GB2591767A

GB2591767A - A method and system for driving a voice coil of a loudspeaker

Info

Publication number: GB2591767A
Application number: GB2001549.1A
Authority: GB
Inventors: Albert Bullimore George; Minoru Tuemp Millyard Ruben
Original assignee: Tymphany Acoustic Technology Huizhou Co Ltd
Current assignee: Tymphany Acoustic Technology Huizhou Co Ltd
Priority date: 2020-02-05
Filing date: 2020-02-05
Publication date: 2021-08-11
Anticipated expiration: 2040-02-05
Also published as: GB202001549D0; GB2591767B

Abstract

The method comprises the steps of providing a magnetic circuit 2 having an air gap 3, providing a voice coil 1 suspended in the air gap 3, and applying an audio signal 30 to the voice coil 1 to move the voice coil along a travelling axis 4. The voice coil 1 comprises a centre voice coil section 21, an upper voice coil section 22a, and a lower voice coil section 22b arranged on respective sides of the centre voice coil section 21. A centre driving signal 41 is provided to the centre voice coil 21. Respective upper and lower passively rectified driving signals 43a, 43b are provided to the upper and lower voice coil sections. A corresponding voice coil driving system is described (fig 8). This driving arrangement is said to reduce Joule heating of the voice coil.

Description

A Method and System for Driving a Voice Coil of a Loudspeaker Field of the invention [0001] The present invention relates to a method for driving a voice coil of a loudspeaker, to a voice coil driving system and to a loudspeaker comprising a voice coil driving system, and in particular to a voice coil arranged to improve power handling and reduce power consumption of the driving electronics.

Background of the invention

[0002] Referring to fig. la-lb, a voice coil driving system of a loudspeaker in the art is illustrated. The voice coil driving system is equipped with a voice coil 1 comprising a plurality of coil windings. The coil windings are powered by a driving signal 40, such that the voice coil 1 reciprocally actuates the diaphragm 7 which generates an acoustic sound signal [0003] The coil windings are partially disposed within an air gap 3 of a magnetic circuit 2 with the greatest magnetic flux density within the air gap 3. When the coil windings are powered they interact with the magnetic field of the magnetic circuit 2 to produce an electromotive force for translation (ie movement) of the voice coil 1. However, only the windings of the voice coil 1 substantially disposed within the gap 3 provide a substantial force to reciprocally translate the voice coil 1. The windings of the voice coil outside the air gap 3 which do not contribute a significant electromotive force are also powered at the same time and will as a result contribute to voice coil heating which is a major limiting factor in loudspeaker design.

Summary of the invention

[0004] The inventors have identified the above-mentioned problems and challenges related to loudspeaker power consumption, and subsequently made the below-described invention which may decrease power consumption of the voice coil and avoid unnecessary voice coil heating.

[0005] An aspect of the invention relates to a method for driving a voice coil of a loudspeaker comprising the steps of providing a magnetic circuit having an air gap and a voice coil suspended in said air gap; applying an audio signal to said voice coil suspended in said air gap to produce an electromotive force moving said voice coil along a travelling axis; wherein said voice coil comprises a plurality of voice coil sections, arranged along said travelling axis, said plurality of voice coil sections comprising a centre voice coil section, an upper voice coil section and a lower voice coil section, said upper voice coil section and said lower voice coil section arranged respectively on either side of said centre voice coil section; wherein said step of applying an audio signal comprises providing a centre driving signal based on said audio signal to said centre voice coil section and providing an auxiliary driving signal based on said audio signal to said upper voice coil section and said lower voice coil section, said providing an auxiliary driving signal comprising providing an upper rectified driving signal to said upper voice coil section and providing a lower rectified driving signal to said lower voice coil section; wherein said upper rectified driving signal is provided by attenuating and/or blocking a first direction of current of said auxiliary driving signal by passive rectification; wherein said lower rectified driving signal is provided by attenuating and/or blocking a second direction of current of said auxiliary driving signal by passive rectification; and wherein said first and second direction of current of said auxiliary driving signal are opposite directions of current The terms 'upper' and 'lower' are used to refer to the relative positions of features, such as the voice coil sections, when the travelling axis is orientated in a substantially vertical direction. The invention is not limited to the travelling axis being orientated in a substantially vertical direction. In accordance with the invention, the travelling axis may be orientated in any direction.

The 'upper' and 'lower' features described herein may alternatively be termed 'first auxiliary' and 'second auxiliary' features throughout the specification. Also the 'first upper', 'second upper', 'first lower' and 'second lower' features described herein may alternatively be termed 'first inner auxiliary', 'first outer auxiliary', 'second inner auxiliary' and 'second outer auxiliary' features, respectively, throughout the specification.

[0006] A voice coil may be understood as a coil of wire which under the influence of a magnetic field may generate an electromotive force to move a diaphragm of a loudspeaker in order to produce acoustic sounds. The magnetic field may be established by a magnet, such as a permanent magnet or an electromagnet, present in a magnetic circuit. The magnetic circuit may comprise an air gap in which the voice coil reciprocates to produce acoustic sound by reciprocation of the diaphragm of the IS loudspeaker.

[0007] When applying an audio signal, a current is sent to the voice coil windings, in the form of driving signals, e.g. a centre driving signal and an auxiliary driving signal, resulting in an electromotive force on the coil windings, due to the magnetic field, which drives the voice coil along a travelling axis which may be substantially perpendicular to the coil windings.

[0008] A driving signal provided to a voice coil will typically comprise current alternating between flowing in a first direction of current and flowing in a second direction of current through the voice coil windings, where the first direction of current and the second direction of current are opposite directions of current. When current flows in a first direction of current through the voice coil windings, an electromotive force may be generated onto the voice coil in a first direction of the travelling axis, and when current flows in a second direction of current through the voice coil windings, an electromotive force may be generated onto the voice coil in a second direction of the travelling axis, where the first direction of the travelling axis and the second direction of the travelling axis are opposite directions along the travelling axis. Thus, forces may be applied to the voice coil in both directions of travel along the travelling axis, and this enables reciprocation of the voice coil within the air gap [0009] An audio signal is typically a type of electronic signal. In various embodiments it may be an analogue signal, continuous or pulsed. In various embodiments it may be a digital signal. When referring to the amplitude of an audio signal, it may be the amplitude of an analogue audio signal, or it may be the audio signal level of a digital audio signal.

[0010] Typically, the reciprocating excursion, i.e. reciprocating displacement, of a voice coil in a loudspeaker aims to reproduce the audio signal delivered to the loudspeaker through reciprocation of the diaphragm of the loudspeaker. Thus, an audio signal increasing in amplitude results in an increase of excursion (eg movement along the travelling axis), within the limitations of the loudspeaker. The audio signal may be provided by an external unit such as an audio source arranged to output an electrical audio signal and with connecting means to deliver the audio signal to the loudspeaker.

Examples of connecting means are wired connections such as a cabled electrical or optical connection, and wireless connections such as a Bluetooth connection, e.g. Bluetooth A2DP or Bluetooth aptX, or a Wi-Fi connection.

[0011] According to various embodiments of the invention, the voice coil comprises a plurality of voice coil sections, e.g. comprises an upper voice coil section, a centre voice coil section, and a lower voice coil section, but the invention is not restricted to three sections only, and further voice coil sections of the voice coil may be perceived in other embodiments of the invention, located along the direction of the travelling axis.

[0012] In an embodiment of the invention said upper voice coil section may be a first auxiliary voice coil section and said lower voice coil section may be a second auxiliary voice coil section. In a different embodiment, said lower voice coil section may be a first auxiliary voice coil section and said upper voice coil section may be a second auxiliary voice coil section. By an auxiliary voice coil section is understood an additional voice coil section which may supplement the centre voice coil section in producing an electromotive force for reciprocation of the voice coil.

[0013] A voice coil section is understood as an individual segment of a voice coil. The voice coil sections may be electrically isolated from each other or be subsections of a single coil with multiple connections to provide for individual electrical connections to each voice coil section.

[0014] In various embodiments, voice coil sections may have the same or different heights, number of windings, density of windings, and comprise windings of the same or different materials. The material of the windings of the voice coil sections may be selected from the list consisting of alloys, aluminium, silver, copper or gold, or any combinations thereof [0015] In various embodiments of the invention, the voice coil comprises an upper voice coil section, a centre voice coil section and a lower voice coil section with the upper voice coil section and the lower voice coil section arranged on either side of the centre voice coil section along the direction of the travelling axis. In various embodiments, each of these voice coil sections has a height of one third of the height of the voice coil. The voice coil sections, however, are not limited to having equal heights or equal number of windings etc. A 'height' of a voice coil in the present disclosure refers to the voice coil's extension along the traveling axis.

[0016] Other embodiments include more than one centre voice coil section, more than one upper voice coil section and/or more than one lower voice coil section, e.g. an embodiment may comprise a second upper voice coil section, a first upper voice coil section, a centre voice coil section, a first lower voice coil section, and a second lower voice coil section.

