JP5123319B2 - Speaker line inspection device - Google Patents

Description

  The present invention relates to a speaker line inspection apparatus for inspecting whether or not a problem such as disconnection or short circuit has occurred in a speaker line in a public address system constructed in a building or the like.

  Conventionally, as such an inspection apparatus, for example, there is one disclosed in Patent Document 1. According to Patent Document 1, in a public address system, a plurality of speakers are connected in parallel to a speaker line, and a power amplifier is connected to the speaker line. The audio signal and the test signal are synthesized before the power amplifier, and the power amplifier amplifies the synthesized signal and supplies it to the speaker line. The test signal has a constant voltage. A detection circuit is provided on the output side of the power amplifier. The detection circuit includes a filter that extracts a current of a test signal flowing through each speaker via the speaker line. The output signal from this filter represents the combined impedance of the speaker line and each speaker because the voltage of the test signal is constant. The speaker line inspection device disclosed in the above document compares the value of the output signal from this filter with the disconnection detection threshold and the short detection threshold to determine whether the speaker line is disconnected or short-circuited. . Further, the inspection apparatus uses a filter output signal value when the speaker line is in a normal state as a reference value, and a value obtained by adding a predetermined first value thereto as a disconnection detection threshold value. A value obtained by subtracting the determined second value is used as a short-circuit detection threshold.

JP 2007-37024 A

  As described above, in the conventional inspection apparatus, two threshold values are determined using the output signal value from the filter in a state where the speaker line is normal as a reference value. In order to detect disconnection and short circuit with high accuracy, it is necessary to set these threshold values strictly. However, the output signal value obtained by measuring the above-mentioned inspection apparatus to determine these threshold values, and then the output signal value obtained by measuring in a normal state in which no disconnection or short circuit occurs in the speaker line, Then, the values may vary greatly. For example, measurement is performed with the output signal value obtained by measuring only the test signal being supplied to the speaker line, and the audio signal having various frequencies and the test signal being supplied to the speaker line during public system operation. The value may differ from the output signal value obtained as described above. In particular, when the level of the audio signal is higher than the level of the test signal, the difference in value is significant. Therefore, in the conventional inspection apparatus, by setting the first and second values strictly, there is a possibility of erroneous determination that the wire is disconnected or short-circuited despite being normal.

  It is an object of the present invention to provide an inspection apparatus that can detect such a disconnection or a decrease in impedance of a speaker line with a minimum number of erroneous determinations as much as possible.

An inspection apparatus according to an aspect of the present invention is provided in a public address system. This public address system includes a signal source for audio signals. This audio signal is amplified by an amplifier and supplied to a speaker line. A plurality of speakers are connected in parallel to the speaker line. The inspection apparatus includes a signal source of a test signal including one or both of a frequency near the lowest frequency and a frequency near the highest frequency in a human audible frequency band (generally 20 Hz to 20 KHz). As the test signal, an analog signal can be used, or a digital signal converted into an analog signal by a D / A converter can be used. The test signal is combined with the audio signal by a synthesizer and supplied to the amplifier. Therefore, the amplified audio signal and the test signal are supplied to each speaker via the speaker line. The impedance specifying means extracts the component of the test signal included in the combined signal that is the output signal of the amplifier, and the impedance when the speaker side is viewed from the output side of the amplifier based on the extracted component of the test signal Is identified. For example, the impedance specifying means can specify one or a plurality of impedances by extracting the voltage and current of the test signal included in the output signal of the amplifier. Alternatively, the impedance specifying means can specify one or a plurality of impedances corresponding to the frequency of the test signal by analyzing the frequency of the output signal of the amplifier and extracting the frequency component of the test signal, as will be described later. . The determination means determines at least one of disconnection and impedance reduction of each speaker line by comparing the impedance specified by the impedance specifying means with a predetermined threshold. For example, when a threshold value for disconnection is used, if the measured impedance is larger than the threshold value for disconnection, it is determined that the speaker line is disconnected or one of the speakers is poorly connected. Or when the threshold value for impedance reduction is used, when the specified impedance is smaller than the threshold value for impedance reduction, it is determined that the impedance reduction has occurred in the speaker line. It is also possible to prepare a threshold value for disconnection detection and a threshold value for impedance reduction, and determine both. When the ratio of the synthesized signal to the test signal is larger than a predetermined value and the synthesized signal is increased as compared with the synthesized signal when the previous threshold correction is performed, the threshold is determined by the determination unit. The threshold value correcting means is changed in the direction of decreasing the determination accuracy. The threshold value is set based on, for example, the impedance measured with only the test signal supplied from the amplifier to the speaker line.

