Abstract: A radial magnetic circuit assembly device includes a magnetic central column, a lower lantern ring and an upper lantern ring, the magnetic central column includes a large-diameter section and a small-diameter section which form a limit step on which each tile-shaped magnet is annularly and uniformly arranged, the lower lantern ring is sleeved on the tile-shaped magnet in a direction from the large-diameter section towards the small-diameter section and is configured to limit a radial displacement of each tile-shaped magnet, the upper lantern ring is sleeved on the tile-shaped magnet in a direction from the small-diameter section towards the large-diameter section to press the upper axial magnetic sheet and the lower axial magnetic sheet against the upper axial side surface and the lower axial side surface of each tile-shaped magnet respectively.

Abstract: In some examples, a computing device may include one or more planar speakers. Individual planar speakers may include damping material adhered to either a top surface of a front pole or a bottom surface of a cone. The damping material may reduce a noise caused by the cone hitting the front pole (e.g., when reproducing loud passages in media content) to an inaudible (e.g., 30 db or less) level. The noise may be reduced by up to 35 decibels between about 250 Hertz to about 450 Hertz. The damping material may comprise a polyurethane foam and may have a height of between about 0.1 millimeters to about 1.0 millimeters and preferably about 0.2 millimeters.

Abstract: The present invention provides a sound generator, including a magnetic circuit system having a magnet and a lower plate for carrying the magnet. The magnet includes a first surface opposite to the lower plate and a second surface opposite to the first surface. The first surface of the magnet protrudes to form a first bolt, the lower plate is provided with a lower plate jack matching with the first bolt, and the first bolt is inserted into the lower plate jack. The sound generator of the present disclosure improves the structural stability of the magnetic circuit system and is convenient for positioning.

Abstract: The present invention provides a sound generator. A magnetic circuit system of the sound generator forms a mortise-and-tenon structure between a magnet and a lower plate, and the magnet and a pole plate, through tenons and mortises, which enlarges the mutual contact areas, and is more convenient for processing positioning, preventing assembling dislocation, enlarging the gluing area and improving the drop reliability and therefore improving the structural stability of the magnetic circuit system.

Abstract: A coaxial loudspeaker apparatus (10) comprising a first unit (20) being arranged to propagate sound in a first frequency range; a second unit comprising a first waveguide (30) arranged to propagate sound in a second frequency range that is higher than the first frequency range, and a second waveguide (60) arranged to move, during operation, relative to the first waveguide (30); wherein the second waveguide (60) extends substantially in prolongation of the first waveguide (30). The invention also extends to a loudspeaker (190) incorporating the coaxial loudspeaker apparatus (10).

Abstract: Several embodiments of the instant invention incorporate a loudspeaker design utilizing hard magnetic poles and yokes. The magnetic field of the loudspeaker is created and guided with a series of critically formed hard magnetic structures guiding the magnetic field from the primary magnet to the gap in a loop of hard magnetic material, replacing the soft magnetic materials normally used. Magnetization of the components of the hard magnetic loudspeaker driver with radial pole patterns—a yoke radial magnet, a washer pole magnet and a yoke upper ring magnet—is performed with these components in their final assembly relationships.

Abstract: Driver for an acoustic transducer having a moving coil of substantially equal length to the air gap. The air gap may itself be extended in length using an upper or lower lip, or both. A stationary coil is also provided. The moving and stationary coils can be controlled by suitable control blocks to form an electromagnet-based transducer with reduced distortion.

Abstract: A magnetic assembly for a speaker is disclosed in this disclosure. The magnetic assembly includes a yoke including a receiving space; a main magnet received in the receiving space and installed on the yoke; a pole plate received in the receiving space, and including a base plate attached on the main magnet and a sidewall extending substantially perpendicularly from a periphery of the base plate for increasing an overlapping area between the yoke and the pole plate.

Abstract: An audio transducer apparatus including a component having a first material; and a heating reduction system configured to reduce induced heating in the component. The heating reduction system includes a member at least partially surrounding the component. The member includes a material which has an electrical conductivity that is higher than an electrical conductivity of the first material to thereby reduce induced heating in the component.

