Patent Description:
Loudspeakers are widely used in various areas, for example in consumer products like radios, television sets, audio players, computers, mobile phones and electronic musical instruments, and commercial applications, for example sound reinforcement in theatres, concert halls, and public address systems. Furthermore, in vehicles, for example planes, ships and cars, loudspeakers are widely used.

A loudspeaker may comprise a magnet, in particular a permanent magnet, a voice coil arranged in a magnetic field provided by the magnet, a diaphragm (also called membrane) coupled to the voice coil and elastically coupled via a suspension (also called surround) to a frame of the loudspeaker. For example, the voice coil may be a coil of wire capable of moving axially in a cylindrical gap containing a concentrated magnetic field produced by the permanent magnet. When an alternating electrical current of for example an electrical audio signal is applied to the voice coil, the voice coil is forced to move back and force due to the Faraday's law of induction, which causes the membrane attached to the voice coil to move back and forth, pushing on the air to create sound waves. The combination of magnet and voice coil is also called drive unit or electromagnetic motor system. Arrangement and properties of the magnet and voice coil may affect characteristics of a loudspeaker. Characteristics of a loudspeaker may relate to efficiency, i.e. the sound power output divided by the electrical power input, sensitivity, i.e. the sound pressure level at for example 1W electrical input measured at <NUM> meter, linearity or frequency response, maximum acoustic output power, size and weight. Characteristics may be different for different frequencies, for example small loudspeakers may have lower efficiency at low frequencies than large loudspeakers.

In particular in cars, a plurality of loudspeakers may be arranged at different locations to provide adequate sound output for each occupant. For example, loudspeakers may be arranged in the dashboard, doors, the ceiling, seats and headrests. A full-spectrum audio output may require large installation space, in particular the output of low bass frequencies may require large loudspeakers and large volumes. However, installation space may be sparse, in particular e.g. in headrests. Relevant documents in this context are <CIT>, <CIT>, and <CIT>.

In view of the above, there is a need in the art to improve at least some of the above characteristics of a loudspeaker. For example, there is a need for compact sized loudspeakers providing high efficiency, in particular at low frequencies.

According to the present invention, a loudspeaker as defined in the independent claim is provided. The dependent claims define embodiments of the invention.

According to various examples, a loudspeaker comprises a first diaphragm and a second diaphragm. The first diaphragm is arranged spaced apart from the second diaphragm. The loudspeaker comprises furthermore a first voice coil coupled to the first diaphragm, a second voice coil coupled to the second diaphragm, and a magnet assembly. The magnet assembly comprises a magnet, a magnetic piece and a spacer of non-magnetic material connecting the magnet and the magnetic piece such that a gap is provided between the magnet and the magnetic piece. The first voice coil is arranged at a first end of the gap and the second voice coil is arranged at a second end of the gap opposite the first end of the gap.

For example, the magnet may have a right hollow cylindrical shape and the magnetic piece may have also right hollow cylindrical shape. The magnet may have a ring shaped cross section. The magnetic piece may also have a ring shaped cross section. The magnetic piece may be smaller than the magnet such that it can be inserted into the hollow space of the magnet. In other examples, the magnetic piece may be larger than the magnet such that the magnet can be inserted into the hollow space of the magnetic piece. The gap between the magnet and the magnetic piece may have a right hollow cylindrical shape. In some examples, the gap may have a ring shaped cross section. The magnet, the magnetic piece and thus the gap may have any other appropriate shape, for example a right hollow cylindrical shape with a cross section having an inner and/or outer circumference in the shape of a polygon, an ellipse or a combination of straight and/or curved sections.

A width of the gap may relate to the distance between the magnet and the magnetic piece. The spacer may determine the width of the gap. The spacer may occupy a part of the gap. However, in particular the ends of the gap may not be occupied by the spacer thus providing at each end a corresponding air gap for receiving the first voice coil and the second voice coil, respectively.

The first voice coil may be configured and arranged such that it enters from the first end of the gap into the air gap. The first end of the gap may be a base of the right hollow cylindrical shape. The second voice coil may be configured and arranged such that it enters from the opposite second end or base of the gap into the air gap. The air gaps may have a width of a few millimeters, for example in a range of <NUM> to <NUM> millimeters.

The non-magnetic spacer may be arranged at a center along a height of the gap. The non-magnetic spacer may define the gap width and assuring a fixed arrangement of the magnet with respect to the magnetic piece. The height of the gap may be in a range of a few millimeters to a few centimeters, for example in a range of <NUM> to <NUM> millimeters.

The magnet may be made of a magnetic material, i.e. the magnet may be a permanent magnet. The magnet may have a first magnetic polarity at the first end of the gap and a second magnetic polarity at the second end of the gap. In other words, the magnet may have a first magnetic polarity at a first end or base of the magnet and a second magnetic polarity at a second opposing end or base of the magnet. The first magnetic polarity may be different from the second magnetic polarity. For example, the first magnetic polarity may be a magnetic north pole and the second magnetic polarity may be a magnetic south pole, or vice versa.

