This invention relates to a headphone or earphone, particularly but not exclusively an earphone that is placed by a user in the end of his ear.

Headphones and earphones are often used by a person who wishes to listen to music or to a radio in such a way that other nearby people don't also hear it. Earphones may be referred to as “in-ear monitors” or IEMs, or “in-ear headphones”, and may be sized to fit within the user's ear canal, so they may be almost invisible in use. Headphones in contrast typically fit over the outside of the ear, being supported by a band passing over the top of the head, and are therefore considerably larger. By way of example an earphone may incorporate a diaphragm of diameter less than 10 mm, for example 8 mm or 5 mm, whereas a headphone may incorporate a diaphragm typically less than 60 mm, for example 35 mm or 20 mm. In each case the sound source is much smaller than a conventional loudspeaker, so that there may be problems in achieving accurate sound reproduction over the entire audible sound spectrum.

According to the present invention there is provided a headphone or earphone consisting of a casing adapted to fit to a user's ear, the casing defining a cavity to locate a driver and also defining a sound outlet duct that communicates with a front end of the cavity to provide sound to the user's ear, and the casing being provided with a rear closure element, the casing enclosing a driver with a diaphragm at a front face of the driver, so that the driver divides the driver-locating cavity into a rear cavity behind the driver and a front cavity in front of the driver, wherein the front cavity communicates with the sound outlet duct; and also comprising at least one resilient element, such that the driver is clamped between a resilient element that engages with its front face near the periphery and a rear element that engages the rear face, the resilient element that engages the front face being compressed between an end face of the front cavity and the front face of the driver.

The resilient element may be an O-ring seal or gasket, and may seal the periphery of the front face of the driver to the end face of the front cavity.

In one option the rear element is also a resilient element, and engages the rear face of the driver near its periphery; the rear element in this case may be compressed between the rear face of the driver and the end face of the rear cavity.

The rear closure element may be connected to the casing by a threaded connection, or may be secured by a latch or clip mechanism. In particular the rear closure element may at least partly fit within an end portion of the cavity, and the threaded connection may comprise a screw thread on the inside wall of that end portion of the cavity.

The sound outlet duct preferably includes a tapered duct portion, which may be where the front end of the cavity communicates with the sound outlet duct, and the taper may for example be inclined at between 40° and 50°, for example at 45°, to a longitudinal axis of the sound outlet duct.

The sound outlet duct is of less width than the diaphragm, and may define a restrictive duct portion with a cross-sectional area between 19% and 30% of the cross-sectional area of the diaphragm. The restrictive duct portion is the portion of the sound outlet duct of the least cross-sectional area. If both the diaphragm and the restrictive duct portion are of circular cross-section, then this limitation is equivalent to requiring that the diameter of the restrictive duct portion is between about 44% and 55% of the diameter of the diaphragm, the optimum being about 49% of the diameter of the diaphragm.

The rear cavity may be an enclosed airtight cavity; or alternatively the rear cavity may define a rear outlet port. The rear outlet port, where it is provided, may be axially aligned with the sound outlet duct, and desirably defines a rear restrictive duct portion of the same cross-sectional area as the restrictive duct portion of the sound outlet duct. These features are discussed in more detail below in relation to other aspects of the invention.

It will be appreciated that an electrical connection must be made to the driver. This requires a cable connected to the rear of the driver. This may utilise a cable guide.

In another aspect the invention provides a cable guide for use in a casing of an earphone, headphone or microphone, the casing defining a cylindrical cavity with a wall that defines a slot for entry of a cable, and the casing being provided with a rear closure element, wherein the cable guide defines an inlet duct that can locate in the slot, and a clamping ring that fits coaxially within the cylindrical cavity, wherein the cable guide comprises two mating parts: a first part that defines one side of the inlet duct and defines an arcuate portion of one face of the clamping ring so as to define a circumferential gap between the ends of the arcuate portion; and a second part that defines the other side of the inlet duct, and also defines the remainder of the clamping ring, such that when the two parts are put together the clamping ring has a substantially continuous front face and a substantially continuous rear face.

During assembly there is no requirement to feed the cable through the cable guide, which may indeed be difficult if the end of the cable has been soldered to a an electro-acoustic transducer such as a driver within the casing. It is merely necessary to lay the cable into the first part of the cable guide, passing the cable through the circumferential gap between the ends of the arcuate portion, and then mate the first part and the second part of the cable guide together. In combination the first part and the second part form a clamping ring that has a substantially continuous front face and a substantially continuous rear face.

In one embodiment the second part defines a ring that forms a rear face of the clamping ring, from which projects an arcuate portion that fits in the circumferential gap between the ends of the arcuate portion of the first part. In an alternative embodiment the first portion defines not only the arcuate portion, but also a rearwardly-projecting arcuate part; and the second portion defines an arcuate ring-portion with a gap into which the rearwardly-projecting arcuate part fits.

