WO2020188298A1

WO2020188298A1 - Ear protection

Info

Publication number: WO2020188298A1
Application number: PCT/GB2020/050759
Authority: WO
Inventors: Olav KVALØY; Knut Håkon BREIVIK; Odd Kr. Ø. PETTERSEN; Erik SWENDGAARD
Original assignee: Minuendo AS
Current assignee: Minuendo AS
Priority date: 2019-03-21
Filing date: 2020-03-20
Publication date: 2020-09-24
Anticipated expiration: 2021-09-21
Also published as: GB201903912D0; GB2596981B; GB2596981A; GB2607539B; GB2607539A; GB202212675D0; GB202115093D0

Abstract

A device for insertion into an ear canal of a mammalian subject including a body (2), a first, adjustable acousto-mechanical portion, a second acousto-mechanical portion and an adjustment arrangement (8, 16). At least one sound path (52) extending through the body. The first, adjustable acousto-mechanical portion includes an adjustable channel (4) forming at least part of the sound path and the second acousto-mechanical portion includes a membrane (26). The second, adjustable acousto-mechanical portion is arranged acoustically in series with the first adjustable acousto-mechanical portion. The adjustment arrangement is arranged to adjust the first, adjustable acousto-mechanical portion to alter an acoustic response of the at least one sound path.

Description

Ear Protection

The present invention relates to ear protection used, for example, to reduce the intensity of sounds experienced by a user.

Exposure to high intensity noises can cause damage to a person’s hearing. The damaging effects are increased when a person is frequently exposed to loud noises. In extreme cases, frequent exposure to loud noises can cause noise- induced hearing loss. Therefore, in order to protect hearing it is necessary to reduce the effects of continuous, intermittent and impact noises. As a result of the increasing awareness of the damaging effects of loud noises, for example from industrial sources, there are now various industry requirements for personnel to use ear protection. There are many situations in which personnel may be exposed to loud noises, for example when operating loud machinery. A common form of noise protection widely used are earplugs, these reduce the intensity of the sound entering a person’s ears and thus reduce the damaging effects of high intensity noises. There are two main types of earplugs that are commonly used: passive earplugs and active earplugs. Passive earplugs attenuate the intensity of all levels of sound equally, i.e. they provide a uniform level of attenuation, regardless of the intensity of sound present, for example, a reduction of 20 dB. Passive earplugs come in various forms including: foam, silicon, flanged and custom moulded earplugs. Passive earplugs are typically inserted into a user’s ear canal. Passive earplugs use the material of the earplug itself to attenuate the sound which passes through it. As the incident sound passes through the earplug, the sound is attenuated by the material of the earplug. Some sound will propagate through the earplug and pass out of the earplug into the air volume of the user’s ear canal where it will be detected by the user. The intensity of the sound will be reduced and thus the risk of damage to the user’s hearing may be reduced. Unfortunately, however, such passive earplugs also change other properties of the sound as the attenuation is usually frequency dependent and as a result the sound quality is often reduced. This may be problematic, for example for musicians as they need to hear sounds in high fidelity to ensure that what they hear is actually what is being played. In addition, if they are inserted properly, the fixed level of attenuation provided by passive earplugs is relatively high. As a result, users of passive earplugs typically have to periodically remove them in order to be communicate orally with fellow workers. The inconvenience associated with having to repeatedly remove and replace the earplugs, depending on the noise levels, may lead to reduced compliance with requirements to wear the earplugs in certain situations.

The aforementioned disadvantages can be overcome using active earplugs which comprise electronic components which enable the earplug to attenuate high intensity sounds whilst being relatively acoustically transparent and providing only low levels of attenuation when the surrounding sound has low intensity. Active earplugs often comprise a passive earplug used in conjunction with a microphone on the external side of the earplug and a speaker on the internal side of the earplug. Active earplugs typically listen to the sound on the outside of the earplug, and then replay it to a user via the speaker at a reduced intensity. Active earplugs can employ control circuitry to apply different levels of attenuation at different times or different frequencies - known as‘adaptive attenuation’. Some other systems contain circuitry that detects the incident sound and produces an out-of-phase signal that destructively interferes with the incident sound thus reducing the intensity of the incident sound as it propagates into the user’s ear canal - this is often known as‘active noise cancelling’. One of the disadvantages of active earplugs is that they are often relatively expensive due to their electrical components. Additionally, active earplugs often have a relatively high power consumption due to the need to constantly monitor and replay detected sound.

The present invention seeks to address or mitigate the problems outlined above and according to a first aspect there is provided a device, for insertion into an ear canal of a mammalian subject, comprising:

a body, having at least one sound path extending therethrough;

a first, adjustable acousto-mechanical portion comprising an adjustable channel forming at least part of the sound path;

a second acousto-mechanical portion, arranged acoustically in series with the first adjustable acousto-mechanical portion, comprising a membrane; and an adjustment arrangement for adjusting the first, adjustable acousto mechanical portion to alter an acoustic response of the at least one sound path.