The magnetic material of the magnetic piece may comprise any ferromagnetic material, for example iron, a cobalt, nickel or a combination thereof.

The non-magnetic material of the spacer may comprise for example plastics. However, the non-magnetic material may comprise any other paramagnetic, diamagnetic or antiferromagnetic material. The non-magnetic material may comprise a combination of non-magnetic materials, for example plastics, resin, paper, glass fibers, carbon fibers and so on. The spacer may be coupled to the magnet and the magnetic piece by any appropriate mounting technology, for example gluing or press fitting.

The first diaphragm may be arranged proximate to the first end of the gap and the second diaphragm may be arranged proximate to the second end of the gap such that the first diaphragm and the second diaphragm are arranged at opposite sides of the gap. At least within the gap of the magnet assembly a first magnetic field is provided at the first end of the gap and a second magnetic field is provided at the second end of the gap due to the arrangement of the magnet and the magnetic piece. Thus, two voice coils in connection with two diaphragms may be driven in corresponding first and second magnetic fields, wherein these first and second magnetic fields are created by a single magnet assembly, comprising in particular a single magnet only. Thus, the loudspeaker may have a compact and light weight design and may require small installation space while providing high efficiency and high power output due to the two driven diaphragms.

The magnet assembly may comprise at least one hollow cylindrical (washer-shaped) pole piece. In particular, the magnet assembly may comprise two pole pieces. For example, a first pole piece may be arranged at the first end of the gap, and a second pole piece may be arranged at the second end of the gap. Each pole piece may be made of magnetic material, for example iron. Each pole piece may be coupled to the magnet. For example, the magnet may be a single ring magnet arranged coaxially between the first and second pole pieces.

In various examples, an outer diameter of the magnetic piece is smaller than an inner diameter of the magnet. In some examples, a height of the magnetic piece may be larger than the height of the magnet, for example the height of the magnetic piece may correspond essentially to the height of the magnet plus the height of the first pole piece and the height of the second pole piece. In other examples, the height of the magnetic piece may be essentially the same as a height of the magnet. The magnetic piece may be arranged within the magnet with the spacer arranged between the magnetic piece and the magnet. The spacer may have at least partially a smaller height than the magnetic piece and the magnet. The spacer may be arranged at the center in the height direction of the magnetic piece and/or magnet. The spacer may have at least partially an annular shape in cross section. An inner surface of the spacer may be mounted at an outer surface of the magnetic piece, for example by gluing or press fitting. An inner surface of the magnet may be mounted at an outer surface of the spacer, for example by gluing or press fitting. As a result, the gap between the magnet and the magnetic piece is at least partially filled with the spacer, wherein at least the ends of the gap are not filled with the spacer to accommodate the voice coils. However, the voice coils may be configured and arranged such that they do not contact the magnetic piece and the magnet, and are movable within the gap in the height direction of the gap upon a magnetic force induced by a driving current through the corresponding voice coil and the magnetic field within the gap. Arranging the magnet outside the magnetic piece reduces restrictions on the form and size of the magnet thus allowing the use of powerful magnets and appropriate magnet designs.

In further examples, an inner diameter of the magnetic piece is larger than an outer diameter of the magnet. In some examples, a height of the magnetic piece may be larger than the height of the magnet, for example the height of the magnetic piece may correspond essentially to the height of the magnet plus the height of the first pole piece and the height of the second pole piece. In other examples, the height of the magnetic piece may be essentially the same as a height of the magnet. The magnet may be arranged within the magnetic piece with the spacer arranged between the magnetic piece and the magnet. The spacer may have at least partially a smaller height than the magnetic piece and the magnet. The spacer may be arranged at the center in the height direction of the magnetic piece and/or magnet. The spacer may have at least partially an annular shape. An inner surface of the spacer may be mounted at an outer surface of the magnet, for example by gluing or press fitting. An inner surface of the magnetic piece may be mounted at an outer surface of the spacer, for example by gluing or press fitting. As a result, the gap between the magnet and the magnetic piece is at least partially filled with the spacer, wherein at least the ends of the gap are not filled with the spacer to accommodate the voice coils.

For example, the first voice coil is arranged at least partially inside the gap at one end of the gap, and the second voice coil is arranged at least partially inside the gap at another opposite end of the gap. The voice coils may be configured and arranged such that they do not contact the magnetic piece and the magnet, and are movable within the gap in the height direction of the gap upon a magnetic force induced by a driving current through the corresponding voice coil and the magnetic field within the gap. Arranging the magnet inside the magnetic piece may reduce the size of the magnet assembly thus allowing a compact design of the loudspeaker.

