JP2017017717A - Sound reproducer, sound reproduction method and sound reproduction program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound reproducer capable of increasing the reproduction sound level at a specific hearing position, with no adverse effect on the surroundings, and without requiring a large scale system.SOLUTION: A sound reproducer is applied to an acoustic space, e.g., a passenger compartment, and controls the level of a reproduction sound at two evaluation points set at the seat, or the like, in the passenger compartment. The sound reproducer controls the phase of an audio signal from a sound source 2 of 1 channel inputted externally, at a phase correction unit 6, and supplies to a pair of speakers SP1, SP2. Phase control is carried out so that the sum of reproduction sound level at two evaluation points becomes larger compared with a case where the audio signal is reproduced with only one of the pair of speakers SP1, SP2, in the whole audible band.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a technique for adjusting the level of sound heard by a listener in an acoustic space such as a passenger compartment.

  A method for adjusting the sound pressure level of reproduced sound in an acoustic space such as a passenger compartment has been proposed. For example, Patent Document 1 proposes a method of adjusting the sound pressure level according to the acoustic space and listening position by correcting the level of reproduced sound for each frequency band using an equalizer. Patent Document 2 proposes a method of forming a high sound pressure region in a specific place by arranging a speaker array including a plurality of speakers and controlling the phase and volume of an audio signal output from each speaker. ing.

Japanese Patent No. 4757034 JP 2011-151559 A

  Generally, in a passenger compartment, a listener (driver) in a driver's seat tends to have difficulty in listening because the sound of a rear speaker is smaller than the sound of a front speaker. This is probably because the sound output from the rear speaker is blocked by the seat or reflected by the window.

  In order to make it easier to listen to the reproduced sound of the rear speaker in the driver's seat, there is a method of using an equalizer to increase the reproduced sound level in a certain band as in Patent Document 1. However, this method has a disadvantage that the volume of the rear speaker is increased, so that the volume is too high for the person in the rear seat.

  On the other hand, a method of increasing the sound pressure near the driver's seat using a speaker array as in Patent Document 2 is also conceivable. However, the method of Patent Document 2 requires a large-scale system to perform control using a plurality of speakers, and is not suitable for application to a vehicle.

  Examples of the problems to be solved by the present invention include those described above. An object of the present invention is to provide an audio reproduction device capable of increasing the reproduction sound level at a specific listening position without causing adverse effects on the surroundings and without requiring a large-scale system. To do.

  The invention according to claim 1 is an audio reproducing device, wherein a pair of speakers arranged before and after two evaluation points in an acoustic space, an input means for receiving an audio signal of one channel, and the 2 The sum of the reproduced sound levels at the two evaluation points is larger than the case where the audio signal is reproduced by only one speaker of the pair of speakers in at least a desired band of the audible band. And a phase control means for controlling the phase difference of the audio signal supplied to the speaker.

  The invention according to claim 11 is an audio reproducing method executed by an audio reproducing apparatus including a pair of speakers arranged in front and back with respect to two evaluation points in an acoustic space. More than the case where the audio signal is reproduced by only one speaker of the pair of speakers in the receiving step and the sum of the reproduced sound levels at the two evaluation points at least in a desired band of the audible band. A phase control step of controlling a phase difference between audio signals supplied to the pair of speakers so as to increase.

  A twelfth aspect of the present invention is an audio reproduction program executed by an audio reproduction device including a pair of speakers arranged before and after two evaluation points in an acoustic space. The input means for receiving and the sum of the reproduced sound levels at the two evaluation points are at least in a desired band of the audible band, compared to the case where the audio signal is reproduced by only one speaker of the pair of speakers. The audio reproduction device is caused to function as phase control means for controlling a phase difference between audio signals supplied to the pair of speakers so as to increase.

It is a top view which shows typically the environment of a vehicle interior. An arrangement example of a listening position and a pair of speakers is shown. A method for giving a phase difference to signals to two speakers will be schematically shown. 1 shows a schematic configuration of a first embodiment of an audio reproducing apparatus according to the present invention. An example of a method of calculating the delay amount Z will be shown. It is a figure which shows the characteristic in 1st Example. The schematic structure of 2nd Example of the audio | voice reproduction apparatus based on this invention is shown. The phase characteristics of an anechoic room and a passenger compartment are shown. The relationship between the axis | shaft with which the reproduced sound of two speakers synchronizes and a listening position is shown. The amplitude level of a synthesized wave obtained by synthesizing two sine waves with different phase differences is shown. The amplitude level of a synthesized wave obtained by synthesizing two sine waves with different phase differences is shown. It is a figure which shows the characteristic in 2nd Example. It is another figure which shows the characteristic in 2nd Example. It is another figure which shows the characteristic in 2nd Example. It is a figure which shows the effect by 2nd Example compared with a prior art.

