JP2003504981A - Panel drive - Google Patents

Abstract

(57) [Summary] A loudspeaker is made up of a panel (1) that supports bending waves and a transducer (3) that covers a substantial part of the panel surface. At least one restraining means, such as a clamp or mass, is attached to the panel. Each restraint reduces the mobility of a small area of the panel. Excitation of the transducer excites a bending wave in the panel. The restraint prevents simple movement but encourages the generation of multiple bending waves. The restraining means can restrain the excitation panel and cause a good distribution of resonant bending wave modes.

Description

Detailed Description of the Invention

[0001]     (Technical field)   The present invention relates to a flexural wave panel speaker and a method for exciting the speaker.

BACKGROUND OF THE INVENTION WO 97/09842 by the applicant discloses a bending wave loudspeaker, which loudspeaker is shown in FIG. A flexural wave loudspeaker generally comprises a panel 1 having at least one transducer 3 coupled to the panel 1 at one or more segmented points or subregions. One or more positions of the transducer are selected to excite the distributed resonant bending wave mode and cause the panel to cause acoustic emission.

As taught by WO 97/09842, prior art arrangements with separate exciters have the disadvantage that in certain applications it may be difficult to place the exciter in the desired selected position. For example, a loudspeaker may need to be integrated into existing equipment, and the desired transducer position may not be achieved if another component gets in the way. Alternatively, in a transparent speaker using a transparent panel, it is very difficult to make a conventional exciter transparent, and it is difficult to place the exciter in a suitable position without obstructing the field of view. Therefore, it would be advantageous to eliminate the need to actually mount the exciter in the preferred location, and benefit from the selective exciter placement.

Applicant's WO 00/02417, published after the priority date of this application, describes various configurations using transparent loudspeakers and exciters coupled to the panel. Although no specific embodiment is disclosed, it is suggested that the exciter may comprise piezoelectric or electret material on the panel.

Another prior application describing a transparent flat panel speaker is Hitachi's G
There is B2052919. This application describes a transparent piezoelectric speaker with a layer of piezoelectric material on one side. The problem with this configuration, as described in GB2052919, is that the speaker can only operate over a narrow frequency band. In GB2052919, some improvement can be achieved by choosing an elliptical loudspeaker panel, but the result is still not noticeable, and the best result is to obtain acoustics other than a very narrow band from 1kHz to 3kHz. Almost no output is seen.

GB2052919 is a WO capable of exciting multiple modes at different frequencies.
Unlike 97/09842, it basically teaches that only one mode is excited. However, in order to obtain a good acoustic output over the frequency band using the resonant bending wave mode, the exciter needs to excite a large number of resonant modes distributed in frequency. Therefore, there is a need for improved performance in order for such speakers to be useful in any application other than the most basic.

DISCLOSURE OF THE INVENTION According to the first aspect of the present invention, a panel that can support a bending wave and that has opposing surfaces, and extends over a large area of the panel surface and is connected to the area. A transducer and at least one restraint means coupled to at least one subregion of the panel to restrain movement of the panel, the activation of the transducer material exciting a plurality of resonant bending wave modes of the panel. A flexural wave loudspeaker is provided.

Instead of placing the transducer in place, the transducer extends over an effective portion of the panel area and the panel is constrained in one or more constrained positions. Large area of the panel surface is at least 60%, preferably 75% of the panel area
Alternatively, it may be 90%. The larger the area, the larger the transducer,
As a result, a large output becomes possible. This is particularly useful when the transducer material, which is often found in piezoelectric materials, provides small movements per unit input.

The large area is preferably substantially the entire surface area of the panel, and each small area may be smaller than the panel area. Each small area may be less than 10% of the panel area, preferably less than 1%. Furthermore, each small area may have a linear size of less than 20% of the panel width, preferably less than 10%, and more preferably less than 4%. If the binding force is too large, it will be very difficult to bend the panel and driving will be very difficult. The panel may be a panel of material particularly suitable for supporting resonant bending waves in a given operating frequency band.

As mentioned above, Applicants believe that one problem that causes GB2052919 to produce unsatisfactory results is that piezoelectric exciters do not excite a good resonant bending wave mode distribution.

In the loudspeaker according to the present invention, by providing the local restraint means, the transducer extending over the panel surface can appropriately excite a plurality of resonant bending wave modes, that is, satisfactorily. A single sheet of transducer material may be provided that extends over a large area of one side of the panel and is connected to the panel surface. A transducer can be added to the opposite side of the panel, such as what is known as a so-called "bimorph" structure. The other transducer may include a sheet of transducer material that extends over a large area of the surface of the panel opposite the first transducer.

The bimorph structure offers many advantages. First, because the plate is sandwiched between two transducer sheets, the top sheet expands when the bottom sheet expands, rather than the linear stress applied to one side that occurs in a structure with only one transducer material sheet (so-called unimorph). Can be configured to contract and apply true flexural stress to the plate.

Further, the panel and the plurality of transducer sheets form an integral unit optimized as a unit to better distribute the resonant bending wave modes. The restraint means may be, for example, a mass that attaches to or is integrated into the panel on one side of the panel. The restraining means may also be a rigid connecting piece connected to the panel over a small area of the panel so as to substantially prevent movement of the small area.

The constraining positions can be selected such that the resonant bending wave modes of the constraining panel, particularly those below the operating frequency band, are conveniently spaced to obtain the desired acoustic effect. In practice, the constrained position and parameters can be selected to substantially optimize the acoustic output. The restraint position can be determined by mathematical or numerical methods, or by systematic experiments.

The restraint means can be placed in any suitable position for mounting a conventional miniature exciter on a free panel. Rather than driving the free panel in a separate position, the panel is driven over a large area of its surface and is "pinned" in a position that may be suitable for driving with a local transducer. In other words, the loudspeaker according to the invention with local restraints instead of local transducers is virtually the opposite of conventional distributed mode loudspeakers.

In an embodiment, the restraining means may be spaced from the edge, ie at least 20% of the panel width from the edge. Generally, width refers to the distance from one edge of the panel to the other in the direction orthogonal to the longitudinal direction of the panel. The restraint means may be arranged in an asymmetrical position. If the panel is symmetrically shaped with one or more axes of symmetry, the restraining means may be spaced from one or all axes of symmetry by at least 3%, preferably 5% of the panel width.

The restraint position is not always possible. Therefore, the restraint means may be arranged at the end of the panel, or at least less than 20% of the distance from the end to the entire panel. This is especially useful when the central area of the panel needs to be transparent.

Each sheet of transducer material may be sandwiched between a pair of electrodes to form a transducer film. The electrodes may be on either side of the transducer film and may be transparent. One suitable transparent electrode material is indium tin oxide.

The transducer film can be adhered to cover one or both sides of the panel surface. One of this pair of electrodes can cover a large area on one side of the panel,
The transducer material can be mechanically coupled to the panel. The transducer material may change shape when electricity is applied. Thus, the material can be a piezoelectric lead lanthanum zirconate (PLZT) or a piezoelectric material such as polyvinylidene fluoride PVDF.

In embodiments, the panel and piezoelectric material can be transparent. This is particularly advantageous when combined with transparent panels. The panel can be hung or supported so that the support has as little effect on the resonant mode. Alternatively, the panel may be supported by restraining means, or the panel may be supported on the frame in the manner typical for flexural wave panels. In the latter case, the restraint means has a function of simply restraining the movement of the panel at a predetermined position.

In another aspect, a method of making a flexural wave loudspeaker having a panel with opposed surfaces includes the steps of determining the shape, size and characteristics of the panel and adding over a selected large area of the panel surface. Selecting the properties of the transducer material sheet, the position of the at least one subregion and the at least one constraint applied on the at least one subregion of the panel so that the panel provides effective acoustic effects. The parameter of the means is selected, and the selected transducer material is added over the large area of the panel surface, and the selected restraint parameters are used to add the selected panel restraint means to the selected area. Making a loudspeaker from the panel.

For a better understanding of the present invention, specific embodiments of the present invention will be described with reference to the accompanying drawings, which are for illustrative purposes only.

BEST MODE FOR CARRYING OUT THE INVENTION Generally, as shown in FIG. 2, a loudspeaker according to the present invention comprises a panel 1, which has a top surface 23 and a bottom surface 25 which face each other. Hold. The panels need not be flat and can be made in any shape required for a particular application. The transducer layer 3 is provided in a region covering most of one side of the panel. The signal connector 9 provides an input signal to the loudspeaker, typically in the form of an electrical signal.

The at least one restraint means may be a clamp or a mass, C1-C
It is added at one of the positions indicated by 6. The mass is attached to or connected to the panel to apply a mass load to the panel, and the panel is locally connected to a solid support to clamp the panel.

The selection of the restraint position will be described. The method according to the invention is in a sense WO 97
The reverse of the conventional distributed mode method described in '09842. Instead of exciting the panel at selective excitation points, the panel is excited over a substantial area of the panel surface and pinned at one or more discrete locations.

A good origin for the restraint position is a suitable excitation position as taught by WO97 / 09842. That is, suitable restraint positions are typically spaced from a significant number of low frequency nodal lines, typically they are spaced from both the ends and the axis of symmetry.

Accordingly, positions such as C1 and C4 where the constraint points are at a distance of at least 10% of the panel width from the edge of the panel may be suitable. Further, the selected position may be a position that is at least 5% of the panel width from the axis parallel to the end of the rectangle and further passes through the center point of the panel. If the constrained position inside the panel is not feasible, positions such as C2, C3, C5, or C6 may be used.

For panel design, the method shown in the flowchart of FIG. 5 can be used. First, the required panel shape, ie size and characteristics, is determined (step 51). These are generally set by other factors such as the application in which the loudspeaker is installed. Next, an appropriate transducer material is selected (step 53). Next, the region to which the transducer material is added is selected. This area should be as large as possible to obtain maximum acoustic output.

Panels designed as above are unlikely to provide acceptable acoustics.
To address this issue, at least one small area applied to the panel,
At least one constraint parameter is selected (step 55). This step can be performed by calculation such as finite element analysis or systematic experiment.

The constraining parameters and position are selected to effectively provide uniform acoustic output. A figure of merit for effective optimization is given in the Applicant's WO 99/41939, the disclosure of which is incorporated herein by reference.

In this embodiment, the panel needs to be transparent, so providing a restraining mass or clamp inside the panel may hinder the transparency of the loudspeaker as a whole. It is not practical. In this case, the panel is preferably clamped at one or more discrete locations around the edge of the panel. Suitable positions are the end drive position, which is taught in Applicant's WO99 / 37121 as a suitable position, and the end clamp position, which is taught in Applicant's WO99 / 52324 as a suitable position. Both disclosures are incorporated herein by reference. Positions along the entire length of the edge at a distance of about 0.38 to 0.50 may be particularly suitable.

Clamps at or near the ends are particularly suitable as a means of providing a constraint in the restrained position. The closer to the center of the panel, the more convenient it is to add constraints by adding mass. However, this choice may vary depending on the particular design.

Choosing the proper restraint position and type creates a loudspeaker with a panel that depends on the selected transducer material applied over most of the surface (
Step 57). The selected restraint means is added to the panel in the small area selected using the selected restraint parameters.

With reference to FIG. 3, a specific embodiment of the invention is described for illustrative purposes only. The panel 1 with opposite top and bottom surfaces (19, 21) comprises a lead lanthanum zirconate titanate (PLZT) piezoelectric transducer layer 3 applied over the central region of the top surface 19 of the panel 1. The piezoelectric layer 3 is sandwiched by a top electrode 5 and a bottom electrode 7 connected to an electric input wire 9. The bottom electrode 7 covers the central area of the panel, that is, most of the panel area, and the transducer layer 3 is attached to the panel 1.
Connect to. The panel is attached to the frame 13 on a soft elastic coupling 17 which is connected to the outer part of the bottom surface 21 of the panel.

To apply a mass load to the panel at position C4 (FIG. 2), mass 11 is attached to that position on the panel. To clamp the panel at position C6 (FIG. 2), the panel is connected to the frame 13 at that position using a rigid coupling piece 15 instead of the elastic coupling used elsewhere.

Another preferred embodiment of the loudspeaker will be described with reference to FIG. The lightweight multimedia loudspeaker comprises a rectangular panel 1 having a mass of 10 grams and an aspect ratio, ie a length to width ratio of 1.3 to 1. A 10 gram restraint mass 11 is secured to the back of the panel at one end of the panel at a position of 4/9 of the total panel length and from one side of the panel at a position of 3/7 of the panel width, ie, spaced from axis 23. Has been done. As mentioned above, substantially all of the front surface of the panel is covered by the piezoelectric electrode sandwich structure 3, 5, 7. The electrode sandwich is laterally spaced from the edge of the panel. The panel is supported on the foam support 15.

