JP2020053970A - Method of manufacturing piezoelectric speaker - Google Patents

Abstract

To provide a speaker for emitting a clear and easy-to-hear guidance sound even in noises.SOLUTION: In a speaker device 11, in a middle of a surface layer member such as a metal foil having a different coefficient of thermal expansion from a honeycomb core, a sheet adhesive is inserted, and a honeycomb vibration plate 3 is formed by a hot press. After cooling, at least two ceramic piezoelectric elements 1 are placed on a honeycomb diaphragm in which stress due to a difference in a heat shrinkage rate remains. A vibration center axis is fixed to the honeycomb vibration plate 3 by resin bolts and nuts 2. A surface vibration and a bending vibration of the piezoelectric elements are transmitted to the vibration plate to generate a sound.SELECTED DRAWING: Figure 1

Description

Detailed description of the invention

  The present invention is a large station premises where various noises are mixed, a construction site where loud noise is generated, a pachinko ball stadium, and from a drone flying over the sky, on the ground without being eliminated by noise such as drone wind noise, The present invention relates to a piezoelectric speaker capable of transmitting clear and easy-to-hear human voice.

  2. Description of the Related Art Conventionally, in order to overcome noise and transmit sound in a loud noise environment, a method of increasing sound pressure by using a speaker having a large wattage (W) or a method of increasing the number of speakers to be installed and increasing the volume In addition, there is a method of attaching a hood to the speaker to increase the directivity. There is also a method of electronically adjusting the frequency of a sound by an equalizer to make it easier to hear in noise.

  However, in a commonly used dynamic type (conductive type) speaker, if a large current is suddenly applied to the voice coil to increase the sound pressure, deformation of the speaker cone due to acceleration or a magnet forming the voice coil may occur. Due to the inertia due to the weight of the metal parts and metal parts, a delay occurs in the reversal of the speaker cone, and a phenomenon that the sound becomes ambiguous with a decrease in response also occurs. These phenomena have the advantage of providing a smooth and comfortable effect when the sound is music, but in the transmission of human voice, there is a problem that the voice content is unclear and difficult to hear.

  One prominent example is that even if loud sounds are emitted from large-scale disaster prevention wireless speakers installed in each municipality for disaster prevention measures so that the guidance sound reaches far away, the sound is vague and difficult to hear. Have been done. In addition, the disaster prevention wireless speaker has a problem that the disaster prevention guidance sound is turned off by natural environment noises such as wind and rain and waves, making it difficult to hear.

  By installing an equalizer and electronically enhancing the mid-high frequency range, the ease of listening can be slightly improved, but as mentioned above, the response of the cone diaphragm of the dynamic speaker is slow and the sound Since there is a fundamental problem that the decay time is long, the effect of overcoming noise and making it easier to hear cannot be expected.

Patent No. 5888294

  The present invention has a problem that it is difficult to hear a person's guidance sound in a large station premises where various noises are mixed, an outdoor construction site where a loud noise is generated, and a pachinko hall where a loud noise is generated due to a ball flow or a collision. In addition, when watching a TV drama or the like, since the background music and sound effects are loud, especially those who have difficulty in hearing the high frequency range due to aging cannot hear the contents of the dialogue and cannot enjoy the program sufficiently. Can be solved.

  In recent years, in disaster countermeasures, a method of mounting a dynamic type speaker on a drone has been studied in order to convey disaster prevention warning guidance voices from the sky to a wide area, but the influence of wind noise and motor noise of propellers of flying drones has been studied. As a result, the problem that the warning sound is not clearly transmitted to people on the ground can be solved by the piezoelectric speaker.

  The present invention provides (1) a method of disposing a vibration center axis of a piezoelectric element at the center of a honeycomb structure having a sandwich structure in which sheet surface members are joined to both main surfaces of a honeycomb core, and / or Arranging the vibration center axes of at least two circular piezoelectric elements at positions where the vibration center axes of the piezoelectric elements are arranged on concentric circles whose diameter is 1.2 to 2.4 times the diameter of the element. A piezoelectric speaker characterized by: "

  And (2) "the diaphragm has a honeycomb structure, a hot melt adhesive sheet is inserted between a honeycomb core and an aluminum foil sheet, and the two sheets are joined by hot press molding. 2. The piezoelectric speaker according to claim 1, wherein a stress remains on the honeycomb diaphragm due to a difference in thermal shrinkage.

