GB1586432A - Method of producing an ear insert for a hearing aid - Google Patents

Description

(54) A METHOD OF PRODUCING AN EAR INSERT FOR A HEARING AID (71) We, THE VICTORIA UNIVER SITY OF MANCHESTER, a British Institution constituted according to Royal Charter, of Oxford Road, Manchester, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of producing an ear insert for a hearing aid, and to an ear insert produced by the said method.

There are two principal kinds of hearing aid known respectively as "body-worn" and "post-aural" hearing aids. In both cases a piece for insertion into the ear of the wearer is produced by moulding a material as near as possible to the inner shape of the ear. In the case of a body-worn aid, a telephonic receiver is attached directly to the ear insert and is connected by a lead to an amplifier usually attached to the wearer's clothing. In the case of a post-aural aid, an acoustic tube passes through the ear mould and is connected to a miniaturised amplifier usually located behind the ear.

The ear insert is usually formed of a rigid material, for example. an acrylic resin, for example, polymethyl-methacrylate which may contain some colouring matter for cosmetic purposes. This may be formed either in a two-stage process from monomeric material. or bv a one stage cold-cure process from a mixture of monomeric material and polymer in powder form. In the two stage process the initial impression is taken using a pliable material.

from which a mould is made for subsequent casting. Normally the casting stage of the process must be carried out at a location remote from that where the impression was taken so that a considerable delav may be experienced before the ear insert is available for use. This delav can be particularly disadvantageous when the ear insert is being produced for a child, as growth may take place in the shape of the child's ear before the insert is ready, so that even when new the insert is a poor fit and of poor acoustic efficiency. In any case, the use of such rigid materials where growth of the ear is rapid results in discomfort and the necessity for frequent renewal.

The alternative one-stage process in which the material is moulded and cured in the ear, suffers from the disadvantage that the curing process is exothermic to a degree which can cause acute discomfort and anxiety, particularly in young patients. There is also the danger that the insert may be removed before the cold curing process is completed which can result in distortion of the insert, and, again, a poor fit.

It is important that the ear insert should fit the ear as closely as possible so that there is minimum leakage of sound around the insert thus reducing the likelihood of acoustic feedback to the amplifier. Therefore, the better the fit of the ear insert the better the acoustic efficiency of the device as a whole, and in cases of very poor hearing, the amplifier must be capable of being set to a high level of amplification without incurring the audible squeal created by acoustic feedback.

An object of the present invention is to provide a method of producing an ear insert for a hearing aid, wherein the insert is produced rapidly using simple equipment, whilst ensuring minimal discomfort and anxiety to the wearer and resulting in an insert of improved acoustic efficiency.

According to the present invention there is provided a method of producing an ear insert for a hearing aid, comprising the steps of inserting into the wearer's ear a plug of a cold-curing resilient material. for example, silicone rubber in an uncured pliable state and working same into the meatal canal; forming a plug of a cold-curing material which cures to a substantially rigid state, for example, an acrylic resin and inserting same, or a former representing same, into the ear after the resilient material before the latter has cured so that the two materials take up complementary mating surfaces one with the other; removing the whole from the ear after the resilient material has cured; bonding the resilient and rigid materials together to form a two-part ear insert and forming a passage through the entire ear insert to define an acoustic channel therethrough.

Preferably, said plug of rigid material is formed by providing the material in an uncured pliable state and working same against the yet uncured plug of resilient material and against the walls of the outer part of the ear, said two plugs being removed from the ear after both materials have completely cured.

Further according to the invention, there is provided an ear insert for a hearing aid, comprising an inner part of a resilient material; for example, silicone rubber bonded to an outer part of a substantially rigid material, for example. an acrylic resin; there being a passage defining an acoustic channel through the entire ear insert.

Several embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure I is a section through an ear insert for a body-worn hearing aid, and illustrating a telephonic ear piece attached thereto; Figure 2 is a section through a similar ear mould for use with a post-aural hearing aid; Figure 3 is a section through an ear mould being a modification of that shown in Figure 1.

