Speaker device and sound system

Abstract

To provide a speaker device and an acoustic system in high sound quality with a simple configuration.SOLUTION: A speaker device includes at least one driver including a diaphragm, an enclosure for accommodating the driver, and a plurality of driver circuits for outputting control signals to vibrate the diaphragm of the at least one driver according to a source signal. In a part of driver circuit of the plurality of driver circuits, a low-pass filter is provided, and the low-pass filter is configured such that a dip frequency on a frequency characteristic of a synthesized signal of the control signals outputted from each of the plurality of driver circuits corresponds to a peak frequency on a frequency characteristic of sound pressure outputted according to the shape of the enclosure.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a speaker device and an audio system. [Background technology]

[0002] A speaker has been known that includes a speaker, a cabinet that houses the speaker, and a means for correcting the difference in frequency sound pressure characteristics between the low frequency range and the mid and high frequency ranges due to the diffraction effect of the cabinet (Patent Document 1).

[0003] Also known is a speaker that includes a coil bobbin coupled to a diaphragm, a voice coil wound around the coil bobbin, a first terminal and a second terminal derived from both ends of the voice coil, an intermediate terminal derived from the middle of the voice coil, and a bandpass filter connected to the second terminal, and is driven by supplying a driving current between the first terminal and the intermediate terminal, and supplying the driving current between the second terminal and the intermediate terminal via the bandpass filter (Patent Document 2). In this speaker, the playback sound pressure level is controlled by the driving current supplied between the second terminal and the intermediate terminal via the bandpass filter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 61-41299 [Patent Document 2] Japanese Patent Application Publication No. 9-163486 Summary of the Invention [Problem to be solved by the invention]

[0005] The prior art has room for improvement in achieving a low-cost, high-quality sound system by correcting for changes in driver output characteristics due to the diffraction effect of the enclosure baffle.

[0006] In consideration of the above, an object of the present invention is to provide a speaker device and an audio system that have a simple configuration and produce high-quality sound. [Means for solving the problem]

[0007] The speaker device of the present invention includes a drive unit consisting of at least one driver including a diaphragm, an enclosure that houses the driver, and a plurality of drive circuits that output control signals to vibrate the diaphragm of the at least one driver based on a sound source signal, wherein the drive unit vibrates the diaphragm in accordance with the outputs of the plurality of drive circuits, and a low-pass filter is provided in some of the plurality of drive circuits, and the low-pass filter is set so that a dip frequency in the frequency characteristics of a signal obtained by combining the control signals output by each of the plurality of drive circuits corresponds to a peak frequency in the frequency characteristics of the sound pressure output in accordance with the shape of the enclosure.

[0008] According to the present invention, the low-pass filters provided in some of the plurality of drive circuits are set so that the peak frequency of the frequency characteristic of the sound pressure output according to the shape of the enclosure corresponds to the dip frequency in the frequency characteristic of the signal obtained by combining the control signals output from each of the plurality of drive circuits, and the plurality of drive circuits then output a control signal that vibrates the diaphragm of the at least one driver based on the sound source signal.

[0009] In this way, the low-pass filters provided in some of the multiple drive circuits are set so that the peak frequency of the frequency characteristics of the sound pressure output according to the shape of the enclosure corresponds to the dip frequency in the frequency characteristics of the signal obtained by combining the control signals output by each of the multiple drive circuits, thereby making it possible to provide a high-quality speaker device with a simple configuration.

[0010] The enclosure according to the present invention can be an enclosure that generates a peak (inflection point) in the intermediate band between the low frequency range where sound pressure is low and the high frequency range where sound pressure is high, due to the diffraction effect, with respect to the driver sound pressure characteristics of an infinite baffle. For example, the enclosure can be a rectangular parallelepiped housing.

[0011] The drive section according to the present invention is made up of one driver, and each of the plurality of drive circuits can output a control signal that vibrates the diaphragm of the driver based on a sound source signal.

[0012] The driving unit according to the present invention comprises a plurality of drivers corresponding to the plurality of driving circuits, each of which outputs a control signal to vibrate the diaphragm of the corresponding driver based on a sound source signal, and the driving unit can vibrate the diaphragm corresponding to each of the plurality of driving circuits in accordance with the output of the driving circuit.

[0013] The driver according to the present invention may include a voice coil and a magnetic circuit.

[0014] An acoustic system according to the present invention includes the speaker device described above, a signal input unit that receives the sound source signal, and an amplifier that outputs the received sound source signal to the speaker device.

[0015] According to the present invention, a signal input unit receives the sound source signal. An amplifier outputs the received sound source signal to the speaker device. In the speaker device, a plurality of drive circuits output control signals that vibrate the diaphragm of at least one of the drivers based on the sound source signal. Here, low-pass filters provided in some of the plurality of drive circuits are set so that a dip frequency in the frequency characteristics of a signal obtained by combining the control signals output by each of the plurality of drive circuits corresponds to a peak frequency in the frequency characteristics of the sound pressure output according to the shape of the enclosure. This makes it possible to provide a high-quality sound system with a simple configuration. [Effects of the Invention]

