JP2017092531A - Parametric speaker, signal processing device and signal processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a parametric speaker capable of improving a degree of freedom in setting an audible range.SOLUTION: The parametric speaker comprises: a carrier generation part 31 for generating a carrier in an ultrasonic band; a modulation part 32 for generating a modulated wave by performing amplitude modulation on the carrier in accordance with a sonic signal in an audible band; a band separation part 33 for separating the modulated wave into a first separated wave having a frequency component of the carrier and a second separated wave having a frequency component of a side band; a speaker body 21 which includes a plurality of ultrasonic wave generation elements 23 and radiates the first separated wave and the second separated wave from the ultrasonic wave generation elements 23 that are different from each other; and a phase control part 34 for controlling phases of the first separated wave and the second separated wave in such a manner that the first separated wave and the second separated wave are radiated from the ultrasonic wave generation elements 23 in directions that are different from each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a parametric speaker, a signal processing device, and a signal processing program.

  Conventionally, a parametric speaker that realizes high directivity using ultrasonic waves is known (see, for example, Patent Document 1). The parametric speaker radiates a modulated wave obtained by modulating a carrier wave in an ultrasonic band with an audio signal, and transmits the sound by self-demodulating the modulated wave with non-linear characteristics in the air. The audible region by the parametric speaker exists linearly due to the high directivity of the modulated wave (ultrasound). Therefore, it is possible to deliver sound only to those who are present in the linear audible area.

JP 2004-349816 A

  However, parametric speakers are easily affected by reflection from walls, ceilings, and the like due to their high directivity, and sound easily reaches an area bent by reflection from an audible area extending linearly from the parametric speaker. Therefore, when a person who does not need sound is in the reflected area, the sound reaches the person. In addition, if it is within an audible area extending linearly from the parametric speaker, it is easy for sound to reach a position away from the parametric speaker. For example, it is difficult to set the audible area only in the vicinity of the parametric speaker. .

  In view of the above circumstances, an object of the present invention is to provide a parametric speaker, a signal processing device, and a signal processing program capable of increasing the degree of freedom in setting an audible region.

(1) The parametric speaker of the present invention is
A carrier generation unit that generates a carrier wave in an ultrasonic band;
A modulation unit that modulates the carrier wave by an acoustic wave signal in an audible band to generate a modulated wave;
A band separation unit for separating the modulated wave into a first separated wave having a frequency component of a carrier wave and a second separated wave having a frequency component of a sideband;
A speaker body having a plurality of ultrasonic generating elements;
A phase control unit that controls the phases of the first separated wave and the second separated wave so that the first separated wave and the second separated wave are radiated from different ultrasonic generating elements in different directions. And.

  A modulated wave generated by amplitude-modulating a carrier wave with an acoustic wave signal in an audible band is composed of a carrier frequency component and a sideband frequency component, and in the air, the carrier wave frequency component and the sideband frequency component The difference sound is played as an audible sound. That is, the target audible sound is reproduced in a region where the frequency component of the carrier wave and the frequency component of the sideband wave exist.

  In the parametric speaker having the above configuration, the modulated wave is separated into the first separated wave and the second separated wave by the band separation unit, and the first separated wave and the second separated wave are different from each other from different ultrasonic elements. The phase is controlled so as to be emitted. Therefore, the target audible sound can be reproduced only in a limited region where both the first separated wave and the second separated wave overlap, and the directivity direction of the audible region can be adjusted. Therefore, the degree of freedom in setting the audible area can be increased.

(2) The phase control unit is configured to set the first separated wave and the second separated wave so that a region where the first separated wave and the second separated wave overlap each other is set in the vicinity of the speaker body. The phase can be controlled.
With such a configuration, an audible region can be set only in the vicinity of the parametric speaker, and sound can be prevented from reaching a person away from the parametric speaker.

(3) The phase control unit may adjust the first separated wave and the second separated wave so that a region where the first separated wave and the second separated wave overlap with each other becomes narrower as the distance from the speaker body increases. The phase may be controlled.
With such a configuration, an audible area can be set so that sound is delivered to a person near the parametric speaker, but sound is not delivered to a person away from the parametric speaker.

(4) The band separation unit further divides the second modulated wave into a plurality according to frequency components,
It is preferable that the phase control unit controls the phase of each second separated wave so as to radiate the second separated wave divided into a plurality of directions from different ultrasonic wave generating elements.
With such a configuration, it is possible to suppress the reproduction of unintended audible sound due to the difference between the plurality of frequency components included in the sideband.

