Abstract:
The present invention provides a sound producing apparatus which suppresses an increase in electric power consumption and cost, and an increase in a number of wiring when a plurality of speaker apparatuses is configured. A speaker driving apparatus supplies electric power to a speaker apparatus, acquires information about an electroacoustic characteristic and maximum input electric power of each speaker apparatus from the speaker apparatus, and executes characteristic correction and output electric power restriction according to the information.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sound player including a speaker apparatus and a speaker driving apparatus, and its control method. Particularly, the present invention relates to the sound player in which the speaker apparatus and the speaker driving apparatus mutually transmits and receives a speaker characteristic and electric power to control an audio signal, and its control method. 
     2. Description of the Related Art 
     Conventionally, a Motional Feedback (MFB) has been known as a technique to correct an electroacoustic characteristic of a speaker apparatus. The MFB technique feeds back a detection signal of a vibration speed in the speaker apparatus and corrects the electroacoustic characteristic based on the detection signal. 
     A speaker driving apparatus using the MFB easily causes oscillation due to a phase rotation of a detection signal which becomes a feedback signal. Japanese Patent Application Laid-Open No. 3-203498 discusses a speaker system that internally includes a Digital Signal Processor (DSP) which executes correction computing and a digital interface. The speaker system adds the data that correct an electroacoustic characteristic of a speaker apparatus to an input signal in advance, thereby resolving the oscillation problem of the MFB technique. 
     Further, conventionally, a speaker protection circuit has been known. The speaker protection circuit regulates an output electric current of an amplifier circuit to be equal or less than an allowable limit. The speaker protection circuit prevents an accident such as disconnection of wire due to heating of a voice coil when a speaker apparatus is driven in a large sound volume. 
     In a conventional speaker protection circuit, there is a problem of a power loss since the speaker protection circuit detects an electric current applied to a speaker by a dropped voltage of a resistor. Further, together with decrease in power efficiency of the speaker protection circuit, distortion may be caused. 
     Japanese Patent Application Laid-Open No. 8-172693 discusses a speaker driving circuit that detects a signal current which flows through an output resistance of the output stage of an audio amplifier circuit, and controls the sound volume of a sound volume control circuit by the detected signal electric current to regulate the amount of output electric current. 
     However, according to the speaker apparatus discussed in Japanese Patent Application Laid-Open No. 3-203498, power needs to be supplied to each speaker apparatus. Therefore, electric power consumption and a cost of the speaker apparatus are increased when a plurality of speaker apparatuses is arranged, for example, in a home theater system that has a 5.1 channel configuration. 
     Further, unlike a general sound player illustrated in  FIG. 10 , as illustrated in  FIG. 11 , according to the above conventional sound player, an output signal of a signal source needs to be input to an amplifier through a speaker apparatus, which increases a number of wirings. Furthermore, according to the conventional sound player, power has to be supplied to a correction unit, and an input and output unit inside the speaker apparatus, which increases a number of wirings of a power supply and complicates the wiring. 
     Still furthermore, the speaker protection circuit discussed in Japanese Patent Application Laid-Open No. 8-172693 may supply electric power exceeding maximum input electric power to the speaker apparatus when an arbitrary speaker apparatus is connected to an output of the speaker apparatus. This is because the speaker protection circuit discussed in Japanese Patent Application Laid-Open No. 8-172693 does not include a unit configured to identify maximum input electric power and a unit configured to adjust a limit of an output electric current, in the connected speaker driving circuit. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a sound player including a speaker apparatus and a speaker driving apparatus, and its control method. 
     According to a first aspect of the present invention, a speaker driving apparatus adapted to be connected to a speaker apparatus, the speaker driving apparatus includes an amplification unit for amplifying an input audio signal to generate an output audio signal for driving the speaker apparatus, a power signal generation unit operable to generate a power signal for transmission to the speaker apparatus, a transmission unit operable to transmit the output audio signal and the power signal to the speaker apparatus, a reception unit for receiving, from the speaker apparatus, a data signal representing data relating to one or more characteristics of the speaker apparatus, and a signal modification unit operable to modify at least one audio signal in dependence upon the received data signal. 
