GB2461929A

GB2461929A - Earphones with compound drive units and level control

Info

Publication number: GB2461929A
Application number: GB0815691A
Authority: GB
Inventors: James Strong; Stefan Andren; K K Ko
Original assignee: STRONG PACIFIC
Current assignee: STRONG PACIFIC
Priority date: 2008-07-17
Filing date: 2008-08-28
Publication date: 2010-01-20
Also published as: WO2010007440A2; GB0813115D0; WO2010007440A3; GB0815691D0

Abstract

An earphone uses a compound or dual drive unit 40 comprising a first driver 42 and a second driver 44. The two drivers share a common magnetic system 48 and are coaxial with each other. A plurality of vents 126 allow sound from region 124 behind the diaphragm 58 to pass into the mixing region 128 and ultimately into the listener's ears. Variable resistors (figs 10a, 10b) are used to control the relative levels of audio signals passed to the drivers.

Description

EARPHONE

The present invention relates to earphones for use with audio devices such as MP3 players, mobile phones and the like, and in particular to an improved speaker driver for use in such earphones, and to an earphone incorporating the improved speaker driver.

Earphones are worn in close proximity to the ears and are used to convert electrical signals from an audio device into audible sound waves. Earphone devices may include a pair of earphones, one for each ear, or a single earphone, for example in the case of a hands-free accessory for a mobile phone.

Traditionally, earphones for portable devices have employed dynamic' speaker drivers, also known as moving coil' drivers. A cross-section through a conventional dynamic driver 10 is shown schematically in Figure 1. Referring to Figure 1, the dynamic driver 10 includes a driver housing 12 supporting a diaphragm 14. The diaphragm 14 has a dome-shaped central radiator 16, and is surrounded by a suspension ring 18 of convex cross-section. The diaphragm 14 is fixed to the driver housing 12 about a circular outer periphery 20 of the suspension ring 18. A voice coil 22 is attached to the diaphragm 14 at a circular boundary 24 between the radiator 16 and the suspension ring 18, on a concave-curved side 26 of the diaphragm 14. A circular permanent magnet 28 is fixed within the driver housing 12, on the same side of the diaphragm 14 as the voice coil 22.

The magnet 28 extends into a region 30 bounded by the voice coil 22 and the radiator 16. To protect the diaphragm 14, a metal grill 32 is secured to the driver housing 12 on a convex-curved side 34 of the diaphragm 14.

When an alternating current signal, corresponding to an audio signal, is passed through the voice coil 22, an alternating magnetic field is generated around the voice coil 22. The alternating magnetic field interacts with the magnetic field of the permanent magnet 28 to cause the voice coil 22, and hence the attached diaphragm 14, to move back and forth relative to the permanent magnet 28. This back and forth motion moves the air surrounding the diaphragm 14, thereby generating sound waves.

The performance of a speaker driver, that is its ability to reproduce high quality sound over a wide frequency range, is limited by the physical properties of the material forming the diaphragm. To effectively reproduce low-frequency bass' sounds (approximately 20 Hz -400 Hz) the diaphragm should be soft to allow a wide range of movement.

Whereas, to effectively reproduce high-frequency treble' sounds (approximately 4 kHz to kHz), the diaphragm should be stiff, so that it can move relatively fast. For high-quality sound, the driver must also be capable of effectively reproducing mid-range sounds (approximately 400 Hz -4 kHz). At present, dynamic drivers that are suitable for use in earphones are not able to reproduce sound to a suitably high quality over the entile audible frequency range (approximately 20 Hz -20kHz).

Rapid advances in portable multi-media device technology have sparked a demand for increasingly sophisticated earphones capable of reproducing high quality sound over a wide frequency range. Consequently, high-end earphones have been developed which include two, or sometimes three, speaker drivers in each earphone. These earphones are referred to hereafter as multi-driver' earphones. In multi-driver earphones, each driver is optimised to reproduce sound over a different frequency range. For example, one driver is often dedicated to reproducing bass and lower-mid-range frequencies, whilst the other driver is often dedicated to reproducing treble and higher-mid-range frequencies. This arrangement enables suitably high quality sound to be achieved over a wider frequency range than has previously been possible with a single driver.

Existing multi-driver earphones generally employ balanced-armature' speaker drivers, in view of their ability to reproduce high quality sound, and their small size, which enables two or three drivers to fit within a suitably-small earphone housing. However, balanced-armature drivers are expensive and less robust than dynamic drivers. Consequently, existing multi-driver earphones are more expensive, and less robust, than traditional dynamic driver earphones.

It is desirable to be able to adjust the relative levels of bass, mid-range or treble when listening to music. To this end, many portable devices include a graphic equaliser, or a number of preset sound profiles that the user can select between. However, it is not always convenient to adjust the sound profile via the portable device: for example, in circumstances when the device is inaccessibly-placed within a bag or inside pocket, or if the user is required to navigate through complicated menu systems to access this functionality. Furthermore, the adjustments on the portable device may not complement the user's particular earphones, leading to sub-optimal sound quality.

The present invention aims to overcome some or all of the problems described above.

Summary of the invention

According to a first aspect of the present invention, there is provided a compound driver for an earphone, the compound driver comprising a first driver and a second driver, wherein the first and second drivers share a common magnetic system. The compound driver is conveniently compact because the first and second drivers share the magnetic system. Furthermore, fewer parts may be required as a result of the drivers sharing the magnetic system.

The first driver may include a first diaphragm having a first voice coil attached to an inner side. Similarly, the second driver may include a second diaphragm having a second voice coil attached to an inner side. The first and second diaphragms may be arranged such that their respective inner sides are facing, and the common magnetic system may be located therebetween. In this configuration, the first and second drivers are dynamic drivers, and hence the compound driver benefits from being robust and relatively inexpensive. It will be appreciated that the dynamic driver may contain more than two drivers.

The magnetic system may include a single magnet or a plurality of magnets. When multiple magnets are employed, the magnetic field is advantageously strengthened.

Preferably, the magnetic system includes an inner magnet and an outer magnet. The inner magnet may be substantially circular, and the outer magnet may be annular. The outer magnet may surround the inner magnet, which is a conveniently compact arrangement.

The inner and outer magnets may be spaced apart to define a groove therebetween.

