HK1182253B - Loudspeaker and diaphragm therefor - Google Patents

Description

Loudspeaker and vibrating diaphragm thereof

Technical Field

The present invention relates to the field of speakers, and more particularly, to a diaphragm and a speaker including the diaphragm.

Background

Typically, the radial diaphragm of a loudspeaker vibrates axially, thereby generating a pressure wave outside the loudspeaker enclosure with one side. At certain frequencies, there are natural structural resonances in the diaphragm and other moving parts. These resonances can be excited when the diaphragm is driven by a voice coil. They correspond to the peak displacement of the diaphragm, but apart from the main resonance (where the diaphragm can move pistonically), the displacement is in the form of a dynamic bending deformation. These deformations affect the magnitude and directionality of the radiated pressure and are very frequency dependent. Thus, disadvantageously, they affect the sound of the loudspeaker. The lowest frequency at which this occurs is referred to as the "crash frequency" of the drive.

For a desired radiation pressure, driver collapse/destruction must be controlled in one or more of a number of possible ways. The material or geometry of the deformation portion can be designed for high stiffness to increase the collapse frequency above the operating range of the driver. Alternatively, the material of the deformation portion may be selected for strong damping in order to reduce the magnitude of the deformation at resonance.

These methods to control breakup operate in different ways and therefore the most suitable method will depend on other factors such as size, shape, operating frequency range, moving mass objects, cost etc.

Geometries commonly used for added strength include cones and domes; their curvature gives them much more stiffness than a planar diaphragm. Reinforcing ribs may be added to the geometry; these stiffening ribs project generally perpendicular to the diaphragm rear surface and extend in the direction of resonant deformation to increase the frequency of resonance.

Factors such as build height, moving mass objects, cost and decoration may mean that a diaphragm with the geometry described above does not give a sufficiently high collapse frequency. This is especially true in the following cases: the diaphragm must be flat to fit the driver into a shallow enclosure.

Disclosure of Invention

The present invention is generally directed to a method of stiffening a diaphragm of a radial loudspeaker to help increase the collapse frequency above the operating frequency range of the associated driver.

The diaphragm is composed of an integrally formed part and an attached shaped part. The integrally formed part is a radiating surface with reinforcing ribs; its surface may be of any shape, e.g. conical, dome-shaped, planar disc-shaped, rectangular, etc. These ribs are most effective when they run straight perpendicular to the surface (typically, parallel to the axis of motion) and along the longer dimension of the surface geometry (i.e., along the direction of resonant deformation). Additional ribs extending at right angles to these may also be beneficial.

Preferably, the second portion is formed as a thin surface of high coefficient of elasticity material. It may also be conical, dome-shaped, planar, etc. Ideally it will have the same profile as all or part of the back face of the rib, and it may be attached to the back face of the rib.

Slots or holes may be provided at the edges of the radiating surface, in the rib structure and in the shaping surface to allow airflow through the structure. Straight reinforcing ribs inside the structure will define uninterrupted/continuous air passages and in assemblies where the diaphragm is close to other closed air bags, this may be beneficial to avoid high air pressure fluctuations due to diaphragm vibrations. These holes can be sealed in situations where no airflow is required.

The unitary structure may have a substantially higher stiffness than either of the two portions. This helps to design a loudspeaker driver that does not collapse over its operating frequency range.

The adhesive used to attach the two parts may be selected for flexibility and high damping. This may limit the overall stiffness of the structure, but may reduce the magnitude of the resonant deformation.

Accordingly, the present invention provides a diaphragm for a loudspeaker, comprising: the acoustic wave generator includes a radiating surface from which acoustic waves can be projected, a plurality of ribs, a projection away from the radiating surface in a direction transverse to the radiating surface, and at least one stiffening member including a surface connected to the ribs and disposed axially offset from the radiating surface. The radiating surface has a first stiffness and the surface of the stiffening member has a second, greater stiffness.

In one embodiment, the stiffening member is made of a material having a coefficient of elasticity that is greater than the coefficient of elasticity of the material forming the radiation surface.

The radiating surface and the at least one stiffening member may take a variety of shapes including conical, frustoconical, dome-shaped, and planar. They may have the same shape or different shapes from each other.

