JP2005109969A - Audio system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an adverse effect caused by the mutual interference of sound waves from a tweeter and woofer and to enable the tweeter to fully demonstrate its performance at the same time. <P>SOLUTION: An audio system is provided with: high-frequency and low-frequency filters 11 and 12 for dividing the band of an input sound signal into high-frequency and low-frequency components according to a prescribed crossover frequency; and a tweeter 17 and woofer 18 which are respectively driven by the band-divided high frequency and low-frequency components and respectively output high-frequency and low-frequency sound waves. The high-frequency and low-frequency filters have such attenuation characteristics that the transition region between the high-frequency and low-frequency sound waves is so steep so that a listener cannot perceive interference between the high-frequency and low-frequency sound waves. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an audio system.

  In general, in an audio system, it is desirable that a high-frequency speaker is installed at the height of the ear due to the straightness and non-diffractive nature of high sounds, and the installation position of a low-frequency speaker is not so limited due to low-frequency diffractive properties. For example, in the case of an in-vehicle audio system, since the installation position is limited in the vehicle interior, the speaker is installed at the height of the passenger's feet on the door. Because of this behavior, it is difficult for the treble to reach the listener. Therefore, a high sound speaker is provided and installed at a high position in the passenger compartment.

  FIG. 6 illustrates the arrangement of speakers in such an on-vehicle audio system. This system has a high-frequency speaker 61 and a low-frequency speaker 62. The low sound speaker 62 is installed at the position of the foot, and the high sound speaker 61 is installed at a high position such as the upper part of the front door.

  FIG. 7 shows a part of this in-vehicle audio system. This system includes a power amplifier 71 that amplifies a reproduction signal, a high-pass filter 72 and a low-pass filter 73 that divide the amplified audio signal into high-frequency and low-frequency components, and a divided high-frequency side and low-frequency side. The high-frequency speaker 75 and the low-frequency speaker 76 are respectively driven based on the above components and output sound waves on the high frequency side and the low frequency side, respectively. The high pass filter 72 and the low pass filter 73 constitute a band division filter. A reproduction signal from a CD receiver or the like is amplified by a power amplifier 71, further divided into a low-frequency side and a high-frequency side by a band division filter, and converted into a sound wave signal by a high-frequency speaker 75 and a low-frequency speaker 76 for listening. Reach the ears of the person.

  In the system in which the speakers 75 and 76 dedicated to the respective bands are driven by the reproduction signals divided into the respective bands as described above, an inductor and a capacitor are used as band dividing filters in order to smooth the characteristics of the synthesized sound by the speakers 75 and 76. A primary or secondary analog filter configured using is used. Such a band division filter has a relatively gentle attenuation characteristic in the transition region.

FIG. 8 exemplifies the amplitude frequency characteristics of the band division filter by the high pass filter 72 and the low pass filter 73. Curves 8H and 8L in the figure are characteristic curves of the high-pass filter 72 and the low-pass filter 73, respectively. The cutoff characteristics of the filters 72 and 73 are 6 [dB / oct]. Centering on the crossover frequency fc of both filters, the frequency bands of the signals passing through both filters overlap. Therefore, the sound waves output from both speakers 75 and 76 also have the same frequency over the frequency band. Since the attenuation characteristic is gradual, the overlapping frequency bands cover a wide range. As an example of such a system, the one described in Patent Document 1 can be given, for example.
Japanese Patent Laid-Open No. 4-318800

  However, if there are overlapping frequency bands in the sound waves from both the high-frequency sound and low-frequency speakers in this way over a wide band, the sound waves from both speakers in that frequency band are mutually affected by the phase rotation of the filter. There is a frequency point that has an opposite phase, and there is a problem that sound waves from both speakers cancel each other and disappear. In order to suppress the influence of such phase rotation, there is a method of causing a time difference by shifting the installation surface of both speakers. However, according to this method, only the point where the phase becomes opposite is shifted, and this is not a fundamental solution. .

  Also, if the cutoff characteristic is gentle, the high-frequency filter passes the low-frequency component having a considerably low frequency and supplies it to the high-frequency speaker. Then, it is necessary to operate the loudspeaker with low power so that the loudspeaker with lower input power resistance than the bass speaker is not destroyed by the low frequency component having a large amplitude. In addition, a signal considerably lower than the resonance frequency of the high temperature speaker is input. In order to avoid these problems, there is a method of increasing the cutoff frequency of the filter, but in order to obtain an appropriate reproduced sound, the cutoff frequency cannot be increased excessively. Therefore, due to these restrictions, the performance of the loudspeaker cannot be fully exhibited.