The first voice coil may extend into the groove. The second voice coil may extend into a region surrounding the outer magnet. The first and second diaphragms may be substantially concentrically arranged. Arranging the diaphragms concentrically is an efficient use of space, and contributes to the compactness of the compound driver. This concentric arrangement can accommodate any number drivers, each having a diaphragm of increasing diameter.

In preferred embodiments of the invention, the first diaphragm is relatively small and the second diaphragm is relatively large. The relatively small first driver is configured to reproduce relatively low frequency sounds and the relatively large second driver is configured to reproduce relatively high frequency sounds. However, in other embodiments of the invention, a relatively small diaphragm could be used to reproduce relatively high frequency sounds, and a relatively large diaphragm could be used to reproduce relatively low frequency sounds. This could be achieved by suitable selection of the materials from which the diaphragms are made, and by suitable selection of the relative sizes of the radiator and suspension rings of the respective diaphragms.

Conveniently, the first and second diaphragms may be supported by a common driver housing. The common magnetic system may advantageously be located within the common driver housing to further increase the compactness of the driver. The first diaphragm may be supported at a first end of the common driver housing and the second driver may be supported at a second end of the common driver housing.

The first end of the common driver housing may be closed by a first cover spaced apart from an outer side of the first diaphragm. The first cover may include a plurality of apertures to allow sound waves to pass from the outer side of the first diaphragm towards a user's ear in use. The second end of the driver housing may be closed by a second cover spaced apart from an outer side of the second diaphragm. The second cover may have a substantially continuous surface to substantially prevent sound waves from the outer side of the second diaphragm escaping from the common driver housing.

This ensures that the driver appears relatively quiet to others. Nevertheless, the substantially continuous surface may be interrupted by an aperture to allow air to pass into and out of a region defined between the second diaphragm and the second cover, so that the second diaphragm is not having to move against a fixed volume of air.

The common driver housing may include at least one vent positioned to allow sound waves from the inner side of the second diaphragm to enter a mixing chamber in which those sound waves combine with sound waves from an outer side of the first diaphragm.

The common driver housing may include an annular base having a tubular skirt depending from a radially-inner periphery, in which the magnetic system may be located.

The or each vent may be provided in the annular base.

A duct may be provided that extends from a first volume defined at least in part by the inner side of the first diaphragm. The duct may be configured to allow air to flow into and out of the first volume whilst simultaneously isolating sound waves produced by the inner side of the first diaphragm from sound waves in a mixing chamber. The sound waves in the mixing chamber may be a combination of sound waves from an outer side of the first diaphragm and the inner side of the second diaphragm. The duct advantageously prevents mixing between the out of phase sound waves that are produced from respective opposite sides of the first diaphragm. Furthermore, the duct prevents the out of phase sound waves from the inner side of the first diaphragm from interfering with the combined sound waves in the mixing chamber. The duct may extend through the mixing chamber. In preferred embodiments, the duct is provided by a pipe received within an aperture in the skirt of the outer driver housing.

The compound driver may be arranged substantially to prevent air flow between the respective inner sides of the first and second diaphragms. This prevents the out of phase sound waves from the inner side of the first diaphragm from interfering with the sound waves from the inner side of the second diaphragm.

The inventive concept encompasses an earphone including a compound driver as described above. The earphone may comprise an earphone housing supporting the compound driver. The mixing chamber may be defined, at least in part, by the earphone housing. The duct may extend between the first volume and an aperture in the earphone housing. The inventive concept also encompasses a stereo earphone device comprising a pair of earphones, each as described above. The stereo earphone device may be a pair of earphones for a portable audio device such as an MP3 player.

According to a second aspect of the present invention, there is provided an earphone for connecting to an audio device, the earphone comprising: a compound driver having a first diaphragm and a second diaphragm, the first and second diaphragms being arranged such that an inner side of the first diaphragm faces towards an inner side of the second diaphragm, and further being arranged such that, in use, an outer side of the first diaphragm, and the inner side of the second diaphragm, each face towards a user's ear canal; a volume defined, at least in part, by the inner side of the first diaphragm, and in which sound waves from the inner side of the first diaphragm are generated; a mixing chamber in which sound waves from the outer side of the first diaphragm combine with sound waves from the inner side of the second diaphragm prior to entering the user's ear canal; and a duct configured to allow air to flow into and out of the volume whilst simultaneously isolating sound waves from the volume from the combined sound waves in the mixing chamber.

The duct prevents mixing between sound waves from the inner side of the first diaphragm and sound waves from the outer side of the first diaphragm. Since the sound waves from opposite sides of a diaphragm are out of phase, the duct prevents destructive interference from occurring between these sound waves, which would otherwise reduce the performance of the earphone. The duct further prevents the sound waves from the inner side of the first diaphragm from mixing with the sound waves in the mixing chamber. This increases the performance of the earphone because the sound waves from the inner side of the first diaphragm are out of phase with the combined sound waves within the mixing chamber. Generally speaking, the duct prevents mixing between out of phase sound waves.

The mixing chamber may be defined, at least in part, by an inner surface of the earphone housing. The duct may communicate with an aperture provided in the earphone housing. The duct may extend through the mixing chamber.

The first and second diaphragms may be supported by a common driver housing, thereby making the compound driver conveniently compact. To further reduce the size and number of parts of the compound driver, a common magnetic system may be disposed between the respective inner sides of the first and second diaphragms.

In preferred embodiments of the invention, the first diaphragm is configured to reproduce relatively low frequency sounds and the second diaphragm is configured to reproduce relatively high frequency sounds. The first diaphragm is relatively small whilst the second diaphragm is relatively large. However, as described above, it will be appreciated that through suitable selection of the diaphragm's properties, a relatively small diaphragm could be used to reproduce relatively high frequency sounds, whilst a relatively large diaphragm could be used to reproduce relatively low frequency sounds.

The compound driver may be arranged to substantially prevent air flow between the respective inner sides of the first and second diaphragms. This arrangement prevents out of phase sound waves from the inner sides of the respective diaphragms from mixing, and hence improves the performance of the earphone.