  When the ratio of the synthesized signal to the test signal is large, the ratio of the audio signal to the synthesized signal is large, and the speaker line and the impedance of the speaker are affected by the audio signal. Therefore, if the current threshold value is used as it is, there is a possibility of erroneous determination, so the threshold value is changed.

  The threshold value correcting means can increase the determination accuracy, which is lowered when the combined signal is increasing, when the combined signal is changed from an increasing state to a decreasing state. In this case, the change rate in the direction of decreasing the determination accuracy is large, and the change rate in the direction of increasing the determination accuracy is small.

  For example, when the impedance of the speaker line and the speaker changes due to the increase in the level of the audio signal, even if the level of the audio signal subsequently decreases, the impedance changes from the changed state to the original state. May take some time. In order to cope with such a case, the rate of change in the direction of increasing the determination accuracy is reduced.

In the aspect described above , the impedance specifying unit can specify the impedance during a time period when the signal source of the audio signal is stopped. In this case, the threshold setting unit sets the threshold based on the identified impedance. The second determination means determines whether the specified impedance is within a predetermined allowable range.

  The speaker line and the impedance of the speaker change due to aging. Therefore, if the threshold set based on the speaker line and speaker impedance specified at a certain time is used as they are, the actual speaker line and speaker impedance and the speaker line and speaker impedance specified for the threshold There is a gap between them. Therefore, it is possible to prevent erroneous determination by specifying the impedance of the speaker line and the speaker in a time zone when no audio signal is supplied, and setting a threshold based on the impedance. Further, it is possible to know the replacement time of the speaker by determining by the second determination means whether or not the impedance Z thus specified is within the allowable range.

  In the two aspects described above, the impedance identification unit may include a current detection unit that detects a current flowing through the speaker line and a voltage detection unit that detects a voltage applied to the speaker line. In this case, the frequency component of the test signal included in the current detected by the current detector and the voltage detected by the voltage detector is detected by the frequency component detector. The frequency component can be detected by, for example, cross spectrum analysis of the detected current and voltage. The calculating means calculates the impedance from the detected frequency components of the test signal.

  Thus, since the impedance of the speaker line and the speaker is measured based on the test signal component, the impedance of the speaker line and the speaker can be measured without being affected by the audio signal.

FIG. 1 is a block diagram of a public address system in which a speaker inspection apparatus according to an embodiment of the present invention is implemented. FIG. 2 is a flowchart of frequency analysis processing performed by the DSP of the inspection apparatus of FIG. FIG. 3 is a flowchart of an effective value measurement process performed by the DSP of the inspection apparatus of FIG. FIG. 4 is a flowchart of a short circuit, disconnection, impedance increase determination process performed by the DSP of the inspection apparatus of FIG. FIG. 5 is a flowchart of threshold correction processing performed by the DSP of the inspection apparatus in FIG. FIG. 6 is a detailed flowchart of the Zopen and Zinc correction processing in the threshold value correction processing of FIG. FIG. 7 is a diagram showing a change state of the measurement accuracy Ra corrected by the process of FIG. FIG. 8 is a detailed flowchart of the Z1open and Z1inc calculation processing in the Zopen and Zinc correction processing of FIG. FIG. 9 is a flowchart of the aged deterioration determination process performed by the DSP of the inspection apparatus of FIG.

  The inspection apparatus according to one embodiment of the present invention is implemented in a public address system as shown in FIG. Public address systems, for example, amplify voices at various locations in large-scale stores. This public address system has a signal source 2 for audio signals. The signal source 2 may be, for example, a sound source for playing background music in a store, or a microphone for performing store guidance or emergency broadcasting. The audio signal from the signal source 2 is amplified by an amplifier, for example, a power amplifier 4 through a notch filter 3 and supplied to a plurality of speakers 8 through a speaker line 6 connected to the output side of the power amplifier 4. ing. The notch filter 3 is intended to prevent interference with the test signal by attenuating the same frequency component as that of the test signal described later, among the frequency components of the audio signal. Therefore, the audio signal is input to the amplifier through the notch filter 3 only when the test signal is output, and is input to the amplifier without passing through the notch filter 3 when the test signal is not output. Such a circuit configuration may be used. Further, instead of the notch filter 3, a low pass filter, a high pass filter, or both may be used. Each speaker is arranged at various positions in the store. Although only one speaker line 6 is shown in FIG. 1, it is actually a pair of lines. Each speaker 8 is also actually connected in parallel between the pair of speaker lines.

