GB1595320A - Loudspeaker - Google Patents

Description

(54) LOUDSPEAKER (71) I, OSKAR HEIL, a German citizen of Grafelfing, Hubert Reisnerstr. 30, West Germany, do hereby declare this invention, for which I pray that a patent may be granted to me, 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 loudspeaker which not only reproduces the whole frequency range of interest, e.g. for a high note or a low note loudspeaker, with a good efficiency, but which is above all also capable of reproducing rapidly varying frequency characteristics with high fidelity.

In the reproduction of tones and sounds it will be necessary not only to produce the entire frequency range covered by musical instruments, but the loudspeaker must also reproduce without any time lag frequencies which vary rapidly, such as for example those which occur at the start and at the end of a note, so that intonations, glissandos and fading notes can be faithfully reproduced, i.e. without any interfering frequencies arising out of the characteristics of the loudspeaker. Until now little attention has been paid to this problem, as conventional research, conditioned by the instruments used, was mainly restricted to the reproaduction as a function of the frequency characteristics. However, the human ear in particular is very sensitive to frequencies which vary over very short intervals and it is precisely such frequency changes that are characteristic features of certain musical instruments, particularly of string instruments and also of the players of such instruments.

Such phenomena which occur for very short time intervals are not well dealt with by conventional loudspeakers because the above-mentioned fine detail is lost in the reproduction due to unavoidable attenuation caused by the materials used for loudspeaker diaphragms at the present time.

According to the invention there is provided a loudspeaker comprising a base member, with a diaphragm suPported thereon and with a drive device for the diaphragm, wherein the diaphragm defines a plurality of individual stiff portions, and is supported on the base member by a plurality of rigid or tensioned support elements which support elements are connected by respective flexible or pivotal connections to respective spaced apart points between the stiff portions on the diaphragm, the diaphragm being relatively flexible at the support points between the stiff portions and the support elements making an acute angle with the diaphragm, whereby the diaphragm is constrained to move as a whole in a direction defined by pivoting movement of the support elements with substantially no transverse vibrations within the diaphragm.

In a preferred embodiment the diaphragm is made from at least one thin foil, which as such has no bending strength and would therefore not be capable of transmitting transverse acoustic waves. In order that such a diaphragm shall be capable of emitting acoustic waves, the diaphragm is divided into individual elements between the support points and the rigidity of the elements is not produced by the materials used, but by other means, for example, by providing the appropriate shape or tension over an area. However, in order that all individual elements of a diaphragm manufactured in this manner can be made to vibrate simultaneously, the diaphragm is fastened to a solid base at various points so that it will have only one degree of freedom of movement, such that, if all the points are fastened in the same manner, the diaphragm will move as a single unit, as would a rigid plate, without having the weight or mass of the rigid plate. The forces required for producing these vibrations, are also appropriately introduced at various points in a direction which lies entirely or at least has a large component in the remaining single direction of motion of the diaphragm because of its restriction.

In order to avoid undesirable phase shifts, which could arise by the acoustic propagation in the diaphragm, the diaphragm is manufactured from a material which has a high propagation velocity constant for the longitudinal waves. A particularly favourable effect will be produced if acoustic conducting elements are inserted between the individual elements of the diaphragm; they will propagate the sound at an extremely high velocty in the form of longitudinal waves, so that all the individual elements of the diaphragm will practically be displaced almost simultaneously by the vibration energy introduced by the oscillations.

ln order to understand the response of the loudspeaker to beginning and fading notes, the energy stored in the air space in front of the loudspeaker diaphragm is explained by way of example of the spherical emitter in Fig. 30 and by way of the example of a cylindrical emitter in Fig. 31.

Fig. 30 shows the total energy contained in a spherical shell as a function of the radius, measured in wavelengths. The broken line which is parallel to the abscissae shows the useful energy given off. The hatched area between this line and the curve drawn in represents a measure of the energy which is stored in front of the diaphragm when starting a note and which is given off during the delay when fading the note. It will take a certain amount of time for the energy store to build up, and the total useful energy can only be given off after this storage period. Conversely, there will be an undesirable echo at the end of the note. Fig. 31 shows the characteristics of the cylindrical emitter, and it is evident that considerably less energy has to be stored, before the useful energy can be given off to the surroundings.

It will therefore be possible for a note to begin or fade more quickly, if a cylindrical instead of a spherical emitter is used. If an approximately plain surface is now used as the emitter, it will be found that the characteristics will be more favourable and the correct reproduction of the notes at the right time will also be achieved.

When reproducing tones by a diaphragm, other tones with frequencies that are not part of the original notes, i.e. in the notes emitted by the musical instrument, wll be created because of the forces acting in the diaphragm. The causes of such distortion can for example be as a consequence of a stiffening of the diaphragm when it is excited by oscillation of a given frequency.

If another frequency is imparted to the diaphragm, it will act on a diaphragm already stiffened by the first frequency and will therefore be affected. Should the note of the first frequency fade, this will cause the elastic properties of the diaphragm to change, and will therefore also affect the frequency of the second note. This means that the loudspeaker will produce notes which are a functipn of its design and which will distort the reproduction. If, however, as is provided for in the invention, the diaphragm is divided into stiff individual elements which nevertheless execute parallel oscillatory movements, it will not be possible for this phenomenon to occur.