According to a third aspect of the present invention, there is provided an earphone having a first driver for reproducing relatively low frequency sounds from a first electrical signal, and a second driver for reproducing relatively high frequency sounds from a second electrical signal, wherein the earphone further includes control means for adjusting: (I) the level of the first electrical signal independently from the level of the second electrical signal, thereby to control the level of low frequency sounds reproduced by the first driver substantially independently from the level of high frequency sounds reproduced by the second driver; and/or (ii) the level of the second electrical signal independently from the level of the first electrical signal, thereby to control the level of high frequency sounds reproduced by the second driver substantially independently from the level of low frequency sounds reproduced by the first driver.

Conveniently, the sound output of the earphone can be adjusted on the earphone itself rather than through the audio player to which the earphone is attached.

To minimise the size of the earphone, the first and second drivers may share a common magnetic system. Furthermore, to this end the first and second drivers may be supported by a common driver housing.

The control means may be configured to allow the user to adjust the relative levels of the first and second electrical signals, thereby enabling the user to adjust the relative levels of the relatively low frequency and the relatively high frequency sounds produced by the earphone. To this end, the control means may include one or more control elements for allowing the user to select between two or more predetermined sound settings in which the relative levels of the first and second electrical signals are different. Alternatively, or additionally, the control means includes continuously-variable adjustment means for allowing the user to continuously adjust the relative levels of the relatively low frequency and the relatively high frequency sounds. The continuously-variable adjustment means may be provided by a knob, slider or other continuously adjustable control element.

The control means may be provided inline with a cable for connecting the earphone to the portable audio system. This allows the user conveniently to adjust the sound properties of the earphone, even when the portable device, to which the earphone is connected, is not easy to access. Alternatively, the control means may be provided on the earphone housing, or concealed within the earphone housing if it is not intended to be accessible by the end-user.

The control means may include a variable resistor associated with the first driver for adjusting the level of the first electrical signal, and/or a variable resistor associated with the second driver for adjusting the level of the second electrical signal. The or each variable resistor may be located within the earphone housing, or within an inline control means.

The inventive concept includes a stereo earphone device comprising two earphones as described above.

Accordingly, in a fourth aspect of the present invention, there is provided a stereo earphone device comprising two earphones, each having a first driver for reproducing relatively low frequency sounds from a first electrical signal, and a second driver for reproducing relatively high frequency sounds from a second electrical signal, wherein the earphone further includes common control means for adjusting: (i) the level of the first electrical signal independently from the level of the second electrical signal, thereby to control the level of low frequency sounds reproduced by the first driver substantially independently from the level of high frequency sounds reproduced by the second driver; andfor (ii) the level of the second electrical signal independently from the level of the first electrical signal, thereby to control the level of high frequency sounds reproduced by the second driver substantially independently from the level of low frequency sounds reproduced by the first driver.

In a fifth aspect of the present invention, there is provided a method of customising the sound output of an earphone, the earphone comprising a first driver for reproducing relatively low frequency sounds, and a second driver for reproducing relatively high frequency sounds, wherein the method includes adjusting the relative volume output of the first and second drivers, thereby to adjust the relative levels of the relatively low frequency and relatively high frequency sounds output by the earphone.

The method may include presetting the relative volume levels of the first and second drivers in accordance with an end-user's preferences. The method may also include providing control means for allowing the end user to adjust the relative volume levels of the first and second drivers. For example, the method may include providing control means for allowing the end user to select between two or more preset sound settings, and/or for allowing the end-user to continuously adjust the relative volume output of the first and second drivers.

It will be appreciated that optional and preferred features are interchangeable between the various variants and embodiments of the invention.

Brief description of the drawincis

Reference has already been made to Figure 1, which is a schematic cross-section through a conventional dynamic speaker driver. In order that the invention may be more readily understood, reference will now be made, by way of example only, to Figures 2 to 12, in which: Figure 2 is a schematic cross-section through a dual driver constructed in accordance with the invention; Figure 3a is a front view of an earphone constructed in accordance with the invention, in which a front part of an earphone housing is shown; Figure 3b is a side view of the earphone of Figure 3a, in which a rear part of the earphone housing has been removed to expose a dual driver constructed in accordance with the invention and similar to the dual driver shown in Figure 2; Figure 4 is a cross-sectional side view of the dual driver shown in Figure 3b, including a schematic representation of the earphone housing; Figures 5a, 5b and 5c are, respectively, side, front, and rear elevations of the dual driver of Figure 4; Figures 6a and 6b are, respectively, perspective and side views of the dual driver of Figures 4 and 5, in which a 14 mm driver and a magnetic system are shown in exploded form; Figures 7a and 7b are, respectively, perspective and side views of the dual driver of Figures 4 to 6, in which a 10 mm driver is shown in exploded form; Figure 8 is a perspective view of the earphone of Figure 3, in which the front and rear parts of the earphone housing are transparent to enable the dual driver of Figures 4 to 7 to be seen; Figure 9a is a graph showing the acoustic performance of the 10mm and 14mm drivers of the dual driver of Figures 4 to 8 when tested separately; Figure 9b is the graph of Figure 9a, additionally showing the acoustic performance of the dual driver of Figures 4 to 8; Figure lOa is a schematic of a dual driver earphone constructed in accordance with the invention, and incorporating an inline controller for adjusting the relative levels of low frequency and high frequency sounds; Figure 1 Ob is a schematic of a stereo earphone device comprising two dual driver earphones and a common inline controller; Figure 1 la is a graph showing the variation in acoustic performance of the dual driver at various settings of a variable resistor associated with the 10 mm driver; and Figure 11 b is a graph showing the variation in acoustic performance of the dual driver at various settings of a variable resistor associated with the 14 mm driver.

Detailed description of the preferred embodiments

Referring to Figure 2, this shows a compound driver 40 constructed in accordance with the invention. In this example, the compound driver 40 includes two drivers (a first driver 42 and a second driver 44) and is therefore referred to hereafter as a dual driver', The first driver 42 and the second driver 44 are each supported by an outer driver housing 46 and share a common magnetic system 48. The first driver 42 includes a relatively small first diaphragm 50 having a central dome-shaped radiator 52 surrounded by a suspension ring 54 of convex cross-section, whilst the second driver 44 has a relatively large second diaphragm 56 also having a central dome-shaped radiator 58 surrounded by a suspension ring 60 of convex cross-section. The first diaphragm 50 is fixed to a first end 62 of the outer driver housing 46 about a circular outer periphery 64 of its suspension ring 54, whilst the second diaphragm 56 is fixed to a second end 66 of the outer driver housing 46 about a circular outer periphery 68 of its suspension ring 60.

