Speaker system

Abstract

Faithfully reproduce natural sounds that are faithful to the original sound. 【Solution means】 The LPF 13 removes high-frequency components from the original sound signal and outputs a first drive signal. The woofer 10 is driven by the first drive signal and reproduces sounds in the low-frequency range. The vibration detection unit 12 outputs a first reproduction signal corresponding to the vibration of the vibration system of the woofer 10. The subtractor 14 generates a first difference signal by subtracting the first reproduction signal from the original sound signal. The LPF 23 removes high-frequency components from the first difference signal and outputs a second drive signal. The full-range speaker 20 is driven by the second drive signal. The vibration detection unit 22 outputs a second reproduction signal corresponding to the vibration of the vibration system of the full-range speaker 20. The subtractor 24 generates a second difference signal by subtracting the second reproduction signal from the first difference signal. The tweeter 30 is driven based on the second difference signal and reproduces sounds in the high-frequency range.

Description

Technical Field

[0001] The present invention relates to a speaker system in the mu .

Background Art

[0002] A full-range speaker reproduces sound with a single speaker from a low-frequency sound to a high-frequency sound. A multi-way speaker reproduces sound with speakers suitable for each of a plurality of sound ranges. For example, in a three-way speaker, a woofer suitable for reproducing low-frequency sound, a squawker suitable for reproducing mid-frequency sound, and a tweeter suitable for reproducing high-frequency sound are used. Further, a sub-woofer (also referred to as a super woofer) suitable for reproducing ultra-low-frequency sound or a super tweeter suitable for reproducing ultra-high-frequency sound may be used.

[0003] In a multi-way speaker, a network circuit is used to divide the band of the sound to be reproduced by each speaker. The network circuit includes a low-pass filter and a high-pass filter. The low-pass filter passes low frequencies, and the high-pass filter passes high frequencies.

[0004] Also, MFB (Motional feedback) detects the vibration of the vibration system of the speaker, and feeds back a signal corresponding to the vibration to the drive circuit of the speaker to correct the drive signal. Thereby, it is possible to output sound faithful to the original sound from the speaker. The vibration system of the speaker includes a diaphragm (for example, cone paper), a voice coil bobbin, a damper, and a center cap, etc.

[0005] As a vibration detection circuit for detecting the vibration of the vibration system of a speaker for MFB, there are known a vibration detection circuit that detects a change in an electrical signal generated in a piezoelectric element due to the vibration of the vibration system, a vibration detection circuit that detects a change in the sound pressure level received from a diaphragm with a microphone, and a vibration detection circuit that detects vibration by causing light emitted from a light emitting element to be incident on a light reflecting member attached to the vibration system and receiving the reflected light with a light receiving element (see, for example, Patent Document 1).

[0006] Also, a vibration detection circuit is known in which an MFB detection coil is provided in parallel with a voice coil near the voice coil of a speaker, and the vibration of the speaker is detected by this MFB detection coil. An MFB speaker equipped with this vibration detection circuit is on the market (see, for example, Non-Patent Document 1).

[0007] Also, a metal plate is fixed to a surface close to the center cap (metal) of a speaker so as not to contact the center cap, and a vibration detection circuit (based on the principle of a condenser microphone) that detects the vibration of the speaker from a change in the capacitance between the center cap and the metal plate is known. An MFB speaker equipped with this vibration detection circuit is also on the market (see, for example, Non-Patent Document 2).

[0008] Also, Patent Document 2 describes a vibration detection device including a light source that emits light, a first light receiving element that receives the light emitted by the light source, a second light receiving element that receives the light emitted by the light source, a light reception amount adjustment means that changes the light reception amounts of the first light receiving element and the second light receiving element according to the movement of a vibration part that generates sound in an acoustic reproduction part, a pair of the first light receiving element and the second light receiving element operating as a differential pair, and a signal detection part that outputs a reproduction signal according to the difference between the light reception amount of the first light receiving element and the light reception amount of the second light receiving element.

[0009] Further, Patent Document 3 describes a 3D speaker device including a pair of left and right high-frequency speakers, first and second amplifiers for driving the speakers, first and second detectors for detecting the vibration acceleration of the speakers, a comparator for comparing the outputs of the first and second detectors with the original input signal to the high-frequency speakers, a high-cut filter for cutting the high-frequency component of the output signal of the comparator, a third amplifier for amplifying the output signal of the high-cut filter, and a low-frequency speaker driven by the third amplifier. This 3D speaker device has a motional feedback in which the vibration acceleration detection signal of the high-frequency speaker and the original input signal to the high-frequency speaker are input to the comparator, and the driving of the low-frequency speaker is controlled by the output of the comparator. Note that Patent Document 3 describes a woofer and a super-woofer as examples of the high-frequency speaker and the low-frequency speaker, respectively.

[0010] Further, Patent Document 4 describes a speaker system including a main speaker driven by an original sound signal output from a sound source, a vibration detection unit that detects the vibration of the vibration system of the main speaker and outputs a reproduction signal corresponding to the vibration, a subtractor that outputs an error signal indicating the difference between the original sound signal and the reproduction signal, and a sub-speaker that outputs a sound having the same phase as the sound of the main speaker to increase the sound pressure level when the sound pressure level of the main speaker is insufficient based on the error signal, and outputs a sound having a phase opposite to that of the sound of the main speaker to decrease the sound pressure level when the sound pressure level of the main speaker is excessive.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Document

[0012]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] In a multi-way speaker, the same sound is output from two speakers in the crossover frequency range of each speaker. In the crossover frequency range, for example, a low-pass filter and a high-pass filter included in a network circuit attenuate the sound of each speaker, but an unnatural change in sound pressure level is likely to occur. To prevent this, a precise filter design is required.

[0014] An object of the present invention is to provide a speaker system that can faithfully reproduce the original sound and comprehensively reproduce natural sound. the mu To provide.

Means for Solving the Problems

[0015] To achieve the above object, the speaker system of the present invention A first low-pass filter that removes high-frequency components from an input signal and outputs a first drive signal, and A first speaker that is driven by the first drive signal and reproduces sound in the low-frequency range, and A first vibration detection unit that outputs a first reproduction signal corresponding to the vibration of the vibration system of the first speaker; A first subtractor that generates a first difference signal by subtracting the first reproduction signal from the input signal; A second low-pass filter that has a cut-off frequency higher than the cut-off frequency of the first low-pass filter, removes high-frequency components from the first difference signal, and outputs a second drive signal; A full-range speaker driven by the second drive signal; A second vibration detection unit that outputs a second reproduction signal corresponding to the vibration of the vibration system of the full-range speaker; A second subtractor that generates a second difference signal by subtracting the second reproduction signal from the first difference signal; A third speaker that is driven based on the second difference signal and reproduces high-frequency sounds; Comprising.

[0016] Also, the filter of the present invention A low-pass filter that removes high-frequency components from the input signal and outputs a low-frequency signal containing only low-frequency components; A subtractor that subtracts the low-frequency signal from the input signal and outputs a low-frequency removal signal containing only the high-frequency components removed by the low-pass filter; Comprising.

[0017] Also, the speaker system of the present invention A first low-pass filter that removes high-frequency components from the input signal and outputs a first low-frequency signal; A first speaker driven by the first low-frequency signal; A first subtractor that subtracts the first low-frequency signal from the input signal and outputs a first low-frequency removal signal containing only the high-frequency components removed by the first low-pass filter; A second speaker driven based on the first low-frequency removal signal; Comprising.

[0018] Preferably, the speaker system of the present invention is a second low-pass filter having a cut-off frequency higher than the cut-off frequency of the first low-pass filter, removing high-frequency components from the first low-frequency removal signal, and outputting a second low-frequency signal; a second subtractor that subtracts the second low-frequency signal from the first low-frequency removal signal and outputs a second low-frequency removal signal including only the high-frequency components removed by the second low-pass filter; a third speaker driven based on the second low-frequency removal signal; and includes the second speaker is driven by the second low-frequency signal.

[0019] Also, the speaker system of the present invention is a first low-pass filter that removes high-frequency components from an input signal and outputs a drive signal; a first speaker driven by the drive signal and reproducing a sound in a low frequency range; a vibration detection unit that outputs a reproduction signal corresponding to the vibration of the vibration system of the first speaker; a first subtractor that subtracts the reproduction signal from the input signal and outputs a difference signal; a second low-pass filter having a cut-off frequency higher than the cut-off frequency of the first low-pass filter, removing high-frequency components from the difference signal, and outputting a low-frequency signal; a full-range speaker driven by the low-frequency signal; a second subtractor that subtracts the low-frequency signal from the difference signal and outputs a low-frequency removal signal including only the high-frequency components removed by the second low-pass filter; a third speaker driven based on the low-frequency removal signal and reproducing a sound in a high frequency range; and includes.

[0020] Also, the filter of the present invention is a high-pass filter that removes low-frequency components from an input signal and outputs a high-frequency signal including only high-frequency components; A subtractor that subtracts the high-frequency signal from the input signal and outputs a high-frequency removal signal containing only the low-frequency components removed by the high-pass filter. is provided.