According to various examples, the magnet comprises a ring magnet with an axial magnetization, i.e. the magnet may have a right hollow cylindrical shape with a ring shaped cross section. However, the magnet may have any other shape which may be rotationally symmetrical or non-rotationally symmetrical, for example an ellipsoid shape, a polygon shape, a curved shape, or a combination of straight and curved sections. A shape of an inner surface of the magnet may have the same shape as an outer surface of the magnet or the inner surface of the magnet and the outer surface and of the magnet may have different shapes, for example, the inner surface may have a circular shape and the outer surface may have a polygonal shape. In any case, the magnetization may be in the height direction, for example along an axis of rotational symmetry. In combination with the magnetic piece, within the gap a magnetic field (e.g. B-field) may extend in a radial direction, at least at the first end and second end of the gap. The magnetic field at the first end of the gap may extend in a direction opposite to a direction of the magnetic field at the second end of the gap. For example, at the first end the magnetic field may be directed in a radially inward direction, and at the second end the magnetic field may be directed in a radially outward direction.

Furthermore, the loudspeaker comprises a basket or frame coupled to at least one of the magnet and the magnetic piece. The basket may be made of plastics or metal, e.g. aluminum, and may provide supports for mounting the loudspeaker at the place of installation, for example in a door or a headrest of a car.

The diaphragms may be mounted at the basket. According to the invention, the loudspeaker comprises a first surround coupling an outer circumference of the first diaphragm to the basket, and a second surround coupling an outer circumference of the second diaphragm to the basket. The first surround and second surround may be made of elastic materials, for example rubber or plastics. The basket may support the first diaphragm, the second diaphragm and the magnet assembly in a sandwiched manner with the magnet assembly being arranged between the first diaphragm and the second diaphragm. Thus, a main direction of sound radiation of the first diaphragm and a main direction of sound radiation of the second diaphragm may be oppositely directed. When the loudspeaker is arranged for example in a headrest of a car, an interior can be effectively provided with sound.

In various examples, the first voice coil is coupled to the first diaphragm near or at an outer circumference of the first diaphragm and the second voice coil is coupled to the second diaphragm near or at an outer circumference of the second diaphragm. Arranging and coupling the voice coil at or near an outer circumference of the diaphragm results in a large diameter of the voice coil and a correspondingly large diameter of the gap of the magnet assembly. Large mechanical forces can be generated between the voice coil and the magnetic field in the gap and transferred homogeneously to the diaphragm. Large acoustic output power and high efficiency may be achieved at a compact design.

According to the invention, the loudspeaker comprises an elastic element arranged between the first diaphragm and the second diaphragm, wherein a first end of the elastic element is coupled to a center of the first diaphragm and a second end of the elastic element is coupled to a center of the second diaphragm. The first and second ends of the elastic element may be ends at opposite sides of the elastic element in a longitudinal direction. The elastic element may be configured to exert a counterforce upon compression and/or extension of the elastic element in the longitudinal direction of the elastic element. The elastic element may comprise for example a spring element comprising one or more springs of elastic material, for example plastics or metal. In other examples, the elastic element may comprise an element made of rubber or foam having a cylindrical shape or bellows shape. The elastic element may support a linear guidance of the diaphragms thus controlling amplitude of the diaphragms and avoiding lateral movement of the diaphragms. Furthermore, the elastic element may support linearity of deflection of the diaphragms in operation.

In various examples of the present application, a coupling of an end of the elastic element to a center of a diaphragm is described. However, such a coupling does not necessarily mean that the elastic element is in contact with the center of the diaphragm. For example, the end of the elastic element may be coupled to the diaphragm in any appropriate way around or near the center of the diaphragm, for example in a symmetric way with respect to an axis of rotational symmetry of the diaphragm such that a force from the elastic element is applied evenly to the surface of the diaphragm. As a result, a deflection movement may preferably evenly performed over a large area along the longitudinal direction.

In some examples, each end of the elastic element may be coupled directly to the corresponding diaphragm. In other examples, a first fixation pad is arranged between the first end of the elastic element and the first diaphragm, in particular the center of the first diaphragm, and a second fixation pad is arranged between the second end of the elastic element and the second diaphragm, in particular the center of the second diaphragm. The fixation pads may enable homogeneous transmission of forces between the elastic element and the first and second diaphragms.

According to various examples, the gap has a rotational symmetry with an axis of rotational symmetry. The first diaphragm may have a rotationally symmetric shape with its axis of rotational symmetry extending coaxially with the axis of rotational symmetry of the gap. Likewise, the second diaphragm may have a rotational symmetric shape with its axis of rotational symmetry extending coaxially with the axis of rotational symmetry of the gap. Thus, the first and second diaphragms are aligned and may share the magnetic field provided in the gap by a single magnet.