Furthermore, the sizes of the individual elements can be chosen such that the resonance frequency of the individual elements is very much higher than the highest frequency of interest in reproduction. The size of the whole diaphragm can be designed for a particular frequency range, e.g. high or low note ranges, without it being necessary to change the design principle.

Summarising, it can therefore be established that distortions of the reproduction of music which would impose an additional peculiarity onto the individuality of the musical instrument or the player, could be avoided by the design of a loudspeaker according to the invention. Acoustic vibrations will occur in the diaphragm in such a way that a major component of these oscillations will lie in the plane of the diaphragm. In contrast to conventional the limit being set by the strength of a diaphragm having to be sufficient to be able the limit beng set by the strength of a diaphragm saving to be sufficient to be able to transmit longitudinal waves. Suitable additional acoustic conducting elements with a high sound velocity characteristic for longitudinal waves are provided for propagating the sound. It will cease to be necessary to transmit transverse waves.

Such a diaphragm can for example consist of a very fine fabric which by the appropriate treatment, for example by coating, has been made impervious to air. The necessary stiffening will then be achieved by shaping the individual regions of the diaphragm, so as to form separate stiff diaphragm elements. The shaping can consist of simple convexity, where the diaphragm is pre-stressed by an over- or under-pressure, or it would otherwise be possible to produce a particularly suitable design, by shaping two membranes arid fitting one on top of the other, so as to produce cushion-shaped individual elements which are for example polygonal and are joined via a flexible section.

The oscillations introduced with a component of motion in the direction of the diaphragm must be linked in such a way that the stiff individual elements of the diaphragm will vibrate with a component of motion at right angles to the surface of the diaphragm, as the sound will be given off from the diaphragm in this direction.

This will be achieved in that the diaphragm is held in such a way at various points that it will only have a single degree of freedom of motion, whereby the direction of this degree of freedom will form an angle with the direction of the surface of the diaphragm. Because of this method of support, the acoustic oscillations introduced in the direction of the diaphragm can only cause the diaphragm to move along the only remaining degree of freedom, and an acoustic radiation will only be possible in this manner because of the vibration energy introduced into the direction of the plane of the diaphragm.

In the simplest form, the support elements, which on the one hand will hold the diaphragm and on the other hand will allow only a predetermined movement, can consist of filaments held under tension which at one end are attached to a rigid wall which does in fact transmit sound and at the other end to the diaphragm. Such a wall, which can be considered as a base, can for example be lattice-shaped. The end of the filament connected to the diaphragm could on its own be capable of moving over a spherically-shaped surface; however, this would be on the one hand be prevented as the diaphragm will be stretched in one direction and on the other hand such transverse movements are very unlikely in the diaphragm, as there are no oscillating forces operating in this direction. However, to be on the safe side it will be possible to use double filaments instead of single filaments which emanate from a common point on the diaphragm and are taken to two fixing points on the wall of the housing, so that the two filaments will only execute a motion at right angles to the plane defined by these two filaments.

It will also be possible to use more stable elements instead of filaments, for example shaped rods, which could absorb both tensile and compressive forces. The rods could be tubular or cone shaped, or they may be triangular, and can then be reinforced by additional fishplate-type foils.

It will suffice to support the diaphragm on one sde when using support elements which can take both tensile and compressive forces. It will, however, be necessary to support the diaphragm from the other side when using filaments, for example by a diiference in air pressure or by other filaments which would be extended in the same direction as the direction of the filaments on the first side of the diaphragm. However, if any movement is to be possible in this case, it will be necessary for one of the filaments to be flexible or be made from an elastic material when two filaments from different sides are attached to one point on the diaphragm.

Although it will be possible to use any oscillatory source to produce these acoustic vibrations, nevertheless certain systems of oscillation generators have proved to be effective on this particular design of loudspeaker diaphragms.

Thus it would, for example, be possible to attach a permanent magnetic sheet made from a highly permeable material, such as for example samarium cobalt, either directly to one end of the diaphragm or via a connecting link, thereby placing it between the gap of a magnet such that only a section will extend into this gap. This little sheet will then be resiliently mounted on the side away from the diaphragm.

A different form of drive adapted to the present diaphragm design consists of a special double magnet where two magnets with horse-shoe shaped cross sections are placed opposite each other such that opposite poles are facing. This magnetic arrangement has the advantage that only a small stray field will be produced, so that the losses will be very small. A flat coil which can be fitted directly onto the diaphragm or onto a little plate connected to this diaphragm is then inserted into the gap between this double magnet.

Certain embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. 1 is a schematic drawing of a diaphragm constructed from individual elements; Fig. 2 is section along the line II-II of Fig. 1; Fig. 3 shows a diaphragm similar to Fig.