(5) It is preferable that the plurality of ultrasonic wave generating elements are arranged in a planar shape.
With such a configuration, it is possible to increase the degree of freedom in setting an audible area using a speaker body with a simple configuration.

(6) The speaker body may be used by being attached to a human body.
According to this configuration, it is possible to deliver sound only to the user by mounting the speaker body on the user's body and setting an audible area in the vicinity of the user's ear.

(7) The phase control unit may determine the first separated wave and the second separated wave based on the size of a region where grating lobes generated with the radiation of the first separated wave and the second separated wave overlap each other. It is preferable to control the phase of the two separated waves.
According to this configuration, for example, by controlling the phase of the first separated wave and the second separated wave so as to reduce the region where the grating lobes generated by the separated waves overlap each other, It is possible to suppress generation of audible sound that does not occur.

(8) The signal processing apparatus according to the present invention includes a modulated wave generated by amplitude-modulating a carrier wave in an ultrasonic band with a sound wave signal in an audible band, a first separated wave having a frequency component of the carrier wave, and the modulated signal A band separation unit that separates the second separated wave having a frequency component of a sideband of the wave;
A phase control unit that controls phases of the first separated wave and the second separated wave so that the first separated wave and the second separated wave are radiated from mutually different ultrasonic wave generating elements in different directions. And.

(9) The signal processing program of the present invention uses a modulated wave generated by amplitude-modulating a carrier wave in an ultrasonic band by an acoustic wave signal in an audible band, a first separated wave having the frequency component of the carrier wave, and the modulation A band separation unit for separating the second separated wave having a frequency component of a sideband of the wave; and
A phase control unit that controls phases of the first separated wave and the second separated wave so that the first separated wave and the second separated wave are radiated from mutually different ultrasonic wave generating elements in different directions. As a computer function.

  ADVANTAGE OF THE INVENTION According to this invention, the freedom degree of the setting of the audible area | region in a parametric speaker can be raised.

1 is a schematic configuration diagram of an acoustic system including a parametric speaker according to an embodiment. It is front explanatory drawing of a speaker main body. It is explanatory drawing which shows the principle of a parametric speaker. It is explanatory drawing which shows the principle by which a modulated wave is demodulated to an audible sound. It is a figure explaining the division | segmentation of a sideband. It is a figure explaining phase control of a modulated wave. It is a figure which shows arrangement | positioning of the microphone in evaluation experiment. It is explanatory drawing which shows the radiation | emission direction of the carrier wave in the evaluation experiment 1, a low region sideband, and a high region sideband. It is a figure which shows the sound pressure level of the reproduced audible sound. It is a figure which shows the sound pressure level of a carrier wave, a low frequency sideband, and a high frequency sideband. It is explanatory drawing which shows the radiation | emission direction of the carrier wave in the evaluation experiment 2, a low frequency sideband, and a high frequency sideband. It is a figure which shows the sound pressure level of the reproduced audible sound. It is a figure which shows the sound pressure level of a carrier wave, a low frequency sideband, and a high frequency sideband. It is explanatory drawing which shows the radiation | emission direction of the carrier wave in the evaluation experiment 3, a low frequency sideband, and a high frequency sideband. It is a figure which shows the sound pressure level of the reproduced audible sound. It is a figure which shows the sound pressure level of a carrier wave, a low frequency sideband, and a high frequency sideband. It is explanatory drawing which shows the radiation | emission direction of the carrier wave in the evaluation experiment 4, a low region sideband, and a high region sideband. It is a figure which shows the sound pressure level of the reproduced audible sound. It is a figure which shows the sound pressure level of a carrier wave, a low frequency sideband, and a high frequency sideband. It is explanatory drawing which shows the generation direction of a grating lobe. It is explanatory drawing which shows the audible area | region by a grating lobe.

<Embodiment>
Hereinafter, parametric speakers according to embodiments will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an acoustic system including a parametric speaker according to the embodiment.
The acoustic system 10 includes a signal generation device 11 and a parametric speaker 12. The signal generation device 11 includes a signal source 13 and a filter processing unit 14. The signal source 13 generates an audible sound wave signal such as an audio signal or an audio signal, and outputs the sound wave signal to the filter processing unit 14. The filter processing unit 14 gives a predetermined characteristic to the signal wave and outputs the signal wave to the parametric speaker 12.