[0016] As described above, according to the present invention, it is possible to provide an audio system with high sound quality and a simple configuration. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of an acoustic system according to first, second, and third embodiments of the present invention. [Figure 2] 1 is a cross-sectional view showing a configuration of a speaker device according to a first embodiment of the present invention. [Figure 3] 1 is a circuit diagram showing an electrical configuration of a speaker device according to a first embodiment of the present invention. [Figure 4] 10 is a graph showing frequency characteristics of control signals output by each of the drive circuits and a synthesized signal. [Figure 5] 1 is a circuit diagram showing an example of a configuration of a speaker device according to a first embodiment of the present invention. [Figure 6] FIG. 1 is a circuit diagram showing an example of a speaker device configured using a first-order low-pass filter. [Figure 7] FIG. 10 is a circuit diagram in which the voice coil is a pure resistor. [Figure 8] 1 is a vector diagram showing a voice coil voltage. [Figure 9] 10 is a graph showing frequency characteristics of control signals output by each of the drive circuits and a synthesized signal. [Figure 10] FIG. 10 is a circuit diagram showing an equivalent circuit of a speaker device configured using a second-order low-pass filter. [Figure 11] 1 is a vector diagram showing a voice coil voltage. [Figure 12] 10 is a graph showing frequency characteristics of control signals output by each of the drive circuits and a synthesized signal. [Figure 13] 10 is a graph showing frequency characteristics of the control signals output by each of the drive circuits and the combined signal when ζ is changed. [Figure 14]FIG. 10 is a circuit diagram showing an equivalent circuit of a speaker device configured using a third-order low-pass filter. [Figure 15] 10 is a graph showing frequency characteristics of a signal obtained by combining control signals output from the respective drive circuits when ζ is changed. [Figure 16] 10 is a vector diagram showing a voice coil voltage when a first to fourth order low pass filter is used. [Figure 17] FIG. 2 is a circuit diagram showing an equivalent circuit of a drive circuit including a low-pass filter. [Figure 18] FIG. 2 is a circuit diagram showing an equivalent circuit of a drive circuit including a low-pass filter. [Figure 19] 10 is a graph showing the characteristics of each impedance. [Figure 20] 10 is a graph showing the frequency characteristics of a signal obtained by combining control signals output from each of the drive circuits when the load is changed. [Figure 21] FIG. 10 is a cross-sectional view showing a configuration of a speaker device according to a second embodiment of the present invention. [Figure 22] FIG. 10 is a circuit diagram showing a configuration of a speaker device according to a second embodiment of the present invention. [Figure 23] FIG. 1A is a perspective view showing a single voice coil bobbin, and FIG. 1B is a cross-sectional view of a voice coil configured in two systems. [Figure 24] FIG. 10 is a circuit diagram showing a speaker device configured without using a low-pass filter. [Figure 25] 10 is a graph showing the anechoic chamber characteristics in a 2π space and a bass reflex enclosure in a speaker device configured without using a low-pass filter. [Figure 26] This is a graph showing the difference between the measured values ​​of a bass reflex enclosure and a 2π space, compared with the calculated data. [Figure 27] 1 is a circuit diagram showing a configuration of a speaker device according to an embodiment; [Figure 28] 10 is a graph showing a simulation result of frequency characteristics of a signal obtained by combining control signals output from each of the drive circuits. [Figure 29] 10 is a graph showing the results of actual sound pressure measurements with and without a low-pass filter. [Figure 30] 10 is a graph showing the difference in sound pressure depending on whether a low-pass filter is used or not. [Figure 31] 1 is a circuit diagram showing an example of a configuration of a speaker device according to an embodiment; [Figure 32] 10 is a graph showing a simulation result of frequency characteristics of a signal obtained by combining control signals output from each of the drive circuits. [Figure 33] 10 is a graph showing the results of actual sound pressure measurements with and without a low-pass filter. [Figure 34] 10 is a graph showing the difference in sound pressure depending on whether a low-pass filter is used or not. [Figure 35] FIG. 10 is a circuit diagram showing a state in which one of the voice coils is short-circuited. [Figure 36] 24 is a graph showing the results of measuring sound pressure when one voice coil is short-circuited and when it is not (the case of the connection in FIG. 24). [Figure 37] FIG. 10 is a circuit diagram showing a state in which one of the voice coils is open. [Figure 38] 10 is a graph showing the results of measuring sound pressure when one of the voice coils is open and when one of the voice coils is short-circuited. [Figure 39] FIG. 1 is a circuit diagram showing the configuration of a speaker device in an example used as a WF. [Figure 40] 10 is a graph showing the frequency characteristics of a control signal for each driver and a synthesized signal. [Figure 41] FIG. 1 is a perspective view illustrating an example of an enclosure. [Figure 42] FIG. 1 is a circuit diagram showing the configuration of a two-way audio system. [Figure 43] 10 is a graph showing the frequency characteristics of a control signal for each driver and a synthesized signal. [Figure 44] 10 is a graph showing the frequency characteristics of the control signals for each driver and the combined signal when the influence of the diffraction effect of the baffle is taken into consideration. [Figure 45]FIG. 1 is a circuit diagram showing a configuration of a speaker device provided with a compensation circuit. [Figure 46] 10 is a graph showing the frequency characteristics of a control signal for each driver and a synthesized signal. [Figure 47] 10 is a graph showing filter characteristics when white noise is used as a signal source. [Figure 48] FIG. 10 is a circuit diagram showing the configuration of a speaker device in an example used as a TW. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] <Outline of the embodiment of the present invention> An acoustic system that prioritizes high-quality sound reproduction requires a wide bandwidth, low distortion, and flat sound pressure frequency characteristics.

[0020] In sound systems for general users, emphasis is placed on the space factor when it comes to enclosures, and rectangular parallelepiped types such as small sound systems and tallbow types (extended in all height directions to increase volume for the benefit of bass reproduction) are the norm (see Figures 41(A) and (B)). These include systems that use a full-range driver that can radiate the entire frequency range with a single driver, and multi-way sound systems that use a dividing network circuit to divide the input signal into bass, midrange, treble, etc., and play each with a dedicated driver.

[0021] As the enclosure volume and driver diameter become smaller, problems such as a higher minimum frequency that can be reproduced and insufficient sound pressure in the low-frequency range can easily occur. For this reason, adding a subwoofer sound system to reproduce frequencies below the sound system's minimum frequency range has been proposed. Here, a subwoofer sound system utilizes the fact that listeners cannot sense direction in the lowest frequency range, and reproduces frequencies below the minimum frequency range of the main sound system using a single sound system.

[0022] The effect of a subwoofer is that it can reinforce the main sound system below the lowest frequency limit, but it does not compensate for the diffraction effect of the baffle (driver mounting part), which is another major factor in the lack of bass in small sound systems.

[0023] Furthermore, with a multi-way acoustic system, it is possible to control characteristics such as the difference in sound pressure between each unit, but because the reproducible frequency band of each unit is limited, it may not be possible to create characteristics that match the frequency range or peak frequency of the sound pressure difference caused by the diffraction effect of the baffle. For example, if the sound pressure step caused by the diffraction effect of the baffle is within the reproduction band of the bass driver, it cannot be corrected.

[0024] Here, we will explain the diffraction effect of the baffle. In bass drivers and full-range drivers of Hi-Fi sound systems used for listening to music, the driving section is generally an electrodynamic type, and the radiating section is a direct radiation type (cone type, flat panel type, etc.).

