JP2012239026A - Parametric speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost by using a piezoelectric speaker for generating audible sound as an ultrasonic speaker, and to prevent the resonance sound of audible band generated in the piezoelectric speaker 2 from being heard from a vehicle.SOLUTION: At the ultrasonic sound radiation port of an ultrasonic speaker 3, an audible sound absorption filter 6 which absorb sound wave of an audible band and passes ultrasonic waves is provided. The ultrasonic waves generated from a piezoelectric speaker 2 provided for generating an audible sound are passed through the audible sound absorption filter 6 and emitted forward of a vehicle. But the resonance sound of audible band generated from the piezoelectric speaker 2 is absorbed by the audible sound absorption filter 6, and does not exit the housing 16. Consequently, there is no problem that the resonance sound of audible band generated from the piezoelectric speaker 2 is heard from the vehicle.

Description

  The present invention relates to a parametric speaker that generates an ultrasonic wave obtained by ultrasonically modulating an audible sound from an ultrasonic speaker and reproduces the audible sound in the air away from the ultrasonic speaker. The present invention relates to a technique suitable for use in a vehicle presence notification device that informs the surroundings of the vehicle.

(Conventional technology)
Waveform signal (electric signal) of audible sound is ultrasonically modulated and irradiated into the air from an ultrasonic speaker, and the modulation component contained in the ultrasonic wave (sound that cannot be heard by the ear) is self-demodulated in the air that is being propagated. Thus, there is known a parametric speaker that generates an audible sound (notification sound) at a location away from the ultrasonic speaker.

Since this parametric speaker is a technology that uses ultrasonic waves with strong directivity (straightness), audible sound can be generated only in an arbitrary direction.
For this reason, a notification sound (a pseudo engine sound or the like) can be generated only in a specific direction (such as the front) of the vehicle, and a proposal for use in a vehicle presence notification device has been made (for example, see Patent Document 1).

(Background technology)
An ultrasonic speaker used for a parametric speaker needs to generate a dense wave having an ultrasonic wavelength in the air.
For this reason, as shown in FIG. 7A, the ultrasonic speaker collects a plurality of ultrasonic generation elements SS (ultrasonic transducers) provided for generating ultrasonic waves, and generates a plurality of ultrasonic waves. It is provided to generate ultrasonic waves from the element SS. FIG. 7A is a reference example shown for assisting understanding, and is not a well-known technique.

Here, due to the necessity of generating a dense wave having an ultrasonic wavelength in the air, the vibration system (vibrating plate + driving element or the like) of the ultrasonic wave generating element SS is required to be ultralight and vibrate at high speed.
Specifically, as shown in FIG. 7B, the ultrasonic generator SS has a primary resonance portion (primary resonance frequency: primary component) of the vibration system within the ultrasonic band (in this example, about 40 kHz). It is provided to exist.
As described above, the ultrasonic generation element SS having an ultralight vibration system is low in versatility, and thus costs are increased. For this reason, it becomes a factor of the cost increase of a parametric speaker.

(problem)
In order to solve this problem, an ultrasonic sound is generated using an audible sound generating piezoelectric speaker (a piezoelectric speaker provided to generate an audible sound wave) in which the primary resonance unit exists in the audible band. (It is a technique for suggesting a problem, not a well-known technique).
However, the audible sound generating piezoelectric speaker is not provided for generating ultrasonic waves, and a movable part such as a diaphragm is provided for audible sound. Therefore, when an audible sound generating piezoelectric speaker is oscillated at an ultrasonic frequency and an ultrasonic wave is generated from the audible sound generating piezoelectric speaker, as shown in FIG. (Audible sound from the primary resonance part or the like) occurs.
For this reason, when a piezoelectric speaker for generating an audible sound is used as the ultrasonic speaker, there is a problem that a resonance sound A (audible sound) in the audible band can be heard from the ultrasonic speaker.