The first and second diaphragms 50, 56 are coaxially arranged and spaced apart from one another such that an inner side 70 of the first diaphragm 50 faces an inner side 72 of the second diaphragm 56. Whilst not shown in Figure 2, the first end 62 of the outer driver housing 46 would be closed by a first protective metal cover, located outwardly with respect the first diaphragm 50, i.e. adjacent an outer side 74 of the first diaphragm 50. The second end 66 of the driver housing 46 is closed by a second metal cover 76 located outwardly with respect to an outer side 78 of the second diaphragm 56, i.e. adjacent the outer side 78 of the second diaphragm 56.

The outer driver housing 46 has a substantially flat, annular base 80, with a circular rim 82 extending upwardly from its outermost periphery 83 towards the second end 66, and a tubular skirt 84 extending downwardly from its innermost periphery 85 towards the second end 62. An inner driver housing 86 is located within the tubular skirt 84. The inner driver housing 86 has an annular base 88 with a circular wall 90 extending upwardly from its outermost periphery 91. The inner driver housing 86 is disposed within the skirt 84 such that its annular base 88 is substantially parallel to, but spaced apart from, the plane of the annular base 80 of the outer driver housing 46, whilst an outer surface 92 of the circular wall 90 forms an interference fit with an inner surface 94 of the skirt 84. It will be appreciated that terms such as upwardly' and downwardly' refer to the dual driver in the orientation shown on the page, and are not intended to limit the scope of the invention.

The common magnetic system 48 is disposed in a region between the respective opposed inner sides 70, 72 of the two diaphragms 50, 56. The common magnetic system 48 comprises a combination of inner and outer magnets 96, 98 to produce a stronger magnetic field than would otherwise be achieved with a single magnet. The inner magnet 96 is a substantially circular disc, whilst the outer magnet 98 is annular.

The inner and outer magnets 96, 98 are arranged coaxially within the inner driver housing 86, with the outer magnet 98 completely surrounding and coplanar with the inner magnet 96. The inner and outer magnets 96, 98 are spaced apart to define a first annular groove 100 therebetween, whilst the outer magnet 98 is inwardly-spaced from the circular wall 90 of the inner driver housing 86 to define a second annular groove 102 therebetween.

The outer magnet 98 is fixed to the annular base 88 of the inner driver housing 86 and surmounts an innermost circular periphery of that base 88. A first circular metal washer 106 is glued to an upper surface 108 of the outer magnet 98, and the inner magnet 96 is glued to a central region of the first washer 106. A second circular metal washer 110 is glued to a lower surface 112 of the inner magnet 96.

A first voice coil 114 is attached to the inner side 70 of the first diaphragm 50, whilst a second voice coil 116 is attached to the inner side 72 of the second diaphragm 56. The first voice coil 114 extends into the first annular groove 100, such that it surrounds the inner magnet 96 and the second washer 110, and is surrounded by the outer magnet 98 (or in other words, the inner magnet 96 and the attached second washer 110 extend into a region 118 bounded by the first voice coil 114 and the inner side 70 of the first diaphragm 50). The second voice coil 116 extends into the second annular groove 102 and surrounds the outer magnet 98 and the attached first washer 106 (or in other words, the outer magnet 98 and the attached first washer 106 extend into a region 120 bounded by the second voice coil 116 and the inner side 72 of the second diaphragm 56).

The first driver 42 is optimised to produce relatively low-frequency bass and mid-range sounds, whilst the second driver 44 is optimised to produce relatively high-frequency mid-range and treble sounds. In use, the dual driver 40 would preferably be oriented such that the first driver 42 is closer to a user's ear canal than the second driver 44. In this orientation, the outer side 74 of the relatively small first diaphragm 50 would face towards the user's ear canal, whilst the outer side 78 of the relatively large, second diaphragm 56, would face away from the user's ear canal. In other words, the first diaphragm 50 has an inboard position and the second diaphragm 56 has an outboard position.

A first volume 122 is defined between the inner side 70 of the first diaphragm 50 and the common magnetic system 48, and a second volume 124 is defined between the inner side 72 of the second diaphragm 56 and the common magnetic system 48. A plurality of vents 126 are provided in the annular base 80 of the outer driver housing 46 to allow sound waves within the second volume 124, which are produced by the inner side 72 of the second diaphragm 56, to pass from the second vo'ume 124 into a mixing region 128 outside the outer driver housing 46, where those sound waves combine with sound waves from the outer side 74 of the first diaphragm 50. When the dual driver 40 is incorporated into an earphone, the combined sound waves in the mixing region 128 are channelled towards a user's ear by part of an earphone housing, as described in further detail later. Generally speaking, the vents 126 are provided in an annular region defined between the outer periphery 64 of the first diaphragm 50, and the outer periphery 68 of the second diaphragm 56. Providing the vents 126 in this region maximises the compactness of the dual driver 40.

The inner driver housing 86 and the magnetic system 48 together provide a substantially airtight barrier between the first and second diaphragms 50, 56. This arrangement prevents airflow between the respective inner sides 70, 72 of the first and second diaphragms 50, 56, and hence substantially prevents interference between the sound waves from the two diaphragms 50, 56.

Referring now to Figures 3a and 3b, these show an earphone 130 comprising a dual driver 132 similar to the one described above with reference to Figure 2, but constructed in accordance with a preferred embodiment of the invention. The earphone 130 has an earphone housing 134 comprising inboard and outboard parts that come together to enclose the dual driver 132. The terms inboard' and outboard' refer to the respective locations of the two parts relative to a user's ear in use. Only the inboard part of the earphone housing 134 is shown in Figures 3a and 3b, whilst the outboard part has been removed to expose the dual driver 132. A sound tube 136 projects from a circular, convex-curved external surface 138 of the inboard part. The sound tube 136 extends from a generally elliptical root 140 at the curved surface 138, towards a free end 142.

The sound tube is asymmetrical about a central longitudinal axis 144 of the inboard part of the earphone housing 134, and angled, in the sense that a central longitudinal axis 146 of the sound tube 136 is inclined with respect to the central longitudinal axis 144 of the inboard part of the earphone housing 134.

