EP2875652B1

EP2875652B1 - Public address system and monitoring device for a public address system

Info

Publication number: EP2875652B1
Application number: EP12745575.6A
Authority: EP
Inventors: Tomohiro JONAN
Original assignee: Toa Corp
Current assignee: Toa Corp
Priority date: 2012-07-20
Filing date: 2012-07-20
Publication date: 2019-12-04
Anticipated expiration: 2032-07-20
Also published as: EP2875652A1; WO2014013530A1; JP6033397B2; JP2015525985A

Description

[TECHNICAL FIELD]

The invention relates to a public address system having a number of loudspeakers. More specifically, the invention relates to a public address system including a branched transmission medium and a monitoring device for the 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, as 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 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 within specified areas in the event of an emergency. The EN 60849 standard requires a redundant system that assures operability of its alarm function even when a disconnection in the line is present.
US 2007/0035407 A and US 4528610 A disclose a public address system and a short circuit fault isolation system respectively, comprising a transmission medium including a main transmission path and at least one branch transmission path branching from the main transmission path, the transmission medium being configured to carry a transmission signal.

[SUMMARY OF INVENTION]

[TECHNICAL PROBLEM]

The public address system may include one or more branches of a speaker line so that signals are transmitted in a divergent manner. Previously there was no solution to redundantly secure a public address system with branched speaker line.
One object of the invention as disclosed herein is to achieve improved reliability for broadcasting from a public address system that utilizes a branched signal transmission path.

[SOLUTION TO PROBLEM]

An embodiment of the invention includes a public address system according to claim 1.

[ADVANTAGEOUS EFFECTS OF INVENTION]

According to the above embodiment of the invention, it is possible to achieve improved reliability for broadcasting from a public address system that utilizes a branched signal transmission path.

[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 the public address system in a state that disconnection has occurred in a branched speaker line;
[fig. 3]
FIG. 3 is a schematic diagram of a control device for the public address system shown in FIG. 1;
[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 monitoring device shown in FIG. 4;
[fig. 7]
FIG. 7 is a schematic diagram of a public address system according to Embodiment 2 which does not form part of the claimed invention;
[fig. 8]
FIG. 8 is a schematic diagram of a monitoring device according to Embodiment 2.

[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 for illustration only 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 (an 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. In this embodiment, the left side of the public address system 1 as shown in FIG. 1 is referred to as an "upstream side", which is nearer to the amplifier 2 along the speaker line 4. The right side of the public address system 1 as shown in FIG. 1 is referred to as a "downstream side".
The public address system 1 includes an amplifier 2, a number of loudspeakers 3, a speaker line 4 (an example of a transmission medium), a control device 5, and a number of monitoring devices 10 each associated with a different loudspeaker 3.
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 also 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 includes a main transmission path 4-1 (an example of a main transmission path) and a branch transmission path 4-2 (an example of a branch transmission path) that is branched from the main transmission path 4-1. The branch transmission path 4-2 is connected to a plurality of loudspeakers 3. The branch transmission path 4-2 joins the main transmission path 4-1 on a downstream side of the speaker line 4 (which is the right side shown in FIG. 1). The main transmission path 4-1 of the speaker line 4 may be arranged in a loop.
The speaker line 4 may be a power line for the loudspeakers 3. The power supply in this embodiment is a DC (Direct Current) power supply.
In the public address system 1, the amplifier 2 outputs an audio signal to broadcast in 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 power supplied from a power source (not shown) and transmitted through the speaker line 4. The control device 5 produces and outputs a communication signal. The communication signal may have a frequency greater than or equal to 60 kHz. The communication signal is then superimposed on the audio signal and DC power transmitted through the speaker line 4. The superimposed signal (an example of a transmission signal) including an audio signal and a communication signal is sent through the speaker line 4.
The monitoring devices 10 are polled by the control device 5 intermittently or continuously. The polling signal, which is an example of a communication signal, is produced by and sent from the control device 5 to a designated monitoring device 10. The designated monitoring device 10 that receives the polling signal produces and sends a reply signal to the control device 5 through the speaker line 4. If a reply signal is not received within a predetermined time, it is assumed that the designated monitoring device 10 is not responding, and it may be concluded that there is a fault or disconnection in the public address system 1 due to short-circuiting and/or open-circuiting of speaker line 4.