JP 2011-050184 A

  The present invention has been made in view of the above problems, and its purpose is to reduce the cost by using an audible sound generating piezoelectric speaker as an ultrasonic speaker and to make an audible resonance sound audible from the ultrasonic speaker. It is in providing a parametric speaker that can prevent noise.

[Means of Claim 1]
Since the audible sound generating piezoelectric speaker is highly versatile and mass-produced, the cost can be suppressed. Therefore, the cost of the ultrasonic speaker used for the parametric speaker can be suppressed.
In addition, the ultrasonic wave generated by the audible sound generating piezoelectric speaker passes through the “audible sound absorbing filter that absorbs the sound wave in the audible band and transmits the ultrasonic wave” and is emitted to the outside.
For this reason, only the ultrasonic wave that has passed through the audible sound absorbing filter can be emitted to the outside (target direction), and the audible resonance sound generated by the piezoelectric speaker is absorbed by the audible sound absorbing filter. It is possible to avoid the problem that the resonance sound can be heard in the ultrasonic speaker.
That is, the means of claim 1 can avoid the demerit (demerit that the audible band resonance sound can be heard from the ultrasonic speaker) by using the audible sound generating piezoelectric speaker in order to reduce the cost.

[Means of claim 2]
Since the audible sound generating piezoelectric speaker is highly versatile and mass-produced, the cost can be suppressed. Therefore, the cost of the ultrasonic speaker used for the parametric speaker can be suppressed.
Further, the ultrasonic wave generated by the audible sound generating piezoelectric speaker is reflected by the “ultrasonic reflecting means that transmits the sound wave in the audible band and reflects the ultrasonic wave” and is emitted to the outside.
For this reason, only the ultrasonic waves reflected by the ultrasonic reflecting means can be emitted to the outside (target direction), and the audible resonance sound generated by the piezoelectric speaker is transmitted to the side different from the ultrasonic reflection direction. Therefore, it is possible to avoid the problem that the audible resonance sound can be heard in the ultrasonic speaker.
That is, the means of claim 2 can avoid the demerit (demerit that the audible band resonance sound can be heard from the ultrasonic speaker) by using the audible sound generating piezoelectric speaker in order to reduce the cost.

[Means of claim 3]
Since the ultrasonic wave has a short wavelength and excellent reflectivity, the ultrasonic wave is reflected on a thin cloth film clogged with tension.
On the other hand, the sound wave in the audible band has a longer wavelength than the ultrasonic wave and is excellent in permeability, and therefore passes through a thin cloth film clogged with tension.
Due to this property, it is possible to use a thin, clogged cloth film to which tension is applied as an ultrasonic reflection means.

[Means of claim 4]
According to a fourth aspect of the present invention, there is provided an ultrasonic speaker comprising transmitted sound control means for performing at least one of absorption and reflection of a sound wave at a site hit by a sound wave transmitted through the ultrasonic reflection means.
By this transmitted sound control means, it is possible to control the generation direction and sound pressure of a sound wave (audible band resonance sound) transmitted through the ultrasonic reflection means.

[Means of claim 5]
The parametric speaker according to claim 5 is used in a vehicle presence notification device that generates a notification sound outside the vehicle to notify the presence of the vehicle.
The cost of the vehicle presence notification device (specifically, the cost of an ultrasonic speaker in a parametric speaker mounted on the vehicle presence notification device) can be suppressed, and an audible sound generating piezoelectric speaker is used to reduce the cost. The demerit (demerit that the audible resonance sound can be heard outside the vehicle) can be avoided.

It is explanatory drawing of the parametric speaker which applies the sound generated of the audible sound generation piezoelectric speaker to an audible sound absorption filter, and permeate | transmits only an ultrasonic wave (Embodiment 1). It is explanatory drawing of the parametric speaker which applies the sound generated of the audible sound generation piezoelectric speaker to an ultrasonic wave reflection means, and reflects only an ultrasonic wave (Embodiment 2, Example 2). FIG. 3 is a vehicle mounting diagram of an ultrasonic speaker and a vehicle horn (Example 1). (A) It is explanatory drawing which shows the example of arrangement | positioning of the audible sound generation piezoelectric speaker, (b) It is a frequency characteristic figure at the time of making the audible sound generation piezoelectric speaker oscillate ultrasonically (Example 1). 1 is a schematic diagram of a vehicle presence notification device (Example 1). (Example 1) which is a principle explanatory drawing of a parametric speaker. (A) It is explanatory drawing which shows the example of arrangement | positioning of an ultrasonic wave generation element, (b) It is a frequency characteristic figure of an ultrasonic wave generation element (reference example).

