GB2229339A

GB2229339A - Acoustic transducer

Info

Publication number: GB2229339A
Application number: GB9005574A
Authority: GB
Inventors: Hans Woelfel
Original assignee: Microtel BV
Current assignee: Microtel BV
Priority date: 1989-03-14
Filing date: 1990-03-13
Publication date: 1990-09-19
Also published as: NL8900613A; JPH02274200A; GB9005574D0

Abstract

An acoustic transducer comprising - a box-shaped housing consisting of two housing sections 2,3 each comprising a rectangular base and four side walls and means for converting an electrical signal into an acoustic signal, including a membrane 30 extending substantially the entire area of a base of the housing and movably mounted in said housing by a flexible foil 40; - characterised in that said flexible foil 40 is secured to the inner sides of the four side walls of one of the housing sections, for example, by and adhesive. <IMAGE>

Description

Title: Acoustic transducer This invention relates to an acoustic transducer comprising: - a box-shaped housing consisting of two housing sections each comprising a rectangular base and four side walls positioned at right angles to the edges of the base, the two bases having substantially equal areas; - means for converting an electrical signal into an acoustic signal, including a membrane extending substantially the entire area of a base of the housing and movably mounted in said housing by a flexible means; and - an energizing means for setting the membrane into vibration under the influence of said electrical signal.

Such an acoustic transducer, which is capable of converting electrical signals into acoustic signals and the other way round, is known from U.S. Patent 3,573,397, and is used for example in a hearing aid. In it, the membrane is set into vibration in response to an electrical signal by an energizing means to generate sound waves which can leave the housing through an opening formed therein. The flexible means serves to secure the membrane within the housing in such a manner that a sound generating movement of the membrane is possible. For this purpose, in the known acoustic transducer, the flexible means is secured on the one hand to the circumference of the membrane, and on the other hand to a mounting plate, while there is further provided a second frame secured to a section of the housing, and to which the mounting plate is bonded.As a consequence, the prior acoustic transducer has a rather complex structure.

It is an object of the present invention to provide an acoustic transducer which has a simple structure and thus can be made at lower cost.

To this effect, the present invention provides an acoustic transducer of the above-defined kind, in which the flexible means is secured to the inner sides of the four side walls of one of the housing sections.

In a preferred embodiment of the invention, the flexible means has attachment portions, preferably portions bent over at right angles, extending parallel to corresponding sides of the housing sections, the flexible means being secured to the sides through said attachment portions.

To provide sufficient space for the attachment portions to be firmly secured to the side walls, the height of the inner sides of the housing section is preferably greater than the height of the attachment portions. This has the additional advantage that, in forming the flexible means, the starting product may be a flat piece of foil, made to size, on which the attachment portions can be formed, for example, by a thermal treatment. After the formation, these portions may exhibit ragged edges, which now require no trimming operation or the like owing to the overlap of the side walls of the housing section.

According to the invention, it is achieved in a simple way that the height of the inner sides of the housing section is greater than the height of the attachment portions when the height of one housing section is equal to that of the other housing section. In that case both housing sections can be formed using only one tool, it being additionally achieved that the two housing sections always fit accurately one on the other, even in the case of wear on the tool.

The invention further relates to a membrane provided with a flexible attachment means, evidently intended for use in an acoustic transducer according to this invention.

One preferred embodiment of the acoustic transducer according to this invention will now be describe, by way of example, wit preference to the accompanying drawings; in said drawings: Figure 1 is a perspective view of an acoustic transducer according to the present invention; Figures 2A-B show a cross-sectional view of the armature of the acoustic transducer shown in Figure 1; Figure 3 shows a longitudinal sectional view of the acoustic transducer of Figure 1, taken on the line III-III; and Figure 4 shows a detail of the cross-sectional view of Figure 3.

Figure 1 shows an acoustic transducer according to the present invention, generally designated by reference numeral 1. Transducer 1 comprises a first housing section 2 and a second housing section 3, each comprising a base 21, 31 and side walls 22, 23, 24, 25 and 32, 33, 34, 35, as also shown in Figure 3. The two sections 2, 3 have the same dimensions.