Hence if there is a driver in the casing, the cable to the driver may be fed through the cable guide, and the rear closure element may then provide pressure to the rear face of the clamping ring. The clamping ring enables substantially uniform pressure to be provided around the entire periphery of the driver, while the cable guide ensures that the cable itself is not compressed.

The inlet duct preferably defines a clamp to clamp the cable, for example an internal ridge, so that tension on the cable is transferred to the cable guide and so to the casing, rather than acting directly on a soldered joint where the cable is fixed to the driver.

Such a cable guide may in some cases be made of metal. More typically it is made of a plastics material such as polyurethane, polyvinyl chloride, nylon (polyamide) and Delrin™ (polyoxymethylene or acetal). The choice of plastic may depend on use and flexibility required in a particular context. With a larger casing containing a larger driver it may be desirable to use a more flexible plastic so that there is some flexibility in the inlet duct; while with a smaller casing it may be preferable to use a harder plastic. The cable guide, if made from a plastic material, typically provides some resilience, helping to seal the periphery of the driver to the casing. Consequently in this case it is not generally necessary to use a gasket or O-ring behind the driver.

According to another aspect of the present invention there is provided a headphone or earphone consisting of a casing adapted to fit to a user's ear, the casing enclosing a driver with a diaphragm, and defining an enclosed airtight cavity behind the driver, and a cavity in front of the driver that communicates with a sound outlet duct adapted to provide sound to the user's ear, the sound outlet duct defining a restrictive duct portion with a cross-sectional area between 19% and 30% of the cross-sectional area of the diaphragm.

As mentioned above, the restrictive duct portion is the portion of the sound outlet duct of the least cross-sectional area. If both the diaphragm and the restrictive duct portion are of circular cross-section, then this limitation is equivalent to requiring that the diameter of the restrictive duct portion is between about 44% and 55% of the diameter of the diaphragm, the optimum being about 49% of the diameter of the diaphragm.

Preferably the driver is sealed to the casing. The driver may for example be sealed to the casing by being clamped with a seal that engages with its front face near the periphery, the seal being compressed between end face of the cavity in front of the driver and the face of the driver. Indeed the driver may be clamped between two such seals, which respectively engage the front face and the rear face. These may be O-ring seals or gaskets, which correspond in shape to the external shape of the driver, for example being circular ring-shaped where the casing and the driver are cylindrical. These ensure that the driver as a whole does not vibrate or rattle in the casing.

The cavity in front of the driver, i.e. the front cavity, may be less than 3 mm deep, and the casing is preferably arranged to minimise the depth of the front cavity; but clearly the end wall of the front cavity must not be so close as to obstruct the transmission of sound from the driver.

The airtight cavity behind the driver (i.e. the rear cavity) may also be less than 3 mm deep and preferably no more than 2 mm deep. As with the front cavity, the driver may be spaced apart from the opposite end of the rear cavity by a compressed seal, so that the thickness of the compressed seal defines the depth of the rear cavity. The rear cavity may be of the same depth as the front cavity, or may be less deep than the front cavity. It will be appreciated that the driver typically has at least one vent hole behind the diaphragm, which communicates with the rear cavity; the airtight cavity behind the driver, i.e. the rear cavity, is therefore in communication with the free space within the driver but behind the diaphragm. In an extreme case the rear cavity may therefore be of zero depth, merely sealing the rear of the driver so that the free space within the driver behind the diaphragm is rendered airtight. However, since it is usually necessary to make electrical contact at the rear of the driver, it is typically advantageous to provide a rear cavity which is sufficiently deep to accommodate the requisite electrical connections, but no deeper than that. The electrical connection may use a cable guide as described above.

It appears that the provision of the restrictive duct portion in the sound outlet duct, in combination with the airtight cavity behind the driver, causes pressure increases both in front of the diaphragm and behind the diaphragm, and it is surmised that these counteract each other. This surprisingly has been found to increase the operating range of the driver so it can provide a linear response over the entire audible frequency range, for example between 20 Hz and 20 kHz. It is surmised that in use, when the headphone or earphone is held against or in an ear so that the sound outlet duct communicates into an enclosed space defined by or within the ear itself, there is effectively a balance between the pressures behind the diaphragm and in front of the diaphragm. If the cross-sectional area of the restrictive duct portion is larger than 30% of the diaphragm's cross-sectional area, then the reproduction of both bass and treble frequencies becomes less effective; while if the cross-sectional area of the restrictive duct portion is smaller than 19% of the diaphragm's cross-sectional area then there is distortion of the bass and treble sounds, presumably due to excess sound pressure.