1, however, with acoustic conducting elements embedded between the rows of elements; Fig. 4 is a section along the line IV-IV of Fig. 3; Fig. 5 shows schematically the arrangement of the pivotal supports; Fig. 6 shows the construction of the pivotal supports as filaments; Fig. 7 shows a diaphragm which is indirectly supported on two wall sections of the base by means of acoustic conducting rods; Fig. 8 shows an arrangement similar to the one in Fig. 7, where, however, the acoustic vibrations are transmitted from one acoustic conducting rod to the other conducting rod by a polygonal route; Fig. 9 shows a diagram similar to Fig.

8, where, however, the tension in the line at the corner is not produced by an external pull, but is supported from the inside; Fig. 10 shows the construction of a curved diaphragm; Fig. 11 shows a filament support for preventing the generation of undesirable transverse oscillations; Fig. 12 shows a loudspeaker with diaphragms subjected to pressure on one side; Fig. 13 shows the construction of the diaphragm into an acoustic wall as a side view of Fig. 12; Fig. 14 shows a joint at the edge of the diaphragm; Fig. 15 shows a variation of the shape of the loudspeaker; Fig. 16 shows a triangular hollow support element; Fig. 17 shows a side view of this element; Fig. 18 represents a leaf-shaped support element with reinforcement; Fig. 19 shows the use of foils as support elements; Fig. 19a and 19b show forms of pivotal connections; Fig. 20 shows a loudspeaker with two parallel diaphragm sections linked by a curved section: Fig. 21 shows a loudspeaker with an external diaphragm and two internal bases; Fig. 22 represents a loudspeaker with two internal diaphragms and a base surrounding these diaphragms like a casing; Fig. 23 is a section along the line 23-23 of Fig. 22; Fig. 24 shows a cone loudspeaker; Fig. 25 is a section along the line 25-25 in Fig. 24; Fig. 26 shows a sketch of the principle of a magnetic drive; Fig. 27 shows a magnetic drive with rotatably mounted permanent magnet; Fig. 28 represents a double magnet drive; Fig. 29 shows the shape of the associated coil; Fig. 30 shows a diagram of the energy storage of a spherical emitter; and Fig. 31 shows the energy storage of a cylindrical emitter.

Fig. 1 shows a diaphragm 1 which is divided into individual elements 2, which form rows 3 and columns 4 and as a whole forms a flat rectangle. The elements of the diaphragm are more clearly shown in Fig.

2. They consist of cushion-shaped individual elements which give the element the necessary stiffness where the individual elements are interconnected via connecting seams. The elements could have other polygonal configurations.

The diaphragm is constructed from two separate foil membranes which are joined at the edges of the individual elements.

The individual elements are joined by pivoting-type connections.

Fig. 3 shows an embodiment where acoustic conducting rods are embedded at the seams 5. In this case the acoustic conducting rods 6 and 7 which run along the longitudinal direction are connected to a drive operating in the direction of the double arrow, whereas the acoustic conducting rods 9 along the transverse seams are at right angles to this direction. Fig. 4 shows a very effective way of embedding the acoustic conducting rods, where the rods 6 and 7 are embedded between the semicircular cross-section ribs of the individual elements 2 which are formed in one foil, while the rods 9 running in a transverse direction are embedded in a similar way in another foil, so that both foils can first be formed separately, for example by vacuum forming and then be welded to form a seam, so that then the acoustic conducting rods running in the longitudinal and transverse direction will not interfere with each other.

The diaphragm could be formed of a single film and may be stiffened by shaping it into individual shell or cone-shaped portions. The material of the diaphragm may have a high speed sound conducting characterstic, and may be, for example, keflar polyimide resin film, polyester or polycarbonate foil or a metal foil such as aluminium or titanium.

The acoustic conducting elements have a high acoustic speed and could be rods with rectangular, circular, or semi-circular crosssection. A particularly suitable material is a mixture of approximately 60% graphite and 40% epoxy resin.

Fig. 5 shows a schematic section of how the diaphragm is held by the pivotal supports. These pivotal supports are each connected to a rigid base 11 on one side via a pivot 12 and to the diaphragm 1 on the other side via a pivot 13. Two adjacent pivotal supports in conjunction with the base and the diaphragm will form a parallelogram. The diaphragm will therefore practically have only one degree of freedom of movement, namely a movement along the arc of a circle around a base pivot 12 with a radius equal to the length of the pivotal support. In use the diaphragm will be positioned so that the supports make an acute angle with the diaphragm.

The diaphragm is fastened at the base and all the individual elements of this diaphragm will inevitably have to perform the same movement. The angle between the pivotal support and the diaphragm surface can then be approximately 45 degrees and the drive from the motor, which for example can also be introduced at the pivot point 13, will be in the direction along the support 14, i.e. approximately in the direction of a tangent of the compulsorily described circular motion of the point 13.

The direction of drive of the motor is not restricted to a specific angle, it could also occur in the direction of the diaphragm or in the direction at right angles to it, as long as only the component of the drive motion in the direction of the compulsory motion and in the direction of the plane of the diaphragm are sufficiently large to ensure a sufficient efficiency of the loudspeaker. A suitable angle will be when the component of motion at right angles to the surface of the diaphragm is about twice the size of the component in the direction of the diaphragm.

