Piezoelectric acoustic component

Abstract

The present invention provides a piezoelectric acoustic component capable of making sounds of a plurality of scales in the frequency band of 1-3 kHz audible even in highly noisy settings. A piezoelectric acoustic component 1 has a case body 8 comprising: a lower-side case section 3 having a bottom wall section 3A; and an upper-side case section 5 joined to the lower-side case section 3. In the interior of the case body 8, a piezoelectric sounding element 11 is fixed so as to be capable of vibrating, and so as to divide the interior space into a forward air chamber AC and a rear air chamber PC. The case body is formed so that one or more secondary sound emission holes 7 emit sound in the same direction as the sound emission direction of one or more primary sound emission holes 6. The total opening area of the one or more primary sound emission holes and the total opening area of the one or more secondary sound emission holes are determined so that sound pressures of frequency characteristics in the frequency band of 1-3 kHz are 80 dB or more.

Description

Piezoelectric acoustic component

[0001] The present invention relates to a piezoelectric acoustic component in which a piezoelectric sound generation element is housed in a case provided with a sound emission hole, and a predetermined sound pressure or more can be obtained in a frequency band range of a plurality of musical scales in a frequency band of 1 kHz to 3 kHz.

[0002] In FIG. 7 of Japanese Patent No. 3436205 (Patent Document 1), a piezoelectric acoustic component is disclosed in which a piezoelectric vibrator having a piezoelectric element with a rectangular contour attached to a metal diaphragm with a rectangular contour is housed in a case with a sound emission hole. This piezoelectric acoustic component is a so-called piezoelectric speaker that can emit sound in a wide frequency range. The sound is in opposite phases on the front and back surfaces of the piezoelectric sound generation element of the piezoelectric acoustic component, canceling each other out. Therefore, generally, the rear air chamber is sealed to confine the sound from the back. A technique of enhancing the sound on the front surface by setting the resonance frequency of the rear air chamber as a resonance chamber to an appropriate value has been used for a long time as a bass-reflex method in a speaker system, and the same technique is also used in piezoelectric acoustic components. For example, Japanese Utility Model Laid-Open No. 62-66496 (Patent Document 2) proposes a piezoelectric buzzer that provides a sound emission hole in a bottom plate that closes the opening of the case body and uses the rear air chamber as a resonance chamber.

[0003] Japanese Patent No. 3436205 Japanese Utility Model Laid-Open No. 62-66496

[0004] In the piezoelectric acoustic component shown in Patent Document 1, although the usable frequency range is wide, the sound pressure is low. For example, it may not be audible in places with noise such as outdoors or inside an automobile. Also, like the piezoelectric buzzer shown in Patent Document 2, it is difficult to increase the sound pressure only by using the rear air chamber as a resonance chamber, and there is a limit to expanding the frequency range. Therefore, the piezoelectric acoustic components described in Patent Documents 1 and 2 may not be audible in places with noise such as outdoors or inside an automobile.

[0005] An object of the present invention is to provide a piezoelectric acoustic component that can make audible sounds of a plurality of musical scales in a frequency band of 1 kHz to 3 kHz even in a noisy place.

[0006] The present invention relates to a piezoelectric acoustic component comprising a piezoelectric sound-producing element and a case body that is vibrably fixed inside the piezoelectric sound-producing element so as to divide the resonance chamber into a front air chamber and a rear air chamber, the case body having one or more main sound-emitting holes communicating with the front air chamber and one or more sub-sound-emitting holes communicating with the rear air chamber. In the present invention, the case body is formed such that one or more sub-sound-emitting holes emit sound in the same direction as the sound-emitting direction of one or more main sound-emitting holes. The total opening area of ​​one or more main sound-emitting holes and the total opening area of ​​one or more sub-sound-emitting holes are determined so that the sound pressure of the frequency characteristics in the frequency band of 1 kHz to 3 kHz is 80 dB or more. The sound on the front and back of the piezoelectric sound-producing element of the piezoelectric acoustic component is in opposite phase and cancels out each other's sound. However, as in the present invention, if one or more secondary sound vents are formed to emit sound in the same direction as the sound vents from one or more main sound vents, the sound inside the rear chamber is reflected by the bottom wall of the rear chamber, and the phase of the sound emitted from one or more secondary sound vents becomes the same as the phase of the sound emitted from the main sound vents. Therefore, the sound emitted from one or more secondary sound vents is superimposed on the sound emitted from one or more main sound vents, increasing the sound pressure and expanding the frequency range. With the piezoelectric acoustic component of the present invention, by increasing the sound pressure to 80 dB or more in the frequency band of 1 kHz to 3 kHz, it is possible to provide a piezoelectric acoustic component that allows multiple musical notes to be heard even in noisy environments.

