JP2009268014A - Audio amplification device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio amplification device which can suppress the degradation of quality of an audio signal outputted from a loudspeaker by removing its low frequency zone. <P>SOLUTION: The audio amplification device includes a low cut filter 11 for removing a frequency component lower than a cut-off frequency fc of an output transformer on a transmission line from an audio signal, a harmonic tone generator 12 for extracting a frequency component removed by the low cut filter 11 from the audio signal as a fundamental tone and generating harmonic tone signals having frequencies corresponding to a double or more of an integral multiple of the frequency of the fundamental tone, a combined signal generator 13 for generating an audio combination signal by combining the audio signal after the low frequency zone is removed and the harmonic tone signals, a pulse modulator 14 for generating a pulse modulation signal on the basis of the audio combination signal, and a switching amplifier 15a for switchingly amplifying the audio combination signal on the basis of the pulse modulation signal and supplying the amplified signal to a transmission line. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an audio amplifying apparatus, and more particularly to an improvement of an audio amplifying apparatus that amplifies an audio signal and transmits the amplified audio signal to a speaker via a transmission line.

  A sound expansion system is known as an audio broadcasting system configured by connecting an audio amplifying device and a plurality of speakers via a transmission line. When this loudspeaker system is applied to a large-scale facility such as an airport, a school, or a shopping mall, the length of the transmission line may reach several kilometers. For this reason, such a loudspeaker system employs high-impedance transmission with good transmission efficiency.

  For such high-impedance transmission, a switching amplifier capable of obtaining a high output with high efficiency is often used. A switching amplifier is a power amplifier that amplifies an audio signal by causing a plurality of switching elements to perform high-speed switching operation based on an audio-modulated pulse signal, and is sometimes called a digital amplifier (for example, Patent Document 1). ).

  Usually, the output of the switching amplifier is supplied to a speaker via a low-pass filter for removing harmonic components and an output transformer for boosting. In general, the transformer has a property that the impedance becomes smaller and the gain is lowered as the frequency component is lower. Since the impedance decreases as the frequency decreases, when an audio signal containing a frequency component lower than the cutoff frequency in such an impedance characteristic is input to the output transformer, saturation occurs and an overcurrent flows through the switching amplifier. Will end up. For this reason, in an audio amplifying apparatus that performs high-impedance transmission using a switching amplifier, a low-frequency component must be removed from the audio signal, resulting in a problem that sound quality deteriorates.

In the amplification of an audio signal using a switching amplifier, a power supply pumping phenomenon is conventionally known as a phenomenon in which a capacitor constituting a switching amplifier is overcharged by a regenerative current from a coil constituting a low-pass filter. In general, the lower the frequency component, the longer the time during which one of the switching elements is on, and the degree of overcharging due to power pumping increases. For this reason, in the conventional audio amplifying apparatus as described above, when an audio signal including a lower frequency component is to be amplified in order to improve sound quality, the capacity of the capacitor in the switching amplifier must be increased. There is also a problem that the device becomes large.
JP 2005-203968 A

  The present invention has been made in view of the above circumstances, and provides an audio amplifier that can amplify an audio signal and suppress deterioration in sound quality when the audio signal is transmitted to a speaker via a transmission line. Objective. In particular, it is an object of the present invention to provide an audio amplifying apparatus that can suppress deterioration of the sound quality of an audio signal output from a speaker due to low-frequency removal. It is another object of the present invention to provide an audio amplifying device that can reduce the size of the device without deteriorating sound quality.

  An audio amplifying device according to a first aspect of the present invention is an audio amplifying device that amplifies an audio signal and transmits the amplified audio signal to a speaker via a transmission line, and has a frequency component lower than the cutoff frequency of the transformer on the transmission line. From the audio signal, and a frequency component removed by the low frequency removing means is extracted as a fundamental tone from the audio signal to generate a harmonic signal whose frequency is an integer multiple of 2 or more of the fundamental tone. Overtone generating means for combining, an audio signal after low-frequency removal by the low-frequency removing means, and a synthesized signal generating means for synthesizing the harmonic signal to generate an audio synthesized signal, and a pulse modulation signal based on the audio synthesized signal And a pulse modulation means for generating the audio synthesized signal based on the pulse modulated signal. Amplified, and provided with a switching amplifier for supplying to the transmission line.

