Low-profile loudspeaker

Abstract

The present invention relates to a loudspeaker which can be arranged to minimise its overall depth while also increasing the breakup frequency and reducing potential rocking vibrations. Accordingly, the present invention is directed to a loudspeaker, comprising a magnet structure, and a voice coil lying within a magnetic field established by the magnet structure and responsive to electrical signals to undergo excursions from a rest position along an axis of motion; a driven body, connected to the voice coil and moveable to project acoustic waves from a front of the loudspeaker; and a suspension for providing a restoring force to the driven body towards the rest position, the suspension extending from an attachment point on the driven body to an attachment point on a fixed portion of the loudspeaker; wherein the driven body comprises a diaphragm and a support structure extending rearwardly from a connection point with the voice coil to a connection point with the suspension located rearward of the frontal part of the magnet structure.

Claims

1. A loudspeaker, comprising: a magnet structure, and a voice coil lying within a magnetic field established by the magnet structure and responsive to electrical signals to undergo excursions from a rest position along an axis of motion; a driven body, having a front connected to a voice coil former and moveable to project acoustic waves from a front of the loudspeaker; and a suspension for providing a restoring force to the driven body towards the rest position, the suspension extending from an attachment point on the driven body to an attachment point on a fixed portion of the loudspeaker; wherein the driven body comprises a diaphragm and a support structure for supporting the diaphragm, the support structure having a front and a first conical portion extending rearwardly from a connection point with the voice coil former to a connection point with the suspension located rearward of the frontal part of the magnet structure, the diaphragm extending across the front of the driven body and across the front of the support structure, and being connected to the support structure at the connection point with the voice coil former.

2. The loudspeaker according to claim 1 wherein the support structure comprises a second conical portion extending forwardly outwardly from the connection point with the suspension.

3. The loudspeaker according to claim 2 in which the diaphragm is connected to the support structure at an outer region of the second conical portion.

4. The loudspeaker according to claim 2 further comprising a flexible surround, attached to at least one of the support structure and the diaphragm at an outer region of the second conical portion.

5. The loudspeaker according to claim 4, wherein the support structure has at least one transition portion between slanted portions, at the connection point between the support structure and the suspension.

6. The loudspeaker according to claim 5, wherein the at least one transition portion and the conical portions form a substantially U shape.

7. The loudspeaker according to claim 5, wherein the transition portion is substantially perpendicular to the axis of motion, when the loudspeaker is in the rest position.

8. The loudspeaker according to claim 1, wherein the support structure has at least one aperture to allow fluid communication therethrough.

9. The loudspeaker according to claim 8 in which the support structure has a plurality of apertures.

10. The loudspeaker according to claim 9 in which the apertures are spaced substantially symmetrically around the support structure.

11. The loudspeaker according to claim 1, wherein the support structure has a plurality of undulations formed in its surface.

12. The loudspeaker according to claim 11, in which the undulations are spaced substantially symmetrically around the support structure.

13. The loudspeaker according to claim 1, further comprising a frame at a rear of the loudspeaker.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which;

(2) FIG. 1 shows a section through a loudspeaker embodying the present invention;

(3) FIG. 2 shows a diaphragm of a loudspeaker embodying the present invention in perspective;

(4) FIG. 3 shows frequency response curves for comparison between a loudspeaker with a double-cone diaphragm such as disclosed by US2010/0208934, and a loudspeaker embodying the present invention having a diaphragm with a support structure; and

(5) FIG. 4 shows a step of an assembly process of a loudspeaker embodying the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) FIG. 1 shows a loudspeaker 10 embodying the present invention. This has a magnet structure 12, of a conventional format. A permanent magnet 11 is held within a pair of pole pieces 8, 9 which are shaped to direct the magnetic flux and create a strong localised magnetic field across a short annular gap 13 between opposing faces of the pole pieces 8. 9. A cylindrical voice coil former 14 lies within the magnetic field established in the gap 13 by the magnet structure 12, and carries a voice coil 15 which is then responsive to electrical signals to undergo excursions from a rest position along an axis of motion X. A driven body 16 is connected to the voice coil 14 and is moveable to project acoustic waves from a front F of the loudspeaker 10. A suspension 18 provides a restoring for to the driven body 16 towards the rest position, the suspension 18 extending from an attachment point 20 on the driven body 16 to an attachment point 22 on a fixed portion of the loudspeaker 10.