There will be losses during the propagation of the acoustic energy, which will result in a weaker acoustic emission, the more remote the input position. This phenomenon can be compensated for by making the angle between the surface formed by the diaphragm and the support elements more acute as the distance of the input position increases and hence will ensure a uniform acoustic emission.

Fig. 6 shows an embodiment of the invention where the pivotal elements are formed by filaments. Of course no special joints will be necessary if the filaments are flexible; however, the filaments 15 are suitably supported on the base via a spring 16, as in this embodiment the diaphragm is supported on both sides. If there are rows of filaments, the spring support can be fitted alternately on one side of the diaphragm and then on the other side of the diaphragm for the neighbouring filaments. It will of course also be possible for all the filaments to be supported via a single spring.

Fig. 7 shows a very special embodiment of the invention, where two rows of support elements 17 and 18 are used to connect the diaphragm 1 to a base, not directly, but indirectly via acoustic conducting rods 19 and 20.

The support elements connected to the diaphragm make an acute angle with the diaphragm and are approximately perpendicular to each other. As is shown in Fig.

7, the diaphragm will be pulled to the left when the two acoustic conducting rods move in opposite directions, in the direction of the full arrows 21. The angle formed by the support elements, in this case filaments, with the acoustic conducting rod 20 will become more acute, while the angle made with the other acoustic conducting rod will become more obtuse. When the movement is reversed, the two acoustic conducting rods will move in the opposite direction shown by the dotted arrows 22, and the movement of the diaphragm in the drawing will then be to the right. It will be possible to drive the two acoustic conducting rods separately; however, a single drive can also suffice, as is shown in Fig. 8. Two acoustic conducting rods adjacent the same end of the diaphragm are interconnected via a link stiand with a polygonal path. The strand is supported by a support element 25 bisecting the angle in the corner 24 of the polygon, which in turn is attached to the base, which in this case is taken around the entire diaphragm. It will also be possible for this connecting strand to be supported from the inside instead of from the outside, for example by a support system comprising a pivoting wheel segment 27 as shown in Fig. 9. This support system pivots around the point 28. Contrary to the design according to Fig. 8, where a stable neutral position is guaranteed by means of the supports 25, the embodiment according to Fig 9 has no stable neutral position.

In the present embodiment the diagram is shown as a flat surface. However, in principle it is also possible for the diaphragm to have a curved surface, which can be particularly desirable in the top section of a diaphragm mounted in a high poistion because of a better sound radiation.

Such a diaphragm 29 (Fig. 10) will then be held by supports 30 to a base 31 with a path which follows that of the diaphragm.

Such bending of the diaphragm should naturally not be so severe as to produce any perceptible energy storage in front of the diaphragm.

The diaphragm will have to be supported on both sides if filaments are used as pivotal supports, as the filaments are only capable of absorbing tensile stresses.

By itself it would be possible for the end of a filament attached to the diaphragm to move along a spherical surface; however, this movement facility will in practice be of hardly any significance for the reasons stated above. However, undesirable transverse vibrations can be eliminated with certainty by replacing the single filament shown in Fig. 6 by double filaments inclined at an angle to each other as is shown in Fig. 11. In this example a diaphragm 31 is supported on one side on a base 34 by a single filament 32 via a spring 33 and on the other side to a base 36 via two filaments 35. The plane in which the two filaments are located is at right angles to the vibrations of the diaphragm 31. The sideways movements will in this way be neutralised.

Fig. 12 shows a section of a loudspeaker with two diaphragms 37 and 38 radiating in opposite directions. The diaphragms are held by rows of support filaments 39 and 40, which in turn are attached to acoustic conducting rods 41 and 42. Further rows of support elements 43 and 44 lead from these acoustic conducting rods to a solid central wall 45 which extends to a baffle 46 outside of the loudspeaker. As the diaphragms in this embodiment are only held on one side by rows of filaments 39 and 40, and these filaments can only be sub jected to tensile stresses, it will require another force to press the diaphragm outwards. This force is produced by air blown out of the orifice 47 in the direction of the arrow. Naturally the housing should be mainly airtight, and this is achieved by providing the diaphragm 37 wth border strips 48-as is shown in Fig. 13, which are attached on one side to closure plates 49 fixed to the housing and have an airtight connection to the diaphragm on the other side. The elements of the diaphragms have a half-shell section.

The border strips are made flexible in order that the amplitude of the loudspeaker diaphragm can become larger as is clearly shown in the section in Fig. 14. The border strip 48 with a central hinge 51 is coupled to the plate 49 via a folded foil 50 and is connected to the diaphragm 37 at the end 52. The border strain can be reinforced at the positions 53 and 54 between the joints 50 and 51 and 52, for example by using a double foil, while using a single foil at the joints 50, 51 and 52, so that there will not be any appreciable reaction forces when the joint angle widens or narrows. There are blocks 55 fitted at the four corners of the assumed rectangular diaphragm 37, leaving a narrow air gap between these blocks and the border strips. The quantity of air escaping from this air gap is so small, that it is easily replaced by the air blown out at 47, so that the excess pressure in the loudspeaker chamber will be guaranteed.