[Embodiment 1]
The first embodiment will be described with reference to FIG.
The parametric speaker 1 of Embodiment 1 is
An ultrasonic speaker 3 using an audible sound generating piezoelectric speaker 2 (piezoelectric speaker provided to generate an audible sound wave) having a primary resonance portion (primary component of the resonance frequency) in the audible band. When,
An ultrasonic modulation means 4 for generating an ultrasonic signal obtained by ultrasonically modulating an audible sound signal;
Ultrasonic driving means 5 (amplifying means) for driving the audible sound generating piezoelectric speaker 2 by the ultrasonic signal generated by the ultrasonic modulation means 4;
An audible sound absorption filter 6 that absorbs sound waves in the audible band and transmits ultrasonic waves;
Is provided.
Then, the ultrasonic wave generated by the audible sound generating piezoelectric speaker 2 passes through the audible sound absorbing filter 6 and is emitted in the target direction.

Since the audible sound generating piezoelectric speaker 2 is highly versatile and mass-produced, the cost can be suppressed, so the cost of the ultrasonic speaker 3 can be suppressed.
Further, since the ultrasonic wave generated by the audible sound generating piezoelectric speaker 2 passes through the audible sound absorption filter 6 and then is emitted to the outside, only the ultrasonic wave that has passed through the audible sound absorption filter 6 is externally (target direction). Therefore, it is possible to avoid the problem that the audible resonance sound can be heard from the ultrasonic speaker 3.

A specific example of the audible sound absorption filter 6 is a porous member that absorbs only sound waves in the audible band by the resonance action of Helmholtz and transmits ultrasonic waves that do not match the resonance frequency. For example, it is an infinite number of resonance chambers (having air permeability). It is provided by a ceramic or resin having a large number of open cells).
Note that the audible sound absorption filter 6 may absorb a wide audible band, or may absorb only resonance sound in the audible band pinpoint.

[Embodiment 2]
A second embodiment will be described with reference to FIG.
The parametric speaker 1 of Embodiment 2 is
An ultrasonic speaker 3 using an audible sound generating piezoelectric speaker 2 (piezoelectric speaker provided to generate an audible sound wave) having a primary resonance portion (primary component of the resonance frequency) in the audible band. When,
An ultrasonic modulation means 4 for generating an ultrasonic signal obtained by ultrasonically modulating an audible sound signal;
Ultrasonic driving means 5 (amplifying means) for driving the audible sound generating piezoelectric speaker 2 by the ultrasonic signal generated by the ultrasonic modulation means 4;
An ultrasonic reflection means 7 that transmits sound waves in the audible band and reflects ultrasonic waves;
Is provided.
Ultrasonic waves (including resonance sound in the audible band) generated by the audible sound generating piezoelectric speaker 2 are applied to the ultrasonic reflection means 7 and only the ultrasonic waves reflected by the ultrasonic reflection means 7 are emitted in the target direction. .

Since the audible sound generating piezoelectric speaker 2 is highly versatile and mass-produced, the cost can be suppressed, so the cost of the ultrasonic speaker 3 can be suppressed.
Further, since the ultrasonic waves generated by the audible sound generating piezoelectric speaker 2 are reflected by the ultrasonic reflecting means 7 and emitted to the outside, only the ultrasonic waves reflected by the ultrasonic reflecting means 7 are directed to the outside (target direction). Therefore, it is possible to avoid the problem that the audible resonance sound can be heard from the ultrasonic speaker 3.