Furthermore, the first diaphragm may have a dome shape or spherical shape with the base of the dome/spherical shape extending in a first plane perpendicular to the axis of rotational symmetry of the gap. The second diaphragm may also have a dome shape or spherical shape with the base of the dome/spherical shape extending in a second plane perpendicular to the axis of rotational symmetry of the gap. An apex of the dome/spherical shape of the first diaphragm is outside the area between the first and second planes, and an apex of the dome/spherical shape of the second diaphragm is outside the area between the first and second planes. In other words, the height of the dome/spherical shape of the first diaphragm extends in a direction opposite to a direction in which the height of the dome/spherical shape of the second diaphragm extends. As a result, the first and second diaphragms may radiate sound in opposite directions. The gap may extend between and outer circumference of the first diaphragm and an outer circumference of the second diaphragm. Thus, the magnet assembly is at least partially arranged within a volume defined by the first and second diaphragms. This enables a compact design of the loudspeaker and a use of the loudspeaker in confined installation spaces, for example in a headrest of a vehicle.

In various examples, the axes of rotational symmetry of the voice coils, the magnet, the magnetic piece, the gap, the first and second diaphragms and/or the elastic element may be aligned to each other.

It is to be understood that the features mentioned above and those described in detail below may be used not only in the described combinations, but also in other combinations or in isolation without departing from the scope of the invention.

Any connection or coupling between functional blocks, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling.

Some examples of the present disclosure generally provide for a plurality of mechanical and electrical components. All references to the components and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various components disclosed, such labels are not intended to limit the scope of operation for the components. Such components may be combined with each other and/or separated in any manner based on the particular type of implementation that is desired.

<FIG> shows a sectional view of a loudspeaker <NUM>. The sectional view is taken along a longitudinal axis <NUM> of the loudspeaker <NUM>. Several of the below described components may have an axis of rotational symmetry, for example cylindrical or tubular components, and the axis of rotational symmetry of such a component may be aligned to the longitudinal axis <NUM>.

The loudspeaker <NUM> comprises a magnet assembly <NUM>, a first diaphragm <NUM>, a second diaphragm <NUM> and a basket <NUM>. The magnet assembly <NUM>, the first diaphragm <NUM>, the second diaphragm <NUM> and at least parts of the basket <NUM> may each have a rotationally symmetrical shape with an axis of rotational symmetry aligned to the longitudinal axis <NUM>.

The first diaphragm <NUM> is arranged spaced apart from the second diaphragm <NUM>. The first diaphragm <NUM> has a dome shape with an apex of the dome shape directing in an upward direction along the longitudinal axis <NUM> in <FIG>. The second diaphragm <NUM> has a dome shape with an apex of the dome shape directing in a downward direction along the longitudinal axis <NUM> in <FIG>. The first and second diaphragms <NUM>, <NUM> may have essentially the same shape which may be rotationally symmetric with respect to the longitudinal axis <NUM>. The basket <NUM> is provided between the first diaphragm <NUM> and the second diaphragm <NUM>. The first diaphragm <NUM> may be coupled to the basket <NUM> via a surround <NUM>, and the second diaphragm <NUM> may be coupled to the basket <NUM> via a surround <NUM>. The surrounds <NUM> and <NUM> may be made of an elastic material, for example a rubber or plastics. The surrounds <NUM> and <NUM> enable a back and forth movement of the diaphragms <NUM> and <NUM>, respectively, in the direction of the longitudinal axis <NUM>.

The above described shape of the first and second diaphragms <NUM>, <NUM> is an example only and the first and second diaphragms <NUM>, <NUM> may have any other shape, for example a conical shape, a flat disk shape, a spherical shape, a dome shape, a horn shape, a funnel shape or a combination thereof. Each of the first and second diaphragms <NUM>, <NUM> may be made from one piece or assembled from several pieces, which are made of the same or different materials.

For example, the basket <NUM> in combination with the first and second diaphragms <NUM>, <NUM> and the surrounds <NUM>, <NUM> may form a closed enclosure such that the volume inside the loudspeaker <NUM> is essentially decoupled from a surrounding. In other examples, the volume inside the loudspeaker <NUM> may be coupled with surrounding volume, for example via openings in the basket <NUM>.

The magnet assembly <NUM> is mounted within the basket <NUM>. The magnet assembly <NUM> comprises a magnet <NUM>, a magnetic piece <NUM> and a spacer <NUM>. The magnet <NUM>, the magnetic piece <NUM> and the spacer <NUM> may each have a rotationally symmetrical shape with an axis of rotational symmetry aligned to the longitudinal axis <NUM>.

The spacer <NUM> is made of non-magnetic material, for example a paramagnetic, diamagnetic, or antiferromagnetic material. For example, the spacer <NUM> may be made of plastics or a non-magnetic metal like aluminum.

