WO1988002977A1

WO1988002977A1 - Arrangement in loud speakers

Info

Publication number: WO1988002977A1
Application number: PCT/SE1986/000483
Authority: WO
Inventors: Claes Malmqvist
Original assignee: Claes Malmqvist
Priority date: 1985-04-17
Filing date: 1986-10-17
Publication date: 1988-04-21
Also published as: SE447692B; SE8501872D0; SE8501872L

Abstract

An arrangement in loud speakers comprises a driving means (7) for transforming electrical oscillations into mechanical ones. The driving means which may consist of a voice coil, is connected to at least one acoustical first diaphragm (1), so that its kinetic energy is propagated to the diaphragm and transformed into sound energy. The edge (6) of the diaphragm (1) is of an oblong rounded shape. The driving means (7) is connected to the diaphragm at a driving area (3) which, projected perpendicularly to the edge plane of the diaphragm, is situated laterally of a first reference line (13) connecting the two maximally distant points (11, 12) of the edge line, and also laterally of a second reference line (16) which perpendicularly intersects said first reference line midway between said points, so that said two lines (13, 16) divide the edge plane into four quadrants, one of which comprises said driving area (3).

Description

ARRANGEMENT IN LOUD SPEAKERS

TECHNICAL FIELD

The invention relates to an arrangement in loud speakers comprising a driving means for transforming electrical oscillations into mechanical ones, said driving means being connected to an acoustical diaphragm, so that the kinetic energy thereof is propagated to the diaphragm and transformed into sound energy.

STATE OF THE ART

As good as all existing loud speakeers are built on the same basic principle: a voice coil constituting a driving means, is connected to an axially movable stiffened diaphragm of cardboard, plastic material or similar. When an electrical signal current flows through the voice coil, it will oscillate axially, the kinetic energy being propagated to the diaphragm and transformed into sound energy. The weak link of said chain is the speaker diaphragm; many attempts have been made to improve the sound quality by reconstructing the diaphragm. The distorsion of the original sound is due particular to delayed vibrations in the material of the diaphragm, which can be heard as so called coulering of the original sound. Among the great number of patent specifications in the field the following examples may be mentioned: US patent Nos 2 551 556, 2923 371, 3 153 463, 3 180 945, 3 211 834, 3 364315, 3 483 946 and 3 603 427.

BRIEF DISCLOSURE OF THE INVENTION

The object of the invention is to provide a loud speaker of a better sound reproduction than known speakers. Another object is to offer a speaker of a comparatively reduced external size, and nevertheless capable of good reproduction within a wide range of frequencies. Still another object is to be able to manufacture the article in a simple manner and at a low cost. These and other objects are fulfilled by giving the diaphragm a specific shape and by connecting the driving means to said particular diaphragm at a particularly selected point or restricted region. The shape of the diaphragm which I have found the best and the point of connection of the driving means which I believe is the most favourable have been based upon extensive empirical tests and not upon any particular theory. Said tests have shown that several parameters in cooperation are required In order to obtain the best conditions. However, the decisive improvements are reached if the edge of the diaphragm is of an oblong rounded shape, e.g. elliptical shape, and if the driving means is connected to the diaphragm at a region which, projected perpendicularly to the edge plan or base of the diaphragm, is situated laterally of a first reference line connecting the two mutually most distant points of the edge line and also laterally of a second reference line which at right angles intersects said first reference line midway between said points. In a preferred embodiment the diaphragm takes the general shape of an inclined cone, i.e. the shape of a body not curved in two direction. However, a double-curved shape of the diaphragm, common per se, is not excluded. Thus, the denomination "cone" applied to the diaphragm is not meant to be a strictly mathematical definition but is herein used as a general term for a more or less funnel-shaped speaker diaphragm, as is usual in this technical field. On the other hand, I regard it as very important and probably a prerequisite for a good sound transmission from the driving means to the diaphragm that the driving means, consisting of a voice coil, is attached to the diaphragm via a non-magnetic portion tapering into an apex, so that the transmission of the oscillations to the diaphragm takes place at a very concentrated area at the apex of the cone. Said area which is termed "driving point" in the following and which, forms the area of contact between the cone and the vibration transmitting member of the tapering driving means (the voice coil), should not be of a diameter or maximum extension exceeding 10 per cent and preferably not exceeding 5 per cent of the maximum extension of the diaphragm In the edge plan. The diaphragm may be stiffened in various ways. In the chosen embodiment the diaphragm has been stiffened by "plaiting", i.e. by folds extending from the apex to the edge of the cone in a manner known per se. Other means of stiffening are also possible, such as stiffening ribs extending along the cone similarly as the "plaiting folds".

A treble cone should be placed inside the first-mentioned cone which is termed "main cone" in the following. Preferably the treble cone should also be of oval shape. The main cone and the treble cone are joined to each other at the driving point which is common to both cones. The driving point is situated so close to the edge of the main cone that the edge of the treble cone, projected perpendicularly to the edge plane of the main cone, reaches substantially up to or beyond the edge of the main cone. It is important that the two cones do not disturb each other when oscillating in their respective frequency ranges. In order to prevent the occurrence of interference phenomena the capability of the main cone of reproducing high-frequency sounds, i.e. sounds in the treble range, should be prevented or curtailed which can be realized in many different ways:

The main cone may be "coated" in respect of the treble frequences, which involves that the part of the diaphragm of the main cone situated closely to the driving point is made heavier. Said part, termed zone D - the treble zone - in the following, corresponds on the whole to the part that is "shaped" by the treble cone. In order that the total mass of the main cone be too great to allow the voice coil and the magnet to drive the cone with sufficient force, i.e. the damping being too great, said "loading" may be compensated by reducing the mass of the remaining part of the main cone correspondingly. In principle a lighter material could be used in those part of the main cone lying remote from the driving point, but then the oscillations of high frequencies will be favoured which is not desirable. Therefor, a better alternative is to perforate the diaphragm at suitable places, so that air can pass therethrough, which in practice means a reduced mass load upon the cone, considering that the cone when oscillating, can be regarded as forming an integral body with the air volume next thereto.

