WO2020070467A1

WO2020070467A1 - A planar magnetic driver

Info

Publication number: WO2020070467A1
Application number: PCT/GB2019/052556
Authority: WO
Inventors: Kyle HUTCHISON
Original assignee: Rha Technologies Ltd
Priority date: 2018-10-03
Filing date: 2019-09-12
Publication date: 2020-04-09
Also published as: GB2577713A

Abstract

The invention relates to a driver, or a planar magnetic driver, for headphones, particularly in-ear headphones. The driver includes a voice coil, a diaphragm and a first and second magnet. The diaphragm is disposed on a first side of the voice coil and is attached to the voice coil. The first and second magnets are disposed on a second side of the voice coil. The first and second magnets arranged such that a magnetic field is created in which the voice coil can interact with.

Description

A PLANAR MAGNETIC DRIVER

The invention relates generally to a planar magnetic driver, specifically an improved construction of a planar magnetic driver for use with headphones and, more particularly, in-ear headphones. The invention also relates to wired or wireless headphones, specifically in-ear headphones, comprising the improved planar magnetic driver as described.

INTRODUCTION

A number of drivers are known in the art for converting an electrical signal, received from an electronic device, into a sound wave.

In particular, a conventional driver for use in headphones includes a magnet, a voice coil and a cone-like diaphragm. The magnet is a permanent magnet, and the voice coil typically comprises a conductive wire wrapped around the permanent magnet. Thus, the voice coil acts as an electromagnet to cause a vibrating motion of the diaphragm, which is directly connected to the voice coil.

When alternate current, from the connected electronic device, is passed through the voice coil, the voice coil acts towards and away from the permanent magnet as the current is alternated. Since the voice coil is attached to the diaphragm, the movement of the diaphragm creates sound waves that can be heard by the user when the headphones are worn over, or in, their ears.

The construction of the driver largely depends on the size of the headphone for which it is to be used. For example, over-the-head headphones typically use larger drivers, whilst in-ear headphones tend to use smaller drivers. A variety of drivers are known in the art for each type of headphone.

Dynamic drivers are conventionally used in in-ear headphones owing to their smaller size, thus allowing for miniaturisation of in-ear headphone technology. A dynamic driver typically includes a single permanent magnet having a voice coil wrapped around it. A diaphragm is attached to the voice coil for movement therewith when the voice coil moves. The voice coil acts as an electromagnet and is connected, by wires, to a power source, for instance an electronic device. When current is supplied through the wire and to the voice coil, the voice coil is magnetised, thus causing an attraction, or repulsion, to the permanent magnet. When the current is alternated, the magnetism of the voice coil is reversed, i.e. causing repulsion or attraction to the permanent magnet. This alternation of magnetism, and thus attraction and repulsion to the permanent magnet, causes the diaphragm to move, or vibrate, thereby creating sound waves. Depending on the electric signal input into the voice coil, the diaphragm vibrates appropriately to provide what the user perceives as sound, for example, a song.

Dynamic drivers are effective and are fairly inexpensive to manufacture and implement. However, there are problems with dynamic drivers in the art. For example, although the technology is small enough to be included in an in-ear headphone, such drivers suffer from non-linear distortion. Non-linear distortion is the known phenomenon where poorer audio quality is experienced by the user at higher volumes. Therefore, it has been an objective for manufacturers to improve the sound quality of in-ear headphones, either through various implementations of dynamic drivers, or by using a different type of driver.

Planar magnetic drivers are also known in the art, but only for use in over-the-head headphones, owing to their increased size and weight. Such drivers make use of two magnets with a diaphragm sandwiched therebetween. The diaphragm includes a circuit distributed across its entire breadth, through which current is applied in use. When current is applied, the magnetic field is forced to change, thus causing the diaphragm to vibrate and produce sound waves.

Such constructions provide excellent audio quality and low-distortion sound even at high volumes, in addition to excellent bass response. This is largely owing to the diaphragm that can be vibrated across its entire breadth. However, for such a construction to be implemented, a magnet is required on either side of the diaphragm. That is to say, the diaphragm is required to be sandwiched between two permanent magnets. The use of two magnets in this way increases the size and weight of such drivers, thus planar magnetic drivers have only been implemented in such a construction in over-the-head headphones and speakers. Therefore, there is a need to mitigate and obviate the problems known with the drivers in the art. Specifically, there is a need for a construction of a planar magnetic driver that has a reduced weight and size. Moreover, there is a need for a construction of a planar magnetic driver that can be implemented into an in-ear headphone.