     According to a second aspect of the present invention, a speaker apparatus, adapted to be connected to a speaker driving apparatus, the speaker apparatus includes a power signal receiving unit for receiving a power signal from the speaker driving apparatus, a power conversion unit for converting the received power signal into DC power, and a data signal transmission unit operable to transmit to the speaker driving apparatus data relating to one or more characteristics of the speaker apparatus using the DC power from the power conversion unit as a power supply. 
     An embodiment of the present invention can provide sound player capable of suppressing not only an increase in electric power consumption and cost, but also an increase in a number of wirings. 
     Another embodiment of the present invention can provide a sound player capable of faithful reproduction that executes a suitable characteristic correction corresponding to an electroacoustic characteristic of the speaker apparatus, and capable of safe reproduction that restricts output so that the output does not exceed maximum input electric power. 
     The above effects are significant in embodiments of the invention in which a plurality of speaker apparatuses is provided and the speaker apparatus is changed to a different one. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram illustrating a sound player according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating a sound player according to a second exemplary embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a sound player according to a third exemplary embodiment of the present invention. 
         FIG. 4  is a block diagram illustrating a sound player according to a fourth exemplary embodiment of the present invention. 
         FIG. 5  is a block diagram illustrating a sound player according to a fifth exemplary embodiment of the present invention. 
         FIG. 6  is a block diagram illustrating a sound player according to a sixth exemplary embodiment of the present invention. 
         FIG. 7  is a block diagram illustrating a sound player according to a seventh exemplary embodiment of the present invention. 
         FIG. 8  is a block diagram illustrating a sound player according to an eighth exemplary embodiment of the present invention. 
         FIG. 9  is a block diagram illustrating a sound player according to a ninth exemplary embodiment of the present invention. 
         FIG. 10  is a block diagram illustrating a general sound player. 
         FIG. 11  is a block diagram illustrating a conventional sound player. 
         FIG. 12  is a flowchart illustrating processing of a sound player according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a block diagram illustrating a sound player according to a first exemplary embodiment of the present invention. 
     The sound player connects a speaker driving apparatus  1  and a speaker apparatus  2  through a cable  7 . The speaker apparatus  1  includes the following configuration. The speaker driving apparatus  1  inputs an audio signal from a signal source to an audio input unit  14 . The speaker driving apparatus  1  executes predetermined correction processing of the input audio signal in a correction unit  13 . An amplification unit  15  amplifies an output of the correction unit  13  to a level at which a speaker unit  16  of the speaker apparatus  2  can be driven. An output restriction unit  27  limits the amount of output electric power in the amplification unit  15  to be less or equal to a predetermined restriction value. A power supply unit  6  outputs a high-frequency power signal that is beyond the range of human hearing. A reception unit  12  receives a data signal transmitted by a transmission unit  9  in the speaker apparatus  2 . The speaker driving apparatus  1  also includes a selection unit  4  connected to a connection terminal  5  (input and output unit). The selection unit  4  selectively connects the output restriction unit  27 , the power supply unit  6 , and the reception unit  12  with the output terminal  5 . A control unit  3  not only controls the selection unit  4 , but also sets a correction characteristic in the correction unit  13  and a restriction value in the output restriction unit  27 . 
     The speaker apparatus  2  includes the following configuration. The speaker unit  16  converts an audio signal input from an input terminal  11  into an audible sound. An electroacoustic characteristic storage unit  10  stores data of electroacoustic characteristic and maximum input electric power about the speaker apparatus  2 . The speaker apparatus  2  converts at least one of the electroacoustic characteristic data and the maximum input electric power data stored in the storage unit  10  into a data signal including a high-frequency component beyond the range of human hearing and transmits the data signal from the transmission unit  9  to the speaker driving apparatus  1 . That is, the data signal is a signal corresponding to the data of the electroacoustic characteristic and/or the maximum input electric power. A power conversion unit  8  converts a power signal output from the power supply unit  6  of the speaker driving apparatus  1  into a power to be supplied to the transmission unit  9 . The power conversion unit  8  includes a Band Pass Filter (BPF), a detection unit, and an electricity accumulation unit. The speaker apparatus  2  converts the power signal whose frequency band is restricted through the BPF, into a direct current signal in the detection unit. The speaker apparatus  2  accumulates the power signal in the electricity accumulation unit. The transmission unit  9  can transmit the data signal while the accumulated direct current signal serves as a power source for the transmission unit  9 . A Low-Pass Filter (LPF) unit  17  cuts off a high frequency beyond the range of human hearing. 