  A piezoelectric speaker is a device in which a piezoelectric element is mounted on a thin and lightweight diaphragm, and the diaphragm is resonated by its surface vibration to emit sound. The present invention adjusts the mounting position of the vibration center axis of the piezoelectric element attached to the diaphragm and the number of piezoelectric elements together with the physical characteristics such as the bending rigidity and the density of the diaphragm so that individual peaks of the frequencies in the mid-high range can be adjusted. Increasing the number of waveforms and their peak heights to generate multiple peak waveforms that exceed the frequency waveform of the noise, and strengthening the mid-high pitches where there are many consonants in the speech of human words, Clarify the audio content of the words. In addition to the good responsiveness of the piezoelectric element, an effect that is easy to hear even in noise is provided. Furthermore, in a piezoelectric speaker with a ceramic piezoelectric element mounted on a sandwich-structured diaphragm in which surface members are joined to both main surfaces of a honeycomb core, a honeycomb core molded from kraft paper or aramid sheet and a metal such as aluminum foil After inserting the sheet adhesive in the middle of the surface member such as foil or glass epoxy sheet with excellent strength, it is pasted on the honeycomb core with a heating press machine, and due to the difference in the heat shrinkage rate between the honeycomb core and the metal foil sheet generated during cooling By using a diaphragm with a built-in tensile stress, a higher sound pressure is generated, and a sound composed of a middle-high range can reach a distant place with little attenuation. In addition to the effect of the residual stress of the diaphragm, in an environment where various types of noises are mixed, the piezoelectric speaker of the present invention can exhibit distinctive features that are clear and easy to hear.

Piezoelectric speaker Honeycomb diaphragm Comparison of frequency characteristics with and without internal stress of honeycomb diaphragm Comparison of frequency characteristics by surface member of diaphragm Arrangement of piezoelectric elements on honeycomb diaphragm Frequency characteristics when the number of piezoelectric elements and the mounting position are changed (1) Square diaphragm Frequency characteristics when the number and mounting position of piezoelectric elements are changed (2) Circular diaphragm Frequency characteristics when the number and mounting position of piezoelectric elements are changed (3) Rectangular diaphragm Frequency characteristics when the number and the mounting position of the piezoelectric elements are changed (4) Arrangement other than claims Speech listening evaluation based on distance from speaker Comparison of frequency characteristics between dynamic type loudspeaker and piezoelectric speaker Drone for voice transmission equipped with piezoelectric speaker device Composite sound characteristics with drone sound and piezoelectric speaker sound (3 piezoelectric elements) Sound arrival measurement of a piezoelectric speaker from an altitude of 100m TV receiver that can output from both dynamic speakers and piezoelectric speakers

  An embodiment for carrying out the invention will be described with reference to the drawings and tables.

  FIG. 1 is an overall view of the piezoelectric speaker of the present invention. The center axis of vibration of the circular ceramic piezoelectric element 1 is fixed to the honeycomb vibration plate 3 by resin bolts and nuts 2, and the vibration plate transmits surface vibration and bending vibration of the piezoelectric element to generate sound. The outer periphery of the diaphragm is sandwiched between the upper vibration isolator 5 and the lower vibration isolator 4, and is attached to the speaker housing 10 by the guide member 7. The front surface of the speaker housing has a protective screen 6 and the rear surface has a cover 8 provided with a sound hole 9.

  FIG. 2 shows the structure of the honeycomb diaphragm of the present invention. The honeycomb structure has a sandwich structure in which a metal foil 3 (a) such as a thin film of aluminum is adhered as a sheet surface member to both surfaces of the honeycomb core 3 (b). In this aluminum foil honeycomb structure, a hot melt adhesive sheet was inserted between the aluminum foil and the honeycomb structure, and heated to about 130 ° C. to maintain uniform tension on both surfaces of a honeycomb core made of kraft paper. Compression bonding is performed while maintaining balance in the state. When this honeycomb structure is cooled to room temperature, a tensile stress is generated due to the difference in the heat shrinkage between the aluminum foil and the honeycomb core, and has a uniformly elongated surface with no internal stress remaining and no undulation or bending. Can be manufactured. In addition to the metal foil sheet, an epoxy resin sheet reinforced with glass fiber or carbon fiber can be used.