The Applicant has recognised that with the claimed arrangement of the adjustable channel and the membrane, it is possible to achieve an acoustic response of the sound path which does not unacceptably reduce the quality of the sound passing through the sound path whilst maintaining the ability to control the sound, e.g. by attenuating the sound. This is because it allows the channel and the membrane to be designed so that they complement one another in maintaining a favourable acoustic response.

As will be understood by those skilled in the art, the acoustic response of the sound path should be understood to be how the sound path affects the sound which passes through it. The acoustic response of the sound path may change the frequency, amplitude and/or phase of the sound passing through it and thus ultimately change the sound heard by a user of the device.

As will be appreciated by those skilled in the art, devices in accordance with the invention advantageously do not necessarily require the presence of the complex electronic circuitry included in active earplugs, such as a speaker to replay sounds to a user, whilst maintaining the ability to control the sound and so avoid the need to remove and replace earplugs to adapt to a changing sound environment. As a result, the device may have a zero or very low power consumption when compared to typical active earplugs. Additionally, when compared to purely passive earplugs, devices in accordance with the invention advantageously may better maintain the quality of the sound passing through the device.

The adjustment arrangement may comprise any suitable arrangement for adjusting the first, adjustable acousto-mechanical portion. In a set of embodiments the adjustment arrangement comprises an actuator for adjusting the first adjustable acousto-mechanical portion. The actuator may, for example, be connected to a controller capable of controlling the first adjustable acousto-mechanical portion.

In a set of embodiments the actuator comprises an electric motor. The use of an electronic motor may advantageously mean that the device can automatically adjust the acousto-mechanical portion without requiring physical input from a user. For example the use of an electric motor may mean that the device can automatically adjust to attenuate the sound in the presence of a loud environment, without requiring the user to take any action, thereby helping to ensure that the sound path has an appropriate acoustic response for the acoustic environment the user is in, thus protecting the user.

In another set of embodiments, the actuator comprises a user operable member arranged to operate at least part of the adjustment arrangement. The user operable member may directly drive the adjustment arrangement. The user operable member may, for example, comprise a rotatable knob arranged to adjust the first, adjustable acousto-mechanical portion. The Applicant has recognised that a user operable member arranged to operate part of the adjustment arrangement may advantageously simplify the device and potentially reduce its cost. Through the use of a user operable member, it may be possible to achieve a device which does not comprise any electrical/electronic components, thereby potentially providing a device which does not require electrical power. Achieving a device which does not require power may mean that the device is more frequently used as users do not have to concern themselves with ensuring that the device has enough battery power for operation. This may help to improve compliance with, for example, industry requirements to use hearing protection.

The first, adjustable acousto-mechanical portion comprising the adjustable channel may be adjusted in any appropriate manner in order to achieve the desired acoustic response. In a set of embodiments the adjustment arrangement is configured to adjust a length of the adjustable channel. The Applicant has recognised that adjusting the length of the adjustable channel may in general increase the effect of the channel. Additionally or alternatively, the adjustment arrangement is configured to adjust a width of the adjustable channel. The Applicant has found that adjusting the width of the adjustable channel may serve to adjust the specific acoustic properties of the sound path. For example, decreasing the width of the channel will typically increase the effective acoustic mass and the acoustic loss of the channel and vice versa. Conversely decreasing the length of the channel will typically decrease the effective acoustic mass and the acoustic loss of the channel and vice versa. In other words the acoustic mass and loss typically have a positive relationship with the length of the channel and a negative relationship with the width of the channel. The terms acoustic mass and acoustic loss are well known to those skilled in the art but will be further explained later.

As will be appreciated, the length and width of the adjustable channel may be adjusted independently of one another, or simultaneously together. In a potentially overlapping set of embodiments, the adjustment arrangement is configured to adjust a shape of the adjustable channel.

The adjustable channel may be defined by any suitable structure within the device. For example, the channel may simply comprise a cylindrical or other shaped channel extending through the body of the device. Adjustment of such a channel may, for example, comprise constricting and expanding the body so as to decrease/increase the size of the channel, or comprise providing a constriction at the entrance to or exit from the channel or part way along the channel. In a set of embodiments the channel comprises an adjustable barrier member.

In a set of embodiments, the barrier member comprises an adjustable closure, such as a lid. In a set of embodiments, the adjustment arrangement enables adjustment of a position of the barrier member. For example, the adjustment arrangement may comprise a hinge enabling the position of the barrier member with respect to the rest of the channel to be adjusted. In another example, the adjustment arrangement may comprise a sliding mechanism arrangement allowing the barrier member to be pushed and/or pulled from one position to another. Preferably, the barrier member has at least an open position and a closed position. In the open position, sound may be able to propagate through the channel relatively unattenuated such that attenuation is provided mainly by the membrane at a relatively low level. In the closed position, sound may be substantially attenuated by the barrier member.