[0007] Furthermore, by making the total opening area of ​​one or more secondary sound vents larger than the total opening area of ​​one or more main sound vents, it is easy to broaden the frequency band with high sound pressure. It is also possible to broaden the frequency band with high sound pressure by adjusting other requirements.

[0008] Furthermore, the number and placement of one or more secondary sound holes, as well as the number and placement of one or more primary sound holes, are arbitrary.

[0009] Piezoelectric acoustic components using a rectangular metal diaphragm produce less unusable space (dead space) when mounted compared to piezoelectric acoustic components using circular or elliptical diaphragms, and therefore a certain demand is expected for products that utilize piezoelectric acoustic components. However, when using a rectangular metal diaphragm, it is difficult to obtain a sufficiently large sound pressure in a given frequency range. However, according to the present invention, even when using a rectangular metal diaphragm, it has been found that by appropriately setting the ratio of the total opening area of ​​one or more main sound emitting holes to the total opening area of ​​one or more sub-sound emitting holes, the sound pressure in the intermediate frequency range between the first and third resonant frequencies can be increased. Therefore, in a preferred embodiment of the present invention, a piezoelectric sound-producing element is used which comprises a rectangular diaphragm having a pair of opposing long sides and a pair of opposing short sides shorter than the long sides, and a piezoelectric element with a circular contour provided in the center of the diaphragm. In this case, in particular, a diaphragm is used in which the ratio L1 / W1 of the length of the long side L1 to the length of the short side W1 is set to fall within the range of 1.25 to 2.0.

[0010] When a sinusoidal signal is input as the input signal, the frequency characteristics obtained may be configured such that, within the frequency band of 1 kHz to 3 kHz, a first peak appears at the frequency closest to 1 kHz, a second peak appears at a frequency higher than the frequency at which the first peak appears, a third peak appears at a frequency higher than the second peak, and a fourth peak appears at a frequency higher than the third peak.

[0011] Specifically, for example, by changing the total volume of the main sound emitting port and the capacitance of the resonator, a first peak is made to appear at a frequency of around 1 kHz. Furthermore, by changing the total volume of the secondary sound emitting port and the capacitance of the resonator, a sound emitting port is set to appear at a frequency of around 2 kHz. Then, by setting the ratio L1 / W1 of the length of the long side L1 to the length of the short side W1 of the diaphragm of the piezoelectric sound-producing element to within the range of 1.25 to 2.0, a second peak is made to appear at a frequency of around 1.5 kHz, and a fourth peak is made to appear at a frequency of around 3 kHz. By setting L1 and W1 in this way, a sound pressure of 80 dB or more can be secured within the frequency band of 1 kHz to 3 kHz, thus achieving the performance that the market demands from piezoelectric acoustic components.