[0025] When this type of driver is mounted on an infinite baffle to separate the sound radiated in front of and behind the diaphragm (radiating into 2π space), the characteristics are theoretically roughly flat within that band, since the sound pressure at the listening point on the driver axis in the mass control band (frequency band higher than the lowest resonant frequency) is proportional to the input voltage.

[0026] However, since it is not practical to construct an infinite baffle, it is common to use a rectangular enclosure that surrounds the rear-radiating sound of the driver.

[0027] The baffle has a finite size, and diffraction of sound waves occurs at the edge of the baffle. As a result, the radiation space in the low frequency range (long wavelength range) where directivity is weaker becomes essentially a 4π space, resulting in a 6dB drop in sound pressure compared to the high frequency range where directionality is stronger. In other words, the low frequency side is 6dB lower than the high frequency side. In addition, the creation of a virtual sound source at the edge of the baffle causes undulation in the characteristics on the driver axis.

[0028] Thus, there are two notable features of the sound pressure characteristics when a conductive driver is mounted on the baffle of a typical rectangular enclosure. First, the high-frequency range is 6 dB higher than the low-frequency range. Second, the mid-range range has a peak of about 1 to 3 dB higher than the high-frequency range.

[0029] Correcting at least these two characteristics is effective in improving the bass deficiency of an acoustic system, i.e., in order to achieve a flat sound pressure frequency characteristic. Note that a conductive driver has a sound pressure characteristic that is proportional to the voltage, and has a flat sound pressure characteristic with an infinite baffle.

[0030] As an example of a measure to compensate for these, in the case of a two-way sound system consisting of a treble driver (tweeter: hereinafter also referred to as "TW") and a bass driver (woofer: hereinafter also referred to as "WF"), there is a method of correcting the sound pressure difference and peaks between the low and high frequency sides by adjusting each constant of the crossover network (dividing network / hereinafter also referred to as "network").

[0031] Figure 42 is a basic circuit diagram showing the speaker device of a two-way acoustic system. HPF is a high-pass filter that converts the input signal into signal components in an appropriate band for the TW. LPF is a low-pass filter that converts the input signal into signal components in an appropriate band for the WF. ATT is an attenuator that is a circuit for adjusting the magnitude of the input voltage to the TW. In the example of Figure 42 above, resistors are arranged in an L-shape, making the impedance seen from the HPF closer to pure resistance. This makes the characteristics of the HPF less susceptible to the influence of the voice coil inductance and motional impedance of the TW.

[0032] Impedance correction is performed by correcting the driver's electrical impedance, which is composed of the motional impedance, the DC resistance of the voice coil, and the voice coil inductance of the WF. The circuit shown in Figure 42 above can eliminate the influence of the voice coil inductance of the WF in the LPF band. In other words, it can appear as a pure resistance.

[0033] Fig. 43 is a graph showing an example of the frequency characteristics of the control signals input to each driver and the frequency characteristics of the combined signal, assuming that the output characteristics of each driver are flat and of the same efficiency within their respective bands. Fig. 43 shows calculated values ​​for a circuit connected so that the TW side is in reverse phase, where Ein is the input voltage from the amplifier, Ewf is the voltage of the signal input to the WF side driver, and Etw is the voltage of the signal input to the TW side driver.

[0034] Also, a graph showing an example of the frequency characteristics of the control signals input to each driver and the frequency characteristics of the synthesized signal when the influence of the baffle diffraction effect is further taken into consideration is shown in Figure 44. Compared to the example shown in Figure 43 above, Figure 44 shows an example in which the inductance L1 of the LPF is tripled so that the output gradually decreases from a lower frequency, and the ATT is used to make the TW output 6 dB lower than the WF output, thereby correcting the baffle diffraction effect.

[0035] In the example shown in Figure 44 above, correction is possible by simply changing the constants of the elements while leaving the typical dividing network circuit configuration of a 2-way acoustic system intact, but in order to create a depression near the crossover frequency of WF and TW, the TW must be able to reproduce sufficiently up to the frequency where the baffle effect causes a peak in sound pressure. In the example shown in Figure 44 above, the TW must be able to reproduce sufficiently in the frequency range of 1 kHz or higher.

[0036] Furthermore, if a diaphragm with an effective diameter of 145 mm is attached to a rectangular enclosure with a baffle measuring approximately 300 x 450 mm, for example, the baffle effect will cause a peak in the sound pressure characteristics at 700 Hz. To correct this using a similar method, a TW (in the case of a two-way sound system) that can adequately reproduce frequencies above 700 Hz is required. In this way, the TW that can be used is limited to those with high low-frequency reproduction capabilities depending on the external dimensions of the sound system.

[0037] As another example, if the lowest reproducible frequency of the TW is high or the TW's input power handling capability is low, it may be necessary to raise the crossover frequency to improve the system's input power handling capability. Also, some systems intentionally set the crossover frequency high to utilize wideband WF or full-range drivers, or do not use TW. In these cases, the frequency band where the sound pressure difference occurs due to the baffle effect is within the output band of the low-frequency driver or full-range driver.

[0038] For example, a method is known in which a compensation circuit is provided to make the frequency characteristics of the signal input to the driver the inverse characteristics of the baffle effect, as shown in Fig. 45. Fig. 46 is a graph showing an example of the frequency characteristics of the input signal to each driver in the circuit of Fig. 45 and the frequency characteristics of the synthesized signal.

[0039] In the method shown in the example of Figure 42 above, if the baffle is large, the reproduction band of the TW becomes wider toward the low frequency side, and the TW voice coil is easily damaged due to heat generation or excessive amplitude. This results in a problem of lower input power resistance of the system. Another problem is that the TW's low frequency reproduction limit must be sufficiently low, which reduces the number of TW options.

[0040] In the method shown in the example of Figure 45 above, the resistors in the compensation circuit generate a lot of heat, which can cause changes in characteristics and pose safety issues. Furthermore, because audio or music signals have low energy in the high frequency range and high energy in the mid-low frequency range, resistors are primarily used in the high frequency range when used in the network. Furthermore, extending the TW playback band to the low frequency range is disadvantageous in terms of reliability. International standards specify the characteristics of signals used in speaker input resistance tests (see Figure 47). Figure 47 shows the filter characteristics when white noise is used as the signal source.