The ultrasonic reflection means 7 is provided by a thin film material (such as a film film or a cloth film that is thin and has a smooth ultrasonic reflection surface) that has excellent ultrasonic wave reflectivity and excellent sound wave permeability in the audible band.
As a specific example, the ultrasonic reflecting means 7 is formed by a cloth film made of a thin chemical fiber that is stretched in a tensioned state and is woven by stuffing eyes with a thin thread and having a smooth surface. Provided. The surface of the cloth film may be coated with a resin, a wax material, or the like that increases the degree of smoothness and improves the reflectivity of ultrasonic waves.

Further, the ultrasonic speaker 3 is provided with transmitted sound control means for performing at least one of absorption and reflection of sound waves at a site to which a sound wave (audible band resonance sound) transmitted through the ultrasonic reflection means 7 is applied.
For this reason, it is possible to avoid the inconvenience that the resonance sound in the audible band transmitted through the ultrasonic reflecting means 7 becomes a noise source in a direction different from the ultrasonic irradiation direction (ultrasonic reflection direction).

Hereinafter, a specific example (example) to which the present invention is applied will be described with reference to the drawings. The embodiment described below is a specific example, and it goes without saying that the present invention is not limited to the embodiment.
In the following examples, the same reference numerals as those in the “DETAILED DESCRIPTION OF THE INVENTION” denote the same functional objects.

[Example 1]
Embodiment 1 will be described with reference to FIGS.
In this example, the above-described first embodiment is applied to a parametric speaker 1 mounted on a vehicle presence notification device, and details thereof will be described below.

  The vehicle presence notification device notifies the presence of a vehicle by a notification sound (for example, pseudo engine sound: not limited), for example, a vehicle (electric vehicle, fuel cell vehicle) not equipped with an engine (internal combustion engine). Etc.), vehicles that may stop the engine while traveling and stopped (hybrid vehicles, etc.), vehicles that may stop the engine while stopped (such as idle stop vehicles), or engine vehicles It is mounted on a convex vehicle with a quiet running sound.

This vehicle presence notification device
A parametric speaker 1 that emits an ultrasonic wave that is generated by ultrasonically modulating a frequency signal forming a notification sound toward the outside of the vehicle;
A vehicle horn 11 used as a dynamic speaker that emits an audible notification sound directly outside the vehicle;
A control circuit 12 for controlling the operation of the parametric speaker 1 and the vehicle horn 11,
It is configured with.

(Description of parametric speaker 1)
The ultrasonic speaker 3 used for the parametric speaker 1 generates air vibration having a frequency (20 kHz or higher) higher than the human audible band, and is mounted on the vehicle so as to emit ultrasonic waves toward the front of the vehicle. ing.
Specifically, the ultrasonic speaker 3 of this embodiment is provided on the front surface of the vehicle horn 11 (the surface facing the front of the vehicle when mounted on the vehicle: for example, a spiral horn). As shown in FIG. 14 and the heat exchanger 15 (a radiator or a heat exchanger for air conditioning, etc.) are attached to the vehicle horn 11 so that the ultrasonic speaker 3 can be connected to the vehicle in a state where the ultrasonic radiation direction is directed to the front of the vehicle. Mounted on.

The ultrasonic speaker 3 of this embodiment is
A plurality of piezoelectric speakers 2 that generate ultrasonic waves;
A housing 16 that houses the plurality of piezoelectric speakers 2;
Is provided.

  The plurality of piezoelectric speakers 2 are mounted on a support plate 17 fixedly disposed inside the housing 16 and are collectively disposed as a speaker array as shown in FIG. Each piezoelectric speaker 2 uses a piezoelectric element (piezoelectric element) that expands and contracts according to an applied voltage (charge / discharge) and a diaphragm that is driven by the expansion and contraction of the piezoelectric element to generate a dense wave in the air. Composed.

