JP2007281669A - Speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a peak and a dip in a frequency characteristic caused in higher order vibration modes of the diaphragm of a speaker. <P>SOLUTION: An outer circumferential part of the circular diaphragm 1 is fixed to a frame 2. A disk shaped piezoelectric ceramic element 3 is adhered to in the center of a backside of the diaphragm 1. An outer circumferential end of a sub diaphragm 4 of a doughnut shape (ring disk) having a circular hole 6 in the center is concentrically joined to the center of the diaphragm 1 by a joining part 5 on a side opposite to the side of the diaphragm 1 to which the piezoelectric ceramic element 3 is adhered. Particularly the outer circumferential part of the circular sub diaphragm 4 is joined by a joining part 5 along a loop part between nodes in the vibration mode (secondary resonance mode) wherein two vibration nodes are concentrically formed to the center of the circular diaphragm 1 in the higher-order vibration modes of the circular diaphragm 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a speaker, and more particularly to a structure of a diaphragm used for a speaker.

  A conventional piezoelectric speaker is provided with a diaphragm having a piezoelectric material attached to the back surface of the center and a frame for fixing and supporting the outer periphery of the diaphragm, and the diaphragm performs a bending motion by expansion and contraction of the piezoelectric material. As a result, sound waves were emitted. Further, as the drive frequency increases, the vibration of the diaphragm changes from the fundamental vibration mode to the higher-order vibration mode, so that the diaphragm also vibrates in a complicated manner (see Patent Document 1). In the undulating vibration mode, sound cancellation occurred and a dip occurred in the frequency characteristics of the speaker. Here, the frequency characteristic (sound pressure frequency characteristic) represents what kind of sound pressure level is balanced in a frequency band from a low sound such as 20 Hz to a high sound such as 20 kHz. Further, in the frequency characteristics shown by a line graph or a bar graph, a portion where the sound pressure level of a certain frequency falls like a valley from the surroundings is called a dip, and a portion like a mountain peak is called a peak.

  FIG. 7 shows the configuration of a conventional piezoelectric speaker. FIG. 7A is a plan view of a conventional piezoelectric speaker, and FIG. 7B is a cross-sectional view taken along the line a-a ′ shown in FIG. As shown in FIG. 7, the outer peripheral portion of one circular diaphragm 1 is supported by a frame 2. A piezoelectric body 3 is attached to the center of the back surface of the diaphragm 1. Further, FIGS. 8A to 8D are schematic cross-sectional views showing an example of a higher-order vibration mode of the diaphragm 1 in the conventional piezoelectric speaker of FIG. In particular, in the present specification, among the higher-order vibration modes of the circular diaphragm whose periphery is fixed, the vibration mode in which the vibration node (the portion where the displacement is zero) can be concentrically formed with respect to the center of the circular diaphragm (two An example of the next resonance mode) is shown. In this vibration mode, as shown in FIG. 8A, when the diaphragm 1 is displaced upward, the sound pressure becomes higher than the atmospheric pressure. Therefore, if the polarity of the sound pressure at this time is positive, the diaphragm 1 The central part of the upper surface of the slab has a positive sound pressure and the peripheral part has a negative sound pressure. When the diaphragm 1 is displaced downward as shown in FIG. 8C through the state of FIG. 8B, the central portion of the upper surface of the diaphragm 1 has a negative sound pressure and the peripheral portion has a positive value. Of sound pressure. Therefore, in the vibration mode as shown in FIG. 8, air movement (indicated by an arrow in the figure) occurs from the positive sound pressure portion to the negative sound pressure portion, thereby canceling the sound (cancelling). Will occur. That is, in the high-order vibration mode of the circular diaphragm, the directions of displacement of the parts on both sides of the diaphragm at the boundary of vibration are opposite to each other, so that sound cancellation occurs. As a result, the sound pressure level drops at a frequency that causes higher-order mode vibration, and a dip appears in the frequency characteristics.