     Operation of the sound player according to the present exemplary embodiment will be described in detail below using a processing flowchart illustrated in  FIG. 12 . 
     When the speaker driving apparatus  1  is turned on in step S 101 , in step S 102 , the control unit  3  performs control to connect the selection unit  4  to a terminal B. As a result, the sound player supplies a high-frequency power signal beyond the range of human hearing from the power supply unit  6  to the power conversion unit  8  of the speaker apparatus  2  via the cable  7 . 
     In step S 104 , the power conversion unit  8  of the speaker apparatus  2  filters out and detects the input power signal. Then, the power conversion unit  8  supplies the filtered and detected power signal to the transmission unit  9  as a direct current signal, which indicates a supply of the power signal. In step S 105 , the power conversion unit  8  electrically accumulates the detected direct current signal. At this time, the sound player blocks the high-frequency power signal input to the speaker apparatus  2  with the LPF unit  17  so that the high-frequency power signal is not input to the speaker unit  16 . If there appears no negative effect due to a high-pass block action effect even when the sound player inputs the high-frequency power signal to the speaker unit  16 , the LPF unit  17  is not required. The high-pass block effect includes a mechanical high-pass block effect by a vibration system of the speaker unit  16  and an electrical high-pass block effect by inductance. 
     In step S 103 , the speaker driving apparatus  1  maintains a supply of the power signal, for example, for one second so that the power conversion unit  8  completes electricity accumulation. The power conversion unit  8  supplies the electrically accumulated electric power to the transmission unit  9  as a power supply. 
     In step S 106 , the control unit  3  controls the selection unit  4  to connect to a terminal C. The control unit  3  ends a supply of the power signal. The reception unit  12  starts reception of a data signal. 
     In step S 205 , the transmission unit  9  of the speaker apparatus  2  detects an end of a supply of the power signal from termination of a detection output from the power conversion unit  8 . 
     When the speaker apparatus  2  detects an end of a supply of the power signal, in step S 206 , the transmission unit  9  uses an electricity accumulation output from the power conversion unit  8  as a power to read data stored in the storage unit  10 . The read data includes maximum input electric power data of the speaker apparatus  2 . Further, the transmission unit  9  outputs the read data to an input terminal  11  as a data signal including a high-frequency component beyond the range of human hearing. The transmission unit  9  transmits the data signal to the speaker driving apparatus  1 . 
     The speaker driving apparatus  1  receives the data signal that the speaker apparatus  2  transmits through transmission processing in step S 206 , with the reception unit  12  via the selection unit  4  which selects the terminal C. The reception unit  12  outputs the received data signal to the control unit  3  as electroacoustic characteristic data and maximum input electric power data about the speaker apparatus  2 . In step S 307 , the control unit  3  determines existence or non-existence, and correctness of the acquired data. 
     When the control unit  3  detects that the reception is completed (YES in step S 307 ), in step S 309 , the control unit  3  sets a correction characteristic in the correction unit  13  so as to correct an audio signal by a reverse characteristic corresponding to the acquired electroacoustic characteristic data. In step S 310 , the control unit  3  sets a restriction value in the output restriction unit  27  which corresponds to and does not exceed the maximum input electric power data. 
     When the control unit  3  does not detect that the reception is completed successfully (NO in step S 307 ), in step S 308 , the control unit  3  controls, for example, a correction characteristic in the correction unit  13  to be a flat characteristic. In step S 312 , the control unit  3  sets maximum output electric power in the amplification unit  15  as a restriction value in the output restriction unit  27 . 