(7) The driven body 16 comprises a diaphragm 24 and a support structure 26; the support structure 26 extends rearwardly from a connection point 28 with the voice coil 14 to the connection point 20 with the suspension 18. The support structure 26 has a first conical portion 30 extending rearwardly outwardly from the connection point 16 with the voice coil 14, and a second conical portion 32 extending forwardly outwardly from the connection point 20 with the suspension. Between the first conical portion 30 and the second conical portion 32 and at the connection point 20 with the suspension, the support structure has a transition portion 34. The transition portion 34 is substantially perpendicular to the axis of motion X, when the loudspeaker 10 is in the rest position. The first conical portion 30, the second conical portion 32, and the transition portion 34 together form a U-shape.

(8) The diaphragm 24 extends across the front of the driven body 16 and is connected to the support structure 26 at the connection point 16 with the voice coil, and at an outer region 36 of the second conical portion 32. A flexible surround 38 is attached to the support structure 26 at an outer region 36 of the second conical portion 32. The diaphragm 24 is gently curved; this lends a generally flat profile to the frontal part of the loudspeaker and assists in creating a thin overall form factor. In this case, the diaphragm has a convex curve, i.e. creating a domed shape as viewed from the front of the loudspeaker, but other shapes are compatible with the present invention.

(9) The support structure 26 has undulations or ribs (not shown in FIG. 1) formed therein for added stiffness, the ribs are spaced substantially symmetrically around the support structure 26. It also has apertures (not shown in FIG. 1) which allow air flow into and out of the enclosed region 44 between the diaphragm 24 and the support structure 26. This air flow can allow pressure differences resulting from ambient pressure changes to equalise, and (more importantly) means that the enclosed region 44 forms part of the acoustic volume behind the diaphragm 24. A large acoustic volume allows the movement of the diaphragm to be accommodated with less compression of the air within the volume, thereby reducing the acoustic impedance to movement of the diaphragm. The loudspeaker 10 also has a frame 42 at its rear which supports and houses the elements of the loudspeaker.

(10) FIG. 2 shows the support structure 26 of FIG. 1 in more detail. The support structure 26 has a first conical section 30, a second conical section 32, and a transition portion 34 joining the two first 30 and second 32 conical sections. Thus, the support structure 26 has a U-shape. A plurality of structures 40 are symmetrically distributed around the support structure 26; each of these are in the form of an aperture 46 surrounded by an upstanding rib or ridge 48, to allow for fluid communication as noted above and also give added stiffness to the support structure.

(11) Thus, the described structure gives rise to the advantages set out above, in the form of a stiff diaphragm in a shallow structure, which is resistant to rocking motions. The spacing of the suspension and surround from the centre of the rotation and from each other results in a leverage which has the effect of magnifying the radial stiffness of the suspension and the surround. As a result, the magnitude of any rocking motion will be reduced, thereby reducing the likelihood of the coil touching the adjacent stationary structures and resulting in less distortion of the output and a reduced likelihood of failure.

(12) FIG. 3 shows a comparison between a frequency response of a loudspeaker with a double-cone diaphragm, shown as a dashed line, and a frequency response of a loudspeaker embodying the present invention, having a diaphragm with a support structure, shown as a solid line. It can be seen that a better frequency response is provided; non-linearities in the achieved sound pressure are less significant and/or are moved to higher frequencies.

(13) FIG. 4 shows a loudspeaker 10 embodying the present invention at a stage during its assembly process. Many of the features described above with respect to FIG. 1 are present in this drawing, but are not labelled in order to aid clarity. The voice coil 14 and the support structure 26 have been pre-assembled as a unit and are being centralised in the magnetic field gap of the magnet structure 12 using a shim-type jig 100. With the support structure 26 and voice coil 14 in the correct position, the suspension 18 and the surround 38 can be fitted and adhered to the frame 42 to secure the support structure 26 and voice coil 14 in that location. Once this has been fitted, jig 100 can be removed and the diaphragm 24 can be attached to the front of the support structure 26, for example by an adhesive attachment to the support structure 26. As noted above, the loudspeaker 10 may be assembled in a generally conventional way.

(14) It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.