  FIG. 3 is an explanatory diagram showing the principle of the parametric speaker 12. The parametric speaker 12 generates, as a carrier wave, an ultrasonic wave that humans cannot perceive as a sound at a high frequency of 20 kHz or higher, and amplitude-modulates the carrier wave by a sound wave signal that is an audible sound generated by the signal generation device 11. Waves radiate into the air. The radiated modulated wave is distorted by the nonlinearity of air in the process of propagating in the air, and the audible sound is self-demodulated by this distortion.

  Specifically, the parametric speaker 12 includes a speaker body 21 and a signal processing unit 22. FIG. 2 is an explanatory front view of the speaker main body 21. The speaker main body 21 includes a plurality of ultrasonic wave generating elements 23 that emit ultrasonic waves. The plurality of ultrasonic wave generating elements 23 are provided in a state of being arranged on the support substrate 24 in a planar shape. For example, a plurality of ultrasonic wave generating elements 23 arranged in a line in the vertical direction in FIG. 2 are provided in a plurality of lines in the horizontal direction in FIG. In the example shown in FIG. 2, a plurality of (for example, ten) ultrasonic wave generation elements 23 arranged in a vertical row are arranged in left and right N rows. In FIG. 2, the interval between the columns is indicated by d.

As shown in FIG. 1, the signal processing unit 22 includes a carrier wave generation unit 31, a modulation unit 32, a band separation unit 33, a phase control unit 34, and an amplification unit 35.
The carrier wave generation unit 31 generates a carrier wave composed of ultrasonic waves having a predetermined frequency and outputs the carrier wave to the modulation unit 32. The carrier wave generation unit 31 is configured to include a high frequency oscillator using, for example, a crystal resonator. In the present embodiment, a 40 kHz carrier wave is generated and output to the modulation unit 32.

The modulation unit 32 amplitude-modulates the carrier wave input from the carrier wave generation unit 31 with the sound wave signal input from the signal generation device 11 to generate an amplitude-modulated wave.
The band separation unit 33 separates the modulated wave into a plurality of separated waves according to frequency components.

Here, when the frequency of the carrier _{f C,} time t, the maximum amplitude of the carrier wave and _{A C,} the carrier _v C (t) can be expressed by the following equation (1).

Further, when the frequency of the sound wave signal generated by the signal generation device 11 is f _S and the maximum amplitude of the audible sound is A _S , the audible sound v _S (t) can be expressed by the following equation (2).

When the modulation degree indicating the audible sound content is m (m ≦ 1) and the carrier wave v _C (t) is amplitude-modulated with the audible sound v _S (t), the generated modulated wave v _M (t) is These can be represented by the following formulas (3) and (4).

The modulated wave v _M (t) expressed by the equations (3) and (4) can be expressed by the following equation (5) using the addition theorem of trigonometric functions.

From equation (5), the modulated wave v _M (t) is a sideband wave having a frequency (f _C + f _S ) of the sum of the frequency f _{C of} the carrier and the frequency f _S of the audible sound wave signal in addition to the carrier wave. And sidebands having a difference frequency (f _C −f _S ). When such a modulated wave v _M (t) is radiated from the parametric speaker 12 into the air at a high sound pressure, the modulated wave is distorted due to the non-linearity of the air, and the difference sound between the carrier wave and the sideband waves is reproduced as an audible sound. .

In this embodiment, the sideband wave having the sum frequency (f _C + f _S ) of the frequency f _{C of} the carrier wave and the frequency f _S of the sound wave signal of the audible sound and the difference frequency (f _C −f _S ) are used. In order to prevent deterioration of sound quality due to generation of harmonic distortion due to a difference sound with the sideband wave, the sum frequency (f _C + f _S ) is removed using a filter or the like, so that the sideband wave difference between the carrier wave and the difference is removed. An SSB (Single Side Band) modulation method using a difference sound with (f _C −f _S ) is used. FIG. 4 exemplifies that a difference sound between two sidebands having a difference frequency (f _C −f _S1 ) and (f _C −f _S2 ) and a carrier wave is reproduced as an audible sound.

  Returning to FIG. 1, the band separation unit 33 of the signal processing unit 22 converts the modulated wave into a first separated wave (hereinafter, also simply referred to as “carrier wave”) having the above-described carrier frequency component and a sideband wave. Separated into a second separated wave having frequency components (hereinafter also simply referred to as “sideband wave”).

  Further, the band separation unit 33 further divides the separated sideband wave (second separation wave) into a plurality of pieces according to the frequency. Since audible sounds such as general sounds and music contain many frequencies, when the carrier wave is amplitude-modulated with such audible sounds, the modulated wave becomes a broadband signal. For this reason, when the modulated wave is separated into a carrier wave and a sideband wave, the sideband wave contains many frequencies, and a large amount of difference sound is generated between the sideband waves. (Modulation distortion) may occur.

