JP6752427B2 - Parametric speaker - Google Patents

Description

The present invention relates to a drip-proof parametric speaker that uses ultrasonic waves as a carrier wave, which can reduce costs while maintaining good sound quality and sound pressure.

A device that realizes audible sound with narrow directivity by arranging multiple independent ultrasonic speakers and emitting modulated ultrasonic waves from each ultrasonic speaker is called a parametric speaker, and is called a parametric speaker in a specific area such as a museum or outdoors. It is used to convey announcement information to speakers.
Further, in recent years, it is considered that the quietness of hybrid vehicles and electric vehicles has increased, and it is difficult for visually impaired people among pedestrians to notice even if these vehicles are in close proximity, and the risk of accidents increases.
In response to this problem, it is being studied to make an artificial engine sound when driving a highly quiet vehicle, and research on a parametric speaker that transmits the sound only to a specific target is expanding.
FIG. 1 shows a schematic view of a conventional ultrasonic sensor constituting a sounding body called an open ultrasonic sensor used for a large number of conventional parametric speakers arranged in an array.
Conventionally, in order to vibrate an ultrasonic speaker at a resonance frequency of around 40 kHz in the ultrasonic band, a unimorph oscillator in which a piezoelectric element 3 is bonded to a vibrating plate 2 made of a nickel alloy or an aluminum alloy having a high flexural modulus is used. We are using.
A cone-shaped resonator 1 made of an aluminum alloy is adhered to the opposite side of the surface of the diaphragm 3 to which the piezoelectric elements are attached.
A low-viscosity silicone resin is coated on the inside of the resonator 1 in order to finely adjust the resonance frequency.
The surface of the diaphragm 2 to which the piezoelectric element 3 is adhered is held in the resin mold 5 by using a high-viscosity silicone resin.
Lead wires 4 are soldered to the electrodes provided on both sides of the piezoelectric element 3, and one end of each lead wire 4 is soldered to an input / output terminal 6 provided on the resin mold 5.
By connecting the input / output terminal 6 to the drive circuit of the parametric speaker, it is possible to transmit the drive signal from the drive circuit to the unimorph oscillator and further to the cone the vibration generated from the unimorph.

Japanese Patent Application Laid-Open No. 60-167597 JP-A-62-296698

The ultrasonic speaker used for the conventional parametric speaker uses a unimorph oscillator composed of a piezoelectric element and a metal plate having a low vibration damping ability, and the unimorph oscillator is attached in a state of being exposed to the outside air. ..
When used outdoors, it is necessary to install it in a place where it is not directly exposed to rain or the like so that the electrodes of the piezoelectric element and the soldered lead wires are not short-circuited due to the adhesion of water droplets.
For this reason, it is difficult to mount a parametric speaker using a conventional open ultrasonic sensor on the outside of the vehicle body where water droplets cannot be avoided due to rain or car wash, and it is necessary to have a drip-proof structure.
In addition, since one parametric speaker is composed of tens to thousands of ultrasonic speakers, the number of parts and manpower related to the assembly of each ultrasonic speaker and the arrangement in the parametric speaker are increased, and the manufacturing cost is increased. Highness is also an issue.
The above-mentioned problem of manufacturing cost can be solved by reducing the number of parts and man-hours by using a diaphragm in which a plurality of piezoelectric elements are bonded on the same metal plate or resin plate.
As a solution to the drip-proof structure, it is conceivable to seal the surface of the diaphragm on which the piezoelectric element is arranged so as not to come into contact with the atmosphere, or to seal the diaphragm with a resin or the like. New challenges have arisen due to this.
When a plurality of piezoelectric elements are attached to a metal plate, unnecessary vibration is generated due to the vibrations of the vibrators consisting of the piezoelectric elements arranged via the metal plate and the vibrating portion interfering with each other, resulting in sound pressure and sound quality. Decreases.
Further, if the interval for adhering the piezoelectric elements is widened in order to suppress the interference, there is a problem that the directivity is widened and the sound pressure is lowered.
When a general resin having a flexural modulus of 20 GPa or less is used for the diaphragm, there has been a problem that the required sound pressure cannot be obtained when vibrating at the resonance frequency of the ultrasonic band.