  The inspection apparatus includes a DSP (digital signal processing apparatus) 10 that functions as a signal source of a test signal having an inaudible frequency. The DSP 10 outputs a digital test signal as a test signal. This digital test signal is converted into an analog test signal by the D / A converter 12. The analog test signal and the audio signal from the signal source 2 are synthesized by the synthesizer 13. A combined signal from the combiner 13 is supplied to the power amplifier 4. This analog test signal is a signal including two frequency components of 40 Hz and 20 KHz, for example, and has a constant voltage. The human audible frequency band is generally 20 Hz to 20 KHz. Each speaker 8 is designed to output an optimum sound in this human audible frequency band. The purpose of the test signal is to measure the combined impedance of the speaker line and each speaker 8 connected in parallel thereto. Therefore, the frequency of the test signal is preferably a frequency within the audible frequency band. By combining and outputting, it is not preferable that the test signal component reaches the human ear as noise. Therefore, it is desirable to use the frequency near the lowest frequency of the audible frequency band, the frequency near the highest frequency, or both of them as the frequency of the test signal, which is difficult for humans to hear in the human audible frequency band. A sound signal and a test signal are amplified by the power amplifier 4 and supplied to each speaker 8. The test signal is continuously supplied from the D / A converter 12 to the synthesizer 13. The audio signal is not supplied to the synthesizer 13 when it is unnecessary. Alternatively, the audio signal from the signal source 2 may be combined with a digital test signal after A / D conversion. In this case, the combined signal is supplied to the D / A converter 12.

  A current detection circuit 14 is provided in series on the output side of the power amplifier 4. The current detection circuit 14 detects the output current supplied from the power amplifier 4 to the speaker line 6. Similarly, a voltage detection circuit 16 is provided in parallel on the output side of the power amplifier 4. The voltage detection circuit 16 detects the output voltage supplied from the power amplifier 4 to the speaker line 6.

  The output signal of the current detection circuit 14 and the output signal of the voltage detection circuit 16 are digitized by the A / D converters 18 and 20 and supplied to the DSP 10. The digitized output signal of the current detection circuit 14 is referred to as a digital current detection signal, and the digitized output signal of the voltage detection circuit 16 is referred to as a digital voltage detection signal.

  The DSP 10 processes the digital current detection signal, the digital voltage detection signal, and the digital test signal to determine whether each speaker 8 and speaker line 6 is not disconnected or short-circuited, or each speaker 8 and speaker line 6. It is determined whether the impedance of the battery is greatly reduced. The determination result is notified by the notification device 28 attached to the DSP 10. As the notification device, for example, a display device can be used, and a determination result is displayed.

  In the processing in the DSP 10, the frequency analysis processing shown in FIG. 2 is performed each time the sequentially supplied digital current detection signal and digital voltage detection signal are input to the DSP 10.

  In the frequency analysis process, first, a noise frequency component is removed from the digital current detection signal and the digital voltage detection signal by a band pass filter (step S2). The digital current detection signal and digital voltage detection signal from which the noise frequency component has been removed are averaged (step S4). That is, the same number of memories as the digital current detection signal and digital voltage detection signal for one cycle of the test signal are prepared in the DSP 10, and each time the digital current detection signal and digital voltage detection signal are supplied from the bandpass filter. , Storing in the corresponding memory is performed over a plurality of cycles, and the stored value of each memory is divided by the number of the plurality of cycles. Cross spectrum analysis of the digital current detection signal and digital voltage detection signal thus averaged is performed, and the correlation between the test signal included in the digital current detection signal and the digital voltage detection signal is obtained and included in the test signal. The impedance Z1 at a frequency of 20 kHz, the impedance Z2 at a frequency of 40 Hz, and the coherence of the digital current detection signal and the digital voltage detection signal are calculated (step S6). If the processing capacity of the DSP 10 is high, only the cross spectrum analysis process of step S6 may be performed without performing the processes of step S2 and step S4.