  In this audio amplifying device, the audio signal from which the frequency component lower than the cutoff frequency of the transformer on the transmission line is removed by the low-frequency removing means is switched and amplified and supplied to the transmission line, so that the transformer is saturated. Can be prevented. At that time, a harmonic signal is generated corresponding to the frequency component removed from the audio signal, and an audio synthesis signal obtained by synthesizing the harmonic signal and the audio signal after the low frequency band is switched and amplified. According to such a configuration, the audio synthesis signal obtained by synthesizing the harmonic signal and the audio signal after the low frequency band is switched and amplified and supplied to the transmission line, so that the low frequency band removed from the audio signal before the switching amplification is supplied. A harmonic signal corresponding to the frequency component can be output from the speaker. At that time, even if the audio signal output from the speaker does not contain a frequency component that is a fundamental tone, if the harmonic component is contained, the fundamental tone is also perceived when a person listens to the output tone. It is possible to suppress the deterioration of the sound quality of the audio signal output from the low frequency band removal.

  In addition, since low frequency components can be removed without degrading sound quality, the switching amplifier can be downsized without degrading sound quality by widening the removal band of such frequency components to the high sound side. it can. Note that the cut-off frequency when the low frequency removing means removes the low frequency component from the audio signal may be higher or lower than the cut-off frequency of the transformer, but here both cases are included. Shall.

  In addition to the above configuration, the audio amplifying device according to the second aspect of the present invention transmits, as the transformer, an insulating output transformer disposed on the output side of the switching amplifier and the switching amplifier via the transmission line. A step-down transformer for stepping down the signal output and inputting the signal output to the speaker is disposed on the transmission line, and the low-frequency removing means includes a cutoff frequency of the output transformer and a cutoff frequency of the step-down transformer. A frequency component lower than the highest cutoff frequency and higher than the lowest cutoff frequency is also configured to be removed from the audio signal. According to such a configuration, frequency components are removed according to the transformer with the highest cut-off frequency, so that the audio signal can be high without having to improve the performance of the transformer with the high cut-off frequency to the lower one. Impedance can be transmitted.

  In addition to the above configuration, the audio amplifying device according to the third aspect of the present invention includes transmission mode switching means for switching the operation mode to either high impedance transmission or low impedance transmission based on an input signal from the operation unit, The pulse modulation means generates a pulse modulation signal from the audio signal before the low-frequency removal by the low-frequency removal means based on the operation mode selected by the transmission mode switching means, and the switching amplifier Based on the signal, the audio signal before the low-frequency removal by the low-frequency removing means is switched and amplified and supplied to the transmission line. According to such a configuration, since pulse modulation and switching amplification are performed according to the operation mode selected by the transmission mode switching means, when the operation mode is switched from low impedance transmission to high impedance transmission by an operator operation. The low frequency band can be automatically removed to perform pulse modulation and switching amplification.

  According to the audio amplifying device of the present invention, since the audio composite signal is switched and amplified and supplied to the transmission line, the harmonic signal corresponding to the low frequency component removed from the audio signal before the switching amplification is output from the speaker. Can be output. At that time, even if the audio signal output from the speaker does not contain the fundamental frequency component, if the harmonic signal is included, the fundamental tone is also perceived when a person hears the output sound. It is possible to suppress deterioration of the sound quality of the audio signal output from the speaker due to the low frequency band removal. Therefore, it is possible to suppress deterioration in sound quality when transmitting to the speaker via the transmission line. In addition, since low frequency components can be removed without degrading sound quality, the switching amplifier can be downsized without degrading sound quality by widening the removal band of such frequency components to the high sound side. And downsizing of the apparatus can be realized.

Embodiment 1 FIG.
<Sound system>
FIG. 1 is a system diagram showing an example of a schematic configuration of a loudspeaker system 100 including an audio amplifying apparatus 2 according to Embodiment 1 of the present invention. The loudspeaker system 100 includes a sound source device 1, an audio amplifying device 2, an output transformer 3, a transmission line 4, and an audio output unit 5.

