JP5806832B2 - Parametric speaker - Google Patents

Description

  The present invention relates to a parametric speaker that transmits acoustic information by providing directivity with ultrasonic waves.

  2. Description of the Related Art Conventionally, parametric speakers that transmit information in a specific direction or position using ultrasonic signals with strong directivity have been put into practical use. A parametric speaker is a device that utilizes a phenomenon in which a modulated ultrasonic signal having a relatively high sound pressure is self-demodulated into an audible sound by air nonlinearity. For example, Patent Document 1 proposes a parametric speaker that controls the demodulation distance to audible sound by changing the frequency of ultrasonic waves.

JP 2004-349817 A

  Such a parametric speaker is configured by arranging a plurality of ultrasonic generating elements in order to increase the directivity and sound pressure of ultrasonic waves. And in order to mutually raise the sound pressure of the ultrasonic wave which generate | occur | produces, it is necessary to vibrate each ultrasonic wave generation element with the same phase.

  However, since each ultrasonic wave generating element has a unique resonance frequency and each resonance frequency is different, for example, when the drive frequency is the same as the resonance frequency fb as shown in FIG. The phase of the sound wave generated from the ultrasonic wave generating element having fa is greatly different from the phase of the sound wave generated from the ultrasonic wave generating element having a higher resonance frequency fc.

  As a result, the sound wave generated by each of the ultrasonic wave generation element having the resonance frequency fa lower than the drive frequency and the ultrasonic wave generation element having the resonance frequency fc higher than the drive frequency cancels each other, so that a sufficient sound pressure cannot be obtained. . Further, as shown by the curve Q in FIG. 7, the phase moves greatly with respect to the frequency change near the resonance point where the curve P reaches the peak. Can not demonstrate.

  The present invention has been made in view of such circumstances, and provides a parametric speaker that prevents cancellation of sound waves generated by a plurality of ultrasonic wave generating elements and stably obtains sufficient sound pressure. With the goal.

  (1) In order to achieve the above object, a parametric speaker according to the present invention is a parametric speaker that transmits acoustic information by providing directivity with ultrasonic waves, and an oscillator that oscillates a signal at a predetermined frequency in an ultrasonic band. A modulator that modulates the oscillating signal with an audio signal, and a plurality of ultrasonic wave generating elements each of which has a resonance frequency that is higher or lower than the predetermined frequency and generates an ultrasonic wave based on the modulated signal It is characterized by providing these.

  As described above, in the parametric speaker of the present invention, each of the plurality of ultrasonic wave generating elements has a resonance frequency on one side of the high and low sides with respect to the predetermined drive frequency. Thereby, cancellation of the sound waves generated by the plurality of ultrasonic wave generating elements is prevented, and sufficient sound pressure can be obtained stably.

  (2) Further, the parametric speaker of the present invention is characterized in that each of the plurality of ultrasonic wave generating elements has a resonance frequency lower than the predetermined frequency. As a result, the heat generation of the ultrasonic wave generating elements can be suppressed more than when the plural ultrasonic wave generating elements have a resonance frequency higher than a predetermined frequency. Once heat generation occurs, the resonance frequency of the element shifts to a lower side, so that it is easy to prevent cancellation of sound waves. Further, by suppressing heat generation, the shift of the resonance frequency can be reduced, and an ultrasonic wave generating element having a resonance frequency closer to the drive frequency can be used.

  (3) Further, the parametric speaker of the present invention is characterized in that each of the plurality of ultrasonic generating elements has a resonance frequency lower than the predetermined frequency at −40 ° C. Thereby, cancellation of sound waves can be reliably prevented, and sufficient sound pressure can be obtained stably.

  According to the present invention, cancellation of sound waves generated by a plurality of ultrasonic wave generating elements is prevented, and sufficient sound pressure can be stably obtained.

(A), (b) is the front view and side view which respectively show the parametric speaker of this invention. It is sectional drawing which shows an ultrasonic wave generation element. It is a block diagram which shows the electric constitution of the parametric speaker of this invention. It is a graph which shows the relationship of the amplitude with respect to the frequency of an ultrasonic wave generation element. It is a graph which shows the characteristic with respect to the frequency of an ultrasonic wave generation element. It is a graph which shows the relationship of the amplitude with respect to the frequency of an ultrasonic wave generation element. It is a graph which shows the characteristic with respect to the frequency of an ultrasonic wave generation element.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Configuration of parametric speaker)
FIGS. 1A and 1B are a front view and a side view showing the parametric speaker 100, respectively. The parametric speaker 100 generates an ultrasonic wave modulated with a strong sound pressure and causes an audible sound to appear due to nonlinear characteristics when the ultrasonic wave propagates through the air. In this way, it is possible to specify the direction and distance and give directivity to convey acoustic information. As shown in FIG. 1, the parametric speaker 100 is configured by providing a plurality of ultrasonic wave generating elements 110 on a substrate 120. The ultrasonic wave generation element 110 generates an ultrasonic wave based on the modulation signal. The substrate 120 fixes and supports the ultrasonic wave generating element 110. In addition, in FIG. 1, the external appearance structure is shown and the electrical configuration is omitted.