Abstract: An electromagnetic drive unit for a loudspeaker of the type where an air gap is arranged in a magnet system such that magnetic flux lines are substantially linear across the air gap, and that a voice coil is arranged in said air gap, wherein the magnet system comprises a central yoke separated by said air gap from a ring-shaped magnet system, which magnet system at least comprises a bottom plate connected to said central yoke, and a magnet and a top plate, characterized in that at least a section of the central yoke corresponding to the extent of the air gap and at least a corresponding section of the top plate is made from a soft magnetic composite material.

Abstract: An improved electrodynamic acoustic transducer eliminates or reduces the need for flexible or elastic materials to suspend an internal magnetic element by using both static and dynamic signal-dependent magnetic fields to control its movement. In one implementation, the transducer has a magnet that moves within a surrounding tube. This tube in turn supports one or more electromagnetic coils that generate a dynamic signal-dependent magnetic field that causes the internal magnetic element to vibrate. The surrounding tube also supports one or more magnets whose location on the tube is fixed and whose magnetic fields provide appropriate restoring forces acting on the internal magnetic element. These fixed magnets may be replaced or supplemented by ferromagnetic materials.

Abstract: The loudspeaker magnetic circuit is an external-magnet type, and has a magnet, an upper plate, and a lower plate. The magnet is sandwiched between the upper plate and the lower plate. At least one of the lower plate and the upper plate is formed of magnetic powder or a mixture of a magnetic powder and resin.

Abstract: A multi-function vibrating device is disclosed. The multi-function vibrating device providing sound producing and vibration functions includes a holder having a hollow space, a suspension divided into at least two parts, a vibration member suspended by the suspension and having at least a pair of receiving concaves for fixing the corresponding two parts of the suspension. The multi-function vibrating device has larger vibrating amplitude and small size.

Abstract: A loudspeaker has a short support post joined to the forward plate; upper end of the support post in association with the fixing post is joined to the middle part of the drum paper with the fixing post; the voice coil has the upper end thereof joined to the drum paper; when the voice coil drives the drum paper to vibrate and emit sound, the upper end of the short support post sways and generates a small offset because of the lower end of the support post being retained by the forward plate such that the voice coil moves axially in the magnetic clearance without deviation, and the voice coil is incapable of touching the yoke or the forward plate to produce noise; therefore, quality of sound output from the loudspeaker is enhanced effectively.

Abstract: An apparatus related to a magnetic circuit design is disclosed. The apparatus includes a magnetic assembly and an electrically-conductive mobile member. The magnetic assembly includes an inner magnet, an outer magnet, an inner cap, an outer cap and a washer. The magnetic assembly is configured to produce a magnetic field having a zone of operation between the inner cap and the outer cap. The zone of operation has substantially uniform magnetic field strength. The zone of operation has magnetic field directions substantially perpendicular to an ideal motion direction. The electrically-conductive mobile member is disposed in the zone of operation of the magnetic field and electrically coupled to a diaphragm of a driver. The electrically-conductive mobile member is configured to move within the zone of operation of the magnetic field in response to the magnetic field when an alternating current is passed through the electrically-conductive mobile member.

Abstract: Disclosed is a crossover double speaker having a small speaker and a large speaker on the upper side and on the lower side thereof. The crossover double speaker includes a cover integrally formed on the outer circumference of a flange of the yoke; a frame disposed below the cover; a first speaker unit including a first magnet disposed in a first speaker space, a first vibration plate arranged over the first magnet, and a first voice coil inserted into a first air gap; and a second speaker unit including a second magnet disposed in a second speaker space, a second vibration plate arranged between the yoke and the frame, and a second voice coil inserted into a second air gap. The yoke has sound release holes to output the sound generated from the second speaker unit in the direction of the first speaker unit.

Abstract: A slimline speaker comprises: a magnetic circuit having a magnet and yoke disposed to form a separating space in the horizontal direction; a bobbin on which a voice coil is mounted and of which the lower side is inserted in the separating space between the magnet and yoke; a base frame for mounting the magnetic circuit; a damper having an inside edge coupled to the bobbin and an outside edge coupled to the base frame; and a diaphragm having an inside edge coupled to a point lower down than the point where the damper is coupled on the bobbin, and an outside edge coupled to the base frame.