Another preferred embodiment will be described with reference to FIGS. 6 to 8. In this embodiment, two piezoelectric layers are provided on each side of the panel. That is, the panel is a bimorph type. The rectangular panel 1 was made of 1 mm thick Rohacell with a length of 150 mm and a width of 135 mm. Two commercially available polyvinylidene fluoride with manufacturer-prepared electrodes (
The PVDF film was attached to each side of the panel so as to sandwich the panel. The film used was from Pennwalt, Norristown, PA, under the trade name "Kynar Piezo Film sa.
It is sold as a "plep type S28K". The film comprises a vinylidene fluoride sheet sandwiched by silver electrodes. Each piece of PVDF covered approximately 90% of the area of rectangular panel 1 except at the edges. The adhesive used was a thermoplastic polyurethane adhesive "Puro H-25g".

The film used is slightly anisotropic, and when a voltage is applied, it flexes slightly more in one direction, which is the displacement direction, than in the direction orthogonal to the displacement direction. Both the top and bottom films were aligned in the displacement direction parallel to the longitudinal direction of the panel. To act as a restraint, a 1.2 gram mass was added from one end of the panel to 3/7 of the panel length and from one side of the panel to 4/9 of the panel width. For comparison, the mass of the panel was 7 g. Due to the small size of the mass, it covers only a small area of less than 1% of the panel area.

The following estimations were made for various panel properties. That is, calculated using the measured or known properties of each element. The flexural rigidity of the panel and the piezoelectric layer is 0.
9 Nm, mass per unit area 1.78 kg / m2, mechanical impedance 1
It was estimated to be 0.12 Ns / m. The resonance frequency, that is, the frequency at which the speed of sound in air matches the speed of sound in the panel was estimated to be 26.7 kHz. The basic frequency is about 120
Hz.

The electrodes 5 and 7 of the top film 61 and the bottom film 63 were electrically connected in parallel. Experimented to 0.5m with 20V input for parallel connected films
We measured the sound pressure level as a function of frequency, produced by a loudspeaker at different distances. The result is shown in FIG. 7. This loudspeaker is useful and produces a uniform frequency response over a wide frequency range. Note that no transformer was used for this experiment and the resulting acoustic output is highly efficient.

As mentioned above, the slight anisotropy of the film used means that some low frequency resonant modes of the panel are not strongly excited. This causes a slight drop in output below about 1.5 kHz, as seen in FIG. If this is a problem, multiple sets of films can be attached to each surface of the panel, with each set of films having orthogonal displacement directions. That is, four films can be used.

FIG. 8 shows the electrical impedance of the two piezoelectric films. As can be seen from FIG. 8, the impedance is high at low frequencies, which is characteristic of piezoelectric transducers.

The invention is not limited to the embodiments described above and many modifications can be made without departing from the scope of the invention. Any suitable transducer material responsive to an electrical signal can be used including, for example, PLZT or polyvinylidene fluoride (PVDF) described above. In practice, the transducer may be an array of microactuators covering a substantial area of the panel surface.

The electrodes can be made of any suitable conductive material such as silver, conductive polymers, and copper. The electrodes may be transparent electrodes such as indium tin oxide (ITO). The position and constraint type can be fine-tuned by either calculating the exact position or systematically analyzing the results.

The mass may be attached by various attachment means such as adhesives, adhesive tape, screws or bolts, or other attachments known in the art. The mass can be incorporated into a panel, eg, within the core material of the core and skin structure. Further, the mass body can be attached to the center, the vicinity of the center, or the peripheral portion on one side or both sides.

The term “clamp” is not limited to conventional clamps and can be used for any means of securing one localized area of the panel. For example, there may be a rigid connecting member that allows one point of the panel to be firmly connected to the rigid frame, or a portion of the panel sandwiched between clamp members. The frame itself may be shaped to clamp a portion of the panel. One of ordinary skill in the art can readily devise another method of clamping the panel, that is, substantially immobilizing one area of the panel. The panel material 9 that can support the bending wave and its size and shape can be changed as necessary.

[Brief description of drawings]

[Figure 1]   1 illustrates a conventional flexural wave panel loudspeaker.

[Fig. 2]   Figure 2 shows a schematic plan view of a loudspeaker according to the invention.

[Figure 3]   FIG. 3 shows a side view of a loudspeaker according to an embodiment of the invention.

[Figure 4]   FIG. 6 shows a plan view of a loudspeaker according to another embodiment of the invention.

[Figure 5]   3 shows a flow chart of a method of making a loudspeaker according to the invention.

[Figure 6]   FIG. 6 shows a side view of another embodiment of the invention.

[Figure 7]   7 shows the acoustic output of a loudspeaker according to the embodiment of FIG. 6.

[Figure 8]   7 shows the terminal impedance of a loudspeaker according to the embodiment of FIG. 6.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, MZ, SD, SL, SZ, TZ, UG , ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, BZ, C A, CH, CN, CR, CU, CZ, DE, DK, DM , DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, K E, KG, KP, KR, KZ, LC, LK, LR, LS , LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, R U, SD, SE, SG, SI, SK, SL, TJ, TM , TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (20)

[Claims] 1. A panel capable of supporting flexural waves and having opposing surfaces, a transducer extending over a large area of the panel surface and coupled to the area, and a panel coupled to at least one sectioned subregion of the panel. A bending wave loudspeaker, wherein at least one restraint means for restraining the movement of the panel, and the activation of the transducer material can excite a plurality of resonant bending wave modes of the panel. 2. The flexural wave loudspeaker of claim 1, wherein the transducer includes a transducer material sheet extending over and coupled to the large area of the panel surface. 3. The flexural wave loudspeaker of claim 2, wherein the transducer material sheet is sandwiched between a pair of electrodes. 4. A flexural wave loudspeaker according to claim 3, wherein one of the electrodes of the set covers the large area of one side of the panel and mechanically couples the transducer material to the panel. Speaker. 5. The bending wave loudspeaker according to claim 2, wherein the transducer material is a piezoelectric material. 6. The bending wave loudspeaker according to claim 5, wherein the piezoelectric material is transparent. 7. The flexural wave loudspeaker according to claim 1, wherein the at least one restraint means is a mass. 8. The at least one restraint means is a rigid connecting piece connected to the panel over a small area of the panel and substantially impeding movement of the small area of the panel. A flexural wave loudspeaker according to any one of the preceding claims characterized. 9. A flexural wave loudspeaker according to any one of the preceding claims, characterized in that the area of the large area of the panel is at least 75%. 10. A flexural wave loudspeaker according to any one of the preceding claims, wherein each small area linear size is no greater than 20% of the panel width. 11. A flexural wave loudspeaker according to any one of the preceding claims, wherein the area of each subregion is not greater than 1% of the area of the panel. 12. One on each of the panel areas on opposite sides of the panel,
A flexural wave loudspeaker according to any one of the preceding claims, characterized in that opposing transducers are mounted over the large area. 13. The flexural wave loudspeaker of claim 12, wherein the transducer comprises a sheet of transducer material sandwiched between a pair of conductive electrodes. 14. A flexural wave as claimed in any one of the preceding claims, wherein the at least one restraining means is spaced from the panel end by at least 20% of the panel width. Loudspeaker. 15. The panel has at least one axis of symmetry, and the at least one restraint means is spaced from each axis of symmetry by at least 4% of the panel width. A flexural wave loudspeaker according to any one of the preceding claims. 16. The bending wave loudspeaker according to claim 1, wherein the panel is supported by the restraining means. 17. A resonant flexural wave mode of the panel constrained by the at least one constraining means being substantially evenly distributed with respect to frequency. Flexural wave loudspeaker. 18. A method of making a flexural wave loudspeaker having a panel with opposed surfaces, the method comprising determining the shape, size and characteristics of the panel, and over a selected large area of the panel surface. Selecting the characteristics of the transducer material sheet to be applied, the location of at least one sub-area, and the application on the at least one sub-area of the panel, such that the panel provides an effective acoustic effect. Selecting at least one parameter of the restraint means, adding the selected transducer material over a large area of the panel surface, and using the selected restraint parameter, the panel restraint selected in the selected area Making a loudspeaker from the panel determined by adding means. 19. A step of selecting said at least one restraint position and parameters to obtain substantially the best uniform acoustic output of a flexural wave loudspeaker over a predetermined operating frequency band. 18. The method according to 18. 20. Selecting at least one restraint position and parameters to obtain a substantially best uniform frequency spread of a flexural wave loudspeaker over a predetermined operating frequency band. Item 18. The method according to Item 18.