  In response to such problems, in the conventional technology, a vibration damping material for changing the vibration mode with respect to the higher-order vibration mode is added to the diaphragm, the shape of the diaphragm is changed, or resonance due to an acoustic load is applied. Point damping (vibration suppression) was performed.

In general, a dynamic speaker is used in which a main diaphragm and a sub diaphragm are joined to one voice coil. In this case, since the vibration modes of the respective diaphragms are different, the sound waves generated by the respective diaphragms interfere with each other, and peaks and dips occur in the frequency characteristics. In the prior art, the interference of sound waves has been reduced by adjusting the shape and size of each diaphragm.
JP 2000-201399 A (see FIG. 2, paragraph [0010])

  In a piezoelectric speaker with a conventional structure, if a damping material for changing the vibration mode relative to the higher-order vibration mode is added to the diaphragm, the mass of the vibration system may change, affecting the basic vibration mode. . Further, when the shape of the diaphragm is changed or the resonance point is dumped by an acoustic load, there are problems that affect the fundamental vibration mode and the overall frequency characteristics. For this reason, it has been difficult to suppress the occurrence of peaks and dips at specific frequencies in the frequency characteristics. Further, even though such a countermeasure can suppress the peak generated at the resonance point, it cannot suppress the occurrence of dip due to the cancellation of the sound.

  In view of the above-described problems, an object of the present invention is to provide a specific frequency (in particular, a frequency characteristic) in a speaker such as a piezoelectric speaker that vibrates a diaphragm using bending motion or a dynamic speaker that performs piston motion of the diaphragm. An object of the present invention is to provide a diaphragm structure that can suppress the occurrence of peaks and dips at a frequency that is a higher-order vibration mode.

  In order to achieve the above object, a speaker according to the present invention comprises a circular diaphragm having a fixed outer periphery, vibration means for vibrating the circular diaphragm, and a first member having an outer peripheral portion joined to one surface of the circular diaphragm. And a single ring-shaped sub diaphragm. The joint between the sub-diaphragm and the diaphragm is a high-order vibration mode of the circular diaphragm, and the antinode or node in the vibration mode in which the antinode or node of the vibration can be circular with respect to the center of the circular diaphragm. It is arranged along the part.

  According to such a configuration, the vibration of the fundamental vibration mode is not prevented by fixing the ring-shaped sub-diaphragm to the antinodes or nodes of the higher vibration mode of the circular diaphragm. Furthermore, by setting the sub diaphragm in this way, it is possible to suppress the movement of air that occurs on the circular diaphragm in the higher-order vibration mode from a portion higher than the atmospheric pressure to a lower portion. Thereby, in the frequency characteristic, it is possible to eliminate a dip that occurs at a specific frequency that becomes a higher-order mode.

  Further, in the above configuration, the diaphragm and the sub diaphragm perform a synchronized movement in the basic vibration mode and perform independent movements in the higher order vibration mode. Due to the independent movement of the higher-order vibration mode diaphragm and the sub-diaphragm, mutual interference of sound waves by the diaphragm and the sub-diaphragm having different vibration modes occurs, resulting in a peak or dip in the frequency characteristics. However, by adjusting the fixed position of the sub diaphragm and the hole size of the sub diaphragm at this time, the influence of mutual interference due to different vibration modes is adjusted, and the peak at a specific frequency in the frequency characteristics is adjusted. And the effect of controlling the dip. Moreover, the effect that a new sound wave is generated by the movement of air from the hole of the diaphragm is also obtained.

  As described above, according to the diaphragm used in the speaker of the present invention, it is possible to suppress the occurrence of a peak or dip at a specific frequency in frequency characteristics (particularly a frequency that becomes a higher-order vibration mode).

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1A is a plan view of a speaker as a first embodiment of the present invention. FIG.1 (b) is sectional drawing along the aa 'line of Fig.1 (a).