The barrier member may be configured to provide a plurality or a continuum of different positions between, for example, the open and closed position.

In an alternative set of embodiments, the channel is defined by a space between a wall of a cavity within the body and a piston arranged in the cavity, wherein adjustment of the channel is achieved by moving the piston relative to the cavity. The cross-section of the channel will depend on the shape of the wall of the cavity and the outer profile of the piston. The piston may have a complementary sectional shape to the wall of the cavity, e.g. if the wall has a circular sectional shape, the piston may have a circular sectional shape. In such an example, the channel defined between the wall and piston would effectively be an elongate annular channel. The Applicant has recognised that the arrangement of a piston in the cavity provides for a relative simple means to adjust the length and/or cross- sectional area and/or shape of the channel.

The piston may be arranged in the device in any suitable manner such that it can be moved relative to the cavity. For example, the piston may be a part of, or attached to, a linear actuator capable of moving the piston into, and out of, the cavity. In a set of embodiments, the piston is arranged to move axially within the cavity and the device comprises at least one resilient member arranged to bias the piston out of the cavity, wherein the adjustment arrangement comprises an actuation member arranged to drive the piston against the resilient bias axially into the cavity. The actuation member may be driven by an electric motor or a user operable member. The Applicant has recognised that the provision of a resilient member arranged in the manner according to the above set of embodiments means that the actuation member needs only to be able to drive movement in one axial direction as the resilient member is arranged to drive movement of the piston in the other axial direction. This may simplify the manufacture and construction of the device. In a set of embodiments, the actuation member is arranged to rotate relative to the piston, and the device further comprises an arrangement for converting rotational movement of the actuation member into axial movement of the piston.

The resilient member may be integrally provided with the piston. In a further set of embodiments, a plurality of resilient members is provided. In another set of embodiments, the at least one resilient member is in the form of a resilient arm extending between the piston and the body.

In another set of embodiments, the piston comprises a threaded portion, arranged to engage with a threaded portion on the body such that rotation of the piston causes linear movement of the piston within the cavity. Such a set of embodiments may utilise a motor to drive movement of the piston, or a user operable member. As will be appreciated by those skilled in the art, the pitch of the threaded portion may be chosen to allow for highly controlled movement of the piston within the cavity. Such control may be required in order to precisely control the acoustic response of the adjustable channel. The threaded engagement between the piston and the body, specifically the static frictional force which arises between the threaded portions, may also mean that the piston is held in its position without requiring action from a further component e.g. a motor. This may mean that once the piston has been moved to its desired position any power being supplied, for example, to a motor, may be turned off. This may help to reduce the power consumption of the device.

Of course, in addition or alternatively, the piston may be arranged to move in other directions other than just axially. For example, the piston may be moved at a non zero angle to the axis, be translated from side-to-side within the cavity or even twisted, in order to adjust the channel so as to achieve a desired acoustic response.

In a set of embodiments, the piston is arranged such that it can be held stable in a plurality of different positions in the cavity. This may be achieved due to the presence of, for example, static friction as described above with respect to the embodiment wherein the piston comprises a threaded portion. Alternatively, the device may comprise different means for holding the piston stable. For example, the piston and body may each comprise a series of recesses and corresponding protrusions acting therebetween to hold the piston stable when the recesses and protrusions are in engagement with one another.

The Applicant has recognised that in order to appropriately control the acoustic response of the sound path, it may be necessary to adjust the length and cross- section of the adjustable channel simultaneously. In a further set of embodiments, the cavity and the piston each have a frusto-conical shape such that the adjustable channel has the form of a frusto-conical shell. The Applicant has recognised that in such an arrangement axial movement of the piston within the cavity may

simultaneously adjust both the length of the channel and the width. It may also mean that a relatively large axial movement can be converted into a relatively small change in width. This may help to simplify the manufacture and construction of the device and to provide fine control over the width The piston and cavity are preferably shaped so that the channel remains of uniform shape throughout the travel of the piston but this is not essential.

The adjustment mechanism may be arranged to allow continuous adjustment of the first, adjustable acousto-mechanical portion over a given range. In a set of embodiments however it is arranged such that the first, adjustable acousto mechanical portion can only adopt a plurality of discrete positions. In the simplest such embodiments the first, adjustable acousto-mechanical portion can only adopt two positions - high and low attenuation respectively. This may allow a particularly low cost implementation of the invention.

The membrane may be in the form of a relatively thin sheet of material arranged on, or in, the device and may have any appropriate shape, for example a circular shape. In an exemplary set of embodiments the membrane is made from a low density plastic film, e.g. polyethylene terephthalate.