  Conventionally, as a method of leaving internal stress in a diaphragm, a method of mechanically applying a bending stress to the diaphragm to form a curved surface has been proposed. However, a pressure mechanism for bending to a curved surface is necessary, and the internal stress of a bent diaphragm is relaxed due to permanent strain over a long period of time, and the acoustic performance may change. The present invention has devised a method of manufacturing a flat honeycomb diaphragm in which stress remains in a flat state without bending the diaphragm.

  FIG. 3 is a comparison of frequency characteristics graphs of an aluminum foil honeycomb diaphragm having no built-in stress by bonding aluminum foil at room temperature and a speaker having an aluminum foil honeycomb diaphragm having built-in stress by thermal bonding. is there. A diaphragm having an internal stress in the diaphragm has a higher sound pressure over the entire sound range than in a case where there is no internal stress.

  FIG. 4 shows a speaker diaphragm having an aluminum foil (46 μm) and a glass epoxy sheet (50 μm) as a surface member, each of the surface members being heated in a bonding press process, and having a built-in stress during cooling. did. Comparing the frequency response graphs, all of them generate high sound pressure peaks, but the speaker with the diaphragm using aluminum foil has the characteristics of a metal film, the peak of the high range is high, and the mid-high sound is easy to output. Demonstrate.

  The technology that should be emphasized most in the present invention is to adjust the number of piezoelectric elements attached to the diaphragm and the position of the center axis of the vibration of the piezoelectric element to reduce the number of peaks and heights of the mid-high frequency band generated from the diaphragm. It is possible to increase or decrease.

  Generally, ceramic piezoelectric elements (drivers) are generally of a circular type having a diameter of 40 mm to 50 mm. In the present invention, a piezoelectric element having a bimorph structure with a diameter of 50 mm was used. It has a structure in which circular piezoelectric ceramics are arranged on both sides of a metal electrode plate. When a voltage is applied, a piezoelectric element having a diameter of 50 mm causes bending vibration together with the metal electrode plate due to expansion and contraction of the piezoelectric ceramics. The upper and lower surface vibrations are transmitted to the honeycomb diaphragm via the diaphragm, and the honeycomb diaphragm resonates to generate sound.

  FIG. 5 shows four types of patterns in which the number of piezoelectric elements and the mounting positions are changed on the honeycomb diaphragm. (1) is one at the center of the diaphragm, (2) is two on the circumference of 60 mm in diameter, 1.2 times the diameter of the 50 mm piezoelectric element, and (3) is three on the circumference of the same 60 mm. , {Circle around (4)} are patterns in which one piezoelectric element and two on the circumference of 120 mm which is 2.4 times the diameter of the piezoelectric element. Hereinafter, a frequency characteristic graph when the vibration center axis of the piezoelectric element is arranged on a square, circular, or rectangular diaphragm will be described.

FIG. 6 shows a frequency characteristic graph of speaker output sound when the piezoelectric elements having the above four patterns are arranged on a square (225 mm × 225 mm) diaphragm.
(1) shows a photograph and a characteristic graph of a speaker in which one piezoelectric element is attached to the center of the diaphragm. {Circle around (2)} is a photograph and a characteristic graph in which two are arranged on a circumference having a diameter of 60 mm. (3) is a photograph and three characteristic graphs arranged on a circumference of 60 mm in diameter. {Circle around (4)} is a photograph and characteristic graph in which one is disposed at the center of the diaphragm and two are disposed on a circumference having a diameter of 60 mm. Looking at these frequency characteristic graphs, the frequency characteristic graphs of (2), (3), and (4) have a larger number of peak waveforms in the mid-high range and a higher peak height than those of (1). It is high. This is presumably because the number of piezoelectric elements mounted on the diaphragm is increased and the mounting position is selected to increase the resonance of the mid-high frequency on the honeycomb diaphragm.

  FIG. 7 shows photographs and frequency characteristic graphs of five types of speakers in which the number of piezoelectric elements on the circular (diameter 300 mm) diaphragm and the arrangement of the vibration center axis are changed.