«Normal State»

In a normal state, in which no fault or disconnection has been detected in the public address system 1 as shown in FIG. 1, the superimposed signal S-1 from the amplifier 2 is transmitted downstream through the speaker line 4. The superimposed signal S-1 is then carried by both the main transmission path 4-1 and the branch transmission path 4-2. The superimposed signal S-1 passes through the branch transmission path 4-2 until it reaches the monitoring device 10b. A monitoring device 10a is arranged at a branch point (an example of a first branch point) where the branch transmission path 4-2 begins as shown in FIG. 1 and FIG. 2. It transmits the superimposed signal S-1, received from the main transmission path 4-1, into the branch transmission path 4-2 while simultaneously letting the superimposed signal S-1 go through the main transmission path 4-1.
Another monitoring device 10b is arranged at another branch (an example of a second branch point) where the branch transmission path 4-2 ends, as shown in FIG. 1 and FIG. 2. The monitoring device 10b serves to receive the superimposed signal S-1 from the branch transmission path 4-2 while letting the superimposed signal S-1 go through the main transmission path 4-1. The monitoring device 10b monitors the superimposed signal S-1 received from the branch transmission path 4-2.

«Disconnected State»

When any fault or disconnection has occurred in the branch transmission path 4-2, as shown in FIG.2, the superimposed signal S-1 is not received by the monitoring device 10b from the branch transmission path 4-2. The monitoring device 10b detects whether the superimposed signal S-1 is received from the branch transmission path 4-2. When the monitoring device 10b detects that there was no transmission of the superimposed signal S-1 from the branch transmission path 4-2, the monitoring device 10b determines that there is some fault or disconnection in the branch transmission path 4-2, and then starts transmitting the superimposed signal S-2, from the main transmission path 4-1 into the branch transmission path 4-2. At the same time, the monitoring device 10b allows the superimposed signal S-1 received through the main transmission path 4-1 to be transmitted to its downstream side.
Accordingly, even if a disconnection or fault occurs in the branch transmission path 4-2 that disables the superimposed signal S-1 from passing through the branch transmission path 4-2, which is received from the monitoring device 10a located at a branch point where the branch transmission path 4-2 begins, the transmission of the superimposed signal through the branch transmission path 4-2 can be recovered by another monitoring device 10b located at another branch point where the branch transmission path 4-2 ends. As a result, the branch transmission path 4-2 can be kept more secure due to redundancy in the public address system 1.
A detailed description of each device connected to the speaker line 4 in the public address system 1 will now be made.