Such air gaps, which in principle can run along the entire edge of the diaphragm, are constructed such that the width of the air gap will remain unchanged when there is a movement of the diaphragm or the edge of the diaphragm. The inside side walls of such a block 55 are in fact perpendicular to the plane of the diaphragm. However, this arrangement is not obligatory and in many cases it can be practical for the boundary walls to be designed in such a way that the air gap becomes wider when the diaphragm is moved outwards. The amount of air escaping because of the wider deflection of the diaphragm is greater and the air pressure in this position will decrease as a function of the width of this gap. It will be possible for the boundary surface to be made undulating in order to achieve a particular function.

The drive is only shown schematically in Figs. 12 and 13, and the disc 56 can in principle be set into oscillation by any magnetic system, where the vibrations are transmitted to acoustic conducting rods 58 via a pulling line 57. Fig., 15 shows an embodiment which is similar in principle; however, in this case the middle body 59 is approximately lenticular, and the acoustic conducting rods 60 have a similar shape and are connected to the diaphragm 63 via a system of filaments 61 and 62 which in this case are connected to rigid supports 65 via hinged joints 64. It will be possible for the side edges of the diaphragm to be attached to the walls of the housing leaving a narrow air gap as described in the explanation of Fig. 14, and can be assumed to run parallel at the front and at the back of the plane of the diagram shown in Fig.

15.

Fig. 16 shows a pivotal support element which has the shape of a triangle and which can be subjected to tensile as well as compressive stresses The apex of this hollow triangular element is attached to the diaphragm via a pivot and to the base via a longer pivot. The mass of such a pivotal support element is naturally greater than the mass of a filament; however, not the whole greater mass has an effect, as the support element tapers towards the diaphragm, and furthermore because a larger amplitude of the motion will only occur at the tapered section, so that the loading produced by the mass of such a support element will be acceptable. Fig. 17 shows a section of one such element.

The support element in Fig. 18 is similar in principle to the one in Fig. 17; however, there will be a triangular foil 66 reinforcement in the hollow section, with the foil fitted at an angle. The connection to the diaphragm is made via a pivot and to the base via another pivot.

Fig. 19 shows a completely different form of the construction of such a pivotal support element. In this case a diaphragm 67 is supported on both sides on a base 70 and 71 respectively via a foil 68 and 69. These foils which can be provided with holes 72 to achieve a better sound transmission, have one edge 73 attached to the diaphragm 67 and the opposite edge 74 attached to the base 71. The attachment to the base should in this case be via resilient devices as is shown in Figs. 19a and 19b. Such a device can consist of a simple bend (see Fig. 19a) or a multiple fold (see Fig. 19b). The support elements could be formed of fabric.

The support elements could be formed as small tubes crimped flat at the ends to form pivots at these positions.

Fig. 20 shows a loudspeaker with a diaphragm made from two foil sections 88 and 89 which are joined via a curved piece 90. <RTI I be transmitted via acoustic conducting rods 93 and 94, which are driven in an opposite sense, so that a downward movement of the acoustic conducting rod 94 means an upward movement of the acoustic conducting rod 93. When a diaphragm section is moved downwards by the acoustic conducting rod, the distance between the diaphragm section and the base will be reduced, while the distance of the other diaphragm section from the base will be increased. The volume of air enclosed by the diaphragm will therefore produce a reciprocating motion on the inside of the loudspeaker. In this embodiment, the tension in the diaphragm is produced by an excess pressure which is generated by a pump attached to the supports 95, not shown in the diagram.

Fig. 21 corresponds mainly to the embodiment of Fig. 20; however, the base in this case is constructed differently. It consists mainly of two perforated baseplates 96 and 97, with the support elements 98 of the diaphragm section 99 attached to the baseplate 97, while the support elements 100 of the diaphragm section 101 are attached to the baseplate 96, e.g. at 102. In this case the support elements 98 are fed through the baseplate 96, such that no contact will be made with this plate, even when the deflections of the support element are made larger by larger sound amplitudes. As compared to the embodiment of Fig. 20, the embodiment of Fig. 21 has the advantages of being thinner and having a smaller air volume enclosed by the diaphragm.

The embodiment of Fig. 22 is particularly effective, because in this case the delicate diaphragm foils 103 and 104 are located on the inside of a chamber-like base 105 with perforations to provide passages for the sound. In this embodiment the tension in the diaphragm foils 103 and 104 is produced by a pressure reduction between the two diaphragm foils. It is evident from the section shown in Fig. 23 that the reduced pressure is applied along the entire length of the edges of the foil sections 103 and 104. The connecting pipes 106 and 107 are linked to a pump (not shown).

Figs. 24 and 25 show a cone loudspeaker.

The diaphragm is divided into a large number of cone-shaped individual elements 108, of which a longitudinal section is shown in Fig. 24 and a transverse section in Fig.