SUMMARY OF INVENTION

In a first aspect, there is provided a planar magnetic driver for a headphone, comprising: a voice coil including a first side and a second side; a diaphragm disposed on the first side of the voice coil and attached thereto; a first magnet and a second magnet disposed on the second side of the voice coil, wherein the first and second magnets are arranged such that a magnetic field is created, and wherein the voice coil is configured to interact with the magnetic field.

In other words, the driver includes first and second magnets on one side of the voice coil, and a diaphragm on the other side of the voice coil. That is, the voice coil separates the diaphragm from the magnets, and is disposed therebetween.

The first and second magnets are arranged such that they interact to provide a magnetic field. That is to say, the first and second magnets are configured in construction and location to provide a permanent magnetic field. The permanent magnetic field may be a result of constructive interference, or otherwise a constructive cooperation, between the first and second magnets.

The voice coil is also configured such that it can interact with the created permanent magnetic field. That is, the voice coil is constructed and located such that is can interact with the permanent magnetic field. For example, the voice coil can interact with the permanent magnetic field when electrical current is supplied to the voice coil. Thus, the magnetic field may be aligned such that the voice coil is able to interact with the permanent magnetic field when electrical current is supplied thereto. That is, the permanent magnetic field is provided such that the voice coil is able to interact therewith upon application of electrical current. The permanent magnetic field may be confined to a particular location, for example a particular plane or zone, by virtue of the first and second magnets’ construction and location.

This provides the advantage that the size, and thus the weight, of a driver can be reduced whilst addressing problems with non-linear distortion. Such a driver can be regarded as a planar magnetic driver, but the construction of which allows the driver to be utilised in smaller sized headphones.

In some aspects, the first magnet may partly, substantially or entirely surround the second magnet. That is to say, the second magnet may be partly, substantially or entirely surrounded by the first magnet. For example, the first magnet may be substantially U-shaped or horseshoe shaped, and surrounds the second magnet, which is disposed within the enclosed space therein. In other embodiments, the first magnet may be an annulus and the second magnet, which may be a disk, disposed within the hole or aperture of the annulus, thus the second magnet is entirely surrounded by the first magnet. In other embodiments, the first magnet may comprise one or more arcuate portions of such an annulus with the second magnet, which may be a disk, disposed within the hole or aperture of the annulus defined by those one or more arcuate portions.

In some aspects, the first magnet and second magnet may be planar structures. The first and second magnets may be planar structures with the same thickness. The first and second magnet may be within, or occupy, the same plane.

Preferably, the first magnet of the driver may be an annulus; and the second magnet may be disposed within the aperture of the annulus. For example the second magnet may be a disk concentric with the first magnet and disposed within the aperture of the annulus of the first magnet.

That is to say, the first magnet may be annular in shape, defining an aperture therein, and the second magnet may be disposed within the aperture of the first magnet. The first and second magnets may also be concentric, that is to say that they share a common central axis. Thus, the first magnet may be an annulus and the second magnet may be a disk, wherein the second magnet, which is a disk, is disposed within the hole of the first magnet, which is an annulus.

In some aspects, the second magnet is disposed substantially within the first magnet. In some aspects, the first magnet may be an annulus having a radius n , measured from a central point of the aperture of the annulus to the outermost edge of the annulus, and a second radius r₂, measured from a central point of the aperture of the annulus to the innermost edge of the annulus. The second magnet may be a disk having a radius r₃. The second magnet may be disposed within the annular first magnet.

In some aspects, the width of the annulus, defined by w = n - r₂, may be substantially the same as, or identical to, the radius of the second magnet, r₃. In some aspects, the radius r₂ of the first magnet may be greater than the radius r₃ of the first magnet, thus defining a gap, or space, between the first and second magnets. This gap, or the difference r₂ - r₃, may be of any appropriate size, for example, between 0.1mm and 0.9mm, preferably between 0.3mm and 0.7mm or between 0.5mm and 0.7mm, and most preferably approximately 0.65mm.

