GB2499228A - A low-frequency loudspeaker with a low damping suspension system and an anti-rocking arrangement - Google Patents

Abstract

The loudspeaker 12 comprises an enclosure 18, 20 and a planar membrane or diaphragm 14 that moves along an axial direction A when submitted to an excitation. The membrane 14 is attached to the enclosure through a surround suspension 24 that provides low damping. The low damping property is achieved by reducing the stiffness and/or the thickness of the surround material. Guiding means 30, 32 in the form of twin or double spiders 32a, 32b guides the membrane 14 during its axial movement and reduces rocking motions of the voice coil (figs 3A, 3B). Alternative surround constructions are described (figs 4A, 4B, 4C). The loudspeaker is said to have improved low frequency characteristics.

Description

1

A low-frequency loudspeaker with a low damping suspension system

5 The invention relates to loudspeakers.

Several types of low frequency loudspeakers are known and used.

Low frequency electrodynamic loudspeakers are a first type of loudspeakers. These conventional loudspeakers have suspension systems that consist generally of a spider and a surround. Such suspension systems have a 10 very low axial stiffness and enable high displacement. They have multiple roles: guiding role, air proof and high damping (high damping enables a natural equalization of loudspeakers).

However, there are today emerging innovations in loudspeakers such as resonant systems. US 7,702,114 discloses a second type of loudspeakers in 15 which a natural resonance of the loudspeaker is promoted. These resonance systems are very useful to get high dBSPL (SPL standing for "Sound Pressure Levef) even with compact, flat loudspeakers. Such loudspeakers have a very different behaviour as compared to conventional systems: they do not need an initially flat equalized response, whereas high damping behaviour inhibits the 20 performances.

The Applicant has noticed that such loudspeakers are not fully compatible with the guiding means used in the conventional loudspeaker designs.

The Applicant has also noticed that the high damping viscoelastic 25 nature of the suspension system strongly limits the performances.

There is therefore a need to have a new loudspeaker design that remedies at least one of the above-mentioned drawbacks.

Having the foregoing in mind the invention concerns a loudspeaker comprising :

30 - an enclosure,

2

- a membrane that is operable to move along an axial direction when submitted to an excitation, wherein the membrane is attached to the enclosure through a surround suspension that provides low damping,

- guiding means for guiding the membrane during its axial 5 movement.

Thanks to a low damping surround suspension and distinct membrane guiding means the thus configured loudspeaker provides better performances than conventional loudspeakers.

The low damping surround suspension has less a guiding role than 10 conventional surround suspensions. This guiding role is mainly performed by the separate membrane guiding means.

Low damping enables higher magnitudes of displacement of the membrane for the same power supply. A low damping provides the loudspeaker with a low axial stiffness.

15 It is to be noted that the low damping surround suspension is air-

proof.

According to a possible feature, the damping provided by the surround suspension is less than 0.5 kg/s.

According to a possible feature, the damping provided by the 20 surround suspension is less than 0.15 kg/s.

According to a possible feature, the surround suspension has a small thickness so as to provide low damping.

Due to a small thickness, the surround suspension cannot much guide the membrane during its axial movement/displacement. The guiding role 25 is therefore mainly taken over by the separate membrane guiding means.

It is to be noted that the invention makes provision for reducing the thickness of the conventional surround suspensions without changing the material constituting the latter.

According to a possible feature, the surround suspension has a 30 thickness that is less than 0.4 mm.

According to another possible feature, the suspension has a thickness that is less than 0.25 mm.

3

According to a possible feature, the loudspeaker comprises a magnetic circuit located within the enclosure vis-a-vis the membrane along the axial direction, the membrane extending in a radial direction perpendicular to the axial direction and over a dimension that is greater than the radial 5 dimension of the magnetic circuit.

This configuration of the loudspeaker is thus rather flat compared to configurations in which the membrane has a frusto-conical shape.

According to a possible feature, the membrane comprises supporting means, the membrane guiding means being attached to the supporting means 10 and the enclosure.