In this embodiment, each piezoelectric speaker 2 mounted on the ultrasonic speaker 3 generates an acoustic wave in the audible band instead of the ultrasonic generating element SS {reference numeral, see FIG. 7 (a)} manufactured for ultrasonic generation. In order to generate an audible sound, the primary resonance portion A (primary resonance frequency: primary resonance portion, etc.) is present in the audible band as shown in FIG. .
As a specific example, each piezoelectric speaker 2 of this embodiment is a diversion of what is provided to provide vehicle information to the vehicle occupant by hearing (sound, warning sound, etc.) The outer diameter size of the piezoelectric speaker 2 used in this embodiment is compared with the ultrasonic wave generator SS {reference numeral, see FIG. 7 (a)} manufactured for generating ultrasonic waves so as to be suitable for generating an audible frequency. About twice as large.

The piezoelectric speaker 2 is provided for generating an audible sound, but a higher-order resonance part (resonance frequency) also exists in the ultrasonic band.
As a specific example, the piezoelectric speaker 2 of this embodiment has a sound pressure increasing portion X {reference numeral, see FIG. 4 (b)} due to a high-order resonance portion (for example, a seventh-order resonance portion: a seventh-order component) in the ultrasonic band. Is something that exists.

The housing 16 may be provided integrally with a member constituting the vehicle horn 11 or may be provided separately and attached to the vehicle horn 11.
Specifically, the housing 16 is formed with a volume chamber in which the ultrasonic speaker 3 is accommodated, and an ultrasonic radiation opening (opening) that emits ultrasonic waves emitted from each piezoelectric speaker 2 toward the front of the vehicle. Part). The housing 16 is provided in a substantially sealed container except for the ultrasonic radiation port.

The ultrasonic radiation opening of the housing 16 is provided with waterproof means for preventing rainwater from entering the mounting portions of the piezoelectric speakers 2.
As an example of this waterproofing means, this embodiment includes an ultrasonically permeable waterproof sheet 18 that covers the ultrasonic radiation opening, and a louver 19 disposed on the front surface of the waterproof sheet 18.

Note that the louver 19 is an armor door (louver) in which rainwater reaches the waterproof sheet 18 as much as possible, and has long and narrow wings arranged horizontally with a gap.
As shown in FIG. 3, the louver 19 is provided with an inclination of approximately 45 ° with respect to the vehicle horizontal direction. As a result, the ultrasonic waves radiated from each piezoelectric speaker 2 change the direction downward on the inner surface of the louver 19 and change the direction again toward the front of the vehicle on the outer surface of the lower louver 19, and consequently toward the front of the vehicle. Is emitted.

In addition, an audible sound absorption filter 6 that absorbs sound waves in the audible band and transmits ultrasonic waves is provided at the ultrasonic radiation port of the housing 16.
The audible sound absorbing filter 6 is a porous member that absorbs only sound waves in the audible band by the Helmholtz resonance action and transmits ultrasonic waves that do not match the resonance frequency. These are provided by ceramics or resins having open cells.
Note that the audible sound absorption filter 6 may absorb a wide audible band, or may absorb only the audible band resonance sound generated by the piezoelectric speaker 2 pinpoint.
3 shows an example in which the audible sound absorbing filter 6 is arranged outside the waterproof sheet 18, the arrangement position of the audible sound absorbing filter 6 is not limited, and the audible sound absorbing filter 6 is arranged inside the waterproof sheet 18. An audible sound absorbing filter 6 may be arranged.

(Description of vehicle horn 11)
As described above, the vehicle horn 11 is fixedly disposed between the front grille 14 and the heat exchanger 15, and provides an alarm when a horn switch (for example, a steering horn button) is operated by an occupant. It is an electromagnetic horn with a known structure that generates sound.
The vehicle horn 11 is mounted on the vehicle such that the opening of the spiral horn faces downward (road surface) so that the notification sound generated from the vehicle horn 11 reaches the vehicle substantially uniformly. It is.

(Description of the control circuit 12)
The control circuit 12 is configured by using a microcomputer chip 21 (abbreviation of a micro computer chip) as shown in FIG. 3. For example, as shown in FIG. Arranged inside (specifically, inside the horn housing) (not limited).