     The control unit  3  controls the correction unit  13  in correction processing in step S 309  after the control unit  3  completes reception successfully, or in correction processing performed in step S 308  when the control unit  3  does not complete reception successfully. Then, in step S 311 , the control unit  3  controls the selection unit  4  to select a terminal A. The correction unit  13  corrects the audio signal input to the audio input unit  14  of the speaker driving apparatus  1  so that a characteristic is suitable for an electroacoustic characteristic of the speaker apparatus  2 . The amplification unit  15  amplifies the corrected audio signal. Further, the output restriction unit  27  performs output restriction to the audio signal so that the output does not exceed maximum input electric power. Then, the speaker unit  16  of the speaker apparatus  2  produces sound based on the corrected audio signal. 
     Second Exemplary Embodiment 
       FIG. 2  is a block diagram illustrating a sound player according to a second exemplary embodiment of the present invention. In the second exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated, and the same reference numerals are provided to them. In the present exemplary embodiment, the output restriction unit  27  in the speaker driving apparatus  1  restricts a power supply to the amplification unit  15 , which restricts output electric power in the amplification unit  15 . 
     The output restriction unit  27  determines a voltage supplied to the amplification unit  15 , or a restriction value of over current protection, according to a restriction value of the output electric power in the amplification unit  15  so that the output power of the amplification unit  15  does not exceed the maximum input electric power of the speaker apparatus  2 . The maximum input electric power is instructed from the control unit  3 . Thus, the sound player restricts electric power supplied to the speaker apparatus  2  so that the output does not exceed the maximum input electric power. 
     Third Exemplary Embodiment 
       FIG. 3  is a block diagram illustrating a sound player in a third exemplary embodiment of the present invention. In the third exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. 
     In the present exemplary embodiment, instead of restricting output electric power in the amplification unit  15  by the output restriction unit  27  in  FIG. 1 , the sound player restricts the output electric power by the amplification unit  15  by controlling a sound volume in the correction unit  13 . 
     The control unit  3  controls the correction unit  13  to correct an audio signal by a reverse characteristic corresponding to electroacoustic characteristic about the speaker apparatus  2 . Simultaneously, the control unit  3  controls amplitude of the audio signal input to the amplification unit  15  so as to restrict a sound volume according to the maximum input electric power of the speaker apparatus  2 . Thus, the sound player restricts an output signal in the amplification unit  15  so that the output does not exceed the maximum input electric power of the speaker apparatus  2 . 
     Fourth Exemplary Embodiment 
       FIG. 4  is a block diagram illustrating a sound player according to a fourth exemplary embodiment of the present invention. In the fourth exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. 
     In the sound player according to the present exemplary embodiment, an impedance unit  29  is disposed between the power supply unit  6  and the selection unit  4  to add impedance to a power signal output. Further, the power signal output is connected to a data signal input in the reception unit  12 . The transmission unit  9  switches the power signal in response to a data signal by operating a switching unit  28  disposed on the speaker apparatus  2 . 
     The control unit  3  controls the selection unit  4  to select the terminal B for predetermined time after the speaker driving apparatus  1  is turned on. A power signal output from the power supply unit  6 , to which impedance is added, is output to the output terminal  5  to supply the power signal to the speaker apparatus  2  via the cable  7 . 
     The power conversion unit  8  electrically accumulates the power signal in the speaker apparatus  2  and supplies the power signal to the transmission unit  9  as a power source. When a sufficient amount of power for transmission is supplied to the transmission unit  9 , the transmission unit  9  controls the switching unit  28  to perform ON/OFF operation according to data on the storage unit  10  so that a data signal in the storage unit  10  is transmitted to the speaker driving apparatus  1  as a digital signal. That is, the data signal is a pulse signal which converts a power signal based on electroacoustic characteristic and/or maximum input electric power. The reception unit  12  of the speaker driving apparatus  1  receives the data signal formed by the power signal subjected to the switching. The present exemplary embodiment omits power supply termination processing in step S 204  which controls the selection unit  4  to select the terminal C as is described in the exemplary embodiments described above. Accordingly, the configuration according to the present embodiment is simplified. 