(Configuration of ultrasonic generator)
FIG. 2 is a cross-sectional view showing the ultrasonic wave generating element 110. The ultrasonic generation element 110 includes a metal plate 111, a piezoelectric element 112, lead wires 113 and 114, a parabolic body 115, and a support body 118. The metal plate 111 is formed in a disk shape from a metal such as brass, 42 alloy, SUS304, or aluminum.

  The piezoelectric element 112 is formed in a disc shape, and is installed by being bonded to one main surface of the metal plate 111. The other main surface of the metal plate 111 is a vibration surface, and the piezoelectric element 112 can transmit and receive ultrasonic waves by the parabolic body 115 via the vibration surface. Electrodes are formed on both main surfaces of the piezoelectric element 112, and the piezoelectric body of the main body is polarized. The resonance frequency of the ultrasonic generator 110 varies depending on the shape, Young's modulus, weight, and other characteristics of the vibrating portion of the ultrasonic generator 110, that is, the shape, weight, and material of the metal plate 111, the piezoelectric element 112, and the parabolic body 115. To do. The ultrasonic generator 110 is designed in advance to have a constant resonance frequency.

  Such a design is such that any ultrasonic wave generation element 110 has a resonance frequency on one side of high and low with respect to a predetermined driving frequency. That is, the resonance frequency of all the ultrasonic generation elements 110 is higher than the drive frequency, or otherwise, the resonance frequency of all the ultrasonic generation elements 110 is lower than the drive frequency. As a result, cancellation of sound waves generated by the plurality of ultrasonic wave generation elements 110 is prevented, and a sufficient sound pressure can be stably obtained.

  Furthermore, it is preferable that each of the plurality of ultrasonic generating elements 110 is designed to have a resonance frequency lower than a predetermined frequency. Thereby, the heat generation of the ultrasonic wave generation element 110 can be suppressed more than when the plurality of ultrasonic wave generation elements 110 have a resonance frequency higher than a predetermined frequency. Once heat generation occurs, the resonance frequency of the ultrasonic wave generating element 110 shifts to the lower side, and it is easy to prevent cancellation of sound waves. Further, by suppressing heat generation, the shift of the resonance frequency can be reduced, and the ultrasonic wave generation element 110 having a resonance frequency closer to the drive frequency can be used.

  Further, it is more preferable that the plurality of ultrasonic wave generating elements 110 have a resonance frequency lower than a predetermined frequency at −40 ° C. Thereby, cancellation of sound waves can be reliably prevented, and sufficient sound pressure can be obtained stably. Details of the design of the resonance frequency will be described later.

  The lead wires 113 and 114 are connected to a circuit on the substrate 120 so that voltage can be applied and detected. The lead wire 113 is connected to an electrode on the metal plate 111 side of the piezoelectric element 112 on one main surface side of the metal plate 111 via the metal plate 111. The lead wire 114 is connected to the electrode on the substrate 120 side of the piezoelectric element 112. With such a configuration, it is possible to transmit an electric signal to the piezoelectric element 112 and generate an ultrasonic wave.

  The parabolic body 115 is formed in a parabolic shape with metal, for example, and is fixed on the metal plate 111. By providing the parabolic body 115 on the metal plate 111, the sound pressure of the generated ultrasonic waves is increased. The parabolic body 115 is preferably formed of a light material such as aluminum or an aluminum-magnesium alloy.

  The support body 118 is provided at several places on the substrate 120 side of the piezoelectric element 112 and is formed of an elastic body such as silicon rubber, for example, and supports the ultrasonic wave generation element 110. The support body 118 is provided at the position of the vibration node of the substrate 120. Thereby, the vibration from the ultrasonic wave generation element 110 is prevented from being transmitted to the substrate 120. A hole is provided in the center of the arrangement location of the ultrasonic wave generating element 110 on the substrate 120, and the sound absorbing material 121 is filled in the hole. The sound absorbing material 121 is formed of a sponge-like material, and blocks sound transmitted from the ultrasonic wave generating element 110 to the back side thereof. The ultrasonic generator 110 is merely an example, and the present invention can be applied as long as the resonance frequency can be adjusted by design.