  In a preferred embodiment of the present invention, the audio reproducing device includes a pair of speakers arranged in front of and behind two evaluation points in the acoustic space, input means for receiving an audio signal of one channel, and the audio signal. Phase control means for controlling the phase and supplying the phase to the pair of speakers, wherein the phase control means has a sum of reproduced sound levels at the two evaluation points of the pair of speakers in the entire audible band. The phase difference between the audio signals supplied to the pair of speakers is controlled to be larger than when the audio signal is reproduced by only one of the speakers. In a preferred example, the one speaker is a speaker with a smaller sum of levels of reproduced sound at the two evaluation points.

  The above sound reproducing device is applied to an acoustic space such as a passenger compartment, for example, and controls the level of reproduced sound at two evaluation points set on a seat in the passenger compartment. Specifically, the audio reproduction device controls the phase of an audio signal of one channel input from the outside and supplies it to a pair of speakers. Here, the phase control is performed so that the sum of the reproduced sound levels at the two evaluation points becomes larger in the entire audible band than when the audio signal is reproduced by only one speaker of the pair of speakers. Therefore, it is possible to control so that the reproduced sound can be clearly heard at a place corresponding to two evaluation points in the acoustic space.

  In one aspect of the above-described audio reproduction device, the phase control unit gives a different phase difference for each band to the audio signal supplied to the pair of speakers. As a result, even in an environment where the acoustic characteristics are complicated such as in a passenger compartment, the reproduced sound level at the evaluation point can be increased in the entire audible band.

  In another aspect of the above sound reproducing device, the phase difference is a value within a range of ± 120 degrees from the phase difference when the sum of the reproduced sound levels at the two evaluation points is maximized. As a result, the reproduced sounds output from the pair of speakers cancel each other, and the level of the reproduced sound is prevented from being lowered.

  In another aspect of the above-described audio reproduction device, the phase control unit gives a fixed delay amount to the audio signals supplied to the pair of speakers in all bands. In this aspect, for example, in an acoustic space with simple acoustic characteristics such as an anechoic room, the reproduced sound level at the evaluation point can be increased by simple phase control.

  In another aspect of the above sound reproduction device, one speaker of the pair of speakers is opposite to the other speaker of the pair of speakers with respect to a line segment connecting the two evaluation points. Is arranged. As a result, it is possible to synchronize the reproduced sound output from the two speakers and effectively increase the level.

  In a preferred example, the two evaluation points correspond to the positions of two ears of a listener located at a listening position in the acoustic space. In another preferred example, the acoustic space is a vehicle cabin, the pair of speakers is a front speaker and a rear speaker arranged on the right or left side of the vehicle cabin, and the two evaluation points are This corresponds to the positions of the left and right ears of the listener located in the front seat in the passenger compartment.

  In another preferred embodiment of the present invention, an audio reproducing method executed by an audio reproducing apparatus including a pair of speakers arranged in front and back with respect to two evaluation points in an acoustic space, outputs a one-channel audio signal. An input step for receiving, and a phase control step for controlling the phase of the audio signal and supplying the phase to the pair of speakers, wherein the sum of the reproduced sound levels at the two evaluation points is an audible band. Overall, the phase difference between the audio signals supplied to the pair of speakers is controlled to be larger than when the audio signal is reproduced by only one speaker of the pair of speakers. Thereby, it is possible to control so that the reproduced sound can be heard clearly in a place corresponding to two evaluation points in the acoustic space.

  In another preferred embodiment of the present invention, an audio reproduction program executed by an audio reproduction apparatus including a pair of speakers arranged in front of and behind two evaluation points in an acoustic space outputs a one-channel audio signal. The audio reproduction device functions as an input means for receiving and a phase control means for controlling the phase of the audio signal and supplying it to the pair of speakers, and the phase control means determines the level of the reproduced sound at the two evaluation points. The phase difference between the audio signals supplied to the pair of speakers is controlled so that the sum is larger in the entire audible band than when the audio signal is reproduced by only one of the pair of speakers. Thereby, it is possible to control so that the reproduced sound can be heard clearly in a place corresponding to two evaluation points in the acoustic space.