The control circuit 12 will be specifically described with reference to FIG.
The control circuit 12 is connected to a power source (battery) and is supplied with a horn switch signal or a vehicle speed signal (for example, a vehicle speed pulse signal).
(A) determination means 22 for determining “whether the driving state of the vehicle conforms to the condition for generating the notification sound”;
(B) When this determination unit 22 determines that “the driving state of the vehicle is suitable for the generation condition of the notification sound”, the notification sound generation unit 23 that generates the “frequency signal that forms the notification sound”;
(C) an ultrasonic modulation unit 4 that modulates the “frequency signal forming the notification sound” output from the notification sound generation unit 23 into an ultrasonic frequency;
(D) ultrasonic driving means 5 for driving the ultrasonic speaker 3 (a plurality of piezoelectric speakers 2 constituting the ultrasonic speaker 3);
(E) horn driving means 24 for driving the vehicle horn 11;
Is provided.
Below, each means of said (a)-(e) mounted in the control circuit 12 is demonstrated.

(Description of determination means 22)
For example, when the vehicle speed is a predetermined speed (for example, 20 km / h) or less, the determination unit 22 determines that the driving state of the vehicle is suitable for the generation condition of the notification sound, and sets the notification sound generation unit 23. (It is a specific example for explaining the embodiment and is not limited).

(Description of notification sound generating means 23)
The notification sound generation means 23 is provided by a notification sound generation program (acoustic software). When an operation instruction is given from the determination means 22, a digital signal “frequency signal that makes a notification sound (electric signal of audible frequency: for example, pseudo engine” Electrical signal that makes sound) ”.

(Description of Ultrasonic Modulator 4)
The ultrasonic modulation unit 4 ultrasonically modulates the “frequency signal forming the notification sound (an example of an audible sound signal)” output from the notification sound generation unit 23.
As a specific example of the ultrasonic modulation unit 4, in this embodiment, the output signal of the notification sound generation unit 23 is expressed as “ultrasonic frequency (high-order resonance unit existing in the ultrasonic band of the reproducible frequency of the piezoelectric speaker 2). AM modulation (amplitude modulation) that modulates to “amplitude change (voltage increase / decrease change) at the frequency of the sound pressure increase portion X by: about 25 kHz”, for example, is used. That is, the “frequency signal forming the notification sound” is modulated to “the ultrasonic frequency of the sound pressure increasing portion X”.
The ultrasonic modulation means 4 is not limited to AM modulation, and PWM modulation that modulates the output signal of the notification sound generation means 23 to a predetermined “pulse width change (pulse generation time width) at an ultrasonic frequency”. Other ultrasonic modulation techniques such as (pulse width modulation) may be used.

A specific example of ultrasonic modulation by the ultrasonic modulation means 4 will be described with reference to FIG.
For example, it is assumed that the “frequency signal forming the notification sound” input to the ultrasonic modulation means 4 is a voltage change shown in FIG. 6A (in the figure, a single-frequency waveform is used for assisting understanding). Showing).
On the other hand, the ultrasonic oscillator mounted on the control circuit 12 is assumed to oscillate at the ultrasonic frequency (the ultrasonic frequency of the sound pressure increasing portion X) shown in FIG. The ultrasonic oscillator may form a predetermined ultrasonic frequency from a clock signal (computer control clock signal) mounted on the microcomputer chip 21, or may be ultrasonic modulation independent of the microcomputer chip 21. For example, an oscillator may be used.

Then, as shown in FIG.
(I) Increasing the amplitude of the voltage due to ultrasonic vibration as the signal voltage of the frequency forming the “frequency signal forming the notification sound” increases,
(Ii) As the signal voltage of the frequency forming the “frequency signal forming the notification sound” decreases, the amplitude of the voltage due to the ultrasonic vibration is decreased.
In this way, the ultrasonic modulation unit 4 modulates the “frequency signal forming the notification sound” output from the notification sound generation unit 23 into “amplitude change in oscillation voltage” of the ultrasonic frequency.