The magnet <NUM> may comprise a permanent magnet comprising ferromagnetic materials, for example iron, nickel, cobalt and/or neodymium. Additionally, the magnet <NUM> may be provided at each end in the direction of longitudinal axis <NUM> with a corresponding pole piece, i.e. a first pole piece <NUM> at an upper end in <FIG> and a second pole piece <NUM> at a lower end in <FIG>. The magnet <NUM> may be a hollow cylindrical magnet, a so-called ring magnet with a first magnetic polarity at the upper end in <FIG>, for example a north pole N, and a second magnetic polarity at the lower end in <FIG>, for example a south pole S. The first and second pole pieces <NUM>, <NUM> may each have a washer shape with an axis of rotational symmetry aligned to the longitudinal axis <NUM>. The first and second pole pieces <NUM> and <NUM> may be made of a ferromagnetic material, for example iron, nickel or cobalt such that they guide the magnetic field from the magnet <NUM> and may be considered to extend the poles of the magnet <NUM>. Therefore, when the pole pieces <NUM> and <NUM> are present, in the following, the combination of magnet <NUM> and pole pieces <NUM>, <NUM> will be referred to as magnet <NUM> also.

The magnetic piece <NUM> may be made of ferromagnetic material, for example iron, nickel or cobalt, and may have a hollow cylindrical shape with an axis of rotational symmetry aligned to the longitudinal axis <NUM>. As shown in <FIG>, an outer diameter of the magnetic piece <NUM> may be smaller than an inner diameter of the magnet <NUM>. The spacer <NUM> couples the magnet <NUM> with the magnetic piece <NUM> such that at least at the upper and lower ends of the magnet <NUM> (including the pole pieces <NUM>, <NUM>) a gap <NUM> exists between the magnet <NUM> and the magnetic piece <NUM>. The gap <NUM> may have a width in the radial direction of a few millimeters, for example in a range of <NUM> to <NUM> millimeters. The non-magnetic spacer may be arranged at a center of the gap <NUM> in a direction of the longitudinal axis <NUM>. The spacer <NUM> defines the width of the gap <NUM> and assures a fixed arrangement of the magnet <NUM> with respect to the magnetic piece <NUM>. A length of the magnet <NUM> and the magnetic piece <NUM> in the direction of the longitudinal axis <NUM> may be essentially the same and defines a length of the gap <NUM> in the direction of the longitudinal axis <NUM>. The length of the gap <NUM> may be in the range of a few millimeters to a few centimeters, for example in a range of <NUM> to <NUM> millimeters. It is to be noticed that the gap <NUM> may be partly filled with the spacer <NUM>. However, in particular the end sections of the gap <NUM>, i.e. the upper end and the lower end in the direction of the longitudinal axis <NUM>, may not be occupied by the spacer <NUM>.

Due to the ferromagnetic properties of the magnetic piece <NUM>, a magnetic field generated by the magnet <NUM> is guided in radial direction through the gap <NUM> and the magnetic piece <NUM>. In detail, a magnetic field <NUM> (for example B-field) may propagate from the north pole N at the upper end of the magnet <NUM> (if present, via the first pole piece <NUM>) in a radial direction to the upper end of the magnetic piece <NUM> which guides the magnetic field <NUM> in the downward direction within the magnetic piece <NUM> to the lower end of the magnetic piece <NUM>, where it propagates in a radial direction to the south pole S at the lower end of the magnet <NUM> (if present, via the second pole piece <NUM>).

Near an outer circumference of the first diaphragm <NUM> a first voice coil <NUM> is provided which extends into the gap <NUM> at the upper end of the magnet assembly <NUM>. The first voice coil <NUM> comprises a tubular carrier <NUM> on which a plurality of coil windings <NUM> are arranged. The carrier <NUM> may be made of a non-magnetic material, for example paper, aluminum or plastics, like polyimide, for example Kapton. An inner diameter of the carrier <NUM> is larger than an outer diameter of the magnetic piece <NUM>. An outer diameter of the coil windings <NUM> is smaller than an inner diameter of the magnet <NUM>. The voice coil <NUM> is movable in the direction of the longitudinal axis <NUM> in the up and down directions in <FIG>.

Likewise, near an outer circumference of the second diaphragm <NUM>, a second voice coil <NUM> is provided which extends into the gap <NUM> at the lower end of the magnet assembly <NUM>. The second voice coil <NUM> comprises a tubular carrier <NUM> on which a plurality of coil windings <NUM> are arranged. The carrier <NUM> may be made of non-magnetic material. An inner diameter of the carrier <NUM> is larger than an outer diameter of the magnetic piece <NUM>. An outer diameter of the coil windings <NUM> is smaller than an inner diameter of the magnet <NUM>. The voice coil <NUM> is movable in the direction of the longitudinal axis <NUM> in the up and down directions in <FIG>.

As a result, the first and second diaphragms <NUM> and <NUM> can be deflected independently by energizing the first and second voice coils <NUM> and <NUM>. However, only a single magnet assembly <NUM> is needed which provides a gap <NUM> with magnetic fields in which both voice coils <NUM> and <NUM> may be operated.