[Basic principle]
First, the basic principle of the embodiment will be described. The present embodiment aims to increase the sound pressure level at a specific place in an acoustic space such as a passenger compartment, for example, a driver's seat. Therefore, in this embodiment, a special environment in the vehicle is used.

  FIG. 1 is a plan view schematically showing an in-vehicle environment according to the present embodiment. In FIG. 1, there are four seats in the vehicle, and a listener L (driver) is seated in the driver seat corresponding to the listening position. Here, a front speaker SP1 and a rear speaker SP2 are provided on the right side of the driver's seat. In an actual vehicle, a front speaker and a rear speaker are similarly provided on the left side of the vehicle, but illustration thereof is omitted here. As shown in FIG. 1, in this embodiment, as a special environment in the vehicle, the fact that two speakers SP1 and SP2 are arranged in front and back so as to sandwich the driver's seat is used. In this embodiment, the sound pressure levels of the left and right ears of the listener L are simultaneously controlled so that the listener L in the driver's seat can easily hear the reproduced sound.

  In general, the volume of sound perceived by humans is determined based on a value obtained by adding the strengths of both ears. That is, humans feel the same loudness when listening to sound with a sound pressure of 6 dB in both ears and listening to sound with a sound pressure of 12 dB with only one ear. This is also pointed out in the following literature.

References: “Hisao Sakai, Tsuyoshi Nakajima,“ The Acoustical Society of Japan, Auditory and Acoustic Psychology ”, Corona, pp. 173 to 174, “The volume of sound when listening with both ears is equal to the volume of sound when listening with one ear by increasing the sound pressure level of the sound applied to both ears by 6 dB. ""
Therefore, in this embodiment, the positions of the left and right ears of the listener L are used as evaluation points, and the signals input to the speakers SP1 and SP2 are controlled so that the sum of the sound pressure levels at the two evaluation points is increased. . As a result, the listener L feels that the reproduced sound is loud.

  Here, first, the positional relationship between the listener L and the pair of speakers SP1 and SP2 will be examined. As shown in FIG. 2, when the listener L is located on the center line CL equidistant from the pair of speakers SP1 and SP2, and the left and right ears of the listener L are on the center line CL, the listener L can listen to the sound output from the speakers SP1 and SP2 in synchronization. That is, the sum of the sound pressure levels in the left and right ears of the listener L (hereinafter also referred to as “the binaural level sum”) is maximized. Therefore, if the speakers SP1 and SP2 can be arranged in the positional relationship as shown in FIG. 2 with respect to the driver's seat, the audio signal is output as it is from the two speakers SP1 and SP2, and the binaural level of the listener L is obtained. The sum is the maximum. In this case, it is not necessary to perform any processing or adjustment on the audio signal supplied to the speakers SP1 and SP2.

  However, in an actual passenger compartment, it is not always possible to arrange the two speakers SP1 and SP2 in the positional relationship as shown in FIG. Therefore, in the present embodiment, the sum of the binaural levels in the driver's seat is maximized by giving an appropriate phase difference to the audio signals supplied to the two speakers SP1 and SP2.

  FIG. 3 schematically shows a method of giving a phase difference to the audio signals supplied to the two speakers SP1 and SP2. FIG. 3A shows a configuration for supplying an audio signal to the two speakers SP1 and SP2. In the anechoic chamber, the dummy head 3 is disposed at the listening position, and the front speaker SP1 and the rear speaker SP2 are disposed before and after the right side thereof. The audio signal from the sound source 2 is input as it is to the rear speaker SP2, and after being delayed by a fixed delay amount “Z” in the entire band by the delay device 4, is input to the front speaker SP1.

  As shown in FIG. 3A, when a pair of speakers are arranged in the vertical direction, the sound pressure distribution of the reproduced sound output from the speakers becomes horizontal stripes due to interference. Specifically, in FIG. 3A, the black region including the position of the dummy head 3 has a high sound pressure level, the white region has a low sound pressure level, and the sound pressure distribution forms horizontal stripes. Therefore, by changing the delay amount Z, the binaural level can be changed synchronously, and the binaural level sum can be controlled.