(Description of ultrasonic driving means 5)
The ultrasonic drive means 5 drives the ultrasonic speaker 3 based on the ultrasonic signal modulated by the ultrasonic modulation means 4 (for example, push-pull class B amplifier or push-pull class D amplifier). By controlling the applied voltage (charge / discharge state) of each piezoelectric speaker 2, an ultrasonic wave that modulates a “frequency signal that makes a notification sound” is generated from each piezoelectric speaker 2.

(Description of horn driving means 24)
The horn driving means 24 is
(I) While the notification sound generating means 23 is generating the “frequency signal that makes the notification sound”, the vehicle horn 11 is operated as a dynamic speaker, and the “frequency signal that makes the notification sound” is amplified to make the vehicle horn. A power amplifier function for generating an audible notification sound from 11;
(Ii) a continuous ON function that applies a battery voltage to the vehicle horn 11 and generates an alarm sound from the vehicle horn 11 while the horn switch is ON;
Is provided.
Note that “ON of the horn switch” has priority over the “instruction to generate notification sound”, and the horn 11 for the vehicle is always configured to generate an alarm sound when the horn switch is turned ON.

(Operation of vehicle presence notification device)
When the driving state of the vehicle matches the generation condition of the notification sound, the notification sound generation means 23 outputs a “frequency signal that generates the notification sound”, and the “frequency signal that generates the notification sound” shown in FIG. ”Is emitted toward the front.
The ultrasonic waves generated by the piezoelectric speaker 2 pass through the waterproof sheet 18 and the audible sound absorbing filter 6, pass through the louver 19, and are emitted toward the front of the vehicle.

Then, as shown in FIG. 6D, as the ultrasonic wave propagates in the air, the ultrasonic wave having a short wavelength is distorted and blunted by the viscosity of the air.
As a result, as shown in FIG. 6E, the amplitude component contained in the ultrasonic wave in the air being propagated is self-demodulated, and as a result, “notification sound” is reproduced in front of the vehicle.
On the other hand, the notification sound generating means 23 outputs a “frequency signal that forms a notification sound”, whereby an audible “notification sound” is directly emitted from the vehicle horn 11 to the surroundings of the vehicle.

(Effect 1 of Example 1)
As described above, the ultrasonic speaker 3 of this embodiment uses the piezoelectric speaker 2 provided for generating sound waves in the audible band. From the piezoelectric speaker 2 for generating audible sound, the parametric speaker 1 is used. The ultrasonic wave used for the is generated.
The audible sound generating piezoelectric speaker 2 is low in cost because it is highly versatile and mass-produced. For this reason, the manufacturing cost of the ultrasonic speaker 3 can be suppressed low, and the cost of the vehicle presence notification apparatus using the parametric speaker 1 can be suppressed.

(Effect 2 of Example 1)
In this embodiment, as described above, ultrasonic waves are generated from the piezoelectric speaker 2 provided to generate sound waves in the audible band.
When ultrasonic waves are generated using the piezoelectric speaker 2 provided to generate sound waves in the audible band in this way, as shown in FIG. 4B, the resonance sound A (primary resonance section etc.) is generated in the audible band. Audible sound).

Since the audible sound absorption filter 6 is provided at the ultrasonic radiation opening which is the only opening provided in the housing 16, the resonance sound of the audible band generated by the piezoelectric speaker 2 is absorbed by the audible sound absorption filter 6, and the ultrasonic wave Only is released forward of the vehicle.
Thus, the audible resonance sound generated by the piezoelectric speaker 2 does not go out of the housing 16.
For this reason, the malfunction that the resonance sound of the audible band which the piezoelectric speaker 2 generate | occur | produced from the vehicle can be avoided.

[Example 2]
A second embodiment will be described with reference to FIG.
In Example 2, Embodiment 2 is applied to a vehicle presence notification device.
Specifically, the ultrasonic wave irradiated from the piezoelectric speaker 2 is reflected by the “ultrasonic reflecting means 7 having excellent ultrasonic wave reflectivity and excellent sound wave transmission property in the audible band” and directed toward the front of the vehicle. The speaker 3 is mounted on the vehicle.