The membrane may be integral to the body. For example, the membrane may be integrally moulded with the body, or the body may be milled in order to form the membrane. However, the Applicant has recognised that integrally providing the membrane with the body may be complicated to manufacture. In a set of embodiments, the membrane is a separate component attached to the body. In a further set of embodiments the body defines a circumferential rim to which the membrane is attached. This may allow for more simple manufacture of the body. Additionally, it may allow the body and the membrane to be manufactured from different materials which may be necessary in order to provide a sound path having the required acoustic response.

In a set of embodiments, the membrane is circular. It has been appreciated by the Applicant that when the pressure exerted on the membrane changes, for example due to sound pressure changes, a membrane which is not perfectly flat or planar may produce undesirable‘clicking’ noises which are perceived by the user. These ‘clicking’ noises may be irritating and reduce the overall quality of the sound perceived by the user. Practically, it is difficult to ensure that a membrane is perfectly planar, due to limitations on accuracy of machining tools. Therefore, in a set of embodiments, the membrane comprises at least one corrugation. The introduction of a corrugation (e.g. a controlled raised portion of the membrane) may help to control the production of the membrane, and thus the clicking noises perceived by the user.

In a set of embodiments, the corrugation comprises a ridge. In a potentially overlapping set of embodiments, the corrugation comprises an indentation.

Depending on the orientation of the membrane, an identical corrugation could be described as either a ridge or an indentation. Preferably the maximum height of the ridge above or depth of the indentation below the plane of the membrane is in the range of 0.02 mm to 2 mm e.g. 0.1 mm to 1 mm e.g. 0.3 mm.

In a set of embodiments, the corrugation is circular and centred on the geometric centre of the membrane. The ridge or indentation preferably has a uniform cross- section (e.g. the circular corrugation has a constant cross-section throughout the circumference of the circle formed).

In a set of embodiments, the adjustable membrane comprises a plurality of corrugations. Different corrugations, or different subsets of the corrugations within the plurality of corrugations, may have different shapes and sizes. However, preferably the plurality of corrugations all have the same shape. Corrugations which are uniform in shape may deform similarly under the same pressure. Therefore, implementing a plurality of uniform corrugations (especially in combination with a uniform arrangement of corrugations on the adjustable membrane) may help to avoid undesirable‘clicking’ noises.

The Applicant has envisaged a particular arrangement in which the plurality of corrugations comprises a subset of circular ridges and subset of circular indentations, which may be centred on the geometric centre of the membrane. The various circular indentations and ridges would have various diameters, and therefore could be arranged at various distances (i.e. locations) from the geometric centre of the adjustable membrane. The circular indentations and ridges may be arranged to alternate, e.g. if the innermost circular corrugation is an indentation, the second innermost circular corrugation is a ridge, the third innermost circular corrugation is an indentation etc. However, in a set of embodiments the corrugation is a spiral. The spiral may be centred on the geometric centre of the membrane and may extend to across between 60-90% of the diameter of the membrane in embodiments in which the membrane is circular. The spiral is preferably formed from a single arm spiral.

Research has shown that the spiral corrugation may be a more effective shape for reducing undesirable‘clicking’ noises compared with other corrugation shapes e.g. circular corrugations.

Whilst the corrugation can be provided in any suitable and desired way, in a set of embodiments the corrugation is stamped into the membrane. Preferably the membrane is essentially planar (e.g. in the plane perpendicular to the central axis of the adjustable member) and smooth, apart from the corrugations.

In embodiments comprising a user operable member to operate at least part of the adjustment arrangement, when a user hears, or expects to hear, a particular type of sound, they may operate the user operable member to adjust the adjustment arrangement and thus alter the acoustic response of the at least one sound path. Such a set of embodiments may be suitable for achieving a relatively inexpensive device. In a set of embodiments, however, the device further comprises a controller arranged to control the adjustment arrangement so as to alter the acoustic response of the at least one sound path. The inclusion of a controller may allow the device to control the adjustment arrangement in a more sophisticated manner in order to provide the most appropriate acoustic response of the sound path. It may, for example, try to achieve the highest sound quality whilst providing the necessary amount of attenuation. The controller may comprise a series of other components connected thereto or integrally provided therewith, for example a microphone or a transceiver. Such a set of embodiments may also advantageously automatically adjust the acoustic response of the sound path based on a detected sound environment in which the device is present. Additionally, or alternatively, the device may comprise a user input, e.g. in the form of at least one button, which enables the user to control operation of the device. This may, for example, allow a user to select a particular mode of operation.

The Applicant has appreciated that an arrangement comprising a barrier member is novel and inventive in its own right. Therefore, according to a second aspect of the invention, there is provided a device for insertion into an ear canal of a mammalian subject, comprising:

a body, having at least one sound path extending therethrough;

a first, adjustable acousto-mechanical portion comprising a barrier member arranged to alter an acoustic response of the at least one sound path; and

a second acousto-mechanical portion, arranged acoustically in series with the first adjustable acousto-mechanical portion, comprising a membrane.