  The sound source device 1 is a device that generates an audio signal having an audible frequency, for example, a microphone or a recording / reproducing device that generates an analog audio signal including a frequency component of 20 Hz to 20 kHz. The audio signal generated by the sound source device 1 is amplified by the audio amplifying device 2, boosted by the output transformer 3, and supplied to the audio output unit 5 through the transmission line 4.

  The transmission line 4 is a transmission line composed of two wiring cables, and a plurality of audio output units 5 are connected thereto.

  The output transformer 3 is an insulating transformer in which the audio amplifying device 2 is connected to the primary side and the audio output unit 5 is connected to the secondary side via the transmission line 4. In this case, the audio amplified signal amplified in the audio amplifying device 2 is boosted, for example, in the output transformer 3 and sent to the transmission line 4 as a high-voltage audio transmission signal. As the audio transmission signal, a signal having an effective voltage of 100 V can be used.

  The audio output unit 5 is a high impedance loudspeaker device including a matching transformer 6 and a speaker 7. The matching transformer 6 is a step-down transformer that steps down the signal output transmitted from the audio amplifying apparatus 2 through the transmission line 4 and inputs the signal output to the speaker 7. The speaker 7 is connected to the transmission line 4 in parallel. That is, on the transmission line 4 between the audio amplifying device 2 and the speaker 7, the insulating output transformer 3 and the step-down matching transformer 6 are arranged.

  The audio signal sent to the transmission line 4 is supplied to the speaker 7 on the transmission line 4, and the same sound is output from each speaker 7.

  The speaker 7 has an input impedance of about 4 to 8Ω, whereas the audio output unit 5 has a high input impedance due to the interposition of the matching transformer 6, and may have an input impedance of 1 kΩ or more, for example.

  In this loudspeaker system 100, the audio amplified signal output from the audio amplifying device 2 is converted into a higher voltage signal and transmitted. Such a transmission method is called high impedance transmission. In high impedance transmission, transmission loss can be reduced as compared with the case of transmitting an audio signal as it is. For example, in the case of a local broadcasting system of a large-scale facility such as an airport, a school, or a shopping mall, the length of the transmission line 4 reaches several kilometers, and the transmission loss cannot be ignored. High impedance transmission is suitable as a transmission system for such a large-scale facility loudspeaker system.

  Moreover, since the audio output unit 5 used for high impedance transmission has a high input impedance, many audio output units 5 can be connected in parallel to the same transmission line 4.

  Furthermore, if an insulating transformer is used as the output transformer 3, the audio amplifying device 2 and the audio output unit 5 can be electrically insulated. For this reason, even if a ground fault of the transmission line 4 or a lightning strike to the transmission line 4 occurs between the output transformer 3 and the audio output unit 5, the audio amplifying device 2 is not easily affected by the transmission line 4. It is suitable for a loudspeaker system laid outdoors.

<Amplifier for audio>
FIG. 2 is a block diagram showing a configuration example of the audio amplifying apparatus 2 in the loudspeaker system 100 of FIG. The audio amplifying apparatus 2 includes an input terminal 10, a low cut filter 11, a harmonic overtone generator 12, a synthesized signal generator 13, a pulse modulator 14, a switching amplifier 15 a, a low pass filter 16, and an output terminal 17.

  The audio signal generated by the sound source device 1 is input via the input terminal 10, amplified by the switching amplifier 15 a, and then output from the output terminal 17 to the output transformer 3.

  The low cut filter 11 is a band limiting unit for preventing the transformer on the transmission line 4 from being saturated, removes a frequency component lower than a predetermined frequency from the audio signal input to the input terminal 10 and is high. This is a high-pass filter that passes the frequency component as it is. The cut-off frequency of the low cut filter 11 may be higher or lower than the cut-off frequency of the transformer on the transmission line 4. Here, it is assumed that both the cut-off frequencies substantially coincide with each other. . That is, the low cut filter 11 performs an operation of removing all frequency components lower than the cutoff frequency of the transformer on the transmission line 4 from the audio signal and passing the high frequency components as they are.