For example, in operation of the loudspeaker <NUM>, the diaphragms <NUM>, <NUM> may be controlled such that they are moving in opposite directions. However, this is only an example and the diaphragms <NUM>, <NUM> may be controlled independent from each other such that a movement of the first diaphragm <NUM> is controlled independent from the movement of the second diaphragm <NUM>.

As further shown in <FIG>, an elastic element <NUM> is provided between the first diaphragm <NUM> and the second diaphragm <NUM>. A first end of the elastic element <NUM> is coupled to a center, for example the apex, of the first diaphragm <NUM>. A second end of the elastic element <NUM> is coupled to a center, for example the apex, of the second diaphragm <NUM>. Optionally, a first fixation pad <NUM> may be arranged between the first end of the elastic element <NUM> and the first diaphragm <NUM>, and a second fixation pad <NUM> may be arranged between the second end of the elastic element <NUM> and the second diaphragm <NUM>. As shown in <FIG>, the elastic element <NUM> may comprise a spring element, made for example of metal or plastics. Although not shown, the elastic element <NUM> may comprise a plurality of springs or may comprise a cylindrical or bellows-shaped hollow element of elastic material, for example rubber or foam.

As described above, some of the components of the loudspeaker <NUM> may have a rotational symmetry with respect to longitudinal axis <NUM>. Therefore, components on the right-hand side in <FIG> are shown in symmetry to components on the left-hand side of <FIG>. For further clarification, <FIG> shows a sectional view along sectional plane A-A and <FIG> and <FIG> show sectional views of various examples along sectional plane B-B.

<FIG> shows a sectional view along sectional plane A-A of <FIG>. The sectional plane A-A extends perpendicular to the longitudinal axis <NUM>. As shown, the basket <NUM> encloses the washer-shaped upper pole piece <NUM>. Although, the basket <NUM> in the illustrated example completely encloses the pole piece <NUM>, this is only an example, and the basket may have cutouts or may comprise of a plurality of parts coupled to the pole pieces <NUM>, <NUM> and the magnet <NUM>, for example by gluing or press fitting. Furthermore, the basket <NUM> may comprise support structures, for example connecting straps, for mounting the loudspeaker <NUM> at an installation space, for example in a door, dashboard, ceiling, seat or headrest of a vehicle. The upper pole piece <NUM> has an inner opening in which the magnetic piece <NUM> is arranged with a gap <NUM> between an inner circumference of the upper pole piece <NUM> and an out circumference of the magnetic piece <NUM>. The first voice coil <NUM> comprising the carrier <NUM> and the coil windings <NUM> is at least partly arranged in the gap <NUM>. A gap between an outer circumference of the coil windings <NUM> and an inner circumference of the pole piece <NUM> is provided such that the voice coil <NUM> does not contact the pole piece <NUM> when moving up and down along the direction of the longitudinal axis <NUM>. Within the inner circumference of the voice coil <NUM>, the magnetic piece <NUM> is arranged spaced apart from the inner circumference of the voice coil <NUM> such that the voice coil <NUM> does not contact the magnetic piece <NUM> when moving up and down along the direction of the longitudinal axis <NUM>. The magnetic piece <NUM> may have a hollow cylindrical shape such that the cross section is a ring as shown in <FIG>.

<FIG> shows a sectional view along sectional plane B-B of <FIG>. The sectional plane B-B extends perpendicular to the longitudinal axis <NUM> essentially in the center of the length of the magnet assembly <NUM>. In particular, plane B-B extends through the spacer <NUM>. As shown in <FIG> and described above in connection with <FIG>, the basket <NUM> encloses the washer-shaped pole pieces <NUM>, <NUM> and the magnet <NUM>. The magnet <NUM> may be glued or press fitted to the basket <NUM>. The magnet <NUM> is a ring magnet, i.e. the magnet <NUM> has hollow cylindrical shape. At an inner circumferential surface of the magnet <NUM> the spacer <NUM> is mounted, for example by gluing or press fitting. At an inner circumference surface of the spacer <NUM>, the magnetic piece <NUM> is mounted, for example by gluing or press fitting. It is to be noticed that in <FIG> and <FIG> the elastic element <NUM> is not shown for reasons of clarity.

<FIG> shows a sectional view along sectional plane B-B of <FIG> of another example of implementing the spacer <NUM>. In the example of <FIG>, the spacer <NUM> has cutouts thus forming an inner ring 113a, an out ring 113b and a plurality of spokes-like elements 113c. The inner ring 113a is in contact with the magnetic piece <NUM>. The outer ring is in contact with the magnet <NUM> or the pole pieces <NUM>, <NUM>. The spoke-like elements 113c connect the inner ring 113a and the outer ring 113b. In the example shown in <FIG>, the inner ring 113a is connected via twelve spoke-like elements 113c to the outer ring 113b. However, this is an example only and the spacer <NUM> may have any other structure which allows a fixed arrangement of the magnetic piece <NUM> with respect to the magnet <NUM> and/or the pole pieces <NUM>, <NUM>.