Whilst riot shown in Figures 3a and 3b, a soft cap would usually be provided over the sound tube 136. The soft cap and the sound tube 136 together form an in-ear portion', which is inserted directly into a user's ear canal in use. The soft cap forms a seal with the ear canal, thereby isolating the user from external noise, and improving the sound quality of the earphone 130. This type of earphone is generally referred to as an in-ear' earphone or a canal phone'.

The construction of the duaJ driver 132 shown in Figures 3b will now be described in further detail with reference to Figures 4 to 8. Referring firstly to Figure 4, in which the earphone housing 134 is represented schematically by a dashed line, the dual driver 132 comprises a 10 mm driver 148 having a 10 mm diaphragm 150 and a 14mm driver 152 having a 14mm diaphragm 154. The 10 mm and the 14mm diaphragms 152, 154 are supported at respective first and second ends 156, 158 of an outer driver housing 160.

The two diaphragms 150, 154 are arranged such that an inner side 162 of the 10 mm diaphragm 150 faces an inner side 164 of the 14 mm diaphragm 154. An outer side 165 of the 10 mm diaphragm 150 faces towards the sound tube 136, whilst an outer side 166 of the 14 mm diaphragm 150 faces away from the sound tube 136 A common magnetic system 167 is disposed in between the two diaphragms 150, 154, within an inner driver housing 168. A first volume 170 is defined inwardly of the 10 mm diaphragm 150 (or in other words behind the 10 mm diaphragm 150), between the inner side 162 of the 10mm diaphragm 150 and the inner driver housing 168. A second volume 172 is defined inwardly of the 14 mm diaphragm 154 (or in other words behind the 14mm diaphragm 154), between the inner side 164 of the 14mm diaphragm 154 and the common magnetic system 167.

Referring now to Figure 5a, the outer driver housing 160 is generally circular and made of a plastics material. The outer driver housing 160 has a substantially flat, annular base 174, having a circular rim 176 extending from its outer periphery 178 in a first direction perpendicular to the plane of the base 174, and a tubular skirt 180 extending from its inner periphery 182 in a second direction, opposite to the first direction.

The outer driver housing 160 is closed at the first end 156 by a relatively small, substantially circular, first cover 184, and closed at the second end 158 by a relatively large, substantially circular, second cover 186. The first and second covers 184, 186 are each made from metal. Referring to Figure 5b, the 10 mm diaphragm 150 is located inwardly with respect to the first cover 184 (or in other words, behind the first cover 184), whereas the 14 mm diaphragm 154 is located inwardly with respect to the second cover 186 (or in other words, behind the second cover 186). The first cover 184 includes a plurality of apertures 188 to allow air, and thus sound waves, to pass from the outer side of the 10 mm diaphragm 150 towards the sound tube 136 of the earphone housing 134 (Figure 3a, 3b and 4). In contrast, the second cover 186 (Figure 5c) has a substantially continuous surface 190 to attenuate the sound waves produced from the outer side 166 (Figure 4) of the 14 mm diaphragm 154. This closed-back' construction advantageously minimises sound leakage from the outboard part of the earphone 130, which makes the earphone relatively quiet to others. Nevertheless, in order that the 14mm diaphragm 154 is not moving against a fixed volume of air, a small aperture 192 is provided in the centre of the second cover 190.

Referring again to Figure 5b, an arcuate printed circuit board (PCB) 194 is mounted to the annular base 174 of the outer driver housing 160, such that it partially surrounds the skirt 180. The annular base 174 also includes a plurality of vents 196, which are arcuate slots in the base 174, spaced apart from one another in a circular formation substantially surrounding the skirt 180. As described above in relation to Figure 2, and best seen in Figure 4, the vents 196 allow sound waves from the inner side 164 of the 14mm diaphragm 154 to pass from the second volume 172 (located inwardly with respect to the 14 mm diaphragm 154), into a mixing chamber 198 defined between the outer driver housing 160 and an inner surface 200 of the earphone housing 134. Within the mixing chamber 198, the sound waves from the inner side 164 of the 14 mm diaphragm 154 combine with sound waves from the outer side 165 of the 10 mm diaphragm 150. The combined sound waves are channelled into the user's ear canal through the sound tube 136.

Referring still to Figure 4, and also to Figure 5, a pipe 202, the function of which will be described later, extends radially from the skirt 180 of the outer driver housing 160, i.e. in a direction perpendicular to a central longitudinal axis 204 of the outer driver housing 160. As described in further detail later, the pipe 202 provides an enclosed pathway for sound waves generated by the inner side 162 of the 10mm diaphragm 150, i.e. sound waves within the first volume 170, to escape from the earphone 130 without interfering with the combined sound waves within the mixing chamber 198.

Figures 6a and 6b show the dual driver 132 with the 10 mm driver 148 in assembled form, and the 14mm driver 152 and common magnetic system 167 in exploded form.

Referring to Figures 6a and 6b, an inner driver housing 206 is received within the tubular skirt 180 of the outer driver housing 160. The inner driver housing 206 is made of metal and comprises an annular base 208 having a raised circumferential wall 210. The magnetic system 167, which comprises a circular inner magnet 212 surrounded by an annular outer magnet 214, is disposed within the inner driver housing 206, such that the circumferential wall 210 surrounds the outer magnet 214. A first metal washer 216, which is circular and has a diameter substantially equal to that of the outer magnet 214, is glued to an annular outer surface 218 of the outer magnet 214. A relatively large voice coil 220 is provided between the first washer 216 and the 14mm diaphragm 154. The voice coil 220 is attached to the inner side 164 of the 14 mm diaphragm 154 along a circular boundary 222 between a radiator 224 and a suspension ring 226 of the 14 mm diaphragm 154.

Figures 7a and 7b show the dual driver 132 with the 14 mm driver 152 and the magnet assembly 167 in assembled form, and the 10 mm driver 148 in exploded form. A second metal washer 228, which is circular and has a diameter substantially equal to that of the inner magnet 212 (Figure 6), is glued to an outer surface 230 (Figure 6b) of the inner magnet 212 when the 10 mm driver 148 is. A relatively small voice coil 232 is provided between the second washer 228 and the 10 mm diaphragm 150. The voice coil 232 is attached to the inner side 162 of the 10 mm diaphragm 150 along a circular border 234 between a radiator 236 and a suspension ring 238 of the 10 mm diaphragm 150. The pipe 202, which was mentioned above in relation to Figure 5a, is received within an aperture 240 in the skirt 180.