[0017] To drive the voice coil according to the invention, a centre driving signal, based on the audio signal, is provided to a centre voice coil section, and an auxiliary driving signal, also based on the audio signal, is provided to an upper voice coil section and a lower voice coil section. Providing the auxiliary driving signal comprises providing an upper rectified driving signal to the upper voice coil section and providing a lower rectified driving signal to the lower voice coil section. The upper rectified driving signal may be generated by attenuating or blocking a first direction of current of the auxiliary driving signal, whereas the lower rectified driving signal may be generated by attenuating or blocking a second direction of current of the auxiliary driving signal, opposite to the first direction of current.

[0018] The main driving signal and auxiliary driving signal may in various embodiments be the same driving signal or different driving signals. By different may be understood that the auxiliary driving signal is a representation of said main driving signal characterized by having a lower amplitude than the main driving signal, i.e. having a reduced gain compared to the main driving signal.

[0019] In a preferred embodiment, the voice coils sections are arranged relative to each other and coupled to the driving signals in such a way, that the currents flow the same way in all active voice coil sections so as to support each other in interacting with the magnetic circuit to achieve the desired electromotive force [0020] In various embodiments, when current of an auxiliary driving signal flows in a first direction of current, this current may substantially flow to the lower voice coil section, whereas its flow to the upper voice coil section is attenuated or blocked. Similarly, when current of an auxiliary driving signal flows in a second direction of current, this current may substantially flow to the upper voice coil section, whereas its flow to the lower voice coil section is attenuated or blocked. The upper rectified driving signal and lower rectified driving signals are arranged to provide current flowing in an appropriate direction of current to produce an electromotive force on the voice coil such that the audio signal is correctly reproduced.

[0021] Alternatively, the flow of current may be reversed such that current flowing in the first direction of current may substantially flow to the upper voice coil section and its flow to the lower voice coil section is attenuated or blocked. Similarly, as current of an auxiliary driving signal flows in a second direction of current, this current may substantially flow to the lower voice coil section, whereas its flow to the upper voice coil section is attenuated or blocked. The upper rectified driving signal and lower rectified driving signals are arranged to provide current flowing in an appropriate direction of current to produce an electromotive force on the voice coil such that the audio signal is correctly reproduced [0022] An attenuation of a current may be understood as a reduction of current and/or voltage of the signal, e.g. an upper rectified driving signal may be generated by attenuating a first direction of current of an auxiliary driving signal, and thus the magnitude of current flow in a first direction of current in the upper rectified driving signal may be smaller than the magnitude of current flow in a first direction of current in the auxiliary driving signal. Attenuation is a reduction of current and/or voltage of preferably at least 50 %, more preferably at least 75 %, even more preferably at least %, and most preferably at least 99 %.

[0023] Blocking a current may be understood as a reduction of current, such that no substantial current flows after blocking the current.

[0024] The attenuation or blocking of the auxiliary signal is, according to the invention, achieved by passive rectification, meaning attenuation or blocking of one direction of current by passive means, i.e, without requiring active control. As such, passive rectification may not require a control signal or a power source, besides a driving signal. Passive rectification may, for example, be achieved by diodes or other non-active components, or a circuit thereof In various embodiments of the invention, the upper rectified driving signal is created by passing the auxiliary driving signal through a rectifying unit, e.g. a diode. A passive rectifying unit or a rectifying unit may be understood as a unit, device, circuit, or circuit element which processes current asymmetrically, i.e. a rectifying unit may respond in a first way to a current in a first direction, and may respond in a second way to a current in a second direction.

[0025] An example of a rectifying unit is a diode, which may be characterised by an asymmetric conductance, i.e. low resistance for one direction of current, and high resistance for the opposite direction of current, within the current and/or voltage limitations of the diode. To create the upper rectified driving signal, a diode may be integrated to block a first direction of current of the auxiliary driving signal, while allowing passage of a second direction of current of the auxiliary driving signal. Thereby, a first direction of current in the upper voice coil section may be attenuated or blocked by the diode. The above explanation similarly applies to the creation of the lower rectified driving signal which may similarly be created by passing the auxiliary driving signal through a rectifying unit, e.g. a diode, to block a second direction of current of the auxiliary driving signal, while allowing passage of a first direction of current of the auxiliary driving signal. Thereby, a second direction of current in the lower voice coil section may be attenuated or blocked by the diode.

[0026] In various embodiments, when the voice coil is not driven, i.e. resting in balance with no signal applied, the centre voice coil section may be located substantially within the air gap, the upper voice coil section may be located substantially outside the air gap, and the lower voice coil section may be located substantially outside the air gap. If a driving signal is provided to any voice coil section while it is substantially inside the air gap, the generated electromotive force may be greater, compared to an electromotive force generated by providing the same driving signal to the same voice coil section when it is substantially outside the air gap.

[0027] When the voice coil is driven and thus translates along the traveling axis, the voice coil sections may move in and out of the air gap, depending on the direction and amplitude of translation, and the geometry of the voice coil sections. Thus, the contribution to the generation of electromotive force from various voice coil sections may vary while the voice coil reciprocates [0028] For small audio signals, e.g. of low amplitude, which may result in small voice coil excursions, it may primarily be a centre voice coil section which is able to generate an electromotive force, according to the invention. For a larger audio signal, e.g. of larger amplitude, a contribution to the generation of an electromotive force from the upper and/or lower voice coil sections may be required to reproduce an audio signal.

[0029] In various embodiments, when driving signals have a first direction of current, the voice coil may move in a first direction of the traveling axis. This may cause a voice coil section, e.g. the lower voice coil section, to travel substantially into the air gap, allowing it to contribute in the generation of an electromotive force. Similarly, when driving signals have a second direction of current, the voice coil may move in a second direction of the traveling axis. This may cause a voice coil section, e.g. the upper voice coil section, to travel substantially into the air gap, allowing it to contribute in the generation of an electromotive force. As such, in various embodiments, the upper and lower voice coil sections may be able to contribute in the generation of an electromotive force.

[0030] In various embodiments, when the excursion allows the lower voice coil section to contribute substantially to the generation of an electromotive force, the driving signal received by the lower voice coil section may substantially be the auxiliary driving signal. When the excursion is in the opposite direction, i.e. the upper voice coil section is closer to the air gap than the lower voice coil section, the lower rectified driving signal received by the lower voice coil section may be created by attenuating or blocking the auxiliary driving signal, i.e. the lower rectified driving signal may provide no substantial current to the lower voice coil section. Similarly, when the excursion allows the upper voice coil section to contribute substantially to the generation of an electromotive force, the driving signal received by the upper voice coil section may substantially be the auxiliary driving signal. When the excursion is in the opposite direction, i.e. the lower voice coil section is closer to the air gap than the upper voice coil section, the upper rectified driving signal received by the upper voice coil section may be created by attenuating or blocking the auxiliary driving signal, i.e. the upper rectified driving signal may provide no substantial current to the upper voice coil section.

[0031] According to the invention, the current provided to the voice coil sections of the segmented voice coil may be reduced due to attenuation or blocking of driving signals. It is especially advantageous to block current to voice coil sections which do not contribute to the generation of an electromotive force. In various embodiments, this can be achieved by implementing one or more rectifying units, e.g. diodes. This allows the excursion to reproduce an audio signal, while the power consumption and excess heating of a loudspeaker according to this invention may be significantly smaller.

[0032] In various embodiments, rectifying units or diodes may additionally block the auxiliary driving signal below a certain threshold amplitude or/and current. This can 5 further reduce power consumption and heating when only small excursions are required to reproduce audio signals.

[0033] Various embodiments of the invention may be built into active loudspeakers, and other various embodiments of the invention may be built into passive loudspeakers. An active loudspeaker may be understood as a loudspeaker comprising means of signal amplification, which require a power source, e.g. an external power source or a battery. A passive loudspeaker may be understood as a loudspeaker not comprising means of amplification, thus not necessarily requiring a power source.

[0034] In passive loudspeaker embodiments, the audio signal, upon which the centre driving signal and the auxiliary driving signal is based, may be an amplified signal.

The centre driving signal and the auxiliary driving signal may even be the audio signal.

[0035] In loudspeakers known in the prior art, current is typically provided to the entire voice coil, even though significant portions of the voice coil do not contribute to the generation of an electromotive force. This excess current may be considered as a waste of power and may result in heat generation which impose limitations on a loudspeaker system. This problem has previously been addressed by segmenting a voice coil into voice coil sections in combination with a complicated control of the driving signal provided to the individual voice coil sections, typically requiring complex solutions.

[0036] The present invention delivers a solution which is remarkably simple, compared to previous inventions with segmented voice coils. Instead of a complicated control of individual driving signals, the invention utilizes rectifying units, e.g. diodes, which are cleverly arranged in conjunction with voice coil sections. This method may ensure that the power consumption of voice coil sections which are not able to contribute to generation of an electromotive force are lowered considerably. Since the power consumption is reduced, so is the heat generation in the system. Due to the simplicity of the invention, it may even be implemented in passive loudspeakers, or in simple active loudspeaker systems which otherwise cannot support a control procedure for a segmented voice coil. Thus, the invention may extend the capacity of a broad range of loudspeaker systems.

[0037] According to an embodiment of the invention, said upper rectified driving signal is provided by rectifying said auxiliary driving signal in said first direction of current, and said lower rectified driving signal is provided by rectifying said auxiliary driving signal in said second direction of current.

[0038] A rectification of a signal may be understood as a process of converting a signal which contains both positive and negative parts, into a signal which only contains either positive or negative parts.