[0041] The embodiment of the present invention solves the above problems and provides an inexpensive, high-quality sound system.

[0042] Here, the main characteristics of the diffraction effect of a baffle in an enclosure such as a rectangular parallelepiped are that there is a 6 dB difference in sound pressure between the low and high frequencies, and that there is a sound pressure increase section (a peak of about 2 dB) on the high frequency side of the sound pressure step.

[0043] The input signal to a normal driver is corrected to have the opposite characteristics to those described above, and then input to the driver. In this case, no resistor is used.

[0044] Specifically, as a component for compensating for the 6 dB difference in sound pressure between the low and high frequencies, a driver (WF or full-range driver) that emits the band in which the baffle effect causes a difference in sound pressure is electrically driven by two or more systems of drive circuits, and a low-pass filter is installed in the drive circuits of some systems and connected in parallel with the drive circuits of the other systems.

[0045] This increases the driver output in the low range compared to the high range, correcting the difference in sound pressure between the low and high ranges caused by the finite baffle.

[0046] The configuration for electrically driving the device with two or more systems of drive circuits can be any of the following first to third methods, in which each drive circuit generates a force in the same direction in response to an input signal.

[0047] The first method uses multiple drive circuits for multiple drivers connected in parallel.

[0048] In the second method, a single driver (diaphragm) is provided with multiple drive circuits, which are connected in parallel. Specifically, a single driver is provided with multiple pairs of magnetic gaps and voice coils.

[0049] In the third method, multiple systems of voice coil wires are arranged for a single magnetic gap and a single voice coil in a single driver.

[0050] If an even number of driver circuits with the same performance are used, a low-pass filter can be installed in half of the driver circuits, and the remaining driver circuits can be driven by inputting a signal to the driver without installing a low-pass filter. This makes the high-frequency side 6 dB lower than the low-frequency side. In other words, the driving force is halved.

[0051] To correct the sound pressure rise (peak of about 2 dB) on the higher frequency side of the sound pressure step, a low-pass filter of second order or higher is used, consisting of an input-side inductance (coil) connected in series with the voice coil and a capacitance (capacitor) connected in parallel with the voice coil. Also, a dip is created in the frequency characteristics of the signal input to the driver near the peak frequency caused by the baffle effect.

[0052] [First embodiment] <Configuration of the Acoustic System According to the First Embodiment of the Present Invention> FIG. 1 shows a schematic diagram of an audio system 10 according to an embodiment of the present invention.

[0053] As shown in FIG. 1, the sound system 10 includes a sound source input unit 12, an amplifier 14, and a speaker device 16.

[0054] The sound source input unit 12 receives a sound source signal.

[0055] The amplifier 14 outputs the received sound source signal to the speaker device 16 .

[0056] 2, the speaker device 16 includes a driving unit 18 consisting of two drivers 20A and 20B, and an enclosure 22 that houses the driving unit 18. In this embodiment, the enclosure 22 is a rectangular parallelepiped housing and is a bass-reflex type enclosure. The drivers 20A and 20B are full-range drivers.

[0057] 3, speaker device 16 includes a drive circuit 30A that outputs a control signal for vibrating a diaphragm (not shown) of driver 20A based on a sound source signal, a drive circuit 30B that outputs a control signal for vibrating a diaphragm (not shown) of driver 20B based on the sound source signal, and a drive unit 18 that vibrates the diaphragm in accordance with the outputs of drive circuits 30A and 30B. Drive circuit 30B includes a low-pass filter 32.

[0058] The drivers 20A and 20B include voice coils VC1 and VC2 and a magnetic circuit (not shown).

[0059] The drive circuit 30A outputs a control signal corresponding to the input sound source signal to the voice coil VC1, and vibrates the diaphragm of the driver 20A by the magnetic circuit.

[0060] The drive circuit 30B outputs a control signal obtained from the input sound source signal via a low-pass filter 32 to the voice coil VC2, causing the diaphragm of the driver 20B to vibrate via a magnetic circuit.

[0061] Low-pass filter 32 is set so that a dip frequency in the frequency characteristics of the signal obtained by combining the control signals output by drive circuits 30A and 30B corresponds to a peak frequency in the frequency characteristics of the sound pressure output according to the shape of enclosure 22 (see arrows in FIG. 4). In FIG. 4, Ein represents the voltage of the input signal from amplifier 14, Evc1 represents the voltage of the control signal input to voice coil VC1, and Evc2 represents the voltage of the control signal input to voice coil VC2. The dip frequency is the frequency at which the signal frequency characteristics become a minimum value.

[0062] The low-pass filter 32 is a second-order or higher filter that is configured with an inductance (coil) connected in series with the voice coil VC2 and a capacitance (capacitor) connected in parallel with the voice coil VC2.

[0063] For example, as shown in FIG. 5, the low-pass filter 32 includes an inductance L connected in series to the voice coil VC2 and a capacitance C connected in parallel to the voice coil VC2.

[0064] <Explanation about the order of low-pass filters> Here, the reason why the low-pass filter 32 is of second order or higher will be explained.

[0065] First, a case where the low-pass filter is a first-order low-pass filter, that is, a case where the low-pass filter is configured only by a coil, will be described (Fig. 6). Fig. 6 is a circuit diagram showing a speaker device configured using a first-order low-pass filter.

[0066] When the input signal voltage Ein=1, the electrical impedance of each voice coil is resistance Rvc1, Rvc2, and the voltage of the control signal output to the voice coil is voltage Evc1, Evc2 (see FIG. 7), it is expressed by the following equation: Note that FIG. 7 is a circuit diagram showing an equivalent circuit of a speaker device when the voice coil is a pure resistor.

[0067] JPEG0007791740000001.jpg39164

[0068] If the voltage of the control signal to each voice coil is represented by the vector diagram shown in Figure 8, Evc1(ω) is constant at 1 regardless of frequency, so the vector does not rotate (see the dashed arrow in Figure 8).

[0069] For the sake of simplicity, the voice coil is treated as a pure resistor in Figure 7. Strictly speaking, the voice coil is not a pure resistor, so the influence of other reactances will be discussed later.

[0070] As ω (= 2πf) increases from 0, Evc2(ω) moves along the dashed curve from 1 to 0. Therefore, the real part of Evc2(ω) never becomes negative (the phase angle is in the range of 0 to -90°).