(Electric configuration of parametric speaker)
FIG. 3 is a block diagram showing an electrical configuration of the parametric speaker 100. As shown in FIG. 3, the parametric speaker 100 includes an oscillator 101, a modulator 102, an amplifier 105, and an ultrasonic wave generation element 110, and generates ultrasonic waves through these. The oscillator 101 oscillates a signal at a predetermined frequency in the ultrasonic band. The oscillated frequency is a driving frequency for driving the piezoelectric element 112 when an oscillation signal is transmitted to the ultrasonic wave generating element 110, and is determined in advance according to the use of the parametric speaker 100.

  The modulator 102 AM modulates the oscillation signal with the audio signal. The modulation may be DSB modulation, SSB modulation, or FM modulation instead of AM modulation. The amplifier 105 amplifies the modulated oscillation signal and outputs it to the ultrasonic wave generation element 110. The ultrasonic wave generation element 110 converts the amplified oscillation signal into a sound wave.

(Operation of parametric speaker)
The parametric speaker 100 configured as described above oscillates a signal having a frequency in the ultrasonic band, modulates the oscillation signal with a desired audio signal, amplifies the modulation signal, and converts it into a sound wave with the ultrasonic wave generation element 110. Then radiate. In this way, ultrasonic waves with high directivity can be emitted. In this way, for example, guidance can be selectively sent to a person in a narrow area, so that it can be used for art museums, aquariums, museums, amusement facilities, and the like. In the future, it can also be used for traffic information.

(Resonance frequency design)
FIG. 4 is a graph showing the relationship of the amplitude with respect to the frequency of the ultrasonic generator 110. As shown in FIG. 4, the ultrasonic generator 110 is designed so that the driving frequency is slightly higher than the highest resonance frequency. With such a design, it is possible to prevent the ultrasonic waves generated from each of the ultrasonic generation elements 110 from having the same phase and cancel each other. For example, as shown in FIG. 4, when the parametric speaker 100 is configured by arranging the ultrasonic generation elements 110 having the resonance frequencies of f ₁ , f ₂ , and f ₃ , when f ₁ <f ₂ <f ₃ , f ₃ is designed ultrasonic generating element 110 so as to slightly lower than the drive frequency.

  The lower frequency with respect to the drive frequency is mainly determined by the temperature fluctuation of the ultrasonic wave generation element 110. In general, it is known that the resonance frequency of each ultrasonic wave generation element 110 decreases as the temperature of the ultrasonic wave generation element 110 increases. For example, an on-board environmental temperature (−40 ° C. to 85 ° C.) is considered. In this case, it is a guideline that even if the resonance frequency fc becomes −40 ° C., it does not become higher than the drive frequency.

  FIG. 5 is a graph showing characteristics of the ultrasonic generator 110 with respect to frequency. As shown by the curve R in FIG. 5, when the ultrasonic generator 110 is designed so that the resonance frequency is higher than the drive frequency, heat is generated compared to the case where the resonance frequency is designed to be shifted to the lower level. It tends to grow. Therefore, designing the resonance frequency lower has the effect of suppressing heat generation. Furthermore, once the heat generation occurs, the resonance frequency of the ultrasonic wave generating element 110 shifts to the lower side. In this sense, driving at a higher frequency than the resonance frequency can reduce the heat generation and reduce the shift of the resonance frequency. be able to. In addition, there is an effect that a drive frequency closer to the resonance frequency can be set.

DESCRIPTION OF SYMBOLS 100 Parametric speaker 101 Oscillator 102 Modulator 105 Amplifier 110 Ultrasonic wave generation element 111 Metal plate 112 Piezoelectric element 113, 114 Lead wire 115 Parabolic body 118 Support body 120 Substrate 121 Sound absorbing material

Claims (1)

An in- vehicle parametric speaker that conveys acoustic information by providing directivity with ultrasonic waves,
An oscillator that oscillates a signal at a predetermined frequency in the ultrasonic band;
A modulator that outputs a modulation signal obtained by modulating the oscillation signal with an audio signal;
Each has a resonance frequency on one side of high and low with respect to the predetermined frequency, and includes a plurality of ultrasonic wave generating elements that generate ultrasonic waves based on the modulation signal ,
The parametric speaker, wherein each of the plurality of ultrasonic generating elements has a resonance frequency lower than the predetermined frequency at −40 ° C.

Images