Some preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 shows an isometric view of a device in accordance with an embodiment of the present invention;

Fig. 2 shows a view of the underside of the device seen in Fig. 1 ;

Fig. 3 shows an exploded view of the device seen in Fig. 1

Figs. 4a-4b show the actuation member, which forms part of the device in Fig. 1 , in isolation;

Fig. 5 shows a piston, which forms part of the device seen in Fig. 1 , in isolation;

Fig. 6 shows part of the body of the device seen in Fig. 1 in isolation;

Fig. 7 shows part of the body, of the device seen in Fig. 1 , along with the membrane;

Figs. 8a-8b are illustrations demonstrating how the relative position of the piston in the cavity adjusts the channel;

Fig. 9a-9b show a cross-sectional view through the device seen in Fig. 1 in an open configuration;

Figs. 10-10b show perspective views of the device seen in Fig. 1 in a closed configuration;

Figs. 11 a- 11 b show cross-sectional views through the device in the closed configuration;

Fig. 12 shows a perspective view of a device in accordance with a second embodiment of the present invention;

Figs. 13a-13b show cross-sectional views of the device seen in Fig. 12, in an open configuration;

Figs. 14a-14b show cross-sectional views of the device seen in Fig. 12 in a closed configuration; Fig.15a-15b show cross-sectional views of a device in accordance with a third embodiment of the present invention;

Fig. 16a shows a perspective view of the device shown in Figs. 15a-15b;

Fig. 16b shows an isolated view of the membrane forming part of the device shown in Figs. 15a-15b;

Figs 17a-17b show cross-sectional views of the device shown in Figs. 15a-15b in an open configuration; and

Figs. 18a-18b show cross-sectional views of the device shown in Fig. 15a-15b. in a closed configuration; and

Fig. 19 is a graph showing frequency response of an embodiment of the invention compared to those for some prior art earplugs.

Figure 1 shows an isometric view of a device in accordance with an embodiment of the present invention. The device includes a body 2 comprising a first, adjustable acousto-mechanical portion in the form of an adjustable channel 4. The channel 4 is defined by the space between the wall of a cavity 6 and a piston 8 which extends into the cavity 6. The piston 8 is arranged to move axially within the cavity 6 and is mounted to the body 2 by four resilient arms 10 which are received in appropriately shaped arm receiving portions 12 provided on the body 2. The piston 8 further comprises a ridge 14, the purpose of which will become apparent with discussion of later Figures.

The device further comprises an actuation member 16, which forms part of an adjustment arrangement, arranged to move the piston 8 axially within the cavity 6. The actuation member 16 comprises a cylindrical boss 20 for rotatably mounting the actuation member 16. The cylindrical boss 20 is received in an appropriately shaped socket (not shown in the Figures). The actuation member 16 comprises a set of two inclined cam surfaces 22, one of which can be seen in this Figure. The other cam surface 22 is arranged opposite the cam surface 22 seen in this Figure. The cam surfaces 22 interact with the ridge 14 on the piston 8 which acts as a follower to convert rotation of the actuation member 16 into axial movement of the piston 8. This will be described in more detail below. The actuation member 16 further comprises an actuation portion 24 which may be acted upon to drive rotation of the actuation member 16. This actuation portion 24 may, for example, be acted on directly by a user. Accordingly, in this embodiment, the actuation member 16 comprises an integrated user operable member. Of course, as will be appreciated by those skilled in the art, the actuation member 16 may alternatively be driven by an electric motor.

Figure 2 shows a view of the underside of the device seen in Figure 1. Arranged at the base of the body 2 is a second acousto-mechanical portion in the form of a membrane 26. The membrane 26 is bonded to a rim 28 of the body 2.

Figure 3 shows an exploded view of the device seen in Figure 1. Starting from the top, there is shown the actuation member 16 and piston 8. In this particular embodiment, the body 2 has a two-part construction comprising a first part 2a and second part 2b, although it will be recognised that a one-part construction could be used instead. These two parts are secured together using any appropriate means, e.g. gluing.

Figures 4a and 4b show a view of the actuation member 16 in isolation from the other components of the device. The inclined cam surfaces 22 can be seen more clearly in these Figures. Fig. 4b shows a view of the underside of the actuation member 16 and shows the presence of both cam surfaces 22 on the underside of the actuation member 16.

Figure 5 shows an isometric view of the piston 8 in isolation from the other component of the device. The lowermost portion 40 of the piston 8, which extends into the cavity 6 when the device is assembled, is frustoconically shaped and has a corresponding shape to the cavity 6 (seen in Figure 6). As will be appreciated by those skilled in the art, the cavity 6 and lowermost portion 40 of the piston 8 which have a complementary frustoconical shape create an annular channel 4 with a uniform shape and reducing diameter along its length. The ridge 14 extends linearly along the top of the piston and is arranged to interact with the cam surfaces 22 on the actuation member 16 seen in earlier Figures.