[0071] Evc1(ω)+Evc2(ω) (see the tip of the solid arrow in Figure 8) moves on the solid curve from the real part, 2, toward 1 as ω increases from 0. Therefore, the length of the resultant vector (|Evc1(ω)+Evc2(ω)|) is always greater than or equal to 1 and never falls below the value of Ein, so no dip can be formed in the frequency characteristics (see the solid line in Figure 9). Figure 9 is a graph showing the frequency characteristics of the control signals output by each of the drive circuits in the circuit of Figure 7 above, and the resultant signal.

[0072] In order for the length of the resultant vector (|Evc1(ω) + Evc2(ω)|) to be less than 1 (a depression to form), at least the real part of Evc2(ω) must be negative. In other words, the phase angle of Evc2(ω) must be within a range of -90 to +90 degrees.

[0073] Next, we will explain the case where a second-order low-pass filter is used, that is, where a low-pass filter is configured using one coil and one capacitor, as shown in Fig. 10. Fig. 10 is a circuit diagram showing an equivalent circuit of a speaker device configured using a second-order low-pass filter. The voltages Evc1 and Evc2 of the control signals output to the voice coil are expressed by the following equations.

[0074] JPEG0007791740000002.jpg44164

[0075] The real part of Evc2(ω) is (1-ω) because the denominator is always positive. 2 It turns out that it becomes negative when CL)<0. JPEG0007791740000003.jpg1625 (See the case where the dashed curve in FIG. 11 passes through the third quadrant.) FIG. 11 is a vector diagram showing the voltage of the control signal output to the voice coil in the circuit shown in FIG.

[0076] Evc1(ω)+Evc2(ω) (see the tip of the solid arrow in Figure 11 above) moves from 2 to 1 on the solid curve as the frequency increases from 0, and at high frequencies it falls within a circle with an absolute value of 1, converging to 1.

[0077] This shows that a dip can be formed in the frequency characteristics of the voltage of the combined signal at a specific frequency where the real part of Evc2(ω) becomes negative (phase is between -90° and -180°) (Fig. 12). Fig. 12 is a graph showing the frequency characteristics of the control signals output by each of the drive circuits in the circuit shown in Fig. 10 and the combined signal.

[0078] The constants of a second-order Butterworth low-pass filter are JPEG0007791740000004.jpg23164 However, by changing ζ, the shoulder characteristics of the low-pass filter can be changed.

[0079] The characteristic changes due to ζ are specifically as follows:

[0080] The frequency band where sound pressure drops from low to high frequencies due to the baffle diffraction effect is generally wider than 2 octave, and in the case of a second-order filter, it is preferable to make the shoulder characteristic gentler than that of a typical low-pass filter such as a Butterworth type. However, this also makes the depression shallower (see Figure 13). Figure 13 is a graph showing the frequency characteristics of the signal that combines the control signals output by each driver circuit when ζ is changed in the circuit shown in Figure 10 above.

[0081] In this way, by adjusting f and ζ in the second-order low-pass filter, the correction characteristics can be adjusted to approach the inverse characteristics of the baffle diffraction effect.

[0082] Next, a case where a third-order low-pass filter is used will be described as shown in Fig. 14. Fig. 14 is a circuit diagram showing an equivalent circuit of a speaker device configured using a third-order low-pass filter.

[0083] Each constant of the Butterworth type is expressed by the following formula.

[0084] JPEG0007791740000005.jpg33164

[0085] By adjusting each ζ, it is possible to approach the inverse characteristics of the baffle diffraction effect (see Figure 15). The bandwidth of the sound pressure drop band, the level of the depression band, etc. can be adjusted. Figure 15 is a graph showing the frequency characteristics of a signal that combines the control signals output by each driver circuit when ζ is changed in the circuit shown in Figure 14 above.

[0086] Next, a case where a fourth-order or higher low-pass filter is used will be described.

[0087] As the order increases, the phase rotation angle of Evc2 increases, so just like in the cases of second and third orders, in the case of fourth or higher orders, there is a region where the real part of Evc2 becomes negative (phase is -90 to +90 degrees). Therefore, it is possible to form a depression. Figure 16 is a vector diagram showing the vector locus of the voltage Evc2 of the control signal output to the voice coil when each of first to fourth order low-pass filters is used.

[0088] <Explanation of the influence of the driver's electrical impedance> Next, the influence of the electrical impedance of the driver as a load on the low-pass filter will be described.

[0089] The calculation data for the correction characteristics shown so far was calculated by treating the driver's electrical impedance as a pure resistance. The actual driver's electrical impedance has a specific impedance characteristic Ze, which is mainly due to the motional impedance Zem and the reactance Zex due to the voice coil inductance.

[0090] If the frequency band where the reactance becomes larger than the pure resistance due to these factors is close to the frequency band where the low-pass filter creates a 6 dB step, the frequency characteristics of the control signal input to the voice coil will change compared to the characteristics in the case of pure resistance.

[0091] The motional impedance Zem is due to the effect of the back electromotive force generated by the movement of the voice coil within the magnetic gap, and is expressed by the following formula:

[0092] JPEG0007791740000006.jpg22101

[0093] The reactance Zex due to the voice coil inductance is influenced by the voice coil winding and the magnetic material (magnetic circuit) acting as the iron core, and is expressed by the following formula: Zex=jωL

[0094] where L is the inductance of the voice coil, A is the force coefficient (magnetic flux density x effective length of VC2), Mm is the mass of the vibration system, Sm is stiffness, and Rm is mechanical resistance.

[0095] Below, the electrical impedance of a typical dynamic speaker and its effect on the terminal voltage will be explained using the characteristics of the voice coil VC2 in FIG.

[0096] The equivalent circuit of the driver circuit on the voice coil VC2 side is as follows:

[0097] If the voice coil impedance is considered to be pure resistance, the voice coil impedance Ze is expressed by the following equation (Figure 17). Ze=Rvc2

[0098] FIG. 17 is a diagram showing an electrical equivalent circuit of a drive circuit including a low-pass filter when the impedance of the voice coil is pure resistance.

[0099] Furthermore, when the motional impedance Zem and the reactance Zex due to the voice coil inductance are taken into consideration, the electrical impedance Ze of the driver is expressed by the following equation (FIG. 18).