For example, as shown in FIG. 5, when there are sidebands having four frequencies f _{B1 to} f _B4 , many difference sounds are generated between the sidebands of each frequency.
Therefore, the band separation unit 33 of the present embodiment, for example, to divide the plurality of frequencies f _B1 ~f _B4 into two frequency bands sideband (a high-frequency sidebands and low frequency sidebands) the frequency f _B as the threshold Thus, the difference sound existing between the sidebands is reduced, and the cross modulation distortion is suppressed.

  As shown in FIG. 1, the phase control unit 34 divides the phase of the carrier wave and the sideband wave so as to radiate the carrier wave and the sideband wave generated by separating the modulated wave in different directions. Is to control. Details of the control by the phase control unit 34 will be described later.

The amplifying unit 35 is provided for each of the plurality of ultrasonic generating elements 23. The amplifying unit 35 is configured using, for example, an operational amplifier having good amplification characteristics in the ultrasonic band.
The carrier wave generation unit 31, the modulation unit 32, the band separation unit 33, and the phase control unit 34 are configured by a computer including an arithmetic unit such as a CPU, a storage unit such as a memory, and an input / output interface, for example. The calculation unit executes the computer program read into the storage unit, thereby realizing the carrier wave generation unit 31, the modulation unit 32, the band separation unit 33, and the phase control unit 34.

(Control by phase controller 34)
FIG. 6 is a diagram for explaining the phase control of the modulated wave. The phase control unit 34 of the present embodiment radiates a carrier wave in the front direction of the speaker body 21, and radiates a low-frequency sideband and a high-frequency sideband in a direction opposite to each other with respect to the front direction. Controls the phase of the carrier, the low sideband, and the high sideband. In FIG. 6, the region where the carrier wave is radiated is indicated by P2, the region where the low-frequency sideband is radiated is indicated by P3, the region where the high-frequency sideband is radiated is indicated by P4, and the regions P2 to P4 overlap. The region is indicated by P1.

  As shown in FIG. 2, in each row of the ultrasonic wave generation elements 23 in the speaker main body 21, the carrier wave, the low-frequency side band wave, and the high-frequency side band wave are radiated from different ultrasonic wave generation elements 23. Further, the carrier wave, the low-frequency sideband, and the high-frequency sideband are radiated from all the rows of the ultrasonic wave generating elements 23, respectively. The phase of the low-frequency sideband and the high-frequency sideband is controlled by adding a delay time between adjacent columns, and the low-frequency sideband and the high-frequency sideband are inclined and radiated with respect to the front direction. That is, the phase control unit 34 is configured by a delay filter that gives a delay time to the sound wave radiated from each ultrasonic wave generation element 23.

In FIG. 6, t is time, x _B (t) and x _{B ′} (t) are low sidebands and high sidebands, x _C (t) is a carrier wave, θ _k (where k = B, B ′ ) Is the radiation direction of the low-frequency sideband and high-frequency sideband, d is the row spacing of the ultrasonic wave generating elements 23 (see FIG. 2), c is the speed of sound, and τ _k (where k = B, B ′) is adjacent The difference in delay time between the low-frequency sideband and the high-frequency sideband radiated from the row of matching ultrasonic wave generation elements 23, N is the number of rows of the ultrasonic wave generation elements 23 (see FIG. 2), D _ki (where k = B, B ′, C, i = 1, 2,..., N) are given to the low-frequency sideband, the high-frequency sideband, and the sound wave radiated from the i-th row ultrasonic generating element 23 with respect to the carrier wave. Delay time.

The low-frequency sideband and the high-frequency sideband are decomposed into the number N of the rows of the ultrasonic wave generating elements 23, and each is given a delay time _Dki . As a result, the phase of each sideband wave radiated from each ultrasonic wave generating element 23 is shifted, and the angle θ at which the wavefront of each sideband wave x _k (t−D _ki ) in phase is inclined with respect to the front direction. is formed perpendicular to _k, each sideband x _{k (t-D ki)} is emitted in a direction inclined with respect to the front direction.

The delay time D _ki (where k = B, B ′, C, i = 1, 2,..., N) is determined by the row interval d of the ultrasonic wave generating elements and the radiation directions θ _k of the sidebands and the carrier wave. , K = B, B ′, C), the difference τ _k (where k = B, B ′, C) of the delay time of each sideband and carrier wave, and the fixed delay D ₀ , ), (7).