Abstract: A bond magnet according to the present invention is anisotropic, and a magnetic field is oriented from a lowest edge of side surface of the bond magnet toward an upper section of side surface of the bond magnet. Further, the bond magnet is configured such that the upper section of side surface of the bond magnet is disposed closer to a yoke side surface of a yoke than the lower side surface of the bond magnet is, and the upper section of side surface of the bond magnet faces against the yoke side surface. With this, a magnetic gap is provided between the upper section of side surface of the bond magnet and the yoke side surface. Thus, it is possible to improve a magnetism characteristic of the bond magnet, and to achieve both of magnetic efficiency and productivity of a magnetic circuit for a speaker.

Abstract: A loudspeaker includes an outer frame with an annular magnet partially exposed from a bottom thereof; a voice coil located inside the annular magnet; a diaphragm glued to between an expanded front opening of the outer frame and the voice coil; a flexible suspension ring having an outer edge fixed to a stepped section of the outer frame and a central opening edge clearance-fitted to a middle/front portion of the annular magnet; and an inner frame having a front portion fitted around the voice coil, a rear portion located on the central opening edge of the flexible suspension ring, and legs extended between the front and rear portions to locate in front of slots formed on the annular magnet. Therefore, the loudspeaker has reduced depth and volume, increased vibration amplitude and stability, and high quality sound output.

Abstract: A frame has a notch having an opening at a side plane of the frame. A diaphragm is vibratably attached to one plane of the frame. A voice coil is attached to the diaphragm. A terminal is attached to the other plane of the frame. A lead is connected to the voice coil, drawn from one plane to the other plane through the notch, and connected to the terminal. One of intersection points at which a normal to the side plane that passes through the position of the lead in the notch and the side plane intersect that is closest to the opening and the lead in the notch are intervened therebetween by the frame.

Abstract: A multifunctional vibrator includes a frame, a vibrating unit receiving in the frame and including a magnetic circuit part with a magnetic gap, a plurality of elastic members connecting the vibrating unit and the frame, and a voice coil partially inserted into the magnetic gap. Each elastic member includes a retaining portion assembling to an inner face of the frame, a connecting portion attached to the vibrating unit, and an elastic portion extending from the retaining portion to the connecting portion along a devious way. The elastic portion of elastic members includes a first arm capable of generating elastic deformation along a short axis direction of the vibrating unit and a second arm capable of generating elastic deformation along a long axis direction of the vibrating unit.

Abstract: A frame has a notch having an opening at a side plane of the frame. A diaphragm is vibratably attached to one plane of the frame. A voice coil is attached to the diaphragm. A terminal is attached to the other plane of the frame. A lead is connected to the voice coil, drawn from one plane to the other plane through the notch, and connected to the terminal. One of intersection points at which a normal to the side plane that passes through the position of the lead in the notch and the side plane intersect that is closest to the opening and the lead in the notch are intervened therebetween by the frame.

Abstract: A multi-magnet speaker is disclosed. The multi-magnet speaker includes a frame defining a hollow space, a magnetic system defining a yoke and a plurality of magnetic gaps positioned in the hollow space, a diaphragm mounted on the frame and a plurality of coils attached to the bottom of the diaphragm. The diaphragm includes a plurality of vibrating membranes each defining a dome part and an arcuate portion radially extending from the periphery of the dome part. Each of the coils is received in the corresponding magnetic gap to drive the corresponding vibrating membrane to vibrate.

Abstract: In one embodiment, a loudspeaker system is provided comprising a motor assembly for driving a diaphragm assembly, where the motor assembly includes a pole piece configured to receive an inductance sleeve. The motor assembly also comprises a permanent magnet, a first shorting ring, and a second shorting ring, with the first and second shorting ring being positioned at least partially within an air gap adjacent the pole piece, and with the first ring positioned adjacent a first side of the permanent magnet and the second shorting ring positioned adjacent a second side of the permanent magnet. The permanent magnet preferably is preferably coated with an insulative material, and may also comprise a plurality of arcuate segments.

Abstract: A speaker unit and a portable information terminal that are reduced in size and thickness and still produce a high sound pressure. A speaker unit includes: a yoke having a rectangular outline as seen in a plan view; a magnet member placed on the yoke and magnetized so that an upper surface of the magnet member has an N pole and an S pole aligned in one direction; a coil placed above and spaced from the upper surface of the magnet member; a diaphragm attached to the coil; and a frame supporting the diaphragm. The yoke includes an attachment which protrudes upward from an outer periphery of the yoke for attachment to the frame. The attachment has a recess at least in a central portion of the attachment which crosses the one direction.