[0100] Ze=Rvc2+Zex+Zem

[0101] Fig. 18 is a diagram showing an equivalent circuit of a drive circuit including a low-pass filter when taking into consideration the motional impedance Zem and the reactance Zex due to the voice coil inductance. (1) in Fig. 18 corresponds to the motional impedance Zem, and (2) in Fig. 18 corresponds to the reactance Zex due to the voice coil inductance.

[0102] Moreover, the characteristics of the electrical impedance of the driver in the circuit shown in Fig. 18 are shown in Fig. 19. Fig. 19 is a graph showing the characteristics of |Zex|, |Zem|, |Ze|, and the pure resistance Rvc2.

[0103] Furthermore, changes in the frequency characteristics of the signal obtained by combining the control signals to each voice coil due to differences in load are shown in Fig. 20. Fig. 20 is a graph showing the frequency characteristics of the signal obtained by combining the control signals output by each of the drive circuits when the driver's electrical impedance is pure resistance and when the reactance Zex due to the motional impedance Zem and the voice coil inductance is taken into account.

[0104] The influence of motional impedance is shown around 200 Hz (see (1) in FIG. 20), and the influence of voice coil inductance is shown around 1.5 kHz (see (2) in FIG. 20).

[0105] These effects can be addressed by conducting simulations calculated according to the driver specifications or by conducting actual measurements, and adjusting the constants of the low-pass filter to achieve the desired characteristics.

[0106] Furthermore, if a circuit that cancels inductance (the aforementioned impedance compensation circuit) is provided between the low-pass filter on the voice coil VC2 side and the driver, or if a short ring or similar (which cancels the magnetic flux changes that occur with the voice coil current) is used, the inductance component in the low-pass filter load will be reduced, and the impact of reactance Zex due to the voice coil inductance will also be reduced. Also, voice coils with fewer turns, such as full-range drivers, generally have smaller inductance than WF, so the impact will be less.

[0107] <Operation of the acoustic system according to the embodiment of the present invention> A sound source input unit 12 receives an input of a sound source signal from an audio player or the like.

[0108] The amplifier 14 then outputs the received sound source signal to the speaker device 16 .

[0109] Then, the driving circuit 30A of the speaker device 16 outputs a control signal to the driver 20A based on the sound source signal, causing a diaphragm (not shown) of the driver 20A to vibrate.

[0110] Furthermore, the driving circuit 30B of the speaker device 16 outputs a control signal to the driver 20A using a low-pass filter 32 based on the sound source signal, thereby vibrating the diaphragm of the driver 20B.

[0111] Here, low-pass filter 32 is set so that the dip frequency in the frequency characteristics of the signal obtained by combining the control signals output by each of drive circuits 30A and 30B corresponds to the peak frequency of the frequency characteristics of the sound pressure output according to the shape of enclosure 22. Therefore, in the frequency characteristics of the signal obtained by combining the input signals to drivers 20A and 20B, a dip occurs near the frequency of the peak caused by the baffle effect of enclosure 22. This allows acoustic system 10 to achieve a flat sound pressure frequency characteristic.

[0112] As described above, in the acoustic system according to the first embodiment of the present invention, the low-pass filter provided in one of the two drive circuits is set so that the peak frequency of the frequency characteristic of the sound pressure output according to the shape of the enclosure corresponds to the dip frequency in the frequency characteristic of the signal obtained by combining the control signals output by each of the two drive circuits. This makes it possible to provide a speaker device with high sound quality with a simple configuration.

[0113] Furthermore, by correcting the driver input to produce the opposite characteristics to the changes in driver output characteristics caused by the diffraction effect of the enclosure baffle, it is possible to provide a low-cost, high-quality sound system with a simple circuit configuration.

[0114] Furthermore, since the speaker device does not use resistors and generates little heat, the characteristics during use are stable, and this is also advantageous for designing a highly durable acoustic system.

[0115] In addition, by adjusting the output balance and element constants of each driver circuit, it is possible to make corrections to match the characteristics of the diffraction effect of the rectangular baffle, as well as to correct the driver characteristics.

[0116] [Second embodiment] Next, an audio system according to a second embodiment will be described. Note that parts having the same configuration as those in the first embodiment will be given the same reference numerals and descriptions thereof will be omitted.

[0117] The second embodiment differs from the first embodiment in that a single driver is provided with a plurality of drive circuits, and the plurality of drive circuits are connected in parallel.

[0118] As shown in FIG. 1, the sound system 210 includes a sound source input unit 12, an amplifier 14, and a speaker device 216.

[0119] As shown in FIG. 21, the speaker device 216 includes a driving section 218 made up of a driver 220 and an enclosure 22 that houses the driver 220.

[0120] 22, speaker device 216 includes drive circuits 30A and 30B, and a drive unit 218 that vibrates a diaphragm in accordance with the outputs of drive circuits 30A and 30B. Drive circuit 30B includes a low-pass filter 32.

[0121] Each of the driving circuits 30A and 30B outputs a control signal that vibrates the diaphragm of a single driver 220 based on a sound source signal.

[0122] The driver 220 includes a plurality of pairs of a magnetic circuit and a voice coil. Specifically, the driver 220 includes a pair of a voice coil VC1 and a magnetic circuit, and a pair of a voice coil VC2 and a magnetic circuit.

[0123] The driving circuit 30A outputs a control signal to the voice coil VC1 based on the sound source signal, thereby vibrating the diaphragm of the single driver 220. The driving circuit 30B outputs a control signal to the voice coil VC2 based on the sound source signal, thereby vibrating the diaphragm of the single driver 220.

[0124] The other configurations and operations of the acoustic system according to the second embodiment are the same as those of the first embodiment, and therefore will not be described again.

[0125] In the acoustic system according to the second embodiment, even in the case of a single driver, the influence of the diffraction effect of the baffle can be corrected with a simple circuit.

[0126] [Third embodiment] Next, an audio system according to a third embodiment will be described. Note that parts having the same configuration as those in the first and second embodiments will be given the same reference numerals and descriptions thereof will be omitted.

[0127] The third embodiment differs from the second embodiment in that the driver is configured by arranging multiple systems of voice coil wires in a single magnetic circuit and a single voice coil.