< Control Device 5>

FIG. 3 schematically shows a structure of the control device 5. The control device 5 controls communication via the speaker line 4 according to a predetermined communication protocol. 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 testing that checks the operational statuses of the monitoring devices 10, the loudspeakers 3, and the speaker line 4. In the drawing, the speaker line 4 is shown as a single line for simplicity.
The control device 5 includes a filter unit 51, a receiver 53, a transmitter 54, an A/D converter 55, a D/A converter 56, and a CPU 57 (an example of a processor).
The filter unit 51 is connected to the speaker line 4. The filter unit 51 includes a band-pass filter that is designed to allow passage of a communication signal, including a reply signal, and attenuate any other signal.
The receiver 53 and the transmitter 54 are switched to one another to receive and send signals from and to the speaker line 4 by a switch (not shown) according to a command from the CPU 57. The receiver 53 receives a communication signal, for example a reply signal, from the respective monitoring devices 10 connected to the speaker line 4 via the filter unit 51. The receiver 53 then sends the communication signal to the CPU 57 via the A/D converter 55. The transmitter 54 sends a communication signal received from the CPU 57 via the D/A converter 56 to the monitoring devices 10 on the speaker line 4. The communication signal received from the CPU 57 is, for example, a polling signal.
The A/D converter 55 converts an analog communication signal into a digital communication signal to be processed by the CPU 57. The D/A converter 56 converts a digital communication signal that has been processed by the CPU 57 into an analog communication signal.
The CPU 57 controls the reception and transmission of a communication signal. The CPU 57 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 57 also receives a reply signal from the designated monitoring device 10.
The CPU 57 may sequentially send a polling signal to each monitoring device 10 and determines whether a corresponding reply signal from each of the designated monitoring device 10 has been received; thereby detecting the status of the public address system 1. The CPU 57 then outputs status information of the public address system 1. For example, the CPU 57 outputs fault data or information about the public address system 1 to an external management system which monitors and controls operation of the public address system 1 via a network. The CPU 57 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 structure of the monitoring device 10. In this embodiment, the left side of the monitoring device 10 as shown in FIG. 4 is an upstream side, and the right side of the monitoring device 10 as shown in FIG. 4 is a downstream side. The monitoring device 10 may serve as a monitoring device 10a or a monitoring device 10b at a branch point, which is operated differently from monitoring devices not at branch points. The monitoring device 10a (hereinafter called a first branch monitoring device 10a) is provided at a beginning branch point from which the superimposed signal S-1 is transmitted into the branch transmission path 4-2, as shown in FIG. 1 and FIG. 2. The monitoring device 10b (hereinafter referenced as a second branch monitoring device 10b) is provided at an end branch point where the superimposed signal S-1 is received from both the main transmission path 4-1 and the branch transmission path 4-2.
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 connected to the speaker line 4, a filter unit 12 (an example of a filter unit), a receiver 13, a transmitter 14, an A/D converter 15, a D/A converter 16, a CPU (Central Processor Unit) 17 (an example of a control unit), a main monitoring unit 18a, a branch monitoring unit 18b, and a DC power supply 19. The monitoring device 10 further includes a switch 20 (an example of a switch) to be connected to the branch transmission path 4-2 that is branched from the main speaker line 4-1 at a branch point 40. The monitoring device 10 also includes an input 60. The input 60 is operated by a user, and it produces and outputs a selection signal to the branch monitoring unit 18b. The branch monitoring unit 18b switches the switch 20 according to the selection signal from the input 60, as will be described later.
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. The speaker line 4 continuously carries direct current when in a normal state. 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 any fault or disconnection has occurred between the monitoring devices 10 on the speaker line 4, the current flow is prevented so that the voltages at both ends of the switch 111 become different. The relay control 113 monitors and detects the change in voltage to determine whether a fault or disconnection in the speaker line 4 has occurred. When the relay control 113 determines that a fault or disconnection in the speaker line 4 has occurred, the relay control 113 controls the switch 111 to open, so that the monitoring device 10 is isolated from the speaker line 4. Accordingly, the isolated monitoring device 10 is no longer able to send a communication signal, and the control device 5 can determine that a fault or disconnection occurred near the monitoring device 10 when 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 a communication signal to pass, and attenuate other signals.
The receiver 13 and the transmitter 14 are switched to one another to receive signals from and send signals to the speaker line 4 by a switch (not shown) according to a command from the CPU 17. The receiver 13 receives a communication signal; for example, a polling signal from the control device 5. The receiver 13 then sends the communication signal to the CPU 17 via the A/D converter 15. The transmitter 14 sends a communication signal received from the CPU 17 via the D/A converter 16, a reply signal for example, to the control device 5.
The A/D converter 15 converts an analog communication signal into a digital communication signal to be processed by the CPU 17. The D/A converter 16 converts a digital communication signal that has been processed by the CPU 17 into an analog communication signal. The A/D converter 15 and the D/A converter 16 are switched according to a command from the CPU 17.
The CPU 17 is connected to the receiver 13 and the transmitter 14 via the A/D and D/ A converters 15, 16. The CPU 17 determines whether the received communication signal is directed to the monitoring device 10 itself by determining whether the address data of the monitoring device 10 matches the data included in the received communication signal. If the address data matches its own address, the CPU 17 produces a reply signal and sends it to the control device 5. The CPU 17 also controls its associated loudspeaker 3. The CPU 17 may perform these operations according to a program read from a memory (not shown).
The main monitoring unit 18a is connected to the main transmission path 4-1 of the speaker line 4. The main monitoring unit 18a monitors the transmission of the superimposed signal S-1 through the main transmission path 4-1.
The branch monitoring unit 18b is connected to the branch transmission path 4-2 of the speaker line 4 at a branch point 40 where the branch transmission path 4-2 is branched from the main transmission path 4-1. The branch monitoring unit 18b is operated only when the monitoring device 10 is set up as a second branch monitoring device 10b. The branch monitoring unit 18b monitors the transmission of the superimposed signal S-1 from the branch transmission path 4-2 to the switch 20. The transmission of the superimposed signal S-1 may be detected by monitoring, for example, voltage shift. When the branch monitoring unit 18b detects that there is no transmission of the superimposed signal S-1 from the branch transmission path 4-2, the branch monitoring unit 18b produces a signal to switch the switch 20 to the ON position.
The DC power supply 19 receives a DC signal, which is received from the speaker line 4. The DC signal is rectified to power the monitoring device 10.
The switch 20 allows passage of the superimposed signal S-1 from the main transmission path 4-1 into the branch transmission path 4-2 when it is in the ON position (an example of a first position). When the switch 20 is in the OFF position (an example of a second position), the passage of the superimposed signal S-1 from the main transmission path 4-1 into the branch transmission path 4-2 is blocked. The ON and OFF positions may be applied vice versa. When the monitoring device 10 is a first branch monitoring device 10a, the switch 20 is in the ON position to allow the superimposed signal S-1 from the main transmission path 4-1 into the branch transmission path 4-2. When the monitoring device 10 is a second branch monitoring device 10b, the switch 20 is initially in the OFF position to prevent the superimposed signal S-1 from the main transmission path 4-1 into the branch transmission path 4-2.
At the second branch monitoring device 10b, the branch monitoring unit 18b is operated to monitor the transmission of the superimposed signal S-1 from the branch transmission path 4-2 to the switch 20. When the branch monitoring unit 18b detects that there is no transmission of the superimposed signal S-1 from the branch transmission path 4-2, it is assumed to indicate a disconnection or fault has occurred in the branch transmission path 4-2. The branch monitoring unit 18b then sends a signal to the switch 20 to switch to the ON position, which allows passage of the superimposed signal S-2 from the main transmission path 4-1 into the branch transmission path 4-2. When the monitoring device 10 is neither a first branch monitoring device 10a nor a second branch monitoring device 10b (hereinafter referenced as a non-branch monitoring device 10), the switch 20 is switched to the OFF position.
The second branch monitoring device 10b produces and sends a detection signal to the control device 5 via the main transmission path 4-1 when it has detected that there is no transmission of the superimposed signal S-1 from the branch transmission path 4-2. Upon receiving the detection signal from the second branch monitoring device 10b, the control device 5 determines that a disconnection or fault has occurred in the branch transmission path 4-2 connected to the branch monitoring device 10b. Therefore, the control device 5 is able to identify which branch path has a disconnection or fault based on the address data included in the detection signal sent from the second branch monitoring device 10b.
The input 60 is operated manually or by any other means. The input 60 is operated by a user, and it produces and outputs a selection signal to the branch monitoring unit 18b. According to the selection signal from the branch monitoring unit 18b, the switch 20 is switched to the ON or OFF position so that the monitoring device 10 can be set up as a first branch monitoring device 10a, a second branch monitoring device 10b, or a non-branch monitoring device 10.
The selection signal may be:

(i) a signal that activates the branch monitoring unit 18b to hold the switch 20 in the ON position when the monitoring device 10 is set up as a first branch monitoring device 10a that is located at a branch point where the branch transmission path 4-2 begins;
(ii) a signal that activates the branch monitoring unit 18b to hold the switch 20 in the OFF position and monitor the branch transmission path 4-2 when the monitoring device 10 is set up as a second branch monitoring device 10b that is located at a branch point where the branch transmission path 4-2 ends; or
(iii) a signal that activates the branch monitoring unit 18b to keep the switch 20 in the OFF position when the monitoring device 10 is set up as a non-branch monitoring device 10 that is not located at a branch point.

The monitoring device 10 is operated in accordance with the setting of input 60.

During operation of the public address system 1, a superimposed signal S-1 including an audio signal and a communication signal is sent from the amplifier 2 and the control device 5. The superimposed signal S-1 is transmitted through the main transmission path 4-1. At a first branch monitoring device 10a, the superimposed signal S-1 is transmitted into the branch transmission path 4-2 and simultaneously transmitted through the main transmission path 4-1. The superimposed signal S-1 is then transmitted through the branch transmission path 4-2 to a second branch monitoring device 10b..
When the branch monitoring unit 18b of the branch monitoring device 10b detects that there is no transmission of the superimposed signal S-1 due to a disconnection or fault having occurred in the branch transmission path 4-2, the switch 20 is switched to the ON position by the branch monitoring unit 18b of the branch monitoring device 10b. Then, the superimposed signal S-2, which is branched from the superimposed signal S-1 transmitted through the main transmission path 4-1, is transmitted to the branch transmission path 4-2 by the second branch monitoring device 10b. The superimposed signal S-2 is then transmitted through the branch transmission path 4-2 to the first branch monitoring device 10a and then to the main transmission path 4-1.