In the invention of claim 1, the diaphragm used for the ultrasonic speaker is made of a resin material having a larger vibration damping than metal, so that the vibration insulation between the vibrators is improved and a complicated shape or configuration is not formed. But
By arranging multiple vibrating elements on the same vibrating plate, the sound pressure drop and the generation of unnecessary vibration due to the interference of each other's vibrations are suppressed, and the piezoelectric elements can be arranged more densely to increase the sound pressure, and as a parametric speaker. It is possible to increase the sound pressure of the demodulated sound and narrow the sound quality and directivity.
In addition, by setting the flexural modulus of the resin used for the vibrating plate to 24 GPa or more, the sound pressure is greatly reduced even if the resonance frequency of the unimorph oscillator is increased as compared with the conventional resin having a flexural modulus of 20 GPa or less. It is possible to realize a sounding body without any need.
Further, in the past, the same number of diaphragms required for the configuration of the parametric speaker was required as the number of unimorph structures, but in the present invention, the number of parts is reduced by providing a plurality of unimorph structures in one diaphragm.
Furthermore, by forming the individual unimorph oscillators in the same diaphragm, the man-hours for arranging them on the substrate can be reduced, so that the manufacturing cost can be suppressed.
By using a composite material with an epoxy resin containing silicon dioxide, carbon fiber, aluminum silicate filler and powder containing crystals as the main component, the flexural modulus can be increased compared to conventional epoxy resins, which is excellent. It is a resin that can be used to manufacture ultrasonic sensors and sounding bodies with excellent acoustic characteristics.
In the invention according to claim 2, by providing a horn integrated with the diaphragm on the back surface of the diaphragm, it is possible to sharpen the directivity of the parametric speaker and increase the sound pressure.

In the invention according to claim 3, by providing a concave shape on the back surface of the diaphragm, the focus of the ultrasonic wave emitted from the parametric speaker can be adjusted, so that the directivity of the parametric speaker is sharpened and the sound pressure is increased. It becomes possible.

In the invention according to claim 4, since the focus of the ultrasonic wave emitted from the parametric speaker can be adjusted by making the back surface of the diaphragm a curved surface, the directivity of the parametric speaker is sharpened and the sound pressure is increased. Is possible.

As described above, the present invention uses a resin having a high bending elasticity for the diaphragm of the parametric speaker, and by providing a plurality of unimorph vibrators on the diaphragm, low cost while maintaining sound pressure and directivity. Can provide a drip-proof parametric speaker.

Schematic cross-sectional view of a conventional ultrasonic speaker Schematic diagram of the parametric speaker according to the embodiment of the present invention. Resonance frequency and output voltage of speakers using diaphragms with different flexural modulus Transition of output voltage when the resonance frequency of a speaker using diaphragms with different flexural modulus is 40 kHz Schematic diagram of the parametric speaker according to the embodiment of the present invention. Schematic diagram of the parametric speaker according to the embodiment of the present invention. Schematic diagram of the parametric speaker according to the embodiment of the present invention. Schematic diagram of the parametric speaker according to the embodiment of the present invention.

FIG. 2 shows a schematic view of a parametric speaker according to an embodiment of the present invention.
The diaphragm 2 is a molded product using a thermosetting epoxy resin containing a metal filler.
The material used for the diaphragm 2 may be a thermosetting resin or a thermoplastic resin as long as the flexural modulus is 24 GPa or more, which is practically required, and carbon fiber or organic fiber is used as the filler. May be good.
The diaphragm 2 has a disk shape with an outer diameter of φ50 and a thickness of 6 mm, and has a honeycomb structure in which recesses 9 having a bottom portion of φ11 are provided at equal intervals on the surface 2a.
The φ10 piezoelectric element 3 having the folded electrode 7 and the electrode 8 is bonded to the inside of the bottom surface of the recess 9 with epoxy resin so that the opposite side of the surface of the piezoelectric element 3 having the electrode 8 is an adhesive surface, and is a unimorph oscillator. Is forming.
The folded electrode 7 and the electrode 8 are electrically connected to an external parametric speaker drive circuit by a cable.
When the pulse signal transmitted from the drive circuit is input to each piezoelectric element 3 via a cable, each unimorph oscillator vibrates and ultrasonic waves are emitted from the back surface 2b of the diaphragm.
The surface 2a side of the diaphragm 2 is sealed with a silicone resin as a waterproof measure so that a liquid such as water does not infiltrate and a short circuit occurs between the folded electrode 7 and the electrode 8.
As a waterproof measure, sealing with urethane resin or foamed resin may be used as long as the folded electrode 7 and the electrode 8 are hermetically sealed so as not to come into direct contact with the outside air.
In order to make the resonance frequencies of the unimorph oscillators equal, the thickness of the diaphragm 2 on the adhesive surface of the piezoelectric element 3 in the diaphragm 2 is made the same.
The thickness of the diaphragm 2 on the adhesive surface of the piezoelectric element 3 in the diaphragm 2 may be different when a plurality of piezoelectric elements 3 having different dimensions are used or when a plurality of different resonance frequencies are used. ..
FIG. 3 shows the sound pressure of the speaker when the flexural modulus of the diaphragm 2 is changed from 21 GPa to 26 GPa in the speaker shown in FIG. 2 when measured using a microphone installed at a position 1 m away from the speaker. It is a graph of the output voltage of.
The resonance frequency of a speaker made of a diaphragm 2 having the same bending elasticity is adjusted by changing the plate thickness of the adhesive portion of the piezoelectric element 3 in the diaphragm 2, and the resonance frequency is increased by increasing the plate thickness. be able to.
As is clear from FIG. 3, if the diaphragm 2 has the same flexural modulus, the output voltage decreases as the resonance frequency increases.
Further, if the diaphragms 2 have different flexural moduluses, a higher output voltage can be obtained even at a higher resonance frequency as the flexural modulus increases.
FIG. 4 is a graph in which the horizontal axis is the flexural modulus of the resin of the diaphragm 2 used for each speaker, and the vertical axis is the output voltage of each speaker at 40 kHz.
When using the resonance frequency region near 40 kHz as in the conventional speaker, the output voltage is practically required to be 1.5 mV or more.
As is clear from FIG. 4, by using a resin having a flexural modulus of 24 GPa or more having an output voltage of 1.5 mV or more, the effect desired by the present invention can be obtained.
In addition, by using the diaphragm 2 as a resin material, improvement in sound quality was observed by shortening the reverberation time, which was not initially expected.