[0128] Specifically, the driver is configured using two systems of conductor wire wound in parallel in the same direction around a single voice coil bobbin, as shown in Figures 23(A) and 23(B). Figure 23(B) shows a cross section of the winding section, showing how the coil wire of voice coil VC1 and the coil wire of voice coil VC2 are wound in parallel around the voice coil bobbin.

[0129] The driving circuit 30A outputs a control signal to the voice coil VC1 based on the sound source signal, thereby vibrating the diaphragm of the single driver 220. The driving circuit 30B outputs a control signal to the voice coil VC2 based on the sound source signal, thereby vibrating the diaphragm of the single driver 220.

[0130] The other configurations and operations of the acoustic system according to the third embodiment are the same as those of the second embodiment, and therefore will not be described further.

[0131] [Example] An example of the acoustic system described in the third embodiment will now be described. In this example, a voice coil (DCR 6.9 + 6.9Ω) was used, in which two lines of conductor wire were wound in parallel in the same direction around a single voice coil bobbin with an inner diameter of Φ25. The magnetic circuit was a ferrite magnet external magnet type, and a cone diaphragm (curved cone, cloth edge) with an effective vibration diameter of Φ80 was used. A bass-reflex enclosure with external dimensions of W214 x H384 x D150 was also used.

[0132] As a comparative example, a speaker device configured without a low-pass filter, as shown in FIG. 24, was used. FIG. 25 is a graph showing the anechoic chamber characteristics of a 2π space and a bass-reflex enclosure for a speaker device configured without a low-pass filter. The 2π space is an anechoic chamber with a baffle on one side that simulates a 2π space. FIG. 26 is a graph showing a comparison of the difference between the measured values ​​of a bass-reflex enclosure and the 2π space with calculated data. Here, the difference in the measured values ​​corresponds to the diffraction effect of the baffle.

[0133] Below 200Hz, the characteristics of the bass reflex enclosure become apparent, but above 300Hz, the effect of baffle diffraction is generally consistent with the calculated data obtained from the simulation.

[0134] 27 is a circuit diagram showing the configuration of a speaker device 216 according to an embodiment using a second-order low-pass filter, where the inductance L of the low-pass filter is set to 3 mH and the capacitor C is set to 20 μF.

[0135] FIG. 28 is a graph showing the results of a simulation of the frequency characteristics of a signal (composite voltage) obtained by combining the control signals output by the drive circuits in the circuit shown in FIG.

[0136] Fig. 29 is a graph showing the results of actual sound pressure measurements with and without a low-pass filter. Fig. 30 is a graph showing the difference in sound pressure with and without a low-pass filter. The values ​​in Fig. 30 are calculated values ​​from actual measurements.

[0137] 31 is a circuit diagram showing the configuration of a speaker device 216 according to an embodiment using a third-order low-pass filter. Here, the inductance L1 of the low-pass filter is set to 3 mH, the capacitor C is set to 15 μF, and the inductance L2 is set to 0.5 mH.

[0138] FIG. 32 is a graph showing the results of a simulation of the frequency characteristics of a signal (composite voltage) obtained by combining the control signals output by the drive circuits in the circuit shown in FIG.

[0139] Fig. 33 is a graph showing the results of actual sound pressure measurements with and without a low-pass filter. Fig. 34 is a graph showing the difference in sound pressure with and without a low-pass filter. The values ​​in Fig. 34 are calculated values ​​from actual measurements.

[0140] Next, the effect of electromagnetic coupling of the voice coils will be explained. In this embodiment, two voice coils are located in the same position in the coaxial vibration direction. Therefore, they are coupled to share the magnetic flux generated by the current, and an electromotive force is generated in each voice coil in response to changes in the current in the other voice coil. As a result, the current generated in the other voice coil flows in the opposite direction to the input voltage to each voice coil, and becomes larger at higher frequencies where the magnetic flux changes more significantly over time. These currents have the effect of reducing the driving force generated by each input, and this becomes particularly noticeable at higher frequencies. Note that the effect of this phenomenon is reduced when the aforementioned short ring is provided.

[0141] Furthermore, when there is no low-pass filter (Figure 24 above), the circuits of each voice coil system are considered to be the same as when the other voice coil is short-circuited (Figure 35) (typically, the amplifier's output impedance is much lower than the voice coil impedance), and the characteristics when both terminals are input without a low-pass filter can be said to be a combination (+6 dB) of the two characteristics in this case (see the solid line in Figure 36) (see the dashed line in Figure 36). Figure 35 is a circuit diagram when one voice coil is short-circuited. Figure 36 is a graph showing the results of actual sound pressure measurements when one voice coil is short-circuited (Figure 35) and when it is not short-circuited (Figure 24).

[0142] Also, a circuit diagram with the voice coil VC2 side open is shown in Fig. 37. Fig. 38 shows the results of comparing the characteristics of the sound pressure measurement results for the circuit shown in Fig. 35 (where one voice coil is shorted) and the sound pressure measurement results for the circuit shown in Fig. 37 (where one voice coil is open).

[0143] From Figure 38 above, it can be seen that by shorting the voice coil VC2 side, the high frequencies are reduced due to the current generated by coupling. Also, the sound pressure is reduced in the low frequencies even though there is almost no effect of electromagnetic coupling. This is because a braking force is generated by the back electromotive force that is generated when the coil wire of voice coil VC2 oscillates within the magnetic gap.

[0144] In the case of a speaker device using a third-order low-pass filter (FIG. 31), the inductance L2 of the low-pass filter is connected in series with the voice coil VC2, so that although a back electromotive force is generated in the voice coil VC2 by the current on the voice coil VC1 side, the current is difficult to flow at high frequencies. Therefore, the output characteristics due to the input signal on the voice coil VC1 side in the high frequency range are similar to those when the voice coil VC2 side is open. FIG. 31 is a circuit diagram showing an example of the configuration of a speaker device according to an embodiment using a third-order low-pass filter.

[0145] As a result, the sound pressure drop in the high range is less than 6 dB compared to when there is no low-pass filter. This phenomenon has little effect when configured as a WF that handles only the low range, but it needs to be taken into consideration when using a full-range driver like in this example.

[0146] Next, an embodiment in which a speaker device is used as a WF (an embodiment in which a difference in sound pressure between low and high frequencies and a peak occur within the WF band due to the diffraction effect of the baffle) will be described. When used as a WF, it is necessary to limit the output of frequencies that fall within the TW band within the output of the WF. When using a dividing network, it is sufficient to provide a desired network circuit on the voice coil VC1 side of a circuit designed to have the inverse characteristics of the diffraction effect of the baffle (see Figures 27 and 31).