[0021] Also, the speaker system of the present invention A first high-pass filter that removes low-frequency components from the input signal and outputs a first high-frequency signal, A first speaker driven by the first high-frequency signal, A first subtractor that subtracts the first high-frequency signal from the input signal and outputs a first high-frequency removal signal containing only the low-frequency components removed by the first high-pass filter, A second speaker driven based on the first high-frequency removal signal, is provided.

[0022] Preferably, the speaker system of the present invention A second high-pass filter having a cut-off frequency lower than the cut-off frequency of the first high-pass filter, removing low-frequency components from the first high-frequency removal signal, and outputting a second high-frequency signal, A second subtractor that subtracts the second high-frequency signal from the first high-frequency removal signal and outputs a second high-frequency removal signal containing only the low-frequency components removed by the second high-pass filter, A third speaker driven based on the second high-frequency removal signal, is provided, The second speaker is driven by the second high-frequency signal.

Advantages of the Invention

[0023] According to the present invention, it is possible to faithfully reproduce a natural sound that is faithful to the original sound.

Brief Description of the Drawings

[0024]

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Embodiments for Carrying Out the Invention

[0025] Hereinafter, a speaker system according to an embodiment of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, common components are denoted by the same reference numerals, and repeated explanations are omitted.

[0026] In the 3D speaker device described in Patent Document 3, a detector for detecting vibration acceleration is provided in the high-frequency side speaker. This 3D speaker device inputs the vibration acceleration detection signal of the high-frequency side speaker and the input original signal to the high-frequency side speaker to a comparator, and controls the driving of the low-frequency side speaker according to the output of the comparator. That is, this 3D speaker device corrects the sound of the high-frequency side speaker with the sound of the low-frequency side speaker.

[0027] However, usually the vibration system of the low-frequency side speaker is heavier than that of the high-frequency side speaker. Due to the action of inertia, the movement of the vibration system of the low-frequency side speaker is slower than that of the vibration system of the high-frequency side speaker. For this reason, when correcting the sound of the high-frequency side speaker with the sound of the low-frequency side speaker, the correction is delayed in time compared to correcting the sound of the low-frequency side speaker with the sound of the high-frequency side speaker, and it is likely to become an unnatural sound.

[0028] FIG. 1 shows an example of the configuration of a speaker system 200 according to an invention using the invention described in Patent Document 4. The speaker system 200 includes a woofer 10, an amplifier 11, a vibration detection unit 12, a subtractor 14, a full-range speaker 20, an amplifier 21, an LPF (low-pass filter) 23, a tweeter 30, an amplifier 31, and an HPF (high-pass filter) 35.

[0029] An original sound signal output from a sound source is input to the input terminal 100. The original sound signal is amplified by the amplifier 11 and drives the woofer 10. That is, the woofer 10 is driven based on the original sound signal and reproduces the sound in the low frequency range. The vibration detection unit 12 detects the vibration of the vibration system of the woofer 10 and outputs a reproduction signal corresponding to the vibration. The vibration system includes, for example, the diaphragm (e.g., cone paper) of the woofer 10, the voice coil bobbin, the damper, and the center cap. The same applies to the full-range speaker 20 and the tweeter 30. The same also applies to the subwoofer 60 and the super tweeter 70 described later. The vibration detection unit 12 has the same configuration as the vibration detection circuit used in the motional feedback. The subtractor 14 is, for example, a differential amplifier. The original sound signal is input to the non-inverting input terminal (+) of the subtractor 14, and the reproduction signal is input to the inverting input terminal (-). The subtractor 14 generates a difference signal indicating the difference between the original sound signal and the reproduction signal by subtracting the reproduction signal from the original sound signal. The subtractor 14 outputs a difference signal indicating the difference between the original sound signal and the reproduction signal. The difference signal is defined by the following equation (1).

[0030] Difference signal = Original sound signal - Reproduction signal (1)

[0031] The LPF 23 passes a difference signal lower than a predetermined upper limit frequency. That is, the LPF 23 removes the high frequency component from the difference signal and outputs a drive signal for driving the full-range speaker 20. The drive signal is amplified by the amplifier 21 and drives the full-range speaker 20. The HPF 35 passes a difference signal higher than a predetermined lower limit frequency. That is, the HPF 35 removes the low frequency component from the difference signal and outputs a drive signal for driving the tweeter 30. The drive signal is amplified by the amplifier 31 and drives the tweeter 30. The LPF 23 and the HPF 35 constitute the network circuit 110. The network circuit 110 is the same as that used in a normal three-way speaker.

[0032] FIG. 2 shows an example of the relationship between frequency and sound pressure in the speaker system 200. FIG. 2 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. The full-range speaker 20 outputs sound based on the differential signal. The sound of the woofer 10 is corrected by the sound of the full-range speaker 20. When the sound pressure level of the woofer 10 is the same as that of the original sound signal, the full-range speaker 20 does not output sound. When the sound pressure level of the woofer 10 is insufficient, the full-range speaker 20 outputs sound with the same phase as the sound of the woofer 10 to increase the sound pressure level. When the sound pressure level of the woofer 10 is excessive, the full-range speaker 20 outputs sound with the opposite phase to the sound of the woofer 10 to decrease the sound pressure level. When the sound pressure level of the woofer 10 is 0, the full-range speaker 20 outputs sound with the same sound pressure level as the original sound signal.

[0033] As the frequency increases, the sound pressure level of the woofer 10 decreases. However, at this time, the full-range speaker 20 outputs sound with the same phase as the sound of the woofer 10, and increases the sound pressure level of the entire speaker system 200 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the woofer 10 and the sound of the full-range speaker 20 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 200, there is no unnatural change in the sound pressure level between the sound range reproduced by the woofer 10 and the sound range reproduced by the full-range speaker 20. A network circuit is not required between the sound range reproduced by the woofer 10 and the sound range reproduced by the full-range speaker 20.

[0034] The network circuit 110 mainly causes the full-range speaker 20 to reproduce components of a frequency lower than a predetermined crossover frequency (fc) based on a differential signal, and mainly causes the tweeter 30 to reproduce components of a frequency higher than fc. However, in the crossover range, the full-range speaker 20 and the tweeter 30 autonomously output sound based on the differential signal. For this reason, the speaker system 200 may cause an unnatural change in sound pressure level in the crossover range between the sound range reproduced by the full-range speaker 20 and the sound range reproduced by the tweeter 30.

[0035] The speaker system 200 corrects the sound of the woofer 10 with the sound of the full-range speaker 20. The vibration system of the full-range speaker 20 is usually lighter than the vibration system of the woofer 10. The movement of the vibration system of the full-range speaker 20 is faster than the movement of the vibration system of the woofer 10. For this reason, compared with a configuration in which the sound of the full-range speaker 20 is corrected by the sound of the woofer 10 as in the 3D speaker device described in Patent Document 3, the speaker system 200 corrects the sound of the woofer 10 by the full-range speaker 20 more quickly and can reproduce natural sound.

[0036] Also, resonance of the speaker and resonance inside the speaker box may have a serious impact on the sound quality. Especially in the low-frequency range, when resonance or resonance occurs, the sound may become muddy and the clear sound quality may be impaired. This is because resonance or resonance emphasizes sound waves at a specific frequency and suppresses other frequency components. According to the speaker system 200, for example, when the level of sound at a specific frequency increases due to resonance or resonance in the woofer 10, the full-range speaker 20 emits sound so that the level of sound at that specific frequency decreases. For this reason, the influence of resonance and resonance is suppressed in the speaker system 200.

[0037] Furthermore, the cone paper (paper material) used in many speakers has its reproduction characteristics change over time (even over the years) depending on the usage environment, especially humidity. The heavier the mass of the cone paper in a speaker for reproducing bass, the more susceptible it is to the influence of humidity. Also, the mass of the edge and damper increases. For this reason, it is more likely to be affected by physical property changes (aging hardening, etc.) of the edge and damper. As a result, the sound output by the speaker may change. In the speaker system 200, the full-range speaker 20 corrects the change in sound due to the change over time of the vibration system (hereinafter referred to as the change over time of the vibration system) including the cone paper and damper of the woofer 10 within the audible range that it can output.

[0038] FIG. 3 shows an example of the configuration of a speaker system 201 according to the first embodiment of the present invention. The speaker system 201 includes a woofer 10, an amplifier 11, a vibration detection unit 12, a subtractor 14, a full-range speaker 20, an amplifier 21, a vibration detection unit 22, a subtractor 24, a tweeter 30, an amplifier 31, and an HPF (high-pass filter) 120. The speaker system 201 differs from the speaker system 200 in FIG. 1 in that it has a vibration detection unit 22 and a subtractor 24 for the full-range speaker 22, has an HPF 120, and does not have a network circuit 110. In other respects, the configuration of the speaker system 201 is the same as the configuration of the speaker system 200 in FIG. 1.

[0039] The input terminal 100 receives the original sound signal output from the sound source. The original sound signal is amplified by the amplifier 11 and drives the woofer 10. That is, the woofer 10 is driven based on the original sound signal and reproduces the sound in the low frequency range. The vibration detection unit 12 detects the vibration of the vibration system of the woofer 10 and outputs a first reproduction signal corresponding to the vibration. Note that the first differential signal corresponds to the differential signal in the speaker system 200 of FIG. 1. The subtractor 14 is, for example, a differential amplifier. The original sound signal is input to the non-inverting input terminal (+) of the subtractor 14, and the first reproduction signal is input to the inverting input terminal (-). The subtractor 14 generates a first differential signal indicating the difference between the original sound signal and the first reproduction signal by subtracting the first reproduction signal from the original sound signal. The first differential signal is defined by the following equation (2).