In the conventional loudspeakers the membrane guiding means are typically attached to the voice-coil.

According to another possible feature, the supporting means are arranged around the magnetic circuit.

15 Put it another way, the supporting means are arranged outwardly relative to the magnetic circuit, which leaves more room to place the supporting means.

This outer configuration enables improvement of membrane guiding and stability.

20 According to a possible feature, the supporting means are located between the magnetic circuit and the enclosure.

According to a possible feature, the supporting means extend axially from the membrane over a distance that is greater than the axial distance between the membrane and the magnetic circuit.

25 This arrangement makes it possible to lower and therefore adjust the position of the rocking center of the loudspeaker moving part comprising the membrane and the membrane supporting means.

This is because the membrane guiding means may be attached to the supporting means in a lower position compared to the prior art loudspeaker 30 design in which the membrane guiding means are attached to the voice-coil.

4

According to a possible feature, the enclosure comprises a wall to which the magnetic circuit is fixed, the supporting means extending axially from the membrane towards the wall.

According to a possible feature, the membrane guiding means are 5 attached to the supporting means at least partially in a portion thereof that is radially spaced apart from the magnetic circuit, the membrane guiding means being thus attached so that the rocking center of the loudspeaker moving part comprising the membrane and the guiding membrane means is axially located at an axial distance relative to the membrane that is greater than the axial 10 distance between the membrane and the magnetic circuit.

Thanks to this configuration, the position of the rocking center may be more appropriately adjusted and placed in a low position, thereby leading to small oscillations of the voice-coil in the magnetic circuit. Axial stability of the membrane is therefore enhanced.

15 According to a possible feature, the membrane guiding means comprise at least two spiders.

The two-spider configuration provides improved guiding efficiency.

When the two spiders are attached to outwardly arranged supporting means, adjustment, and even maximization, of the axial distance between said 20 two spiders may be obtained. A greater spider inter-distance d provides a better axial guiding of the membrane. This is because the mechanical torque that prevents rocking of the membrane depends on d2for a two-spider configuration.

According to a possible feature, said at least two spiders are spaced apart from each other in a parallel relationship.

25 According to a possible feature, the membrane substantially lies in a plane when at rest.

According to a possible feature, the surround suspension comprises first and second suspension members that are spaced apart one from another so as to define a volume therebetween, the volume being filled with air. 30 This arrangement makes it possible to avoid that a single too thin surround suspension winds around itself during the axial movement of the membrane.

5

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

- Figure 1 is a schematic cross-sectional view of a loudspeaker according to the invention;

5 - Figure 2A is a cross-sectional view of the left-hand part of a loudspeaker with a first double spider configuration;

- Figure 2B is a cross-sectional view of the right-hand part of a loudspeaker with a second double spider configuration according to the invention;

10 - Figure 3A schematically illustrates the oscillation of the Figure 2A

left-hand part loudspeaker moving part configuration;

- Figure 3B schematically illustrates the oscillation of the Figure 2B right-hand part loudspeaker moving part configuration;

- Figure 4A is a schematic partial enlarged view illustrating a 15 surround suspension made of two suspension members according to a first configuration;

- Figure 4B is a schematic view, similar to Figure 4A, of a surround suspension system made of two suspension members according to a second configuration;

20 - Figure 4C is a schematic cross-sectional view of the Figure 1

loudspeaker incorporating the Figure 4B second configuration of the surround suspension.

As schematically represented in Figure 1, a loudspeaker 10 comprises an enclosure 12 and a membrane 14 that is attached to the 25 enclosure.

Membrane 14 is operable to move along an axial direction A when submitted to an excitation. Enclosure 12 such as represented forms a closed casing.

A magnetic circuit 16 is mounted inside the casing and is facing 30 membrane 14.

More particularly, magnetic circuit 16 is disposed vis-a-vis the lower face 14a of the membrane that is oriented towards the interior of the casing,

6

whereas the opposite upper face 14b is oriented towards the outside of the enclosure 12.

The casing comprises a bottom wall 18 which is substantially flat and which is provided at its periphery with an upwardly peripheral edge 18a.