[0039] According to an embodiment of the invention, said rectification of said auxiliary driving signal is half-wave rectification.

[0040] Half-wave rectification may be understood as a type of rectification, where one direction of current is allowed to flow, while another direction of current is blocked, e.g. a half-wave rectification of a signal will block either the positive or the negative parts of the signal, while not affecting other parts.

[0041] In various embodiments, the upper rectified driving signal is provided by a first half-wave rectification of the auxiliary driving signal, and the lower rectified driving signal is provided by a second half-wave rectification of the auxiliary driving signal, where the first half-wave rectification blocks a first direction of current, and the second half wave rectification blocks a second direction of current.

[0042] According to the invention, contrary to, for example, an AC-to-DC converter or a full-wave bridge rectifier, the rectification is not intended to move the full signal or energy content to the positive or negative domain, but indeed to exclude all negative content from, e.g., the lower rectified driving signal, and exclude all positive content from, e.g., the upper rectified driving signal, and transferring the remaining content as unchanged as possible. This is because the upper and lower voice coil sections driven by these signals, and due to the voice coil geometry according to the invention, only operate effectively on either the positive or negative signal content, respectively, depending on the geometric configuration.

[0043] According to an embodiment of the invention, providing said upper rectified driving signal comprises processing said auxiliary driving signal using an upper rectifying unit and providing said lower rectified driving signal comprises processing said auxiliary driving signal using a lower rectifying unit [0044] According to the invention, an upper rectified driving signal is provided by attenuating or blocking a first direction of current of an auxiliary driving signal.

Similarly, a lower rectified driving signal is provided by attenuating or blocking a second direction of current of an auxiliary driving signal. The attenuation and/or blocking of an auxiliary driving signal may comprise one or more rectifying units.

[0045] A rectifying unit may be a passive rectifying unit [0046] Preferably, a rectifying unit will process an auxiliary driving signal by attenuating or blocking one first direction of current and passing the opposite direction of current. In various embodiments, a rectifying unit will process the auxiliary driving signal to create an upper rectified driving signal, and a rectifying unit will process the auxiliary driving signal to create a lower rectified driving signal. The processing of the auxiliary driving signal to create an upper rectified driving signal will be characterised by an asymmetric response to the direction of the current, e.g. current in a first direction is attenuated or blocked, while current in a second direction is allowed to pass to the upper voice coil section. The processing of the auxiliary driving signal to create a lower rectified driving signal may be characterised by the opposite asymmetric response, compared to the processing of the auxiliary driving signal to create an upper rectified driving signal, e.g. current in a second direction is attenuated or blocked, while current in a first direction is allowed to pass to the lower voice coil section. 1.3

[0047] In various embodiments, when one or more rectification units may attenuate or block a direction of current, the same direction of current of the auxiliary driving signal may be similarly attenuated or blocked [0048] The rectifying unit processing the auxiliary driving signal to provide an upper rectified driving signal may be referred to as an upper rectifying unit and the rectifying unit processing the auxiliary driving signal to provide a lower rectified driving signal may be referred to as a lower rectifying unit.

[0049] In various embodiments, the upper rectifying unit and the lower rectifying unit are constructed from similar or identical components, but are integrated into the invention to provide opposite processing of the auxiliary driving signal, e.g. an upper rectifying unit blocks a first direction of current and allows current in a second direction to pass with no substantial attenuation, while a lower rectifying unit blocks a second direction of current and allows current in a first direction to pass with no substantial attenuation.

[0050] In some embodiments, the upper rectifying unit and the lower rectifying unit may refer to the same unit, device, circuit or circuit element, such that this one rectifying unit is capable of providing both an upper rectified driving signal and a lower rectified driving signal on the basis of an auxiliary driving signal.

[0051] A rectifying unit may have a characteristic voltage and/or current threshold.

Below this voltage and/or current threshold, any current supplied to the rectifying unit is attenuated or blocked. This may also be referred to as forward voltage drop.

[0052] In various embodiments a rectifying unit with a certain threshold current and/or threshold voltage is integrated. An auxiliary driving signal which has a current and/or voltage lower than the threshold current and/or threshold voltage is attenuated or blocked by the rectifying unit. For a small audio signal, e.g, low amplitude, sufficient excursion may be produced by the centre voice coil section and may not require electromotive force generated from the upper voice coil section and/or the lower voice coil section to reproduce the audio signal In this scenario, a rectifying unit may block or attenuate current to the upper voice coil section and a rectifying unit may block or attenuate current to the lower voice coil section, i.e. block both directions of current in both rectifying units. If an audio signal has an amplitude sufficiently large, such that it may not be correctly reproduced by the excursion generated by a centre voice coil section alone, the current of the auxiliary driving signal may be greater than the threshold current and/or threshold voltage of the rectifying unit. This allows the upper voice coil section and the lower voice coil section to contribute to the generation of an electromotive force, allowing the excursion to reproduce the audio signal, within the limitations of the voice coil.

[0053] As such, for small audio signals, e.g. low amplitude, no substantial current is supplied to the upper voice coil section or the lower voice coil section, which may reduce the power consumption and excess heating according to the invention, compared to a prior art voice coil system [0054] In practice, a rectifying unit may be a diode, which may be characterised by an asymmetric conductance, i.e. low resistance for one direction of current, and high resistance for the opposite direction of current, within the current and/or voltage limitations of the diode [0055] A rectification unit may be connected to either connection of a voice coil section [0056] According to an embodiment of the invention, said upper rectifying unit comprises a passive rectifying circuit and/or said lower rectifying unit comprises a passive rectifying circuit.

[0057] In various embodiments, the upper and lower rectifying units comprise circuits arranged to rectify signals.

[0058] In some embodiments, the upper rectifying unit and the lower rectifying unit are one circuit, such that this one circuit is capable of providing both an upper rectified driving signal and a lower rectified driving signal on the basis of an auxiliary driving signal.

[0059] A passive rectifying circuit may be a circuit which performs rectification by passive means, i.e. without requiring active control [0060] According to an embodiment of the invention, each of said upper rectifying unit and said lower rectifying unit comprises a half-wave rectifier circuit.

[0061] A half-wave rectifier circuit refers to a circuit attenuating or blocking either the negative or positive half of a time-varying input signal, and transferring the other half substantially without attenuation other than a forward voltage drop over a typical audio application frequency range, e.g. 20 Hz to 20 kHz. A suitable half-wave rectifier circuit may, for example, comprise a single diode.

[0062] Preferably, smoothing or other filtering of the resulting half-wave signal should be avoided, at least in the above-mentioned frequency range, in order to not distort or filter the audio component of the driving signal According to the invention, contrary to, for example, an AC-to-DC converter or a full-wave bridge rectifier, the rectification is not intended to move the full signal or energy content to the positive or negative domain, but indeed to exclude all negative content from, e.g., the lower rectified driving signal, and exclude all positive content from, e.g., the upper rectified driving signal, and transferring the remaining content as unchanged as possible. This is because the upper and lower voice coil sections driven by these signals, and due to the voice coil geometry according to the invention, only operate effectively on either the positive or negative signal content, respectively, depending on the geometric configuration.

[0063] According to an embodiment of the invention, neither one of said upper rectifying unit and said lower rectifying unit comprises a full-wave rectifier circuit or a full-wave bridge rectifier.

[0064] As explained above, the rectifying unit according to the present invention should not be mirroring the negative signal content to the positive side of the signal, and vice versa Therefore, the rectifying unit should not comprise for example a diode bridge for full wave rectification [0065] According to an embodiment of the invention, said upper rectifying unit comprises a diode and said lower rectifying unit comprises a diode.

[0066] In various embodiments, the upper and lower rectifying unit each comprise a diode, preferably a single diode each, or a number of diodes coupled to be equivalent to a single diode, e.g. in series or parallel with the same forward direction. A diode may refer to a device characterised by an asymmetric conductance, i.e. low resistance for one direction of current, and high resistance for the opposite direction of current, within the current and/or voltage limitations of the diode. A diode may comprise a piece of semiconductor material. According to the invention, different types of diodes include point-contact diodes, p-n junction diodes, and Schottky diodes, but the invention is not limited to these diode types.

[0067] Various diodes may have various characteristics. Diodes typically have two terminals, and within certain characteristic limitations of voltage and/or current, the electrical resistance for current through the diode from one terminal to the other will typically be different from the electrical resistance of a current in the opposite direction. Often, one direction of current through the diode has a large resistance, such that no substantial current may flow in the diode, up to a break-down voltage. Current in the opposite direction through the diode may have a low resistance.

[0068] Often, a certain cut-in voltage across the diode is required for it to conduct in its direction of low resistance. At a voltage above this cut-in voltage, the diode may have a low resistance and allow substantial current through, and below this cut-in voltage, the diode may not allow substantial current to pass through. The voltage cut-in may also be referred to as forward voltage drop or turn on voltage.