  In such an audio system, if the distance from the speaker to the listener is different between the high-pitched speaker and the low-pitched speaker, the sound waves output simultaneously from the two speakers reach the listener's ear at different times. Therefore, it gives an unnatural feeling to the listener. Especially in an in-vehicle audio system, the distance from each speaker to the listener is often different by installing a low-frequency speaker at the foot and installing a high-frequency speaker near the side mirror as described above. , It becomes a problem. Further, in the above-described overlapping frequency bands, the sound waves of the same frequency reach the listener with a time difference, so that the sound waves from both speakers cancel each other at a frequency that is just in the opposite phase according to the time difference. That is, there is a problem that a peak dip corresponding to the frequency occurs.

  An object of the present invention is to solve the problems of the prior art, in an audio system in which high-frequency and low-frequency speakers are driven by an audio signal divided into a high frequency side and a low frequency side. It is intended to prevent the adverse effects due to interference and at the same time to fully demonstrate the ability of the loudspeaker.

  In order to achieve the above object, an audio system according to a first aspect of the present invention includes a high-frequency filter and a low-frequency filter that divide an input audio signal into high-frequency and low-frequency components, The high-frequency and low-frequency speakers are driven on the basis of the high-frequency and low-frequency components and output high-frequency and low-frequency sound waves, respectively. This filter is characterized in that the attenuation characteristic in the transition region is steep so that the listener cannot recognize the deterioration of the sound due to the interference between the sound waves on the high frequency side and the low frequency side.

  Here, the audio system is, for example, an in-vehicle audio system in which a high-pitched speaker is provided on the front door upper part or on the dashboard, and a low-pitched speaker is provided on the foot of the front door lower part. Applicable to the system. “High band side” and “low band side” are used in a relative sense. For example, in the case of a three-way speaker, the present invention can be applied by using a mid-range speaker as a high-frequency speaker and a low-frequency speaker as a low-frequency speaker.

  In this configuration, the input audio signal is band-divided by a high-frequency filter and a low-frequency filter having amplitude frequency characteristics as illustrated in FIG. 2H and 2L in the figure are characteristic curves of the high-pass filter and the low-pass filter, respectively. The characteristic curves 2H and 2L intersect at the crossover frequency fc, and the substantial signal passing ranges in both filters overlap in the frequency range Fw until the amplitude is attenuated with the crossover frequency fc as the center. Therefore, the high-frequency and low-frequency speakers driven by the band-divided high-frequency and low-frequency components output sound waves whose sound ranges overlap in the frequency range Fw. In this overlapping frequency range Fw, the sound waves from the high frequency side and low frequency side speakers cause interference between the same frequency components, and if they are in phase, they are strengthened and if in opposite phases, they are weakened. It is known that sound deterioration as a peak dip occurs due to a difference in distance from each speaker on the side and low frequency side to a listener and a phase difference caused by a phase rotation of a filter.

  Conventionally, the characteristics of the high-pass and low-pass filters have relatively gentle attenuation characteristics as exemplified by the curves 8H and 8L in FIG. It was over a very wide frequency range. Therefore, when the peak dip occurs, the sound recognized by the listener is adversely affected. In addition, if the attenuation characteristic is moderate, a considerably low frequency signal is input to the high frequency speaker. Therefore, in order to prevent destruction of the high frequency speaker, the crossover frequency fc is lowered. And it cannot be driven with sufficient power. On the other hand, in order to obtain an appropriate reproduction sound, the cutoff frequency of the high-frequency speaker cannot be increased forcibly, and a signal having a frequency lower than the resonance frequency is input to the high-frequency speaker. In other words, the conflicting demands were complicated, and the performance of the high frequency side speaker could not be fully exhibited.

  On the other hand, according to the present invention, as illustrated in FIG. 2, as a high-frequency filter and a low-frequency filter, a sound such as a peak dip due to interference between high-frequency and low-frequency sound waves is used. Adopting a steep attenuation characteristic in the transition region to the extent that the listener cannot recognize the deterioration. This is because when the attenuation characteristics of the high-frequency and low-frequency side filters become steep to some extent, the frequency range Fw in which the high-frequency and low-frequency bands overlap is considerably narrowed accordingly. Even if a peak dip occurs in that range, the listener will not be able to recognize it. In the present invention, the high frequency side and low frequency side filters have such a steep attenuation characteristic. It means that In this case, since the low-frequency side signal is hardly input to the high-frequency speaker, the crossover frequency fc can be set lower than that of the conventional example of FIG. 8 in order to obtain an appropriate reproduction sound. Therefore, it is possible to drive with sufficient power and a signal having a frequency lower than the resonance frequency is not input. Therefore, the performance of the high frequency side speaker can be sufficiently exhibited.