5 Peripheral edge 18a extends axially along axial direction A so as to confer a substantially U-shape to enclosure 12 in the cross-sectional view of Figure 1.

In the current embodiment the loudspeaker has a symmetry of revolution around axis A.

10 Bottom wall 18 has a substantially centered aperture 18b in which magnetic circuit 16 is mounted in a fixed manner, e.g. by screwing.

Enclosure 12 further comprises a top wall 20 which rests against the upper portion of peripheral edge 18a.

Top wall 20 has a central opening 22 in which membrane 14 is

15 arranged.

Membrane 14 is attached to peripheral top wall 20 through a surround suspension 24 which here has a symmetry of revolution.

When at rest as illustrated in Figure 1, membrane 14 lies in a plane and extends in a radial direction that is perpendicular to axial direction A. 20 Peripheral top wall 20 also extends radially relative to axis A.

Furthermore, membrane 14 extends radially over a radial dimension that is greater than the radial dimension of magnetic circuit 16.

Magnetic circuit 16 comprises a central portion 16a and a peripheral portion 16b defining together a magnetic gap. The central portion 16a is 25 composed of a permanent magnet 16d, an upper plate 16c and a bottom plate 16e. The upper plate 16c and the peripheral portion 16b contribute to the flow of the magnetic flux in the magnetic circuit. The bottom plate 16e allows a precise positioning of the permanent magnet 16d in the magnetic circuit.

As illustrated in Figure 1, an actuator 26 which is here, for instance, a 30 voice-coil is immersed in the magnetic field created by permanent magnet 16d.

Voice-coil 26 comprises a voice-coil former 27 that is affixed to lower face 14a of the membrane, e.g. by gluing.

7

Voice-coil 26 is equipped at its free end with a coil 28 composed of thin wire or wires wrapped around voice-coil former 27 and that extends axially inside the magnetic gap.

The thickness of the wire or wires is small enough so that voice-coil 26 equipped with such wire or wires is suitable for axially moving within the magnetic gap without mechanically interfering with the edges of central portion 16a and peripheral portion 16b of the magnetic circuit.

In the course of use of the loudspeaker, voice-coil 26 is caused to axially move in the magnetic field due to the current flowing within the wire or wires of the coil 28.

This motion along axis A is therefore transmitted to membrane 14 which then generates sound.

As represented in Figure 1, membrane 14 comprises supporting means 30, also called holding members, which are located between magnetic circuit 16 and enclosure 12.

Supporting means 30 are radially offset relative to magnetic circuit 16 and, more particularly, to voice-coil 26.

More particularly, supporting means are arranged outwardly relative to magnetic circuit 16, at a distance thereof.

Supporting means extend axially from the lower face 14a of the membrane over an axial distance that is greater than the axial distance "a" between face 14a and the top face of upper plate 16c of central portion 16a.

Supporting means 30 are thus spaced apart from magnetic circuit 16 in a radial direction and from bottom wall 18 along an axial direction parallel to axis A.

In the current embodiment, supporting means 30 may, for instance, assume the shape of a substantially cylindrical wall that is fixed close to the free peripheral edge 14c of the membrane but at some distance thereof.

It is to be noted that supporting means or holding members 30 may take other forms and, for example, may be separate members disposed along the same circumference of the membrane.

8

For example, annular wall portions that extend along the same circumference and that are spaced apart from each other may be convenient to serve as supporting means.

More particularly, supporting means 30 serve as a support to guiding 5 means 32 of the loudspeaker.

Guiding means 32 aim at guiding the axial movement (along axis A) of membrane 14 in an efficient and reliable manner.

Membrane guiding means 32 have two opposite ends and are attached at one end to supporting means 30 and at the opposite end to 10 enclosure 12.

More particularly, enclosure 12 comprises a supporting peripheral wall or peripheral portions of wall 34 which extend downwardly from the lower face 20a of top wall 20 towards bottom wall 18.