According to another aspect of the present invention there is provided a headphone or earphone consisting of a casing adapted to fit to a user's ear, the casing defining a driver-locating cavity or chamber at least a portion of which is cylindrical, a driver with a diaphragm located within the cylindrical portion of the chamber, so there is a rear cavity behind the driver, and a front cavity in front of the driver, wherein the front cavity communicates with a front outlet duct adapted to provide sound to the user's ear, the front outlet duct defining a front restrictive duct portion with a cross-sectional area less than that of the diaphragm, and the rear cavity communicates with a rear outlet duct which defines a rear restrictive duct portion with a cross-sectional area less than that of the diaphragm; wherein the rear outlet duct, the cylindrical portion of the chamber, and the front outlet duct are coaxial, so the rear outlet duct and the front outlet duct are aligned with each other, the front restrictive duct portion and the rear restrictive duct portion having the same cross-sectional area.

Preferably the driver is clamped with a resilient element that engages with its front face near the periphery, the resilient element being compressed between the driver and the end face of the front cavity. There may also be a resilient element that engages with the rear face of the driver near the periphery, so the driver is clamped between two such resilient elements. The resilient elements may comprise O-rings or gaskets to provide resilience.

In each aspect of the invention, at least one resilient element may combine an item that is rigid with an item that is resilient, so as to provide greater axial length. Hence an O-ring or gasket may be in contact with a face of the driver, or may be spaced apart by a rigid element, such as a metal ring or washer, from the face of the driver. The driver may effectively be sealed to the casing by at least one of the resilient elements. The resilient elements ensure that the driver as a whole does not vibrate or rattle in the casing.

In each aspect of the invention, the driver may be spaced apart from the opposite end of the front cavity by a compressed seal, so that the thickness of the compressed seal defines the depth of the front cavity. In each type of casing it will be appreciated that the electrical connection to a driver may be made using a cable guide as described above.

The restrictive duct portion, in each case, is the portion of the outlet duct of the least cross-sectional area. The sound outlet duct desirably has a wider portion at the end closest to the driver, tapering down to the restrictive duct portion, so as to efficiently couple sound from the entire width of the diaphragm into the restrictive duct portion. This may have a linear taper. The restrictive duct portion may have a cross-sectional area between 20% and 29% of the cross-sectional area of the diaphragm. The sound outlet duct may also have a widening portion at the end furthest from the driver.

The rear outlet duct and the front outlet duct, where both such outlet ducts are provided, or the sound outlet duct where there is only one such outlet duct, are typically defined by surfaces each of which is a surface of revolution about the longitudinal axis of a cylindrical portion of the driver-locating cavity. In each case they may be cylindrical, or they may vary in diameter along their length, for example having a linear or bell-shaped taper at one end or at each end. Where the or each outlet duct communicates with the driver-locating cavity there is desirably a tapered transition, which may for example be inclined at between 40° and 50°, for example at 45°, to a longitudinal axis of the outlet duct. In each case the restrictive duct portion may have a linear taper, or a bell-shaped taper. There may also be a widening portion at the end furthest from the driver.

In an embodiment in which there is both a rear outlet duct and a front outlet duct, the rear cavity may also be less than 3 mm deep and preferably no more than 2 mm deep. As with the front cavity, the driver is spaced apart from the end of the rear cavity by the compressed seal, so that the thickness of the compressed seal may define the depth of the rear cavity. The rear cavity may be of the same depth as the front cavity, or may be less deep than the front cavity. As mentioned previously, it will be appreciated that the driver typically has at least one vent hole behind the diaphragm, which communicates with the rear cavity; the rear cavity is therefore in communication with the free space within the driver but behind the diaphragm. It is usually necessary to make electrical contact at the rear of the driver, so it is typically advantageous to provide a rear cavity which is at least sufficiently deep to accommodate the requisite electrical connections. The rear outlet duct desirably has a wider portion at the end closest to the driver, tapering down to the restrictive duct portion, so as to couple sound from the rear of the driver efficiently into the restrictive duct portion. The restrictive duct portion may have a linear taper, or a bell-shaped taper. The rear outlet duct may also have a widening portion at the end furthest from the driver.

In one embodiment the front outlet duct and the rear outlet duct have the same longitudinal profile.

It appears that the provision of symmetrically located outlet ducts in front and at the rear of the driver has a beneficial effect on the operation of the driver, ensuring a more consistent response over the entire audible frequency range, for example between 20 Hz and 20 kHz.

In each aspect of the invention, the casing must be substantially rigid in operation, so that the driver is held securely in position and the casing does not vibrate. The casing may for example be of aluminium, stainless steel or titanium, although other materials may also be suitable. The driver may be supported within the casing by two opposed seals, as mentioned above. In embodiments where there is an airtight cavity behind the driver, then this feature and also the rigid casing would ensure that no sound comes out from the rear of the headphone or earphone.

In the case of a headphone, the casing would typically be supported by a strap over the user's head, and may be provided with ear cushions or foam pads. In the case of an earphone, the casing would typically be provided with a foam bud or earphone tip to seal to the ear canal, as is commonly used with earphones.