In the embodiment shown, lxbxh = 6.3x4.29x1.48 mm. Secured to the first housing section 2 are three tinned electrical terminals 4, and secured to the two housing sect ions 2, 3 is a tubular member 5 for passing sound to the outside. To facilitate the attachment of member 5 to housing section 3, the latter is provided with a jutting edge 6. Provided within housing 2, 3 is a membrane 30 and an energizing member indicated generally at 60. Membrane 30 is secured throughout its entire surface, which is virtually equally large as that of base 31 of housing section 3, secured to a flexible foil 40. Foil 40 projects from the surface of membrane 30, which projecting portions are secured, for example by means of an adhesive, to the inner sides of side walls 32, 33, 34, 35 of housing section 3.As best shown in Figure 4, foil 40 is provided for the purpose with portions 41, 42 bent over at right angles, and extending parallel to the corresponding side walls 32, 33 of housing section 3. After a forming procedure, these foil portions 41, 42 exhibit ragged edges 43. As the height H3 of the inside of housing section 3 is greater than the height H40 of foil portions 41, 42, these foil portions 41, 42 do not require any subsequent trimming operation or other treatment.

Energizing member 60 comprises two pole shoes 10, 11, two permanent magnets 12, 13, and a coil 14 connected to terminals 4. If desired, a coil with a center tap may be used. Provided between the permanent magnets is a space 15 terminating in a space 16 in coil 14. Movably disposed within spaces 15, 16 is a central leg 20 of an armature 21. Armature 21 is best shown in Figure 2; in it, Figure 2A illustrates a top plan view of armature 21, and Figure 2B a cross-sectional view taken on the line B-B of Figure 2A. When a current flows through coil 14, then as a result of the magnetic flux thus generated, in interaction with the constant flux of the permanent magnets, a force will be exercised on central leg 20 to movie the same in vertical direction.The vertical movement of leg 20 is transmitted by a motion transmitting member 22 to membrane 30, which is provided with profiling 31, 32 for enhanced stiffness. Foil 40 is provided with bellows-like folds or pleats 44 along the edge 33 of membrane 30 located closest to the motion transmitting member 22, and along the two adjoining edges. As a result, membrane 30 can follow the movements of the central leg 20 of armature 21 as transmitted by motion transmitting member 22 without any impediments. Along the edge 34 of membrane 30 located most remotely from motion transmitting member 22, foil 40 merges into the foil portion bent over at right angles without bellows-like folds, to prevent vertical movements of the edge 34 of membrane 30, so that membrane 30 can only perform a pivoting movement about edge 34. This prevents undesirable movement modes of membrane 30. To restrict the vertical movement of edge 34 still further, housing section 30 is provided with an inward projection 8 (Figure 3) to which the underside of foil 40 is bonded.

When membrane 30 moves, pressure waves are generated in the space 50 defined by housing section 3 and membrane 30, which pressure waves can leave housing section 3 through an opening 9 which terminates in member 5.

Claims

1. An acoustic transducer comprising - a box-shaped housing consisting of two housing sections each comprising a rectangular base and four side walls positioned at right angles to the edges of the base, the two bases having substantially equal areas; - means for converting an electrical signal into an acoustic signal, including a membrane extending substantially the entire area of a base of the housing and movably mounted in said housing by a flexible means; and - an energizing means for setting the membrane into vibration under the influence of said electrical signal; characterized in that said flexible means is secured to the inner sides of the four side walls of one of the housing sections.

2. An acoustic transducer as claimed in claim 1, characterized in that said flexible means has attachment portions extending parallel to corresponding sides of the housing section, and that said flexible means is secured to said sides through said attachment portions.

3. An acoustic transducer according to claim 2, characterized in that said flexible means has portions bent over at right angles.

4. An acoustic transducer as claimed in claim 2 or 3, characterized in that the height of the inner sides of the housing section is greater than the height of said attachment portions.

5. An acoustic transducer as claimed in any of claims 1-4, characterized in that the two housing sections have the same height.

6. A membrane provided with a flexible attachment means, and evidently intended for use in an acoustic transducer as claimed in any of claims 1-5.

7. An acoustic transducer substantially as herein described with reference to, and as shown in, the accompanying drawings.