Referring now to Figures 1 and 2. and with consideration as to the method by which the ear insert is produced. a plug of resilient material. for example. silicone rubber in an uncured pliable state is placed in and worked into the meatal canal of the wcarer's ear. thus producing an inner portion of an ear insert as illustrated at 10. The material used is of the cold-curing kind wherein little or no discernible heat is generated whilst curing. After the silicone rubber. a plug of another cold-curing mate rival, for example. an acrylic resin or other polymer is inserted. which material is work ablc before curing but cures to a rigid state, and this is worked against the walls of the outer part of the ear and against the softer material so that the two materials take up complementary mating surfaces. one with the other. thus to produce the portion illustrated at l 11 . This natilial is of the kind which does generate some heat whilst curing. but being disposed in the outer part of the ear produces little or no discomfort.

After the two materials have cured the two-part insert is removed from the ear and an adhesive, for example, cyanoacrylate glue or a silicone rubber adhesive is used to bond them together.

At this stage, or alternatively before the materials are bonded together, a passage is punched or bored through both materials and a length of P.V.C. or nylon tubing is inserted as illustrated at 12 to define an acoustic channel which extends through the ear insert between the inner and outer extremities thereof.

In the case of a body-worn hearing aid a recess 13 (see Figure 1) within the portion 11 is formed, for example, by placing a recess tool in the material prior to curing. A ring 14 of metal or nylon is inserted after curing using a heated tool to heat the ring and so soften the surrounding material.

Alternatively, the ring 14 can be inserted after curing by dividing a recess and fitting the ring using the heated tool as described above. As a further alternative the portion 11 may be reamed out to receive the ring 14 which is then applied using an adhesive.

Finally, the outer surface of the portion 11 is machined to lie flush with the ring 14 so that the finished mould can receive a telephonic ear piece as shown at 15, the central projection 16 thereof being removably located as a push fit within the ring 14.

The ear piece 15 is electrically connected by a removable lead 17 to an amplifier usually worn upon the wearer's clothing.

In the case of a post-aural hearing aid, the ear insert is produced as illustrated in Figure 2. That is, the acoustic tube passes through the entire insert and extends therefrom as shown at 18 to be connected to the amplifier which is normally located behind the ear.

Referring now to Figure 3, in an alternative method of producing an ear insert for a body-worn hearing aid. the plug of rigid material is made and cured remote from the ear by moulding the material to form a shaped plug as indicated at 20. The resilient portion 10 is impressed whilst curing by the plug 20 itself or by a similarly-shaped former, so that after curing, the mating surfaces of the portion 10 and the plug 20 can be securelv bonded. The undercut form of the impression in the portion 10 which results in the plug 20 being almost complete lv bounded bv the portion 11 serves to produce a good bond and assists in retaining the plug in place. Once again, the ring 14 for locating the receiver projection 16, is fixed in place.

This embodiment may be adopted in cases where the rigidity of the outer part of the insert is not so important and where the in-situ curing of the polymethylmethacrylate is undesirable. However, an ear insert pro duced in accordance with this embodiment is of reduced strength in the outer region where thickness is also reduced.

Tests have been carried out with the various kinds of ear insert already available for hearing aids when compared with the insert made in accordance with this invention. In the tests the maximum output of the amplifier which could be achieved before acoustic feedback occurred was compared, one ear insert against another. In the case of the acrylic resin insert, whether prepared by the one stage cold-cure process or the two-stage process which involves a preformed insert of pliable material, the figures were between 110 dB and 115dB. In contrast, the ear insert made from the two-part construction of silicone rubber and a backing of polymethylmethacrylate, and produced in accordance with the invention produced a figure of 127dB. Thus it can be seen that greater levels of amplification can be achieved with an ear insert made in accordance with the present invention.