<FIG> shows a further loudspeaker <NUM>. Compared to the loudspeaker <NUM> shown in <FIG>, in the loudspeaker <NUM> of <FIG> the magnet assembly <NUM> is modified such that the magnet <NUM> is arranged inside the magnetic piece <NUM>. However, the functionality of the loudspeaker <NUM> of <FIG> is essentially the same as the functionality of the loudspeaker <NUM> of <FIG>. The magnetic fields in the gap <NUM> for the first and second voice coils <NUM> and <NUM> are generated by a single magnet assembly <NUM>, for example a single ring magnet <NUM> in connection with the magnetic piece <NUM>. The spacer <NUM> keeps the magnet <NUM> in position with respect to the magnetic piece <NUM>.

<FIG> illustrates a loudspeaker <NUM> which essentially corresponds to the loudspeaker <NUM> of <FIG>. In contrast to <FIG>, the optional first and second fixation pads <NUM> and <NUM> are not present in the loudspeaker <NUM> of <FIG>. Instead, the first end of the elastic element <NUM> is directly coupled to the center, for example the apex, of the first diaphragm <NUM>, and the second end of the elastic element <NUM> is directly coupled to the center, for example the apex, of the second diaphragm <NUM>, for example by gluing.

<FIG> illustrates a further loudspeaker <NUM>. Compared to the loudspeaker <NUM> shown in <FIG>, the loudspeaker <NUM> of <FIG> comprises a support element <NUM> arranged within the magnetic piece <NUM> at a central position with respect to the longitudinal axis <NUM>. For example, the support element <NUM> may have a disk shape. An outer diameter of the support element <NUM> may be essentially the same as an inner diameter of the magnetic piece <NUM>. In other examples, the support element <NUM> may have a bar shape extending along an inner diameter of the magnetic piece <NUM>. The support element <NUM> may be fixed within the magnetic piece <NUM> by press fitting or gluing.

Instead of the elastic element <NUM> of loudspeaker <NUM> shown in <FIG>, the loudspeaker <NUM> of <FIG> may be provided with a first elastic element 160a between the first diaphragm <NUM> and the support element <NUM>, and with a second elastic element 160b between the second diaphragm <NUM> and the support element <NUM>. A first end of the first elastic element 160a is coupled to a center, for example the apex, of the first diaphragm <NUM>. A second end of the first elastic element 160a is coupled to one side of the support element <NUM>. A first end of the second elastic element 160b is coupled to a center, for example the apex, of the second diaphragm <NUM>. A second end of the second elastic element 160b is coupled to another side of the support element <NUM>. Optionally, a first fixation pad <NUM> may be arranged between the first end of the first elastic element 160a and the first diaphragm <NUM>, and a second fixation pad <NUM> may be arranged between the first end of the second elastic element 160b and the second diaphragm <NUM>. As shown in <FIG>, the first and second elastic elements 160a, 160b may each comprise a spring element, made for example of metal or plastics. Although not shown, the first and second elastic elements 160a, 160b may each comprise a plurality of springs or may comprise a cylindrical or bellows-shaped hollow element of elastic material, for example rubber or foam. The use of the two separate elastic elements 160a, 160b may utilize controlling the diaphragms <NUM>, <NUM> independent from each other, e.g. deflection of diaphragm <NUM> does not influence deflection of diaphragm <NUM>.

<FIG> illustrates a loudspeaker <NUM>. Like the loudspeaker <NUM> of <FIG>, the loudspeaker of <FIG> comprises two elastic elements 160c and 160d. However, loudspeaker <NUM> of <FIG> does not comprise the support element <NUM>. The loudspeaker <NUM> of <FIG> comprises the first elastic element 160c and the second elastic element 160d arranged along the longitudinal axis <NUM> and at least partially within the magnetic piece <NUM>. A first end of the first elastic element 160c is coupled to a center, for example the apex, of the first diaphragm <NUM>. A second end of the first elastic element 160a is coupled to the magnetic piece <NUM>. For example, the first elastic element 160c may comprise a spring. A spring wire at the second end of the first elastic element 160c may be formed as shown in <FIG> to contact the magnetic piece <NUM>, for example at an upper base of the magnetic piece <NUM>. A first end of the second elastic element 160d is coupled to a center, for example the apex, of the second diaphragm <NUM>. A second end of the second elastic element 160d is coupled to the magnetic piece <NUM>. For example, the second elastic element 160d may comprise a spring. A spring wire at the second end of the second elastic element 160d may be formed as shown in <FIG> to contact the magnetic piece <NUM>, for example at a lower base of the magnetic piece <NUM>. The spring wires may be fixed to the magnetic piece <NUM> by gluing, welding or soldering.