  FIG. 3B shows an example of the sound pressure distribution near the dummy head 3 when the delay amount Z is changed. The numerical values displayed as contour lines in the figure indicate the sound pressure level value. In the example of FIG. 3B, when the delay amount Z = 2.0 [ms], the sound pressure level near the both ears of the dummy head 3 is maximum at 4.247 [dB]. Therefore, in this example, the delay amount Z = 2.0 [ms] is optimal.

  In this way, by arranging a pair of speakers before and after the listener's position and giving an appropriate phase difference to the audio signal supplied to those speakers, the listener's binaural level sum is increased. Can do.

[First embodiment]
FIG. 4 shows a schematic configuration of the first embodiment of the audio reproducing apparatus. The first embodiment assumes an anechoic room as the acoustic space.

  As shown in FIG. 4, a pair of speakers, that is, a front speaker SP1 and a rear speaker SP2 are arranged in front and rear with respect to the listening position of the listener L. In this example, the front speaker SP1 is farther from the listener L than the rear speaker SP2.

  The audio signal output from the sound source 2 is supplied to the rear speaker SP2 as it is, and is delayed by a predetermined delay amount Z by the delay device 4 and supplied to the front speaker SP1. The delay device 4 gives a fixed delay amount Z in the entire band of the audio signal output from the sound source.

  A method for determining the fixed delay amount Z will be described. The delay amount Z is determined so that the sum of the binaural levels of the listener L increases. Note that the positions of the left and right ears of the listener L correspond to two evaluation points.

  The delay amount Z can be determined based on the distance between the ears of the listener L and the front and rear speakers SP1, SP2. FIG. 5 is a diagram for explaining a method of determining the delay amount Z. If the distance from the center point of the left and right ears, that is, the center point M of the two evaluation points, to the front speaker SP1 is “d1”, and the distance from the center point M to the rear speaker SP2 is “d2”, the delay amount Z is given by the following equation.

Delay amount Z = (d1-d2) / c [m / s] (1)
Note that “c” is the speed of sound (about 340 [m / s]).

Now, in the acoustic space shown in FIG. 4, when the distance d1 from the center point M to the front speaker SP1 is 1.06 m and the distance d2 from the center M to the rear speaker SP2 is 0.83 m, the delay amount Z is
Z = (1.06-0.83) /340=0.70 [m / s].

  Instead, the delay amount Z can be calculated based on transfer functions between the speakers SP1 and SP2 and both ears (two evaluation points) of the listener L.

  FIG. 6 shows the characteristics in the above case. Specifically, FIG. 6A shows the frequency characteristics of the binaural level sum. In FIG. 6A, a graph 21 shows the sum of levels of both ears when an audio signal is input only to the rear speaker SP2. The graph 22 shows the binaural level sum when audio signals are input to the two speakers SP1 and SP2 but no phase difference is given to them (Z = 0.0 [ms]). The graph 23 shows the binaural level sum when audio signals are input to two speakers and a phase difference Z = 0.7 [ms] is given to them. In the graph 23, the audio signal input to the rear speaker SP2 is actually delayed by the delay amount Z with respect to the audio signal input to the front speaker SP1.

  The binaural level sum (graph 23) when the audio signal is input to the two speakers with a phase difference is the binaural level when the audio signal is input only to the rear speaker SP2 in the entire band of 100 Hz to 1 kHz. It is larger than the sum (graph 21). Also, the binaural level sum (graph 22) when the audio signal is input to the two speakers without giving the phase difference is the binaural level when the audio signal is input only to the rear speaker SP2 up to about 100 to 500 Hz. Although it is larger than the sum (graph 21), in the vicinity of 600 to 800 Hz, it is smaller than the binaural level sum (graph 21) when an audio signal is input only to the rear speaker SP2. This is because when a sound signal is input to two speakers without giving a phase difference, there is a band where the sum of binaural levels becomes smaller due to the relationship of the phase of the reproduced sound from the two speakers. I mean. Therefore, in order to increase the level sum of both ears in a desired band, it is necessary to input an audio signal to the two speakers with an appropriate phase difference as shown in the graph 23.