  If the coherent results in that there are many frequency components other than the frequency components of the test signal, for example, the DSP 10 increases the voltage of the test signal having a constant voltage.

  Following the process of FIG. 2, the effective values Vrms and Irms of the digital voltage detection signal and the digital current detection signal are calculated as shown in FIG. 3 (step S8).

  Next, as shown in FIG. 4, using the impedances Z1 and Z2 obtained by the cross spectrum analysis as described above and the effective value Irms of the digital current detection signal, the speaker line 6 and the speaker 8 are short-circuited. It is determined whether any of a drop in impedance (an increase in the output current of the power amplifier 4) or an open circuit has occurred.

  First, the effective value Irms of the digital current detection signal is larger than a predetermined threshold value, for example, the short-circuit current value Isl of the speaker line, or the measured impedance Z1 is a predetermined threshold value, for example, of the speaker line 6 and the speaker 8. It is determined whether the short-circuit impedance Z1sl at 20 KHz is smaller and the measured impedance Z2 is smaller than a predetermined threshold, for example, the short-circuit impedance Z2sl at 40 Hz of the speaker line 6 and the speaker 8 (step S14). The short-circuit current Isl and the short-circuit impedances Z1sl and Z2sl are determined in advance from the viewpoint of protecting the speaker line 6 and the speaker 8. If the answer to the determination in step S14 is yes, it can be determined that the speaker line 8 or the like is in a short circuit state, so a short circuit is displayed (step S16), and this determination process is terminated.

  If the answer to the determination in step S14 is no, it is determined whether the measured impedance Z1 is smaller than the lower limit value Z1inc for 20 KHz or whether the impedance Z2 is smaller than the lower limit value Z2inc for 40 Hz (step S18). . The lower limit values Z1inc and Z2inc will be described later. If the answer to this determination is yes, the speaker line current has not increased until the short-circuit state, but since the output current from the power amplifier 4 has increased to some extent and is in a state of caution, an increase display is performed. (Step S20), the determination process is terminated.

  If the answer to the determination in step S18 is no, it is determined whether the measured impedance Z1 is greater than an upper limit value Z1open for 20 KHz or whether the impedance Z2 is greater than an upper limit value Z2open for 40 Hz (step S22). . The upper limit values Z1open and Z2open will be described later. If the answer to this determination is yes, it can be determined that the speaker line 6 and the speaker 8 are open, so that an open display is made (step S24), and the processing of this determination ends.

  In order to make the above determination, upper limit values Z1open and Z2open and lower limit values Z1inc and Z2inc are used. These are determined based on the reference impedance Z1ave at 20 KHz and the reference impedance Z2ave at 40 Hz of the speaker line 6 and the speaker 8, respectively. The reference impedances Z1ave and Z2ave are set by the worker at the time of initialization when the public address system is installed and used for the first time. Alternatively, it is set by the worker when the public address system is reinitialized for some reason. However, the reference impedances Z1ave and Z2ave may be greatly different from the impedances Z1 and Z2 measured in a normal state in which the speaker line 6 and the speaker 8 are not disconnected or short-circuited thereafter. For example, when impedances Z1 and Z2 are measured in a state where audio signals having various frequencies and a test signal are supplied to the speaker line 6 when the public address system is operated, the impedance Z1 is the reference impedance Z1ave. Unlikely, the impedance Z2 may be different from the reference impedance Z2ave. In particular, when the level of the audio signal is higher than the level of the test signal, the difference in value is significant. Therefore, as shown in FIG. 5, the correction processing is performed after the above-described determination is performed on the upper limit values Z1open and Z2open and the lower limit values Z1inc and Z2inc based on the reference impedances Z1ave and Z2ave.

  In this correction process, first, it is determined whether the effective value Vrms of the digital voltage detection signal is larger than the effective voltage value Vtest of the digital test signal by a predetermined rate, for example, 1.2 times (step S26). If the answer to this determination is yes, it is determined that many of the same frequency components other than the test signal are included in the audio signal, so that correction processing of the upper limit values Z1open, Z2open, lower limit values Z1inc, Z2inc is performed ( Step S28). The predetermined rate is not limited to 1.2.