  The audio system according to a second aspect is characterized in that, in the first aspect, the high-frequency and low-frequency side filters have a transition band width of 1/3 [oct] or less.

  The audio system according to a third aspect is characterized in that, in the second aspect, the high band side and low band side filters have an attenuation of 80 [dB] or more in the transition band.

  The audio system according to a fourth invention is the audio system according to any one of the first to third inventions, wherein the high-frequency and low-frequency speakers are separately provided based on the divided high-frequency and low-frequency audio signals. It is characterized by having a power amplifier for driving a high frequency side and a low frequency side.

  The audio system according to a fifth invention is the audio system according to any one of the first to fourth inventions, wherein the high frequency side divided so that the sound waves from the high frequency side and low frequency side speakers simultaneously reach the listening position. Alternatively, delay means for delaying the audio signal on the low frequency side is provided.

  An audio system according to a sixth invention is any one of the first to fifth inventions, wherein the filter is a digital filter.

  An audio system according to a seventh invention is characterized in that, in any one of the first to sixth inventions, the filter is a linear phase filter.

  An audio system according to an eighth invention is characterized in that in the invention according to any one of the first to seventh inventions, there is provided means for changing the cutoff frequency of the high-frequency side or low-frequency side filter.

  According to the present invention, as a high-frequency filter and a low-frequency filter, attenuation characteristics of each transition region between the two to such an extent that a listener cannot recognize sound distortion due to interference between high-frequency and low-frequency sound waves. Since the steep one is used, it is possible to prevent the adverse effects due to the mutual interference of sound waves from the high-frequency and low-frequency speakers, and at the same time, to fully demonstrate the ability of the high-frequency speaker.

  FIG. 1 is a block diagram showing an audio system according to an embodiment of the present invention. As shown in the figure, this speaker system includes a high-pass filter 11 and a low-pass filter 12 that divide a reproduction signal from a CD receiver or the like into a high frequency side and a low frequency side, and divided high frequency side and low frequency side audio. Time delay units 13 and 14 for performing predetermined time delay processing on the signals, power amplifiers 15 and 16 for separately driving the high-frequency speakers and the low-frequency speakers based on the outputs of the time delay devices 13 and 14, and the power amplifier 15 And a high-frequency speaker 17 and a low-frequency speaker 18 for converting the output signals of 16 and 16 into sound wave signals. The high-pass filter 11 and the low-pass filter 12 constitute a crossover network (channel divider) that divides an audio signal into a high frequency side and a low frequency side by a predetermined crossover frequency.

  FIG. 2 shows the frequency amplitude characteristics of the high-pass filter 11 and the low-pass filter 12. Each of the filters 11 and 12 is a digital filter having a steep slope characteristic as indicated by curves 2H and 2L, respectively. The width of the transition region of each filter 11 and 12 is 1/3 [oct] or less. The reason why the width of the transition region is set to 1/3 [oct] or less is that the normal sound field analysis is performed in units of 1/3 [oct] width, so that the high frequency region is narrower than this range. This is because even if the side and the low frequency side overlap and cause a peak dip due to interference, it is considered difficult for humans to discriminate in view of auditory function, acoustic psychology, and the like. In this case, the amount of attenuation varies depending on the reproduction sound field, but as the amount of attenuation in the transition region, 80 [dB] is sufficient in consideration of the performance of the power amplifiers 15 and 16, and 60 [dB] on hearing. It is considered sufficient.

  FIG. 3 shows impulse responses of the high-pass filter 11 and the low-pass filter 12. As each of the filters 11 and 12, an FIR (finite impulse response) filter showing an impulse response as shown in FIG. 3 is used so as to have a steep characteristic as shown in FIG. Each filter 11 and 12 is configured as a linear phase filter.

  The time delay devices 13 and 14 are set so that sounds from the high-frequency speaker 17 and the low-frequency speaker 18 reach the same time at the listening position. When the distance from the high sound speaker 17 to the listening position is a [m], the distance from the low sound speaker 18 to the listening position is b [m], and the sound speed is v [m / second], the listening from each speaker 17 and 18 is performed. The time difference t [seconds] required for the sound wave to reach the position is t = (ab) / v. Therefore, for example, when the time difference t is a positive value, the sound wave from the high-frequency speaker 17 arrives later than the sound wave from the low-frequency speaker 18, and therefore the time in the time delay unit 14 on the low-frequency speaker side. Set the delay amount to -t [seconds].