Furthermore, the soft nature of the silicone rubber provides an increased level of comfort for the wearer, whilst the harder backing material which is used in the outer part where the dimensions of the insert are greater serves to strengthen the insert as a whole. In addition, in the case of a bodyworn hearing aid, the metal or nylon ring used to locate the telephonic receiver can be anchored firmly in the rigid material and is prevented from falling out when the receiver is removed.

The completed ear insert is preferably coated with a flexible varnish to provide a smooth surface texture which can be readily cleaned.

The process in accordance with the invention is simplified to the extent that an ear insert can be produced rapidly by relatively inexperienced personnel thus the means for carrying out the process can be made available in the form of a kit comprising a supply of silicone rubber in an uncured pliable state, a separate supply of acrylic resin in an uncured state, and a further separate supply of an adhesive for bonding the materials together when cured.

It is not intended to limit the invention to the above examples only, many variations such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention as defined by the appended claims.

For example. the acoustic tube 12 can be placed in the insert whilst the materials thereof are still not fully cured, thus rendering the insertion of the tube easier. Furthermore, if required. in the case of a bodyworn hearing aid. the telephonic receiver can be permanently fixed to the outer surface of the portion' 11 or 20 of the insert, or alternatively the operative parts thereof can be integrally moulded into the portion 11 or 20, the lead 17 being arranged to connect electrically to the portion 11 or 20.

With the ever-increasing miniaturisation of electronic circuitry, it is conceivable that the whole of the amplification system can be moulded within the rigid portion of the ear insert.

WHAT WE CLAIM IS: 1. A method of producing an ear insert for a hearing aid, comprising the steps of inserting into the wearer's ear a plug of a cold-curing resilient material, for example, silicone rubber in an uncured pliable state and working same into the meatal canal; forming a plug of a cold-curing material which cures to a substantially rigid state, for example, an acrylic resin, and inserting same, or a former representing same, into the ear after the resilient material, before the latter has cured, so that the two materials take up complementary mating surfaces one with the other; removing the whole from the ear after the resilient material has cured; bonding the resilient and rigid materials together to form a two-part ear insert, and forming a passage through the entire ear insert to define an acoustic channel therethrough.

2. A method according to claim 1, wherein said plug of rigid material is formed by providing the material in an uncured pliable state and working same against the yet uncured plug of resilient material and against the walls of the outer part of the ear, said two plugs being removed from the ear after both materials have completely cured.

3. A method according to claim 1 or claim 2, wherein a recess is formed in said rigid material to receive a projecting member of a telephonic receiver.

4. A method according to claim 3, wherein a locating member is permanently fixed within said recess, removably to receive said projecting member.

5. A method according to any one of claims 1 to 4, wherein a length of tubing is located in said passage and extends from the outer surface of the ear mould to be attached to an amplifier.

6. A method according to any one of claims 1 to 5. wherein the materials are bonded using a cyanoacrylate glue.

7. A method according to claim 1, wherein said rigid material is made and cured remote from the ear to form a shaped plug, and the plug of resilient material is impressed whilst curing by the cured plug itself.

