Electroacoustic Transducer

Abstract

An electroacoustic transducer having an edge of special shape supporting a diaphragm, which edge is provided with a succession of pleats disposed along the circumferential direction of the diaphragm and a multiplicity of pleats running in the radial direction of the diaphragm. The pleats of the edge make a folding movement in response to movement of the diaphragm so that the edge expands and contracts in its circumferential direction thereby to follow the movement of the diaphragm.

Description

This invention relates to electroacoustic transducers and more particularly to an electroacoustic transducer which is provided with an edge that can follow the movement of the diaphragm in the axial direction of the voice coil in such a manner as to expand and contract in the circumferential direction of the diaphragm.

The edge supporting the outer peripheral portion of a diaphragm in an electroacoustic transducer such as a loudspeaker has a great influence on the bass response as well as the distortion characteristic of the loudspeaker. As is commonly known, the edge is generally embodied in two forms, that is, in the form of a fixed edge which utilizes the outer peripheral portion 41 of a diaphragm 40 itself as shown in FIG. 1, and in the form of a free edge which consists of a material 42 such as soft leather, cotton cloth or moltopren, i.e. an elastic polyurethane foam obtained by polymerizing an ester formed by a reaction of a dibasic acid with a polyhydric alcohol, an isocyanate, water and a catalyst and then subjecting (a trade name of Polyurethane foam developed by Farbenfabriken Bayer A.G.) supporting a diaphragm 40 of different material therein. FIGS. 1 and 2 are longitudinal sectional views of known dynamic speakers which comprise a diaphragm 40, an edge 41 or 42, a damper 43, a voice coil 44, a permanent magnet 45, a pole yoke 46, a pole piece 47 and a frame 48.

Ideal conditions essentially required for an edge supporting a diaphragm are as follows:

A. The edge should have a sufficiently high compliance with respect to the axial movement of the diaphragm.

B. The edge should have a sufficient stiffness with respect to the lateral movement of the diaphragm.

C. The edge should show a good linearity in the vibration of large amplitudes.

D. The surface of the edge should be substantially free from warping which may result in divisional vibrations. Further, the edge should not produce any resonance.

E. The edge should be light in weight so as not to obstruct the free movement of the diaphragm.

The operation of the edge in the prior art speakers shown in FIGS. 1 and 2 will now be discussed to see whether the edge satisfies the various conditions described above. The diaphragm must not move in a direction perpendicular to the axis of the voice coil in the speaker and must make a perfect piston movement in the axial direction of the voice coil. Actually, the diaphragm is subject to a complex movement when an AC input is applied to the speakers shown in FIGS. 1 and 2.

When the diaphragm is moved in a direction perpendicular to the axis of the voice coil, the ability of the edge of corrugated shape, for example, to prevent the above movement of the diaphragm is quite small, with the result that the edge tends to follow the above movement of the diaphragm. Any one of the edges shown in FIGS. 1 and 2 has such a shape that it is very pliable to follow the movement of the diaphragm in the direction perpendicular to the axis of the voice coil. Therefore, the voice coil is easily displaced to give rise to a result which is objectionable for the satisfactory performance of the speaker. Further, any unusual movement of the edge gives rise to an undesirable peak-valley phenomenon in the response of the speaker since the edge occupies a considerable portion of the radiation area of the speaker as viewed from the front side of the speaker. Each of the edges of the prior art speakers shown in FIGS. 1 and 2 expands and contracts and thus makes a sort of divisional vibrations when the diaphragm is moved not only in the axial direction of the voice coil but also in a direction perpendicular to the axis of the voice coil. Due to the fact that the vibration of the edge has a component which is in inverse phase to the vibration of the diaphragm, a valley appears in the response as pointed out in the above. Further, the prior art edge gives rise to a resonance of a phase inverse to the vibration phase of the diaphragm at a specific frequency, and a valley appears in the response as a result of such a resonance.