[0012] This is a perspective view of a piezoelectric acoustic component equipped with the piezoelectric sound-producing element of this embodiment. This is a bottom view of the embodiment of Figure 1 with the lower case portion, which constitutes the bottom wall portion, removed. This is a schematic longitudinal cross-sectional view of this embodiment. This figure shows the sound pressure and frequency characteristics of this embodiment. (A) is a perspective view of a conventional product, and (B) is a transverse cross-sectional view of a conventional product. This is a schematic longitudinal cross-sectional view of a conventional product. This figure is used to explain the broadbanding of the f-dB characteristics (CAE analysis) by utilizing case resonance (sound emission from the rear air chamber) when sound in the rear air chamber is emitted from the secondary sound emission port. This figure is used to explain the change in f-dB characteristics (CAE analysis) due to the difference in the design frequency of the sound emitted from the secondary sound emission port (rear sound). This figure shows the trend of change in frequency characteristics when the aspect ratio (L / W) of the piezoelectric sound-producing element is changed. Figures (a) through (c) of (A) through (C) show configurations where the number of secondary sound holes is set to two and the number of primary sound holes is changed. The waveform diagrams on the right side of these figures show the frequency characteristics of the corresponding configurations (a) through (c). Figures (a) through (c) of (A) through (C) show configurations where the number of primary sound holes is set to one and the number of secondary sound holes is changed. The waveform diagrams on the right side of these figures show the frequency characteristics of the corresponding configurations (a) through (c).

[0013] Hereinafter, embodiments of the piezoelectric acoustic component of the present invention will be described with reference to the drawings. Figure 1 shows a perspective view of the piezoelectric acoustic component 1 equipped with the piezoelectric sound-producing element of this embodiment, Figure 2 shows a bottom view of the embodiment of Figure 1 with the lower case portion 3 constituting the bottom wall portion removed, and Figure 3 shows a schematic vertical cross-sectional view of this embodiment.

[0014] The piezoelectric acoustic component 1 of this embodiment is a piezoelectric acoustic component used for applications such as generating an alarm with multiple pitches in noisy environments, such as inside an automobile. The piezoelectric acoustic component 1 comprises a case 9 having a case body 8 which includes a lower case portion 3 with a bottom wall portion 3A and an upper case portion 5 coupled to the lower case portion 3. As shown in Figure 3, a piezoelectric sound-producing element 11 is fixed inside the case body 8 so as to be vibrable, dividing the resonance chamber into a front air chamber AC and a rear air chamber PC.

[0015] The lower case portion 3 and the upper case portion 5 are each integrally molded from an insulating resin such as polypropylene, and the two are joined together with a silicone adhesive. In this embodiment, the lower case portion 3 constitutes the bottom wall portion 3A of the case body 8. The upper case portion 5 comprises a convex upper wall portion 51 with curves at the corners, a first half portion 53 having a first peripheral wall portion 52 extending from the peripheral edge of the upper wall portion 51, and a second half portion 54 provided integrally with the first half portion 53. One main sound vent 6 is formed in the upper wall portion 51. The second half portion 54 comprises a pair of extension portions 54A that extend in accordance with the lower portions of two recesses 53B located on both sides of the convex portion 53A of the first half portion 53. As shown in Figure 3, the pair of extension portions 54A are provided to expand the rear air chamber PC and form a pair of secondary sound vents 7. Furthermore, a pair of mounting portions 54C are integrally provided on the second circumferential wall portion 54B of the second half portion 54, which is formed by extending the first circumferential wall portion 52.

[0016] As shown in Figure 3, a piezoelectric sound-producing element 11 is fixed inside the upper case portion 5 so as to close the opening of the first half portion 53 of the upper case portion 5 and form a front air chamber AC. The piezoelectric sound-producing element 11 consists of a metal diaphragm 12 and a piezoelectric element 15 provided on at least one side of the diaphragm 12. The diaphragm 12 has a pair of opposing long sides 13A and a pair of opposing short sides 13B that are shorter in length than the long sides 13A. The piezoelectric element 15 is provided on the central region of the back surface of the diaphragm 12.

[0017] As shown in Figure 3, in this embodiment, the case body 8 is formed such that the two secondary sound vents 7 emit sound in the same direction as the sound venting direction of the one main sound vent 6. In this embodiment, when the case body 8 is viewed from above, the one main sound vent 6 is positioned to correspond to the vertex angle of an isosceles triangle, and the two secondary sound vents 7 are positioned to correspond to the two interior angles of the isosceles triangle. To realize the present invention, the sound venting direction of the secondary sound vents 7 should be the same as the sound venting direction of the main sound vent 6. The number and position of the one or more secondary sound vents 7, and the number and position of the one or more main sound vents 6 are arbitrary.