  In this configuration, the reproduction signal is divided by the high-pass filter 11 and the low-pass filter 12 into high-frequency and low-frequency components according to a predetermined crossover frequency fc according to the frequency characteristics shown in FIG. At this time, since the transition region of each component overlaps with other components, an overlapping frequency range Fw having a certain width around the crossover frequency fc occurs. However, since the width of the transition region of each filter is narrow, the frequency range Fw is very narrow. Further, since the cutoff characteristic of the high-pass filter 11 is steep, the low-frequency component having a low frequency is not duplicated and included in the high-frequency component.

  Each of the divided components is time-delayed according to the above setting by the time delay units 13 and 14 and supplied to the speakers 17 and 18 via the power amplifiers 15 and 16. At this time, interference between the speakers 17 and 18 can be suppressed as compared with a case where each speaker is driven by being divided into a high frequency side and a low frequency side after passing through the power amplifier. That is, since the speakers 17 and 18 are independently driven by the separate power amplifiers 15 and 16 after the division, the division accuracy changes depending on the AC impedance characteristics of the speaker, or the other speaker is caused by the back electromotive force of one speaker coil. It is possible to prevent the driving of the camera from being affected.

  The high-frequency component supplied from the power amplifier 15 to the high-frequency loudspeaker 17 is surely excluded from the low-frequency component due to the steep cutoff characteristics of the high-pass filter 11. Even if the rate is increased, there is no fear that the loudspeaker 17 is destroyed by the large energy of the low frequency component. Therefore, the high-frequency speaker 17 is driven by the high-frequency component amplified with a relatively high degree of amplification, and its performance is sufficiently exhibited. In addition, this makes it possible to set the crossover frequency to a lower value, so that appropriate reproduction sound can be supplied as a whole by the high-frequency side component due to the lower cutoff frequency. Even in that case, since the low frequency component lower than the resonance frequency of the high sound speaker 17 is not input, the performance of the high sound speaker 17 can be more effectively exhibited.

  The sound waves output from the high-frequency and low-frequency speakers 17 and 18 are subjected to the above-described delay processing on the corresponding high-frequency and low-frequency component audio signals so that the time to reach the listener is the same. As it is done, it reaches the listener at the same time. Therefore, the listener does not feel discomfort due to the sound waves on the high frequency side and the low frequency side shifting to different times and reaching the ear. At this time, since the width of the frequency range Fw that overlaps between the high-frequency and low-frequency sound waves is narrow, even if a peak dip occurs, the listener cannot recognize it. Note that the high-pass filter 11 and the low-pass filter 12 are linear phase filters, and the time delay is the same (constant) in all frequency bands, so that no peak dip occurs due to mutual interference of the filters. That is, there is no phase distortion due to phase characteristics as in a conventional analog filter, and appropriate reproduction can be performed.

  FIG. 4 shows an audio system according to another embodiment of the present invention. In this system, the high-pass filter 11, the low-pass filter 12, and the time delay units 13 and 14 are configured by a DSP (digital signal processor) 41. In the figure, 42 and 43 are DA converters for converting the outputs of the time delay units 13 and 14 into analog signals, respectively, and 44 and 45 are volumes provided on the output side of the DA converters 42 and 43, respectively. The output sides of the volumes 44 and 45 are connected to the power amplifiers 15 and 16, respectively. A microcomputer 46 controls the DSP 41 and the volumes 44 and 45. The user can change the cutoff frequencies of the high-pass filter 11 and the low-pass filter 12 by giving a command to the microcomputer 46.

  The DSP 41 performs a filter operation on an audio signal based on PCM (Pulse Code Modulation) based on a filter coefficient set by the microcomputer 46. Further, a delay process is performed based on the delay time set by the microcomputer 46 and output to the DA converters 42 and 43. The outputs of the DA converters 42 and 43 are converted into sound waves by the high-frequency and low-frequency speakers 17 and 18 via the volumes 44 and 45 and the power amplifiers 15 and 16, respectively. Other points are the same as in the case of FIG.

  FIG. 5 shows a DSP portion in an audio system according to another embodiment. As shown in the figure, the DSP 51 constitutes a tap delay 52 having one input and two outputs, and a high-pass filter 53 and a low-pass filter 54 respectively connected to two output sides of the tap delay. The delay time of each output of the tap delay 52 can be adjusted independently via the microcomputer 46. Further, the cutoff frequencies of the high pass filter 11 and the low pass filter 12 can be changed. The configuration of other parts in the speaker system is the same as in FIG. 4, and the output sides of the high-pass filter 53 and the low-pass filter 54 are connected to DA converters 42 and 43, respectively, and the DSP 51 is controlled by the microcomputer 46.