[0040] First differential signal = original sound signal - first reproduction signal (2)

[0041] The first differential signal is amplified by the amplifier 21 and drives the full-range speaker 20. That is, the full-range speaker 20 is driven based on the first differential signal. The vibration detection unit 22 detects the vibration of the vibration system of the full-range speaker 20 and outputs a second reproduction signal corresponding to the vibration. The vibration detection unit 22 has the same configuration as the vibration detection circuit used in the motional feedback. The subtractor 24 is, for example, a differential amplifier. The first differential signal is input to the non-inverting input terminal (+) of the subtractor 24, and the second reproduction signal is input to the inverting input terminal (-). The subtractor 24 generates a second differential signal indicating the difference between the first differential signal and the second reproduction signal by subtracting the second reproduction signal from the first differential signal. The second differential signal is defined by the following equation (3).

[0042] Second differential signal = first differential signal - second reproduction signal (3)

[0043] The HPF 120 passes a second differential signal having a frequency higher than a predetermined lower limit frequency. The HPF 120 removes frequency components from the second differential signal that may damage the vibration system of the tweeter 30. The second differential signal is amplified by the amplifier 31. The tweeter 30 is driven by the amplified second differential signal with low frequency components removed. That is, the tweeter 30 is driven based on the second differential signal and reproduces high-pitched sounds.

[0044] FIG. 4 shows an example of the relationship between frequency and sound pressure in the speaker system 201. FIG. 4 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. The relationship between the sound of the woofer 10 and the sound of the full-range speaker 20 in the speaker system 201 is the same as the relationship in the speaker system 200 of FIG. 1.

[0045] The tweeter 30 is driven by the second differential signal and outputs high-pitched sounds. That is, the tweeter 30 is driven based on the second differential signal and outputs high-pitched sounds. The sound of the full-range speaker 20 is corrected by the sound of the tweeter 30. When the sound pressure level of the full-range speaker 20 is the same as the sound pressure level of the original sound signal, the tweeter 30 does not produce sound. When the sound pressure level of the full-range speaker 20 is insufficient, the tweeter 30 outputs a sound with the same phase as the sound of the woofer 10 to increase the sound pressure level. When the sound pressure level of the full-range speaker 20 is excessive, the tweeter 30 outputs a sound with a phase opposite to that of the sound of the full-range speaker 20 to decrease the sound pressure level.

[0046] As the frequency increases, the sound pressure level of the full-range speaker 20 decreases. However, at this time, the tweeter 30 outputs a sound with the same phase as the sound of the full-range speaker 20, and increases the sound pressure level of the entire speaker system 201 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the full-range speaker 20 and the sound of the tweeter 30 is the same as the sound pressure level of the original sound signal. Different from the speaker system 200 in FIG. 1, in the speaker system 201, the network circuit 110 is unnecessary. In the speaker system 201, no unnatural change in the sound pressure level occurs between the sound range reproduced by the full-range speaker 20 and the sound range reproduced by the tweeter 30.

[0047] Also, in the speaker system 201, the tweeter 30 corrects the sound of the full-range speaker 20 in the sound range that it can output. For example, even if the sound changes due to the temporal change of the vibration system in the full-range speaker 20, the sound of the full-range speaker 20 is corrected by the sound of the tweeter 30.

[0048] Also, in the speaker system 201, it is important to prevent the output of low-frequency sounds by the tweeter 30 and prevent damage to the tweeter 30. To achieve this purpose, an HPF 120 is provided. As shown in FIG. 4, the lower limit frequency of the sound range in which the tweeter 30 can output sound is set by the HPF 120 to a frequency at which there is no risk of the tweeter 30 being damaged. The HPF 120 may be a simple high-pass filter, for example, it may be composed only of a capacitor.

[0049] FIG. 5 shows an example of the configuration of the speaker system 202 according to the second embodiment of the present invention. The speaker system 202 includes a woofer 10, an amplifier 11, a vibration detector 12, an LPF 13, a subtractor 14, a full-range speaker 20, an amplifier 21, a vibration detector 22, an LPF 23, a subtractor 24, a tweeter 30, an amplifier 31, and an HPF 120. The speaker system 202 is different from the speaker system 201 in FIG. 3 in that it has the LPF 13 and the LPF 23. In other respects, the configuration of the speaker system 202 is the same as that of the speaker system 201 according to the first embodiment. Hereinafter, the differences between the speaker system 202 and the speaker system 201 will be described.

[0050] FIG. 6 shows an example of the relationship between the frequency and the sound pressure in the speaker system 202. FIG. 6 is an example in which an original sound signal with a constant sound pressure level is input at all frequencies. The LPF 13 removes high-frequency components of high frequencies from the original sound signal and outputs a first drive signal. The first drive signal is amplified by the amplifier 11 to drive the woofer 10. The woofer 10 is driven by the first drive signal. That is, the woofer 10 is driven based on the original sound signal and reproduces sounds in the low frequency range. The LPF 23 removes high-frequency components of high frequencies from the first difference signal and outputs a second drive signal. The second drive signal is amplified by the amplifier 21 to drive the full-range speaker 20. The full-range speaker 20 is driven by the second drive signal. That is, the full-range speaker 20 is driven based on the first difference signal. The cut-off frequency (blocking frequency) of the LPF 23 is higher than the cut-off frequency of the LPF 13. That is, the cut-off frequency of the LPF 13 is lower than the cut-off frequency of the LPF 23. Also, the cut-off frequency of the HPF 120 is set lower than the cut-off frequency of the LPF 23.

[0051] The cut-off frequencies of LPF13 and LPF23 can be set, for example, to the same cut-off frequencies as those of the low-pass filters included in the network circuits in a conventional three-way speaker, respectively. That is, the speaker system 202 can set the sound ranges of the sounds reproduced by the woofer 10, the full-range speaker 20, and the tweeter 30, for example, in the same way as the sound ranges of the sounds reproduced by a conventional three-way speaker, respectively. However, the cut-off frequencies of LPF13 and LPF23 may be different from the cut-off frequencies of the low-pass filters included in the network circuits in a conventional three-way speaker. Also, in the speaker system 202, a strict (sharp) crossover frequency setting as in the prior art is not required. For this reason, LPF13 and LPF23 may be simpler filters than those in the prior art, respectively.

[0052] Note that the original sound signal is an example of the input signal in the present invention. The woofer 10 and the tweeter 30 are examples of the first speaker and the third speaker in the present invention, respectively. LPF13 and LPF23 are examples of the first low-pass filter and the second low-pass filter of the present invention, respectively.

[0053] FIG. 7 shows an example of the configuration of a speaker system 203 according to a third embodiment of the present invention. The speaker system 203 is an extension of the speaker system 202 according to the second embodiment to stereo. The speaker system 203 includes a woofer 10, an amplifier 11, a vibration detection unit 12, an LPF 13, a subtractor 14, a subtractor 15, an amplifier 16, an amplifier 17, a full-range speaker 20, an amplifier 21, a vibration detection unit 22, an LPF 23, a subtractor 24, a tweeter 30, an amplifier 31, a full-range speaker 40, an amplifier 41, a vibration detection unit 42, an LPF 43, a subtractor 44, a tweeter 50, an amplifier 51, an HPF 120, and an HPF 121. The speaker system 203 is obtained by adding a subtractor 15, an amplifier 16, an amplifier 17, a full-range speaker 40, an amplifier 41, a vibration detection unit 42, an LPF 43, a subtractor 44, a tweeter 50, an amplifier 51, and an HPF 121 to the speaker system 202 according to the second embodiment. Hereinafter, the differences between the speaker system 203 and the speaker system 202 will be described.

[0054] A first original sound signal and a second original sound signal output from a sound source are input to an input terminal 101 and an input terminal 102, respectively. The amplifier 16 amplifies the first original sound signal, and the amplifier 17 amplifies the second original sound signal. The output terminals of the amplifier 16 and the amplifier 17 are connected at a connection point 18. The amplified first original sound signal and the second original sound signal are added at the connection point 18. The added first original sound signal and the second original sound signal pass through the LPF 13 and are amplified by the amplifier 11 and input to the woofer 10. The LPF 13 removes high-frequency components from the added first original sound signal and the second original sound signal and outputs a drive signal. The drive signal is amplified by the amplifier 11 to drive the woofer 10. That is, the woofer 10 is driven based on the added first original sound signal and the second original sound signal and reproduces a sound in the low frequency range.

[0055] The first original sound signal is input to the non-inverting input terminal (+) of the subtractor 14, and the first reproduction signal is input to the inverting input terminal (-). The subtractor 14 generates a first difference signal indicating the difference between the first original sound signal and the first reproduction signal by subtracting the first reproduction signal from the first original sound signal. The first difference signal is defined by the following equation (4).

