GB2373399A

GB2373399A - Exciter for a bending wave loudspeaker includes elastomer between magnet and coil

Info

Publication number: GB2373399A
Application number: GB0130326A
Authority: GB
Inventors: Martin Colloms; Martin Roberts
Original assignee: New Transducers Ltd
Current assignee: NVF Tech Ltd
Priority date: 2000-12-20
Filing date: 2001-12-19
Publication date: 2002-09-18
Also published as: GB0130326D0; GB0031244D0

Abstract

An electrodynamic vibration transducer 1 comprising a magnet assembly 2 and a coil 5 movable relative to the magnet assembly 2. The magnet assembly 2 has an array of magnets 3 and windings 13 of the coil 5 are disposed in gaps 14 between the magnet 3. There is also an elastomeric means 6 e.g. silicone rubber mechanically coupling the magnet assembly 2 and the coil 5 together to form a unitary member. The transducer may be attached to a bending wave panel by an adhesive layer 12.

Description

TITLE : VIBRATION TRANSDUCER DESCRIPTION TECHNICAL FIELD The invention relates to vibration transducers and more particularly to electrodynamic, that is moving coil, transducers for loudspeakers, e. g. for use in applying bending wave energy to panel-form loudspeakers, more particularly, but not exclusively, distributed mode acoustic radiators of the general kind described in International patent application W097/09842.

It is an object of the present invention to utilise a principle extant for linear motors and similar electrodynamic actuators where the coil winding is developed as an array of linear elements interleaved between linear, alternated magnetic fields generated by an

array of bar magnets.

BACKGROUND ART It is known for loudspeaker actuators to operate on the linear motor principle with freely suspended diaphragms and with the actuator magnets bonded to large panels and frames.

DISCLOSURE OF THE INVENTION From one aspect the invention is an electrodynamic vibration transducer comprising a magnet assembly, a coil movable relative to the magnet assembly disposed adjacent to the magnet assembly to define a gap therebetween, and elastomeric means in the gap and mechanically coupled between the magnet assembly and the coil, whereby the magnet assembly and the coil together form a unitary member. The elastomeric means may substantially fill the gap and may be bonded to the magnet assembly and to the coil. The magnet assembly and the coil may form a linear motor. The coil may be flat. The coil may be bonded to a thermally conductive substrate. The elastomeric means may comprise a thermally conductive filler.

The transducer may comprise a ferro-magnetic pole plate as part of the magnet assembly.

The substrate (whether or not it is thermally conductive) may comprise a self adhesive backing layer by which the transducer can be fixed in a position of use.

The transducer may be inertial with the magnet

assembly forming the inertial mass.

From another aspect, the invention is a loudspeaker comprising a stiff lightweight bending wave panel and a transducer as described above attached to the panel to launch bending waves into the panel to cause it to vibrate to provide an acoustic output. The panel is preferably a distributed mode acoustic radiator.

BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammatically illustrated, by way of example, in the accompanying drawings in which : Figure 1 is a perspective view of a bending wave panel loudspeaker having a square-form unitary transducer of the present invention; Figure 2 is a plan view diagram of an arrangement of coils and magnet poles illustrating current flow in a transducer of the present invention; Figure 3 is a sectional side view of the transducer of Figures 1 and 2 on a speaker panel; Figure 4 is a plan view of a second embodiment of transducer of the invention showing a circular coil winding and magnet assembly, and Figure 5 shows the coil winding pattern of the arrangement of Figure 4.

BEST MODE FOR CARRYING OUT THE INVENTION In the drawings, and referring more particularly to Figure 1, there is shown a bending wave panel-form

loudspeaker (7) comprising a bending wave panel (8) and a generally rectangular inertial electrodynamic vibration transducer (1) mounted on the panel to apply bending wave energy thereto to cause the panel to radiate an acoustic output. The panel may be a resonant device as described in W097/09842. The panel may comprise an opposed pair of skins (9) separated by a core (10). The transducer (1) has a pair of electrical leads (11) attached thereto and by means of which an electrical audio signal is applied to actuate the transducer.