In the correction calculation process in step S28, the measurement accuracy Ra of the measured impedances Z1 and Z2 is used. The measurement accuracy Ra is a unit, and the smaller the value, the higher the measurement accuracy of the measurement impedances Z1, Z2, and the higher the value, the lower the measurement accuracy of the measurement impedances Z1, Z2. . The measurement accuracy Ra is set to the smallest value, for example, 5% when Vrms is equal to Vtest. As shown in FIG. 6, in the correction calculation process in step S28, it is determined whether the digital voltage detection signal Vrms is larger than the digital voltage detection signal ΔVrms when the correction calculation process was performed last time (step S30). If the answer to this determination is yes, the audio signal having the same frequency component other than the test signal has increased compared to the previous correction, so that the value of the measurement accuracy Ra needs to be largely corrected. for that reason,
Ra = βRa + αf (Vrms / Vtest)
Is performed. Here, α and β are predetermined coefficients and have a relationship of α + β = 1 and α> β. f (Vrms / Vtest) is a function having Vrms / Vtest as an argument, and its value increases when the value of Vrms / Vtest increases, and when the value of Vrms / Vtest decreases. Get smaller. Therefore, since the value of Vrms / Vtest has changed greatly and α> β, the ratio of αf (Vrms / Vtest) to the corrected measurement accuracy Ra is large, and the corrected measurement accuracy Ra is When the value of Vrms / Vtest is increasing, it quickly increases as shown in the first half of FIG.

If the answer to the determination in step S30 is no, since the audio signal having the same frequency component other than the test signal is decreased as compared with the previous correction, the measurement accuracy Ra is set to be smaller. Will be corrected. However, the rate of change in the direction of decreasing is reduced. for that reason,
Ra = αRa + βf (Vrms / Vtest)
The operation is performed. Since the value of Vrms / Vtest is small, the value of f (Vrms / Vtest) is small, but β smaller than α is multiplied by f (Vrms / Vtest). The ratio of βf (Vrms / Vtest) in the signal is small, and the corrected Ra value is slowly decreased as shown in the latter half of FIG. 7 when the value of Vrms / Vtest is decreased.

  Z1open, Z2open, Z1inc, and Z2inc are calculated using the measurement accuracy Ra thus corrected (step S36). Vrms is stored as ΔVrms for use in the next execution of step S30 (step S38).

The calculation of Z1open and Z1inc in step S36 is performed as shown in FIG. First, it is determined whether the measurement accuracy Ra is larger than the impedance open ratio initial value Rul (step S40). The impedance open ratio initial value R1ul is expressed as a unit, and is an upper limit value that is an impedance that the speaker line 6 is considered to be open when the measurement accuracy Ra is the highest accuracy, that is, when the smallest value is the smallest. It is an increment with respect to the reference impedance (Z1ave, Z2ave) . This impedance open ratio initial value Rul is set by the worker at the time of initialization or re-initialization, and is commonly used for Z1open and Z2open. If the answer to the determination in step S40 is no, it is not necessary to make the measurement accuracy Ra larger than the impedance open ratio initial value Rul.
Z1open = Z1ave (1 + Rul / 100)
(Step S42).

If the answer to the determination in step S40 is yes, it is necessary to correct Z1open according to the measurement accuracy Ra.
Z1open = Z1ave (1 + Ra / 100)
(Step S44).

  Subsequent to step S42 or S44, it is determined whether Z1open is larger than the upper limit value Z1ul of impedance at 20 KHz (step S46). The upper limit value Z1ul of impedance is an upper limit value of impedance that is predicted to actually occur at 20 KHz when the speaker line 6 or the like is opened. The upper limit value Z1ul is manually set by an operator at the time of initialization or reinitialization. Alternatively, Z1ave measured at the time of initialization or reinitialization by the DSP 10 is multiplied by a coefficient larger than 1, and the multiplication value is set as the upper limit value Z1ul. Since the Z1open value corrected based on the measurement accuracy Ra may be an impedance value that does not actually occur, the determination in step S46 is performed. If the answer to the determination in step S46 is yes, Z1open cannot be larger than Z1ul, so Z1open is set to Z1ul (step S48).