8. An ear insert for a hearing aid, comprising an inner part of a resilient material. for example, silicone rubber, shaped to fit into an ear and bonded to an outer part of a substantially rigid material,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. duced in accordance with this embodiment is of reduced strength in the outer region where thickness is also reduced. Tests have been carried out with the various kinds of ear insert already available for hearing aids when compared with the insert made in accordance with this invention. In the tests the maximum output of the amplifier which could be achieved before acoustic feedback occurred was compared, one ear insert against another. In the case of the acrylic resin insert, whether prepared by the one stage cold-cure process or the two-stage process which involves a preformed insert of pliable material, the figures were between 110 dB and 115dB. In contrast, the ear insert made from the two-part construction of silicone rubber and a backing of polymethylmethacrylate, and produced in accordance with the invention produced a figure of 127dB. Thus it can be seen that greater levels of amplification can be achieved with an ear insert made in accordance with the present invention. Furthermore, the soft nature of the silicone rubber provides an increased level of comfort for the wearer, whilst the harder backing material which is used in the outer part where the dimensions of the insert are greater serves to strengthen the insert as a whole. In addition, in the case of a bodyworn hearing aid, the metal or nylon ring used to locate the telephonic receiver can be anchored firmly in the rigid material and is prevented from falling out when the receiver is removed. The completed ear insert is preferably coated with a flexible varnish to provide a smooth surface texture which can be readily cleaned. The process in accordance with the invention is simplified to the extent that an ear insert can be produced rapidly by relatively inexperienced personnel thus the means for carrying out the process can be made available in the form of a kit comprising a supply of silicone rubber in an uncured pliable state, a separate supply of acrylic resin in an uncured state, and a further separate supply of an adhesive for bonding the materials together when cured. It is not intended to limit the invention to the above examples only, many variations such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention as defined by the appended claims. For example. the acoustic tube 12 can be placed in the insert whilst the materials thereof are still not fully cured, thus rendering the insertion of the tube easier. Furthermore, if required. in the case of a bodyworn hearing aid. the telephonic receiver can be permanently fixed to the outer surface of the portion' 11 or 20 of the insert, or alternatively the operative parts thereof can be integrally moulded into the portion 11 or 20, the lead 17 being arranged to connect electrically to the portion 11 or 20. With the ever-increasing miniaturisation of electronic circuitry, it is conceivable that the whole of the amplification system can be moulded within the rigid portion of the ear insert. WHAT WE CLAIM IS:

1. A method of producing an ear insert for a hearing aid, comprising the steps of inserting into the wearer's ear a plug of a cold-curing resilient material, for example, silicone rubber in an uncured pliable state and working same into the meatal canal; forming a plug of a cold-curing material which cures to a substantially rigid state, for example, an acrylic resin, and inserting same, or a former representing same, into the ear after the resilient material, before the latter has cured, so that the two materials take up complementary mating surfaces one with the other; removing the whole from the ear after the resilient material has cured; bonding the resilient and rigid materials together to form a two-part ear insert, and forming a passage through the entire ear insert to define an acoustic channel therethrough.

2. A method according to claim 1, wherein said plug of rigid material is formed by providing the material in an uncured pliable state and working same against the yet uncured plug of resilient material and against the walls of the outer part of the ear, said two plugs being removed from the ear after both materials have completely cured.

3. A method according to claim 1 or claim 2, wherein a recess is formed in said rigid material to receive a projecting member of a telephonic receiver.

4. A method according to claim 3, wherein a locating member is permanently fixed within said recess, removably to receive said projecting member.

5. A method according to any one of claims 1 to 4, wherein a length of tubing is located in said passage and extends from the outer surface of the ear mould to be attached to an amplifier.

6. A method according to any one of claims 1 to 5. wherein the materials are bonded using a cyanoacrylate glue.

7. A method according to claim 1, wherein said rigid material is made and cured remote from the ear to form a shaped plug, and the plug of resilient material is impressed whilst curing by the cured plug itself.

8. An ear insert for a hearing aid, comprising an inner part of a resilient material. for example, silicone rubber, shaped to fit into an ear and bonded to an outer part of a substantially rigid material,

for example, polymethyl methacrylate; there being a passage defining an acoustic channel through the entire ear mould.

9. An ear insert according to claim 8, wherein a recess is formed in said outer part and has a locating member permanently fixed therein, removably to receive a projecting member of a telephonic receiver.

10. An ear insert according to claim 8, wherein a length of tubing is disposed in said passage and extends from the outer surface of the ear insert to be attached to an amplifier.

11. An ear insert according to claim 8, wherein said outer part is a pre-formed plug located and bonded within a similarly shaped recess in said inner part thus to be substantially bounded by the latter, said plug containing a locating member for a telephonic receiver.

12. A method of producing an ear insert for a hearing aid, substantially as hereinbefore described.

13. An ear insert substantially as hereinbefore described, with reference to, and as illustrated in any one of Figures 1 to 3 of the accompanying drawings.