  FIG. 6B shows the relationship between the phase difference given to the audio signals input to the two speakers, the frequency of the audio signals, and the binaural level sum. A solid line 24 shown in FIG. 6B indicates the binaural level sum when a phase difference (Z = 0.7 [ms]) is given to the audio signals input to the two speakers. Is passing through a large area. A broken line 25 indicates the binaural level sum when no phase difference is given to the audio signals input to the two speakers (Z = 0.0 [ms]), and is similar to the graph 22 in FIG. In the vicinity of 100 to 500 Hz, the region where the binaural level sum is large passes, but in the vicinity of 600 to 800 Hz, the region where the binaural level sum is small passes. That is, in FIG. 6B as well, in order to increase the binaural level sum in the entire band of 100 to 1 kHz, it is necessary to give an appropriate phase difference to the audio signals input to the two speakers SP1 and SP2. Is shown.

  FIG. 6C shows the frequency characteristics of the binaural level sum in the so-called audible band of 20 to 16 kHz. Similar to FIG. 6A, the graph 21 shows the level sum of both ears when an audio signal is input only to the rear speaker SP2. The graph 23 shows the levels of both ears when audio signals are input to two speakers and a phase difference (Z = 0.7 [ms]) is given to them. According to FIG. 6C, it is understood that the binaural level sum can be increased in the entire audible band by giving an appropriate phase difference to the audio signals input to the two speakers.

[Second Embodiment]
Next, a second embodiment will be described. FIG. 7 shows a schematic configuration of the second embodiment of the audio reproducing apparatus. The second embodiment assumes a passenger compartment as an acoustic space. As shown in FIG. 7, a front speaker SP1 and a rear speaker SP2 are arranged on the right side of the driver's seat. The audio signal from the sound source 2 is supplied to the rear speaker SP2, and after the phase is corrected by the phase correction unit 6, it is supplied to the front speaker SP1. Here, the phase correction unit 6 gives a different phase difference (phase correction value) θ (f) for each band f of the audio signal.

  Specifically, the phase difference θ (f) is set as follows.

θ (f) = A + α (2)
Here, “A” is a phase value that maximizes the binaural level sum of the listener, and is calculated based on a transfer function between two speakers and two evaluation points. Specifically, based on the positional relationship between the two speakers SP1, SP2 and the listener's ears (evaluation points), a transfer function between each speaker and the listener's ears is obtained, and the transfer function is Based on the simulation, a binaural level sum distribution with respect to phase and frequency is generated as shown in FIG. In the distribution, a line segment connecting the regions with the highest binaural level sum (line segment 34 in FIG. 12B) indicates the phase difference θ (f) for each band.

  Note that, in the second embodiment in which the passenger compartment is assumed as the acoustic space, the reason why the phase difference θ (f) different for each band is given to the audio signals input to the two speakers is as follows. FIG. 8A shows the phase characteristics in an anechoic chamber, and FIG. 8B shows the phase characteristics in a certain cabin. In an anechoic room, a linear phase characteristic as shown in FIG. 8 (A) is obtained, whereas in an actual vehicle compartment, the reproduced sound is reflected by a window or blocked by an obstacle, As shown in FIG. 8B, the phase characteristics become complicated. For this reason, as in the first embodiment assuming an anechoic room as the acoustic space, there is a band where the binaural level sum is reduced even if a fixed delay amount Z is given to the entire band. Therefore, in the second embodiment, a phase difference that maximizes the binaural level sum is calculated for each frequency band based on the transfer function between each speaker and the two evaluation points, and is input to the two speakers. It is necessary to give to the audio signal.

  In the method of the second embodiment, sound is reproduced from the two speakers SP1 and SP2, but the influence on the person in the rear seat is small. That is, the person in the rear seat does not feel that the reproduced sound is noisy. This is due to two reasons. The first reason is that there is a certain distance between the front speaker SP1 and the rear seat, and there is an obstacle such as a driver's seat between the front seat and the front speaker SP1. Is difficult to reach the back seat. The second reason is that the reproduced sound from the two speakers is difficult to synchronize because the rear seat is located outside the two speakers. This will be described with reference to FIG.

  FIG. 9 shows the positional relationship between the two speakers and the listener L. As shown in FIG. 9A, when sounds are reproduced from the two speakers SP1 and SP2, the axis at which the reproduced sounds from the two speakers are synchronized is the center line CL of the two speakers. When the listener L is located inside the two speakers, both ears of the listener L are on the center line CL or close to the center line CL. The sum is likely to change.