Subsequent to step S48 or if the answer to the determination in step S46 is no, it is determined whether the measurement accuracy Ra is greater than the impedance increase rate initial value Rll (step S50). The impedance increase rate initial value Rll is obtained from the reciprocal of the ratio of the reference impedance (Z1ave or Z2ave) to the impedance that can be considered that the impedance of the speaker line 6 and the speaker 8 is lowered when the measurement accuracy Ra is the highest accuracy. The value obtained by subtracting 1 is expressed as a percentage. The impedance increase rate initial value Rll is set by the worker at the time of initialization or reinitialization, and is used in common for Z1inc and Z2inc. If the answer to the determination in step S50 is no, the measurement accuracy Ra does not need to be smaller than Rll, so Z1inc is Z1inc = Z1ave (1 + Rll / 100)
(Step S52).

If the answer to the determination in step S50 is yes, Z1inc needs to be corrected according to the measurement accuracy Ra, so Z1inc is Z1inc = Z1ave / (1 + Ra / 100)
(Step S54).

  Subsequent to step S52 or S54, it is determined whether Z1inc is smaller than the lower limit value Z1ll at 20 KHz of impedance Z1 (step S56). The lower limit value Z1ll of the impedance is a lower limit value of the impedance at 20 KHz that is predicted to actually occur as a drop in impedance although the speaker line 6 or the speaker 8 is not short-circuited. The lower limit value Z1ll is manually set by an operator at the time of initialization or reinitialization. Alternatively, Z1ave measured by the DSP 10 at the time of initialization or reinitialization is multiplied by a coefficient smaller than 1, and the multiplied value is set as the lower limit value Z1ll. Since Z1inc corrected in step S54 may be an impedance that does not actually occur, step S56 is executed. If the answer to the determination in step S56 is yes, Z1inc cannot be smaller than Z1ll, so Z1inc is set to Z1ll (step S58). If step S58 ends or if the answer to the determination in step S56 is no, this Z1open, Z2inc calculation processing ends.

  By the same processing as described above, Z2open and Z2inc are impedance open ratio initial value Rul, impedance increase ratio initial value Rll, upper limit value Z2ul of impedance Z2 at 40 Hz, lower limit value Z2ll of impedance Z2 at 40 Hz, impedance Z2 at 40 Hz. Is calculated using the reference impedance Z2ave. A description of this process is omitted.

For example, Z2ave is 1000Ω, Z2ul is 2000Ω, Z2ll is 500Ω, Z2sl is 20Ω, Z1ave is 1500Ω, Z1ul is 3000Ω, Z1ll is 750Ω, Z1sl is 30Ω, Isl is 5A, Rul is 10%, Rll is 10%, Ra is 5% %, Vtest is assumed to be 5V. Note that Ra is 5% as the highest accuracy. In this state, if the state where Vrms is 5V continues, since Ra <Rul, Z1open and Z2open are
Z2open = 1000Ω * (1 + 5/100) = 1050Ω
Z1open = 1500Ω * (1 + 5/100) = 1575Ω
It becomes. Since Ra> Rll, Z2inc and Z1inc are
Z2inc = 1000Ω / (1 + 5/100) = 952Ω
Z1inc = 1500Ω / (1 + 5/100) = 1428Ω
It becomes.

  In this state, if the measured impedance Z2 is 1000Ω and Z1 is 1500Ω, it is determined to be normal by the processing shown in FIG. Similarly, when the measurement impedance Z2 is 1100Ω and Z1 is 1500Ω, it is determined to be open by the process shown in FIG. If the measurement impedance Z2 is 1100Ω and Z1 is 1600Ω, it is determined to be open by the process shown in FIG. If the measurement impedance Z2 is 1000Ω and the measurement impedance Z1 is 1400Ω, it is determined to increase by the processing shown in FIG. If the measurement impedance Z2 is 15Ω and the measurement impedance Z1 is 10Ω, it is determined as a short circuit by the process shown in FIG.

Further, as a result of a state in which the audio signal includes some of the same frequency components other than the test signal and Vrms is larger than Vtest, for example, Vrms is 10 V, Ra is rapidly increased by the processing of FIG. For example, assume that Ra is 50%. In this case, since Ra> Rul, Z2open is
Z2open = 1000Ω * (1 + 50/100) = 1500Ω
Z1open = 1500Ω * (1 + 50/100) = 2250Ω
It becomes. Since Ra> Rll, Z2inc is
Z2inc = 1000Ω / (1 + 50/100) = 667Ω
Z1inc = 1500Ω / (1 + 50/100) = 1000Ω
It becomes.