The axial extension of peripheral supporting wall or portions of wall 15 34 is substantially the same as that of supporting means 30 when the membrane is at rest (Figure 1).

It is to be noted that supporting wall 34 may take another shape and be located at another place within the enclosure.

As represented in Figure 1, guiding means 32 are attached to the 20 lower part of supporting means 30 in a region that is closed to the free end of supporting means 30.

More particularly, membrane guiding means 32 comprise two spiders 32a and 32b that are parallel and spaced apart from each other by a distance d.

The double spider configuration provides an efficient guiding of the 25 moving part of the loudspeaker.

Since each spider is stiff in the radial direction the use of two axially spaced apart spiders makes it possible to avoid rocking of the loudspeaker moving part with a too large magnitude. The more the two spiders are spaced apart, the less rocking is obtained.

30 It is to be noted that the spiders 32a and 32b are made of a very low damped material, which is made possible for large, non-air-proofed spiders.

9

The spiders have also a very low stiffness in the axial direction (due to geometric effects) so that they have a limited effect on the compliance and damping values.

Instead of being directly fixed to the voice-coil the spiders are fixed to 5 supporting means 30 located around the magnetic circuit.

This arrangement makes it possible to have more space to place the spiders within the enclosure.

This arrangement also makes it possible to freely choose the axial position of both spiders as well as adjust their radial dimension. 10 It is to be noted that the two spiders act as two parallel stabilization systems the main objective of which is to avoid or, at least, reduce the rocking of the loudspeaker membrane.

Figure 2A is a cross-sectional view of the left-hand part of a loudspeaker in which a double spider configuration 40 is integrated between the 15 top wall 20 of the enclosure and the voice-coil former 27.

Figure 2B is a cross-sectional view of the right-hand part of a loudspeaker corresponding to an embodiment of the invention in which the double spider configuration 32 of Figure 1 is fixed to supporting means 30 (additional body or member) located outside the magnetic circuit which, 20 therefore, frees peripheral space to vertically locate the two spiders 32a and 32b.

Figures 2A and 2B have been placed next to each other for comparison purpose only.

As illustrated in Figure 2B, S1 and S2 are the spider fixing points, C1 25 and C2 are the top and bottom points inside the magnetic gap (i.e. these points are possible collision points between the coil and the magnetic circuit elements) and G is the rocking center of the loudspeaker moving part (membrane, membrane supporting means 30, spiders 32a-b and voice-coil).

The equilibrium equations of the loudspeaker moving-part subjected 30 to rocking are given by the following expressions:

-IC02Q- rrestoring perturbation l~restoring=~kr* d2* 0/2

10

where I is the moment of inertia,

roerturbation is the moment of the perturbation forces in the system,

kr is the radial stiffness of each spider (assumed to be identical),

0) is the system pulsation,

5 d is the distance between the two spiders (d=S1 S2),

6 is the rocking angle.

Using the two previous equations, 0 may be expressed as follows:

6= roerturbation / (kr d2/2 - I CO2)

Thus, the maximum radial displacement Ar of the coil within the 10 magnetic gap is given by the following:

AM* 6=1* rperturbation/(kr* d2/2 - lOJ2) (*)

with I being the largest distance between the rocking center G and the coil extremities inside the magnetic gap (/=max(GC1, GC2)).

Figure 3A illustrates the axial position of the rocking center of the 15 loudspeaker moving part that corresponds to the configuration represented in Figure 2A.

The double spider configuration 40 is therefore directly fixed to the voice-coil former. It results from this arrangement that the rocking center G of the loudspeaker moving part is axially located above the magnetic circuit 16 at 20 an axial distance hi which corresponds to the largest distance between the rocking center and the lowest voice-coil extremity C2.

This high axial position of rocking center G leads to high magnitude oscillations inside the magnetic gap g.

As represented in Figure 3A, the lowest extremity C2 of voice-coil 26 25 collides with the inner walls of the magnetic gap.

Figure 3B illustrates the axial position of the rocking center of the loudspeaker moving part that corresponds to the configuration represented in Figure 2B.