[0056] First difference signal = First original sound signal - First reproduction signal (4)

[0057] The subtractor 15 is, for example, a differential amplifier. The second original sound signal is input to the non-inverting input terminal (+) of the subtractor 15, and the first reproduction signal is input to the inverting input terminal (-). The subtractor 15 generates a fifth difference signal indicating the difference between the second original sound signal and the first reproduction signal by subtracting the first reproduction signal from the second original sound signal. The fifth difference signal is defined by the following equation (5).

[0058] Fifth difference signal = Second original sound signal - First reproduction signal (5)

[0059] The full-range speaker 40, the amplifier 41, the vibration detector 42, the LPF 43, and the subtractor 44 operate in the same manner as the full-range speaker 20, the amplifier 21, the vibration detector 22, the LPF 23, and the subtractor 24, respectively. The LPF 43 removes high-frequency components from the fifth difference signal and outputs a drive signal. The drive signal is amplified by the amplifier 41 to drive the full-range speaker 40. That is, the full-range speaker 40 is driven based on the fifth difference signal. The cut-off frequency of the LPF 43 is higher than the cut-off frequency of the LPF 13. The vibration detector 42 outputs a fifth reproduction signal. The fifth difference signal is input to the non-inverting input terminal (+) of the subtractor 44, and the fifth reproduction signal is input to the inverting input terminal (-). The subtractor 44 generates a sixth difference signal indicating the difference between the fifth difference signal and the fifth reproduction signal by subtracting the fifth reproduction signal from the fifth difference signal. The sixth difference signal is defined by the following equation (6).

[0060] 6th differential signal = 5th differential signal - 5th reproduced signal (6)

[0061] HPF121 operates in the same manner as HPF120. The cut-off frequency of HPF121 is set lower than the cut-off frequency of LPF43. HPF121 removes frequency components from the 6th differential signal that may damage the vibration system of tweeter 50. Tweeter 50 and amplifier 51 operate in the same manner as tweeter 30 and amplifier 31. The 6th differential signal from which high-frequency components have been removed is amplified by amplifier 51 and supplied to tweeter 50. Tweeter 50 has low-frequency components removed and is driven by the amplified 6th differential signal to output sound in the high-frequency range. That is, tweeter 50 is driven based on the 6th differential signal and outputs sound in the high-frequency range.

[0062] FIG. 8 shows an example of the relationship between the frequency and sound pressure of the sound reproduced by woofer 10 in speaker system 203 of FIG. 7. FIG. 8 is an example in which there is a difference in the levels of the first original sound signal and the second original sound signal, and the level of the first original sound signal is greater than the level of the second original sound signal. Woofer 10 is driven by the sum of the first original sound signal and the second original sound signal. For this reason, woofer 10 reproduces sound at a level that is the average of the levels of the first original sound signal and the second original sound signal.

[0063] FIG. 9 shows an example of the relationship between the frequency and sound pressure of the sound reproduced by one full-range speaker 20 and tweeter 30 in speaker system 203 of FIG. 7. Full-range speaker 20 and tweeter 30 reproduce sound based on the first original sound signal. The example of FIG. 9 shows the case where the first original sound signal shown in FIG. 8 is input to input terminal 101. Since the level of the sound reproduced by woofer 10 is lower than the level of the first original sound signal, full-range speaker 20 outputs sound in the same phase as the sound of woofer 10 to increase the sound pressure level.

[0064] FIG. 10 shows an example of the relationship between the frequency and sound pressure of the sound reproduced by the other full-range speaker 40 and the tweeter 50 in the speaker system 203 of FIG. 7. The full-range speaker 40 and the tweeter 50 reproduce sound based on the second original sound signal. The example of FIG. 10 shows the case where the second original sound signal shown in FIG. 8 is input to the input terminal 102. In the region A surrounded by the dashed ellipse, the level of the sound reproduced by the woofer 10 is greater than the level of the second original sound signal. Therefore, in the region A, the full-range speaker 40 outputs a sound with a phase opposite to that of the sound of the woofer 10 to reduce the sound pressure level. In the portion where the frequency is higher than the region A, the sound reproduced by the woofer 10 gradually becomes smaller due to the action of the LPF 43. In this portion, since the level of the sound reproduced by the woofer 10 is smaller than the level of the second original sound signal, the full-range speaker 40 outputs a sound with the same phase as the sound of the woofer 10 to increase the sound pressure level.

[0065] In the 3D speaker device described in Patent Document 3, the low-frequency side speaker is driven based on the sum of two signals respectively indicating the vibrations of the vibration systems of the pair of high-frequency side speakers on the left and right and the sum of the two input original signals. And the sound reproduced by one low-frequency side speaker corrects the sound reproduced by the pair of high-frequency side speakers on the left and right. Therefore, strictly speaking, it cannot be said that the levels of the sounds of the left and right high-frequency side speakers are respectively corrected to the levels of the two input original signals. On the other hand, as shown in FIGS. 9 and 10, in the speaker system 203 according to the third embodiment of the present invention, the level of the sound reproduced by the woofer 10 is corrected to the level of the first original sound signal and the level of the second original sound signal by the pair of full-range speakers 20 and the full-range speaker 40, respectively.

[0066] Note that in the first to third embodiments, the woofer is an example of the first speaker of the present invention, but is not limited thereto, and the first speaker may be, for example, a subwoofer (super woofer). Also, in the first to third embodiments, the tweeter is an example of the third speaker of the present invention, but is not limited thereto, and the third speaker may be, for example, a super tweeter.

[0067] FIG. 11 shows an example of the configuration of a speaker system 204 according to a fourth embodiment of the present invention. The speaker system 204 is obtained by adding a subwoofer 60 to the speaker system 202 according to the second embodiment. The speaker system 204 includes a woofer 10, an amplifier 11, a vibration detection unit 12, an LPF 13, a subtractor 14, a full-range speaker 20, an amplifier 21, a vibration detection unit 22, an LPF 23, a subtractor 24, a tweeter 30, an amplifier 31, a subwoofer 60, an amplifier 61, a vibration detection unit 62, an LPF 63, a subtractor 64, and an HPF 120. The speaker system 204 differs from the speaker system 202 according to the second embodiment in that it includes a subwoofer 60, an amplifier 61, a vibration detection unit 62, an LPF 63, and a subtractor 64. In other respects, the configuration of the speaker system 204 is the same as that of the speaker system 202 according to the second embodiment. Hereinafter, the differences between the speaker system 204 and the speaker system 202 will be described.

[0068] An original sound signal is input to the input terminal 100. The LPF 63 removes high-frequency components from the original sound signal and outputs a drive signal. The cut-off frequency of the LPF 63 is lower than the cut-off frequency of the LPF 13. The drive signal is amplified by the amplifier 61 and drives the subwoofer 60. The subwoofer 60 is driven by the drive signal. That is, the subwoofer 60 is driven based on the original sound signal. The subwoofer 60 reproduces an extremely low-frequency sound having a frequency lower than the sound in the low-frequency range reproduced by the woofer 10. The vibration detection unit 62 detects the vibration of the vibration system of the subwoofer 60 and outputs a third reproduction signal corresponding to the vibration. The vibration detection unit 62 has the same configuration as the vibration detection circuit used in the motional feedback. The subtractor 64 is, for example, a differential amplifier. The original sound signal is input to the non-inverting input terminal (+) of the subtractor 64, and the third reproduction signal is input to the inverting input terminal (-). The subtractor 64 generates a third difference signal indicating the difference between the original sound signal and the third reproduction signal by subtracting the third reproduction signal from the original sound signal. The third difference signal is defined by the following equation (7).

[0069] Third difference signal = original sound signal - third reproduction signal (7)

[0070] Different from the speaker system 202 according to the second embodiment, the third difference signal is supplied to the LPF 13. The LPF 13 removes high-frequency components from the third difference signal and outputs a first drive signal. The first drive signal is amplified by the amplifier 11 and supplied to the woofer 10. The cut-off frequencies of the LPF 63, the LPF 13, and the LPF 23 can be set to the same cut-off frequencies as the low-pass filters included in the network circuit in a conventional four-way speaker, for example. However, the cut-off frequencies of the LPF 63, the LPF 13, and the LPF 23 may be different from the cut-off frequencies of the low-pass filters included in the network circuit in a conventional four-way speaker. Also, in the speaker system 204, it is not necessary to set a strict (sharp) crossover frequency as in the conventional case. Therefore, the LPF 63, the LPF 13, and the LPF 23 may be simpler filters than the conventional ones, respectively.

[0071] The woofer 10 outputs sound based on the third difference signal. The sound of the subwoofer 60 is corrected by the sound of the woofer 10. When the sound pressure level of the subwoofer 60 is the same as that of the original sound signal, the woofer 10 does not output sound. When the sound pressure level of the subwoofer 60 is insufficient, the woofer 10 outputs sound with the same phase as the sound of the subwoofer 60 to increase the sound pressure level. When the sound pressure level of the subwoofer 60 is excessive, the woofer 10 outputs sound with a phase opposite to that of the sound of the subwoofer 60 to decrease the sound pressure level. When the sound pressure level of the subwoofer 60 is 0, the woofer 10 outputs sound with the same sound pressure level as that of the original sound signal.