[0018] In this embodiment, the shape of the diaphragm 12 is determined such that the ratio L / W of the length L of the long side 13A to the length W of the short side 13B of the diaphragm 12 falls within the range of 1.25 to 2.0. Furthermore, in this embodiment, the total opening area of ​​the two secondary sound emitting holes 7 is larger than the total opening area of ​​the main sound emitting hole 6, and the sound pressure of the frequency response in the 1 kHz to 3 kHz frequency band is set to 80 dB or more. As a result, the frequency band with high sound pressure can be extended, making it possible to achieve a sound pressure of 80 dB or more in the 1 kHz to 3 kHz frequency band.

[0019] The sound from the front and back of the piezoelectric sound-producing element 11 is in opposite phase, causing them to cancel each other out. However, as in this embodiment, when the two secondary sound-emitting holes 7 are formed to emit sound in the same direction as the sound-emitting direction of the one main sound-emitting hole 6, the sound inside the rear air chamber PC is reflected by the bottom wall 3A of the rear air chamber PC, and the phase of the sound emitted from the two secondary sound-emitting holes 7 becomes the same as the phase of the sound emitted from the main sound-emitting hole 6. Therefore, the sound emitted from the two secondary sound-emitting holes 7 is superimposed on the sound emitted from the one main sound-emitting hole 6, increasing the sound pressure and expanding the frequency band with high sound pressure. As a result, the piezoelectric acoustic component 1 of this embodiment can obtain a frequency band with high sound pressure, making it possible to provide a piezoelectric acoustic component that allows multiple musical scales to be heard even in noisy environments.

[0020] Figure 4 is used to illustrate the frequency response trend when the case body is formed so that the secondary sound vents emit sound in the same direction as the main sound vent. In Figure 4, frequency response curve F1 is the frequency response of this embodiment, and frequency response curve F2 is the frequency response of a typical conventional piezoelectric acoustic component called a piezoelectric buzzer, as shown in Figures 5(A) and (B) and Figure 6. In Figures 5(A) and (B) and Figure 6, components similar to those of the piezoelectric acoustic component of this embodiment shown in Figures 1 to 3 are denoted by the same reference numerals as those shown in Figures 1 to 3, with a dash added. As is clear from Figure 4, by having the secondary sound vent 7 emit sound in the same direction as the main sound vent 6, the frequency band with high sound pressure can be widened.

[0021] Figure 7 shows the trend of broadening the f-dB characteristics (CAE analysis) by utilizing case resonance (sound emission from the rear air chamber) when sound from the rear air chamber is emitted from the secondary sound emission port, as in this embodiment. In Figure 7, "diaphragm alone" refers to the frequency characteristics when sound is emitted using only a piezoelectric sound-producing element equipped with a so-called rectangular metal diaphragm without using a case; "resonance (front sound only)" refers to the frequency characteristics when sound is emitted using only the main sound emission port without using the secondary sound emission port, although the case is used; and "resonance (front sound + rear sound)" refers to the frequency characteristics when the main sound emission port and secondary sound emission port are used, as in the above embodiment. From Figure 7, it can be seen that by designing case resonance not only for the first and third resonances of the rectangular diaphragm and the case resonance of sound emission from the main sound emission port of the front air chamber (diaphragm front sound), but also for sound emission from the secondary sound emission port from the rear air chamber (diaphragm rear sound), it is possible to secure sound pressure on the low-frequency side and broaden the f-dB characteristics.

[0022] Figure 8 shows the change in f-dB characteristics (CAE analysis) due to the difference in the design frequency of the sound emitted from the secondary sound holes (rear sound). In Figure 8, "Resonance (front) 2kHz + Resonance (rear) 0.5kHz" refers to the frequency characteristics when the frequency of the sound emitted from the main sound hole is 2kHz and the frequency of the sound emitted from the secondary sound hole is 0.5kHz. Also, "Resonance (front) 2kHz + Resonance (rear) 0.75kHz" refers to the frequency characteristics when the frequency of the sound emitted from the main sound hole is 2kHz and the frequency of the sound emitted from the secondary sound hole is 0.75kHz. Furthermore, "Resonance (front) 2kHz + Resonance (rear) 1.0kHz" refers to the frequency characteristics when the frequency of the sound emitted from the main sound hole is 2kHz and the frequency of the sound emitted from the secondary sound hole is 1.0kHz. Figure 8 shows that the resonant frequency of the rear sound emitted from the secondary sound outlet can be adjusted by the case design, and that higher sound pressure can be secured in the resonant frequency band.

