AU746673B2

AU746673B2 - Panel-form loudspeakers

Info

Publication number: AU746673B2
Application number: AU74390/98A
Authority: AU
Inventors: Henry Azima; Christien Ellis; Neil Harris
Original assignee: New Transducers Ltd
Current assignee: NVF Tech Ltd
Priority date: 1997-05-15
Filing date: 1998-05-13
Publication date: 2002-05-02
Anticipated expiration: 2018-05-13
Also published as: AR012696A1; CA2290476A1; WO1998052381A3; AU7439098A; JP2002505814A; WO1998052381A2; IL132686A0; TW444510B; KR20010012527A; EP0981928A2; CO4780081A1; ID20339A; CN1255277A; ZA983986B; GB9709959D0; BR9809642A

Description

WO 98/52381 PCT/GB98/01362 TITLE: PANEL-FORM LOUDSPEAKERS

DESCRIPTION

FIELD OF THE INVENTION The invention relates to panel-form loudspeakers, and more particularly, but not exclusively, to panel-form loudspeakers of the kind described in our International Application W097/09842 and known as distributed mode loudspeakers.

BACKGROUND ART In theory and given the availability of the right materials, a distributed mode loudspeaker can cover the full audio range in a single panel. Since the current state of the art in materials technology precludes such a solution, our International Application WO/9709846 envisages small distributed mode loudspeaker panel suspended in a larger distributed mode loudspeaker panel of lower cut-off frequency to produce a wider acoustic bandwidth loudspeaker. This requires at least two exciters of appropriate type and also requires careful design of the mechanical interface between the two panels.

As both panels cover a wide frequency range within their individual capabilities, there will also be a broad frequency range within which the outputs of the two panels may overlap. An electrical cross-over network may therefore be desirable, although it may tend to degrade the sound quality and will add to the manufacturing cost.

An object of the invention is to provide arrangements which alleviate or overcome these difficulties.

GENERAL ASPECTS OF THE INVENTION In one aspect of the invention there is provided a panel-form loudspeaker comprising at least two bending wave resonant distributed mode acoustic panels, including a larger low frequency panel and a smaller higher frequency panel, the larger panel having a lower bending wave stiffness than the smaller, wherein both the larger and smaller panels are excited by a common driver arranged such that bending wave energy is efficiently transferred to both of the larger and smaller panels to excite distributed mode resonance in the larger and smaller panels to provide acoustic output and in that the smaller and larger panels are attached together by a material forming a controlling S 20 compliant coupling whereby differentiation of the high and lower frequency parts of the oo. loudspeaker is achieved.

•go• ooo oo rR\I.IBCC10O91' docemn Desirably, the control of the compliance frequency dependent damping of the coupling allows a preferred cross-over point to be determined mechanically.

Preferably the smaller panels is formed within and attached by the compliant coupling to the larger panel, and a driver being attached to the smaller panel.

Alternatively, a coupler passing through and attached to the larger panel, the smaller panel being mounted on one end of the coupler, and the driver being attached to drive the coupler.

The smaller of said panels is desirably positioned eccentrically with respect to the larger panel.

The driver is desirably positioned eccentrically with respect to the smaller of said panels.

o *go rR \BlRCC102)1) doc-mm WO 98/52381 PCTIGB98/01362 4 BRIEF DESCRIPTION OF THE DRAWINGS The above aspects, features and advantages of the invention will become apparent from the following description of embodiments of the invention now made with reference to the accompanying drawings, in which:- Figure 1 shows at A and B respectively rear face and side views of a first panel-form loudspeaker embodying the invention, Figure 2 is a sectional side view of a second panelform loudspeaker embodying the invention, Figure 3 is a sectional side view of a third panelform loudspeaker embodying the present invention, and Figure 4 is a rear face view of a modified form of the loudspeakers shown in Figure 1 to 3.

BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 shows a smaller distributed mode loudspeaker panel (10) driven by an appropriate driver or exciter preferably an electro-dynamic type for greater bandwidth. The smaller panel (10) is attached face to face to a largerdistributed mode loudspeaker panel (14) of appropriately lower stiffness and of dimensions appropriate to cover the required lower frequency range. By the choice of the right materials and driver design it can be shown that when the smaller panel (10) is driven it will continue to produce its useful bandwidth superimposed on the lower range frequency output resulting from the larger panel (14) giving a much wider bandwidth.

WO 98/52381 PCT/GB98/01362 The smaller distributed mode loudspeaker panel may be attached to the larger one by application of suitable adhesives of low mechanical loss in order to maintain efficient transfer of mechanical energy at low frequencies as well as maintaining good high frequency transmissibility with little loss. Epoxy resin adhesives are suitable for this purpose. The position of attachment of the smaller panel (10) to the larger panel (14) will be chosen in accordance with the distributed mode principle as explained in our International Application WO/97/09842, as will the position of attachment of the exciter (12) to the smaller panel Figure 2 illustrates another type of panel-form loudspeaker embodying the invention in which a larger, low frequency optimised distributed mode panel (20) is modified by having a smaller, high frequency optimised panel (22) formed in the region of a driver The common driving point of the driver (24) means that both parts or regions of the panel are excited. The smaller, high frequency part or region of the panel is provided by extra stiffening of the local skin region (26) for example by adding bonded carbon fibre, glass fibre or similar high strength material. Alternatively, by adding new higher stiffness skin sections in that region.

Depending upon the wave propagation properties of the larger panel (20) a natural balance of power division with frequency may be obtained. Additionally a suitable compliant boundary (28) is incorporated to WO 98/52381 PCT/GB98/01362 6 differentiate between the high and lower frequency parts of the panel. Control of the compliance frequency dependent damping of the resilient coupling allows the ideal or preferred cross-over point to be determined mechanically together with beneficial control of the damping at the boundary between the two parts of the panel.

Figure 3 illustrates yet another type of panel-form loudspeaker embodying the invention. In the arrangement of Figure 3 a smaller, high frequency, panel (30) is adhesively fixed to one end of a light weight tubular coupler Coupler passes through a larger, low frequency panel (34) and is resiliently attached to it as shown at The resilient attachment of the coupler to the larger panel (34) acts as a mechanical low pass filter to further define the balance of energy between the two panels (30 and 34). It can be seen that the end of the coupler (32) spaced from the high frequency panel is fixed to a driver exciter (38).

Yet another arrangement embodying the invention is illustrated in Figure 4 where a single large resonant distributed mode acoustic panel (50) has associated with it a number of smaller panels (52) each having an associated driver The smaller panels (52) may be associated with the larger panel (50) in the ways described with reference to Figures 1 to 3. That is to say the smaller panel (52) may be adhesively attached face to face to the larger panel (50) and have mounted WO 98/52381 PCT/GB98/01362 7 thereon its own driver Alternatively, the smaller panels (52) may comprise a number of sections of the larger panel (50) which have been appropriately stiffened and provided with an individual driver (54) the stiffened sections (52) being coupled to the larger panel in the manner described with reference to Figure 2.

Lastly, the smaller panels (52) may comprise panels carried by couplers each associated with an individual driver in the manner described with reference to Figure 3. It will be appreciated that the smaller panels (52) in the arrangement of Figure 4 need not all be associated with the larger panel (50) in the same was. Some may be associated in the way described with reference to Figure 1 whilst others are associated in the way described with reference to Figures 2 and/or 3.

In the described embodiments the driver is in each case attached or coupled to a smaller panel, it will of course be appreciated that the driver may be attached or coupled to the larger of the panels if desired.

INDUSTRIAL APPLICABILITY The distributed mode loudspeakers described have the benefits of enabling full audio bandwidth from one loudspeaker and reducing the number of drivers required and therefore the cost and complexity of the loudspeakers.

A loudspeaker in accordance with the present invention may be applied to an automobile headliner, with the benefit of a reduced component count, which results WO 98/52381 PCT/GB98/01362 in higher reliability, no need for electrical cross-over components, and reduced manufacturing costs.

Claims

1. A panel-form loudspeaker comprising at least two bending wave resonant distributed mode acoustic panels, including a larger low frequency panel and a smaller higher frequency panel, the larger panel having a lower bending wave stiffness than the smaller, wherein both the larger and smaller panels are excited by a common driver arranged such that bending wave energy is efficiently transferred to both of the larger and smaller panels to excite distributed mode resonance in the larger and smaller panels to provide acoustic output and in that the smaller and larger panels are attached together by a 1o material forming a controlling compliant coupling whereby differentiation of the high and lower frequency parts of the loudspeaker is achieved.

2. A panel-form loudspeaker as claimed in claim 1, wherein control of the compliance frequency dependent damping of the coupling allows a preferred cross-over point to be 15 determined mechanically. S

3. A panel-form loudspeaker as claimed in claim 1 or claim 2, wherein the smaller panel is formed within and attached by the compliant coupling to the larger panel, a driver •being attached to the smaller panel.

A panel-form loudspeaker as claimed in claim 1 or claim 2, comprising a coupler passing through and attached to the larger panel, the smaller panel being mounted on one end of the coupler, and the driver being attached to drive the coupler.

5. A panel-form loudspeaker as claimed in claim 4, wherein the controlling compliance coupling is attached between the coupler and the larger panel and acts as a mechanical low pass filter to further define the balance of energy between the two panels.

6. A panel-form loudspeaker as claimed in claim 4 or claim 5, wherein the driver is attached to the end of the coupler opposite to the end attached to the corresponding smaller panel.

7. A panel-form loudspeaker as claimed in any one of claims 4 to 6, wherein the coupler is tubular in section. [R'ITRCC1o10 Q doc'mrn

8. A panel-form loudspeaker is claimed in any preceding claim, wherein the smaller panel is positioned eccentrically with respect to the larger panel.

9. A panel-form loudspeaker as claimed in any preceding claim, wherein said driver is positioned eccentrically with respect to the smaller of said panels.

A panel-form loudspeaker as claimed in any preceding claim, comprising a single large resonant distributed mode acoustic panel having associated therewith a number of smaller panels each having an associated driver.

11. A panel-form loudspeaker according to any one of claims 1 to 9, wherein there are exactly two panels.

12. A panel-form loudspeaker substantially as described herein with reference to the 15 accompanying drawings. •DATED this Thirty-first Day of January, 2002 New Transducers Limited •Patent Attorneys for the Applicant 20 SPRUSON FERGUSON [R:\LIBCC]02919 doc: gmm