Abstract: A speaker includes a diaphragm formed as an elongated box-shaped five face body having one open face; an edge for supporting the diaphragm so as to enable vibration of the diaphragm; a voice coil wound around and fixed to four side faces which are among the five faces of the diaphragm and which are adjacent to the open face; and a magnetic circuit for supplying a drive force to the voice coil. The diaphragm is configured such that a height from the open face to an upper face opposed to the open face is greater than or equal to twice a thickness of the voice coil, and a length of a long side of the upper face is greater than or equal to twice a length of a short side of the upper face, and the upper face and two side faces of the diaphragm define a long side direction of the diaphragm. Additionally, reinforcing ribs are formed as recessed and projecting shapes on the upper face and the two side faces of the diaphragm.

Abstract: An electromechanical transducer 180, motor structure 200 and voice coil winding support structure or bobbin 210 are configured to protect and transport heat away from a voice coil 220 which is would solely within the interior of bobbin 210 and configured for reciprocating movement in close proximity to an extended cooling pole piece 204. A compact, economical and efficient adaptation of a pancake style motor includes generous volume for a powerful magnet 208, while providing an extended, linear range of excursion and continuous cooling for the generously overhung voice coil 220.

Abstract: An electroacoustical apparatus and method is described that alters the output properties of an audio device to improve the sound properties for both hearing impaired and normal hearing listeners. The device includes a coil element of specific design and may incorporate digital signal processing techniques to modify audio signal output. The electrical device and method of processing provides for the beneficial alteration of sound waves to an audio signal, and further modification of the audio signal to provide for improved loudness and clarity characteristics. The improved characteristics provide for greater intelligibility of the audio signal to persons with hearing impairments and to persons with normal hearing.

Abstract: A slim speaker includes a casing having an enlarged front opening and a rear end with a magnetic circuit mounted thereto; a voice coil located over a central area of the magnetic circuit; a diaphragm located between the enlarged front opening of the casing and the voice coil; and a damper located behind the diaphragm to space from the latter. The diaphragm has at least one V-shaped bent section provided at a middle portion for bearing on a corresponding position on the damper. With these arrangements, the diaphragm not only has an effectively reduced overall height to largely reduce the assembled volume of the slim speaker and allow the slim speaker to be easily mounted in the limited inner space of an electric product, but also stabilizes the vibration of the voice coil to enable good resonance of sound.

Abstract: An acoustic transducer including a sound producing cone that is activated by a voice coil cylinder having a pair of spaced electrical windings that are retained in spaced relationship from a surround ferromagnetic ring that is carried by a heat sink and wherein a magnetic subassembly is mounted within the voice coil cylinder. The voice coil cylinder is supported by a pair of spaced suspension members or spiders and by the sound producing cone.

Abstract: Disclosed is a linear actuator which includes a core, a coil, a magnet assembly, and a housing. The coil that is shaped to be positioned about the core for movement along a longitudinal axis of the core. The housing is supported by core flanges and positioned about the coil and the core. The magnet assembly includes magnets of the same polarity facing the coil and shaped to be positioned inside or outside of the coil, and supported by the core or by the housing, respectively. The core includes first and second portions, each having an end face, and the first and second portions are positioned along the longitudinal axis so that the end faces oppose each other and are separated by a gap. A cavity is formed in each of the end faces along the longitudinal axis.

Abstract: A magnetic circuit includes a cylindrical yoke member having an inner circumferential surface and a collar formed at one end thereof and turned back substantially at right angles, and a plurality of permanent magnet segments of a partially circular arc in cross section. Each of the permanent magnets has an outer surface attracted magnetically to the inner circumferential surface of the cylindrical yoke member, and one end face attracted magnetically to the collar of the cylindrical yoke member. The magnetic circuit is applied to an actuator or a speaker.

Abstract: The present invention relates to a loudspeaker in the acoustic field and the information communication field. The invention provides a loudspeaker that can realize a thinner size. To achieve this, the loudspeaker of the present invention is structured so that a part of a diaphragm is inserted to a dent or an opening formed at the center poles of a lower plate of a magnetic circuit. This structure allows the diaphragm to be stored within the height of the magnetic circuit, thus allowing the loudspeaker to have a thinner size.