  The DSP 51 applies a delay process to the PCM audio signal based on each delay time set by the microcomputer 46 (FIG. 4), and based on the filter coefficient set by the microcomputer 46 for each delayed audio signal. Filter operation and output to the DA converters 42 and 43. The outputs of the DA converters 42 and 43 are converted into sound waves by the high-frequency and low-frequency speakers 17 and 18 via the volumes 44 and 45 and the power amplifiers 15 and 16, respectively. Other points are the same as in the case of FIG. According to this, the memory required for the time delay device can be reduced while achieving the same effect as compared with the embodiment of FIG.

  As described above, according to each embodiment, the high-pass filter and the low-pass filter that divide the audio signal are used with a steep cut-off characteristic. In addition, it is possible to eliminate an adverse effect caused by interference between sound waves on the high frequency range side and the low frequency range side. Further, since the power amplifier for separately driving the high-frequency and low-frequency speakers is provided based on the divided high-frequency and low-frequency audio signals, interference between the speakers can be suppressed. In addition, a delay device that delays the divided high-frequency or low-frequency audio signals is provided so that sound waves from the high-frequency and low-frequency speakers simultaneously reach the listening position. It is possible to prevent sound waves simultaneously output from the speakers from reaching different times at the listener. In addition, since the FIR type linear phase filter is used as the high pass filter and the low pass filter, phase distortion can be prevented and appropriate reproduction can be performed. Further, since the means for changing the cutoff frequency of the high pass filter or the low pass filter is provided, the cross frequency can be changed to a desired one.

1 is a block diagram showing an audio system according to an embodiment of the present invention. It is a figure which shows the frequency amplitude characteristic of the high-pass filter and low-pass filter in the system of FIG. It is a figure which shows the impulse response of the high pass filter in the system of FIG. 1, and a low pass filter. It is a block diagram which shows the audio system which concerns on other embodiment of this invention. It is a block diagram which shows the DSP part in the audio system which concerns on another embodiment of this invention. It is a figure which illustrates arrangement | positioning of the speaker in the audio system for vehicle mounting. It is a block diagram which shows a part of conventional vehicle-mounted audio system. It is a figure which illustrates the amplitude frequency characteristic of the band division filter by the high-pass filter and low-pass filter in the conventional audio system.

Explanation of symbols

2H, 8H: High-pass filter characteristic curve, 2L, 8L: Low-pass filter characteristic curve, 11: High-pass filter, 12: Low-pass filter, 13, 14: Time delay, 15, 16: Power amplifier, 17: High-frequency speaker 18: Bass speaker 41, 51: DSP, 42, 43: DA converter, 44, 45: Volume, 46: Microcomputer, 52: Tap delay, 53: FIR high pass filter, 54: FIR low pass filter, 61 : High sound speaker, 62: low sound speaker, 71: power amplifier, 72: high pass filter, 73: low pass filter, 75: high sound speaker, 76: low sound speaker.

Claims (8)

A high-frequency filter and a low-frequency filter that divide the input audio signal into high-frequency and low-frequency components;
Driven based on the band-divided high-frequency and low-frequency components, respectively, and provided with high-frequency and low-frequency speakers that output high-frequency and low-frequency sound waves, respectively,
The high band side and low band side filters have steep attenuation characteristics in the transition band to such an extent that a listener cannot recognize sound deterioration due to interference between the high band side and low band side sound waves. Audio system.   2. The audio system according to claim 1, wherein the high band side filter and the low band side filter have a transition band width of 1/3 [oct] or less.   The audio system according to claim 2, wherein the high band side filter and the low band side filter have an attenuation amount of 80 [dB] or more in a transition band.   A high frequency side and low frequency side power amplifier for separately driving the high frequency side and low frequency side speakers based on the divided high frequency side and low frequency side audio signals. Item 4. The audio system according to any one of Items 1 to 3.   The apparatus further comprises delay means for delaying the divided high frequency side or low frequency side audio signals so that sound waves from the high frequency side and low frequency side speakers simultaneously reach the listening position. Item 5. The audio system according to any one of Items 1 to 4.   The audio system according to claim 1, wherein the filter is a digital filter.   The audio system according to claim 1, wherein the filter is a linear phase filter. The audio system according to any one of claims 1 to 7, further comprising means for changing a cutoff frequency of the high frequency side or low frequency side filter.

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