  The cut-off frequency of the low cut filter 11 is determined according to the highest cut-off frequency among the cut-off frequency of the output transformer 3 and the cut-off frequency of the matching transformer 6. That is, in the low cut filter 11, the frequency component lower than the highest cutoff frequency and higher than the lowest cutoff frequency among the cutoff frequency of the output transformer 3 and the cutoff frequency of the matching transformer 6 is also removed from the audio signal. Is done.

  The audio signal whose pass band is limited by the low cut filter 11 is output to the synthesized signal generation unit 13.

  The harmonic generation unit 12 performs an operation of generating a harmonic signal based on the audio signal input to the input terminal 10 and outputting it to the synthesized signal generation unit 13 in order to use the missing fundamental phenomenon in hearing. The missing fundamental phenomenon means that even if the audio signal output from the speaker 7 does not contain a frequency component that is a fundamental tone, if the harmonic component is contained, the fundamental tone is also perceived when a person hears the output tone. It is a perception phenomenon.

  Specifically, the frequency component removed by the low cut filter 11 is extracted as a fundamental tone from the audio signal, and an operation of generating a harmonic signal as an audio signal whose frequency is an integer multiple of 2 or more of the fundamental tone is performed.

  The harmonic signal generated by the harmonic generation unit 12 may include a frequency component lower than the cutoff frequency when the low-cut filter 11 removes the low frequency band. Here, such a frequency component is a high-pass signal. It is assumed that it is output after being removed by a filter.

  The synthesized signal generating unit 13 generates an audio synthesized signal by synthesizing the audio signal after the low frequency band is removed by the low cut filter 11 and the harmonic signal generated by the harmonic generating unit 12, and outputs the synthesized signal to the pulse modulating unit 14. It is carried out.

  The pulse modulation unit 14 generates a pulse modulation signal based on the audio synthesis signal from the synthesis signal generation unit 13 and outputs it to the switching amplifier 15a. For example, the input audio signal is converted into a PWM (Pulse Width Modulation) signal and output.

  The switching amplifier 15 a is a class D amplifier that performs switching amplification of the audio composite signal based on the pulse modulation signal supplied from the pulse modulation unit 14 and supplies the audio synthesis signal to the transmission line 4 as an audio amplification signal. The audio amplification signal is supplied to the output terminal 17 via the low-pass filter 16 and output to the output transformer 3.

  In the class D amplification, the audio composite signal is power-amplified by switching a semiconductor switching element such as a MOS-FET at high speed based on the pulse signal that is voice-modulated by the audio composite signal.

  The low-pass filter 16 is a band limiting means for removing harmonics composed of a coil and a capacitor, and outputs a frequency component higher than a predetermined frequency from the output of the switching amplifier 15a.

<Frequency characteristics of output transformer>
FIG. 3 is a diagram showing an example of the frequency characteristic A1 of the output transformer 3 in the loudspeaker system 100 of FIG. The output transformer 3, a specific frequency fa in the audible band, for example, with respect to the frequency components near fa = 1 kHz, the transformer is used with a constant impedance (input impedance) z _1.

  Generally, the transformer has a higher impedance as the frequency becomes higher than the frequency fa. On the other hand, as the frequency becomes lower than the frequency fa, the impedance becomes smaller and the gain decreases. At zero frequency, the impedance approaches zero as much as possible.

  The cut-off frequency fc of the output transformer 3 is determined within a frequency range lower than the frequency fa based on such a property of the transformer. For example, the cut-off frequency fc is set to about 50 to 100 Hz as a frequency at which the gain is reduced by about 3 dB compared to the frequency fa.

  In general, when an audio signal including a frequency component lower than the cutoff frequency fc is input to the output transformer 3, the output transformer 3 is saturated and an overcurrent flows through the switching amplifier 15a. For this reason, the low-frequency filter 100 is provided with the low cut filter 11 in the loudspeaker system 100. However, since the frequency component lower than the cutoff frequency fc is removed from the audio signal, the low cut filter 11 is not provided. The sound quality will deteriorate compared to Therefore, in order to transmit the lower frequency components to the secondary side without being attenuated, it is conceivable to increase the core of the transformer to lower the cutoff frequency. However, with this method, the transformer becomes enormous and the manufacturing cost increases.