Abstract: A light weight and low profile speaker apparatus is provided. In one embodiment, the speaker apparatus includes: a frame member; a magnetic circuit; a supporting member disposed on a bottom portion of the frame member for securing and supporting the magnetic circuit at an opposite circumferential end portion of a circumferential wall portion of a first yoke relative to a plate portion; a voice coil unit disposed inside a magnetic gap in the magnetic circuit; a coupling member disposed outward of the circumferential wall portion of the first yoke; and a diaphragm having an inner circumferential end portion coupled to the coupling member. The voice coil unit and the coupling member are joined by a joint member that extends in a direction transverse to the circumferential wall portion of the first yoke; and a space where the joint member joining the voice coil unit and the coupling member can move is formed in each of the circumferential wall portion of the first yoke and the supporting member.

Abstract: A diaphragm includes a central portion in a center of the diaphragm and an external portion surrounding the central portion. The central portion includes a central section in a center of the central portion, a peripheral section at an outer periphery of the central portion and a connecting section between the central section and the peripheral section. The peripheral section forms at least one protrusion.

Abstract: An electromagnetic transducer includes an electromagnetic dual-coil or multi-coil driver having at least one spacer member placed between at least two permanent magnets. The inclusion of at least one spacer member increases the axial dimension of the magnetic assembly of the driver so that the magnetic gaps in a dual-coil or multi-coil driver are moved farther apart than would occur with a corresponding electromagnetic driver using a permanent magnet instead of two permanent magnets separated by a spacer member.

Abstract: A speaker is disclosed. A speaker includes a fixing part (500) fastened to a base frame; a motion part moved (400) with respect to the fixing part by an electromagnetic force; a vibration plate (200) that vibrates in communication with the motion part; and a guide member (800) provided between the motion part (400) and the vibration plate (200). Therefore, according to the present invention, a speaker capable of reproducing a high quality sound and high power with a slim design may be embodied.

Abstract: In a loudspeaker, three magnets are disposed to provide magnetic gaps therebetween and a voice coil is fit therein. The magnets disposed at both sides are magnetized so that their opposing poles exhibit the same magnetic polarity. The magnet in the middle has its magnetic poles in the direction perpendicular to the line connecting the poles of the side magnets. The side magnets are fixed to a plate made of non-magnetic material. Those magnetic poles of the side magnets and the middle magnet not facing the magnetic gaps are magnetically coupled by a magnetic member.

Abstract: An audio speaker with at least two electric coils on opposite sides of at least one ferro-magnetic plate, the coils and plate forming a radial electro-magnet. A radial electro-magnet can offer many advantages in stereo loudspeakers. The coils are electrically driven in opposite directions. Multiple sets of two coils and intervening ferro-magnetic plate may be provided, adjacent sets being separated by a non-magnetic plate.

Abstract: A speaker includes a frame, a diaphragm, a cover, a magnetic device, and a voice coil. The cover and the diaphragm are both disposed on a first side of the frame, and the cover covers the diaphragm. The magnet device is disposed on a second side of the frame. The voice coil is disposed on the magnetic loop generated by the magnetic device and integrated with the diaphragm. The magnetic device includes a yoke, a magnet, and a pole piece. The yoke includes a protrusion by bending for the magnet and the pole piece to be mounted upon.

Abstract: A magnetic circuit unit includes a yoke, a magnet positioned on the yoke, a plate on the magnet. The yoke includes a bottom defining a central hole therein, and a wall extending from the bottom. The magnet is positioned on the bottom of the yoke. The plate defines a base coupled to a top surface of the magnet, and a central pole extending from the base and getting through the annular magnet with an end thereof suspended in the central hole of the yoke. Thus, a first magnetic gap is formed between the wall of the yoke and an outer side of the annular magnet, and a second magnetic gap is formed between the central pole of the plate and an inner side of the annular magnet. A speaker using the magnetic circuit unit described above is disclosed.

Abstract: A speaker device includes a magnetic circuit which includes a magnetic gap, a diaphragm which has a recessed part arranged in the magnetic gap and extending in a direction substantially orthogonal with respect to an extending direction of a magnetic flux in the magnetic gap, and a voice coil which is formed into an annular shape and has a first parallel part extending in one direction and a second parallel part extending in a direction in parallel with the first parallel part and opposite to the first parallel part with a constant space. Particularly, the first parallel part and the second parallel part are arranged in a direction in parallel with an extending direction of the recessed part, respectively. The first parallel part is arranged in the recessed part to be positioned in the magnetic gap, and the second parallel part is positioned above the recessed part.