  On the other hand, as shown in FIG. 9B, when the listener L is positioned outside the two speakers SP1 and SP2, the listener L is positioned on the center line CL where the reproduced sounds from the two speakers are synchronized. Even so, since the direction connecting the listener's ears is shifted from the center line CL, the binaural level sum is unlikely to change. For this reason, in the second embodiment, even if sound is reproduced from the front speaker SP1 and the rear speaker SP2, the sound pressure in the rear seat becomes excessive, and the person in the rear seat does not feel that the reproduced sound is noisy.

  Next, “α” in Expression (2) of the phase difference θ (f) will be described. In Formula (2), “α” is a value in the following range.

-120 ° <α <120 ° (3)
This is because, at the evaluation point, if the amplitudes of SP1 and SP2 are substantially the same and α is within this range, the binaural level sum at the driver's seat will be larger than when sound is reproduced from the rear speaker alone. is there. This will be described with reference to FIG. FIG. 10 shows the amplitude level of a combined wave obtained by combining two sine waves with different phase differences. When two sine waves are synthesized in phase (phase difference = 0), the amplitude of the synthesized wave is twice the amplitude of the original sine wave, as shown in graph 41. When two sine waves are combined with a phase difference of 120 °, the amplitude of the two sine waves and the amplitude of the combined wave are equal as shown in the graph 42. On the other hand, when two sine waves are synthesized with opposite phases (phase difference 180 °), the amplitude of the synthesized wave becomes smaller than the amplitude of the original sine wave.

  As shown in the graph 40, when the phase difference is 0 to 120 °, the amplitude of the combined wave of the two sine waves is at least equal to or larger than the amplitude of the original sine wave. On the other hand, when the phase difference exceeds 120 °, the amplitude of the combined wave of the two sine waves becomes smaller than the amplitude of the original sine wave.

  Accordingly, the binaural level sum at the listening position becomes the largest when the phase difference θ (f) given to the signals supplied to the two speakers is α = 0 (in phase), that is, θ (f) = A. If α is in the range of ± 120 °, the binaural level sum can be made larger than at least when the sound is reproduced from only the rear speaker. For this reason, the value of α is in the range of ± 120 °.

  Even if the amplitudes of SP1 and SP2 are different at the evaluation point, if the purpose is to increase the binaural level sum at the driver's seat compared to the level of the smaller amplitude, the value of α is ± By setting the angle within the range of 120 °, the binaural level sum can be reliably increased.

  The reason for this will be described with reference to FIG. FIG. 11 shows the amplitude level of a combined wave obtained by combining two sine waves with different phase differences, as in FIG. However, this is a case where the amplitude of each sine wave is not the same.

  The solid line 71 indicates that the level when the reproduction is performed with only the rear speaker is set as a reference (0 dB), and the rear speaker is smaller than the front speaker (here, the level with only the rear speaker = 3 / the level with only the front speaker) Amplitude level). From this, it can be seen that the range in which the level of the composite wave is larger than the level reproduced by only the rear speaker is wider than 120 °. The reason for this is that when the rear speaker is smaller than the front speaker, even if α is larger than 120 ° and the waves cancel each other out, the front speaker is larger than the rear speaker, so the amplitude of the composite wave remains large. It is because it becomes easy to do.

  On the other hand, a broken line 72 indicates the amplitude level of the composite wave when the rear speaker is larger than the front speaker (here, the level of only the rear speaker = 2/3 times the level of only the front speaker). Contrary to the case of the solid line 71, it can be seen that the range in which the level of the synthesized wave is larger than the level reproduced by only the rear speaker is narrower than 120 °.

However, as a whole, if the objective is to increase the binaural level sum in the driver's seat as compared with the level when playback is performed only with the smaller one of SP1 and SP2 at the evaluation point, FIG. By setting the value of α within a range of ± 120 ° as shown by the solid line 71, the binaural level sum can be reliably increased. FIG. 12 shows characteristics in the second embodiment. Specifically, FIG. 12A shows the frequency characteristics of the binaural level sum. In FIG. 12A, a graph 31 shows a binaural level sum when an audio signal is input only to the rear speaker SP2. The graph 32 shows the binaural level sum when audio signals are input to the two speakers SP1 and SP2 and given a fixed phase difference (Z = 0.7 [ms]). The graph 33 shows the binaural level sum when audio signals are input to two speakers and different phase differences θ (f) are given to the respective bands as described above.