[0023] The following describes a specific example. Figure 9 shows that the volume of the pre-chamber AC is 12 cm³. 3 The volume of the rear air chamber PC is 4 cm 3 The total opening area of ​​the main sound vents 6 is set to 28 mm². 2The depth dimension is set to 2 mm, and the total opening area of ​​the secondary sound vents 7 is 48 mm². 2 This figure shows the results of a simulation of the frequency characteristics when the aspect ratio (L / W) of the piezoelectric sound-producing element is changed, using a calculation formula based on the calculation formula for the resonance frequency of a Helmholtz resonator, when a case body with a depth dimension of 2 mm is used.

[0024] Figure 9 shows the frequency characteristics of a piezoelectric sound-producing element, which has a rectangular diaphragm with a pair of opposing long sides (length L) and a pair of opposing short sides (width W) shorter than the long sides, and a piezoelectric element with a circular outline in the center, when the aspect ratio (L / W) is changed. As shown in Figure 9, when the aspect ratio is greater than 2 (for example, an aspect ratio of 2.24), the sound pressure becomes less than 80 dB at frequencies of 1.1 to 1.2 kHz. When the aspect ratio is less than 1.25, the sound pressure becomes less than 80 dB at frequencies of 2.8 to 3 kHz. Note that the characteristics in Figure 9 are an example using a piezoelectric sound-producing element with a known diaphragm and piezoelectric element, as shown in Patent Document 1, but this specification may change depending on the material of the diaphragm and the performance of the piezoelectric element.

[0025] Although it is also possible to describe this using the total volume of the main sound vent 6 and the total volume of the secondary sound vent 7, since the depth dimension is constant, in this embodiment, the characteristics will be described as being adjusted by the total opening area of ​​the main sound vent 6 and the total opening area of ​​the secondary sound vent 7. In the frequency characteristics shown in Figure 9, and also in the frequency characteristics shown in Figures 10 and 11 which will be described later, in the frequency band of 1 kHz to 3 kHz obtained when a sine wave signal is input as the input signal, a first peak appears at the frequency closest to 1 kHz, a second peak appears at a frequency higher than the frequency at which the first peak appears, a third peak appears at a frequency higher than the second peak, and a fourth peak appears at a frequency higher than the third peak. In this embodiment, in order to specifically obtain a desirable frequency characteristic, the total volume of the main sound vent and the capacitance of the resonator are changed so that a first peak appears at a frequency around 1 kHz, and further, the total volume of the secondary sound vent and the capacitance of the resonator are changed so that a third peak appears at a frequency around 2 kHz. Furthermore, by setting the ratio L1 / W1 of the length of the long side L1 to the length of the short side W1 of the diaphragm of the piezoelectric sound-producing element to within the range of 1.25 to 2.0, the second peak appears at a frequency of around 1.5 kHz, and by setting L1 and W1 so that the fourth peak appears at a frequency of around 3 kHz, a sound pressure of 80 dB or more can be secured within the frequency band of 1 kHz to 3 kHz.

[0026] Figures 10 and 11 are diagrams illustrating examples to confirm the effects of embodiments of the present invention. Figures 10(A) to (C), (a) to (c), show configurations where the number of secondary sound vents is 2 and the number of main sound vents is varied. The waveform diagrams on the right side of these figures show the frequency characteristics of the corresponding configurations (a) to (c). The dimensional conditions of the case body are the same as those used when simulating the frequency characteristics in Figure 9. The upper row of the diagrams (a) to (c) indicates the number of main sound vents and the number of secondary sound vents, and the lower row indicates the total opening area of ​​the main sound vents (in mm²). 2 ) and the total opening area of ​​the secondary sound holes (unit: mm) 2Figure 10 shows that the frequency characteristics change when the number of main sound vents and the total opening area are changed, while keeping the number of secondary sound vents and the total opening area constant. It can be seen that the desired sound pressure can be changed in a specific frequency band by changing the total opening area of ​​the main sound vents and the total opening area of ​​the secondary sound vents. In Figure 10, the combinations of (a) and (c) in (B) and (a) in (C) do not result in a sound pressure of 80 dB or more in the frequency band from 1 kHz to 3 kHz.