Figure 6 shows an isometric view of the upper part 2a of the body 2 in isolation. It can be seen more clearly in this Figure how the cavity 6 has a frustoconical shape. At the base of the cavity 6 is an aperture 42 through which at least part of the piston 8 may extend. This aperture 42 allows sound to more freely pass out through the cavity 6 into the rest of the device.

Figure 7 shows a view of the underside of the lower part 2b of the body 2 along with the membrane 26. The internal ledge 38 of the lower part 2b of the body 2 seen in Figure 3, also defines an external rim 28 to which the membrane 26 is bonded when the components are assembled. As will be appreciated by those skilled in the art, the external rim 28 is relatively large when compared to the size of the membrane 26 and thus provides a substantial surface area on the lower part 2b of the body 2 on which to bond the membrane 26. This may help to ensure that the membrane 26 is securely bonded to the lower part 2b of the body 2.

Figures 8a-8b are illustrations demonstrating how the position of the piston 8 in the cavity 6 can be used to adjust the channel 4. When the piston 8 is in the position seen in Figure 8a, the channel 4 has a length shown by arrow 46 and a width shown by arrow 48. As demonstrated by Figure 8b, when the piston 8 is moved axially into the cavity 6, the length of the channel shown by arrow 46 and the width of the channel shown by arrow 48 are both changed. Accordingly, changing the axial position of the piston 8 relative to the cavity 6 will adjust the channel 4. As will be appreciated by those skilled in the art, adjusting the dimensions of the channel 4 will serve to alter the acoustic response of the channel 4 and thus alter the acoustic response of the sound path. More specifically the width, d, of the channel is related to the acoustic loss and the acoustic mass of the channel. Under the electrical circuit analogy for analysis of acoustic systems which will be familiar to those skilled in the art, the acoustic loss is equivalent to a resistance R and has an inverse cube relationship to the channel width as shown below:

where ki is a constant representing parameters assumed to remain constant such as air density and dimensions.

Under the same electrical analogy, the acoustic mass is equivalent to an inductance, L and has an inverse relationship to the channel width, d: where k2 is a constant representing parameters assumed to remain constant such as air density and dimensions. The resistance R and the inductance L are both directly proportional to the length of the channel.

The device seen in the earlier Figures may form part of a device which is inserted into the ear canal of a mammalian subject. For example, the device may be embedded within a foam, or other appropriate material, insert which is suitably shaped for insertion into the ear canal of a mammalian subject. The insert may be a standard insert which is suitable for a variety of different ear shapes, or alternatively it may be a custom moulded insert which is specific for a particular user. Operation of the device will now be described with reference to Figures 1-8. In use, when inserted into the ear of a mammalian subject, the device is arranged such that the membrane 26 is proximal to a user’s eardrum and the actuation member 16 projects outwards from the user’s ear. This is not essential to the invention and other embodiments are envisaged in which the order of the channel and the membrane is reversed Accordingly, sound will pass through the channel 4 and subsequently through the membrane 26 into a user’s ear canal.

The actuation member 16 may be used to control the position of the piston 8 in order to control the acoustic response of the sound path through the device. As the actuation member 16 is held in a fixed axial position, when the actuation member 16 is rotated, the cam surfaces22 acts on the ridge 14 thereby forcing the piston 8 axially downwards into the cavity 6. The piston 8 is prevented from rotating due to the resilient arms 10 being received in the receiving portions 12 on the body 2. The resilient arms 10 also allow the piston 8 to move axially downwards into the cavity 6. As will be appreciated by those skilled in the art, as the piston 8 is moved into the cavity 6, the length of the channel 4 will change, and its cross section will reduce, as demonstrated earlier in Figures 8a-8b. Adjusting the length and cross-sectional area of the channel 4 alters the acoustic response of the sound path through the device. Changing the acoustic response of the sound path will alter the sound heard by a user of the device. As will be appreciated by those skilled in the art, with this embodiment the piston 8 may be driven to any one of a large number of positions between the channel 4 being in a fully‘open’ position and the channel being in a fully‘closed’ position. Figures 10a and 10b show the device with the piston in the fully open position and Figures 11a, 11b, 12a and 12b show the device with the piston in the fully closed position. This alters the acoustic resistance, inductance and capacitance as previously explained

Figures 9a and 9b show a cross-sectional view through the device with the piston 8 in the position seen in Figure 1 , i.e. in a fully open position, with Figure 9a showing the device side-on and Figure 9b showing the device in isometric view. The arrows 52 represent the sound path through the device. As can be seen in each of these Figures, sound enters the device and passes through the channel 4. The sound then propagates towards, and passes through, the membrane 26. These Figures also more clearly show how the channel 4 has a frustoconical shell shape due to the frustoconical cavity 6 and the frustoconical piston 8.