  On the other hand, in the present embodiment, a harmonic signal is generated corresponding to the frequency component removed from the audio signal, and an audio synthesized signal obtained by synthesizing the harmonic signal and the audio signal after the low frequency band is switched and amplified. This prevents the transformer from being saturated and suppresses the deterioration of sound quality.

<Missing fundamental phenomenon>
FIGS. 4A and 4B are diagrams showing an example of the operation in the loudspeaker system 100 of FIG. 1, and the frequency characteristics of the audio signal are shown. In FIG. 4A, the horizontal axis represents the frequency f (Hz) and the vertical axis represents the signal intensity, and the intensity of the audio signal collected by the microphone is shown for the frequency components f _{1 to} f ₄ . FIG. 4B shows an audio signal in which a frequency component f1 lower than the cut-off frequency fc is removed and overtone components f _{2 to} f _{4 based on} the frequency component f ₁ in the removal band are added. Has been.

In general, a sound generated in nature includes its overtone component. For example, assuming that the frequency component f ₁ = 50 Hz is a fundamental tone, the frequency is a second harmonic component f ₂ consisting of twice the fundamental tone (100 Hz), a triple voice component f 3 consisting of 3 times (150 Hz), f ₃ , and 4 times (200 Hz). such as 4 harmonics f ₄ consisting contains.

For this reason, even if the fundamental component f ₁ is not included in the audio signal, or if the component is reduced, a person can generate such a sound if a plurality of overtone components f _{2 to} f ₄ are included. It is the missing fundamental phenomenon that the fundamental tone is also perceived when listening.

  In the present embodiment, a harmonic overtone signal is generated corresponding to the frequency component removed from the audio signal by the low cut filter 11, and the harmonic overtone signal is output from the speaker 7 by adding it to the audio signal after the low frequency band is removed. This prevents the sound quality of the audio signal from deteriorating due to low frequency band removal.

<Circuit configuration of switching amplifier>
FIG. 5 is a circuit diagram showing a configuration example of the audio amplifying device 2 of FIG. 2, and shows a half-bridge type switching amplifier 15a. The switching amplifier 15a includes a capacitor C1 and a transistor T1 to which a voltage is applied from a DC power source + Vcc, a capacitor C2 and a transistor T2 to which a voltage is applied from a DC power source −Vcc having a polarity opposite to + Vcc, and transistors T1 and T2. And a gate drive circuit 22 to be driven.

  The pulse modulation signal input from the pulse modulation unit 14 to the input terminal 21 is supplied to the gate drive circuit 22. The gate drive circuit 22 controls the transistors T1 and T2 based on the pulse modulation signal, and alternately turns on the gates of the transistors T1 and T2, thereby outputting an amplified audio signal from the output terminal 23. The

  The transistors T1 and T2 are both MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and here, n-channel MOSFETs are used.

  The transistor T1 has a source electrode connected to the DC power source + Vcc and a drain electrode connected to the output terminal 23. The transistor T2 has a source electrode connected to the output terminal 23 and a drain electrode connected to the DC power source -Vcc.

  FIG. 6 is a circuit diagram showing another configuration example of the audio amplifying device 2 of FIG. 2, in which a full-bridge type switching amplifier 15b is shown. The switching amplifier 15b drives a capacitor C and a bridge circuit to which a voltage is applied from the DC power supply Vcc, a gate drive circuit 22a that drives the transistors T11 and T22 in the bridge circuit, and transistors T12 and T21 in the bridge circuit. And a gate drive circuit 22b.

  The pulse modulation signal input from the pulse modulation unit 14 to the input terminal 21 is supplied to the gate drive circuits 22a and 22b. The gate drive circuit 22a controls the transistors T11 and T22 based on this pulse modulation signal, and turns on the gates of the transistors T11 and T22 alternately. The gate drive circuit 22b controls the transistors T12 and T21 based on the pulse modulation signal, and turns on the gates of the transistors T12 and T21 alternately.