The plurality of ribs may include two or more ribs, each rib extending radially from a central region of the diaphragm toward an outer edge of the diaphragm. They may also include one or more ribs located at a point between the central region of the diaphragm and the outer edge of the diaphragm and extending circumferentially/annularly.

The two or more radial ribs and the at least one stiffening member may define one or more air passages for providing air flow through the diaphragm as described above.

There may be more than one reinforcing member, for example a pair of reinforcing members, each comprising a planar annular plate and one of which is located within the other. Preferably, the two annular plates are positioned in a coplanar manner, and more preferably may be positioned in a substantially concentric manner.

Desirably, the plurality of ribs may be integrally molded with the radiating surface. The at least one stiffening member may be attached to the plurality of ribs at a point on the rib furthest from the radiating surface.

Preferably, the at least one planar surface is attached to the plurality of ribs by an adhesive. Ideally it will be substantially parallel to the diaphragm.

The invention also provides a loudspeaker comprising a diaphragm as described above.

Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

figure 1 shows a cross-sectional view of a loudspeaker according to the invention;

FIG. 2 shows a cut-away view of a diaphragm according to the present invention;

FIG. 3 shows an axial rear view of a diaphragm according to the present invention;

FIG. 4 shows a cross-section of a diaphragm according to the present invention; and

fig. 5 shows frequency response curves for comparison between a loudspeaker according to the invention comprising a diaphragm with a stiffening member and a loudspeaker comprising a diaphragm without a stiffening member.

Detailed Description

Fig. 1 shows a loudspeaker driver 500. The magnet assembly 502 carries a permanent magnet 504 and a center pole piece 508 and has a cylindrical outer pole piece 506 to define a magnetic field gap 510. The chassis 512 sits concentrically around the magnet assembly 502 and provides support for the rest of the speaker driver 500.

These include a voice coil 514 supported on a voice coil former 516 so as to be at least partially within the magnetic field gap 510. The voice coil former 516 drives the diaphragm 518, which has a flat front surface, in order to reduce the overall depth of the loudspeaker driver 500 relative to a driver containing a conical diaphragm. To provide a degree of rigidity, the diaphragm has reinforcing ribs on its back face, and the voice coil former 516 is attached to these ribs.

At its radially outermost region, diaphragm 518 is supported by a bead 522, bead 522 helping to center/center diaphragm 518 with respect to field gap 510, bead 522 acting as an air seal and providing a restoring force to return diaphragm 518 to its rest position (shown). To increase the restoring force to a suitable level, a suspension 524 is also provided. In the illustrated case, the suspension 524 is attached to suitable tabs 530 on annular ribs 536 (see fig. 2).

Fig. 2 shows the rearmost face of the diaphragm 518 in accordance with an embodiment of the present invention in a more detailed manner. Fig. 3 shows the diaphragm 518 in a rear plan view, and fig. 4 shows the diaphragm in cross-section.

The diaphragm includes a plurality of radial ribs 520, as previously described. These ribs project rearwardly and transversely to the radiating surface 535 of the diaphragm. Typically, they project radially from the central region of the diaphragm to the outermost region of the diaphragm. A plurality of radial ribs 520 extend along the entire radius of the diaphragm at right angles to the center of the diaphragm. Other radial ribs 520 are formed only on a portion of the radius of the diaphragm.

The diaphragm also contains a plurality of annular ribs 536 that project rearwardly and transverse to the radiating surface 535. The ribs are arranged annularly so that they cross the radial ribs 520 at right angles.

In the illustrated embodiment, the annular ribs 536 are arranged to define two concentric circles. The concentric circles may be continuous or, in the embodiment as illustrated, discontinuous. The discontinuous annular ribs allow the radial air channels to be defined, as will be described in more detail below.

In one embodiment, the radiating surface 535, the radial ribs 520, the annular ribs 536, and the tabs 530 are all integrally formed from a single, integrally formed polymeric material.

The annular ribs and the radial ribs, individually and in combination, provide a certain amount of rigidity to the diaphragm 518. However, according to embodiments of the present invention, by providing one or more reinforcement members 538, 540, the rigidity may be increased.

Each of the stiffening members 538, 540 includes a substantially flat surface disposed substantially along the radiating surface 535 and substantially parallel to the radiating plane, which is attached to one or more stiffening ribs. The stiffening members 538, 540 may be shaped according to the rearmost profile of the rib to facilitate easy attachment thereto.