This provides the advantage that the driver is decreased in size and weight, since the magnets are disposed within each other, thereby eliminating the need for excess space for the second magnet. Thus, the driver, and the associated headphones therewith, are cheaper and easier to manufacture.

More preferably, the first magnet is of a first polarity and the second magnet is of a second polarity that is opposite to the first polarity.

That is, the polarity of the first magnet may be the opposite polarity to that of the second magnet.

The arrangement of the first and second magnets, owing to their opposing polarities, provides an appropriate magnetic field. The voice coil may interact with the magnetic field created by the opposing polarities of the first and second magnets. This provides the advantage that the control of the voice coil, when electrical current is supplied therethrough, is improved such that non-linear distortion is significantly reduced. The arrangement of the magnetic field allows the driver to provide higher quality audio, whilst reducing the size and weight of the driver.

In some aspects, the first and second magnets may be permanent magnets. The first and second magnets may comprise ferromagnetic material, and the first and second magnets are, preferably, rare earth magnets.

Most preferably, the first and second magnets may each be neodymium magnets. That is to say, the first magnet may be a neodymium magnet and the second magnet may also be a neodymium magnet.

This provides the advantage that conventional magnets may be utilised within the driver, thus saving on costs for manufacturing the driver.

In some aspects, the first and second magnets may be of equal magnetic field strength. That is to say, the first magnet may have a magnetic field strength that is substantially or exactly equal to the strength of the second magnet.

This provides the advantage that the first and second magnets cooperate constructively to provide the appropriate magnetic field for the voice coil to interact with.

In some aspects, the voice coil may be planar.

That is to say, the voice coil may be substantially, or entirely, flat. In this aspect, the voice coil is planar such that it does not wrap around, or otherwise surround the sides of, either of the magnets. Instead, the voice coil sits on top of, or is disposed on top of or above, the magnets for interaction therewith.

The provides the advantage that the size of the driver can be reduced, and thus the driver can be used in smaller headphone assemblies. In some aspects, the voice coil may comprise copper. That is to say, the voice coil may be constructed from copper, more specifically copper wire.

In some aspects, the voice coil may be helical. That is to say, the voice coil may have a centrum that spirals radially outwardly towards a circumference.

In some aspects, the diaphragm may have a thickness of between 10 - 40 microns, preferably between 10 - 20 microns, most preferably about 16 microns. That is, the diaphragm may have a thickness of between 10 - 40 x 10⁶ m, preferably between 10 - 20 x 10⁶ m, most preferably about 16 x 10⁶ m.

This provides the advantage that the diaphragm has flexibility imparted thereto, and that the weight of the diaphragm, and thus the overall driver, is reduced. This, in turn, allows the diaphragm to move more easily in response to the movement of the voice coil within the created magnetic field.

In some aspects, the diaphragm may comprise polyethylene. That is to say, the diaphragm may be constructed from polyethylene.

In some aspects, the driver may be substantially cylindrical. Further, the driver may have a diameter between 10mm - 30mm. Most preferably, the driver may have a diameter of approximately 10mm. In some aspects, the diameter may be 10mm.

The thickness of the driver may be approximately 0.1 mm - 10mm. More preferably, the thickness may be approximately 3 - 6mm, and most preferably the thickness may be approximately 4mm.

This provides the advantage that the driver, when used as part of a headphone, particularly an in-ear headphone, does not protrude out of the ear. Instead, the driver can fit comfortably within the user’s ear owing to the driver’s construction. In this way, the user experiences a more comfortable headphone that is truly“in-ear”, rather than protruding outwardly from the user’s ear. In-ear headphones that protrude outwardly from the ear are unsightly, prone to being knocked out of the user’s ear, and are generally uncomfortable. Preferably, the driver may further comprise: a face plate disposed over the diaphragm, and a casing enclosing the diaphragm, voice coil, and the first and second magnets.

That is to say, the driver may also include a face plate and a casing, wherein the diaphragm, voice coil and magnets are enclosed therein. The face plate and casing define a space in which the diaphragm, voice coil and magnets are located and held in place.