  The gate drive circuits 22a and 22b turn on the transistors T11 to T22 in synchronization with each other, so that an audio amplified signal after power amplification is output from the output terminal 23. For example, the transistors T11 and T12 and the transistors T21 and T22 are alternately turned on.

  In general, in audio signal amplification using the switching amplifiers 15a and 15b, capacitors C1 and C2 are generated by regenerative currents from the coil in the low-pass filter 16, the output transformer 3, the matching transformer 6 in the audio output unit 5, the speaker 7, and the like. , C is overcharged, so-called power pumping phenomenon occurs. The degree of overcharging of the capacitor is increased because the frequency component in the lower frequency range is longer for one switching element to be on. For this reason, if an audio signal including a lower frequency component is to be amplified in order to improve the sound quality, the pass band of the frequency component in the low cut filter 11 is widened to the lower sound side and the capacity of the capacitor in the switching amplifier is increased. I had to.

  On the other hand, in this embodiment, since the low frequency component can be removed without deteriorating the sound quality, the sound quality can be improved without increasing the capacity of the capacitor in the switching amplifier. Therefore, the switching amplifier can be made smaller than before.

  The half-bridge type switching amplifier 15a needs to increase the capacity of the capacitor to prevent overcharge as compared with the full-bridge type switching amplifier 15b, but the number of transistors can be reduced. Therefore, if the frequency characteristics are the same, the half-bridge type switching amplifier 15a can be reduced in size and cost than the full-bridge type. In the full bridge type switching amplifier 15b, since it is a single power source, the regenerative current is consumed immediately, and one-side overcharge unlike the half bridge type is unlikely to occur.

  According to the present embodiment, since the audio signal from which the frequency component lower than the cutoff frequency fc of the output transformer 3 on the transmission line 4 is removed is amplified by switching and supplied to the transmission line 4, the output transformer 3 is saturated. Can be prevented. At that time, a harmonic signal is generated corresponding to the frequency component removed from the audio signal, and an audio synthesis signal obtained by synthesizing the harmonic signal and the audio signal after the low frequency band is switched and amplified.

  With this configuration, an audio synthesis signal obtained by synthesizing the overtone signal and the audio signal after low-frequency band removal is switching-amplified and supplied to the transmission line 4, so that the low-frequency band removed from the audio signal before switching amplification. Overtone signals corresponding to the frequency components of can be output from the speaker 7. At that time, even if the audio signal output from the speaker 7 does not include a frequency component serving as a fundamental tone, if the harmonic component is included, the fundamental tone is also perceived when a person listens to the output sound. It is possible to suppress deterioration of the sound quality of the audio signal output from the speaker 7 due to the low-frequency removal.

  Further, since low frequency components can be removed without deteriorating sound quality, the switching amplifiers 15a and 15b can be downsized without degrading sound quality by widening the removal band of such frequency components to the high sound side. can do.

Embodiment 2. FIG.
In the first embodiment, the example in which the audio quality is amplified and transmitted to the plurality of speakers 7 at high impedance and the deterioration of sound quality is suppressed has been described. On the other hand, in the present embodiment, an audio amplifying apparatus capable of switching between high impedance transmission and low impedance transmission will be described.

  FIG. 7 is a block diagram showing a configuration example of the audio amplifying apparatus 30 according to the second embodiment of the present invention. The audio amplifying device 30 is different from the audio amplifying device 2 of FIG. 2 in that an operating unit 31, a transmission mode switching unit 32, and a relay switch 33 are provided.

  The transmission mode switching unit 32 controls the relay switch 33, the pulse modulation unit 14, and the switching amplifier 34 based on the input signal from the operation unit 31, and sets the operation mode to either high impedance transmission or low impedance transmission. Switching operation is performed.

  The relay switch 33 is a switch for transmitting the audio signal input to the input terminal 10 to the pulse modulation unit 14 as it is.

  In the pulse modulation unit 14, based on the operation mode selected by the transmission mode switching unit 32, an operation for generating a pulse modulation signal from the audio signal before the low-frequency removal by the low cut filter 11 is performed. That is, at the time of low impedance transmission, a pulse modulation signal is generated based on the audio signal transmitted from the input terminal 10 via the relay switch 33 instead of the audio synthesis signal from the synthesis signal generation unit 13.

