JPH04364700A - Sound field correction device - Google Patents

Abstract

PURPOSE:To easily realize the improvement of the frequency characteristic at a sound field space in which a reflecting sound or the like in the acoustic reproduction gives adverse effect onto the presence of sound image and the correction of the sound field to make a sense of the presence clear at a low cost. CONSTITUTION:A control frequency is divided by a frequency selection filter 2. Digital filters 5, 6, 7, 8 are employed for a low frequency band and a speaker system 13 having a sharp directivity in which an area for acoustic power radiation is limited for a high frequency band to correct the sound field.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound field correction device that can adapt to a sound field in which reflected sound or the like adversely affects the frequency characteristics at a listening position and the perceptual sound image localization during sound reproduction.

0002

2. Description of the Related Art During sound reproduction, reflected waves may disturb the frequency characteristics at the listening position and become a factor that impairs the sense of localization of a sound image. In particular, the interior space of a vehicle is small in size, and reflective walls such as glass are present near the listening position, so the primary or secondary reflected waves in the interior sound field have a large effect on the direct waves.

FIG. 3 shows calculated values of an echo time pattern in a sound field inside a vehicle. 2~3ms for direct wave
The reflected waves are seen concentrated after ec delay. These responses are close to the time difference between both ears in terms of their temporal order, and act as direct wave phase interference, disturbing the frequency characteristics at the listening position and becoming a factor that impairs the sense of localization of the sound image. Graphic equalizers using analog filters, which have been conventionally used as sound field correction devices, have amplitude characteristics that can be adjusted to flat or arbitrary characteristics, but phase characteristics are not considered at all, so it is not possible to improve sound image localization quality. It was impossible to do so. Therefore, in recent years, sound fields have been corrected using digital filters that can control even the phase characteristics. This method has made it possible to improve the frequency characteristics in sound fields where the influence of reflected waves is large, and to improve the sense of localization in asymmetric sound fields such as the sound field inside a car.

0004

[Problem to be Solved by the Invention] However, since the response in the high frequency band is an extremely important factor for sound image localization, even when correcting the sound field with a digital filter, the response in the high frequency band also remains in the sound field. It is necessary to make corrections. However, signal processing up to the audio frequency band requires a high sampling frequency and high calculation speed within the filter, which increases the burden on the hardware. Therefore,
Although it is theoretically possible to control all audible frequency bands using digital filters, there are significant problems in terms of cost and practicality.

[0005] The present invention reduces the cost by significantly reducing the hardware scale of the digital filter, and also makes it possible to correct the sound field up to a high frequency band.
The aim is to improve frequency characteristics and achieve clear sound image localization.

[0006]

[Means for Solving the Problems] In order to achieve this object, the present invention divides the control frequency, uses a digital filter for the low frequency band, and uses a sharp directivity filter for the high frequency band that can limit the area in which acoustic power is radiated. The sound field is corrected using a speaker system with special characteristics.

[0007]

[Operation] With the above-described configuration, the present invention can easily realize the improvement of the frequency characteristics in the sound field space and the correction of the sound field to clarify the sense of localization at low cost.

[0008]

[Example] Specific examples will be described in detail below. (Figure 1
) is a configuration diagram of a sound field correction device according to an embodiment of the present invention. 1 is an input terminal, 2 is a frequency selection filter that divides the input signal into two bands at an arbitrary frequency f within the audible band, 3 is a power amplifier, and 4 is the analog output of the low frequency band output by the frequency selection filter 2. Analog-to-digital conversion means for converting into a digital signal; 5 is a digital filter having filter coefficients for correcting the response of the R channel signal reaching the right ear; and 6 is a digital filter for correcting the response of the L channel signal reaching the left ear. 7 is a digital filter with filter coefficients for canceling the crosstalk of the R channel signal reaching the left ear, 8 is a digital filter having filter coefficients for canceling the crosstalk of the L channel signal reaching the right ear. 9 is a digital adder; 10 is a digital-to-analog conversion means for converting the output of the digital adder 9 into an analog signal; 1
1 is a clock removal filter, 12 is an analog adder that adds the output of the clock removal filter 11 and the output of the high frequency band output from the frequency selection filter 2, and 13 is an area that radiates acoustic power in a frequency band higher than f. It is a speaker system with sharp directional characteristics that can be limited.

The operation of the sound field correction device configured by the above system will be explained. The signal input to input terminal 1 is passed through frequency selection filter 2 for both L and R channels.
The band is divided by The division frequency f is determined by the directional characteristics of the speaker system 13, and the details will be explained later. The low frequency band output of the frequency selection filter 2 is converted into a digital signal by an analog-to-digital conversion means 4. Next, four digital filters 5, 6, 7, and 8 are used to cancel reflected sounds in the sound field and crosstalk between the left and right channels. Then, after the outputs of the two digital filters for each left and right channel are added by a digital adder 9, the output is returned to an analog signal by a digital-to-analog conversion means 10. Since these digital signal processes are performed in a band below the frequency f, the sampling frequency can be kept low and the amount of calculation by the arithmetic unit can be reduced compared to signal processing up to the upper limit of the audible band. Therefore, the scale of the hardware is significantly reduced, and the cost is also reduced.

Next, digital-to-analog conversion means 10
The analog output of is passed through a clock removal filter 11, this signal is added to the output of the high frequency band outputted by the frequency selection filter 2 by an analog adder 12, and after being amplified by a power amplifier 3, a speaker system 13 is used to add the signal to the sound field space. radiate to.

[0011] Also, the configuration diagram of the second embodiment of the present invention is shown in (
Figure 2) shows this. Compared to the configuration of the first embodiment, a low frequency speaker system 14 does not have an analog adder 12 and emits a signal in a low frequency band that has been subjected to digital signal processing.
It is a configuration with. Therefore, by providing the low-frequency speaker 14, it is possible to reproduce low-frequency radiation with high efficiency and low distortion, and the input resistance characteristics can also be improved.

Next, the speaker system 13 will be described. (Figure 4) shows the echo time pattern when a sharp directional characteristic is given to the sound source under the same calculation conditions as in the previous figure (Figure 3). Compared to (Fig. 3), the temporal pattern of the response remains the same because the spatial geometry is the same, but the energy level in the direction away from the directional axis of the sound source is small due to the sharp directional characteristic, It can be seen that the level of unnecessary reflected waves at the position has decreased. Therefore, by making the directional characteristics of the sound source sufficiently sharp, the influence of reflected waves in the sound field can be reduced.

(FIG. 5) shows the specific shape of the speaker system and its installation inside the vehicle. (Figure 5), 1
5 is a driver unit, and 16 is a dashboard. A plurality of driver units are arranged in a straight line at equal intervals, and each unit is driven with the same phase and amplitude. The orientation axis at this time is the direction A, which is the normal direction at the center of the linearly arranged driver units. Therefore, place the speaker system on the dashboard 1 so that the listening position is on the extension line.
It is embedded in 6. The directional characteristics of this speaker system are shown in FIG. 6.

As shown in FIG. 6, the higher the control frequency, the sharper the directivity characteristics. For example, if the frequency to be divided by the frequency selection filter is 5 kHz, the frequency of 5 kHz or more shown by the thick line in FIG. A directional characteristic of 10 dB or more can be obtained at a position 45 degrees away from the directional axis in the band,
Furthermore, as the frequency increases, the directional characteristics become sharper. Further, at this time, the upper limit frequency of the digital signal processing described above is 5 kHz, and compared to a system that processes signals up to 20 kHz, the cost reduction effect due to the reduction in the size of the hardware is large.

FIG. 7 shows a second embodiment of a speaker system with sharp directional characteristics. In FIG. 7, 15 is a driver unit, 16 is a dashboard, and 17 is an electrical delay means. A plurality of driver units 15 are arranged in a straight line and embedded in the dashboard 16, and a delay means 17 is provided before the input to each driver unit 15, so that the signal propagates from each unit in the vicinity of the unit closest to the listening position. The delay time of each delay means is set so that the phases of the sound pressures of the sound waves are equal and the synthesized sound pressure is the highest. In other words, if the distance between each unit is d and the speed of sound is c, then the delay time tn to be given to the n-th unit is (Equation 1).

[0016]

[Equation 1] At this time, since the directivity axis of the speaker system is in the A direction, if the speaker system is installed so that the listening position is on the extension line of the driver units 15 arranged in a straight line, the directivity axis will be sharp in the direction of the listening position. Directional characteristics can be obtained, and effects similar to those of the first embodiment can be obtained.

(FIG. 8) shows a third embodiment of a speaker system with sharp directional characteristics. In FIG. 8, 15 is a driver unit, 16 is a dashboard, 18 is a sound tube, and 19 is a hole formed in a straight line at equal intervals in the tube wall. A driver unit 15 embedded in the dashboard 16 is connected to one end of the acoustic tube 18 .
Holes 19 formed in a straight line at equal intervals in the tube wall of the speaker system act as a sound source, and the directivity axis of the speaker system is in the A direction as in the speaker system of the second embodiment. Therefore, if the speaker system is installed so that the listening position is on the longitudinal extension of the acoustic tube 18, a sharp directivity characteristic can be obtained in the direction of the listening position, and the same effect as in the first embodiment can be obtained.

[0018]

Effects of the Invention As described above, the present invention divides the control frequency in sound field correction in a sound field where reflected sound etc. adversely affect auditory sound image localization during sound reproduction. Using a digital filter, the sound field is corrected by a speaker system with sharp directional characteristics that can limit the area in which acoustic power is radiated in high frequency bands.As a result, the hardware scale of the digital filter can be significantly reduced. The cost can be reduced by
In addition, it is possible to correct the sound field up to a high frequency band, achieving improved frequency characteristics and clear sound image localization.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

[Figure 2]
Configuration diagram of the second embodiment of the present invention

[Figure 3] Calculated value of echo time pattern when omnidirectional characteristics are given to the sound source

[Figure 4] Calculated value of echo time pattern when sharp directional characteristics are given to the sound source

FIG. 5 Schematic diagram of the first embodiment of the speaker system

[Figure 6] Actual measured values of the directional characteristics of the speaker system

FIG. 7 is a schematic diagram of a second embodiment of the speaker system.

FIG. 8 is a schematic diagram of a third embodiment of the speaker system.

[Explanation of symbols]

1 Input terminal 2 Frequency selection filter 3 Power amplifier 4 Analog-digital conversion means 5, 6, 7, 8 Digital filter 9 Digital adder 10 Digital-analog conversion means 11 Clock removal filter 12 Analog adder 13 Speaker system 14 For low frequency Speaker 15 Driver unit 16 Dashboard 17 Delay means 18 Sound tube 19 Hole

Claims (16)

[Claims] 1. A frequency selection filter that divides an input signal into two bands at an arbitrary frequency f within the audible band, and an analog-digital conversion that converts the low frequency band output of the frequency selection filter into a digital signal. a digital filter that performs sound field correction on the output of the digital filter, a digital-to-analog converter that converts the output of the digital filter into an analog signal, an output of the digital-to-analog converter, and the frequency selector. A sound field characterized by being equipped with an addition means for adding the output of a filter in a high frequency band, and a speaker system having sharp directivity characteristics that can limit the region in which acoustic power is radiated in a frequency band higher than f. correction device. [Claim 2] In a frequency band below frequency f,
2. The sound field correction device according to claim 1, wherein an inverse impulse response of an impulse response including reflected sound of the sound field is set equal to a coefficient of a digital filter. 3. The sound field correction device according to claim 1, wherein the speaker system is constituted by a set of a plurality of sound sources arranged in a straight line at equal intervals. 4. Claim 1, wherein the speaker system includes a plurality of driver units, and is installed such that the listening position is on an extension line in the normal direction at the center of the driver units arranged in a straight line. The sound field correction device described. 5. The digital filter according to claim 1, wherein the digital filter has a transfer function that cancels crosstalk between the left and right channels in stereo reproduction in a low frequency band of the frequency selection filter, and is provided for each left and right channel. Sound field correction device. [Claim 6] In a frequency band below frequency f,
6. The sound field correction device according to claim 5, wherein 2n speakers are provided for each listener number n, and the digital filter is configured with a filter having a transfer function that cancels crosstalk between each channel. 7. The speaker system includes a plurality of driver units, is installed so that the listening position is on an extension of the driver units arranged in a straight line, and further includes a delay means before the input to each of the driver units. The delay time of each delay means is set so that the phase of the sound pressure of the sound waves propagated from each unit is equal and the synthesized sound pressure is the highest in the vicinity of the unit closest to the listening position. The sound field correction device according to claim 1. 8. The delay means is constituted by an acoustic tube having holes arranged in a straight line at equal intervals in the tube wall, and a driver unit is connected to one end of the acoustic tube. 7. The sound field correction device according to 7. 9. A frequency selection filter that divides an input signal into two bands at an arbitrary frequency f within an audible band, and an analog-digital conversion that converts the low frequency band output of the frequency selection filter into a digital signal. a digital filter that performs sound field correction on the output of the digital filter, a digital-to-analog converter that converts the output of the digital filter into an analog signal, and a low-voltage converter that radiates the output of the digital-to-analog converter. sound field correction characterized by comprising: a frequency range speaker; and a speaker system having a sharp directivity characteristic that can limit the area in which acoustic power is radiated within the frequency band of the high frequency band output output from the frequency selection filter. Device. 10. The sound field correction device according to claim 9, wherein in a frequency band below frequency f, an inverse impulse response of an impulse response including reflected sound of the sound field is set equal to a coefficient of a digital filter. 11. The sound field correction device according to claim 9, wherein the speaker system is constituted by a set of a plurality of sound sources arranged in a straight line at equal intervals. 12. Claim 9, wherein the speaker system includes a plurality of driver units, and is installed such that the listening position is on an extension line in the normal direction at the center of the driver units arranged in a straight line. The sound field correction device described. 13. The digital filter according to claim 9, wherein the digital filter has a transfer function that cancels crosstalk between the left and right channels in stereo reproduction in a low frequency band of the frequency selection filter, and is provided for each left and right channel. Sound field correction device. 14. In a frequency band below frequency f, 2n speakers are provided for each listener number n, and the digital filter is configured with a filter having a transfer function that cancels crosstalk between each channel. The sound field correction device according to claim 13. 15. The speaker system includes a plurality of driver units, is installed so that the listening position is on an extension of the driver units arranged in a straight line, and further includes delay means before inputting to each of the driver units. established,
A claim characterized in that the delay time of each delay means is set so that the phase of the sound pressure of the sound waves propagated from each unit is equal and the synthesized sound pressure is the highest in the vicinity of the unit closest to the listening position. 9. The sound field correction device according to 9. 16. The delay means is constituted by an acoustic tube having holes arranged in a straight line at equal intervals in the tube wall, and a driver unit is connected to one end of the acoustic tube. 15. The sound field correction device according to 15.