  The binaural level sum (graph 33) when the audio signal is input to the two speakers with different phase differences θ (f) for each band is the audio signal only to the rear speaker SP2 in the entire band of 100 Hz to 1 kHz. It is larger than the binaural level sum (graph 31) when input. Also, the binaural level sum (graph 32) when a sound signal is input to two speakers with a fixed phase difference (Z = 0.7 [ms]), only the rear speaker SP2 in the range of 250 to 1 kHz. However, in the vicinity of 130 to 200 Hz, the binaural level sum when the audio signal is input only to the rear speaker SP2 (graph 31). 31) It is smaller. This means that in an acoustic space such as a passenger compartment, when a sound signal is input to two speakers with a fixed phase difference, there is a band where the binaural level sum is reduced. Therefore, in order to increase the binaural level sum in the desired band, it is necessary to give different appropriate phase differences for each band to the audio signals input to the two speakers as shown in the graph 33. Become.

  FIG. 12B shows the relationship between the phase difference given to the audio signals input to the two speakers and the frequency of the audio signals, and the binaural level sum. A solid line 34 shown in FIG. 12B indicates the binaural level sum when the audio signals input to the two speakers are given different phase differences θ (f) for each band, and the binaural level sum is large. Has passed through the area. A broken line 35 indicates the level sum of both ears when a fixed phase difference (Z = 0.7 [ms]) is given to the audio signals input to the two speakers, and the graph 32 in FIG. Similarly, in the range of 250 to 1 kHz, it passes through a region where the binaural level sum is large, but in the vicinity of 130 to 200 Hz, it passes through a region where the binaural level sum is small. That is, also in FIG. 12B, in order to increase the sum of the levels of both ears in the entire band of 100 to 1 kHz, the sound signal input to the two speakers SP1 and SP2 has an appropriate level for each band. It shows that the phase difference θ (f) needs to be given.

  FIG. 13 also shows the characteristics in the second embodiment. FIG. 13A shows the frequency characteristics of the binaural level sum. In FIG. 13A, a graph 31 and a graph 33 are the same as those in FIG. The graph 36 shows the binaural level sum when audio signals are inputted to the two speakers SP1 and SP2 and no phase difference is given to them (Z = 0.0 [ms]).

  The binaural level sum (graph 36) when the audio signal is input to the two speakers without giving a phase difference (Z = 0.0 [ms]) is the audio signal only to the rear speaker SP2 in the range of 200 to 1 kHz. However, in the vicinity of 130 to 170 Hz, the binaural level sum (graph 31) when the audio signal is input only to the rear speaker SP2 is larger. It is getting smaller. This means that in an acoustic space such as a passenger compartment, there is a band where the sum of the levels of both ears becomes smaller when an audio signal is input to two speakers without giving a phase difference. Therefore, in order to increase the level sum of both ears in a desired band, it is necessary to give an appropriate phase difference different for each band to the audio signals input to the two speakers as shown in the graph 33. It becomes.

  FIG. 13B shows the relationship between the phase difference and the frequency of the audio signal applied to the audio signals input to the two speakers, and the binaural level sum. A solid line 34 shown in FIG. 12B is the same as FIG. A broken line 37 indicates the sum of levels of both ears when no phase difference is given to the audio signals input to the two speakers (Z = 0.0 [ms]), which is the same as the graph 36 in FIG. In addition, in the range of 200 to 1 kHz, it passes through a region where the binaural level sum is large, but in the vicinity of 130 to 170 Hz, it passes through a region where the binaural level sum is small. That is, also in FIG. 13B, in order to increase the binaural level sum in the entire band of 100 to 1 kHz, an appropriate phase difference for each band is obtained for the audio signals input to the two speakers SP1 and SP2. This shows that θ (f) needs to be given.

  FIG. 14 shows the frequency characteristics of the binaural level sum in the range of 20 to 16 kHz, that is, the so-called audible band. Similar to FIG. 12A, the graph 31 shows the binaural level sum when an audio signal is input only to the rear speaker SP2. Graph 33 shows the binaural level sum when audio signals are input to two speakers and different phase differences θ (f) are given to the respective bands. According to FIG. 14, the binaural level sum can be increased in the entire audible band by giving an appropriate phase difference θ (f) different for each band to the audio signals input to the two speakers. Is understood.