[0069] In various embodiments, a diode with a certain cut-in voltage is selected, such that below this cut-in voltage, no substantial current passes through the diode. For a small audio signal, e.g. low amplitude, an excursion may not require electromotive force generated from the upper voice coil section and/or the lower voice coil section to reproduce the audio signal. In such an embodiment, a diode may be integrated having a cut-in voltage that does not allow substantial current through for voltages of the auxiliary driving signal which correspond to excursions which can be generated by only using a centre voice coil section. That is, if an audio signal has an amplitude that may be reproduced by the excursion generated by a centre voice coil section, the voltage of the driving signal is smaller than the cut-in voltage of the selected diode. If an audio signal has an amplitude sufficiently large, such that it may not be reproduced by the excursion generated by a centre voice coil section, the voltage of the driving signal is greater than the cut-in voltage of the selected diode. This allows the upper voice coil section and the lower voice coil section to contribute to the generation of an electromotive force, allowing the excursion to reproduce the audio signal, within the limitations of the voice coil.

[0070] As such, for small audio signals, e.g. low amplitude, no substantial current is supplied to the upper voice coil section or the lower voice coil section, which may reduce the power consumption and excess heating according to the invention, compared to a prior art voice coil system.

[0071] This behaviour allows a diode to be utilised as a rectifying unit, according to the invention.

[0072] A diode may typically allow a reverse current. A reverse current may be understood as a current which can flow through the diode in the direction of current which is characterised by a high resistance. The reverse current may often be significantly smaller than the current of an auxiliary driving signal. Thus, even though a diode allows a reverse current, for most practical embodiments, the reverse current is without significance.

[0073] According to an embodiment of the invention, said diodes are coupled with means for compensating the forward voltage drop [0074] In embodiments using diodes to achieve the rectification, and where the forward voltage drop is undesired, the forward voltage drop may be compensated for using suitable means. For example, the compensation means may comprise forward biasing the diodes with a DC voltage slightly lower than the intrinsic forward voltage drop of the diodes, e.g. a DC voltage of 0.6V for e.g. silicon diodes with turn on voltage of 0.7V, or 0.2W for germanium or Schottky diodes with turn on voltage of 0.30V. The auxiliary driving signal may alternatively be offset by similar amounts to compensate for the forward voltage drop [0075] In other embodiments the forward voltage drop may be desirable as described above, and no compensation needs to be applied In an embodiment, negative compensation may even be applied to increase the forward voltage drop to require a larger signal to overcome the cut-in voltage, thereby allowing selection of a desired voltage at which the rectified auxiliary driving signal is passed through the diode to the auxiliary voice coil sections.

[0076] According to an embodiment of the invention, said centre driving signal and said auxiliary driving signal are provided by one or more amplifiers.

[0077] Generating a driving signal for a voice coil preferably comprises an amplifier. According to the invention, a centre driving signal may be provided by an amplifier. Additionally, an auxiliary driving signal may be provided by an amplifier.

[0078] According to an embodiment of the invention, said one or more amplifiers is a common amplifier.

[0079] In various embodiments, the amplifier providing an auxiliary driving signal and the amplifier providing the centre driving signal may be the same amplifier.

[0080] According to an embodiment of the invention, providing an upper rectified driving signal comprises amplifying said auxiliary driving signal and providing a lower rectified driving signal comprises amplifying said auxiliary driving signal [0081] In various embodiments, providing the upper and lower rectified driving signals comprises amplifiers. This may be amplifiers which are controlled selectively to generate the rectified driving signals on the basis of the auxiliary driving signal. It may also be amplifiers which are not controlled selectively.

[0082] According to an embodiment of the invention, said auxiliary driving signal has an amplitude different from said centre driving signal.

[0083] The individual voice coil sections of a segmented voice coil may have different geometries, e.g. different number of windings, winding densities, voice coil section heights etc. Therefore, it may be advantageous for the auxiliary driving signal to have a signal amplitude which is different from the amplitude of the centre driving signal. In various embodiments the relative amplitudes may be selected to ensure a linear response of the voice coil to an applied audio signal.

[0084] According to an embodiment of the invention, said auxiliary driving signal has the same amplitude as said centre driving signal.

[0085] The individual voice coil sections of a segmented voice coil may have the same geometries, e.g. same number of windings, winding densities, voice coil section heights etc. Therefore, it may be advantageous for the auxiliary driving signal to have a signal amplitude which is the same as the amplitude of the centre driving signal. In various embodiments the amplitudes may be selected to ensure a linear response of the voice coil to an applied audio signal.

[0086] According to an embodiment of the invention, said upper voice coil section is a first upper voice coil section, said lower voice coil section is a first lower voice coil section, said upper rectified driving signal is a first upper rectified driving signal, said lower rectified driving signal is a second lower rectified driving signal and said auxiliary driving signal is a first auxiliary driving signal; wherein said plurality of voice coil sections arranged along said travelling axis further comprises a second upper voice coil section and a second lower voice coil section, said second upper voice coil section and said second lower voice coil section being arranged respectively on either side of the group of voice coil sections comprising said first upper voice coil section, said centre voice coil section, and said first lower voice coil section; wherein said step of applying an audio signal further comprises providing a second auxiliary driving signal based on said audio signal to said second upper voice coil section and said second lower voice coil section, said providing a second auxiliary driving signal comprising providing a second upper rectified driving signal to said second upper voice coil section and providing a second lower rectified driving signal to said second lower voice coil section; wherein said second upper rectified driving signal is provided by attenuating and/or blocking a first direction of current of said second auxiliary driving signal by passive rectification; and wherein said second lower rectified driving signal is provided by attenuating and/or blocking a second direction of current of said second auxiliary driving signal by passive rectification [0087] In various embodiments of the invention, the voice coil consists of a centre voice coil section, a first upper voice coil section, a first lower voice coil section, a second upper voice coil section, and a second lower voice coil section, with all voice coil sections arranged along the travelling axis, when the travelling axis is viewed in a vertical direction. The first upper voice coil section and the first lower voice coil section are arranged around the centre voice coil section. The second upper voice coil section and the second lower voice coil section are arranged respectively on either side of the group of voice coil sections comprising the first upper voice coil section, the centre voice coil section, and the first lower voice coil section. The second upper voice coil section may have the first upper voice coil section as the nearest neighbouring voice coil section, and the second lower voice coil section may have the first lower voice coil section as the nearest neighbouring voice coil section.

[0088] When an audio signal is applied, a centre driving signal is provided to the centre voice coil section, a first auxiliary driving signal is provided to the first upper voice coil section and first lower voice coil section, and a second auxiliary driving signal is provided to the second upper voice coil section and second lower voice coil section Providing the first auxiliary driving signal comprises generating a first upper rectified driving signal using a rectifying unit and generating a first lower rectified driving signal using a rectifying unit. Furthermore, providing the second auxiliary driving signal comprises generating a second upper rectified driving signal using a rectifying unit and generating a second lower rectified driving signal using a rectifying unit.

[0089] Preferably, a first upper rectified driving signal may be created on the basis of attenuating or blocking a first direction of current of the first auxiliary driving signal using a rectifying unit, a first lower rectified driving signal may be created on the basis of attenuating or blocking a second direction of current of the first auxiliary driving signal using a rectifying unit, a second upper rectified driving signal may be created on the basis of attenuating or blocking a first direction of current of the second auxiliary driving signal using a rectifying unit, and a second lower rectified driving signal may be created on the basis of attenuating or blocking a second direction of current of the second auxiliary driving using a rectifying unit.

[0090] In various embodiments, the rectification units may not be the same, e.g. a first type of rectification unit is responsible for providing the first upper rectified driving signal and the first lower rectified driving signal, while a second type of rectification unit is responsible for providing the second upper rectified driving signal and the second lower rectified driving signal [0091] In some embodiments, the one or more rectifying units generating the first upper rectified driving signal and the first lower rectified driving signal have a first current and/or voltage threshold, e.g. voltage cut-in level. The one or more rectifying units generating the second upper rectified driving signal and the second lower rectified driving signal have a second current and/or voltage threshold, e.g. voltage cut-in level.

[0092] When a first auxiliary driving signal has a current and/or voltage below a first current and/or voltage threshold, the one or more rectifying units generating the first upper rectified driving signal and the first lower rectified driving signal may attenuate or block the current of the first auxiliary driving signal to the first upper voice coil section and attenuate or block the current of the first auxiliary driving signal to the first lower voice coil. When a second auxiliary driving signal has a current and/or voltage below a second current and/or voltage threshold, the one or more rectifying units generating the second upper rectified driving signal and the second lower rectified driving signal may attenuate or block the current of the second auxiliary driving signal to the second upper voice coil section and attenuate or block the current of the second auxiliary driving signal to the second lower voice coil.

[0093] The first current and/or voltage threshold and the second current and/or voltage threshold may respectively be chosen such that currents to voice coils outside the excursion range may be attenuated or blocked. In such embodiments, the power consumption and heat generation may be significantly lower than in a prior art loudspeaker not segmented into voice coil sections, while the excursion is still able to reproduce the audio signal.

[0094] In these embodiments, the centre driving signal, the first auxiliary driving signal, and the second auxiliary driving signal may all be the same or may all be different. Additionally, any combination of two of the driving signals may be the same with a third driving signal being different.