25. These individual elements again form a cone, with the energy of the sound being directed into the apex. The individual elements are enclosed and form coneshaped elements filled with air thereby providing the outer surfaces of the elements with sufficient ridigity. The support is such that two support filaments 110 and 111 are attached to the connecting line 109 between two such individual elements, with the free ends anchored to a solid housing.

These support filaments are applied in several layers as is evident from Fig. 24.

The outer edge of the loudspeaker cone has a circular air gap 113 bounded by a sound screening, ring-shaped plate 114, which in turn is attached to the outer edge of the housing. The cone will become elastcially deformed when sound is introduced at the apex of the loudspeaker cone, which produces an additional elastic force due to the compresson of the individual elements which are built up like air cushions. These individual elements can be provided with holes 115 which will ensure a pressure equilibrium. The size of the hole will determine the time constant of the air cushion, which can be chosen large enough for the elasticity to remain practically constant right down to the lowest frequencies. The elastic restoring force will be reduced for low frequencies if the holes are greater, so that the resonance frequency will be reduced, and furthermore, there will also be damping and widening due to air friction in the holes. The loudspeaker described here has the advantage that the whole diaphragm can be used properly, so that there will be no need for centering devices and it will not be necessary for the outer edge of the cone to be mechanically connected to the housing. In order to increase the stability, the filament pair 110, 111 which run at an angle, can be directed in such a way that the filaments moving away from the edge of one of the individual elements will cross the filaments leaving the adjacent edge. The planes of the pairs of filaments are perpendicular to the axis of the cone.

Although in principle any conventional drive can be used to drive the loudspeaker, nevertheless, there are still certain types of drives which are particularly suitable for the loudspeaker according to the invention. Fig. 26 shows an example of one such drive, which is very suitable if it is desired to cause a rod-shaped acoustic conducting element 75 to oscillate. This drive consists of a magnetic core 76 which is excited by a coil 77 and which has a samarium cobalt disc 79 inserted in the gap. In the rest position this samarium cobalt disc will only extend partly into the space between the poles, so that it can be pulled further into the space on excitation.

Fig. 27 shows a modified embodiment.

Two permanent magnetic discs 80 and 81, each of which only partly extends into the gap of the magnet, are pivoted in such a way as to perform pendulum swings. The discs will be magnetised in such a way that they will experience a pulse in the same direction due to the magnetic field and that one will be pulled into the gap while the other is pushed out of the gap.

Another form of drive is shown in Figs.

28 and 29. Figs. 28 shows a perspective drawing of a motor 82 which drives a flat coil 83. The motor consists in principle of two facing horseshoe magnets 84 and 85, with the opposite poles in each case placed opposite each other. A flat coil 83 is pushed into the space between the poles, to position itself as is shown in Fig. 28. As the magnetic field in the gap 86 is in the opposite direction to the magnetic field in the gap 87, and the current in the magnetic coil 83 in both gaps is also in the opposite directoin, this means that a movement pulse will be exerted on the coil in the same direction in both gaps. The efficiency of this drive is particularly high as the magnetic losses due to stray magnetic fields will be exceptionally small.

WHAT WE CLAIM IS: 1. A loudspeaker comprising a base member, with a diaphragm supported thereon and with a drive device for the diaphragm, wherein the diaphragm defines a plurality of individual stiff portions, and is supported on the base member by a plurality of rigid or tensioned support elements which support elements are connected by respective flexible or pivotal connections to respective spaced apart points between the stiff portions on the diaphragm, the diaphragm being relatively flexible at the support points between the stiff portions and the support elements making an acute angle with the diaphragm, whereby the diaphragm is constrained to move as a whole in a direction defined by pivoting movement of the support elements with substantially no transverse vibrations within the diaphragm 2. A loudspeaker as claimed in claim 1 wherein the support elements all make substantially the same acute angle with the diaphragm.

3. A loudspeaker as claimed in claim 2 wherein the diaphragm is generally planar and the support elements are all substantially parallel.

4. A loudspeaker as claimed in claim 2 wherein the diaphragm is generally planar and a plurality of support elements are connected to each side of the diaphragm, the support elements on the respective sides of the diaphragm being substantially parallel.

5. A loudspeaker as claimed in claim 2 wherein the stiffness of the individual portions of the diaphragm is achieved by means of shaping, for example by a shellshaped or cone-shaped construction.

6. A loudspeaker as claimed in claim 1 wherein the stiffness of the individual portions of the diaphragm is achieved by a pressure exerted on it, for example a gas pressure.

7. A loudspeaker as claimed in claim 6, wherein the pressure producing the stress on the diaphragm is achieved by the dynamic pressure of a gas current operating on the diaphragm, the individual portions being constructed in the shape of half shells.

8. A loudspeaker as claimed in claim 6 wherein the pressure is an underpressure.

9. A loudspeaker as claimed in any of claims 1 to 5, wherein two foils are joined together at the edges of the individual portions, to form cushions each enclosing a volume of gas.

10. A loudspeaker as claimed in claim 5, wherein the two foils are joined together at the edges of the individual portions to form cone-shaped cushions, several of such cone-shaped cushions lying on a coneshaped shell, with the drive introduced through its apex, while the support elements lead from the outside of the cone-shaped shell to the base member where they are held.