     Fifth Exemplary Embodiment 
       FIG. 5  is a block diagram illustrating a sound player according to a fifth exemplary embodiment of the present invention. In the fifth exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. 
     The amplification unit  15  is a digital amplifier. The sound player outputs its switching output signal to the terminal B in the selection unit  4 . The sound player outputs an audio signal obtained by filtering out the switching output signal in the LPF unit  17 , to the terminal A in the selection unit  4 . The amplification unit  15  (i.e., the digital amplifier) is also capable of outputting a switching signal which is another audio signal generated by subjecting a high frequency wave beyond the range of human hearing to pulse modulation. 
     The control unit  3  controls the selection unit  4  to select the terminal B for a predetermined time after a power of the speaker driving apparatus  1  is turned on. A switching output signal is output from the amplification unit  15  to the output terminal  5  as a power signal of high frequency beyond the range of human hearing. Then, the power signal is supplied to the speaker apparatus  2  via the cable  7 . 
     Then, an operation similar to the first exemplary embodiment is performed. In the fifth exemplary embodiment, the power supply unit  6  of the speaker driving apparatus  1  in  FIG. 1  can be omitted and the configuration according to the present embodiment is simplified. 
     Sixth Exemplary Embodiment 
       FIG. 6  is a block diagram illustrating a sound player according to a sixth exemplary embodiment of the present invention. In the sixth exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. 
     A transmission unit in the speaker apparatus  2  is a remote control transmission unit  9  having a similar configuration to an infrared remote control transmission apparatus which operates the speaker driving apparatus  1 . A reception unit in the speaker driving apparatus  1  is an infrared remote control reception unit  12 . 
     The control unit  3  controls the selection unit  4  to select the terminal B for a predetermined time after a power of the speaker driving apparatus  1  is turned on. A power signal of high frequency beyond the range of human hearing that the power supply unit  6  outputs, is output to the output terminal  5  and supplied to the speaker apparatus  2  via the cable  7 . 
     The high-frequency power signal input to the speaker apparatus  2  is input to the power conversion unit  8 . The sound player supplies a detected output to the transmission unit  9  as a power supply. When the sound player supplies the power to the transmission unit  9 , the transmission unit  9  reads electroacoustic characteristic and maximum input electric power of the speaker apparatus  2  stored in the storage unit  10  to execute infrared transmission to the reception unit  12  as a data signal. At this time, the sound player does not transmit the data signal via the cable  7 . Accordingly, an electricity accumulation operation in the power conversion unit  8  and time-division control of communication are not required. 
     The sound player inputs the data signal received by the reception unit  12  to the control unit  3  as electroacoustic characteristic data and maximum input electric power data about the speaker apparatus  2 . 
     The control unit  3  corrects an input audio signal using a reverse characteristic corresponding to electroacoustic characteristic data. The control unit  3  controls the correction unit  13  to restrict output electric power output from the amplification unit  15  according to maximum input electric power. Then, the control unit  3  controls the selection unit  4  to select the terminal A. 
     The apparatus according to the sixth exemplary embodiment operates similar to the first exemplary embodiment as described below. The present exemplary embodiment can omit the terminal C in the selection unit  4  of the speaker driving apparatus  1  and an electricity accumulation unit in the power conversion unit  8  of the speaker apparatus  2  in  FIG. 1 . Thus, cost of the apparatus according to the can be lowered. 
     Seventh Exemplary Embodiment 
       FIG. 7  is a block diagram illustrating a sound player according to a seventh exemplary embodiment of the present invention. In the seventh exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. The present exemplary embodiment includes not only a plurality of speaker apparatuses  2  and cables  7 , but also a plurality of selection units  4 , amplification units  15 , and output terminals  5  in the speaker driving apparatus  1  in order to execute multichannel reproduction. 
     The control unit  3  controls the selection unit  4  (first selection unit) and a selection unit  18  (second selection unit) so that each selects a terminal B thereof for a predetermined time after a power of the speaker driving apparatus  1  is turned on. A power signal of high frequency beyond the range of human hearing is output from the power supply unit  6  to the output terminal  5  (first output terminal) and an output terminal  20  (second output terminal) respectively. The sound player supplies a power signal to the speaker apparatus  2  (first speaker apparatus) and a speaker apparatus  17  (second speaker apparatus) via the cable  7  (first cable) and a cable  21  (second cable). 