This provides the advantage that the enclosed contents of the driver are inaccessible and thus the user cannot damage the assembly. In particular, the face plate prevents damage to the sensitive voice coil and diaphragm.

In another aspect, the driver may be for use in an in-ear headphone.

In yet another aspect, there is provided a headphone comprising the driver as described herein.

That is to say, the driver may be included as part of a headphone, or set of headphones. Such headphones may be over-the-head headphones or earphones. The headphones may be wired, where the headphones are connected directly to an electronic device, or wireless, where the electronic device communicates wirelessly to the headphones.

In yet another aspect, there is provided an in-ear headphone comprising the driver as described herein.

That is to say, the driver may be included as part of an in-ear headphone, or set of in-ear headphones. Such in-ear headphones insert within the user’s ear and are held in place by the user’s ear.

In some aspects, the in-ear headphone includes a driver which may have a diameter of 10mm - 30mm, most preferably approximately 10mm. In this way, the in-ear headphones are truly in-ear in the sense that they can fit snuggly within the user’s ears. That is, that they protrude minimally, or not at all, from the user’s ears in use. The thickness of the driver for the in-ear headphone may be approximately 0.1mm - 10mm. More preferably, the thickness may be approximately 3 - 6mm, and most preferably the thickness may be approximately 4mm.

The in-ear headphones may be wired, where the in-ear headphones are connected directly to an electronic device, or wireless, where the electronic device communicates wirelessly to the headphones.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings illustrate presently exemplary embodiments of the disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain, by way of example only, the principles of the disclosure. In the accompanying drawings:

Figure 1 shows an exploded view of a planar magnetic driver in accordance with the invention;

Figure 2 shows a cross-sectional side view of the planar magnetic driver of Figure 1 ; and

Figure 3 shows the cross-sectional side view of Figure 2 with the permanent magnetic field shown.

DETAILED DESCRIPTION

Referring to Figure 1 , there is shown a planar magnetic driver 10 in accordance with an embodiment of the invention. The planar magnetic driver 10 includes a first magnet 12 and a second magnet 14, the first and second magnets 12, 14 being concentric with one another with respect to a central axis (not shown). The first magnet 12 is annular in shape, or in other words is an annulus, defining an aperture therein, in which the second magnet 14 is received. Thus, the first magnet 12 is an annulus and the second magnet 14 is a disk which is disposed within the hole of the annular second magnet 14. The first magnet 12 is of a first polarity, and the second magnet 14 is of a second polarity that is opposite to the first polarity. Together, the first magnet 12 and the second magnet 14 provide a planar magnetic array and interact constructively to define the permanent magnetic field (see Figure 3) in which the below described voice coil 16 interacts. As can be seen in Figures 1 and 3, this arrangement of concentric magnets 12, 14, particularly disposing them on a single side of the voice coil 16 and diaphragm 18 (as described below), reduces the overall size of the planar magnetic driver 10.

With further reference to Figure 1 , the planar magnetic driver 10 includes a voice coil 16 attached to a diaphragm 18. The voice coil 16 is shown as a completely flat, or planar, voice coil 16 that is constructed from coiled copper wire. The copper wire is coiled in a helix in the depicted embodiment. The diaphragm 18 is constructed from polyethylene and has a thickness of approximately 16 microns. The voice coil 16 can be attached to the diaphragm 18 in any known way.

The planar magnetic driver 10 also includes a faceplate 20 and a housing, or enclosure, 22. The faceplate 20 and housing 22 are constructed from steel. The faceplate 20 is disposed over the diaphragm 18 to prevent damage thereto. The faceplate 20 and housing 22 may, together, define a space in which the magnets 12, 14, voice coil 16 and diaphragm 18 are enclosed. The faceplate 20 and housing 22 are clipped together, thereby preventing the user from accessing the magnets 12, 14, the voice coil 16 and the diaphragm 18 during normal use.