  FIG. 15 is a diagram for explaining the effect when the second embodiment is compared with the method of the prior art. Here, the prior art method refers to a method of increasing the binaural level sum at the driver's seat by increasing the reproduced sound of the rear speaker in a certain band by using an equalizer.

  As shown in the two graphs on the left side of FIG. 15, when the binaural level sum in the driver's seat is increased by the conventional method, the binaural level sum is further increased in the rear seat compared to the driver's seat. There is a problem that the sound of the seat is too loud. On the other hand, as shown in the two graphs on the right side of FIG. 15, even if the binaural level sum in the driver seat is increased according to the second embodiment, the binaural level sum does not change so much in the rear seat as described above. Therefore, the trouble that the reproduced sound of the rear seat becomes too loud does not occur. Thus, in the second embodiment, the reproduced sound level of the driver's seat can be increased without affecting the reproduced sound level in other seats.

  In the above second embodiment, the front and rear speakers provided on the right side of the passenger compartment are used to increase the binaural level sum in the driver seat, that is, the right front seat. Depending on the method, the front and rear speakers provided on the left side of the passenger compartment may be used to increase the binaural level sum in the passenger seat, that is, the left front seat.

2 Sound source 3 Dummy head 4 Delay device 6 Phase adjuster SP1 Front speaker SP2 Rear speaker L Listening position

Claims (12)

A pair of speakers arranged back and forth with respect to two evaluation points in the acoustic space;
Input means for receiving a one-channel audio signal;
The sum of the reproduced sound levels at the two evaluation points is larger than when the audio signal is reproduced by only one speaker of the pair of speakers at least in a desired band of the audible band. Phase control means for controlling a phase difference between audio signals supplied to the pair of speakers;
An audio playback device comprising:   The audio reproducing apparatus according to claim 1, wherein the desired band is 100 Hz to 1 kHz.   The phase control means is configured such that the sum of the reproduced sound levels at the two evaluation points is larger than the case where the audio signal is reproduced by only one of the pair of speakers in the entire audible band. The audio reproduction device according to claim 1, wherein a phase difference between audio signals supplied to the pair of speakers is controlled.   4. The audio reproducing apparatus according to claim 1, wherein the one speaker is a speaker having a smaller level sum of reproduced sounds at the two evaluation points. 5.   5. The audio reproduction device according to claim 1, wherein the phase control unit gives a phase difference different for each band to an audio signal supplied to the pair of speakers. 6. .   6. The audio reproducing apparatus according to claim 5, wherein the phase difference is a value within a range of ± 120 degrees from a phase difference when the sum of reproduced sound levels at the two evaluation points is maximized.   4. The audio reproduction device according to claim 3, wherein the phase control unit gives a fixed delay amount in all bands to the audio signal supplied to the pair of speakers.   One speaker of the pair of speakers is arranged on the opposite side of the other speaker of the pair of speakers with respect to a line segment connecting the two evaluation points. The audio reproduction device according to any one of 1 to 7.   The sound reproduction apparatus according to claim 1, wherein the two evaluation points correspond to positions of two ears of a listener located at a listening position in the acoustic space.   The acoustic space is a vehicle compartment, the pair of speakers is a front speaker and a rear speaker arranged on the right or left side of the vehicle compartment, and the two evaluation points are listening positions located at a front seat in the vehicle compartment. The sound reproducing apparatus according to claim 1, wherein the sound reproducing apparatus corresponds to positions of left and right ears of a person. An audio reproduction method executed by an audio reproduction apparatus including a pair of speakers arranged in front of and behind two evaluation points in an acoustic space,
An input process for receiving an audio signal of one channel;
The sum of the reproduced sound levels at the two evaluation points is larger than when the audio signal is reproduced by only one speaker of the pair of speakers at least in a desired band of the audible band. A phase control step for controlling a phase difference between audio signals supplied to the pair of speakers;
An audio playback method comprising: An audio reproduction program that is executed by an audio reproduction device including a pair of speakers arranged in front of and behind two evaluation points in an acoustic space,
Input means for receiving a one-channel audio signal;
The sum of the reproduced sound levels at the two evaluation points is larger than when the audio signal is reproduced by only one speaker of the pair of speakers at least in a desired band of the audible band. Phase control means for controlling a phase difference between audio signals supplied to the pair of speakers;
An audio reproduction program for causing the audio reproduction apparatus to function as

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