[0072] As the frequency increases, the sound pressure level of the subwoofer 60 decreases. However, at this time, the woofer 10 outputs sound with the same phase as the sound of the subwoofer 60, and increases the sound pressure level of the entire speaker system 204 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the subwoofer 60 and the sound of the woofer 10 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 204, no unnatural change in sound pressure level occurs between the sound range reproduced by the subwoofer 60 and the sound range reproduced by the woofer 10.

[0073] The speaker system 204 can set the sound ranges of the sounds reproduced by the subwoofer 60, the woofer 10, the full-range speaker 20, and the tweeter 30, for example, in the same way as the sound ranges of the sounds reproduced by a conventional four-way speaker, respectively.

[0074] Note that in this embodiment, the third difference signal is an example of the input signal of the present invention. The woofer 10 and the tweeter 30 are examples of the first speaker and the third speaker of the present invention, respectively. Also, the LPF13 and the LPF23 are examples of the first low-pass filter and the second low-pass filter of the present invention, respectively.

[0075] FIG. 12 shows an example of the configuration of a speaker system 205 according to a fifth embodiment of the present invention. The speaker system 205 is obtained by adding a super tweeter 70 to the speaker system 204 according to the fourth embodiment. The speaker system 205 includes a woofer 10, an amplifier 11, a vibration detection unit 12, an LPF 13, a subtractor 14, a full-range speaker 20, an amplifier 21, a vibration detection unit 22, an LPF 23, a subtractor 24, a tweeter 30, an amplifier 31, a vibration detection unit 32, an LPF 33, a subtractor 34, a subwoofer 60, an amplifier 61, a vibration detection unit 62, an LPF 63, a subtractor 64, a super tweeter 70, and an amplifier 71, and an HPF 120. The speaker system 205 differs from the speaker system 204 according to the fourth embodiment in that it includes a vibration detection unit 32, an LPF 33, a subtractor 34, a super tweeter 70, and an amplifier 71. In other respects, the configuration of the speaker system 205 is the same as that of the speaker system 204 according to the fourth embodiment. Hereinafter, the differences between the speaker system 205 and the speaker system 204 will be described.

[0076] HPF120 removes low-frequency components from the second differential signal. LPF33 removes high-frequency components from the second differential signal from which the low-frequency components have been removed and outputs a drive signal. The drive signal is amplified by amplifier 31 and drives tweeter 30. Tweeter 30 is driven by the drive signal. That is, tweeter 30 is driven based on the second differential signal. The cut-off frequency of LPF33 is higher than the cut-off frequency of LPF23 and higher than the cut-off frequency of HPF120. Vibration detection unit 32 detects the vibration of the vibration system of tweeter 30 and outputs a fourth reproduction signal corresponding to the vibration. Vibration detection unit 32 has the same configuration as the vibration detection circuit used in motional feedback. Subtractor 34 is, for example, a differential amplifier. The second differential signal that has passed through HPF120 is input to the non-inverting input terminal (+) of subtractor 34, and the fourth reproduction signal is input to the inverting input terminal (-). Subtractor 34 generates a fourth differential signal indicating the difference between the second differential signal and the fourth reproduction signal by subtracting the fourth reproduction signal from the second differential signal. The fourth differential signal is defined by the following equation (8).

[0077] Fourth differential signal = Second differential signal - Fourth reproduction signal (8)

[0078] The fourth differential signal is amplified by the amplifier 71 and supplied to the super tweeter 70. The super tweeter 70 is driven by the fourth differential signal. That is, the super tweeter 70 is driven based on the fourth differential signal. The super tweeter 70 reproduces an extremely high-frequency sound having a frequency higher than that of the high-frequency sound reproduced by the tweeter 30. The cut-off frequencies of the LPF63, LPF13, LPF23, and LPF33 can be set to the same cut-off frequencies as those of the low-pass filters included in the network circuit of a conventional 5-way speaker, for example. However, the cut-off frequencies of the LPF63, LPF13, LPF23, and LPF33 may be different from the cut-off frequencies of the low-pass filters included in the network circuit of a conventional 5-way speaker. Also, in the speaker system 205, a strict (sharp) crossover frequency setting as in the prior art is not required. For this reason, the LPF63, LPF13, LPF23, and LPF33 may be simpler filters as compared with the prior art, respectively.

[0079] The sound of the tweeter 30 is corrected by the sound of the super tweeter 70. When the sound pressure level of the tweeter 30 is the same as the sound pressure level of the original sound signal, the super tweeter 70 does not emit sound. When the sound pressure level of the tweeter 30 is insufficient, the super tweeter 70 outputs a sound having the same phase as the sound of the tweeter 30 to increase the sound pressure level. When the sound pressure level of the tweeter 30 is excessive, the super tweeter 70 outputs a sound having a phase opposite to that of the sound of the tweeter 30 to decrease the sound pressure level. When the sound pressure level of the tweeter 30 is 0, the super tweeter 70 emits a sound having the same sound pressure level as the sound pressure level of the original sound signal.

[0080] As the frequency increases, the sound pressure level of the tweeter 30 decreases. However, at this time, the super tweeter 70 outputs a sound with the same phase as the sound of the tweeter 30, and increases the sound pressure level of the entire speaker system 205 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the tweeter 30 and the sound of the super tweeter 70 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 205, no unnatural change in the sound pressure level occurs between the sound range reproduced by the tweeter 30 and the sound range reproduced by the super tweeter 70.

[0081] The speaker system 205 can set the sound ranges of the sounds reproduced by the subwoofer 60, the woofer 10, the full-range speaker 20, the tweeter 30, and the super tweeter 70, for example, in the same manner as the sound ranges of the sounds reproduced by a conventional 5-way speaker.

[0082] Note that, in the present embodiment, the third differential signal is an example of the input signal of the present invention. The woofer 10 and the tweeter 30 are examples of the first speaker and the third speaker of the present invention, respectively. Also, the LPF 13 and the LPF 23 are examples of the first low-pass filter and the second low-pass filter of the present invention, respectively.

[0083] Since the vibration system of the speaker has inertia in its movement, a delay occurs with respect to the movement faithful to the original sound signal. For this reason, delay and overshoot (excessive amplitude) occur in the sound reproduced by the speaker. However, according to each speaker system according to the first to fifth embodiments described above, by sequentially correcting the sound of each speaker with the sound of a speaker having a lighter vibration system, the influence of inertia can be minimized.

[0084] FIG. 13 shows an example of the configuration of the low-pass filter 90 according to an embodiment of the present invention. The low-pass filter 90 includes an LPF 91, an amplifier 92, and a subtracter 93. An input signal is input to the input terminal 103. The LPF 91 removes high-frequency components with high frequencies from the input signal and outputs a low-frequency signal including only low-frequency components with low frequencies. The amplifier 92 amplifies the low-frequency signal. The subtracter 93 is, for example, a differential amplifier. The input signal is input to the non-inverting input terminal (+) of the subtracter 93, and the amplified low-frequency signal is input to the inverting input terminal (-). The subtracter 93 generates a low-frequency removal signal indicating the difference between the input signal and the low-frequency signal by subtracting the low-frequency signal from the input signal. The low-frequency removal signal includes only the high-frequency components removed by the LPF 91. The low-pass filter 90 outputs a low-frequency signal and a low-frequency removal signal from the output terminal 104 and the output terminal 105, respectively.

[0085] FIG. 14 shows an example of the configuration of the speaker system 206 according to the sixth embodiment of the present invention. The speaker system 206 includes a woofer 10, an amplifier 11, a full-range speaker 20, an amplifier 21, and a low-pass filter 90A. The low-pass filter 90A includes an LPF 91A, an amplifier 92A, and a subtracter 93A. The low-pass filter 90A has the same structure as the low-pass filter 90 in FIG. 13.

[0086] An original sound signal output from a sound source is input to the input terminal 100. The LPF 91A removes high-frequency components from the original sound signal and outputs a first low-frequency signal. The first low-frequency signal is amplified by the amplifier 11 to drive the woofer 10. That is, the woofer 10 is driven based on the original sound signal. Also, the first low-frequency signal is amplified by the amplifier 92A and input to the inverting input terminal (-) of the subtractor 93A. The original sound signal is input to the non-inverting input terminal (+) of the subtractor 93A. The subtractor 93A generates a first low-frequency removal signal indicating the difference between the original sound signal and the first low-frequency signal by subtracting the first low-frequency signal from the original sound signal. The first low-frequency removal signal includes only the high-frequency components removed by the LPF 91A. The first low-frequency removal signal is amplified by the amplifier 21 to drive the full-range speaker 20. That is, the full-range speaker 20 is driven based on the first low-frequency removal signal. The first low-frequency removal signal is defined by the following equation (9).

[0087] First low-frequency removal signal = original sound signal - first low-frequency signal (9)

[0088] FIG. 15 shows an example of the relationship between frequency and sound pressure in the speaker system 206 of FIG. 14. FIG. 15 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. As the frequency increases, the sound pressure level of the woofer 10 decreases. However, at this time, the full-range speaker 20 outputs a sound with the same phase as the sound of the woofer 10, increasing the sound pressure level of the entire speaker system 206 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the woofer 10 and the sound of the full-range speaker 20 is the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 206, no unnatural change in sound pressure level occurs between the sound range reproduced by the woofer 10 and the sound range reproduced by the full-range speaker 20.