FIG. 6 shows a flow chart of processes performed by a branch monitoring device 10b according to Embodiment 1 as shown in FIG. 4.
When the monitoring device 10 is set up as a second branch monitoring device 10b, the processes steps S101 to S105 are performed. Although not described below, the main monitoring unit 18a of each monitoring device 10 always monitors the transmission path whether or not the monitoring device 10 is a branch monitoring device.
Step S101: When the monitoring device 10 is a second branch monitoring device 10b, the process goes to step S102.
Step S102: A superimposed signal S-1 including an audio signal and a communication signal is received by the branch monitoring device 10b from the branch transmission path 4-2. At this step, the switch 20 is held in the OFF position so that the superimposed signal S-1 is blocked from passing through the switch 20. Also at this step, the branch monitoring unit 18b is monitoring the branch transmission path 4-2.
Step S103: The branch monitoring unit 18b determines whether it has detected a transmission of the superimposed signal S-1 through the branch transmission path 4-2. If no transmission of the superimposed signal S-1 is detected, the process goes to step S104.
Step S104: The branch monitoring unit 18b switches the switch 20 to the ON position, so that the superimposed signal S-2 is allowed to pass through the switch 20 from the main transmission path 4-1 into the branch transmission path 4-2.
Step S105: A detection signal is then produced and sent to the control device 5 via the main transmission path 4-1.
In addition, when a first branch monitoring device 10a receives the polling signal as a communication signal included in the superimposed signal S-1, and the polling signal is determined to be designated to the first branch monitoring device 10a based on the address data, the polling signal is transmitted to neither the main transmission path 4-1 on its downstream side nor the branch transmission path 4-2. If the polling signal is determined to be designated to a monitoring device other than the first branch monitoring device 10a, the polling signal is transmitted to both the main transmission path 4-1 on its downstream side and the branch transmission path 4-2.
Similarly, when a second branch monitoring device 10b receives the polling signal and the polling signal is determined to be designated to the second branch monitoring device 10b, the polling signal is not transmitted to the main transmission path 4-1 on the downstream side of the second branch monitoring device 10b. If the polling signal is determined to be designated to a monitoring device other than the second branch monitoring device 10b, the polling signal is transmitted to the main transmission path 4-1 on its downstream side.

According to the public address system 1 of the above-described embodiment, the second branch monitoring device 10b allows a superimposed signal S-2 to be transmitted into the branch transmission path 4-2 only when the second branch monitoring device 10b has detected that there is no transmission of the superimposed signal S-1 from the branch transmission path 4-2. Accordingly, even if a disconnection or fault occurs in the branch transmission path 4-2 that disables the superimposed signal S-1 to pass through the branch transmission path 4-2, the transmission of the superimposed signal S-1 through the branch transmission path 4-2 can be recovered by another branch monitoring device 10b. As a result, the branch transmission path 4-2 of the public address system 1 can be kept more secure using redundancy.
Furthermore, since the branch monitoring device 10b is provided with a switch 20 that is held in the OFF position to block the superimposed signal S-1 from passing from the branch transmission path 4-2 to the main transmission path 4-1 when in a normal state, it is possible to prevent a communication signal from being sent to monitoring devices 10 on the downstream side through both the main transmission path 4-1 and the branch transmission path 4-2.
In operation, the public address system 1 according to Embodiment 1 acts as follows.
In a normal state, no fault or disconnection is being detected in the public address system 1 as shown in FIG. 1. In this normal state, the first branch monitoring device 10a, in which the switch 20 is held in the ON position, allows passage of the superimposed signal S-1 to both the main transmission path 4-1 and the branch transmission path 4-2. The branch monitoring device 10b, in which the switch 20 is held in the OFF position, monitors a transmission of the superimposed signal S-1 from the branch transmission path 4-2 to the branch monitoring device 10b while keeping allowing passage of the superimposed signal S-1 through the main transmission path 4-1. The non-branch monitoring device 10, in which the switch 20 is held in the OFF position, allows passage of the superimposed signal S-1 through the main transmission path 4-1. In this normal state, the superimposed signal S-1 is able to reach each monitoring device 10 and its corresponding loudspeaker 3. Therefore, all the loudspeakers 3 connected to the main transmission path 4-1 and the branch transmission path 4-2 are able to output sounds based on the audio signal included in the superimposed signal S-1.
In a disconnected state in which a fault or disconnection has occurred, for example, at a point between the monitoring device 10-2 and the monitoring device 10-3 on the branch transmission path 4-2, as shown in FIG.2, the superimposed signal S-1 does not reach the branch monitoring device 10b via the branch transmission path 4-2. When the branch monitoring unit 18b of the branch monitoring device 10b detects there is no transmission of the superimposed signal S-1 from the branch transmission path 4-2, the branch monitoring unit 18b then switches the switch 20 from the OFF position to the ON position, which enables the superimposed signal S-2 to pass from the main transmission path 4-1 into the branch transmission path 4-2 through the switch 20. At this time, as shown in FIG.2, the monitoring devices 10-1 and 10-2 on the branch transmission path 4-2 receive the superimposed signal S-1 from the branch monitoring device 10a, and the monitoring devices 10-3 and 10-4 on the branch transmission path 4-2 receive the superimposed signal S-2 from the branch monitoring device 10b. Accordingly, the sound broadcasting through the branch transmission path 4-2 can be maintained even when a disconnection has occurred in the branch transmission path 4-2.
With the public address system 1, therefore, it is possible to achieve improved reliability for broadcasting from the public address system 1 that utilizes a branched signal transmission path.