  In this state, if the measurement impedance Z2 is 1100Ω and the measurement impedance Z1 is 1600Ω, it is determined to be normal by the process shown in FIG. If the measurement impedance Z2 is 2300Ω and the measurement impedance Z1 is 1000Ω, it is determined to be open by the process shown in FIG. If the measured impedance Z2 is 1400Ω and the measured impedance Z1 is 600Ω, it is determined that the measured impedance Z2 is increased by the process shown in FIG. If the measurement impedance Z2 is 15Ω and the measurement impedance Z1 is 10Ω, it is determined as a short circuit by the process shown in FIG.

Further, as a result of a state in which the audio signal contains a large amount of the same frequency component other than the test signal and Vrms is considerably larger than Vtest, for example, Vrms is 30 V, Ra rapidly increases as a result of the processing of FIG. For example, suppose that it became 300%. In this case, since Ra> Rul, Zopen is
Z2open = 1000Ω * (1 + 300/100) = 4000Ω
Z1open = 1500Ω * (1 + 300/100) = 6000Ω
However, since Z2open> Z2ul and Z1open> Z1ul, Z2open and Z1open are
Z2open = Z2ul = 2000Ω
Z1open = Z1ul = 3000Ω
It becomes. Since Ra> Rll, Z2inc and Z1inc are
Z2inc = 1000Ω / (1 + 300/100) = 250Ω
Z1inc = 1500Ω / (1 + 300/100) = 375Ω
It becomes. Since Z2inc <Z2ll and Z1inc <Z1ll, Z1inc and Z2inc are
Z2inc = Z2ll = 500Ω
Z1inc = Z1ll = 750Ω
It becomes.

  In this state, when the measured impedance Z2 is 1000Ω and Z1 is 1600Ω, it is determined to be normal by the processing shown in FIG. If the measurement impedance Z2 is 2500Ω and Z1 is 2800Ω, it is determined to be open by the process shown in FIG. If the measured impedance Z2 is 400Ω and the impedance Z1 is 1000Ω, it is determined to increase by the processing shown in FIG. If the measurement impedance Z2 is 15Ω and the measurement impedance Z1 is 10Ω, it is determined as a short circuit by the process shown in FIG.

  Even if the state where Vrms is 30 V returns to the state where Vrms is 10 V, for example, the process of step S34 in FIG. 6 is performed, so Ra does not decrease to 50% but slightly decreases. . Therefore, Z2open decreases slightly from 4000Ω, Z1open decreases slightly from 6000Ω, Z2inc increases slightly from 500Ω, and Z1open increases slightly from 750Ω. Thus, for example, even when the speaker 8 generates heat due to a large value of Vrms and it takes a long time for the temperature of the speaker 8 to return to the temperature before starting the heat generation, Z1open, Z2open, Since the values of Z1inc and Z2inc also return to values before heat generation over a long time, it is possible to prevent erroneous determination.

  In this inspection apparatus, the reference impedances Z1ave and Z2ave at 20 KHz and 40 Hz of the speaker line 6 and each speaker 8 are measured in a state where no audio signal is supplied, and the aged deterioration tolerance for 20 KHz for which the reference impedance Z1ave is determined in advance is measured. Whether or not the upper limit value Z1UL is between the aging deterioration allowable lower limit value Z1LL or the reference impedance Z2ave is between the aging deterioration allowable upper limit value Z2UL for 40 Hz and the aging deterioration allowable lower limit value Z2LL for 40 Hz. Is judged. That is, when the public address system is used for many years, the impedance of each speaker 8 changes due to deterioration over time. According to this change, the reference impedances Z1ave and Z2ave also change. The reference impedance Z1ave is within the allowable range defined by the allowable upper limit value Z1UL and the allowable lower limit value Z1LL of 20 KHz, which is a limit that requires replacement of each speaker, or the reference impedance Z2ave allows replacement of each speaker. It is determined whether it is within an allowable range defined by the allowable upper limit value Z2UL and the allowable lower limit value Z2LL of 40 Hz, which is a necessary limit, and the reference impedance Z1ave is an allowable value specified by the allowable upper limit value Z1UL and the allowable lower limit value Z1LL When the value is out of the range or the reference impedance Z2ave is out of the allowable range defined by the allowable upper limit value Z2UL and the allowable lower limit value Z2LL, the notification device 28 is displayed to prompt the user to replace the speaker. This determination is performed every day when the public address system is not used, for example, in the case where the public address system is installed, every time a certain time in the time zone from the store closing time to the opening time is reached.