As represented in Figure 3B, the outwardly-configured double spider 30 configuration relative to the magnetic circuit makes it possible to adjust the axial position of the rocking center G in a lower position.

11

Thus, for the same rocking angle 0 (G is at the distance h2 from the lowest voice-coil extremity C2 which is much less than hi) this makes it possible to reduce the magnitude of the oscillations inside the magnetic gap g, and, therefore, to avoid any collision with the inner walls of the magnetic gap.

5 In order to decrease the radial displacement of the voice-coil extremity C2 the following actions may be performed:

- h2 has to be as small as possible, which means that the rocking center G is as close as possible to the geometric center (half the distance between C1 and C2) of the voice-coil inside the magnetic gap;

10 - the rocking resonance frequency has to be as high as possible,

which means that the moment of inertia I has to be as small as possible; this means that the masses are as close as possible to G (thanks to the outer double spider configuration it is possible to locate most of the mass of the loudspeaker moving part between spider fixing points S1 and S2 on supporting 15 means 30);

- the distance d between the two spiders 32a and 32b has to be as great as possible.

In an embodiment, the two spiders are located at the largest possible distance from each other and the rocking center has to coincide with the 20 geometric center of the voice-coil inside the gap (optimal rocking center). The mass center of the loudspeaker moving part is coincident with the optimal rocking center.

In another embodiment, the ratio h/d2 (h2/d2 in Figure 3B) is minimized and the mass center of the loudspeaker moving part is as close as 25 possible to the optimal rocking center.

Reverting to Figure 2B, the surround suspension 24 provides low damping.

This low damping is obtained in the current embodiment through a decrease in the surround thickness.

30 Thus, by decreasing the surround thickness without changing its constituting material the damping may be less than 0.5kg/s and even less 0.15kg/s.

12

Thanks to a slight modification which is quite easy to implement on a manufacturing line, a low stiffness and low damping value may be obtained.

It is to be noted that the surround suspension with a reduced thickness is still air-proof.

5 By way of example, decreasing by four the surround thickness, e.g.

from 1 mm to 0.25 mm, decreases the damping from 1.6 kg/s to 0.08 kg/s.

The reduced damping is thus twenty times lower than initial damping for a reduction with a factor of four.

At the same time, the compliance is multiplied by nearly twenty, 10 which is well adapted for low-frequency loudspeakers.

Since the spiders have a low damping as compared to surrounds a much lower damping of the loudspeaker is obtained by using two spiders and a thin low damping surround.

With a reduced thickness, the surround suspension of the 15 loudspeaker is no longer rigid enough to correctly guide the membrane during its axial displacement. However, the above-described membrane guiding means 32 (e.g. double spider configuration) take over the guiding role of the suspension system and provide very efficient stabilization with respect to a possible rocking movement of the loudspeaker moving part.

20 It is to be noted that the outwardly-arranged supporting means for fixing thereto membrane guide means 32 make it possible to achieve membrane displacements of greater magnitude than in the Figure 2A configuration. In the loudspeaker configuration according to the invention the surround suspension has a negligible stiffness and the two spiders may be each 25 softer than the conventional spiders since guiding is intrinsically more efficient than in the prior art.

Efficiency of the guiding will now be explained.

• G belongs to the spider plane (because krSUrround « krspidei)

• kn=krSUrround in the above expression (*) since only the 30 surround suspension is strained radially in the system,

• d=S1S2

• /=S1S2

13

The guiding advantages of the new suspension system over the conventional ones are derived from the followings:

• (kr*d2)invention > (kr*d2) conventional because krsurroun(j« krspider

• (I)invention > (I)conventional since, thanks to the outer spider configuration, it is possible to gather the moving part masses near the ORC (Optimal Rocking Center).

• (I)invention < (I) conventional because G can be modified through adjusting the position of the two spiders. In the conventional case, G is in an upper position.

^ (Af)invention ^ (Ar) conventional for the Same rperturbation

Therefore, the guiding system of the invention is more efficient than the conventional ones.