  The switching amplifier 34 performs an operation of switching and amplifying the audio signal before the low-frequency removal by the low cut filter 11 based on the pulse modulation signal and supplying the audio signal to the transmission line 4.

  According to the present embodiment, since pulse modulation and switching amplification are performed according to the operation mode selected by the transmission mode switching unit 32, the operation mode is changed from low impedance transmission to high impedance transmission by the operation of the operation unit 31 by the operator. When the mode is switched to (5), it is possible to automatically remove the low frequency band and perform pulse modulation and switching amplification.

1 is a system diagram showing an example of a schematic configuration of a loudspeaker system 100 including an audio amplifying device 2 according to Embodiment 1 of the present invention. It is the block diagram which showed one structural example of the audio amplifier 2 in the loudspeaker system 100 of FIG. It is the figure which showed an example of the frequency characteristic A1 of the output transformer 3 in the loudspeaker system 100 of FIG. It is the figure which showed an example of the operation | movement in the loudspeaker system 100 of FIG. 1, and the frequency characteristic of an audio signal is shown. FIG. 3 is a circuit diagram illustrating a configuration example of the audio amplifying device 2 of FIG. 2, in which a half-bridge type switching amplifier 15 a is illustrated. FIG. 5 is a circuit diagram showing another configuration example of the audio amplifying device 2 in FIG. 2, in which a full-bridge type switching amplifier 15 b is shown. It is the block diagram which showed the example of 1 structure of the audio amplifier 30 by Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sound source device 2 Audio amplifier 3 Output transformer 4 Transmission line 5 Audio output unit 6 Matching transformer 7 Speaker 10 Input terminal 11 Low cut filter 12 Overtone generator 13 Synthetic signal generator 14 Pulse modulator 15a Switching amplifier 16 Low pass filter 17 Output Terminal 21 Input terminal 22 Gate drive circuit 23 Output terminal 30 Audio amplifier 31 Operation unit 32 Transmission mode switching unit 33 Relay switches C, C1, C2 Capacitors T1, T2, T11 to T22 Transistor 100 Loudspeaker system

Claims (3)

In an audio amplifying apparatus that amplifies an audio signal and transmits it to a speaker via a transmission line,
Low frequency removing means for removing a frequency component lower than the cutoff frequency of the transformer on the transmission line from the audio signal;
Overtone generating means for extracting a frequency component removed by the low frequency removing means as a fundamental sound from the audio signal, and generating a harmonic signal whose frequency is an integer multiple of 2 or more of the fundamental sound;
A synthesized signal generating means for generating an audio synthesized signal by synthesizing the audio signal after the low frequency removal by the low frequency removing means and the harmonic signal;
Pulse modulation means for generating a pulse modulation signal based on the audio synthesis signal;
An audio amplifying apparatus comprising: a switching amplifier that switches and amplifies the audio composite signal based on the pulse modulation signal and supplies the signal to the transmission line. The transformer includes an output transformer for insulation disposed on the output side of the switching amplifier, and a step-down transformer that steps down a signal output transmitted from the switching amplifier via the transmission line and inputs the signal output to the speaker. Placed on the transmission line,
The low-frequency removing means removes a frequency component lower than the highest cutoff frequency and higher than the lowest cutoff frequency from the audio signal among the cutoff frequency of the output transformer and the cutoff frequency of the step-down transformer. The audio amplifying device according to claim 1, wherein: Based on the input signal from the operation unit, equipped with transmission mode switching means for switching the operation mode to either high impedance transmission or low impedance transmission,
Based on the operation mode selected by the transmission mode switching means, the pulse modulation means generates a pulse modulation signal from the audio signal before the low-frequency removal by the low-frequency removal means,
2. The audio amplifier according to claim 1, wherein the switching amplifier switches and amplifies the audio signal before the low-frequency removal by the low-frequency removal means based on the pulse modulation signal and supplies the signal to the transmission line. Amplification equipment.

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