  As shown in FIG. 9, it is determined whether it is the inspection time (step S60). If the answer to this determination is no, this process ends. If the answer to the determination in step S60 is yes, the DSP 10 generates a test signal (step S62). Then, the reference impedances Z1ave and Z2ave are measured as described with reference to FIG. 2 (step S64). It is determined whether Z1ave is within the allowable range defined by Z1UL and Z1LL described above, and whether Z2ave is within the allowable range defined by Z2UL and Z2LL described above (step S66). If the answer to this determination is no, an error is displayed on the notification device 28 (step S68), and the speaker is urged to be replaced. If the answer to the determination in step S66 is yes, the measured Z1ave and Z2ave are stored (step S70). By executing the process of step S70, Z1ave and Z2ave when calculating Z1open, Z2open, Z1inc, and Z2inc in the process shown in FIG. 8 are updated. As a result, it is possible to prevent erroneous determination due to the influence of impedance change due to aging.

  In the above embodiment, the impedances Z1, Z2, Z1ave, and Z2ave are measured by cross spectrum analysis. For example, the current and voltage of the test signal are extracted using a narrow-band bandpass filter that can extract the test signal. The impedance can be measured from these extracted values. In the above embodiment, test signals having frequencies of 40 Hz and 20 KHz are used. However, for example, a test signal having a frequency of only 40 Hz or 20 KHz may be used. In the above embodiment, the digital test signal from the DSP 10 is D / A converted and supplied to the synthesizer 13. Instead, an analog test signal source is provided separately, and the test from the analog test signal source is provided. The signal may be supplied to the synthesizer 13. In this case, the analog test signal is converted into a digital test signal by the A / D converter and supplied to the DSP 10. In the above-described embodiment, it is determined that the speaker line and the speaker are opened and the impedance is reduced. However, only one of them may be performed.

Claims (4)

An audio signal source;
An amplifier for amplifying the audio signal;
A speaker line for transmitting the output signal of the amplifier;
A plurality of speakers connected in parallel to this speaker line,
In the public address system provided,
A signal source of a test signal including one or both of a frequency near the lowest frequency and a frequency near the highest frequency in a human audible frequency band;
A synthesizer that synthesizes the test signal with the audio signal and supplies the synthesized signal to the amplifier;
Impedance specification for extracting the component of the test signal included in the synthesized signal that is the output signal of the amplifier and specifying the impedance viewed from the output side of the amplifier from the speaker side based on the extracted component of the test signal Means,
A determination means for comparing at least one of the speaker line and speaker opening and impedance reduction by comparing the identified impedance with a predetermined threshold;
When the ratio of the composite signal to the test signal is greater than a predetermined value and the composite signal is increased compared to the composite signal when the previous threshold correction was performed , the threshold is determined as the determination unit. Threshold correction means for changing in a direction to lower the determination accuracy in
A speaker line inspection device provided.   The speaker line inspection device according to claim 1, wherein the threshold value correcting means increases the determination accuracy, which is lowered when the composite signal is increasing, when the composite signal is changed from an increasing state to a decreasing state, A speaker line inspection apparatus characterized in that the rate of change in the direction of decreasing the determination accuracy is large and the rate of change in the direction of increasing the determination accuracy is small. The speaker line inspection apparatus according to claim 1,
In the time zone when the signal source of the audio signal is stopped, the impedance specifying means specifies the impedance,
Threshold setting means for setting the threshold based on the specified impedance;
Second determination means for determining whether the specified impedance is within a predetermined allowable range;
A speaker line inspection device provided. The speaker line inspection apparatus according to claim 1, wherein the impedance specifying unit includes:
Current detection means for detecting a current flowing in the speaker line;
Voltage detecting means for detecting a voltage applied to the speaker line;
Frequency component detection means for detecting a frequency component of the test signal included in each of the current detected by the current detection means and the voltage detected by the voltage detection means;
A calculation means for calculating the impedance from the frequency component of the test signal in the detected current and voltage,
A speaker line inspection device provided.

Images