The monitoring device 10 may not include a branch monitoring unit 18b. Alternatively, the CPU 17 may be connected to the switch 20 and send an activation signal to the switch 20. The CPU 17 switches the switch 20 to the ON position by the activation signal when the CPU 17 has received a command signal (an example of a communication signal) from the control device 5. In this example, the input 60, which is operated by a user, is connected to the switch 20. The input 60 produces and outputs a selection signal to the switch 20, so that the monitoring device 10 can be set up as a first branch monitoring device 10a, a second branch monitoring device 10b, or a non-branch monitoring device 10, in the same way as the above description in Embodiment 1.
In this example, the control device 5 stores identification information for identifying not only a monitoring device 10 itself but also whether or not the monitoring device 10 is on the branch transmission path 4-2.
The control device 5 polls each monitoring device 10 based on the identification information. For example, when a fault or disconnection has occurred at a point between the monitoring device 10-2 and the monitoring device 10-3 on the branch transmission path 4-2, as shown in FIG.2, the control device 5 is able to receive a reply signal from the monitoring device 10-2 but not from the monitoring device 10-3. Upon detection of no reply from the monitoring device 10-3, the control device 5 determines whether the monitoring device 10-3 is on the branch transmission path 4-2 based on the identification information. When the control device 5 could not receive a reply signal from the polled monitoring device 10-3 and has determined that the polled monitoring device 10-3 is on the branch transmission path 4-2, it can then determine that the branch transmission path 4-2 has a fault or disconnection near the monitoring device 10-3.
The control device 5 then produces and sends a command signal via the main transmission path 4-1 to the branch monitoring device 10b connected at a branch where the branch transmission path 4-2 ends. Upon receiving the command signal from the control device 5, the CPU 17 of the branch monitoring device 10b sends an activation signal to the switch 20 to switch to the ON position. Accordingly, the switch 20 allows the superimposed signal S-2 to pass through the branch monitoring device 10b from the main transmission path 4-1 into the branch transmission path 4-2.

< Public Address system 201>

FIG. 7 schematically shows a public address system 201 according to Embodiment 2. Those members having the same functions as Embodiment 1 will be numbered the same and will not be described in detail.
In this embodiment, the second branch monitoring device 210b always transmits a superimposed signal from a main transmission path 4-1 into a branch transmission path 4-2, regardless of whether a fault or disconnection has been detected in the branch transmission path 4-2.

FIG. 8 schematically shows a monitoring device 210 according to Embodiment 2. The monitoring device 210 is structurally different from the monitoring device 10 of Embodiment 1, and it includes a filter 225 (an example of a filter) and a switch 227 (an example of a switch) connected to the branch transmission path 4-2. The filter 225 is designed to attenuate a communication signal included in the superimposed signal S-1. The switch 227 activates and deactivates the filter 225. When the filter 225 is activated, the superimposed signal S-1 passes through the path 4-2R with the filter 225. When the filter 225 is deactivated, the superimposed signal S-1 passes through the path 4-2F without the filter 225.
The input 260 is operated by a user, and it produces and outputs a selection signal to the switch 227. According to the selection signal from the input 260, the switch 227 is switched to the ON or OFF position so that the monitoring device 210 can be set up as a first branch monitoring device 210a, a second branch monitoring device 210b, or a non-branch monitoring device 210. The selection signal may be:

(i) a signal that holds the switch 227 in the ON position (an example of a first position) to activate the filter 225 when the monitoring device 210 is set up as a second branch monitoring device 210b that is located at a branch point where the branch transmission path 4-2 ends;
(ii) a signal that holds the switch 227 in the OFF position (an example of a second position) to deactivate the filter 225 when the monitoring device 210 is set up as a first branch monitoring device 210a that is located at a branch point where the branch transmission path 4-2 begins; or
(iii) a signal that keeps the switch 227 in the OFF position when the monitoring device 210 is set up as a non-branch monitoring device 210 that is not located at a branch point.

The ON and OFF positions above may be applied vice versa.
In this example, since the superimposed signal is transmitted bi-directionally through the branch transmission path 4-2 at any given time, the monitoring device 210 may not be provided with a branch monitoring unit 18b for monitoring the signal transmission and a switch 20 as Embodiment 1.

