GB2349034A

GB2349034A - Supporting surround for active panel of distributed mode speaker

Info

Publication number: GB2349034A
Application number: GB9908795A
Authority: GB
Inventors: Robert James Franks; Dudley John Haestier
Original assignee: Hosiden Besson Ltd
Current assignee: Hosiden Besson Ltd
Priority date: 1999-04-16
Filing date: 1999-04-16
Publication date: 2000-10-18
Also published as: GB9908795D0

Abstract

A distributed mode or bending wave loudspeaker comprises an active panel 12 located in an aperture 14 of a co-planar support panel 16 by means of a compliant bead 18 that joins the confronting edges of the two panels. The bead 18 may be formed of a cured resin sealant, eg silicone. The bead and the two panels may be of the same thickness. The loudspeaker may be in the form of a ceiling tile or it may form one wall of a box structure (figs 3 and 4). The active panel 12 and the support panel 16 may take any shape and the active panel may have a different shape to the support panel.

Description

DISTRIBUTED MODE SPEAKERS The present invention relates to distributed mode speakers. In particular, it provides a means for supporting the active panel of a distributed mode loud speaker.

Distributed mode speakers are a recent innovation in audio reproduction in which a rigid planar active panel is driven by a transducer situated asymmetrically on a rear face thereof. This causes the active panel to be excited into fully modal output, thereby producing pressure waves in the surrounding atmosphere. Thus, a sound is emitted. A full description of the design and construction of distributed mode loud speakers is given in WO-A-97/09842, and therefore no further description will be given herein. This document is important in understanding distributed mode loud speakers and the present invention, and therefore the attention of the reader is directed specifically thereto. In particular, the present invention encompasses both that which is set out in this specification and the content hereof in combination with the content of WO-A-97/09842, hereby incorporated by reference.

The principal difficulty with distributed mode loud speakers is in supporting the active panel. As this must be excited in order to emit sound, the support must not hinder high frequency low amplitude movements of the panel. Hitherto, panels in practical application have been held at their corners by compression between clamps lined with cellular foam or other very low modulus materials. However, this method of support is cumbersome and difficult to engineer in a reliable and consistent manner.

Another difficulty inherent to distributed mode loud speakers is that the active panel must not be too symmetrical. Thus, certain shapes such as squares and circles must be avoided. This is obviously not a difficulty for free standing speakers, but where it is intended to integrate the speaker into a larger article this can cause difficulties.

In its first aspect, the present invention provides a distributed mode speaker comprising an active panel located in an aperture formed in a coplanar support panel, the panels being joined at their mutually confronting edges by a compliant bead.

This means that the external shape of the unit need not correspond to the actual shape of the active panel. As a result, the active panel can be any smaller shape whatsoever to optimise audio performance and this would dictate only the shape of the aperture to be formed in the support panel, not the external shape of the panel.

The support panel can be retained by any means and does not have to be free in order to become excited. Thus, it can be clamped or otherwise formed integrally with a larger object. Some acoustic energy will pass through the compliant bead, and this will reflect at edges or discontinuities on the support panel, but this does not adversely affect the audio performance of the active panel as such reflection must pass once more through the compliant bead in order to return thereto. As a result, the acoustic energy is attenuated twice by the compliant panel, and it has been found that such double attenuation is sufficient to reduce the amplitude of any resulting disturbances to the reproduced sound to a level which is immaterial.

Fixing of the active panel assembly is therefore straightforward and there are no constraints on the external shape of the unit. The active panel can therefore be incorporated into a wide variety of situations such as ceiling panels, wall units etc.

The bead is preferably substantially the same thickness as a panel and the panels are preferably substantially the same thickness as each other. The bead causes this part of the system to act as a lossy waveguide, and thus reduces the amptitude of waves as they reflect back and forth from the edge of the active panel and the guard ring. The amptitude of waves reflected back into the panel is damped, reducing the formation of resonant modes.

The support panel can be one face of a box section, which can itself be closed on all faces if desired, or include apertures on some faces covering some or all of those faces.

In its second aspect the present invention provides a distributed mode speaker comprising an active panel supported at its edges by a bead of cured resin material.

This aspect likewise provides a method of making a distributed mode speaker, comprising the steps of providing an active panel, providing a support around the active panel, applying the resinous material in its liquid state to the edge of the active panel and to the support, and curing the resin thereby fixing the active panel in place on the support.

Thus, the bead is formed with an intimate and continuous contact with the panel edge at its perpendicular faces. This produces a defined path for the acoustic energy transferred to the guard ring. The resin also performs the secondary function of sealing the edges of the panel and guard ring thereby preventing ingress of moisture and dust.