[0089] In a conventional two-way speaker, a network circuit is used to separate the sound range reproduced by the woofer from the sound range reproduced by the full-range speaker. The speaker system 206 replaces the network circuit with a low-pass filter 90A. The cut-off frequency of the LPF91A can be set to, for example, the same cut-off frequency as the low-pass filter included in the network circuit in a conventional two-way speaker. That is, the speaker system 206 can set the sound range of the sound reproduced by the woofer 10 and the full-range speaker 20 to be the same as, for example, the sound range of the sound reproduced by a conventional two-way speaker. However, the cut-off frequency of the LPF91A may be different from the cut-off frequency of the low-pass filter included in the network circuit in a conventional two-way speaker. Also, in the speaker system 206, a precise (sharp) crossover frequency setting as in the conventional case is not required. For this reason, the LPF91A may be a simpler filter compared to the conventional one.

[0090] Note that in this embodiment, the original sound signal is an example of the input signal in the present invention. The woofer 10 and the full-range speaker 20 are examples of the first speaker and the second speaker in the present invention, respectively. The LPF91A is an example of the first low-pass filter in the present invention.

[0091] FIG. 16 shows an example of the configuration of a speaker system 207 according to a seventh embodiment of the present invention. The speaker system 207 includes a woofer 10, an amplifier 11, a tweeter 30, an amplifier 31, a squawker 80, an amplifier 81, a low-pass filter 90A, and a low-pass filter 90B. The low-pass filter 90B includes an LPF 91B, an amplifier 92B, and a subtracter 93B. The low-pass filter 90A and the low-pass filter 90B have the same structure as the low-pass filter 90 in FIG. 13. The speaker system 207 differs from the speaker system 206 according to the sixth embodiment in FIG. 14 in that the speaker system 207 has a squawker 80 and an amplifier 81 instead of a full-range speaker 20 and an amplifier 21, and in that the speaker system 207 has a low-pass filter 90B, a tweeter 80, and an amplifier 81. Hereinafter, the differences between the speaker system 207 and the speaker system 206 will be described.

[0092] The LPF 91B has a cutoff frequency higher than the cutoff frequency of the LPF 91A. The LPF 91B removes high-frequency components from the first low-frequency removal signal and outputs a second low-frequency signal. The second low-frequency signal is amplified by the amplifier 81 to drive the squawker 80. The squawker 80 is driven by the second low-frequency signal. That is, the squawker 80 is driven based on the second low-frequency signal. Further, the second low-frequency signal is amplified by the amplifier 92B and input to the inverting input terminal (-) of the subtracter 93B. The first low-frequency removal signal is input to the non-inverting input terminal (+) of the subtracter 93B. The subtracter 93B generates a second low-frequency removal signal indicating the difference between the first low-frequency removal signal and the second low-frequency signal by subtracting the second low-frequency signal from the first low-frequency removal signal. The second low-frequency removal signal includes only the high-frequency components removed by the LPF 91B. The second low-frequency removal signal is amplified by the amplifier 31 to drive the tweeter 30. That is, the tweeter 30 is driven based on the second low-frequency removal signal. The second low-frequency removal signal is defined by the following equation (10).

[0093] Second low-frequency removal signal = First low-frequency removal signal - Second low-frequency signal (10)

[0094] FIG. 17 shows an example of the relationship between frequency and sound pressure in the speaker system 207 of FIG. 16. FIG. 17 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. As the frequency increases, the sound pressure level of the woofer 10 decreases. However, at this time, the squawker 80 outputs a sound with the same phase as the sound of the woofer 10, and increases the sound pressure level of the entire speaker system 207 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the woofer 10 and the sound of the squawker 80 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 207, no unnatural change in the sound pressure level occurs between the sound range reproduced by the woofer 10 and the sound range reproduced by the squawker 80.

[0095] As the frequency further increases, the sound pressure level of the squawker 80 decreases. However, at this time, the tweeter 30 outputs a sound with the same phase as the sound of the squawker 80, and increases the sound pressure level of the entire speaker system 207 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the squawker 80 and the sound of the tweeter 30 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 207, no unnatural change in the sound pressure level occurs between the sound range reproduced by the squawker 80 and the sound range reproduced by the squawker 80.

[0096] In a conventional three-way speaker, network circuits are used to separate the frequency range reproduced by the woofer, the frequency range reproduced by the squawker, and the frequency range reproduced by the squawker and the tweeter, respectively. The speaker system 207 replaces these network circuits with a low-pass filter 90A and a low-pass filter 90B. The cut-off frequencies of the LPF91A and the LPF91B can be set, for example, to the same cut-off frequencies as the low-pass filters included in the network circuits in a conventional three-way speaker, respectively. That is, the speaker system 207 can set the frequency ranges of the sounds reproduced by the woofer 10, the squawker 80, and the tweeter 30, for example, in the same manner as the frequency ranges of the sounds reproduced by a conventional three-way speaker, respectively. However, the cut-off frequencies of the LPF91A and the LPF91B may be different from the cut-off frequencies of the low-pass filters included in the network circuits in a conventional three-way speaker. Also, in the speaker system 207, a precise (steep) crossover frequency setting as in the conventional case is not required. For this reason, the LPF91A and the LPF91B may be simple filters as compared with the conventional ones, respectively.

[0097] Note that, for example, in the speaker system 202 according to the second embodiment of FIG. 5, when the level of the sound of a specific frequency increases due to resonance or resonance in the woofer 10, the full-range speaker 20 emits sound so that the level of the sound of the specific frequency decreases. For this reason, an HPF120 is provided to remove the frequency components that may damage the vibration system of the tweeter 30 from the second difference signal. However, in the speaker system 207 according to the present embodiment, the low-frequency components included in the original sound signal are removed from the second low-frequency removal signal in the low-pass filter 90A and the low-pass filter 90B. For this reason, a high-pass filter for removing the frequency components that may damage the vibration system of the tweeter 30 from the second low-frequency removal signal may not be provided.

[0098] Also, in this embodiment, the original sound signal is an example of the input signal in the present invention. The woofer 10, the squawker 80, and the tweeter 30 are examples of the first speaker, the second speaker, and the third speaker in the present invention, respectively. A full-range speaker can also be used instead of the squawker 80 as the second speaker. The LPF91A and the LPF91B are examples of the first low-pass filter and the second low-pass filter in the present invention, respectively.

[0099] FIG. 18 shows an example of the configuration of a speaker system 208 according to an eighth embodiment of the present invention. The speaker system 208 includes a full-range speaker 20, an amplifier 21, a tweeter 30, an amplifier 31, a low-pass filter 90A, and a low-pass filter 90B. The low-pass filter 90A and the low-pass filter 90B have the same structure as the low-pass filter 90 in FIG. 13, respectively. The speaker system 208 is different from the speaker system 207 according to the seventh embodiment in FIG. 16 in that the woofer 10 and the amplifier 11 are absent, and the full-range speaker 20 and the amplifier 21 are provided instead of the squawker 80 and the amplifier 81. Hereinafter, the differences between the speaker system 208 and the speaker system 207 will be described.

[0100] The LPF91A removes high-frequency components from the original sound signal and outputs a low-frequency signal. The low-frequency signal is amplified by the amplifier 92A and input to the inverting input terminal (-) of the subtracter 93A. The original sound signal is input to the non-inverting input terminal (+) of the subtracter 93A. The subtracter 93A generates a low-frequency removal signal indicating the difference between the original sound signal and the low-frequency signal by subtracting the low-frequency signal from the original sound signal. The low-frequency removal signal includes only the high-frequency components removed by the LPF91A. The low-frequency removal signal is defined by the following equation (11).

[0101] Low-frequency removal signal = original sound signal - low-frequency signal (11)

[0102] The LPF91B removes high-frequency components from the low-pass filtered signal and outputs a first low-pass signal. The first low-pass signal is amplified by the amplifier 21 and drives the full-range speaker 20. That is, the full-range speaker 20 is driven by the first low-pass signal. That is, the full-range speaker 20 is driven based on the low-pass filtered signal. The first low-pass filtered signal contains only the high-frequency components removed by the LPF91B. The first low-pass signal is amplified by the amplifier 92B and input to the inverting input terminal (-) of the subtractor 93B. The low-pass filtered signal is input to the non-inverting input terminal (+) of the subtractor 93B. The subtractor 93B generates a first low-pass filtered signal indicating the difference between the low-pass filtered signal and the first low-pass signal by subtracting the first low-pass signal from the low-pass filtered signal. The first low-pass filtered signal contains only the high-frequency components removed by the LPF91B. The first low-pass filtered signal is amplified by the amplifier 31 and drives the tweeter 30. That is, the tweeter 30 is driven based on the first low-pass filtered signal. The first low-pass filtered signal is defined by the following equation (12).

[0103] First low-pass filtered signal = low-pass filtered signal - first low-pass signal (12)

[0104] FIG. 19 shows an example of the relationship between frequency and sound pressure in the speaker system 208 of FIG. 18. FIG. 19 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. The full-range speaker 20 mainly reproduces the sound range between the cut-off frequency of the LPF91A and the LPF91B. In the speaker system 208, sounds in the low-frequency range with frequencies lower than the cut-off frequency of the LPF91A are not reproduced.

[0105] According to the speaker system 208, for example, in an environment with a large amount of low-frequency noise such as inside a car, it is possible to reproduce with the low frequencies removed.