Figures 10a and 10b show two different isometric views of the device in a second ‘closed’ configuration. In this configuration the actuation member 16 has been rotated relative to the body 2 so as to drive the piston 8 downwards by its maximum amount. As the piston 8 is moved downwards, the resilient arms 10 deform to permit this movement. As can be seen most clearly in Figure 10b, the actuation member 16 has been rotated by a sufficient amount that the graduated drive portion 22 has moved past the ridge 14 on the piston 8 and the ridge 14 now rests against a flat portion 54 on the actuation member 8. As will be appreciated by those skilled in the art, once the ridge 14 rests against the flat portion 54 it can not be driven any further downwards.

Figures 11a and 11b show cross-sectional views through the device in the closed position. The piston 8 has been moved down to a position in which the channel 4 is completely closed. In this position, the sound 52 will no longer be able to pass through the channel 4 and the device may completely, or at least substantially, prevent any sound from passing therethrough. With reference to earlier Figures, as will be appreciated by those skilled in the art, when it is desired to re-open, at least partially, the channel 4, a user may rotate the actuation member 16 in the opposite direction. The resilient arms 10 will bias the piston 8 axially upwards out of the cavity 6 so as to re-open the channel 4.

Figure 12 shows an isometric view of a device in accordance with a second embodiment of the present invention. The device comprises a body 102 comprising an upper part 102a and lower part 102b. Figure 13a shows a cross-sectional view through the device seen in Figure 12. The device comprises many of the same components as the device seen in Figure 1 including a channel 104 which is defined by the space between a cavity 106 and a piston 108. A membrane 126 is bonded to the base of the lower body 102b. The device according to this embodiment differs from the first embodiment, seen in Figure 1 , in that the piston 108 is rotatably mounted in the body 102. The piston 108 comprises an external thread 156 which engages with a corresponding threaded portion 158 on the body 102. Accordingly, as will be appreciated by those skilled in the art, when the piston 108 is rotated, it is caused to advance into, or be drawn out of, the cavity 106. The direction of rotation of the piston 108 will dictate whether it is advanced into, or drawn out of, the cavity 106. The top of the piston 108 is provided with a rectangular slot 160. A drive shaft, for example connected to a motor, (not shown in this Figure), may be inserted into the slot 160 in order to drive rotation of the piston 108. In the view shown in Figure 13a, the device is in an‘open’ configuration in which the sound path 152 is open to allow sound to pass through the device.

Figure 13b shows the device according to the second embodiment in cross- sectional view when viewed side-on. A motor 162 and drive shaft 164, which is inserted into the key hole 160, may be used to drive rotation of the piston 108 and thus advance it into, and draw it out of, the cavity 106.

Figures 14a and 14b show cross sectional views through the device in a‘closed’ configuration, with the motor 162 and drive shaft omitted. In this configuration the piston 108 has been advanced into the cavity 106 such that the channel 104 is now closed. As a result, sound can no longer pass through the channel 104 and thus the device will significantly attenuate any incident sound.

Of course, as will be appreciated by those skilled in the art, the piston 108 may be moved to any intermediate position between the open and closed positions seen in Figures 13a-13b and 14a-14b, in order to achieve a desired acoustic response of the sound path.

In both of the embodiments described above, the mechanisms for moving the piston allow for it to take up intermediate positions between the two ends of its travel. However this is not essential and many other mechanisms may be envisaged which restrict the piston to two or more discrete positions.

Figures 15a-15b show cross-sectional views of a device in accordance with a third embodiment of the present invention, comprising a body 202 formed from an upper part 202a and a lower part 202b. The device also comprises a membrane (see Figures 16a and 16b) and a lid 208. In Figure 15a the lid is shown in an open configuration, in which sound is allowed to pass through the device to be attenuated solely by the membrane. In Figure 15b the lid is shown in a closed configuration, in which sound is largely attenuated by the lid. A hinge (not shown) is provided to allow the lid to be moved, either manually or automatically, from the open to the closed position (and vice versa).

Figure 16a shows another perspective view of the device seen in Figures 15a-15b, showing a membrane 226 attached to the lower part 202b of the body. The membrane 226 includes a spiral corrugation 230. The spiral corrugation 230 is in the form of a hollow ridge extending out of the plane of the otherwise planar membrane 226. The detail of the membrane 226 and the spiral corrugation 230 can be seen in more detail in Fig. 16b, which shows an isolated view of the membrane forming part of the device shown in Figure 16a. The spiral corrugation 230 originates at the geometric centre of the circular membrane 226, ending close to the rim (not shown).

Figures 17a-17b and 18a-18b show additional cross-sectional views of the device shown in Figures 15a-15b and 16a-16b. Figures 17a and 17b in particular show cross-section views through the device with the lid 208 in an open position, with Figure 18a showing the device side-on and Figure 17b showing the device in an isometric view. The arrows 252 represent the sound path through the device. As can be seen in each of these Figures, sound enters the device though and passes along a channel 204. The sound then propagates towards, and passes through, the membrane 226.