[0095] In an embodiment of the invention, said first upper voice coil section may be a first inner auxiliary voice coil section, said second upper voice coil section may be an first outer auxiliary voice coil section, said first lower voice coil section may be a second inner auxiliary voice coil section, and said second lower voice coil section may be an second outer auxiliary voice coil section. In a different embodiment, said first lower voice coil section may be a first inner auxiliary voice coil section, said second lower voice coil section may be an first outer auxiliary voice coil section, said first upper voice coil section may be a second inner auxiliary voice coil section, and said second upper voice coil section may be an second outer auxiliary voice coil section.

[0096] According to an embodiment of the invention, said upper voice coil section is displaced with respect to the centre voice coil section along a first displacement direction along said travelling axis, said lower voice coil section is displaced with respect to the centre voice coil section along a second displacement direction along said travelling axis, and said upper voice coil section and said lower voice coil section are arranged symmetrically around said centre voice coil section, wherein said first displacement direction and said second displacement direction are opposite directions along said travelling axis.

[0097] In various embodiments, at least one upper voice coil section and at least one lower voice coil section are arranged around a central main voice coil section. Since it may be desirable to have a linear response of the voice coil, it is often advantageous to distribute each individual pair of auxiliary voice coils symmetrically along the axis of translation, relative to a central main voice coil section. The plane of symmetry is thus defined by a main voice coil section and is perpendicular to the axis of translation.

[0098] In various embodiments, at least a second upper voice coil section and a second lower voice coil section are arranged around a cent-al main voice coil section, in addition to a first upper voice coil section and a first lower voice coil section arranged around a central main voice coil section. Since it may be desirable to have a linear response of the voice coil, it is often advantageous to distribute the first upper voice coil section and the first lower voice coil section symmetrically along the axis of translation, relative to a central main voice coil section. The plane of symmetry is thus defined by a main voice coil section and is perpendicular to the axis of translation. Similarly, it is often advantageous to distribute the second upper voice coil section and the second lower voice coil section symmetrically along the axis of translation, relative to a central main voice coil section [0099] According to an embodiment of the invention, the height of said voice coil sections are individually either smaller than, greater than and/or of the same height as the height of said air gap along said travelling axis [0100] Prior art in the field of loudspeakers include both voice coils of heights greater than the height of the air gap along the travelling axis, and voice coils of heights smaller than the height of the air gap along the travelling axis The height of the air gap is, in this disclosure, referring the extension of the air gap along the traveling axis, and not to the narrow distance between the magnet or pole parts forming the air gap. A voice coil which has a height greater than the height of the air gap along the travelling axis may be referred to as an overhung coil, whereas a voice coil which has a height smaller than the height of the air gap along the travelling axis may be referred to as an underhung coil. The design and geometry may preferably be based on the intended application of the voice coil system [0101] The present invention is applicable to embodiments where the height of any of the individual voice coil sections are smaller than the height of the air gap along the travelling axis, as well as in embodiments where the height of any of the individual voice coil sections are greater than the height of the air gap along the travelling axis.

[0102] The invention may furthermore be applicable to embodiments where the combined height of the individual voice coil sections is smaller than the height of the air gap along the travelling axis, as well as to embodiments where the combined height of the individual voice coil sections is greater than the height of the air gap along the travelling axis.

[0103] Additionally, the invention is applicable to embodiments where the height of any of the individual voice coil sections is the same height as the air gap along the travelling axis, as well as to embodiments where the combined height of the individual voice coil sections is the same height as the air gap along the travelling axis.

[0104] Furthermore, the invention is applicable to embodiments where the height of any of the voice coil sections is individually smaller, greater, and/or of the same height as the height of the air gap along the travelling axis.

[0105] An aspect of the invention relates to a voice coil driving system of a loudspeaker comprising: a magnetic circuit having an air gap; a voice coil suspended in said air gap, said voice coil comprising a plurality of voice coil sections, arranged along said travelling axis, said plurality of voice coil sections comprising a centre voice coil section, an upper voice coil section and a lower voice coil section, said upper voice coil section and said lower voice coil section being arranged respectively on either side of said centre voice coil section; one or more passive rectifying units arranged to provide an upper rectified driving signal to said upper voice coil section and a lower rectified driving signal to said lower voice coil section.

[0106] The method for driving a voice coil may be used in a voice coil driving system of a loudspeaker, according to the invention As such, the integrated rectifying units may ensure that a reduced amount of current is supplied to selected voice coil sections, when these sections are not able to contribute to the generation of a substantial electromotive force.

[0107] In voice coil systems known in the prior art, a current is often provided to the entire voice coil, even though significant portions of the voice coil do not contribute to the generation of an electromotive force, which may be considered as a waste of power and may result in heat generation which impose limitations on a voice coil system. This invention may ensure that the heat generation and power consumption of voice coil sections which are not able to contribute to generate an electromotive force IS are lowered considerably.

[0108] According to an embodiment of the invention, said one or more passive rectifying units comprise one or more rectifying circuits.

[0109] According to an embodiment of the invention, said one or more passive rectifying units comprise one or more diodes.

[0110] In a preferred embodiment of the invention, the rectifying units comprise one or more diodes, e.g. a diode blocks a first direction of current to the upper voice coil sections, and a diode blocks a second direction of current to the lower voice coil sections.

[0111] According to an embodiment of the invention, said voice coil driving system is arranged to receive an audio signal and to provide a centre driving signal based on said audio signal to said centre voice coil section, and to provide an auxiliary driving signal based on said audio signal to said one or more passive rectifying units [0112] In an embodiment of the invention, a centre driving signal and an auxiliary driving signal are generated based on said audio signal, e.g. by amplification of the audio signal. In other various embodiments, the audio signal is the centre driving signal and the auxiliary driving signal.

[0113] According to an embodiment of the invention, said voice coil driving system comprises two passive rectifying units, each of said two passive rectifying units being arranged to provide respectively either an upper rectified driving signal or a lower rectified driving signal based on said auxiliary driving signal.

[0114] According to an embodiment of the invention, an upper rectifying unit of said one or more passive rectifying units is arranged to process said auxiliary driving signal by attenuating and/or blocking a first direction of current of said auxiliary driving signal to provide said upper rectified driving signal; wherein a lower rectifying unit of said one or more passive rectifying units is arranged to process said auxiliary driving signal by attenuating and/or blocking a second direction of current of said auxiliary driving signal to provide said lower rectified driving signal; and wherein said first and second direction of current of said auxiliary driving signal are opposite directions of current.

[0115] A voice coil driving system as described herein may inherit all the advantages and benefits as described above in relation to the method of driving a voice coil. As such, a loudspeaker according to the present invention may provide the beneficial effect of low power consumption and reduction of excessive heating within the loudspeaker due to the efficiency of the segmented voice coil.

[0116] An aspect of the invention relates to a loudspeaker comprising: a diaphragm; an interface configured to receive an audio signal; and a voice coil driving system according to any of the above.

[0117] A voice coil driving system according to the invention may be integrated into a loudspeaker.

[0118] Various embodiments of the invention may be active loudspeakers, arid other various embodiments of the invention may be passive loudspeakers. An active loudspeaker may be understood as a loudspeaker comprising means of signal amplification, which require a power source, e.g. an external power source or a battery.

A passive loudspeaker may be understood as a loudspeaker not comprising means of amplification, thus not necessarily requiring a power source.

[0119] According to an embodiment of the invention, said loudspeaker comprises one or more amplifiers.

[0120] According to the invention, a loudspeaker may comprise at least one amplifier. An amplifier may amplify an audio signal to generate a centre driving signal and/or an auxiliary driving signal, but embodiments of the invention are not limited to this example.

[012]] A loudspeaker according to the invention has the same advantages as a voice coil driving system according to the invention, i.e. heat generation and power consumption of voice coil sections of the loudspeaker system which are not able to contribute to generation of an electromotive force are lowered considerably.

The drawings [0122] Various embodiments of the invention will in the following be described with reference to the drawings where fig. la-lb illustrate a conventional loudspeaker known in the prior art, fig 2 illustrates a loudspeaker with a voice coil driving system comprising a centre voice coil section, an upper voice coil section, and a lower voice coil section according to an embodiment of the invention, fig 3a-3c illustrate the reciprocating translation of the voice coil according to embodiments of the invention comprising three voice coil sections, fig. 4a-4b illustrate various configurations for providing a centre driving signal and an auxiliary driving signal to the plurality of voice coil sections according to embodiments of the invention, fig. 5 illustrates a loudspeaker according to an embodiment of the invention, fig. 6a-6c illustrate various configurations for applying a centre driving signal and an auxiliary driving signal to the plurality of voice coil sections according to the invention, fig 7a-7b illustrate configurations of the voice coil sections according to various embodiments of the invention, and fig. 8 illustrates a preferred processing of the driving signal according to various embodiments of the invention.

Detailed description

[0123] Fig. la shows a cut-through view of a loudspeaker according to the prior art. Fig. lb illustrates a section view at the line lb-lb in fig. I a. Disposed within the loudspeaker are two concentrically aligned magnetic members 2 forming a magnetic circuit. These magnetic members 2 are arranged such that a circular air gap 3 is formed within the magnetic circuit 2.

[0124] A voice coil 1 comprising a plurality of coil windings is further suspended within the air gap 3. The windings of the voice coil 1 are arranged such that when an electric current is passed through the coil 1, an electromotive force will translate the voice coil 1 within the air gap 3, such that a membrane or diaphragm 7 is actuated An alternating current thereby causes a reciprocating movement of the diaphragm 7, which generates an acoustic sound signal.