Referring again to Figure 4 and also to Figure 8, the aperture 240 extends radially through the skirt 180, i.e. in a direction substantially perpendicular to the central longitudinal axis 204 of the outer driver housing 160, and opens into the first volume 170 behind the first diaphragm 150. The pipe 202 is received within the aperture 240 in the skirt 180, and extends through the mixing chamber 198 to an aperture 242 provided in the earphone housing 134. The pipe 202 provides an enclosed pathway or duct 244 extending from the first volume 170 to atmosphere 246, and allows sound waves within the first volume 170 (i.e. produced by the inner side 162 of the 10 mm diaphragm 150) to exit the earphone housing 134 in a direction away from the user's ear.

The pipe 202 substantially prevents sound waves from the inner side 162 of the 10 mm diaphragm 150 from mixing with sound waves from the outer side 165 of the 10 mm diaphragm 150. Since the sound waves from the inner and outer sides 162, 165 of the mm diaphragm 150 are 180 degrees out of phase, any interference between these sound waves would reduce the effectiveness of the earphone 130 at reproducing relatively low-frequency sounds, i.e. it would reduce the bass performance of the earphone 130. Therefore, by preventing sound from the inner and outer sides 162, 165 of the 10mm diaphragm 150 from mixing, the earphone 130 maximises bass performance.

In addition, the pipe 202 ensures that the 10 mm diaphragm 150 is not moving against a fixed volume of air by allowing air to flow into and out of the first volume 170 behind the mm diaphragm 150. Advantageously, the pipe 202 facilities this airflow, whilst at the same time preventing the sound waves from the inner side 162 of the 10 mm diaphragm from mixing with the sound waves within the mixing chamber 198 (i.e. sound waves from the inner side 164 of the 14 mm diaphragm 154 and sound waves from the outer side 165 of the 10 mm diaphragm 150). This separation of sound prevents interference between sound waves that are 180 degrees out of phase, which interference would otherwise degrade the sound quality.

Visible in Figure 8 is a small hole 248, which is provided in the earphone housing 134, close to the root 140 of the sound tube 136, for tuning the bass performance of the earphone 130. In other embodiments of the invention, a bass tuning hole is not included and the sound tube 136 is not inclined. Also visible in Figure 8, is part of a cable 250 for connecting the earphone 130 to an audio device (not shown).

Acoustic tests have been conducted to evaluate the performance of the dual driver 132.

Referring to Figure 9a, this shows the performance of the 10 mm and 14 mm diaphragms when tested separately. As can be seen from the line corresponding to the 10 mm driver (LINE 10), the 10 mm driver is most effective at reproducing relatively low-frequency sounds, in a frequency range between about 20 -500 Hz. Whereas, as can be seen from the line corresponding to the 14 mm driver (LINE 14), the 14 mm driver is most effective at reproducing relatively high-frequency sounds, in a frequency range of about 500 Hz -8 kHz. Figure 9b additionally includes a third line (LINE DD), which corresponds to the performance of the dual driver 132 with both the 10 mm and the 14 mm drivers 148, 152 operating simultaneously. It is apparent from LINE DD that the dual driver 132 is able to reproduce a wider frequency range, at higher sensitivity, than either of the 10 mm or the 14 mm drivers 148, 152 in isolation.

Referring to Figure ba, this shows a further embodiment of the invention, in which the earphone 130 described above is additionally configured to allow the relative levels of bass, and mid-range/treble to be adjusted. To this end, a first variable resistor 252 is associated with the 10 mm driver 148 to allow the level of relatively low frequency sounds to be increased or decreased without substantially affecting the level of the relatively high frequency sounds produced by the 14mm driver 152. Additionally, a second variable resistor 254 is associated with the 14 mm driver 152 to allow the relatively high frequency sounds to be adjusted without affecting the level of the relatively low frequency sounds produced by the 10 mm driver 148.

The variable resistors 252, 254 are located within a controller 256 provided inline with the cable 250 for connecting the earphone 130 to an audio device. The cable 250 extends from a first end 258 at the earphone housing, towards a free second end 260. The second end 260 is provided with a 3.5 mm jack plug 262, or other suitable connector to allow connection to a corresponding connector on the audio device. The controller 256 includes knobs or sliders (not shown) to allow the user to control the settings of the variable resistors 252, 254, and hence adjust the relative levels of low and high frequency sounds. Providing the controller 256 inline with the cable 250 allows the user to adjust the sound characteristics of the earphone easily. However, in other embodiments of the invention, the variable resistor(s) 252, 254 may be provided within the earphone housing 134.

Referring to Figure lOb, this shows a stereo earphone device 264 comprising two dual driver earphones 130a, 130b (for the user's respective left and right ears), each similar to the earphone 130 in Figure lOa. A common controller 256 is used to control the relative levels of high and low frequency sound output from both of the earphones 1 30a, 1 30b.

To this end, the output of the first variable resistor 252 is connected to the 10 mm driver 1 48a of the left earphone 1 30a and to the 10 mm driver 1 48b of the right earphone 1 30b, whilst the output of the second variable resistor 254 is connected to the respective 14 mm drivers 152a, 152b of the left and right earphones 130a, 130b.

The acoustic performance of an earphone 130 has been tested at various settings of the first variable resistor 252 (associated with the 10 mm driver(s) 148), and the results are shown in Figure ha. Referring to Figure ha, maximum levels of relatively low frequency (bass) sounds were reproduced when the first variable resistor 252 was set to a resistance of zero ohms (LINE 10.0), whereas minimum bass levels were reproduced when the first variable resistor 252 was set to provide a resistance of 500 ohms (LINE 1O5). Intermediate levels of bass were achieved when the first variable resistor was set to provide resistances of 100, 200, 300 and 400 ohms (LINE 10.1, LINE 10.2, LINE 10.3 and LINE 10.4 respectively). Generally speaking, increasing the resistance of the first variable resistor 252 (associated with the 10 mm driver 148) lowers the level of bass reproduced by the dual driver 132.