The spiral corrugation on the membrane 226 helps to reduce undesirable‘clicking’ noises which may be perceived by the user when the pressure exerted on the membrane by sound 252 changes.

Figures 18a and 18b in particular show cross-section views through the device in the closed configuration, with Figure 18a showing the device side-on and Figure 18b showing the device in an isometric view. In this configuration, the lid 208 is closed. The sound 252 is inhibited from being able to pass through the channel 204 and the device will therefore provide greater attenuation.

Fig. 19 shows a graph comparing the frequency response of an embodiment of the invention to those of three prior art passive earplugs. The graph shows the relationship between the frequency on the horizontal axis and attenuation on the vertical axes. Both axes have logarithmic scales. The attenuation shown is that relative to the natural, unimpeded frequency response of the human aural system.

It therefore takes into account the well-known typical variation of sensitivity that humans have dependent on frequency.

The uppermost substantially horizontal plot 170a corresponds to an embodiment of the invention similar to that described above with the piston almost fully open. As may be seen the attenuation provided is essential constant across the frequency spectrum. This means that a user will experience sounds naturally. Similarly plot 170b shows the situation when the piston is half-closed. Here a greater attenuation is provided but it is still substantially constant with frequency. The lowermost plot shows the response when the piston is almost closed. Here the attenuation is at a maximum (approximately 25 dB) but remains substantially constant with frequency. Of course in a more simplified embodiment only open and closed positions might be provided.

By contrast plots 172, 174 and 176 show respective frequency responses for a typical passive earplug which has been inserted into a user’s ear canal to differing degrees. The uppermost plot 172 represents the earplug being inserted by the least amount (significantly less than it is intended to be). This means that at low frequencies there is almost no attenuation at all (which could be dangerous). The other plots 174, 176 show that earplug being inserted more fully and therefore being more effective. However, as may be seen, there is a substantial increase in attenuation with frequency in all three cases meaning that higher frequency sounds are disproportionately filtered out compared to lower frequencies. The result of this is that the user experiences sounds as muffled which may lead to problems with intelligibility of speech when listening to co-workers for example. This might encourage the user to remove the earplug or not to insert it properly, thereby making it less effective than it might be.

Claims

1. A device, for insertion into an ear canal of a mammalian subject, comprising: a body, having at least one sound path extending therethrough;

a second acousto-mechanical portion, arranged acoustically in series with the first adjustable acousto-mechanical portion, comprising a membrane; and

an adjustment arrangement for adjusting the first, adjustable acousto- mechanical portion to alter an acoustic response of the at least one sound path.

2. The device as claimed in claim 1 , wherein the adjustment arrangement comprises an actuator for adjusting the first adjustable acousto-mechanical portion.

3. The device as claimed in claim 2, wherein the actuator comprises a user operable member arranged to operate at least part of the adjustment arrangement.

4. The device as claimed in claim 3, wherein the user operable member comprises a rotatable knob arranged to adjust the first, adjustable acousto- mechanical portion.

5. The device as claimed in any preceding claim, wherein the channel comprises an adjustable barrier member.

6. The device as claimed in claim 5, wherein the barrier member comprises an adjustable closure.

7. The device as claimed in claimed in claim 5 or 6, wherein the adjustment arrangement enables adjustment of a position of the barrier member.

8. The device as claimed in any one of claims 5 to 7, wherein the barrier member has at least an open position and a closed position.

9. The device as claimed in any preceding claim, wherein the adjustment arrangement is configured to adjust a length and/or width of the adjustable channel.

10. The device as claimed claim 9, wherein the channel is defined by a space between a wall of a cavity within the body and a piston arranged in the cavity, wherein adjustment of the channel is achieved by moving the piston relative to the cavity.

11. The device as claimed in claim 10, wherein the piston is arranged such that it can be held stable in a plurality of different positions in the cavity.

12. The device as claimed in claim 10 or 11 , wherein the cavity and the piston each have a frusto-conical shape such that the adjustable channel has the form of a frusto-conical shell.

13. The device as claimed in any preceding claim, wherein the first, adjustable acousto-mechanical portion can only adopt a plurality of discrete positions.

14. The device as claimed in any preceding claim, wherein the membrane is a separate component attached to the body and the body defines a circumferential rim to which the membrane is attached.

15. The device as claimed in any preceding claim, wherein the membrane comprises at least one corrugation.

16. The device as claimed in claim 15, wherein the corrugation comprises a ridge and/or an indentation.

17. The device as claimed in claim 15 or 16, wherein the corrugation is a spiral.

18. The device as claimed in any preceding claim further comprising a controller arranged to control the adjustment arrangement so as to alter the acoustic response of the at least one sound path.

19. The device as claimed in any preceding claim further comprising a user input arranged to enable a user to control operation of the device.

20. A device for insertion into an ear canal of a mammalian subject, comprising: a body, having at least one sound path extending therethrough;