The stiffening member is formed of a material having a higher modulus than the radiating surface.

In the illustrated embodiment, the reinforcement members 538, 540 include a pair of annular plates with the smaller plate being radially located within the larger plate. The two stiffening members 538, 540 are substantially coplanar and concentric. Conveniently, they may be dimensioned to fit within the annular groove defined by the annular rib 536 to allow consistent placement of the stiffening member relative to the diaphragm. However, this is not essential.

Alternatively, the shape of the stiffening members 538, 540, as well as the back profile of the radial ribs 520, annular ribs 536, is envisioned within the scope of the present invention. For example, they may be conical, frustoconical, dome-shaped or planar.

It can be seen that the combination of the radiating surface 535, the radial ribs 520 and the stiffening members 538, 540 serve to define radial air passages through the diaphragm 518, which extend from the central region towards the outer region. In this case, diaphragm 518, voice coil 514, voice coil former 516 and magnet assembly 502 form a sealed air pocket, and the air passages are advantageous in avoiding high air pressure fluctuations therein due to diaphragm vibration.

Fig. 5 is a graph of the frequency response of a speaker.

The dashed lines show the frequency response of a loudspeaker with a planar diaphragm having reinforced radial and annular ribs. It has no stiffening members, but is otherwise similar to the diaphragms disclosed herein. The solid line shows the frequency response of a diaphragm according to an embodiment of the present invention with radial and annular ribs and stiffening members as described above. It can be seen that the response of the reinforced diaphragm is regular when frequencies higher than the frequency of a conventional diaphragm are reached. That is, the collapse frequency of the diaphragm has been increased.

The present invention therefore provides a diaphragm for a loudspeaker in which one or more stiffening members are provided comprising a surface extending along and axially offset from a radiating surface. The stiffening member serves to increase the stiffness of the diaphragm even further, increasing the frequency range over the entire frequency range that can be used by the loudspeaker.

It will, of course, be understood that various modifications may be made to the above-described embodiments without departing from the scope of the invention.

Claims (14)

1. A diaphragm for a loudspeaker, comprising:

a radiation surface from which acoustic waves can be projected;

a plurality of ribs protruding away from the radiation surface in a direction perpendicular to the radiation surface, the radiation surface being formed integrally with the ribs by single molding; and

at least one stiffening member comprising a surface connected to the rib and extending along one side of the radiating surface in a manner substantially parallel to the radiating surface, wherein the material forming the radiating surface has a first stiffness, and wherein the stiffening member comprises a material having a second, greater stiffness.

2. A diaphragm according to claim 1, wherein the plurality of ribs comprises two or more ribs extending radially from a central region of the diaphragm towards an outer edge of the diaphragm.

3. A diaphragm according to claim 2, wherein the two or more radial ribs and the at least one reinforcing member define one or more air channels for providing an air flow through the diaphragm.

4. The diaphragm of claim 1, wherein the plurality of ribs further comprises one or more ribs located between a central region of the diaphragm and an outer edge of the diaphragm and extending annularly.

5. A diaphragm according to claim 4, comprising a pair of stiffening members, each comprising a flat annular plate, one within the other.

6. A diaphragm according to claim 5, wherein the two annular plates are positioned in a coplanar manner.

7. A diaphragm as claimed in claim 5 or claim 6, wherein the two annular plates are positioned in a substantially concentric manner.

8. A diaphragm according to claim 4, wherein the or each annular rib is non-continuous.

9. A diaphragm according to claim 1, wherein the at least one stiffening member is attached to the plurality of ribs at a point on the rib or ribs furthest from the radiating surface.

10. A diaphragm according to claim 1, wherein the stiffening member is attached to the plurality of ribs by adhesive.

11. A diaphragm according to claim 1, wherein the radiating surface is formed in one of the following shapes: conical, frustoconical, dome-shaped, or planar.

12. A diaphragm according to claim 1, wherein the at least one stiffening member is formed in one of the following shapes: conical, frustoconical, dome-shaped, or planar.

13. A loudspeaker comprising a diaphragm as claimed in any one of claims 1 to 12.

14. A loudspeaker comprising a diaphragm as claimed in claim 2, and further comprising a voice coil former for driving the diaphragm, the voice coil former being attached to the back of the radially extending ribs.