  FIG. 8 shows photographs and frequency characteristic graphs of five types of speakers in which the number of piezoelectric elements on a rectangular (180 mm × 260 mm) diaphragm and the pattern of the arrangement of the vibration center axis are changed.

  7 and 8, similarly to FIG. 6, the frequency characteristic graphs of (2), (3), (4), and (5) have a larger number of peaks in the entire sound range as compared with (1). This indicates that the peak height is high in the mid-high range. The following has been found from the results of FIGS.

  A distance of 1.2 to 2.4 times the diameter of the piezoelectric element from the center on the diaphragm is arranged on the concentric circle of the diameter, and the vibration center axes of two or more piezoelectric elements are arranged, or one at the center and one above. A piezoelectric speaker in which a total of two or more piezoelectric elements are arranged on a concentric circle indicates that the peak height and the number of peaks of the middle and high frequency range waveforms constituting the frequency of a human voice increase. Furthermore, it was shown that the phenomena observed in the peak waveforms in the middle and high frequency bands occur similarly irrespective of the shape and size of the speaker diaphragm, that is, square, rectangular, and circular.

  FIG. 9 shows "1. The vibration center axis of the piezoelectric element is arranged at the center of the honeycomb diaphragm, and / or 1.2 times to 2.4 times the diameter of the piezoelectric element from the center on the honeycomb diaphragm." The vibration center axes of at least two circular piezoelectric elements are arranged on a concentric circle having a diameter twice as long as the center axis of the vibration of the piezoelectric element. Is obtained by verifying a frequency characteristic graph in the case of performing. {Circle around (1)} when one piezoelectric element is arranged at the center and one outside the circumference of 120 mm in diameter, [2] when three piezoelectric elements are arranged outside the circumference of 120 mm in diameter, [3] Shows frequency characteristic graphs when one is disposed at the center and two are disposed outside the circumference having a diameter of 120 mm. In each case, the height of the peak waveform was low in the middle and high tone bands, and no clear and audible sound was generated.

  FIG. 10 shows a state in which the evaluation of hearing the guidance voice of a person from a speaker is performed in a pachinko hall in an environment where room noise is 90 dB.

Table 1 shows that listening was performed at a distance of 2 m and 6 m from a dynamic speaker and a piezoelectric speaker in which one piezoelectric element was disposed at the center and three piezoelectric speakers disposed at the apexes of an equilateral triangle in a concentric circle having a diameter of 60 mm to 120 mm. Here is a comparison of ease of use. As a result of the verification, it has been found that the piezoelectric speaker of the present invention is superior in audibility even in noise, as compared with the dynamic type speaker.

  FIG. 11 is a graph comparing frequency characteristics of sound from a dynamic type speaker and a piezoelectric speaker in a quiet and wide indoor environment. This shows that the piezoelectric speaker of the present invention has more and higher sound pressure peak waveforms in the mid-high range than the dynamic type speaker.

  FIG. 12 shows a drone for voice transmission. The drone body includes a main body control unit 12, a propeller 13, and a motor 14, and the piezoelectric speaker 11 is mounted downward. This piezoelectric speaker has a structure in which three piezoelectric elements are arranged on a circumference having a diameter of 60 mm.

  FIG. 13 shows the sound of a drone that is hovering (stopped in the air) at a height of 5 m above the ground, and a single sound of the drone caused by the rotation of a motor and the wind noise of a propeller. It shows the frequency characteristics of a composite sound when sound is played. In the graph, the waveform of the guidance sound of the piezoelectric speaker protrudes above the waveform of the drone single sound in the middle range and the high range. In low altitudes of 5 m to 10 m, noise due to the drone's single sound is transmitted, and the situation was not such that guidance voices from speakers were clearly transmitted.

  However, as the flight altitude of this voice transmission drone increases, the motor noise and the wind noise of the propeller are radiated in all directions, and gradually attenuate. In addition to the excellent directivity of the piezoelectric speaker and the characteristic that the distance attenuation of the sound, which is a characteristic of the flat diaphragm, is small, the guidance sound from the drone-equipped piezoelectric speaker flying at an altitude of 100 m is Demonstration tests confirmed that the aircraft reached the ground, overcoming the sound of the flight, and could clearly hear the audio content.