Further, the audible sound x _S (t) in the audible region P1 shown in FIG. 6 can be expressed by the following formula (8).

In the region P1 in FIG. 6, the carrier wave x _C (t) and the sideband waves x _B (t), x _{B ′} (t) are combined. As described with reference to FIG. 4, since the audible sound demodulated from the modulated wave is generated by the difference between the carrier wave and the sideband wave, the modulated wave x _M (radiated from the conventional parametric speaker) in the region P1. A synthesized wave similar to that in t) exists, and the synthesized wave is demodulated into audible sound in the region P1. On the other hand, since only the carrier wave exists in the region P2, and only the sidebands exist in the regions P3 and P4, the target audible sound is not reproduced in these regions P2 to P4. In addition, the carrier wave and the sideband wave are both ultrasonic waves in the ultrasonic band and become non-audible sound for humans, so the regions P2 to P4 are non-audible regions. Therefore, the audible region P1 can be formed in a limited range in the vicinity of the parametric speaker by radiating the carrier wave and the sideband wave from one parametric speaker 12 (speaker body 21) in different directions.

  Therefore, for example, the sound can be delivered only to the target person in the vicinity of the parametric speaker, and the sound can be prevented from reaching the non-target person away from the parametric speaker. Compared to the case where all the bands are radiated in the front direction while extending the audible area to a position farther away from the parametric speaker by reducing the inclination angle of the low side band and the high side band with respect to the front direction. Thus, the width of the audible area can be reduced, and the audible area can be limited to a range up to a predetermined distance (for example, a range up to reaching a wall or the like as a reflection surface). Therefore, it is possible to prevent the sound reflected by the wall or the like from reaching the non-target person.

  In the above embodiment, the carrier wave (first separated wave) is radiated in the front direction, and the low-frequency side band wave and the high-frequency side band wave (second separated wave) are radiated in a direction inclined with respect to the front direction. However, one of the low-frequency sideband and the high-frequency sideband can be radiated in the front direction, and the other of the low-frequency sideband and the high-frequency sideband and the carrier can be radiated in a direction inclined with respect to the front direction. Further, all of the carrier wave, the low-frequency sideband, and the high-frequency sideband may be radiated in a direction inclined with respect to the front direction. In this case, the directivity direction of the audible area can be set to a direction inclined from the front direction.

<Evaluation experiment>
The inventor of the present application conducted an evaluation experiment in order to confirm that the setting of the audible area of the parametric speaker as described above is effective. Specifically, sound waves (modulated waves) radiated from a parametric speaker were recorded with a plurality of microphones, the sound pressure level of the recorded audible sound was calculated, and the distribution was obtained. As shown in FIG. 7, the microphone M is arranged at 110 points vertically and horizontally at intervals of 0.1 m, and the speaker body 21 of the parametric speaker 12 is positioned at 0 m in width and depth (distance) (coordinates (0, 0)). Arranged. Other conditions are as shown in Table 1 below. The sound source was Japanese 1 speech and the carrier frequency was 40 kHz. The sidebands were set to 39 kHz as a threshold, 32 kHz to 39 kHz as a low-frequency sideband frequency, and 39 kHz to 39.9 kHz as a high-frequency sideband frequency.

(Evaluation Experiment 1)
In the evaluation experiment 1, as shown in FIG. 8, the front direction of the parametric speaker 12 is set to 0 °, the carrier wave (first separated wave) is radiated in the 0 ° direction, and the low-frequency sideband (second separated wave) is set to 0. Radiation was performed in a direction inclined from the ° direction to the minus side (left side in FIG. 8), and a high-frequency band wave was emitted in a direction inclined from the 0 ° direction to the plus side (right side in FIG. 8).

FIG. 9 shows the sound pressure level of the audible sound measured by the plurality of microphones M shown in FIG. The horizontal and vertical axes in FIG. 9 correspond to the microphone arrangement in FIG. Further, in FIG. 9, an audible region having a high sound pressure level is surrounded by a circle A1.
FIG. 9A shows the sound pressure level of the audible sound when a modulated wave is radiated from the conventional parametric speaker in the front direction (0 ° direction). As is clear from FIG. 9A, the audible area A1 extends linearly from the position of the parametric speaker (position where the width and distance are 0 m) in the front direction, and a sound field with high directivity is formed. I understand that.