  Referring to FIGS. 1A and 1B, the outer periphery of a circular diaphragm 1 is fixed to a frame 2. The diaphragm 1 may be a metal foil plate such as SUS or a resin plate such as polycarbonate. A disc-shaped piezoelectric ceramic element 3 is attached to the center of the rear surface of the diaphragm 1. As the piezoelectric ceramic element 3, a monomorph type or bimorph type piezoelectric element can be used.

  On the side of the diaphragm 1 opposite to the surface on which the piezoelectric ceramic element 3 is attached, the outer peripheral end of the donut-shaped (ring-shaped disc) sub diaphragm 4 is connected to the center of the diaphragm 1 by the joint 5. Are concentrically joined. A circular hole 6 is formed in the center of the sub diaphragm 4. Such a diaphragm 1 and the sub diaphragm 4 constitute a composite diaphragm of the speaker of this example. The diaphragm 1 fixed to the frame 2 performs a bending motion by expansion and contraction due to voltage application of the piezoelectric ceramic element 3, thereby generating sound waves.

  In this embodiment, among the higher-order vibration modes of the circular diaphragm 1, the vibration nodes (secondary resonance modes) in which two vibration nodes can be concentrically formed with respect to the center of the circular diaphragm 1 Accordingly, the outer peripheral portion of the circular sub-diaphragm 4 is joined by the joint portion 5. The “node” refers to a portion where the displacement is zero in the vibration mode, and the “node” refers to a maximum displacement portion between the nodes.

  2A to 2C show the movement of the fundamental vibration mode (primary resonance mode) of the diaphragm 1 of FIG. 1 in a cross section taken along the line aa ′ of FIG. FIG. However, in FIGS. 2B and 2C, the piezoelectric ceramic element is omitted. When no voltage is applied to the piezoelectric ceramic element 3, the diaphragm 1 is stationary as shown in FIG. When a voltage is applied to the piezoelectric ceramic element 3, the diaphragm 1 is displaced upward as shown in FIG. Next, when a voltage of reverse polarity is applied to the piezoelectric ceramic element 3, the diaphragm 1 is displaced downward. As described above, in the basic vibration mode, the vibration node is only the outer peripheral portion of the diaphragm 1 fixed to the frame 2, and the diaphragm 1 becomes the vertical vibration in the form of FIGS. At this time, the sub diaphragm 4 vibrates in synchronization with the diaphragm 1 by the joint portion 5 of the sub diaphragm 4. As can be said in all the drawings, the part indicated by a plus sign in the figure is a part where the sound pressure is higher than the atmospheric pressure, and the part indicated by a minus sign is a part where the sound pressure is lower than the atmospheric pressure. .

  FIGS. 3A to 3D are schematic views illustrating an example of a higher-order vibration mode of the diaphragm 1 in FIG. 1 in a cross section taken along the line aa ′ in FIG. . In this example, an example of a vibration mode (secondary resonance mode) in which two vibration nodes can be concentrically formed with respect to the center of the circular diaphragm among the high-order vibration modes of the circular diaphragm having a fixed periphery. However, the piezoelectric ceramic element is omitted in FIG.

  In this higher-order vibration mode, as shown in FIG. 3A, when the central portion of the circular diaphragm 1 is displaced upward, the sub diaphragm 4 performs a motion synchronized with the diaphragm 1. Furthermore, while the circular diaphragm 1 passes through the shape of FIG. 3B and the center portion of the circular diaphragm 1 is displaced downward as shown in FIG. Exercise independent of This is because the outer peripheral portion of the circular sub-diaphragm 4 is joined to the antinode portion of the higher-order vibration mode of this example by the joint portion 5.

  In the state of FIG. 3C, the upper surface on the outer peripheral side of the sub diaphragm 4 is a positive sound pressure portion, and the space between the diaphragm 1 and the sub diaphragm 4 is a negative sound pressure portion with respect to the atmospheric pressure. . Due to this difference in atmospheric pressure, movement of air between the diaphragm 1 and the sub diaphragm 4 from the upper side of the sub diaphragm 4 through the hole 6 occurs. In the present invention, the amount of air movement can be controlled by adjusting the area of the hole 6 of the sub diaphragm 4. Therefore, if this amount of air movement is reduced, sound cancellation can be suppressed. That is, in the frequency characteristics, it is possible to reduce the dip generated at the frequency that becomes the secondary vibration mode.

  According to the present embodiment, the independent movement of the diaphragm 1 and the sub diaphragm 4 in the higher-order vibration mode causes mutual interference of sound waves by the diaphragm 1 and the sub diaphragm 4 in different vibration modes, and the frequency characteristics. Peak and dip occur. However, by adjusting the fixed position of the sub diaphragm 4 and the size of the hole 6 of the sub diaphragm 4 at this time, the influence of mutual interference due to the different vibration modes is adjusted, and at a specific frequency in the frequency characteristics. The effect of controlling the peak and dip is obtained. Moreover, the effect that a new sound wave is generated by the movement of air from the hole 6 of the diaphragm 1 is also obtained.

(Second embodiment)
FIGS. 4A to 4D are schematic cross-sectional views showing an example of the higher-order vibration mode of the circular diaphragm in the speaker as the second embodiment of the present invention. This example also shows an example of a vibration mode (secondary resonance mode) in which two vibration nodes can be concentrically formed with respect to the center of the circular diaphragm, among the higher-order vibration modes of the circular diaphragm whose periphery is fixed. . However, the piezoelectric ceramic element is omitted in FIG.

  The loudspeaker of this embodiment is obtained by joining the sub diaphragm 4 to both surfaces of the diaphragm 1 shown in FIG. The second embodiment is the same as the first embodiment except that the sub diaphragm 4 is provided on both surfaces of the diaphragm 1.

  In this higher order vibration mode, when the central portion of the circular diaphragm 1 is displaced upward as shown in FIG. 4A, the sub diaphragm 4 on the upper side of the diaphragm 1 moves in synchronization with the diaphragm 1. However, the lower sub diaphragm 4 moves independently of the diaphragm 1. Further, when the circular diaphragm 1 passes through the shape of FIG. 4B and the central portion of the circular diaphragm 1 is displaced downward as shown in FIG. 4C, the upper sub diaphragm 4 vibrates. The movement is independent of the board 1. At this time, the lower sub diaphragm 4 moves in synchronization with the diaphragm 1. Thus, in the second embodiment, by providing the sub diaphragm 4 on both surfaces of the diaphragm 1, cancellation of sound radiated from both surfaces of the diaphragm 1 can be suppressed. Therefore, the dip generated at the frequency at which the higher-order vibration mode is set can be further reduced as compared with the first embodiment.

  In the present embodiment, the sub diaphragms 4 respectively joined to both surfaces of the diaphragm 1 have the same shape and are set at the same fixed position. However, the diameter of each sub-diaphragm 4 on both surfaces of the diaphragm 1 and the position of the joint 5 may be different. In particular, the position of the antinode or node of the vibration that can be made concentrically differs for different higher-order vibration modes. For this reason, the fixing position of the joint portion 5 of the first sub diaphragm 4 with respect to one surface of the diaphragm 1 is set to the antinode portion of the secondary vibration mode of the diaphragm 1, and the other position of the diaphragm 1 is set. The fixed position of the joint portion 5 of the second sub-diaphragm 4 with respect to the surface is set to the antinode or node portion of the higher-order vibration mode other than the secondary mode of the diaphragm 1. If the sub diaphragm 4 is attached in this way, the effect of suppressing the occurrence of peaks and dip at each specific frequency in each higher-order vibration mode can be obtained. This modification can also be applied to the following third embodiment.

(Third embodiment)
FIGS. 5A to 5C are schematic cross-sectional views showing an example of the higher-order vibration mode of the circular diaphragm in the speaker as the third embodiment of the present invention. This example also shows an example of a vibration mode (secondary resonance mode) in which two vibration nodes can be concentrically formed with respect to the center of the circular diaphragm, among the higher-order vibration modes of the circular diaphragm whose periphery is fixed. . However, in FIGS. 5B and 5C, the piezoelectric ceramic element is omitted.

  The loudspeaker of this embodiment is one in which the hole 6 of the sub diaphragm 4 shown in FIG. It is the same as the first embodiment except that the braking cloth 7 is attached to the hole 6.

  The braking cloth 7 can control the movement of air passing through the hole 6 of the sub diaphragm 4 described with reference to FIG. For this reason, also in this embodiment, it becomes possible to suppress the occurrence of a dip at a frequency at which the higher-order vibration mode is set.

  In addition, since the braking cloth 7 applies braking to the movement of the diaphragm 1 and the sub diaphragm 4, there is also an effect of suppressing a peak generated at a resonance point of the vibration system.

  In addition, it is also possible to affix the braking cloth 7 to each hole 6 of the sub diaphragm 4 disposed on both surfaces of the diaphragm 1 as in the second embodiment.

(Fourth embodiment)
FIGS. 6A to 6C are schematic cross-sectional views showing the movement of an example of the higher-order vibration mode of the circular diaphragm in the speaker as the fourth embodiment of the present invention. This example also shows an example of a vibration mode (secondary resonance mode) in which two vibration nodes can be concentrically formed with respect to the center of the circular diaphragm, among the higher-order vibration modes of the circular diaphragm whose periphery is fixed. . However, the piezoelectric ceramic elements are omitted in FIGS.

  The speaker of this embodiment is obtained by changing the sub diaphragm 4 of the speaker shown in FIG. 1 from a ring type to a disk type. That is, no hole is formed in the center of the sub diaphragm 4. In addition, the space formed by joining the outer peripheral portion of the disk-shaped sub-diaphragm 4 to the diaphragm 1 by the joint portion 5 causes the sub-vibration of the diaphragm 1 by the vent hole 8 provided in the diaphragm 1. It communicates with the side opposite to the plate 4. That is, the vent hole 8 penetrates from the surface of the diaphragm 1 covered with the disk-shaped sub diaphragm 4 to the opposite side surface.

  Except that the sub diaphragm 4 is a disk type and the vent hole 8 is provided in the diaphragm 1, it is the same as the first embodiment.

  In the high-order vibration mode having such a configuration, as shown in FIGS. 6B and 6C, in the process in which the central portion of the diaphragm 1 is displaced downward, it is opposite to the sub diaphragm 4 of the diaphragm 1. From the surface side, air flows into the space between the diaphragm 1 and the sub diaphragm 4 via the vent hole 8 of the diaphragm 1. Although not shown, in the process in which the central portion of the diaphragm 1 is displaced upward, vibration is generated from the space between the diaphragm 1 and the sub diaphragm 4 via the vent hole 8 of the diaphragm 1. Air flows out to the surface of the plate 1 opposite to the sub diaphragm 4. That is, the movement of the higher vibration mode of the diaphragm 1 is not affected by the joining of the sub diaphragm 4.

  Further, in the state shown in FIG. 6C, since the entire surface of the sub diaphragm 4 is displaced upward from the state of FIG. 6B, the upper surface side of the sub diaphragm 4 becomes positive with respect to the atmospheric pressure. On the other hand, the side of the diaphragm 1 opposite to the sub diaphragm 4 is negative with respect to the atmospheric pressure. As described above, the upper side (speaker front side) of the diaphragm 1 in the secondary resonance mode has only a positive sound pressure portion, and an effect of canceling the sound pressure plus or minus on the upper surface side of the diaphragm 1 is obtained. . In other words, air movement occurs due to a change in air pressure that is distributed positively and negatively on the upper surface side of the vibration plate 1 in the higher-order vibration mode. This air movement is suppressed by the disk-shaped sub diaphragm 4. it can.

  In the basic vibration mode, the diaphragm 1 and the sub diaphragm 4 are synchronized with each other. Therefore, the sub diaphragm 4 is preferably made of a soft and stretchable material that does not interfere with the bending motion of the diaphragm 1.

  In each of the embodiments described above, an example is shown in which the outer peripheral end of the circular sub-diaphragm 4 is joined to the antinode portion of the vibration that can be formed into an annular shape in the secondary vibration mode of the circular diaphragm 1 whose periphery is fixed. It was. However, even if the outer peripheral end portion of the circular sub-diaphragm 5 is joined to the vibration node portion that can be made concentric in the secondary vibration mode of the circular diaphragm 1, the same effects as those of the embodiments can be obtained. it can.

  In each embodiment, the secondary resonance mode has been described as an example. However, even in the case of other different higher-order vibration modes (for example, the third-order resonance mode or the fourth-order resonance mode), If the outer peripheral end of the circular sub-diaphragm 4 is joined along the vibration antinode or node portion, it is possible to reduce the dip generated at the frequency at which the higher order vibration mode occurs.

  Further, the piezoelectric ceramic element 3 has been described as a vibration source. However, the sub diaphragm 4 used in the speaker of the present invention can be applied to a dynamic speaker using a voice coil as the vibration source. The same effect as in the case of the used piezoelectric speaker can be obtained.

It is the top view and sectional drawing which show the speaker by 1st embodiment of this invention. It is sectional drawing which shows a motion of the fundamental vibration mode of the diaphragm of the speaker by 1st embodiment of this invention. It is sectional drawing which shows a motion of the secondary vibration mode of the diaphragm of the speaker by 1st embodiment of this invention. It is sectional drawing which shows a motion of the secondary vibration mode of the diaphragm of the speaker by 2nd embodiment of this invention. It is sectional drawing which shows a motion of the secondary vibration mode of the diaphragm of the speaker by 3rd embodiment of this invention. It is sectional drawing which shows the motion of the secondary vibration mode of the diaphragm of the speaker by 4th embodiment of this invention. It is the top view and sectional drawing which show the piezoelectric speaker of a prior art example. It is sectional drawing which shows the motion of the secondary vibration mode of the diaphragm in the piezoelectric speaker of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diaphragm 2 Frame 3 Piezoelectric ceramic element 4 Sub diaphragm 5 Sub diaphragm joint 6 Sub diaphragm hole 7 Brake cloth 8 Diaphragm vent

Claims (5)

In a speaker having a circular diaphragm having a fixed outer periphery and vibration means for vibrating the circular diaphragm,
Among the higher-order vibration modes of the circular diaphragm, the outer peripheral portion is joined along the antinode or node portion in the vibration mode in which the vibration antinode or node appears in an annular shape with respect to the center of the circular diaphragm. A speaker further comprising a ring-shaped sub diaphragm.   The speaker according to claim 1, further comprising a second ring-shaped sub-diaphragm on a side opposite to a surface of the circular diaphragm on which the first ring-shaped sub-diaphragm is bonded.   The speaker according to claim 2, wherein an outer peripheral portion of the second ring-shaped sub-diaphragm is joined along an annular antinode or node portion in a higher-order vibration mode different from the vibration mode.   The speaker according to claim 1, further comprising a braking cloth that covers a hole formed in at least one of the first and second ring-shaped sub diaphragms.   A speaker in which a disk-shaped sub diaphragm is joined instead of the first ring-shaped sub diaphragm, and the circular diaphragm communicates with the opposite side surface from the surface on which the sub diaphragm is joined. The speaker according to claim 1, wherein the speaker has pores.

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