In general, the elastic elements may provide guidance in the direction of the longitudinal axis <NUM>. For example, the elastic elements may inhibit or reduce a deflection of the corresponding diaphragm <NUM>, <NUM> in the lateral direction, i.e. in a radial direction perpendicular to the longitudinal axis <NUM>. The elastic elements enable deflection in the direction of the longitudinal axis <NUM> and provide a restoring force to the rest position for the corresponding diaphragm <NUM>, <NUM>.

<FIG> shows a further loudspeaker <NUM> with a magnet assembly <NUM> in which the magnet <NUM> is arranged inside the magnetic piece <NUM>. The functionality of the loudspeaker <NUM> of <FIG> is essentially the same as the functionality of the loudspeaker <NUM> of <FIG>. The magnetic fields in the gap <NUM> for the first and second voice coils <NUM> and <NUM> are generated by a single magnet assembly <NUM>, for example a single disk magnet <NUM> in connection with disk shaped pole pieces <NUM>, <NUM> and the magnetic piece <NUM>. The spacer <NUM> keeps the magnet <NUM> in position with respect to the magnetic piece <NUM>. A washer shaped support ring <NUM> is provided between the basket <NUM> and the magnetic piece <NUM> to keep the magnetic piece <NUM> in position with respect to the basket <NUM>. Elastic elements 160i, 160j, <NUM> and <NUM> are provided between the support ring <NUM> and the first and second diaphragms <NUM>, <NUM>. For example, elastic element 160i may be coupled between an upper side of the support ring <NUM> and the first diaphragm <NUM>. At a diametric opposite position the elastic element <NUM> may be coupled between the upper side of the support ring <NUM> and the first diaphragm <NUM>. Likewise, elastic element 160j may be coupled between a lower side of the support ring <NUM> and the second diaphragm <NUM>, and, at a diametric opposite position, the elastic element <NUM> may be coupled between the lower side of the support ring <NUM> and the second diaphragm <NUM>. More than two elastic elements may be provided at each side of the support ring <NUM>, for example three, four, six, eight or any other number. The elastic elements may be provided within an annular space delimited by the magnetic piece <NUM> and the basket <NUM>. At each side of the support ring <NUM>, the elastic elements <NUM> may be arranged at a uniform distance from each other in the circumferential direction, i.e. evenly distributed in the circumferential direction.

In other examples, only one elastic element may be provided at each side of the support ring <NUM>, or one elastic element may be provided extending from the first diaphragm <NUM> to the second diaphragm <NUM>. The elastic element may comprise for example a spring with an inner diameter larger than an outer diameter of the magnetic piece <NUM>, or the elastic element may comprise for example a tubular element or a bellows-shaped hollow element made of rubber or foam with an inner diameter larger than an outer diameter of the magnetic piece <NUM>. The elastic element may surround the magnetic piece <NUM> in a circumferential direction of the magnetic piece <NUM>. The elastic element may be arranged within the annular space between the magnetic piece <NUM> and the basket <NUM> and may contact the first and/or second diaphragms <NUM>, <NUM> near an outer edge of the first and second diaphragms <NUM>, <NUM>, respectively. An axis of rotational symmetry of the elastic element may be aligned to the longitudinal axis <NUM>.

Claim 1:
A loudspeaker, comprising:
- a first diaphragm (<NUM>),
- a second diaphragm (<NUM>) spaced from the first diaphragm (<NUM>),
- a first voice coil (<NUM>) coupled to the first diaphragm (<NUM>),
- a second voice coil (<NUM>) coupled to the second diaphragm (<NUM>),
- a magnet assembly (<NUM>) comprising a magnet (<NUM>), a magnetic piece (<NUM>) and a spacer (<NUM>) of non-magnetic material connecting the magnet (<NUM>) and the magnetic piece (<NUM>) such that a gap (<NUM>) is provided between the magnet (<NUM>) and the magnetic piece (<NUM>), wherein the first voice coil (<NUM>) is arranged at a first end of the gap (<NUM>) and the second voice coil (<NUM>) is arranged at a second end of the gap (<NUM>) opposite the first end of the gap (<NUM>), wherein the gap (<NUM>) is at least partially filled with the spacer (<NUM>), wherein at least the ends of the gap (<NUM>) are not filled with the spacer (<NUM>) to accommodate the first voice coil (<NUM>) and the second voice coil (<NUM>),
- a basket (<NUM>) coupled to at least one of the magnet (<NUM>) and the magnetic piece (<NUM>),
- a first surround (<NUM>) coupling an outer circumference of the first diaphragm (<NUM>) to the basket (<NUM>),
- a second surround (<NUM>) coupling an outer circumference of the second diaphragm (<NUM>) to the basket (<NUM>), and
- an elastic element (<NUM>) arranged between the first diaphragm (<NUM>) and the second diaphragm (<NUM>), characterized in that a first end of the elastic element (<NUM>) is coupled to a center of the first diaphragm (<NUM>), and a second end of the elastic element (<NUM>) is coupled to a center of the second diaphragm (<NUM>).