WO-A-97/09842 does disclose an active panel supported within a box section, and states that the panel is supported within the enclosure by means of a surrounding compliant suspension such as a strip of latex rubber. However in the disclosed arrangement the active panel forms one complete face of the enclosure and thereby dictates the external shape thereof. Thus, the panel is not coplanar with its support. In addition, the compliant suspension is significantly thinner than the active panel, and therefore cannot be a cured in place resin material and will affect the acoustic properties of the active panel at its edges.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying figures, in which; Figure 1 is a front view of a distributed mode loud speaker according to a first embodiment of the present invention; Figure 2 is a section on II-II of Figure 1, Figure 3 is a front view of a distributed mode speaker according to a second embodiment of the present invention, and Figure 4 is a section of II-II of figure 3.

Referring to Figures 1 and 2, a distributed mode speaker 10 is shown, the principal parts being an active panel 12 which fits within a corresponding aperture 14 formed in a support panel 16. The small gap between the panels 12,16 is taken up by a cured resin sealant bead 18. In this embodiment, the two panels and the bead are all of the same thickness.

A transducer 20 is attached asymmetrically to a rear face of the active panel 12 to excite it as set out in WO-A-97/09842.

The edges of the support panel 16 are held in four clamps 22, each comprising first and second jaw members 24,26 either side of the support panel 16, drawn together by a bolt 28 passing through each and tightened via a nut 30. Thus, the support panel is fixed firmly and cannot resonate, forming a guard ring about the active panel 12. Acoustic energy resonating within the panel will be mainly reflected at the interface between the active panel 12 and the bead 18 due to the large difference in modulus between the two materials, and the energy passing into the bead will be attenuated markedly due to the compliancy thereof. To affect the excitation of the active panel, the acoustic energy will need to pass through the paneUbead interface twice, reflect once, and travel through the bead twice. The attenuation over this process will be sufficient for the effect of the small amount of energy that is returned to be minimal.

Thus, the present invention succeeds in providing physical support for an active panel which leaving it acoustically unsupported. This permits a much wider range of applications to employ distributed mode speakers. For example, the panel could be formed integrally with a ceiling tile, not hitherto possible since the tile will commonly be square and must rest at its edges. This offers the possibility of essentially undetectable sound sources in a room. Alternatively, a speaker panel could be integrated conformally into a flat surface of (eg) a hospital operating theatre and used to sound warnings such as fire alarms. The smooth front surface could be disinfected routinely, avoiding the need to dismantle a convention bell and striker for disinfection.

Figures 3 and 4 show an alternative embodiment. This shares many elements with the embodiment of figures 1 and 2, for which like reference numerals have been employed.

The essential difference is that the support panel has been formed as the front face of a closed box section 32, enabling the speaker to be free standing.

It will be apparent that many variations could be made to the above described examples without departing from the scope of the present invention. For example, the rectangular active panels could be any shape, such as an ellipse, parallelogram, triangle and so on. The support panel could be any shape whatsoever, such as a square, circle, ellipse, parallelogram, triangle and so on. The support panel could be held by any suitable means. The materials chosen for the various parts can be freely chose provided the panels are relatively rigid and the bead is compliant. A preferred bead material is silicone, but others are possible.

Claims

CLAIMS 1. A distributed mode loudspeaker comprising an active panel located in an aperture formed in a co-planar support panel, the panels being joined at their mutually confronting edges by a compliant bead.
2. A distributed mode loudspeaker as claimed in claim 1 wherein the active panel and support panel are of different shapes.
3. A distributed mode loudspeaker as claimed in claim 1 or claim 2 wherein the support panel is integral with the larger object.
4. A distributed mode loudspeaker as claimed in claim 3 wherein the larger object is a ceiling panel or a wall unit.
5. A distributed mode loudspeaker as claimed in any preceding claim wherein the bead is substantially the same thickness as one of the panels.
6. A distributed mode loudspeaker as claimed in any preceding claim wherein the panels have substantially the same thickness.
7. A distributed mode loudspeaker as claimed in any preceding claim wherein the support panel is one face of the box section.
8. A distributed mode loudspeaker as claimed in claim 7 wherein the box section includes apertures on one or more faces.
9. A distributed mode loudspeaker comprising an active panel supported at its edges by a bead of cured resin material.
10. A distributed mode loudspeaker as claimed in any preceding claim wherein the bead material is silicone.
11. A method for making a distributed mode loudspeaker comprising the steps of providing an active panel, applying a resinous material in its liquid state to the edge of the active panel and to the support, and curing the resin thereby fixing the active panel in place on the support.
12. A distributed mode loudspeaker substantially as described herein with reference to Figures 1 to 4.
13. A method for making a distributed mode loudspeaker substantially as described herein with reference to Figures 1 to 4.