[0125] Referring to fig. 2, a voice coil driving system 51 according to an embodiment of the invention is illustrated. The voice coil driving system 51 comprises a magnetic circuit 2 formed by two concentrically aligned magnetic members 2. The magnetic members may be permanent magnets or metal poles. The magnetic circuit 2 is arranged such that a circular air gap 3 is formed within the magnetic circuit 2 terminated by the two magnetic members 2. The circular air gap 3 is a volume of air which takes on the form of a volume disposed between two axially aligned cylinders of different widths [0126] As acknowledged by the skilled person, several alternative voice coil based loudspeaker configurations are known in the technical field of loudspeakers and acoustic transducers, having other configurations of magnetic circuits and air gaps, including various configurations of permanent magnets, pole pieces, front and back plates, casing, and various configurations of air gaps, including circular as described above, linear, polygonal, irregular, one or several air gaps, etc. The present invention as defined by the claims is thereby not limited to the magnetic circuit and air gap configuration illustrated in the drawings but may readily be applied to other voice coil based transducers by the skilled person.

[0127] A voice coil 1 is suspended within the air gap 3. The voice coil 1 comprises a plurality of voice coil sections 21-22b, wherein a centre voice coil section 21 is centrally arranged surrounded by an upper voice coil section 2Ia and a lower voice coil section 21b arranged respectively on either side of said main voice coil section, with all voice coil sections axially aligned along a travelling axis 4 of the voice coil and the travelling axis being orientated in a vertical direction in the present embodiment (hence the 'upper' and 'lower' voice coil sections). Each voice coil section comprises a plurality of metal windings coiling around the inner magnetic member 2 and a travelling axis 4 as seen in fig. 2. The voice coil sections are mechanically coupled, but not necessarily electrically coupled, to form the voice coil L The mechanical coupling may comprise a support such as a tube, mesh or wire structure of paperboard, plastic or metal, e.g. a foil.

[0128] The voice coil sections 21-22b are configured such that when an electric current is passed through a voice coil section 21-22b, located at least partly within the air gap 3 of the magnetic circuit 2, an electromotive force will translate the particular voice coil section 21-22b along the travelling axis 4. Since all voice coil sections 2122b are mechanically coupled members of the voice coil 1, an electromotive force generated by any of voice coil sections 21-22b will translate the entire voice coil 1 along the travelling axis 4. The translation of the voice coil 1 along the travelling axis 4 results in the voice coil 1 pushing and pulling a diaphragm 7 of a loudspeaker 50. The reciprocating movement of the diaphragm 7 generates an acoustic sound signal [0129] The coupling of the voice coil 1 and the diaphragm 7 may be established by the above-mentioned mechanical coupling of the voice coil section, e.g. a plastic foil tube, or may involve further support members as known by the skilled person, for example a spider and a diaphragm surround. The idle position of the voice coil 1 may be controlled by the support members, such as a spider and/or a diaphragm surround and frame, as known by the skilled person. In a preferred embodiment, the total voice coil height is centred in the air gap when idle, so that with three voice coil sections as illustrated in the examples, the middle voice coil section is aligned with the magnetic circuit and air gap.

[0130] Since the magnetic field is substantially disposed within the air gap 3 in the magnetic circuit 2, only voice coil sections 21-22b that are at least partly positioned within the air gap may generate a substantive electromotive force upon application of an electric current. Generally, the more of a particular voice coil section is contained within the air gap, the higher the force generated upon application of an electric current. Referring to the instance of time shown in fig. 2, only voice coil section 21 is fully or partially disposed within the air gap 3, whereas voice coil sections 22a and 22b are disposed completely outside the air gap 3. Since the magnetic field density is highest within the air gap 3, and quickly decreasing outside the air gap 3, only voice coil section 21 may generate a substantial electromotive force to translate the voice coil 1, whereas voice coil sections 22a and 22b are located sufficiently far away from the air gap 3 that the efficiency in converting electric driving power into electromotive force is considerably lower, and practically insignificant, compared to the efficiency of converting electric driving power into electromotive force for voice coil section 21.

[0131] Windings of voice coil sections 21-22b, located away from the air gap 3, will primarily only contribute to excessive voice coil heating when an electric driving power is applied, and only contribute marginally in translating the voice coil 1 along the travelling axis 4. In view of these considerations, it is advantageous to avoid applying power to any voice coil sections 21-22b, e.g. 22a-22b, that are not at least partly disposed within the air gap at a given time [0132] Generally, a loudspeaker system aims to reproduce an audio signal 30 in the excursion of a voice coil 1, where the excursion is the position of the voice coil 1, relative to its resting position. An audio signal 30 may comprise a representation of varying sound intensities, which may require varying excursions for reproduction. Thus, an audio signal 30 may require a range of excursions which can be established by only utilizing the electromotive force which can be generated by the centre voice coil section 21, for the audio signal 30 to be reproduced. The reproduction of another audio signal 30 may require a range of excursions which can only be established by utilising the centre voice coil section 21 together with the upper voice coil section 22a and the lower voice coil section 22b.

[0133] Referring to fig. 2, each voice coil section 21-22b receives a driving signal 41, 43a-43b. These driving signals may be provided by any means, e.g. by a controller, by an amplifier, or by an external source. The centre voice coil section 21 receives a centre driving signal 41, the upper voice coil section 22a receives an upper rectified driving signal 43a, and the lower voice coil section 22b receives a lower rectified driving signal 43b. The upper rectified driving signal 43a and the lower rectified driving signal 43b are based on an auxiliary driving signal 42. The auxiliary driving signal 42 and the centre driving signal 41 are based on, or even identical with, the audio signal 30.

[0134] The driving signals 41, 43a-43b are the actual electric signals that pass through the respective voice coil sections 21-22b to generate electromotive force to translate the voice coil 1 along the travelling axis 4. The driving signals 41-43b are provided to the voice coil sections 21-22b via channels, e.g. cables or wires, preferably electrical connections.

[0135] In the exemplary embodiment shown in fig. 2, the centre driving signal 41 and the auxiliary driving signal 42 are the audio signal 30, but the invention is not restricted to this example.

[0136] The upper and lower rectified driving signals 43a-43b may be derived by rectification units 16, based on the auxiliary driving signal 42. A rectifying unit or a passive rectifying unit may process current asymmetrically, i.e. a rectifying unit may respond in a first way to a current in a first direction and may respond in a second way to a current in a second direction.

[0137] Preferably, a rectification unit will attenuate or block one direction of current and let the opposite direction of cuiTent pass.

[0138] An example of a rectifying unit 16 is a diode 17, which may be characterised by an asymmetric conductance, i.e. low resistance for one direction of current, and high resistance for the opposite direction of current, within the current and/or voltage limitations of the diode.

[0139] The two rectification units 16 of the exemplary embodiment shown in fig. 2 may preferably be implemented to block opposite directions of current. As such, when current of an auxiliary driving signal 42 flows in one direction, this current may substantially flow to the lower voice coil section 22b, whereas its flow to the upper voice coil 22a section is blocked. Similarly, when current of an auxiliary driving signal flows in the opposite direction, this current may substantially flow to the upper voice coil section 22a, whereas its flow to the lower voice coil section 22b is blocked. This is further described below.

[0140] For one direction of driving signal current, the lower voice coil section 22b, whose resting position is completely or partly outside the air gap, may be translated (moved) towards the air gap, while for the opposite direction of current, it is translated away from the air gap. By implementation of a rectification unit 16, it is possible to attenuate or block current of the auxiliary driving signal 42 to the lower voice coil section 22b when it is translated away from the air gap, where it is not able to generate a substantial electromotive force. The same principle applies to upper voice coil section 22a, where, preferably, the direction in which the current should be attenuated or blocked should be opposite.

[0141] Since each direction of current of the driving signals can be related to a certain direction of translation or excursion of the voice coil, depending on the magnetic field orientation, the rectification units may thus be utilized to restrict current to the upper and lower voice sections 22a-22b when they are translated away from the air gap.

Notably, the upper rectified driving signal 43a and lower rectified driving signal 43b are arranged to provide current flowing in an appropriate direction of current to produce an electromotive force on the voice coil 1 such that the applied audio signal 30 is correctly reproduced by the excursion of the voice coil.

[0142] The voice coil sections 21-22b of voice coil 1 can be configured in multiple ways, depending on the relative positioning and dimensioning of the voice coil sections 21-22b. In the illustrated embodiments, the voice coil 1 comprises three voice coil sections 21-22b, but the present invention as defined by the claims may be configured with various other number of voice coil sections and voice coil section geometries. A skilled person would be able to change the geometry or increase the number of voice coil sections to, for example, five voice coil sections, i.e. one centre voice coil section, two upper voice coil sections, and two lower voice coil sections, where each of the upper and lower voice coil sections are connected to different rectification units.

[0143] Referring to figs. 3a-3c, the dynamic behaviour of the voice coil 1 is illustrated in an embodiment of the invention.

[0144] Fig. 3a shows a voice coil 1 comprising a centre voice coil section 21, an upper voice coil section 22a, and a lower voice coil section 22b, at an instance of time during application of an audio signal At the shown instance, the excursion (movement) required to reproduce the audio signal can be generated by the centre voice coil section 21 alone Depending on the direction of current of the auxiliary driving signal 42, current may be attenuated or blocked towards either the upper voice coil section 22a or the lower voice coil section 22b.