By way of example, the configuration illustrated in Figure 1 may be further specified as follows.

The bottom spider 32b is located at the lowest possible position on the supporting means 30.

Practically speaking, the distance between the lower spider 32b and bottom wall 18 is preferably the same or lower than the axial distance between the coil bottom end C2 and the bottom of the magnetic gap (Figure 2B). This avoids the spider 32b, or the supporting means 30 if the spider 32b is not at the lowest possible position, to block the movement of the coil by hitting bottom wall 18 when the loudspeaker moving part is at its lowest position.

The upper spider 32a is placed at a distance from the lower spider 32b such that the middle between the two spiders corresponds to the optimal rocking center position. In other words, the optimal rocking center position is located on a median (horizontal) line that is disposed between the two spiders.

Furthermore, the thickness of the surround suspension 24 is 0.2 mm, its modulus of elasticity is 1 Mpa and (3Rayieigh is equal to 1.5 ms.

Each spider has an elasticity of 2000 pm/M, a damping value of 0.18 kg/s, an internal diameter of 92 mm and an external diameter of 178 mm.

According to variant embodiments, the loudspeaker may have a surround suspension composed of two suspension members.

14

More particularly, the surround suspension comprises first and second suspension members that are spaced apart from each other so as to define a volume therebetween as represented in Figures 4A-C.

It is to be noted that the surround suspension has a symmetry of revolution around axis A.

More particularly, the two suspension members provide the surround suspension with an overall substantially toroTdal shape.

As represented in Figure 4A, a surround suspension system 50 comprises first and second suspension members 50a and 50b that are spaced apart from each other so as to define a volume V1 therebetween.

The two suspension members 50a and 50b are arranged on the same side of the loudspeaker enclosure. For example, both members 50a and 50b are fixed, e.g. by gluing, to the upper face 20b of top wall 20 and to the upper face 14b of the membrane.

This configuration is easy to implement since the two members may be fixed together, e.g. by gluing, beforehand in a separate operation and then the whole set of fixed members is fixed, e.g. by gluing, to the outside face of the loudspeaker.

The volume V1 defined between these two suspension members is filled with air.

This arrangement makes it possible to avoid that a single too thin surround suspension winds around itself during the axial movement of the membrane.

It is to be noted that the pressure of the air that is trapped between suspension members 50a and 50b may be selected around the value of the atmospheric pressure or slightly above so as to prevent winding of the suspension system around itself while ensuring a sufficient elasticity.

The first and second suspension members may be each as thin as a single surround suspension.

It is to be noted that the thickness of each suspension member may even be lower than in the Figures 1 and 2B embodiment in some instances.

15

This is because the winding probability is reduced by the virtue of air trapped between the suspension members.

As represented in Figure 4B, a surround suspension system 60 comprises first and second suspension members 60a and 60b that are spaced 5 apart from each other so as to define a volume V2 filled with air therebetween.

In this second variant embodiment the two suspension members are fixed, e.g. by gluing, on either part of the loudspeaker enclosure. More particularly, upper suspension member 60a is fixed both to the upper face 20b and upper face 14b while lower suspension member 60b is fixed both to the 10 lower face 20a and lower face 14a.

Volume V2 is therefore greater than volume V1 of Figure 4A.

Figure 4C is a view similar to that of Figure 1 except that the loudspeaker 70 is equipped with the surround suspension configuration 60 of Figure 4B. All the other elements remaining the same.

15

16

Claims (19)

1. A loudspeaker comprising :

- an enclosure,

- a membrane that is operable to move along an axial direction when submitted to an excitation, wherein the membrane is attached to the enclosure through a surround suspension that provides low damping,

- guiding means for guiding the membrane during its axial movement.

2. The loudspeaker of Claim 1, wherein the damping provided by the surround suspension is less than 0.5 kg/s.

3. The loudspeaker of Claim 1 or 2, wherein the damping provided by the surround suspension is less than 0.15 kg/s.

4. The loudspeaker of any of Claims 1 to 3, wherein the surround suspension has a low thickness so as to provide low damping.