  FIG. 9B radiates a carrier wave (indicated by C in the figure) in the front direction (0 ° direction), radiates a low-frequency sideband (indicated by LS in the figure) in the −5 ° direction, The sound pressure level of an audible sound when a wave (indicated by HS in the figure) is emitted in the + 5 ° direction is shown. In this case, although the audible area A1 extends linearly in the front direction, it can be said that the width of the audible area A1 is narrower and the directivity is sharper than in the case of FIG.

  FIG. 9C shows the case where the carrier C is radiated in the front direction (0 ° direction), the low-frequency sideband LS is radiated in the −10 ° direction, and the high-frequency sideband HS is radiated in the + 10 ° direction. Indicates the sound pressure level of the listening sound. In this case, the audible area A1 extends linearly in the front direction, but the width of the audible area A1 is narrower than in the case of FIGS. Further, in FIG. 9C, it can be seen that the audible area A1 is limited within a range close to the parametric speaker. Therefore, even in the front direction of the parametric speaker, the target audible sound is not reproduced at a position away from the audible area A1. Therefore, the distance of the audible area A1 from the parametric speaker can be limited by independently controlling the phase of the carrier wave and the sideband.

  FIG. 9D shows the case where the carrier wave C is radiated in the front direction (0 ° direction), the low-frequency sideband LS is radiated in the −15 ° direction, and the high-frequency sideband HS is radiated in the + 15 ° direction. Indicates the sound pressure level of the listening sound. FIG. 9 (e) shows a case where the carrier C is radiated in the front direction (0 ° direction), the low-frequency sideband LS is radiated in the −20 ° direction, and the high-frequency sideband HS is radiated in the + 20 ° direction. Indicates the sound pressure level of the audible sound.

  9D and 9E, the audible area A1 is formed in front of the parametric speaker, but hardly extends in the front direction, and the audible area A1 is only in the very vicinity of the parametric speaker. Is formed. Therefore, it is possible to limit the audible area A1 so that sound is delivered only to those who are in the vicinity of the parametric speaker and sound is not delivered to those who are away from the parametric speaker.

  In FIG. 10, as shown in FIG. 9 (e), the carrier wave C is in the front direction (0 ° direction), the low-frequency sideband LS and the high-frequency sideband HS are respectively in the −20 ° direction and the + 20 ° direction. The result of having individually measured the sound pressure levels of the carrier wave C, the low-frequency sideband LS, and the high-frequency sideband HS when radiated is shown. As shown in FIG. 10A, it can be seen that the low-frequency sideband LS is generated in a direction in which a region having a high sound pressure level surrounded by a circle L1 is inclined by approximately −20 ° with respect to the front direction. Similarly, as shown in FIG. 10 (b), the carrier C has a high sound pressure level region in the front direction, and as shown in FIG. 10 (c), the high-frequency sideband HS has a sound pressure level. It can be seen that a high region is generated in the + 20 ° direction. Therefore, it can be said that the phase control unit 34 appropriately controls the phase of the carrier wave C and the sidebands LS and HS (control of the directivity direction).

(Evaluation Experiment 2)
In the evaluation experiment 2, as shown in FIG. 11, the front direction of the parametric speaker is 0 °, the carrier wave (first separated wave) is radiated in the 0 ° direction, and the high-frequency sideband wave (second separated wave) is 0 °. Radiation was radiated in a direction inclined from the direction to the minus side (left side in FIG. 11), and a low-frequency sideband was radiated in a direction inclined from the 0 ° direction to the plus side (right side in FIG. 11).

  FIG. 12 shows the result of measuring the sound pressure level in the same manner as in FIG. Also in the measurement result shown in FIG. 12, it can be seen that the measurement result having the same tendency as the measurement result shown in FIG. 9 is obtained. However, when the sideband emission directions are ± 15 ° and ± 20 °, comparing FIG. 9 (d) (e) with FIG. 12 (d) (e), FIG. 9 (d) ( It can be said that the audible area is set in a range in which e) is smaller.

  In FIG. 13, as shown in FIG. 12E, the carrier wave C is in the front direction (0 ° direction), the low-frequency sideband LS and the high-frequency sideband HS are respectively in the + 20 ° direction and the −20 ° direction. The result of having individually measured the sound pressure levels of the carrier wave C, the low-frequency sideband LS, and the high-frequency sideband HS when radiated is shown. This result also showed the same tendency as the result shown in FIG.

(Evaluation Experiment 3)
In Evaluation Experiment 3, as shown in FIG. 14, the front direction of the parametric speaker is set to 0 °, and the carrier wave (first separated wave) is radiated in the direction inclined to the minus side (left side in FIG. 14). Was radiated in the 0 ° direction, and the high-frequency sideband was radiated in a direction inclined from the 0 ° direction to the plus side (right side in FIG. 14).

  FIG. 15 shows the result of measuring the sound pressure level in the same manner as in FIG. Also in the measurement result shown in FIG. 15, it can be seen that the measurement result having the same tendency as the measurement result shown in FIG. 9 is obtained. However, when the radiation directions of the sidebands LS and HS are the ± 15 ° direction and the ± 20 ° direction, when FIG. 9 (d) (e) is compared with FIG. 15 (d) (e), FIG. d) It can be said that the audible region is set in a range where (e) is smaller.

  FIG. 16 shows a case where the carrier C is radiated in the −20 ° direction, the low-frequency sideband LS in the 0 ° direction, and the high-frequency sideband HS in the + 20 ° direction, as shown in FIG. The result of having individually measured the sound pressure level of the low side band LS and the high side band HS is shown. This result also showed the same tendency as the result shown in FIG.

(Evaluation Experiment 4)
In evaluation experiment 4, as shown in FIG. 17, the front direction of the parametric speaker is set to 0 °, and the carrier wave (first separated wave) is radiated in the direction inclined to the plus side (right side in FIG. 17). Was radiated in a direction inclined to the minus side (left side in FIG. 17), and a high-frequency sideband was radiated in the 0 ° direction.

  FIG. 18 shows the result of measuring the sound pressure level in the same manner as in FIG. Also in the measurement result shown in FIG. 18, it can be seen that the measurement result having the same tendency as the measurement result shown in FIG. 9 is obtained. However, when FIGS. 9 (b) (c) and 18 (b) (c) are compared when the radiation directions of the carrier wave and the low sideband are ± 5 ° and ± 10 °, FIGS. 18 (b) (c) ), The width of the audible area is reduced, and sharper directivity is obtained.

  FIG. 19 shows a case where the carrier C is radiated in the 20 ° direction, the low sideband LS is -20 °, and the high sideband HS is radiated in the 0 ° direction, as shown in FIG. The sound pressure levels of the low-frequency sideband LS and the high-frequency sideband HS are individually measured. This result also showed the same tendency as the result shown in FIG.

(Examination of grating lobes)
For example, as shown in FIGS. 10 (a) and 10 (c), in the low-frequency sideband and the high-frequency sideband, the region with a high sound pressure level is not only the radiation direction of the original sideband shown by circle L1. It can be seen that this also occurs in the region surrounded by the circle L2. This is a sound wave (grating lobe) that becomes an interference wave with respect to the original sideband wave (main lobe) radiated from the ultrasonic wave generating elements arranged in an array. When such a grating lobe overlaps with another grating lobe, for example, as shown in FIG. 9 (e), there is a possibility that an area A2 where audible sound is reproduced is generated in addition to the original audible area A1.

In general, the grating lobe can calculate its generating direction theta _G the following equation (9).

Where θ _G is the grating lobe generation direction (generation angle) with respect to the 0 ° direction, θ _T is the main lobe radiation direction (radiation angle) with respect to the 0 ° direction, f is the sound wave frequency, c is the sound velocity, and d is This is the row interval of the ultrasonic wave generating elements.

As shown in FIG. 20, the radiation direction θ _T of each main lobe of the carrier wave, the low-frequency sideband, and the high-frequency sideband constituting the modulated wave, and the generation direction θ _G of each grating lobe are in the 0 ° direction. Appears on opposite sides of each other. According to Expression (9), the generation direction θ _G of the grating lobe decreases as the frequency f increases. Therefore, when the radiation directions θ _T of the main lobe of the carrier wave, the low-frequency sideband, and the high-frequency sideband are the same, the angle (θ _T + θ _G ) formed by the main lobe and the grating lobe is also larger in frequency f. The carrier wave becomes smaller, and the low-frequency sideband having a smaller frequency f becomes larger.

By considering the properties of the main lobe and the grating lobe as described above, it is possible to control a region where the grating lobes overlap, that is, a region where an unintended audible sound is generated.
For example, in Figure 21, the carrier, the high-frequency sideband, and a low-frequency sideband, if you increase the extent emission angle theta _T having a small frequency (see FIG. 21 (a)), conversely, lowest frequency If you are having a small enough radiation angle theta _T stuff shows (see FIG. 21 (b)). When both are compared, in the region A2 where the grating lobes overlap, the latter is smaller than the former. That is, the audible area A2 generated by the overlapping of grating lobes is reduced. Therefore, it is possible to control the audible region caused by the grating lobe by setting the radiation direction (phase) of the carrier wave, the low band sideband, and the high band sideband according to the magnitude of the frequency. I know that there is. In other words, the grating is controlled by controlling the phase of the carrier, the low sideband, and the high sideband based on the size of the region where the grating lobes of the carrier, the low sideband, and the high sideband overlap. Generation of unintended audible sound due to lobes can be suppressed.

  In addition, when any one of a carrier wave, a low-frequency sideband, and a high-frequency sideband is radiated in the front direction of the speaker body, or at least two are inclined in opposite directions with respect to the front direction. Even in the case of radiation, the phase of the carrier wave, the low-frequency sideband, and the high-frequency sideband can be controlled based on the size of the region where the grating lobes overlap with each other using the relationship of the above formula (9). it can.

The present invention is not limited to the above embodiment, and can be appropriately changed within the scope described in the claims.
For example, the plurality of ultrasonic generating elements constituting the speaker body are not limited to being arranged in a planar shape, but may be arranged in a curved shape.
In the above-described embodiment, the sideband is divided into two, a low-frequency sideband and a high-frequency sideband, but may be divided into three or more.
The speaker body can be used by being mounted on the user's body, for example. For example, by attaching the speaker body to the user's head, face, neck, arm, etc., and setting the audible area near the user's ear, the sound can be delivered only to the user without using headphones etc. Is possible. It should be noted that the “wearing” on the user's body includes, for example, carrying it in the user's clothes pocket.

12: Parametric speaker 21: Speaker main body 23: Ultrasonic wave generation element 31: Carrier wave generation unit 32: Modulation unit 33: Band separation unit 34: Phase control unit

Claims (9)

A carrier generation unit that generates a carrier wave in an ultrasonic band;
A modulation unit that modulates the carrier wave by an acoustic wave signal in an audible band to generate a modulated wave;
A band separation unit for separating the modulated wave into a first separated wave having a frequency component of a carrier wave and a second separated wave having a frequency component of a sideband;
A speaker body having a plurality of ultrasonic generating elements;
A phase control unit that controls phases of the first separated wave and the second separated wave so that the first separated wave and the second separated wave are radiated from mutually different ultrasonic generating elements in different directions. And a parametric speaker.   The phase control unit adjusts the phases of the first separated wave and the second separated wave so that a region where the first separated wave and the second separated wave overlap each other is set in the vicinity of the speaker body. The parametric speaker according to claim 1, which is controlled.   The phase control unit controls the phases of the first separated wave and the second separated wave so that a region where the first separated wave and the second separated wave overlap with each other becomes narrower as the distance from the speaker body increases. The parametric speaker according to claim 1 or 2. The band separation unit further divides the second modulated wave into a plurality of parts according to frequency components,
The said phase control part controls the phase of each 2nd separated wave so that the 2nd separated wave divided | segmented into multiple may be radiated | emitted from a different ultrasonic generation element in a different direction, respectively. Parametric speaker according to item.   The parametric speaker according to any one of claims 1 to 4, wherein the plurality of ultrasonic wave generating elements are arranged in a planar shape.   The parametric speaker according to any one of claims 1 to 5, wherein at least the speaker body is used by being attached to a human body.   The phase control unit is configured to determine the first separated wave and the second separated wave based on a size of a region where grating lobes generated by the radiation of the first separated wave and the second separated wave overlap each other. The parametric speaker according to claim 1, wherein the phase of the parametric speaker is controlled. A modulated wave generated by amplitude-modulating a carrier wave in an ultrasonic band with a sound wave signal in an audible band is divided into a first separated wave having a frequency component of the carrier wave and a frequency component of a side band of the modulated wave. A band separation unit for separating into two separated waves;
A phase control unit that controls phases of the first separated wave and the second separated wave so that the first separated wave and the second separated wave are radiated from mutually different ultrasonic wave generating elements in different directions. And a signal processing device. A modulated wave generated by amplitude-modulating a carrier wave in an ultrasonic band with a sound wave signal in an audible band is divided into a first separated wave having a frequency component of the carrier wave and a frequency component of a side band of the modulated wave. A band separation unit for separating into two separated waves, and
A phase control unit that controls phases of the first separated wave and the second separated wave so that the first separated wave and the second separated wave are radiated from mutually different ultrasonic wave generating elements in different directions. As a signal processing program that causes a computer to function.