[0027] Furthermore, Figures 11(A) to (C), (a) to (c), show configurations where the number of secondary sound holes is varied, with the number of main sound holes set to one. The waveform diagrams on the right side of these figures show the frequency characteristics of the corresponding configurations (a) to (c). The upper row of the figures (a) to (c) indicates the number of main sound holes and the number of secondary sound holes, while the lower row indicates the total opening area of ​​the main sound holes (in mm²). 2 ) and the total opening area of ​​the secondary sound holes (unit: mm) 2 Figure 11 shows that the frequency characteristics change when the number of secondary sound vents and their total opening area are kept constant, and the desired sound pressure can be changed in a specific frequency band by changing the total opening area of ​​the main sound vents and the total opening area of ​​the secondary sound vents.

[0028] In Figures 10 and 11, the present invention is characterized in that, when a sinusoidal signal is input as an input signal, a first peak appears at the frequency closest to 1 kHz within the frequency band of 1 kHz to 3 kHz in the frequency range of 1 kHz, a second peak appears at a higher frequency than the frequency at which the first peak appears, a third peak appears at a higher frequency than the second peak, and a fourth peak appears at a higher frequency than the third peak. However, the present invention is not limited to those that obtain the frequency characteristics shown in the above embodiments.

[0029] According to the present invention, it is possible to provide a piezoelectric acoustic component that allows multiple musical notes in the frequency band of 1 kHz to 3 kHz to be heard even in noisy environments.

[0030] 1 Piezoelectric acoustic component 3 Lower case section 5 Upper case section 6 Main sound vent 7 Secondary sound vent 8 Case body 9 Case 11 Piezoelectric sound-producing element 12 Diaphragm 15 Piezoelectric element

Claims

1. A piezoelectric acoustic component comprising a piezoelectric sound-producing element and a case body in which the piezoelectric sound-producing element is fixed so as to be vibratable inside such that it divides a resonance chamber into a front air chamber and a rear air chamber, wherein one or more main sound-emitting holes communicating with the front air chamber and one or more sub-sound-emitting holes communicating with the rear air chamber are formed in the case body, wherein the case body is formed such that the one or more sub-sound-emitting holes emit sound in the same direction as the sound-emitting direction of the one or more main sound-emitting holes, and the total opening area of ​​the one or more main sound-emitting holes and the total opening area of ​​the one or more sub-sound-emitting holes are determined such that the sound pressure of the frequency characteristics in the frequency band of 1 kHz to 3 kHz is 80 dB or more.

2. The piezoelectric acoustic component according to claim 1, wherein the total opening area of ​​the one or more secondary sound emitting holes is greater than the total opening area of ​​the one or more main sound emitting holes.

3. The piezoelectric sound-producing element comprises a rectangular diaphragm having a pair of opposing long sides and a pair of opposing short sides shorter than the long sides, and a piezoelectric element with a circular contour provided in the center of the diaphragm, wherein the ratio L1 / W1 of the length of the long side to the length of the short side is set to fall within the range of 1.25 to 2.0, as described in claim 1 or 2.

4. The piezoelectric acoustic component according to claim 3, wherein, in the frequency characteristics obtained when a sinusoidal signal is input as an input signal, a first peak appears at the frequency closest to 1 kHz within the frequency band of 1 kHz to 3 kHz, a second peak appears at a frequency higher than the frequency at which the first peak appears, a third peak appears at a frequency higher than the second peak, and a fourth peak appears at a frequency higher than the third peak, and the second and third peaks are larger than the first and fourth peaks.

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