[0145] In some embodiments of the invention, a current and/or voltage threshold may be implemented such that no current is provided to either the upper voice coil section 22a or the lower voice coil section 22b, at instances of time similar to that shown in fig. 3a.

[0146] In fig. 3b, an audio signal is applied such that the voice coil 1 has been translated in an upward direction 5 at the shown instance of time. As such, the current of the centre driving signal 41 and the auxiliary driving signal 42 may have a direction of flow, which is attenuated or blocked towards the upper voice coil section 22a.

[0147] Alternatively, in fig. 3c, an audio signal is applied such that the voice coil 1 has been translated in a downward direction 6 at the shown instance of time. As such, the current of the centre driving signal 41 and the auxiliary driving signal 42 may have a direction of flow, which is attenuated or blocked towards the lower voice coil section 22b.

[0148] Figs. 4a-4b show various embodiments of the invention, both including amplification means.

[0149] In Fig. 4a, an audio signal 30 is provided to an amplifier 12 via an interface 52. The amplifier 12 is powered by a power supply unit (PSU) 13, e.g. a battery, a DC power supply, or an AC-to-DC power supply. The amplifier 12 has two output channels where the centre driving signal 41 and the auxiliary driving signal 42 are provided, respectively. According to the invention, the amplifier 12 may provide two identical amplifications or two different amplifications to provide the two outputs. The centre driving signal 41 is sent to the centre voice coil section 21, and the auxiliary driving signal 42 is sent to rectification units 16 to generate an upper rectified driving signal 43a and a lower rectified driving signal 43b, which are provided to the upper voice coil section 22a and the lower voice coil section 22b, respectively.

[0150] In Fig. 4b, an audio signal 30 is provided to an amplifier 12 via an interface 52, where the amplifier 12 is powered by a power supply unit (PSU) 13. The amplifier 12 has one output channel, where a signal, which serves as both a centre driving signal 41 and an auxiliary driving signal 42, is provided. One channel guides the signal to the centre voice coil section 21, and two other channels are attached to diodes 17, which act as rectification units 16 in the embodiment shown. The diodes 17 are attached with opposite directionalities, such that one direction of current is primarily provided to the lower voice coil section 22b, while the opposite direction of current is primarily provided to the upper voice coil section 22a [0151] Utilizing one or more diodes 17 as rectification units 16 is not restricted to embodiments of the invention where an amplifier 12 with one or more output channels is integrated, as diodes may generally be applied as rectification units in all configurations of the present invention.

[0152] Fig. 5 shows a loudspeaker 50 according to the invention. The loudspeaker 50 receives an audio signal 30, which is applied to a voice coil driving system 51 according to the invention.

[0153] A loudspeaker according to the invention may be a passive loudspeaker which may not require a power source but requires a pre-amplified audio signal, or it may be an active loudspeaker which may require a power source, e.g. for internal amplification for example when receiving a line level or digital audio signal.

[0154] Figs. 6a-6c illustrate various configurations of applying the centre driving signal 41 and the auxiliary driving signal 42, according to embodiments of the invention.

[0155] In fig. 6a, an incoming driving signal 46 is provided to the voice coil I. This driving signal 46 is provided to the centre voice coil section 21 as a centre driving signal 41 and provided to two diodes 17 to generate an upper rectified driving signal 43a and a lower rectified driving signal 43b. The diodes 17 are mounted with opposite directionality, such that the upper rectified driving signal 43a and the lower rectified driving signal 43b respectively comprise currents flowing in opposite directions. Current delivered to the voice coil sections 21-22b are guided out via output channels 44a-45. These channels are electrically connected to provide a single current output 47 of the voice coil 1.

[0156] In fig. 6b, an incoming driving signal 46 is provided to the voice coil 1. This driving signal 46 is only provided to the centre voice coil section 21 as a centre driving signal 41. The current of the signal leaves the centre voice coil section 21 via an output channel 45. This output channel provides the auxiliary driving signal 42, which is provided to two diodes 17 to generate an upper rectified driving signal 43a and a lower rectified driving signal 43b. The diodes 17 are mounted with opposite directionality, such that the upper rectified driving signal 43a and the lower rectified driving signal 43b respectively comprise currents flowing in opposite directions. The current of the upper and lower rectified driving signals 43a-43b leaves the upper and lower voice coil sections 22a-22b through output channels 44a-44b, which are electrically connected to provide a single current output 47 of the voice coil 1.

[0157] In fig. 6c, a centre driving signal 41 and an auxiliary driving signal 42 is provided to the voice coil I. The centre driving signal is provided to the centre voice coil section 21, whereas the auxiliary driving signal 42 is provided to two diodes 17 to generate an upper rectified driving signal 43a and a lower rectified driving signal 43b The diodes 17 are mounted with opposite directionality, such that the upper rectified driving signal 43a and the lower rectified driving signal 43b respectively comprise currents flowing in opposite directions.

[0158] The current of the centre driving signal 41 leaves the centre voice coil section 21 through output channel 45, and the current of the upper and lower rectified driving signals 43a-43b leaves the upper and lower voice coil sections 22a-22b through output channels 44a-44b, which are electrically connected to provide a single auxiliary current output 48.

[0159] The embodiments shown in figs. 6a-6c utilize diodes 17 as rectification units 16, but the illustrated configurations are not limited to using diodes 17. Furthermore, the shown embodiments are only selected examples of providing rectified driving signals through passive rectifications, and the invention is not restricted to these

examples only.

[0160] Fig. 7a shows an alternative embodiment of the invention with a voice coil 1 comprising five distinct voice coil sections, i.e. a second upper voice coil section 24a, a first upper voice coil section 23a, a centre voice coil section 21, a first lower voice coil section 23b, and a second lower voice coil section 24b. The upper and lower voice coil sections 23a-24b may be connected to rectifying units 16 similarly as described in the above embodiments with relation to a voice coil 1 comprising an upper voice coil section 22a and a lower voice coil section 22b. In other words, a voice coil 1 comprising five distinct voice coil sections may comprise e.g. four rectifying units 16.

In this embodiment four rectifying units 16, such as diodes 17, are used, however in other embodiments of the invention, fewer rectifying units 16 may be used for a voice coil 1 comprising five distinct voice coil sections. As an example, one or more rectifying circuits, e.g. two rectifying circuits, may be used to provide rectified driving signals to the voice coil section [016]] As such, when one or more driving signals are provided to the voice coil 1, a first direction of current may only be provided to the first lower voice coil section 23b and the second lower voice coil section 24b, and a second direction of current may only be provided to the first upper voice coil section 23b and the second upper voice coil section 24b.

[0162] Any rectifying units 16 providing rectified driving signals to upper and lower voice coil sections 23a-24b may have different current and/or voltage thresholds. Such a threshold ensures that current is not provided to voice coil sections when it is not required. As such, when the voice coil sections 24a-24b are not required to generate an electromotive force to aid in the movement of the voice coil 1, rectification units 16 connected to the outer voice coil sections 24a-24b may attenuate or block any current. Furthermore, when the voice coil sections 23a-23b are not required to generate an electromotive force to reproduce an applied audio signal, rectifying units 16 connected to the voice coil sections 23a-23b may attenuate or block any current.

Preferably, any current and/or voltage thresholds are chosen such that the audio signal can be reproduced without distortion within the limitations of the full voice coil 1, while minimal current is supplied to voice coil sections which are not substantially within the air gap and are therefore not able to generate an electromotive force.

[0163] Fig. 7b shows another alternative embodiment of the invention, where the height of individual voice coil sections of the voice coil 1 is smaller than the air gap 3 along the direction of the travelling axis 4 [0164] In preferred embodiments, either the upper voice coil section 22a or the lower voice coil section 22b is able to generate an electromotive force to translate the voice coil 1 for very large excursions when the centre voice coil section 21 is substantially outside the air gap, i.e. when the centre voice coil section 21 leaves the air gap, another voice coil section 22a-22b enters. In such embodiments, an audio signal 30 may be reproduced by the excursion without distortion, even though the centre voice coil section 21 leaves the air gap 3.

[0165] Fig. 8 illustrates a method of generating an upper rectified driving signal 43a and a lower rectified driving signal 43b, on the basis of an auxiliary driving signal 42.

[0166] Four panels P 1 -P4 display representations of the driving signals at different stages. These representations describe the amplitude of the driving signals as a function of time. The zero point shown on the four panels PI-P4 illustrates points in time in a driving signal where no current flows in a respective voice coil section.

[0167] In the exemplary embodiment shown in fig. 8, a centre driving signal 41 is provided to a centre voice coil section 21, with a representation of the centre driving signal shown in panel Pl. Additionally, an auxiliary driving signal 42 is provided, with a representation of the auxiliary driving signal 42 shown in panel P2. In this embodiment the representations of the centre driving signal in panel P1 and the auxiliary driving signal in panel P2 are displayed to have similar amplitudes. In various other embodiments, the actual current and/or voltage of the centre driving signal and of the auxiliary driving signal may not be the same, i.e. the signals may differ in amplitude/gain.