In Figures 2 and 3, the transducer (1) of Figure 1 is shown in more detail. Thus the transducer comprises a coil

(5) formed as a linear array of windings (13) fixedly z mounted on a plate-like substrate (12), which is preferably thermally conductive. The coil (5) is terminated with two connections (15). The transducer also comprises a magnet assembly (2) having a parallel spaced array of vertically polarised bar magnets (3), the arrangement being such that the linear windings (13) are disposed in the gaps (14) between the magnets (3). The magnets (3) are fixedly mounted on a plate-like pole piece (4). The coil (5) and the magnet assembly (2) is encapsulated in an elastomeric mass or body (6) which holds the coil and magnet assembly in the correct orientation and such that the transducer is a unitary or integral assembly. The elastomer may be thermally conductive. As shown in Figure 3, the transducer is fixed by the substrate (12) to the panel (8), e. g. by adhesive means which may be a pressure sensitive adhesive.

Figures 4 and 5 illustrate a second embodiment of transducer which is generally similar to that of Figures 1 to 3, but which is circular in shape. Figure 4 shows that the transducer comprises concentric magnet rings (16) with coil windings (17) are disposed in the gaps between the magnet rings (16). The magnet rings (16) may be mounted on an optional ferromagnetic backing ring. Figure 5 shows the detail of the pattern of the windings (17) of the coil.

Thus, in accordance with the present invention the magnet system is mechanically coupled to the coil array via an elastomeric interlayer which holds the two parts in the correct alignment. The interlayer also allows inertial movement of the magnet system relative to the coil. The transducer is thus a unitary member.

The coil may be flat and may be bonded either to a substrate for adhesive attachment to a loudspeaker surface, or may be bonded directly to the diaphragm surface. Advantageously the panel surface may be entirely or locally thermally conductive to aid conduction of heat away from the coil in high power, high loudness applications. The coil bonding medium and/or the elastomeric interlayer may themselves be loaded with ceramic powder or a similar thermally conductive filler to aid heat transfer.

Neodymium alloy magnets will provide good efficiency, though any suitable magnet type will be effective.

This transducer lends itself to easy mounting and easy manufacture, is shock proof and has no closely toleranced elements. An optional ferro-magnetic pole plate behind the

magnets enhances efficiency, provides magnetic shielding and beneficially adds mass, aiding the inertial coupling factor at lower frequencies. The low frequency response is thereby extended.

In a preferred form, the transducer is pre-assembled as a small module e. g. 6 to 25 square cm surface area fitted with a high grip, stable, self-adhesive backing for convenient and economical attachment to a bending wave acoustic panel. Calculations indicate that the electrical driving impedance and the sensitivity of the resulting speaker will be comparable with conventional electrodynamic loudspeakers.

The form of the transducer may be rectangular or square, or alternatively may be arranged concentrically on a circular or similar shaped radiator panel.

Claims

CLAIMS 1. An electrodynamic vibration transducer comprising a magnet assembly, a coil movable relative to the magnet assembly and disposed adjacent to the magnet assembly to define a gap therebetween, and elastomeric means in the gap and mechanically coupling the magnet assembly and the coil together to form a unitary member.
2. A transducer according to claim 1, wherein the elastomeric means substantially fills the gap and is bonded to the magnet assembly and to the coil.
3. A transducer according to claim 1 or claim 2, wherein the magnet assembly and the coil form a linear motor.
4. A transducer according to claim 3, wherein the coil is flat.
5. A transducer according to claim 4, wherein the coil is bonded to a thermally conductive substrate.
6. A transducer according to claim 5, wherein the substrate comprises a self adhesive backing layer by which the transducer can be fixed in a position of use.
7. A transducer according to any preceding claim, wherein the elastomeric means comprises a thermally conductive filler.
8. A transducer according to any preceding claim, comprising a ferro-magnetic pole plate forming part of the magnet assembly.
9. A transducer according to any preceding claim, wherein the magnet assembly forms an inertial mass.
10. A loudspeaker comprising a lightweight bending wave

panel and a transducer as claimed in any preceding claim attached to the panel to launch bending waves into the panel to cause it to vibrate to provide an acoustic output.
11. A loudspeaker according to claim 10, wherein the panel is a distributed mode acoustic radiator.
12. A loudspeaker substantially as hereinbefore described with reference to and as illustrated in Figure 1.
13. A transducer substantially as hereinbefore described with reference to and as illustrated in any one of Figures 2 to 5.