  FIG. 14 is a diagram showing a pattern in which a measurer on the ground changes the position of listening to the guidance sound from the drone 100 m above the sky.

Table 2 is a table showing the results of evaluation of the state of arrival and the listening and listening conditions of voices reaching the ground from a drone at an altitude of 100 m. From this table, the sound from the piezoelectric speaker in which three piezoelectric elements are arranged on a circumference of 60 mm in diameter and the piezoelectric speaker in which one is arranged at the center and two are arranged on a concentric circle with a diameter of 60 mm are directed by the speaker. It was found that within an angle of 30 degrees, it reached the ground and was strong and clearly audible.

  The piezoelectric speaker used in this demonstration test is a planar piezoelectric speaker having a housing size of 190 mm square × 30 mm thickness, a surface honeycomb material of 46 μm, a honeycomb thickness of 2.5 mm, and a paper honeycomb having a core size of 3.2 mm. It was used. The amplifier used a 4 W digital piezoelectric amplifier, and the speaker terminal voltage was 45 V. It was found that when the speaker terminal voltage was increased to 50 V or more, the sound pressure was further increased, and clear voice arrived from a drone flying at an altitude of 150 m or more.

  FIG. 15 shows a circuit in which a piezoelectric speaker is added to a dynamic speaker built in a TV receiver. The dynamic speaker 15 and the piezoelectric speaker 16 are independently provided with volume control adjustment output circuits 17 and 18 in parallel, respectively. It was confirmed that the lines of the actors in the drama were clear and easy to listen to. The reason for this is that in addition to the flat and mild sound of the dynamic speaker, the crispness of the vocal sound due to the short vibration attenuation of the diaphragm, which is a feature of the piezoelectric speaker, and the large sound pressure peak in the mid-high range, It is considered that the consonant part of the voice became clear. Especially for elderly people whose voice listening ability has decreased due to aging, the voice of TV drama can be heard clearly without losing to large background sounds such as music and sound effects, and the effect of enjoying TV viewing can be achieved. It was confirmed that it would bring.

Industrial applicability

  As described above, the piezoelectric speaker of the present invention can be used as a means of overcoming noise and transmitting human voices clearly in various types of noise, such as guide broadcasting in station premises, construction sites in severe noise, and pachinko halls. The present invention provides a simple and low-cost speaker that can be used in various fields, such as voice transmission in a satellite, transmission of a disaster prevention warning from a flying drone to the ground, and further, TV broadcasting in a home.

DESCRIPTION OF SYMBOLS 1 Ceramic piezoelectric element 2 Resin bolt and nut 3 Honeycomb diaphragm 3 (a) Aluminum foil 3 (b) Paper honeycomb 4 Lower vibration insulator 5 Upper vibration insulator 6 Protective screen 7 Press member 8 Cover 9 Sound hole 10 Speaker housing Body 11 Speaker device 12 Drone main body control unit 13 Propeller 14 Motor 15 Dynamic speaker 16 Piezoelectric speaker 17 Sound adjustment output circuit for dynamic speaker 18 Sound adjustment output circuit for piezoelectric speaker 19 Volume adjuster for dynamic speaker 20 Volume adjuster for piezoelectric speaker

Claims (2)

  A vibration center axis of the piezoelectric element is arranged at the center of a honeycomb structure having a sandwich structure in which sheet surface members are joined to both main surfaces of the honeycomb core, and / or a diameter of the piezoelectric element from the center on the honeycomb structure is 1.2 mm. A piezoelectric speaker, wherein the vibration center axes of at least two circular piezoelectric elements are arranged at positions where the vibration center axes of the piezoelectric elements are arranged on concentric circles whose diameters are twice to 2.4 times the distance.   The diaphragm has a honeycomb structure, a hot-melt adhesive sheet is inserted between the honeycomb core and the aluminum foil sheet, joined by hot press molding, and the difference in the heat shrinkage between the honeycomb core and the aluminum foil sheet during cooling. 2. The piezoelectric speaker according to claim 1, wherein a stress is left on the honeycomb diaphragm by the method.