limited to those described in the above embodiments.
AC current may be supplied to the speaker line 4 instead of DC current.
Digital audio signals may be applied to the public address system 1. In this case, the audio signals are converted from digital into analog, and are then modulated and imposed on DC on the speaker line 4. The modulated audio signals include address data for one or more monitoring devices 10 (or 210), and are transmitted to one or more designated monitoring derives 10 (or 210).

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.
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.

Industrial Applicability

The invention may be utilized as a public address system or a communication controller for loudspeakers used in a large-scale facility or building.

Reference Signs List

1: Public address system
2: Amplifier
3: Loudspeaker
4: Speaker line (one example of a transmission medium)
5: control device (one example of a control device)
10: Monitoring device (one example of a communication controller)
11: Isolating unit (one example of an isolating unit)
12: Filter unit
13: Switch
14a: Receiver
14b: Transmitter
15: CPU (one example of a control unit)
51: First filter unit (one example of a first filter unit
52: Second filter unit (one example of a second filter unit)
53: Switch
54a: Receiver
54b: Transmitter
55: CPU (one example of a processor)
57: A/D converter
58: D/A converter
61: Filter unit
62: Rectifier
63: DC supply
210: Monitoring device (one example of a communication controller)
211: Isolating unit (one example of an isolating unit)
221: Filter unit
212a, 212b: Filter unit
213: CPU (one example of a control unit)
214a, 214b: Switch
215a, 216a: Receiver
215b, 216b: Transmitter
217: Switch
218: A/D converter
219: D/A converter

[Citation List]

[Patent Literature]

[PTL 1] US2003/0063755A

Claims

A public address system (1) comprising:
a transmission medium (4) having a loop shape and configured to transmit a transmission signal therethrough in a first direction and in a second direction opposite to the first direction, the transmission signal including a communication signal having a predetermined frequency range and an audio signal having a different frequency range than the communication signal;

a plurality of loudspeakers (3) connected to the transmission medium (4);

characterized by

a first filter unit (51) connected to the transmission medium (4) and configured to filter the transmission signal to attenuate the communication signal and output the audio signal

wherein the first filter unit (51) is connected to the transmission medium (4) such that the communication signal is prevented from transmission in the first direction while the communication signal and the audio signal are transmitted in the second direction.
The public address system (1) according to claim 1, further comprising:
a control device (5) connected to a first end of the loop of the transmission medium (4) and to a second end of the loop of the transmission medium (4), wherein

the transmission signal includes the communication signal and the audio signal combined together,

the control device (5) transmits the transmission signal to the transmission medium (4) both in the first direction through the first end of the loop and in the second direction through the second end of the loop, and

the first filter unit (51) attenuates the communication signal before the transmission signal is transmitted in the first direction.
The public address system (1) according to claim 2, further comprising a plurality of communication controllers (10) connected to the transmission medium (4), each of the plurality of communication controllers (10) being connected to a corresponding loudspeaker (3), wherein,
the communication signal is a polling signal,
the audio signal is an audio signal,
the control device (5) transmits the polling signal to poll each of the plurality of communication controllers (10), and
the loudspeaker (3) corresponding to each communication controller (10) output sound based on the audio signal.
The public address system (1) according to claim 1, further comprising a plurality of communication controllers (10) connected to the transmission medium (4), wherein
each of the communication controllers (10) includes an isolating unit connected to the transmission medium (4) and each isolating unit is configured to isolate its corresponding communication controller (10) from the transmission medium (4) when the isolating unit detects a fault in the transmission medium (4).
A control device (5) applied to a public address system including a transmission medium (4) having a loop shape and a plurality of loudspeakers (3) connected to the transmission medium (4), the control device (5) being connected to both ends of the transmission medium (4),
the control device (5) being configured to transmit a transmission signal through the transmission medium (4) in a first direction and in a second direction opposite to the first direction, the transmission signal including a communication signal having a predetermined frequency range and an audio signal having a different frequency range than the communication signal,
characterized in that
the control device (5) comprises:
a first filter unit (51) configured to filter the transmission signal to attenuate the communication signal and output the audio signal; and

a second filter unit (52) configured to filter the transmission signal to attenuate the audio signal and output the communication signal

wherein the first filter unit (51) is connected to the transmission medium (4) such that the communication signal is prevented from transmission in the first direction while the communication signal and the audio signal are transmitted in the second direction.