Abstract: A long and narrow loudspeaker on an entire wall gives off a cylindrical wave, which covers the entire room. Extra loudspeakers fixed at an angle against the wall will be heard in another direction, producing angle stereo independent of where one is in the room. Electro-dynamic loudspeakers are made of long plates of iron with air gapes between them where magnetic fields are produced. In the air gaps are strips, which conduct the sound currents. The strips influence directly one or more membranes. The magnetic field can be produced by permanent magnets, electromagnets or through concentration of geomagnetic fields. Long loudspeakers, which use other forces such as electrostatic forces, only need to be made for small sound pressure at the membrane.

Abstract: A speaker unit of the present invention includes a frame made of a synthetic resin, inside which a voice coil is disposed in a space between a pole piece and a yoke. A diaphragm is coupled to the voice coil. A pair of lead wires extending from the voice coil are passed between the yoke and the diaphragm, and led out of the frame. The frame has a receiving surface for receiving collisions of the lead wires due to vibrations of the diaphragm, which is formed outer than an end face of the yoke opposed to the diaphragm, and closer to the diaphragm than the end face.

Abstract: The present invention relates to dual-diaphragm electroacoustic transducers wherein a common magnetic flux path comprises first and second magnetic gaps and a magnet assembly. The invention may provide a miniature transducer with a compact magnetic flux path of improved performance. Electroacoustic transducers in accordance with the invention may comprise a small number of separate parts and provide good acoustic conversion efficiency in a miniature or compact housing.

Abstract: A magnetic circuit for a speaker device includes a yoke having a pole piece main body formed into a cylindrical shape or a hollow cylindrical column shape, and a flange part provided on an outer side thereof, a magnet arranged on the flange part, a plate arranged on the magnet, and an annular T-shape forming member arranged on the pole piece main body. A magnetic gap is formed between an inner peripheral wall of the plate and an outer peripheral wall of the T-shape forming member. A configuration formed by combining the T-shape forming member and the pole piece main body forms a T-shaped pole piece.

Abstract: A loudspeaker includes a circular damper, a cone, and a cylindrical bobbin. The circular damper may include a centrally disposed cone attachment protuberance and a peripherally disposed top plate attachment section. The cone may have a central inner portion that may be attached to the cone attachment protuberance of the damper. The cone may be attached to the cylindrical bobbin, which may have a voice coil coupled thereto.

Abstract: A magnet structure for use with a loudspeaker has an interlocking mechanism. The magnet structure can include a magnet, a shell pot and at least one core cap. The shell pot can contain the magnet in its hollow interior. The magnet can be a single magnet or double magnets. The core cap has two surfaces. For a single magnet, one surface of the core cap faces the magnet. For double magnets, the core cap can be vertically disposed between the two magnets. The magnet, the core cap and the shell pot can interlock with one another such that a position of the magnet relative to the core cap and the shell pot can be rigidly preserved. The magnet can be configured to be, for example, overlapped, inserted, staked and/or engaged with at least one of the shell pot or the core cap.

Abstract: An electrodynamic electroacoustic transducer comprises: a first magnetic pole; a second magnetic pole that forms a magnetic gap between itself and the first magnetic pole and is arranged in a space excluding spaces in upper and lower face directions of the first magnetic pole; a yoke; a diaphragm; and a voice coil. The yoke magnetically couples one magnetic pole face of the first magnetic pole with one magnetic pole face of the second magnetic pole so as to support them. The diaphragm is arranged in a space in an upper face direction of the first magnetic pole and in a space in a lower face direction of the second magnetic pole, while its outer periphery is supported by the yoke. The voice coil is arranged in the magnetic gap and adhered to the diaphragm. At least one of the first magnetic pole part and the second magnetic pole part includes a magnet.

Abstract: The present invention is intended as a method for producing an electromagnetic transducer of variable reluctance type, where the transducer's seismic mass side and load side are mounted together in a first step while the inner and/or outer air gaps are supplied with shims in order to create balanced air gaps in an axial direction between the bobbin core's arms and the inner and outer yokes, whereupon in a second step the bobbin core is fixed through the side piece to an adapter already attached in a corresponding free moving end of a spring suspension, with compliant properties working in an axial direction and arranged between the seismic mass side and the load side in resting state in order to maintain balanced air gaps when finally, in a third step, the shims are removed and the air gaps are released.