5. The loudspeaker of any of Claims 1 to 4, wherein the surround suspension has a thickness that is less than 0.4 mm.

6. The loudspeaker of any of Claims 1 to 5, wherein the surround suspension has a thickness that is less than 0.25 mm.

7. The loudspeaker of any of Claims 1 to 6, wherein it comprises a magnetic circuit located within the enclosure vis-a-vis the membrane along the axial direction, the membrane extending in a radial direction perpendicular to the axial direction and over a dimension that is greater than the radial dimension of the magnetic circuit.

8. The loudspeaker of any of Claims 1 to 7, wherein the membrane comprises supporting means, the membrane guiding means being attached to the supporting means and the enclosure.

9. The loudspeaker of any of Claims 7 and 8, wherein the supporting means are arranged around the magnetic circuit.

10. The loudspeaker of Claim 9, wherein the supporting means are located between the magnetic circuit and the enclosure.

17

11. The loudspeaker of any of Claims 8 to 10 when Claim 8 depends on Claim 7, wherein the supporting means extend axially from the membrane over a distance that is greater than the axial distance between the membrane and the magnetic circuit.

5

12. The loudspeaker of any of Claims 8 to 11 when Claim 8 depends on Claim 7, wherein the enclosure comprises a wall to which the magnetic circuit is fixed, the supporting means extending axially from the membrane towards the wall.

13. The loudspeaker of any of Claims 8 to 12 when Claim 8 depends 10 on Claim 7, wherein the membrane guiding means are attached to the supporting means at least partially in a portion thereof that is radially spaced apart from the magnetic circuit, the membrane guiding means being thus attached so that the rocking center of the loudspeaker moving part comprising the membrane and the membrane supporting means is axially located at an axial distance relative to the 15 membrane that is greater than the axial distance between the membrane and the magnetic circuit.

14. The loudspeaker of any of Claims 1 to 13, wherein the membrane guiding means comprise at least two spiders.

15. The loudspeaker of Claim 14, wherein said at least two spiders 20 are spaced apart from each other in a parallel relationship.

16. The loudspeaker of any of Claims 1 to 15, wherein the membrane substantially lies in a plane when at rest.

17. The loudspeaker of any of Claims 1 to 16, wherein the surround suspension comprises first and second suspension members that are spaced

25 apart one from another so as to define a volume therebetween, the volume being filled with air.

18. A loudspeaker substantially as hereinbefore described, with reference to, and as shown in, any of Figures 1, 2B and 4C of the accompanying drawings.

30

19. A loudspeaker surround suspension system substantially as hereinbefore described, with reference to, and as partially shown in, Figure 4A or Figure 4B of the accompanying drawings.

•.'????.• INTELLECTUAL

*.*. .V PROPERTY OFFICE

18

Application No: GB 1202244.8 Examiner: Peter Easterfield

Claims searched: 1-17 Date of search: 27 April 2012

Patents Act 1977: Search Report under Section 17

Documents considered to be relevant:

Category

Relevant to claims

Identity of document and passage or figure of particular relevance

X

1,7, 17

EP 2291004 A1

(HARMAN) see paras [0041]-[0044]

X

1,7, 17

EP 1484941 A1

(HARMAN) see para [0019] and fig 2a

Categories:

X

Document indicating lack of novelty or inventive

A

Document indicating technological background and/or state

step

of the art.

Y

Document indicating lack of inventive step if

P

Document published on or after the declared priority date but

combined with one or more other documents of

before the filing date of this invention.

same category.

&

Member of the same patent family

E

Patent document published on or after, but with priority date

earlier than, the filing date of this application.

Field of Search:

x

Search of GB, EP, WO & US patent documents classified in the following areas of the UKC :

Worldwide search of patent documents classified in the following areas of the IPC

H04R

The following online and other databases have been used in the preparation of this search report

WPI, EPODOC

International Classification:

Subclass

Subgroup

Valid From

H04R

0007/20

01/01/2006

H04R

0009/02

01/01/2006

Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk