EP0077228B1

EP0077228B1 - Electroacoustic transducer

Info

Publication number: EP0077228B1
Application number: EP82401685A
Authority: EP
Inventors: Tadashi Sawafuji
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-09-17
Filing date: 1982-09-16
Publication date: 1986-02-26
Also published as: EP0077228A3; DE3269415D1; JPS5843091U; EP0077228A2

Description

Background of the invention

This invention relates to an electroacoustic transducer for use in a full range speaker for audio, a tweeter speaker and other normal speakers, a handset for telephone, a headphone, microphone units and the like.
One typical known example of an electroacoustic transducers is a speaker comprising a voice coil attached to a top end portion opposite to a front opening portion of a cone-shaped diaphragm with an electromagnetic driving section adapted to constitute a magnetic circuit at fine gaps in the voice coil wherein, when a voice signal is sent to the voice coil, the voice coil will be driven vertically in accordance therewith and diaphragm will produce a sound output.
However, such a speaker has drawbacks in that, since the diaphragm per se is cone-shaped, the unit inherently is oversized and too thick; further the unit is subject to vibration and the diaphragm has a tendency to vibrate sectionally in the high pitched tone area, whereby a voice output cannot be reproduced with high fidelity.
The present inventor previously suggested the electroacoustic transducer illustrated in Fig. 1 as being capable of eliminating the aforementioned drawbacks. This electroacoustic transducer as disclosed in JP-A-57 54 499 published 31.03. 1982 comprises a convex curved sheet like diaphragm 22 supported from end leg portions of casing 21, and having a coil 23 on the surface of the diaphragm adjacent each end, and having a pair of permanent magnets 24 and 25 at each coil 23. When an electric current is applied to the coils 23, an electromagnetic force will displace the surface of the diaphragm, thereby causing the central curved portion to be displaced as seen in the dotted lines, in a direction perpendicular to the diaphragm surface, thereby producing sound. Such an electroacoustic transducer, as designed above, is capable of doubling the displacement of the central curved portion of the diaphragm 22 with respect to each end portion. Therefore, this electroacoustic transducer has a wide directivity, it is thin and further it has better low sound characteristics.
However, the electroacoustic transducer of Fig. 1 has disadvantages in that, since electromagnetic driving sections must be provided at both end portions of the diaphragm 22, a large surface area for the coils 23 is required, four permanent magnets are needed, and thus a large number of parts are required, whereby it is difficult to keep the transducer small and its applications are thereby limited.
Other relevant prior art transducers include FR-A-621,452, WO-A-8,001,128, DE-B-1,251,381, US-A-1,866,090 and Patent Abstract of Japan, Vol. 1, No. 38,19.4.77, pages 2274 E 76; JP-A-51,135,638.

Summary of the invention

It is an object of this invention to provide an electroacoustic transducer which avoids the disadvantages inherent in the above mentioned prior art electroacoustic transducer while retaining its advantages; in other words, providing an electroacoustic transducer that has a relatively small number of parts, is compact and has a wide range of applications.
It is another object of this invention to provide an electroacoustic transducer that can produce sound of a cylindrical wave type which eliminates listener fatigue associated with sheet diaphragm devices, can attain an acoustic efficiency similar to that of the usual cone speaker, which having the advantage of being thin, and is especially suitable as a speaker for car radios and the like.
It is a further object of this invention to provide an electroacoustic transducer so adapted that the sound produced at the side opposite the open portion of the casing by the diaphragm is allowed to leak from between both side edges of the diaphragm and the inner surfaces of both side walls of the casing, so as to prevent the sound emitted from the open portion side of the casing from undergoing interference therefrom, whereby the speaker can readily reproduce especially low-ranged sound (about 150 Hz) and further that the sound from the speaker, especially when the speaker is used in a car radio or the like, will not be interferred with from noises outside the car.
According to this invention, these objects are achieved by providing an electroacoustic transducer of the type defined in the preamble of claim 1 and known from DE-B-1 251 381 which is characterized in that said diaphragm has a curved portion between said edges, and in that there is included a flexible buffer plate connected between the side edges of the diaphragm and the interior of the side walls.

Brief description of the drawing

Fig. 1 is a longitudinal sectional front view of the prior art electroacoustic transducer as disclosed in the background of the invention.
Fig. 2 is a front view of a first embodiment of the electroacoustic transducer according to this invention.
Fig. 3 is a longitudinal sectional side view taken on line 3-3 in the direction of the arrow of Fig. 2.
Fig. 4 is a perspective view illustrating the interior of the electroacoustic transducer of Fig. 2 with the cutaway portion indicated with the dotted line.
Fig. 5 is a plan view of the diaphragm of the electroacoustic transducer illustrated in Fig. 2.
Fig. 6 is a partially enlarged sectional view taken on line 6-6 of Fig. 2.
Fig. 7 is a schematic side view of the main portion of a second embodiment of the electroacoustic transducer according to this invention.

Detailed description of the invention

Figs. 2 to 5 illustrate a first embodiment of the electroacoustic transducer according to this invention.
In these figures, there is seen a casing 1 including upper and lower walls 7 and 8, side walls 9 and 10, and open portion 6 at the front of the casing, and a pair of upper and lower diaphragms being symmetrically disposed in the casing.
As is best seen in Fig. 5, each diaphragm 2 includes a printed plate having thereon a coil 3 formed thereon by applying a copper foil on about the half (the right half in Fig. 5) of the surface of a flexible synthetic resin sheet 11 and subjecting this to chemical etching. Coil 3 may be formed on the surface of sheet 11 in other well known ways.
In Fig. 3, the front edges 12 of diaphragms 2 opposite the coils 3 are fixed to the inner surface of the upper and lower walls 7 and 8 of casing 1 near the open portion 6. The portions of the diaphragms 2 which contain coils 3 and which are adjacent to rear edge of the diaphragms overlap so that coils 3 of both diaphragms 2 are so connected to have a plus terminal and a minus terminal in common. The thus overlapped rear edge 13 forms a free edge which is movably supported in the horizontal direction (the right and left directions in Fig. 3) by a holding member 14 mounted on the inner surface of the lower wall 8. The diaphragms 2 have curved portions 15 between the front edges 12 and coils 3, and, as can be seen from Fig. 3, have the shape of the longitudinal sectional surface of a cone speaker viewed from the side.
The inner surfaces of the upper and lower walls 7 and 8 of casing 1 are provided with permament magnets 4 and 5 located opposite to coils 3, wherein poles S and N of permanent magnet 4 confront poles N and S of the permanent magnet 5, and both minus terminals of the coils 3 are connected to a signal source (not shown) such as an amplifier or the like. The permanent magnets 4 and 5 are surrounded with a magnetic material 16 such as iron or the like.
The gaps formed between the side edges 17 at the curved portions 15 of the diaphragms 2 and the side walls 9 and 10 of casing 1 are closed by means of flexible buffer plates 18 as shown in detail in Fig. 6, wherein one side edge of the buffer plate 18 is connected to the side edge 17 of the diaphragms 2, and the other side edge of the buffer plate is connected to side walls 9 and 10.
The operation of this transducer will now be described.
When an electric signal is applied to the plus and minus terminals of coils 3, forces in the right and left directions (in Fig. 3) are generated in coils 3 due to magnetic field present between permanent magnets 4 and 5, and consequently the rear edge 13 of diaphragms 2 is moved as indicated by the arrow. This movement cause the curved portion 15 to be deformed in a vertical direction as indicated by the dotted lines in Fig. 3, which in turn vibrates the air between the diaphragms 2 and emits through open portion 6 a sound which corresponds to the electric signal.
The electroacoustic transducer constructed as described above can double the amount of movement of the curved portion 15 of the diaphragms in comparison with the movement of coils 3, whereby very satisfactory low-ranged sound reproduction can be obtained. In addition, as there is no need to increase the amount of movement of coils 3, the area for mounting the coils may be decreased. Also, as only two permanent magnets 4 and 5 need be mounted at the locations facing the coils 3, the number of parts may be decreased in comparison with the aforesaid prior art transducer which requires four permanent magnets. Accordingly, the electroacoustic transducer according to this invention can be relatively quite small. This also holds true in regard to electroacoustic transducers in which, unlike the above embodiment, there is provided, not a pair of diaphragms, but only a single diaphragm 2 and only one permanent magnet. This latter electroacoustic transducer would be even thinner and smaller than that described above.
The electroacoustic transducer according to the Figs. 2-5 is also advantageous in that with the provision of a pair of diaphragms 2, there can be obtained a cylindrical wave type sound that is not as fatiguing to the listener as a spherical wave device.
According to the embodiment of Figs. 2-5, furthermore, since both side edges 17 of the diaphragms 2 are connected with both side walls 9 and 10 by means of buffer plate 18, the vibrating wave generated rearwards (to the right in Fig. 3) by the vibration of the diaphragms 2 is allowed to leak forward through the gaps between both side edges 17 of the diaphragms 2 and both side walls 9 and 10 of the casing 1 so that the normal vibrating wave will not face interference therefrom, whereby sound reproduction into the low range, such as approximately 150 Hz, can be properly effected, and in those cases where the invention is used in a car radio speaker, intefer- ence from noises outside the car will be reduced.
Fig. 7 illustrates a second embodiment of the electroacoustic transducer according to this invention. This embodiment differs from the first in that front edges 12' of a diaphragm 2' are free ends and a rear edge 13' thereof is fixed, and coils 3 are disposed adjacent to the front edges 12', with permanent magnets 4' and 5' disposed on the inner surfaces of upper and lower walls of a casing 1, and the rear edge 13' being fixed by means of a holding member 14'.
As the operation of the second embodiment is the same as that of the first embodiment, and entails similar advantages, a detailed explanation of this second embodiment would be superfluous and will be omitted.