[0106] In the present embodiment, the low-frequency removal signal is an example of the input signal in the present invention. The full-range speaker 20 and the tweeter 30 are examples of the first speaker and the second speaker in the present invention, respectively. A subwoofer can also be used instead of the full-range speaker 20 as the first speaker. The LPF91B is an example of the first low-pass filter in the present invention.

[0107] FIG. 20 shows an example of the configuration of a speaker system 209 according to a ninth embodiment of the present invention. The speaker system 209 includes a woofer 10, an amplifier 11, a vibration detection unit 12, an LPF 13, a subtractor 14, a full-range speaker 20, an amplifier 21, a tweeter 30, an amplifier 31, and a low-pass filter 90B. The low-pass filter 90B has the same structure as the low-pass filter 90 in FIG. 13. The speaker system 209 differs from the speaker system 207 according to the seventh embodiment in FIG. 16 in that it has a vibration detection unit 12, an LPF 13, and a subtractor 14 instead of the low-pass filter 90A, and has a full-range speaker 20 and an amplifier 21 instead of the subwoofer 80 and the amplifier 81. Hereinafter, the differences between the speaker system 209 and the speaker system 207 will be described.

[0108] Similar to the speaker system 202 according to the second embodiment in FIG. 5, the LPF 13 removes high-frequency components of high frequencies from the original sound signal and outputs a drive signal. The drive signal is amplified by the amplifier 11 to drive the woofer 10. The woofer 10 is driven by the drive signal. That is, the woofer 10 is driven based on the original sound signal and reproduces sounds in the low-frequency range. The vibration detection unit 12 detects the vibration of the vibration system of the woofer 10 and outputs a reproduction signal corresponding to the vibration. The subtractor 14 is, for example, a differential amplifier. The original sound signal is input to the non-inverting input terminal (+) of the subtractor 14, and the reproduction signal is input to the inverting input terminal (-). The subtractor 14 generates a difference signal indicating the difference between the original sound signal and the reproduction signal by subtracting the reproduction signal from the original sound signal. The difference signal is defined by the following equation (13).

[0109] Differential signal = Original sound signal - Reproduction signal (13)

[0110] LPF91B removes high-frequency components from the differential signal and outputs a low-frequency signal. The low-frequency signal is amplified by amplifier 21 to drive full-range speaker 20. The full-range speaker 20 is driven by the low-frequency signal. That is, the full-range speaker 20 is driven based on the differential signal. The cut-off frequency of LPF91B is higher than the cut-off frequency of LPF13. That is, the cut-off frequency of LPF13 is lower than the cut-off frequency of LPF91B. Subtractor 93B generates a low-frequency removal signal indicating the difference between the differential signal and the low-frequency signal by subtracting the low-frequency signal from the differential signal. The low-frequency removal signal contains only the high-frequency components removed by LPF91B. The low-frequency removal signal is amplified by amplifier 31 to drive tweeter 30. That is, the tweeter 30 is driven based on the low-frequency removal signal. The low-frequency removal signal is defined by the following equation (14).

[0111] Low-frequency removal signal = Differential signal - Low-frequency signal (14)

[0112] Figure 21 shows an example of the relationship between frequency and sound pressure in speaker system 209 of Figure 20. Figure 21 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. The full-range speaker 20 outputs sound based on the differential signal. The sound of woofer 10 is corrected by the sound of the full-range speaker 20. When the sound pressure level of woofer 10 is the same as the sound pressure level of the original sound signal, the full-range speaker 20 does not produce sound. When the sound pressure level of woofer 10 is insufficient, the full-range speaker 20 outputs sound with the same phase as the sound of woofer 10 to increase the sound pressure level. When the sound pressure level of woofer 10 is excessive, the full-range speaker 20 outputs sound with the opposite phase to the sound of woofer 10 to decrease the sound pressure level. When the sound pressure level of woofer 10 is 0, the full-range speaker 20 outputs sound with the same sound pressure level as the original sound signal.

[0113] According to the speaker system 209, as shown in region B surrounded by the dashed ellipse in FIG. 21, for example, when the level of sound at a specific frequency increases due to resonance or sympathetic vibration in the woofer 10, the full-range speaker 20 emits sound so that the level of sound at that specific frequency decreases. Therefore, in the speaker system 209, the influence of resonance and sympathetic vibration on the sound reproduced by the woofer 10 is suppressed.

[0114] As the frequency increases, the sound pressure level of the woofer 10 decreases. However, at this time, the full-range speaker 20 outputs sound with the same phase as the sound of the woofer 10, and increases the sound pressure level of the entire speaker system 209 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the woofer 10 and the sound of the full-range speaker 20 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 209, no unnatural change in the sound pressure level occurs between the sound range reproduced by the woofer 10 and the sound range reproduced by the full-range speaker 20. A network circuit is not required between the sound range reproduced by the woofer 10 and the sound range reproduced by the full-range speaker 20.

[0115] Note that in the present embodiment, the original sound signal is an example of the input signal in the present invention. The woofer 10 and the tweeter 30 are examples of the first speaker and the third speaker in the present invention, respectively. The LPF 13 and the LPF 91B are examples of the first low-pass filter and the second low-pass filter in the present invention, respectively.

[0116] FIG. 22 shows an example of the configuration of the high-pass filter 95 according to an embodiment of the present invention. The high-pass filter 95 includes an HPF 96, an amplifier 97, and a subtracter 98. An input signal is input to the input terminal 106. The HPF 96 removes low-frequency components of low frequencies from the input signal and outputs a high-frequency signal including only high-frequency components of high frequencies. The amplifier 97 amplifies the high-frequency signal. The subtracter 98 is, for example, a differential amplifier. The input signal is input to the non-inverting input terminal (+) of the subtracter 98, and the amplified high-frequency signal is input to the inverting input terminal (-). The subtracter 98 generates a high-frequency removal signal indicating the difference between the input signal and the high-frequency signal by subtracting the high-frequency signal from the input signal. The high-frequency removal signal includes only the low-frequency components removed by the HPF 96. The high-pass filter 95 outputs a high-frequency signal and a high-frequency removal signal from the output terminal 107 and the output terminal 108, respectively.

[0117] FIG. 23 shows an example of the configuration of the speaker system 210 according to the tenth embodiment of the present invention. The speaker system 210 includes a woofer 10, an amplifier 11, a tweeter 30, an amplifier 31, and a high-pass filter 95A. The high-pass filter 95A includes an HPF 96A, an amplifier 97A, and a subtracter 98A. The high-pass filter 95A has the same structure as the high-pass filter 95 in FIG. 22.

[0118] An original sound signal output from a sound source is input to the input terminal 100. The HPF 96A removes low-frequency components from the original sound signal and outputs a first high-frequency signal. The first high-frequency signal is amplified by the amplifier 31 to drive the tweeter 30. The tweeter 30 is driven by the first high-frequency signal. Also, the first high-frequency signal is amplified by the amplifier 97A and input to the inverting input terminal (-) of the subtracter 98A. The original sound signal is input to the non-inverting input terminal (+) of the subtracter 98A. The subtracter 98A generates a first high-frequency removal signal indicating the difference between the original sound signal and the first high-frequency signal by subtracting the first high-frequency signal from the original sound signal. The first high-frequency removal signal includes only the low-frequency components removed by the HPF 96A. The first high-frequency removal signal is amplified by the amplifier 11 to drive the woofer 10. The woofer 10 is driven by the first high-frequency removal signal. That is, the woofer 10 is driven based on the first high-frequency removal signal. The first high-frequency removal signal is defined by the following equation (15).

[0119] First high-frequency removal signal = original sound signal - first high-frequency signal (15)

[0120] FIG. 24 shows an example of the relationship between frequency and sound pressure in the speaker system 210 of FIG. 23. FIG. 24 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. As the frequency decreases, the sound pressure level of the tweeter 30 decreases. However, at this time, the woofer 10 outputs a sound with the same phase as the sound of the tweeter 30, increasing the sound pressure level of the entire speaker system 210 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the woofer 10 and the sound of the tweeter 30 is the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 210, no unnatural change in the sound pressure level occurs between the sound range reproduced by the woofer 10 and the sound range reproduced by the tweeter 30.

[0121] In a conventional two-way speaker, a network circuit is used to separate the frequency range reproduced by the woofer from the frequency range reproduced by the tweeter. The speaker system 210 replaces the network circuit with a high-pass filter 95A. The cut-off frequency of the HPF96A can be set to, for example, the same cut-off frequency as the high-pass filter included in the network circuit in a conventional two-way speaker. That is, the speaker system 210 can set the frequency range of the sound reproduced by the woofer 10 and the tweeter 30 to be the same as, for example, the frequency range of the sound reproduced by a conventional two-way speaker. However, the cut-off frequency of the HPF96A may be different from the cut-off frequency of the high-pass filter included in the network circuit in a conventional two-way speaker. Also, in the speaker system 210, a precise (sharp) crossover frequency setting as in the prior art is not required. For this reason, the HPF96A may be a simpler filter compared to the prior art.

[0122] Note that in this embodiment, the original sound signal is an example of the input signal in the present invention. The tweeter 30 and the woofer 10 are examples of the first speaker and the second speaker in the present invention, respectively. The HPF96A is an example of the first high-pass filter in the present invention.

[0123] FIG. 25 shows an example of the configuration of a speaker system 211 according to the eleventh embodiment of the present invention. The speaker system 211 includes a woofer 10, an amplifier 11, a tweeter 30, an amplifier 31, a squawker 80, an amplifier 81, a high-pass filter 95A, and a high-pass filter 95B. The high-pass filter 95B includes an HPF96B, an amplifier 97B, and a subtracter 98B. The high-pass filter 95A and the high-pass filter 95B have the same structure as the high-pass filter 95 in FIG. 22. The speaker system 211 is different from the speaker system 210 according to the tenth embodiment in FIG. 23 in that it includes a squawker 80, an amplifier 81, and a low-pass filter 95B. Hereinafter, the differences between the speaker system 211 and the speaker system 210 will be described.

[0124] HPF96B has a cut-off frequency lower than that of HPF96A. HPF96B removes low-frequency components from the first high-pass filtered signal and outputs a second high-frequency signal. The second high-frequency signal is amplified by amplifier 81 to drive woofer 80. Woofer 80 is driven by the second high-frequency signal. Also, the second high-frequency signal is amplified by amplifier 97B and input to the inverting input terminal (-) of subtracter 98B. The first high-pass filtered signal is input to the non-inverting input terminal (+) of subtracter 98B. Subtracter 98B generates a second high-pass filtered signal indicating the difference between the first high-pass filtered signal and the second high-frequency signal by subtracting the second high-frequency signal from the first high-pass filtered signal. The second high-pass filtered signal contains only the low-frequency components removed by HPF96B. The second high-pass filtered signal is amplified by amplifier 11 to drive woofer 10. Woofer 10 is driven by the second high-pass filtered signal. That is, woofer 10 is driven based on the second high-pass filtered signal. The second high-pass filtered signal is defined by the following equation (16).

[0125] Second high-pass filtered signal = First high-pass filtered signal - Second high-frequency signal (16)

[0126] FIG. 26 shows an example of the relationship between frequency and sound pressure in speaker system 211 of FIG. 25. FIG. 26 is an example when an original sound signal with a constant sound pressure level is input at all frequencies. As the frequency decreases, the sound pressure level of tweeter 30 decreases. However, at this time, woofer 80 outputs a sound with the same phase as the sound of tweeter 30, increasing the sound pressure level of the entire speaker system 211 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of tweeter 30 and the sound of woofer 80 is the same as the sound pressure level of the original sound signal. Therefore, in speaker system 211, no unnatural change in sound pressure level occurs between the sound range reproduced by woofer 80 and the sound range reproduced by tweeter 30.

[0127] As the frequency becomes even lower, the sound pressure level of the woofer 80 decreases. However, at this time, the woofer 10 outputs a sound with the same phase as the sound of the woofer 80, and increases the sound pressure level of the entire speaker system 211 to the sound pressure level defined by the original sound signal. The sound pressure level of the sound obtained by overlapping the sound of the woofer 10 and the sound of the woofer 80 becomes the same as the sound pressure level of the original sound signal. Therefore, in the speaker system 211, no unnatural change in the sound pressure level occurs between the sound range reproduced by the woofer 10 and the sound range reproduced by the woofer 80.

[0128] In a conventional three-way speaker, network circuits are used to separate the sound range reproduced by the woofer, the sound range reproduced by the midrange speaker, and the sound range reproduced by the midrange speaker and the sound range reproduced by the tweeter. The speaker system 211 replaces these network circuits with the high-pass filter 95A and the high-pass filter 95B. The cut-off frequencies of the HPF96A and the HPF96B can be set, for example, to the same cut-off frequencies as the high-pass filters included in the network circuits in a conventional three-way speaker. That is, the speaker system 211 can set the sound ranges of the sounds reproduced by the woofer 10, the midrange speaker 80, and the tweeter 30, for example, in the same manner as the sound ranges of the sounds reproduced by a conventional three-way speaker. However, the cut-off frequencies of the HPF96A and the HPF96B may be different from the cut-off frequencies of the high-pass filters included in the network circuits in a conventional three-way speaker. Also, in the speaker system 211, a precise (steep) crossover frequency setting as in the conventional case is not required. For this reason, the HPF96A and the HPF96B may be simpler filters than those in the conventional case, respectively.

[0129] Note that in this embodiment, the original sound signal is an example of the input signal in the present invention. The tweeter 30, the squawker 80, and the woofer 10 are examples of the first speaker, the second speaker, and the third speaker in the present invention, respectively. A full-range speaker can also be used instead of the squawker 80 as the second speaker. The HPF96A and the HPF96B are examples of the first high-pass filter and the second high-pass filter in the present invention, respectively.

[0130] Also, in the speaker systems 206 according to the sixth embodiment, 207 according to the seventh embodiment, 208 according to the eighth embodiment, 209 according to the ninth embodiment, 210 according to the tenth embodiment, and 211 according to the eleventh embodiment described above, examples of two-way speaker systems or three-way speaker systems were shown. However, it goes without saying that four-way speaker systems or five-way speaker systems can be realized based on the same technical concept as these.

[0131] Also, in the speaker systems of the sixth to eleventh embodiments, for example, a subwoofer (super woofer) may be used instead of the woofer, or a super tweeter may be used instead of the tweeter.

[0132] Also, in each of the above-described embodiments, examples of using the low-pass filter 90 and the high-pass filter 95 in a multi-way speaker system were shown. However, it goes without saying that the low-pass filter 90 and the high-pass filter 95 can be used for other applications different from speakers.

[0133] Also, each process of the speaker systems and filters according to each of the above-described embodiments can be realized by analog processing or can be implemented by digital processing.

[0134] As described above, according to the present invention, it is possible to faithfully reproduce natural sounds that are faithful to the original sound. According to the present invention, the network circuit in the conventional multi-speaker system the high-pass filter included in can be eliminated, and it is possible to prevent unnatural changes in sound pressure level from occurring between the sound ranges reproduced by each speaker.

[0135] As described above, the embodiments of the present invention have been described. However, various modifications and combinations required due to design or manufacturing convenience and other factors are included in the scope of the invention described in the claims and the invention corresponding to the specific examples described in the embodiments of the invention.

Explanation of Reference Numerals

[0136] 10... woofer, 11... amplifier, 12... vibration detection unit, 13... LPF (low-pass filter), 14, 15... subtracter, 16, 17... amplifier, 20... full-range speaker, 21... amplifier, 22... vibration detection unit, 23... LPF, 24... subtracter, 30... tweeter, 31... amplifier, 32... vibration detection unit, 33... LPF, 34... subtracter, 35... HPF (high-pass filter), 40... full-range speaker, 41... amplifier, 42... vibration detection unit, 43... LPF, 44... subtracter, 50... tweeter, 51... amplifier, 60... subwoofer, 61... amplifier, 62... vibration detection unit, 63... LPF, 64... subtracter, 70... tweeter, 71... amplifier, 80... squawker, 81... amplifier, 90, 90A, 90B... low-pass filter, 91, 91A, 91B... LPF, 92, 92A, 93B... amplifier, 93, 93A, 93B... subtracter, 95, 95A, 95B... high-pass filter, 96, 96A, 96B... HPF, 97, 97A, 97B... amplifier, 98, 98A, 98B... subtracter, 100, 101, 102, 103, 106... input terminals, 104, 105, 107, 108... output terminals, 120, 121... HPF, 200... speaker system according to the invention in use, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211... speaker systems according to each embodiment of the present invention

Claims

1. a first low-pass filter that removes high frequency components from an input signal and outputs a first drive signal; a first speaker that is driven by the first drive signal and reproduces low-frequency sounds; a first vibration detection unit that outputs a first reproduction signal corresponding to a vibration of a vibration system of the first speaker; a first subtractor configured to subtract the first reproduced signal from the input signal to generate a first difference signal; a second low-pass filter having a cutoff frequency higher than a cutoff frequency of the first low-pass filter, removing high frequency components from the first differential signal, and outputting a second drive signal; a full-range speaker driven by the second drive signal; a second vibration detection unit that outputs a second reproduction signal corresponding to the vibration of the vibration system of the full-range speaker; a second subtractor that generates a second differential signal by subtracting the second reproduced signal from the first differential signal; a third speaker that is driven based on the second differential signal and reproduces high-pitched sounds; and A speaker system comprising:

2. a first low-pass filter that removes high-frequency components from an input signal and outputs a drive signal; a first speaker that is driven by the drive signal and reproduces low-frequency sounds; a vibration detection unit that outputs a reproduction signal corresponding to the vibration of a vibration system of the first speaker; a first subtractor that subtracts the reproduced signal from the input signal and outputs a difference signal; a second low-pass filter having a cutoff frequency higher than the cutoff frequency of the first low-pass filter, removing high-frequency components from the difference signal and outputting a low-pass signal; a full-range speaker driven by the low-frequency signal; a second subtractor that subtracts the low-frequency signal from the difference signal and outputs a low-frequency removed signal that includes only the high-frequency components removed by the second low-pass filter; a third speaker that is driven based on the low-frequency removed signal and reproduces high-frequency sounds; A speaker system comprising:

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