11. A loudspeaker as claimed in claim 10, wherein the support elements' each consist of two filaments at an angle attached to the diaphragm at their point of intersection, with their other ends attached to the base member, wherein the plane defined by such filaments is at right angles to the axis of the cone-shaped shell.

12. A loudspeakr as claimd in claim 6, comprising two bases disposed a distance apart between two diaphragms and wherein the support elements are in each case attached to the more remote base from the diaphragm to be supported and pass through apertures in the other base to extend to the diaphragm to be supported without touching that base.

13. A loudspeaker as claimed in claim 6 wherein two diaphragms are arranged a distance apart and a rigid base to which the support elements are attached is located between them.

14. A loudspeaker as claimed in claim 6, wherein two diaphragms are positioned a small distance apart and are prestressed by air pressure, and are supported on external, rigid sound transmitting bases via the support elements.

15. A loudspeaker as claimed in any preceding claim wherein the individual portions of the diaphragm are arranged in parallel rows and have a polygonal outline.

16. A loudspeaker as claimed in claim 15 wherein the individual portions of the diaphragm are arranged in parallel rows and in columns perpendicular to the rows and have a rectangular outline.

17. A loudspeaker as claimed in any preceding claim, wherein the material of

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

Claims (40)

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

   one will be pulled into the gap while the other is pushed out of the gap.

   Another form of drive is shown in Figs.

   28 and 29. Figs. 28 shows a perspective drawing of a motor 82 which drives a flat coil 83. The motor consists in principle of two facing horseshoe magnets 84 and 85, with the opposite poles in each case placed opposite each other. A flat coil 83 is pushed into the space between the poles, to position itself as is shown in Fig. 28. As the magnetic field in the gap 86 is in the opposite direction to the magnetic field in the gap 87, and the current in the magnetic coil 83 in both gaps is also in the opposite directoin, this means that a movement pulse will be exerted on the coil in the same direction in both gaps. The efficiency of this drive is particularly high as the magnetic losses due to stray magnetic fields will be exceptionally small.

   WHAT WE CLAIM IS: 1. A loudspeaker comprising a base member, with a diaphragm supported thereon and with a drive device for the diaphragm, wherein the diaphragm defines a plurality of individual stiff portions, and is supported on the base member by a plurality of rigid or tensioned support elements which support elements are connected by respective flexible or pivotal connections to respective spaced apart points between the stiff portions on the diaphragm, the diaphragm being relatively flexible at the support points between the stiff portions and the support elements making an acute angle with the diaphragm, whereby the diaphragm is constrained to move as a whole in a direction defined by pivoting movement of the support elements with substantially no transverse vibrations within the diaphragm
2. 2. A loudspeaker as claimed in claim 1 wherein the support elements all make substantially the same acute angle with the diaphragm.
3. 3. A loudspeaker as claimed in claim 2 wherein the diaphragm is generally planar and the support elements are all substantially parallel.
4. 4. A loudspeaker as claimed in claim 2 wherein the diaphragm is generally planar and a plurality of support elements are connected to each side of the diaphragm, the support elements on the respective sides of the diaphragm being substantially parallel.
5. 5. A loudspeaker as claimed in claim 2 wherein the stiffness of the individual portions of the diaphragm is achieved by means of shaping, for example by a shellshaped or cone-shaped construction.
6. 6. A loudspeaker as claimed in claim 1 wherein the stiffness of the individual portions of the diaphragm is achieved by a pressure exerted on it, for example a gas pressure.
7. 7. A loudspeaker as claimed in claim 6, wherein the pressure producing the stress on the diaphragm is achieved by the dynamic pressure of a gas current operating on the diaphragm, the individual portions being constructed in the shape of half shells.
8. 8. A loudspeaker as claimed in claim 6 wherein the pressure is an underpressure.
9. 9. A loudspeaker as claimed in any of claims 1 to 5, wherein two foils are joined together at the edges of the individual portions, to form cushions each enclosing a volume of gas.
10. 10. A loudspeaker as claimed in claim 5, wherein the two foils are joined together at the edges of the individual portions to form cone-shaped cushions, several of such cone-shaped cushions lying on a coneshaped shell, with the drive introduced through its apex, while the support elements lead from the outside of the cone-shaped shell to the base member where they are held.
11. 11. A loudspeaker as claimed in claim 10, wherein the support elements' each consist of two filaments at an angle attached to the diaphragm at their point of intersection, with their other ends attached to the base member, wherein the plane defined by such filaments is at right angles to the axis of the cone-shaped shell.
12. 12. A loudspeakr as claimd in claim 6, comprising two bases disposed a distance apart between two diaphragms and wherein the support elements are in each case attached to the more remote base from the diaphragm to be supported and pass through apertures in the other base to extend to the diaphragm to be supported without touching that base.
13. 13. A loudspeaker as claimed in claim 6 wherein two diaphragms are arranged a distance apart and a rigid base to which the support elements are attached is located between them.
14. 14. A loudspeaker as claimed in claim 6, wherein two diaphragms are positioned a small distance apart and are prestressed by air pressure, and are supported on external, rigid sound transmitting bases via the support elements.
15. 15. A loudspeaker as claimed in any preceding claim wherein the individual portions of the diaphragm are arranged in parallel rows and have a polygonal outline.
16. 16. A loudspeaker as claimed in claim 15 wherein the individual portions of the diaphragm are arranged in parallel rows and in columns perpendicular to the rows and have a rectangular outline.
17. 17. A loudspeaker as claimed in any preceding claim, wherein the material of