FIG. 5 shows a schematic view of the parametric speaker according to the embodiment of the present invention.
The parametric speaker shown in FIG. 5 is the parametric speaker shown in the first embodiment in which a tubular horn 11 is provided on the back surface 2b of the diaphragm 2.
Each horn 11 is preferably provided on the opposite side of the recess 9 provided with the piezoelectric element 3 on the surface 2a of the diaphragm 2, and the spread of the sound wave emitted from the unimorph oscillator can be effectively suppressed to sharpen the directivity. ..
Therefore, the directivity of each unimorph oscillator in the diaphragm 2 becomes sharp, and the directivity of the parametric speaker can also be sharpened.
Further, the sharpening of the directivity means that the sound wave is converged, so that the sound pressure is also improved.

FIG. 6 shows a schematic view of the parametric speaker according to the embodiment of the present invention.
The parametric speaker shown in FIG. 6 has a concave shape 12 provided on the opposite side of the concave portion 9 provided with the piezoelectric element 3 on the surface 2a of the diaphragm 2 in the parametric speaker shown in the first embodiment. Since the sound wave emitted from each unimorph oscillator has a focal length depending on the concave shape 12, the directivity in the vicinity of the focal length can be sharpened as compared with the case without the concave shape 12. Therefore, the directivity of each unimorph oscillator in the diaphragm 2 near the focal length becomes sharp, and the directivity of the parametric speaker can also be sharpened.

FIG. 7 shows a schematic view of the parametric speaker according to the embodiment of the present invention.
The surface of the diaphragm 2 opposite to the bonded surface of the piezoelectric element is used as the ultrasonic wave emitting surface.
The parametric speaker shown in FIG. 7 has a concave shape 12 provided on the back surface 2b of the diaphragm 2 in the parametric speaker shown in the first embodiment, and the height of the ultrasonic wave emitting surface is changed at two or more places.
It is preferable that the height of the discharge surface is changed so as to be recessed toward the center of the diaphragm 2. As a result, the synthetic wave of the sound emitted from each unimorph oscillator in the diaphragm 2 has a focal length, and the directivity of the parametric speaker in the vicinity of the focal length can be sharpened.

FIG. 8 shows a schematic view of the parametric speaker according to the embodiment of the present invention.
In the parametric speaker shown in FIG. 8, the back surface 2b of the diaphragm 2 in the parametric speaker shown in the first embodiment has a concave curved surface 12.
As a result, as in the fourth embodiment, the synthetic wave of the sound emitted from each unimorph oscillator in the diaphragm 2 has a focal length, and the directivity of the parametric speaker in the vicinity of the focal length can be sharpened.

The present invention is not limited to the use of announcing to a local area, and can be applied to various fields in which a speaker that transmits sound is used.

1 Resonator 2 Diaphragm 2a Front surface of diaphragm 2b Back surface of diaphragm 3 Piezoelectric element 4 Lead wire 5 Resin mold 6 Input / output terminal 7 Folded electrode 8 Electrode 9 Concave 10 Convex 11 Horn 12 Concave shape

Claims (1)

In a parametric speaker that generates sound in the audible range by modulated ultrasonic waves, which consists of a speaker provided with two or more unimorph structures in which a piezoelectric element is fixed to a diaphragm and a circuit unit that controls the speaker.
A speaker characterized in that the diaphragm is provided with two or more recesses on the surface, and the material constituting the diaphragm is mainly an epoxy resin containing a filler so that the flexural modulus is 24 GPa or more.

Images