During operation of the public address system 201, a superimposed signal S-1 including an audio signal and a communication signal is sent from the amplifier 2 and the control device 5. Like Embodiment 1, the superimposed signal S-1 is transmitted through the main transmission path 4-1. At a first branch monitoring device 210a, the superimposed signal S-1 is transmitted into the branch transmission path 4-2 and simultaneously transmitted through the main transmission path 4-1. When transmitted from the first branch monitoring device 210a, the superimposed signal S-1 passes through a path 4-2F with no filter, which is set up in advance using the switch 227. The superimposed signal S-1 is then carried by the branch transmission path 4-2 to a second branch monitoring device 210b. At the second branch monitoring device 210b, the superimposed signal S-1 passes through a path 4-2R provided with a filter 225, which is set up in advance using the switch 227. At the same time, the second branch monitoring device 210b keeps allowing the superimposed signal S-1 to pass through the main transmission path 4-1.
A filtered transmission signal S-2 (an example of a transmission signal), which has been filtered from the superimposed signal S-1 by the filter 225, is transmitted into the branch transmission path 4-2 by the second branch monitoring device 210b. At the second branch monitoring device 210b, the superimposed signal S-1 passes through the path 4-2R which includes a filter 225. The filter 225 attenuates the communication signal included in the superimposed signal S-1. The remainder of the signal (i.e. other than the communication signal), which is mainly an audio signal, is transmitted through the second branch monitoring device 210b as the filtered transmission signal S-2. The filtered transmission signal S-2 is then transmitted through the branch transmission path 4-2 to the first branch monitoring device 210a. At the first branch monitoring device 210a, the filtered transmission signal S-2 passes through the path 4-2F with no filter.
With the public address system 201, each monitoring device 210 connected to the branch transmission path 4-2 (for example, monitoring devices 210-1 to 210-4 as shown in FIG. 7) sends a reply signal to the control device 5 in response to a polling signal included in the superimposed signal S-1. No reply signal is produced in response to the filtered transmission signal S-2 because the filtered transmission signal S-2 includes no communication signal. In other words, the control device 5 receives reply signals only in response to the superimposed signals S-1. The control device 5 is thus able to properly detect fault or disconnection in the branch transmission path 4-2.
Assuming that the monitoring device 210b allows the superimposed signal S-2 to pass through the path 4-2F without the filter 225 so that all of the monitoring devices 210-1 to 210-4 on the branch transmission path 4-2 receive the polling signals contained in the superimposed signals S-1 and S-2. The monitoring devices 210-1 to 210-4 would then send a reply signal back to the control device 5 in response to each of the superimposed signals S-1 and S-2. In this case, even when a fault or disconnection has occurred in the branch transmission path 4-2 and the control device 5 could not receive a reply signal in response to the superimposed signal S-1, the control device 5 is still able to receive a reply signal in response to the superimposed signal S-2. Therefore, in this case, the control device 5 would not be able to properly detect the fault or disconnection.

According to Embodiment 2, in addition to the effects of Embodiment 1, the second branch monitoring device 210b does not need to monitor or detect the transmission of the superimposed signal S-1 from the branch transmission path 4-2 to the second branch monitoring device 210b. Therefore, it is possible for the public address system 201 to utilize a redundant branched transmission path with simpler operation than Embodiment 1.
In operation, the public address system 201 according to Embodiment 2 acts as follows.
In a normal state, no fault or disconnection has been detected in the public address system 201 as shown in FIG. 7. In this normal state, the first branch monitoring device 210a, in which the switch 227 is held in the OFF position to deactivate the filter 225, allows passage of the superimposed signal S-1 to both the main transmission path 4-1 and the branch transmission path 4-2. The branch monitoring device 210b, in which the switch 227 is held in the ON position to activate the filter 225, allows passage of the superimposed signal S-1 only through the activated filter 225. At the same time, the second branch monitoring device 210b keeps allowing the superimposed signal S-1 to pass through the main transmission path 4-1. The filter 225 attenuates the communication signal included in the superimposed signal S-1 received from the main transmission path 4-1, and the remainder of the signal, which is mainly an audio signal, is transmitted through the second branch monitoring device 210b as a filtered transmission signal S-2. In this normal state, the superimposed signal S-1 is able to reach each monitoring device 210 and its corresponding loudspeaker 3. Therefore, all the loudspeakers 3 connected to the main transmission path 4-1 and the branch transmission path 4-2 are able to output sounds based on the audio signal included in the superimposed signal S-1. Furthermore, the polling signal is included only in the superimposed signal S-1. The monitoring devices 210-1, 210-2, 210-3, and 210-4 connected to the branch transmission path 4-2 as shown in FIG. 7 produce and send a reply signal to a communication signal included in the superimposed signal S-1 sent from the first branch monitoring device 210a when the monitoring devices 210-1, 210-2, 210-3, and 210-4 are polled by the communication signal.
In a disconnected state in which any fault or disconnection has occurred, for example, at a point between the monitoring device 210-2 and the monitoring device 210-3 on the branch transmission path 4-2 shown in FIG.7, the monitoring devices 210-3 and 210-4 are not able to receive the superimposed signal S-1 and therefore, do not produce and send a reply signal. When having received no reply signal from the polled monitoring device 210-3 or 210-4, the control device 5 determines that a fault or disconnection has occurred in the branch transmission path 4-2 on an upstream side of the monitoring device 210-3 or 210-4. Even in this disconnected state, the monitoring devices 210-3 and 210-4 are still able to receive the transmission signal S-2 from the second branch monitoring device 210b. Therefore, the loudspeakers 3 connected to the monitoring devices 210-3 and 210-4 are able to output sounds based on the audio signal carried by the transmission signal S-2. Accordingly, the sound broadcasting through the branch transmission path 4-2 can be maintained even when a fault or disconnection has occurred in the branch transmission path 4-2.