    the diaphragm has a high sound speed.
18. 18. A loudspeaker as claimed in claim 17, wherein polyimide resin film is used as the material of the diaphragm.
19. 19. A loudspeaker as claimed in claim 17, wherein the material of the diaphragm is a polycarbonate or polyester foil or a metal foil such as aluminium or titanium.
20. 20. A loudspeaker as claimed in any preceding claim wherein the support elements make an angle of substantially 45 degrees with the diaphragm.
21. 21. A loudspeaker as claimed in claim 1 or any of claims 5 to 19 wherein the angle of the support elements decreases from support element to support element from a position at which the drive device drives the diaphragm.
22. 22. A loudspeaker as claimed in any of claims 1 to 10 or 15 to 20 wherein the support elements consist of filaments which run from a base to the diaphragm at an angle, are attached to it and then from there are directed in the same direction to a rigid counter base.
23. 23. A loudspeaker as claimed in claim 22 wherein the filaments on the base or the counter base are attached via springs, where these springs are preferably alternately connected on the side of the base and on the side of the counter base for consecutive filaments.
24. 24. A loudspeaker as claimed in claim 22 or 23 wherein two filaments are used for each support element and form an angle with each other, where the apex of the angle is attached to the diaphragm.
25. 25. A loudspeaker as claimed in any of claims 1 to 21 wherein the support elements consist of little tubes which are crimped flat at the ends to form pivots at these positions.
26. 26. A loudspeaker as claimed in any of claims 1 to 21 wherein the support elements have the shape of isosceles triangles with a small base, where the apex of the triangle is pivotally coupled to the diaphragm and the base surface is pivotally coupled to the base member.
27. 27. A loudspeaker as claimed in any of clams 1 to 21 wherein the support elements are formed by pieces of fabric which are corrugated and which are connected to the base member on one side and to the diaphragm on the other.
28. 28. A lòudspeaker as claimed in any of claims 1 to 21 wherein the support elements are formed by pieces of fabric which are connected to the diaphragm on one side and to the base member on the other side.
29. 29. A loudspeaker as claimed in any preceding claim wherein acoustic conducting elements are embedded in the diaphragm between the individual portions, and consist of a material with a high acoustic speed.
30. 30. A loudspeaker as claimed in claim 29, wherein the acoustic conducting elements are rods with rectangular, circular or semicircular cross-sections.
31. 31. A loudspeaker as claimed in claim 29 or 30 wherein the material used for the acoustic conducting elements consists of a mixture of approximately 60 per cent graphite and 40 per cent epoxy resin.
32. 32. A loudspeaker as claimed in any preceding claim wherein support elements are provided on both sides of the diaphragm, which form an acute angle with the diaphragm and are approximately at right angles to each other, and the support elements on each side of the diaphragm are each connected to an acoustic conducting element, which is subjected to the sound oscillations, and these acoustic conducting elements are in turn connected to the base member via support elements.
33. 33. A loudspeaker as claimed in claim 32 wherein the ends of the acoustic rods on the two sides of the diaphragm are interconnected via a polygonal link where the link is held at the corners of the polygon by support elements which bisect the angle of the link in each case.
34. 34. A loudspeaker as claimed in claim 33 wherein two acoustic rods at the sides of the diaphragm are connected to each other via a pivoting wheel segment.
35. 35. A loudspeaker as claimed in any preceding claim wherein the diaphragm is tightly enclosed by a housing, where preferably only one upper or lower air gap is retained between the housing and the diaphragm.
36. 36. A loudspeaker as claimed in any preceding claim wherein the direction of drive of the diaphragm forms an acute angle with the surface of the diaphragm, and wherein the component of motion at right angles to the surface of the diaphragm is at least equal to the component along the surface of the diaphragm.
37. 37. A loudspeaker as in claim 36 wherein the direction of drive is at right angles to the direction of the degree of freedom of the movement of the diaphragm permited by the support elements.
38. 38. A loudspeaker as claimed in any preceding claim comprising an electrical drive which consists of a coil-excited magnet with a flat air gap, wherein the armature consists of a material with a high coercive force, e.g. of a samarium cobalt plate, which is resiliently urged toward the position of rest and which extends in part into the magnetic field produced between the pole shoes.
39. 39. A loudspeaker wherein the drive is produced by motors according to claim 38 mounted at two opposite ends of the diaphragm, which operate on the diaphragm or on acoustic rods embedded in the diaphragm.
40. 40. Loudspeakers substantially as hereinbefore described with reference to the accompanying drawings. -.