Claims

1. An electroacoustic transducer including a casing (1) having an opening portion (6) in one side, a sheet diaphragm (2) disposed in said casing and extending from the opening portion side to its opposite side, said diaphragm having one edge (12) fixed in the casing and another edge (13) movably supported in the casing, a coil (3) positioned in the vicinity of the other edge (13), permanent magnets (4, 5) positioned adjacent to the coil (3) of the diaphragm in the casing, the diaphragm (2) having side edges (17) and the casing having side walls (9, 10), characterized in that said diaphragm has a curved portion (15) between said edges, and in that there is included a flexible buffer plate (18) connected between the side edges (17) of the diaphragm (2) and the interior of the side walls (9, 10).

2. The electroacoustic transducer according to claim 1, wherein the one edge (12) of the diaphragm (2), fixed in the casing, is disposed in the vicinity of the opening portion (6) of casing (1) and the other edge (13), movably supported in the casing, is disposed opposite to the one edge.

3. The electroacoustic transducer according to claim 1, wherein the one edge (12') of the diaphragm (2'), movably supported in the casing, is disposed in the vicinity of the opening portion of the casing (1), and the one edge (13'), fixed in the casing, is disposed opposite to said other edge.

4. The electroacoustic transducer according to claim 1, wherein there are included rear edges (13), and the sheet diaphragm (2) includes a pair of upper and lower diaphragm elements disposed symmetrically to each other and their portions adjacent to the rear edges are overlapped.

5. The electroacoustic transducer according to claim 4, wherein there are at least two front edges (12) for the pair of diaphragms (2) and these edges (12) are fixed in the inner surfaces of upper and lower walls (7, 8) adjacent the opening portion (6) of casing (1), and wherein coil (3) is provided on the upper and lower surfaces of a layer (11) formed adjacent the rear edges of the diaphragms and wherein permanent magnets (4, 5) are arranged on the inner surfaces of upper and lower walls (7, 8) of the casing (1) opposite this coil and the rear edges of the diaphragm are supported floatingly by means of a holding member (14) provided in the casing.

6. The electroacoustic transducer according to claim 4, wherein there are included front edges (12') of the pair of diaphragms (15) which are supported floatingly by means of a holding member (14) provided on the inner surfaces of upper and lower walls (7, 8) adjacent the opening portion (6) of casing (1) and a coil (3) is provided on a surface (11) confronting the inner surfaces of upper and lower walls of the casing in the vicinity of the front edges (12') of the diaphragms (15) and wherein permanent magnets (4', 5') are arranged on the inner surfaces of upper and lower walls (7, 8) of the casing (1) opposite to this coil (3) and wherein the rear edges (13) of the diaphragm are fixed in a holding member (14') provided in the casing.