The above embodiments can be applied to a public address system with a speaker line having two or more branches. For example, a branch transmission path 4-2 (FIG. 1) may be further branched into one or more branch transmission paths, in which case the branch transmission path 4-2 is a main transmission path with respect to a branch transmission path that branches from the branch transmission path 4-2.
The main or branch monitoring unit 18a or 18b may not be included in a monitoring device, or may be connected to the speaker line 4 alone or with some other device.
AC (Alternating Current) may be supplied to the speaker line 4 instead of DC.
Digital audio signals may be applied to the public address system. In this case, the audio signals are converted from digital into analog, and are then modulated and superimposed on a DC power on the speaker line 4. The modulated audio signals include address data for one or more monitoring devices, and are transmitted to one or more designated monitoring derives.

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/or vice versa. 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.

[INDUSTRIAL APPLICABILITY]

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

[REFERENCE SIGNS LIST]

1: Public address system
2: Amplifier
3: Loudspeaker
4: Speaker line (an example of a transmission medium)
5: control device
10: Monitoring device
10a: First branch monitoring device (an example of a first branch monitoring device)
10b: Second branch monitoring device (an example of a second branch monitoring device)
11: Isolating unit
12: Filter unit (an example of a filter unit)
13: Receiver
14: Transmitter
15: A/D converter
16: D/A converter
17: CPU (an example of a control unit)
18a: Main monitoring unit
18b: Branch monitoring unit
19: DC supply
20: Switch (an example of a switch)
40: Branch point
51: Filter unit
53: Receiver
54: Transmitter
55: A/D converter
56: D/A converter
57: CPU
60: Input
201: Public address system
210: Monitoring device
225: Filter
227: Switch
260: Input

[CITATION LIST]

[PATENT LITERATURE]

[PATENT LITERATURE 1] US2003/0063755A

Claims

A public address system (1) comprising:
a transmission medium (4) including a main transmission path (4-1) and at least one branch transmission path (4-2) branching from the main transmission path (4-1), the transmission medium (4) being configured to carry a transmission signal; and

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

a plurality of monitoring devices (10) connected to the transmission medium (4), each of which includes an input (60) operative to produce and output a selection signal to selectively set up the monitoring device as a first branch monitoring device (10a) connected to the transmission medium (4) at a first branch point where the branch transmission path (4-2) begins, as a second branch monitoring device (10b) connected to the transmission path (4) at a second branch point where the branch transmission path (4-2) ends, or as a non-branch monitoring device not being located at any branch point;

wherein

the public address system (1) includes:
a monitoring device (10a) which is arranged at the first branch point and is set up as the first branch monitoring device, and

another monitoring device (10b) which is arranged at the second branch point and is set up as the second branch monitoring device,

the first branch monitoring device (10a) set up as the first branch monitoring device (10a) according to the selection signal is configured to transmit the transmission signal from the main transmission path (4-1) into the branch transmission path (4-2) while transmitting the transmission signal through the main transmission path (4-1), and

the second branch monitoring device (10b) set up as the second branch monitoring device (10b) according to the selection signal is configured to:
determine that it has detected a transmission of the transmission signal through the branch transmission path (4-2),

block passage of the transmission signal from the main transmission path (4-1) into the branch transmission path (4-2) if the transmission of the transmission signal through the branch transmission path (4-2) is detected, while transmitting the transmission signal through the main transmission path (4-1), and

allow passage of the transmission signal from the main transmission path (4-1) into the branch transmission path (4-2) if the transmission of the transmission signal through the branch transmission path (4-2) is not detected.
The public address system (1) according to claim 1, wherein
the transmission signal includes a communication signal, the communication signal being a polling signal in response to which the monitoring devices transmit a reply signal.