[0147] 39 is a circuit diagram showing the configuration of a speaker device 316 in an embodiment used as a WF. An upper drive circuit 330C outputs a control signal to a driver 320 used as a TW. A middle drive circuit 330A outputs a control signal to a voice coil VC1, and a lower drive circuit 330B outputs a control signal to a voice coil VC2.

[0148] Here, the inductance L1 of the low-pass filter is set to 2.5 mH, the capacitor C1 is set to 20 μF, and the inductance L2 is set to 0.5 mH. The inductance L3 of the dividing network is set to 0.5 mH, and the capacitor C3 is set to 2.6 μF. The impedance compensation resistor R is set to 7 Ω, and the capacitor C2 is set to 6.8 μF.

[0149] Fig. 40 is a graph showing the simulation results of the frequency characteristics of the control signals output by each of the drive circuits 330A, 330B, and 330C in the circuit shown in Fig. 39 and the signal (composite voltage) obtained by combining these control signals. The voltage of the control signal output to the voice coil VC3 is Etw, and the voltage of the combined signal is Etotal.

[0150] As in this example, a two-way acoustic system using a TW can also be implemented for WF. In this example, the sound pressure step and peak to be suppressed are in the bass band (WF band), and the band is limited by a low-pass filter provided in the driver circuit for the bass band driver, but this is not limited to this. If the sound pressure step and peak to be suppressed are in the band of the treble driver (TW band) or in the band of the midrange driver (SQ) of a 3-way or other device, the driver circuit of the present invention can be provided in the treble or midrange band driver, and a high-pass filter can be provided to limit the low-frequency band and adjust it. However, in this case, the high-pass filter can be provided just before branching to each VC circuit of the drive circuit of the present invention, as shown in Figure 48.

[0151] The present invention is not limited to the above-described embodiment, and various modifications and applications are possible without departing from the spirit and scope of the present invention.

[0152] For example, in the above embodiment, the sound pressure difference between the low-frequency side and the high-frequency side is 6 dB, but this is not limited to this. When only the diffraction effect of the baffle is considered, the sound pressure difference between the low-frequency side and the high-frequency side is 6 dB. This is the sound pressure difference between a sufficiently high frequency where the radiation space can be considered to be 2π and a sufficiently low frequency where the radiation space can be considered to be 4π. However, since the characteristics of an acoustic system are affected by other factors that change the frequency characteristics, such as the driver cone shape, the magnetic circuit configuration, and other components, it may be possible to achieve optimal final characteristics by slightly increasing or decreasing the output characteristics of the drive circuit from 6 dB.

[0153] In such cases, the desired adjustment can be achieved by setting the impedance of voice coil VC1 and voice coil VC2 to a ratio other than 1:1, or by making the driving forces of the two systems unequal. It is also possible to use three or more driving circuits and adjust the driving forces and driving coefficients of each. For example, if the driving forces on the voice coil VC1 side and the voice coil VC2 side are set to 1.3:1 and a low-pass filter is installed on the voice coil VC2 side, the sound pressure difference will be 5 dB. It should be noted that when using this method, the size of the recess will also increase or decrease slightly.

[0154] Furthermore, when configuring two or more coils on a single voice coil bobbin, other than the embodiment, a method using voice coils wound on the same axis at different positions in the vibration direction may be used. The current direction and gap magnetic flux direction may be set so that when the same voltage is applied to each coil, a force is generated in the same direction.

[0155] Additionally, a ring-shaped conductor with high conductivity (such as a copper ring) may be wound around the pole piece of the speaker device to reduce the AC magnetic flux generated when current flows through the voice coil. This eliminates the impedance of the voice coil, making impedance compensation unnecessary. This means that the design can be performed without regard to the inductance of the voice coil. Furthermore, the reduction in this AC magnetic flux also reduces distortion in the current, resulting in higher sound quality.

[0156] Furthermore, when winding two or more voice coils on a single voice coil bobbin, if the voice coils are wound coaxially but in different positions in the vibration direction, the mutual influence of each system can be reduced by ensuring that the AC magnetic flux generated in each system is in opposite directions when the same voltage is applied to the two windings. This allows the design to ignore the voice coil inductance. Furthermore, reducing this AC magnetic flux also reduces distortion in the current, resulting in higher sound quality. [Explanation of symbols]

[0157] 10, 210 sound system 12 Sound source input section 14 Amplifier 16, 216, 316 Speaker equipment 20A, 20B, 220, 320 drivers 22 Enclosure 30A, 30B, 330A, 330B, 330C drive circuit 32 Low-pass filter VC1, VC2, VC3 voice coils

Claims

1. a driving section comprising at least one driver including a diaphragm; an enclosure that houses the driver; a plurality of drive circuits that output control signals for vibrating the diaphragm of the at least one driver based on a sound source signal; the drive unit vibrates the diaphragm in response to outputs of the plurality of drive circuits; a low-pass filter is provided in some of the plurality of drive circuits; The low-pass filter is set so that a dip frequency in the frequency characteristic of a signal obtained by combining the control signals output from each of the plurality of drive circuits corresponds to a peak frequency in the frequency characteristic of sound pressure output according to the shape of the enclosure. Speaker device.

2. The drive unit is composed of one driver, each of the plurality of drive circuits outputs a control signal for vibrating a diaphragm of the driver based on a sound source signal; 2. The speaker device according to claim 1, wherein the driving section vibrates a single diaphragm in response to outputs from the plurality of driving circuits.

3. the drive unit includes a plurality of drivers provided corresponding to the plurality of drive circuits, each of the plurality of drive circuits outputs a control signal to vibrate a diaphragm of the corresponding driver based on a sound source signal; 2. The speaker device according to claim 1, wherein the driving section vibrates a diaphragm corresponding to each of the plurality of driving circuits in accordance with an output of the driving circuit.

4. 4. The speaker device according to claim 1, wherein the driver includes a voice coil and a magnetic circuit.

5. A speaker device according to any one of claims 1 to 4, a signal input unit that receives the sound source signal; an amplifier that outputs the received sound source signal to the speaker device; Sound system including.

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