Wth reference to Figures 1 and 3, in use, the first and second magnets 12, 14 provide a defined permanent magnetic field, as indicated by the arrows 24, 26 in Figure 3. As can be seen in Figure 3, the first magnet 12 has a polarity that is opposite to that of the second magnet 14. In this way, the first and second magnets 12, 14 interact and cooperate to provide two separate opposing magnetic fields 24, 26. The two opposing magnetic fields 24, 26 provide a magnetic plane, i.e. a zone in which the opposing magnetic fields 24, 26 are confined to, in which the voice coil 16 is located. As shown in Figure 3, the voice coil 16 intersects each of the magnetic fields 24, 26. When electrical current is passed through the voice coil 16, the voice coil 16 becomes an electromagnet and interacts with the permanent magnetic fields 24, 26 to cause vibration of the diaphragm 18, as discussed below. The voice coil 16 is disposed over the first and second magnets 12, 14 and is located on the underside, i.e. the innermost side, of the diaphragm 18. The voice coil 16 is electrically connected to a wire (not shown) for receiving electrical signals from an electronic device (also not shown). When the voice coil 16 receives electrical current from the electronic device, the voice coil 16 becomes magnetised, or in other words acts as an electromagnet. The voice coil 16 can act with or against the permanent magnetic fields 24, 26 such that it moves towards or away from the first and second magnets 12, 14. When the electrical current is alternated, the voice coil 16 acts in the opposite direction, i.e. against or with the permanent magnetic field, such that it moves away or towards the first and second magnets 12, 14.

Given that the diaphragm 18 is connected to the voice coil 16, the movement of the voice coil 16 towards or away from the first and second magnets 12, 14 allows for the diaphragm 18 move therewith, thereby creating sound waves. Dependent upon the electrical signal received by the voice coil 16, the diaphragm 18 will vibrate to a defined extent to provide a defined sound that is communicated from the electrical device to the planar magnetic driver.

The described planar magnetic driver 10 can be used with wired or wireless headphones, in particular in-ear headphones. When included with wired headphones, the electrical signal is provided directly, via a wire, to the voice coil 16.

When the planar magnetic driver 10 is used within wireless headphones, the planar magnetic driver 10 is electrically connected to a wireless power device, for example a Bluetooth® neckband. Such a wireless power device comprises a battery, to provide electrical current to the voice coil 16, and a wireless communications module, for example Bluetooth® capability, to wirelessly communicate with a separate electronic device, such as a mobile phone. The electronic device communicates a wireless signal to the wireless communications module, which then communicates an electrical signal to the voice coil 16 to provide the appropriate audio output.

It will be appreciated for persons skilled in the art that the above embodiment has been described by way of example only and not in any limiting sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS What is claimed is:

1. A planar magnetic driver for a headphone, comprising:

A voice coil including a first side and a second side;

A diaphragm disposed on the first side of the voice coil and attached thereto;

A first magnet and a second magnet disposed on the second side of the voice coil, wherein the first and second magnets are arranged such that a magnetic field is created, and wherein the voice coil is configured to interact with the magnetic field.

2. A driver according to claim 1 , wherein the first magnet disposed at least partly around the second magnet.

3. A driver according to claim 2, wherein the first magnet defines an annulus; and wherein the second magnet is disposed within the aperture of the annulus.

4. A driver according to claim 3, wherein the first magnet is an annulus and the second magnet is a disk and is disposed concentrically with the annulus within the aperture of the annulus.

5. A driver according to any preceding claim, wherein the first magnet is a first polarity and the second magnet is of a second polarity that is opposite to the first polarity.

6. A driver according to any preceding claim, wherein the first and second magnets are each neodymium magnets.

7. A driver according to any preceding claim, wherein the first and second magnets are of equal magnetic field strength.

8. A driver according to any preceding claim, wherein the voice coil is planar.

9. A driver according to any preceding claim, wherein the voice coil comprises copper.

10. A driver according to any preceding claim, wherein the voice coil is helical.

11. A driver according to any preceding claim, wherein the diaphragm has a thickness is 16 microns.

12. A driver according to any preceding claim, wherein the diaphragm comprises polyethylene.

13. A driver according to any preceding claim, wherein the driver is substantially cylindrical and has a diameter of approximately 10mm.

14. A driver according to any preceding claim, further comprising:

A face plate disposed over the diaphragm, and

A casing enclosing the diaphragm, voice coil, and the first and second magnets.

15. A driver according to any preceding claim, for use in an in-ear headphone.

16. A headphone comprising the driver according to any preceding claim.

17. An in-ear headphone comprising the driver according to any preceding claim.