  The ultrasonic reflecting means 7 is provided by, for example, a thin film film or a cloth film having a smooth ultrasonic reflecting surface. As a specific example, the ultrasonic reflecting means 7 is given a tension. The fabric is made of a thin chemical fiber having a smooth surface that is stretched in a stretched state and woven with fine threads.

In addition, the ultrasonic speaker 3 is provided with transmitted sound control means for absorbing and reflecting sound waves at a site where a sound wave (audible band resonance sound) transmitted through the ultrasonic reflection means 7 is applied.
For this reason, it is possible to avoid the problem that the resonance sound in the audible band transmitted through the ultrasonic reflecting means 7 becomes a noise source in a direction different from the direction of ultrasonic irradiation. That is, it is possible to avoid a problem that the resonance sound in the audible band transmitted through the ultrasonic reflection means 7 becomes the noise of the vehicle occupant.

Note that it is preferable that a sound reflector is used as an example of the transmitted sound control means, and the sound wave (audible band resonance sound) transmitted through the ultrasonic reflection means 7 is reflected in the vehicle side direction or obliquely rearward.
By providing in this way, there is an effect that the resonance sound in the audible band that has passed through the ultrasonic reflection means 7 avoids the problem that it becomes a noise of the vehicle occupant and notifies the presence of the vehicle in the vehicle side direction or obliquely rearward. can get.

  In the above embodiment, the example in which the present invention is applied to the parametric speaker 1 of the vehicle presence notification device has been described. However, the present invention is not limited thereto, and the present invention may be applied to the parametric speaker 1 for other uses.

1 Parametric speaker 2 Piezoelectric speaker (piezoelectric speaker for audible sound generation)
3 Ultrasonic speaker 4 Ultrasonic modulation means 5 Ultrasonic drive means 6 Audible sound absorption filter 7 Ultrasonic reflection means

Claims (5)

In a parametric speaker (1) that emits ultrasonic waves obtained by ultrasonically modulating an audible sound signal,
An ultrasonic speaker (3) for generating ultrasonic waves in the parametric speaker (1) absorbs sound waves in the audible band and the audible sound generating piezoelectric speaker (2) in which the primary resonance portion exists in the audible band. An audible sound absorption filter (6) that transmits ultrasonic waves,
A parametric speaker characterized in that ultrasonic waves generated by the audible sound generating piezoelectric speaker (2) are emitted into the air through the audible sound absorbing filter (6). In a parametric speaker (1) that emits ultrasonic waves obtained by ultrasonically modulating an audible sound signal,
In this parametric speaker (1), an ultrasonic speaker (3) that generates ultrasonic waves transmits an audible sound wave in the audible band and an audible sound generating piezoelectric speaker (2) in which a primary resonance part is present in the audible band. An ultrasonic reflection means (7) for reflecting ultrasonic waves,
Irradiating the ultrasonic reflecting means (7) with ultrasonic waves generated by the audible sound generating piezoelectric speaker (2), and releasing the ultrasonic waves reflected by the ultrasonic reflecting means (7) into the air. Characteristic parametric speaker. Parametric speaker (1) according to claim 2,
The ultrasonic reflection means (7) is a parametric speaker characterized in that it is a thin cloth film that is stretched in a state where tension is applied, and is woven with the eyes closed. Parametric speaker (1) according to claim 2 or claim 3,
The said ultrasonic speaker (3) is provided with the permeation | transmission sound control means which performs at least one of the sound absorption or reflection of a sound wave in the site | part which the sound wave which permeate | transmitted the said ultrasonic reflection means (7) hits, The parametric speaker characterized by the above-mentioned. In the parametric speaker (1) according to any one of claims 1 to 4,
The parametric speaker (1) is a parametric speaker that is used in a vehicle presence notification device that generates a notification sound outside a vehicle to notify the presence of the vehicle.

Images