Similarly, the acoustic performance of the earphone 130 was tested at various settings of the second variable resistor 254 (associated with the 14 mm driver 152), and the results are shown in Figure 11 b. Referring to Figure 11 b, maximum levels of high frequency (mid-range and treble) sounds were reproduced when the second variable resistor 254 was set to a resistance of zero ohms (LINE 14.0), whereas minimum levels of high frequency sounds were reproduced when the second variable resistor was set to provide a resistance of 500 ohms (LINE 14.5). Intermediate levels of mid-range and treble were achieved when the second variable resistor was set to provide resistances of 100, 200, 300 and 400 ohms (LINE 14.1, LINE 14.2, LINE 14.3, and LINE 14.4 respectively).

Generally speaking, increasing the resistance of the second variable resistor 254 (associated with the 14 mm driver 152) lowers the mid-range and treble output of the dual driver 132.

It will be appreciated that other embodiments of the invention may employ a single variable resistor, for example associated with the 10 mm driver to allow independent adjustment of the bass, but not independent adjustment of the mid-range and treble. It will also be appreciated that the adjustment provided by the variable resistor(s) could be provided by other suitable means, for example in software.

In other embodiments of the invention, the dual driver or the earphone device may be configured to provide one or more predetermined sound characteristics, i.e. preset levels of bass, and/or mid-range and/or treble. In the case that a plurality of preset sound characteristics are defined, the earphone device is conveniently configured to allow the user to select between the presets; for example via the provision of buttons or switches provided on the earphone housing or inline with the cable.

It is envisaged that a service can be provided whereby one or more preset sound characteristics of the earphone device are determined by the user (or for the user by an expert in consultation with the user) in accordance with the user's particular requirements and preferences. Once the most preferable sound characteristic has been determined, the earphone may be configured to always provide this sound characteristic.

Alternatively, a set of preferred sound characteristics may be preset in the earphone in consultation with a user, and the earphone may be configured with suitable means to allow the user to select between the presets, for example buttons or switches as described above.

The earphone device may be configured to allow the user to continuously adjust the relative levels of bass and/or mid-range and/or treble between maximum and minimum values. To this end, suitable sliders or knobs may be associated with the or each variable resistor. Through the provision of adjustment means, the user can control the sound characteristic of the earphone (i.e. the relative levels of bass and/or mid-range and/or treble).

In summary, a compound driver has been described in which first and second drivers share a common magnetic system. Also described was an earphone in which a duct is configured to allow air to flow into and out of a volume between two drivers in a compound driver in order to prevent mixing between out of phase sound waves.

Furthermore an earphone was described in which the relative output levels of a first and a second driver can be adjusted, for example to increase the level of bass or treble reproduced by the earphone. These and other aspects of the invention are the subject of the claims.

It will be appreciated that many modifications may be made to the devices described above without departing from the scope of the invention as defined in the following claims.