[0168] The auxiliary driving signal 42 is provided to rectification units 16 to generate an upper rectified driving signal 43a, and a lower rectified driving signal 43b Thus, as the auxiliary driving signal 42 is provided, a first direction of current may only be provided to the lower voice coil section 22b and a first direction of current may only be provided to the upper voice coil section 22a. This is illustrated in panel P3 which show a representation of the upper rectified driving signal 43a and in panel P4 which show a representation of the lower rectified driving signal 43b. Tn panel P3, negative parts of the signal are absent, whereas in panel P4, positive parts of the signal are absent. This depicts a preferred embodiment of the invention, where no substantial current of the auxiliary driving signal is provided to either the upper voice coil section 22a or the lower voice coil section 22b, depending on the direction of the current.

[0169] List of reference signs: 1 Voice coil 2 Magnetic circuit 3 Air gap 4 Travelling axis Upward direction 6 Downward direction IS 7 Diaphragm 12 Amplifier 13 Power supply unit 16 Rectifying unit 17 Diode 21 Centre voice coil section 22a Upper voice coil section 22b Lower voice coil section 23a First upper voice coil section 23b First lower voice coil section 24a Second upper voice coil section 24b Second lower voice coil section Audio signal Driving signal 41 Centre driving signal 42 Auxiliary driving signal 43a Upper rectified driving signal 43b Lower rectified driving signal 44a Upper rectified driving signal out 44b Lower rectified driving signal out 45 Centre driving signal out 46 Driving signal in 47 Driving signal out 48 Auxiliary driving signal out Loudspeaker 51 Voice coil driving system 52 Interface PI Panel showing representation of centre driving signal P2 Panel showing representation of auxiliary driving signal P3 Panel showing representation of upper rectified driving signal P4 Panel showing representation of lower rectified driving signal

Claims

Claims 1. A method for driving a voice coil of a loudspeaker comprising the steps of providing a magnetic circuit having an air gap and a voice coil suspended in said air gap; applying an audio signal to said voice coil suspended in said air gap to produce an electromotive force moving said voice coil along a travelling axis; wherein said voice coil comprises a plurality of voice coil sections, arranged along said travelling axis, said plurality of voice coil sections comprising a centre voice coil section, an upper voice coil section and a lower voice coil section, said upper voice coil section and said lower voice coil section arranged respectively on either side of said centre voice coil section along said travelling axis, when the travelling axis is viewed in a vertical direction; wherein said step of applying an audio signal comprises providing current in the form of a centre driving signal based on said audio signal to said centre voice coil section and providing current in the form of an auxiliary driving signal based on said audio signal to said upper voice coil section and said lower voice coil section; wherein providing the auxiliary driving signal comprises providing an upper rectified driving signal to said upper voice coil section and providing a lower rectified driving signal to said lower voice coil section; wherein said upper rectified driving signal is provided by attenuating and/or blocking a first direction of current of said auxiliary driving signal by passive rectification; wherein said lower rectified driving signal is provided by attenuating and/or blocking a second direction of current of said auxiliary driving signal by passive rectification; and wherein said first direction of current and said second direction of current of said auxiliary driving signal are opposite directions of current 2. The method for driving a voice coil according to claim 1, wherein said upper rectified driving signal is provided by rectifying said auxiliary driving signal in said first direction of current and wherein said lower rectified driving signal is provided by rectifying said auxiliary driving signal in said second direction of current.3. The method for driving a voice coil according to claim 1 or 2, wherein said rectification of said auxiliary driving signal is half-wave rectification 4. The method for driving a voice coil according to any one of the preceding claims, wherein providing said upper rectified driving signal comprises processing said auxiliary driving signal using an upper rectifying unit, and providing said lower rectified driving signal comprises processing said auxiliary driving signal using a lower rectifying unit.5. The method for driving a voice coil according to claim 4, wherein said upper rectifying unit comprises a passive rectifying circuit, and/or wherein said lower rectifying unit comprises a passive rectifying circuit.6. The method for driving a voice coil according to claim 4 or 5, wherein each of said upper rectifying unit and said lower rectifying unit comprises a half-wave rectifier circuit.7. The method for driving a voice coil according to any one of claims 4 to 6, wherein neither one of said upper rectifying unit and said lower rectifying unit comprises a full-wave rectifier circuit or a full-wave bridge rectifier.8. The method for driving a voice coil according to any one of claims 4 to 7, wherein said upper rectifying unit comprises a diode and wherein said lower rectifying unit comprises a diode 9. The method for driving a voice coil according to claim 8, wherein said diodes are coupled with means for compensating a forward voltage drop. AnThe method for driving a voice coil according to any one of the preceding claims, wherein said centre driving signal and said auxiliary driving signal are provided by one or more amplifiers 11. The method for driving a voice coil according to claim 10, wherein said one or more amplifiers is a common amplifier.12. The method for driving a voice coil according to any one of the preceding claims, wherein providing an upper rectified driving signal comprises amplifying said auxiliary driving signal and wherein providing a lower rectified driving signal comprises amplifying said auxiliary driving signal.13 The method for driving a voice coil according to any one of the preceding claims, wherein said auxiliary driving signal has an amplitude different from said centre driving signal.14. The method for driving a voice coil according to any one of the preceding claims, wherein said auxiliary driving signal has the same amplitude as said centre driving signal.15. The method for driving a voice coil according any one of the preceding claims, wherein said upper voice coil section is a first upper voice coil section, said lower voice coil section is a first lower voice coil section, said upper rectified driving signal is a first upper rectified driving signal, said lower rectified driving signal is a second lower rectified driving signal and said auxiliary driving signal is a first auxiliary driving signal; wherein said plurality of voice coil sections arranged along said travelling axis further comprises a second upper voice coil section and a second lower voice coil section, said second upper voice coil section and said second lower voice coil section being arranged respectively on either side of the group of voice coil sections comprising said first upper voice coil section, said centre voice coil section, and said first lower voice coil section along said travelling axis, wherein said step of applying an audio signal further comprises providing current in the form of a second auxiliary driving signal based on said audio signal to said second upper voice coil section and said second lower voice coil section; wherein providing the second auxiliary driving signal comprises providing a second upper rectified driving signal to said second upper voice coil section and providing a second lower rectified driving signal to said second lower voice coil section; wherein said second upper rectified driving signal is provided by attenuating and/or blocking a first direction of current of said second auxiliary driving signal by passive rectification; and wherein said second lower rectified driving signal is provided by attenuating and/or blocking a second direction of current of said second auxiliary driving signal by passive rectification.16. The method for driving a voice coil according to any one of the preceding claims, wherein said upper voice coil section is displaced with respect to the centre voice coil section along a first displacement direction along said travelling axis, said lower voice coil section is displaced with respect to the centre voice coil section along a second displacement direction along said travelling axis, and said upper voice coil section and said lower voice coil section are arranged symmetrically around said centre voice coil section, wherein said first displacement direction and said second displacement direction are opposite directions along said travelling axis.17. The method for driving a voice coil according to any one of the preceding claims, wherein the height of said voice coil sections are individually either smaller than, greater than and/or of the same height as the height of said air gap along said travelling axis.18. A voice coil driving system of a loudspeaker comprising: a magnetic circuit having an air gap; a voice coil suspended in said air gap, said voice coil comprising a plurality of voice coil sections, arranged along said travelling axis, said plurality of voice coil sections comprising a centre voice coil section, an upper voice coil section and a lower voice coil section, said upper voice coil section and said lower voice coil section being arranged respectively on either side of said centre voice coil section along said travelling axis, when the travelling axis is viewed in a vertical direction; one or more passive rectifying units arranged to provide current in the form of an upper rectified driving signal to said upper voice coil section and current in the form of a lower rectified driving signal to said lower voice coil section.19. The voice coil driving system according to claim 18, wherein said one or more passive rectifying units comprise one or more rectifying circuits.20. The voice coil driving system according to claim 19, wherein said one or more passive rectifying units comprise one or more diodes 21. The voice coil driving system according to any one of claims 18 to 20, wherein said voice coil driving system is arranged to receive an audio signal and to provide current in the form of a centre driving signal based on said audio signal to said centre voice coil section, and to provide current in the form of an auxiliary driving signal based on said audio signal to said one or more passive rectifying units.22. The voice coil driving system according to any one of claims 18 to 21, wherein said voice coil driving system comprises two passive rectifying units, said two passive rectifying units being arranged to provide respectively said upper rectified driving signal and said lower rectified driving signal based on said auxiliary driving signal.23. The voice coil driving system according to claim 22, wherein one of said passive rectifying units is an upper rectifying unit which is arranged to process said auxiliary driving signal by attenuating and/or blocking a first direction of current of said auxiliary driving signal to provide said upper rectified driving signal; wherein one of said passive rectifying units is a lower rectifying unit which is arranged to process said auxiliary driving signal by attenuating and/or blocking a second direction of current of said auxiliary driving signal to provide said lower rectified driving signal; and wherein said first direction of current and said second direction of current of said auxiliary driving signal are opposite directions of current.24. A loudspeaker comprising a diaphragm; an interface configured to receive an audio signal; and a voice coil driving system according to any one of claims 18 to 23 25. The loudspeaker according to claim 24, wherein said loudspeaker comprises one or more amplifiers