     When the power conversion units  8  and  22  complete electricity accumulation with the power signal input to the speaker apparatuses  2  and  27 , the control unit  3  controls the selection units  4  and  18  so that each unit selects the terminal C. The sound player inputs a data signal corresponding to electroacoustic characteristic data and maximum input electric power data that the respective speaker apparatuses  2  and  27  transmit to the control unit  3  via the reception unit  12 . 
     The control unit  3  controls an audio signal with a reverse characteristic corresponding to electroacoustic characteristic of the speaker apparatus  2  and  17 . The control unit  3  also controls the correction unit  13  to restrict output electric power in the amplification units  15  and  19  according to the maximum input electric power. The sound player controls the selection units  4  and  18  so that each unit selects the terminal A. 
     As described above, the sound player corrects the audio signal that is input to the respective audio input units  14  and  23  of the speaker driving apparatus  1 . The audio signal is changed to a characteristic suitable for an electroacoustic characteristic of the respective speaker apparatus  2  and  17 , by the correction unit  13 . Further, the output is restricted by sound volume correction so that the output does not exceed a maximum input electric power of the respective speaker apparatus  2  and  17 . Then, the amplification units  15  and  19  amplify the input audio signal. Then, the speaker units  16  and  24  each produce sound based on the respective corrected audio signals supplied thereto. 
     Eighth Exemplary Embodiment 
       FIG. 8  is a block diagram illustrating a sound player according to an eighth exemplary embodiment of the present invention. In the eighth exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. In the present exemplary embodiment, a connection detection unit  25 , which detects that the speaker apparatus  2  functioning as a load is connected, is connected to the output terminal  5 . 
     The control unit  3  controls the selection unit  4  to select the terminal B for a predetermined time after a power of the speaker driving apparatus  1  is turned on or for a predetermined time after the connection detection unit  25  detects that the speaker apparatus  2  functioning as a load is connected to the output terminal  5  via the cable  7 . A power signal of high frequency beyond the range of human hearing output from the power supply unit  6  is output to the output terminal  5  and supplied to the speaker apparatus  2  via the cable  7 . 
     The apparatus according to the eighth exemplary embodiment operates similarly to the first exemplary embodiment in other respects. 
     According to the present exemplary embodiment, even if the speaker apparatus  2  is replaced when a power of the speaker driving apparatus  1  is still turned on, the sound player can correct an input audio signal so that a characteristic is suitable for an electroacoustic characteristic and maximum input electric power of a newly connected speaker apparatus. 
     Ninth Exemplary Embodiment 
       FIG. 9  is a block diagram illustrating a sound player according to a ninth exemplary embodiment of the present invention. In the ninth exemplary embodiment, a description about substantially the same configurations as those in the above-described first exemplary embodiment is not repeated and the same reference numerals are provided to them. In the present exemplary embodiment, the power supply unit  6  outputs a power signal of low frequency outside the range of human hearing, or a direct current. 
     The control unit  3  controls the selection unit  4  to select the terminal B for a predetermined time after a power of the speaker driving apparatus  1  is turned on. The power signal of the low frequency outside the range of human hearing, or the direct current output from the power supply unit  6  is output to the output terminal  5  and supplied to the speaker apparatus  2  via the cable  7 . 
     The low-frequency power signal input to the speaker apparatus  2 , is not input to the speaker apparatus  16  because it is cut off by a high-pass filter unit (HPF)  26  but is input to the power conversion unit  8 . An output detected in the power conversion unit  8  is input to the transmission unit  9  as a signal indicating a supply of the power signal. Simultaneously, an output, which is converted into a direct current voltage and electrically accumulated, is supplied to the transmission unit  9  as a power supply. 
     The apparatus according to the ninth exemplary embodiment operates in a similar manner to the first exemplary embodiment in other respects. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2007-036604 filed Feb. 16, 2007, which is hereby incorporated by reference herein in its entirety.