Claims

Claims 1. A compound driver for an earphone, the compound driver comprising a first driver and a second driver, wherein the first and second drivers share a common magnetic system.
2. The compound driver of Claim 1, wherein the first driver includes a first diaphragm having a first voice coil attached to an inner side, and the second driver includes a second diaphragm having a second voice coil attached to an inner side, the first and second diaphragms being arranged such that their respective inner sides are facing, with the common magnetic system being located therebetween.
3. The compound driver of Claim 2, wherein the magnetic system comprises an inner magnet surrounded by an outer magnet, the inner and outer magnets being spaced apart to define a groove therebetween, into which the first voice coil extends.
4. The compound driver of Claim 3, wherein the inner magnet is substantially circular and the outer magnet is annular.
5. The compound driver of Claim 3 or Claim 4, wherein the second voice coil extends into a region surrounding the outer magnet.
6. The compound driver of any of Claims 2 to 5, wherein the first and second diaphragms are substantially concentric.
7. The compound driver of any of Claims 2 to 6, wherein the first diaphragm is relatively small and the second diaphragm is relatively large.
8. The compound driver of Claim 7, wherein the first driver is configured to reproduce relatively low frequency sounds and the second driver is configured to reproduce relatively high frequency sounds.
9. The compound driver of any of Claims 2 to 8, wherein the first and second diaphragms are supported by a common driver housing within which the common magnetic system is located.
10. The compound driver of Claim 9, wherein the first diaphragm is supported at a first end of the common driver housing and the second driver is supported at a second end of the common driver housing.
11. The compound driver of Claim 10, wherein the first end of the common driver housing is closed by a first cover spaced apart from an outer side of the first diaphragm.
12. The compound driver of Claim 11, wherein the first cover includes a plurality of apertures to allow sound waves to pass from the outer side of the first diaphragm towards a user's ear in use.
13. The compound driver of any of Claims 10 to 12, wherein the second end of the driver housing is closed by a second cover spaced apart from an outer side of the second diaphragm.
14. The compound driver of Claim 13, wherein the second cover has a substantially continuous surface to substantially prevent sound waves from the outer side of the second diaphragm escaping from the common driver housing.
15. The compound driver of Claim 14, wherein the substantially continuous surface is interrupted by an aperture.
16. The compound driver of any of Claims 9 to 15, wherein the common driver housing includes at least one vent positioned to allow sound waves from the inner side of the second diaphragm to enter a mixing chamber in which those sound waves combine with sound waves from an outer side of the first diaphragm.
17. The compound driver of Claim 16, wherein the common driver housing comprises an annular base having a tubular skirt depending from a radially inner periphery, wherein the magnetic system is located within the tubular skirt, and the or each vent is provided in the base.
18. The compound driver of any of Claims 2 to 17, further comprising a duct extending from a volume defined at least in part by the inner side of the first diaphragm, wherein the duct is configured to allow air to flow into and out of the volume whilst simultaneously isolating sound waves produced by the inner side of the first diaphragm from sound waves in a mixing chamber, wherein the sound waves in the mixing chamber are a combination of sound waves from an outer side of the first diaphragm and the inner side of the second diaphragm.
19. The compound driver of Claim 18, wherein the duct extends through the mixing chamber.
20. The compound driver of Claim 18 or Claim 19 when dependent upon Claim 17, wherein the duct is provided by a pipe received within an aperture in the skirt.
21. The compound driver of any of Claims 2 to 20, wherein the compound driver is arranged to substantially prevent air flow between the respective inner sides of the first and second diaphragms.
22. An earphone comprising a compound driver as defined in any preceding claim.
23. The earphone of Claim 22 when dependent upon any of Claims 18 to 20, further comprising an earphone housing supporting the compound driver, wherein the mixing chamber is defined, at least in part, by the earphone housing, and the duct extends between the volume and an aperture in the earphone housing.
24. A stereo earphone device comprising a pair of earphones, each as defined in Claim 22 or Claim 23.
25. An earphone for connecting to an audio device, the earphone comprising: a compound driver having a first diaphragm and a second diaphragm, the first and second diaphragms being arranged such that an inner side of the first diaphragm faces towards an inner side of the second diaphragm, and further being arranged such that, in use, an outer side of the first diaphragm, and the inner side of the second diaphragm, each face towards a user's ear canal; a volume defined, at least in part, by the inner side of the first diaphragm, and in which sound waves from the inner side of the first diaphragm are generated; a mixing chamber in which sound waves from the outer side of the first diaphragm combine with sound waves from the inner side of the second diaphragm prior to entering the user's ear canal; and a duct configured to allow air to flow into and out of the volume whilst simultaneously isolating sound waves from the volume from the combined sound waves in the mixing chamber.
26. The earphone of Claim 25, wherein the duct communicates with an aperture provided in an earphone housing.
27. The earphone of Claim 26, wherein the mixing chamber is defined, at least in part, by an inner surface of the earphone housing.
28. The earphone of any of Claims 25 to 27, wherein the duct extends through the mixing chamber.
29. The earphone of any of Claims 25 to 28, wherein the first and second diaphragms are supported by a common driver housing.
30. The earphone of any of Claims 25 to 29, wherein the earphone further comprises a common magnetic system disposed between the respective inner sides of the first and second diaphragms.
31. The earphone of any of Claims 25 to 30, wherein the first diaphragm is configured to reproduce relatively low frequency sounds and the second diaphragm is configured to reproduce relatively high frequency sounds.
32. The earphone of any of Claims 25 to 31, wherein the first diaphragm is relatively small and the second diaphragm is relatively large.
33. The earphone of any of Claims 25 to 32, wherein the compound driver is arranged to substantially prevent air flow between the respective inner sides of the first and second diaphragms.
34. An earphone for an audio device, the earphone having a first driver for reproducing relatively low frequency sounds from a first electrical signal, and a second driver for reproducing relatively high frequency sounds from a second electrical signal, wherein the earphone further includes control means for adjusting: (i) the level of the first electrical signal independently from the level of the second electrical signal, thereby to control the level of low frequency sounds reproduced by the first driver substantially independently from the level of high frequency sounds reproduced by the second driver; and/or (ii) the level of the second electrical signal independently from the level of the first electrical signal, thereby to control the level of high frequency sounds reproduced by the second driver substantially independently from the level of low frequency sounds reproduced by the first driver.
35. The earphone of Claim 34, wherein the first and second drivers share a common magnetic system.
36. The earphone of Claim 34 or Claim 35, wherein the first and second drivers are supported by a common driver housing.
37. The earphone of any of Claims 34 to 37, wherein the control means is configured to allow the user to adjust the relative levels of the first and second electrical signals, thereby enabling the user to adjust the relative levels of the relatively low frequency and the relatively high frequency sounds produced by the earphone.
38. The earphone of Claim 37, wherein the control means includes one or more control elements for allowing the user to select between two or more predetermined sound settings in which the relative levels of the first and second electrical signals are different.
39. The earphone of Claim 37, wherein the control means includes continuously variable adjustment means for allowing the user to continuously adjust the relative levels of the relatively low frequency and the relatively high frequency sounds.
40. The earphone of Claim 39, wherein the continuously variable adjustment means is a knob, slider or other continuously adjustable control element.
41. The earphone of any of Claims 34 to 40, wherein the control means is provided inline with a cable for connecting the earphone to the portable audio system.
42. The earphone of any of Claims 34 to 40, wherein the control means is provided on an earphone housing at least partially surrounding the first and second drivers.
43. The earphone of any of Claims 34 to 42, wherein the control means comprises a variable resistor associated with the first driver for adjusting the level of the first electrical signal, and/or a variable resistor associated with the second driver for adjusting the level of the second electrical signal.
44. The earphone of Claim 43 when dependent upon Claim 42, wherein the or each variable resistor is located within the earphone housing.
45. The earphone of Claim 43, wherein the or each variable resistor is located within an inline control means.
46. A stereo earphone device comprising two earphones as defined in any of Claims 34 to 45, wherein the control means is common to both earphones.
47. A stereo earphone device comprising two earphones, each having a first driver for reproducing relatively low frequency sounds from a first electrical signal, and a second driver for reproducing relatively high frequency sounds from a second electrical signal, wherein the earphone further includes common control means for adjusting: (i) the level of the first electrical signal independently from the level of the second electrical signal, thereby to control the level of low frequency sounds reproduced by the first driver substantially independently from the level of high frequency sounds reproduced by the second driver; and/or (ii) the level of the second electrical signal independently from the level of the first electrical signal, thereby to control the level of high frequency sounds reproduced by the second driver substantially independently from the level of low frequency sounds reproduced by the first driver.
48. A method of customising the sound output of an earphone, the earphone comprising a first driver for reproducing relatively low frequency sounds, and a second driver for reproducing relatively high frequency sounds, wherein the method includes adjusting the relative volume output of the first and second drivers, thereby to adjust the relative levels of the relatively low frequency and relatively high frequency sounds output by the earphone.
49. The method of Claim 48, further including presetting the relative volume levels of the first and second drivers in accordance with an end-user's preferences.
50. The method of Claim 48 or Claim 49, wherein the method includes providing control means for allowing the end user to adjust the relative volume levels of the first and second drivers.
51. The method of any of Claims 48 to 50, further including providing control means for allowing the end user to select between two or more predetermined sound settings, wherein in each sound setting the relative volume levels of the first and second driver are different.
52. A compound driver substantially as herein described, with reference to or as shown in any of Figures 2 to 11 of the accompanying drawings.
53. An earphone substantially as herein described, with reference to or as shown in any of Figures 2 to 11 of the accompanying drawings.
54. A stereo earphone device substantially as herein described, with reference to or as shown in any of Figures 2 to 11 of the accompanying drawings.