Thus, the prior art edge of the diaphragm has various defects which are fatal for use in electroacoustic transducers in that it has not a sufficient stiffness to withstand the movement of the diaphragm in the direction perpendicular to the axis of the voice coil due to its pliability in that direction and it tends to give rise to a divisional vibration and resonance although it has a considerably high compliance with respect to the movement of the diaphragm in the axial direction of the voice coil. As a countermeasure therefor, various attempts have hitherto been made which include varying the shape of the edge and filling a resin in the edge itself. However, none of these attempts have succeeded to provide an edge which satisfies the above-specified conditions.

The edge according to the present invention is characterized by the fact that it has a V-like sectional shape and comprises a multiplicity of pleats which can easily expand and contract along the circumferential direction of a diaphragm thereby pliably to follow the movement of the diaphragm in an axial direction of a voice coil, and which has a sufficient stiffness to withstand the movement of the diaphragm in its radial direction.

It is an object of the present invention to provide an electroacoustic transducer which has a good bass response and can operate with a low distortion in sound.

Another object of the present invention is to provide an electroacoustic transducer having an edge which does not give rise to an undesirable resonance and can follow a large movement of an associated diaphragm.

A further object of the present invention is to provide an edge which has a high compliance with respect to the movement of the diaphragm in the axial direction of an electroacoustic transducer and has a sufficient stiffness against the movement of the diaphragm in a direction perpendicular to the axis of the electroacoustic transducer.

The above and other objects, features and advantages of the present invention will be apparent from the following description when read in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 are longitudinal sectional views of prior art electroacoustic transducers as described previously;

FIG. 3 is a longitudinal sectional view of the electroacoustic transducer according to the present invention;

FIG. 4 is a plan view of an edge in the electroacoustic transducer shown in FIG. 3;

FIG. 5 is an enlarged perspective view of part of the edge shown in FIG. 4; and

FIG. 6 is an enlarged sectional view taken on the line A-A' in FIG. 4.

Referring to FIG. 3 showing a loudspeaker according to the present invention in longitudinal section, a permanent magnet 1 is disposed in a central opening of a pole yoke 2. A pole disc 3 is mounted on the magnet 1, and a disc 4 of sound absorption material is mounted on the pole disc 3. A voice coil bobbin 5 carrying a voice coil 7 therearound is disposed in the space 6 defined between the pole yoke 2 and the pole disc 3. A diaphragm 8 of frustoconical shape is connected to the voice coil bobbin 5 and is supported by an annular edge 9. Reference numerals 10, 11 and 12 designate a center cap, a frame and a damper, respectively.

The edge 9 supporting the diaphragm 8 therein is shown in FIG. 4. The edge 9 shown in FIG. 4 has a V-like sectional shape in which the center is depressed to form the bottom of V as seen from FIG. 6 and is constituted by 120 pleats and 480 faces. The structure of the edge 9 will be described in more detail with reference to FIGS. 5 and 6.

FIG. 5 is an enlarged perspective view of part of the edge 9 shown in FIG. 4, and FIG 6 is an enlarged sectional view taken on the line A-A' in FIG. 4.

Reference numerals 13 and 13' designate circumferential pleats which are continuously arranged substantially centrally of the edge 9 along the circumferential direction of the diaphragm 8 in the form of a zigzag line. These circumferential pleats 13 and 13' run in such a direction in a zigzag fashion with a certain length defined between their break points D', D and D". Faces 14 and 14' extend upwardly from the circumferential pleat 13 in opposite directions with a breadth which is equal to the length of the line D-D'. Similarly, faces 15 and 15' extend upwardly from the circumferential pleat 13' in opposite directions with a breadth which is equal to the length of the line D-D". Thus, these faces 14, 14', 15 and 15' intersect with each other. Pleats 16, 16' and 17, 17' which are continuously arranged in the form of a zigzag line along the circumferential direction of the diaphragm 8, like the circumferential pleats 13 and 13', are formed at the upper end of these faces 14, 14' and 15, 15', respectively. The pleats 16 and 16' have break points C, C' and C", while the pleats 17 and 17' have break points E, E' and E". Radial pleats 18 and 19 arranged in the radial direction of the diaphragm 8 connect the break points C, D and E. Similarly, radial pleats 20 and 21 connect the break points C', D' and E', while radial pleats 22 and 23 connect the break points C", D" and E". By virtue of the provision of the circumferential pleats 13, 13', 16, 16', 17 and 17' and the radial pleats 18, 19, 20, 21, 22 and 23, the edge 9 can easily expand and contract in the circumferential direction of the diaphragm 8. However, in the radial direction of the diaphragm 8, the circumferential pleats 13, 13', 16, 16', 17 and 17' are merely flexed when a force to move the diaphragm 8 in that direction is applied thereto, and the remaining portions of the edge 9 can not be flexed in the radial direction of the diaphragm 8 because of the combined action of the radial pleats 18, 19, 20, 21, 22 and 23 resisting the force. A succession of these pleats and faces constitute the annular edge of the present invention.

Referring to FIG. 6, the edge 9 is cemented to the diaphragm 8 at a portion a and to the frame 11 at a portion b. In FIG. 6, the radial pleats 18 and 19 shown in FIG. 5 are represented by hatched portions 24, 24, while the radial pleats 20 and 21 are represented by lines 25, 25. Points c, c', d, d', e and e' in FIG. 6 correspond to the break points C, C', D, D', E and E' in FIG. 5. In making such an edge, an edge material which may be a nonwoven material of synthetic fibers is pressed by a male die and a female die having convexities and concavities conforming to the shape of the pleats.

Various modes of operation of the edge shown in FIGS. 4 to 6 with which the present invention is featured will be described in detail. Referring to FIG. 6 showing a part of the edge in enlarged section, one-dot chain lines 26, 26; 27, 27; 28, 28; and 29, 29 indicate various positions of the radial pleats 24, 24 which are variable depending on the movement of the diaphragm 8, and a two-dot chain curve 30 indicates the locus of movement of the break point d between the radial pleats 24, 24. A three-dot chain line 31 indicates the locus of movement of the point c of the edge.

Description will first be given as to how the edge follows the movement of the diaphragm 8 when the diaphragm 8 moves vertically upwardly from its neutral position in FIG. 6. As the diaphragm 8 moves upwardly, the points c and d of the edge 9 follow that movement by moving on the chain line and curve 31 and 30 in directions shown by the arrows F and G, respectively. That is to say, the point d moves to a point Q on the chain curve 30 when the point c moves to a point P on the chain line 31, so that the pleats 24, 24 move to the positions 26, 26. As the diaphragm 8 moves further upwardly, the points c and d move to respective points R and S so that the pleats 24, 24 move to the positions 27, 27 which align on the same straight line. Thus, a certain angle is maintained between the pleats 24, 24 when the amount of movement of the diaphragm 8 is small, and this angle is gradually increased as the amount of movement of the diaphragm 8 becomes larger until finally the pleats 24, 24 take their positions 27, 27 at which they align on the same straight line. The edge 9 follows the upward movement of the diaphragm 8 in the manner described above. Suppose that the pleats 24, 24 have moved to the positions 26, 26 in FIG. 6, the point d shifts to the point Q. This means that the circle drawn by the series of the circumferential pleats 13, 13', --about the diaphragm 8 shown in FIG. 5 must contract correspondingly. That is, the result is that the pairs of the radial pleats 18, 19, 20, 21, 22, 23 and so on are folded to a greater degree so that the edge 9 is contracted in its circumferential direction. The edge 9 in the present invention can expand and contract pliably in its circumferential direction to follow unresistingly the large movement of the diaphragm 8 until the pleats 24, 24 are moved to their parallelly disposed positions 27, 27.

Operation of the edge 9 when the diaphragm 8 moves in the opposite direction or downwardly from its neutral position will next be described. Referring to FIG. 6, the points c and d of the edge 9 follow the downward movement of the diaphragm 8 by moving on the chain line and curve 31 and 30 in directions shown by the arrows H and K, respectively. When the amount of movement of the diaphragm 8 is small, the points c and d move to a point T on the chain line 31 and a point U on the chain curve 30, respectively. On the other hand, when the amount of movement of the diaphragm 8 is maximum, the point c and d move to a point V and a point W which lies at substantially the same position as that initially occupied by the point d , respectively. Thus, the pleats 24, 24 move first to their positions 28, 28 and then move to their positions 29, 29. When the point d is situated at the point U, the series of the circumferential pleats 13, 13', --shown in FIG. 5 must draw a correspondingly enlarged circle about the diaphragm 8. That is, in such a case, the fold formed between the pairs of the radial pleats 18, 19, 20, 21, 22, 23 and so on is stretched with the result that the edge 9 is expanded in its circumferential direction.

The edge according to the present invention has a V-shaped cross section and the radial pleats 18, 19, 20, 21, 22, 23 and so on are formed on the slopes constituting a V-shape. If these radial pleats were not present on the slopes, the slopes would arbitrarily vibrate resulting in the resonance of the edge because the slopes are made from a soft and pliable edge material. However, according to the present invention, radial pleats are provided on the slopes. By virtue of the provision of the alternately concaving and convexing radial pleats, these slopes are quire quite rigid with respect to a force applied perpendicularly thereto. Therefore, these slopes can not arbitrarily vibrate in the direction perpendicular with respect thereto, and as a result, no resonance occurs in the edge.

The above description has referred to the case in which the diaphragm moves in the direction of the axis of the electroacoustic transducer. However, the diaphragm moves not only in the axial direction but also in a direction perpendicular to the axis of the electroacoustic transducer. The following description is directed to the excellency of the edge of the present invention in its behavior to counteract the effect of such a movement of the diaphragm.

The movement of the diaphragm in the direction perpendicular to the axis of the electroacoustic transducer occurs in a direction as shown by the arrow M in FIG. 6. The tendency of the diaphragm to easily move in such a direction is objectionable since it gives rise to trouble such as, for example, displacement of the voice coil from its proper position Therefore, such a movement of the diaphragm must be absorbed by the edge.

As described previously with reference to FIGS. 5 and 6, the edge according to the present invention is formed with the pairs of the pleats 24, 24 and 25, 25 in the radial direction of the diaphragm, and these pleats 24, 24, 25, 25 are alternately convexed and concaved relative to each other. Suppose now that a force is applied to the point c in the direction M in FIG. 6. This force tends to flex the pleats 24, 24, 25, 25 and to shift the point d . However, the pleats 24, 24, 25, 25 and the faces 14, 14' and 15, 15' defined between the pleats 24, 24 and 25, 25 have a very high strength to withstand the force applied in this direction. Thus, the faces as well as the pleats would not be flexed to resist the force applied in that direction and the individual portions maintain the positions of the initial state.

It will be understood that the edge according to the present invention which comprises circumferential pleats and radial pleats rising from the circumferential pleats is capable of making expansion and contraction in the circumferential direction like a bellows. Thus, the pleats of the edge can expand and contract in the circumferential direction in response to large movement of the diaphragm in the axial direction of the electroacoustic transducer, and as a result, the edge can freely follow the above movement of the diaphragm. Further, the radial pleats of the edge according to the present invention reinforce the slopes of the edge in the form of V, prevent the edge from resonating and withstand a bending force applied in a direction perpendicular to the axis of the electroacoustic transducer. By the sufficient supporting force of the radial pleats, the edge can be maintained at its original position.

Claims

I claim:

1. An electroacoustic transducer having an edge for supporting a diaphragm of said transducer, said edge comprising a succession of first pleats disposed substantially centrally thereof along the circumferential direction of said diaphragm in such a manner as to form a zigzag line, said first pleats defining a V-like cross section of said edge, a pair of second pleats rising from each break point of said first pleats and running in the radial direction of said diaphragm so as to define a succession of slopes forming the V-shape of said edge, and a succession of third pleats connecting the upper end of said second pleats on each side of said first pleats and running in the form of a zigzag line along the circumferential direction of said diaphragm.

2. An electroacoustic transducer according to claim 1, in which said edge supporting said diaphragm of the transducer is made from a nonwoven material of synthetic fibers.

3. An electroacoustic transducer according to claim 2, further including a frame to which said edge is attached, a center cap disposed coaxially with said diaphragm and a damper mounted coaxially with said diaphragm and attached to said frame.