The main cone can be made of material which, is different in the treble frequency zone D, in the intermediate frequency zone M and in the parts most remote from the driving point, the base frequency zone B. So the treble zone D can be manufactured from a material not reproducing treble frequencies (frequencies higher than 7 kHz). Consequently, the material of the treble zone should damp said frequencies. At the same time it should be so stiff as to be able to transfer the oscillations to the next zone, the intermadiate frequency zone M. Preferably the same base material is used in the entire main zone, e.g. coal-fibre-reinforced plastic material, a combination of materials that is lightweight as well as stiff. In order to prevent reproduction of frequences in the treble range, in the treble zone D a silicon. layer may be applied to the fore side as well as the back side of the base material of the cone. In the intermediate zone M there may be applied a metallic coating, e.g. an aluminum alloy, and in the region most remote from the driving point, the base frequency zone B, the base material may have a cellulose layer.

The treble cone can be manufactured from a thin layer of aluminum having a thin layer of cellulose on its back side. However, this is merely one of many possible material combinations. Also the treble cone can be folded, if suitable, and preferably It is oval like the main cone.

The speaker should be designed so as to stimulate the oscillation of the main cone in the base frequency zone B, for if no such stimulating measures are taken, the diaphragm of the main cone will primerily oscillate merely in the areas close to the driving point. That can be prevented, i.e. oscillations in the base frequency zone B can be stimulated in many ways; the cone suspension can be made more flexible along the base frequency zone by making it broader in said region than in the region close to the driving point, and/or the central axis of the voice cone can be tilted in the direction towards the base frequency zone.

Further characteristic features and advantages of the invention will appear from the claims and the following description of a preferred embodiment.

SHORT DESCRIPTION OF THE DRAWINGS In the following description of a preferred embodiment reference is made to the accompanying drawing figures, where

Fig. 1 is a front view of the speaker according to the invention,

Fig. 2 is a sectional view taken along the line II-II in Fig. 1 and in a plane coinciding with the driving point and said first reference line,

Fig. 3 is a perspective view of the speaker as seen obliquely from the front, and

Fig. 4 shows the speaker in a perspective view seen obliquely from the back side, certain parts being omitted in Fig. 3 and Fig. 4 in order to make essential parts more clearly visible.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the figures, 1 designates a first diaphragm forming the main cone.

A treble cone is designated by 2, the same also consisting of a diaphragm. The treble cone 2 is placed inside the main cone 1 and is joined to the main cone at the common point, the so-called driving point 3. The main cone 1 is suspended in a chassis 5 by means of the so-called conical support 4. 6 designates the edge of the main cone 1.

The edge 6 forms the border between the stiff sound-emitting diaphragm of the cone 1 and the flexible non-emitting material of the support 4. 7 designates a voice coil. The coil 7 is held floating in a magnetic air gap 8 by means of a resilient guiding disk 9. The main cone 1 consists of an inclined cone, the generatrix of which runs along an elliptical curve forming the edge 6 of the sound- emitting diaphragm. 11 and 12 designate the points upon the edge 6 having the maximum mutual distance from each other. The major axis 13 connecting the points 11 and 12 is the line having in the Introduction been termed the first reference line. Correspondingly, said second referrence line forms the minor axis 16 of the edge ellips 6.

As mentioned earlier, the main cone is oblique and more distinctly, it is oblique in the sense that its apex - which coincides with the driving point 3 - as projected perpendicularly to the plane of the edge line 6, will be seen laterally of the major axis and laterally of the minor axis 16, i.e. within one of the four quadrants of the ellips 6. In the shown embodiment the driving point 3 is situated so close to the edge 6 of the main cone 1 that the edge 17 of the treble cone 2, as projected upon the edge plane of the main cone 1, almost forms a tangent to the edge 6 of the main cone. The major axis 18 of the treble cone 2 is approximately half as long as the major axis 13 of the main cone, and the minor axis 19 of the treble cone is slightly shorter than half the length of the minor axis 16 of the main cone.

The cone angle of the main cone 1, measured In the plane of the major axis 13, is 140 to 150 degrees In the shown embodiment. The main cone 1 may be manufactured of various, preferably quite stiff materials,such as cardboard, plastics, metal foils, coated fabric or of combinations of several materials. In one instance the cone 1 was made of thin aluminum foil coated with cellulose on the front side. An other suitable material is carbon-flbre-relnforced plastic material coated on one or both sides with different materials in the zones D, M and B representing the approximate regions for reproduction of frequences in the treble range (5 to 7 kHz) , the intermediate frequency range (200 Hz to 5kHz) and the base frequency range (75 Hz to 200Hz), respectively. The treble cone 2 which may consist of cardboard or thin aluminum foil, emits sound In the frequency range of 5 to 20 kHz. In order to prevent mutual distorsion of the treble cone 2 and the main cone 1, the zone D of the main cone 1 may be coated with a silicon layer on one or both sides, this having a damping effect upon the reproduction. In the zone M the cone 1 may be coated with a metallic layer on one or both sides, and in the base zone B the cone may be coated with a cellulose layer on one or both sides (said layers not shown in the figures). The cone 1 may also be provided with apertures 21, allowing air to pass through, which acts as relieving the cone of part of its mass, in consideration of that the cone when oscillating, may be regarded as a body integrated with the next surrounding air volume.

The voice coil 7 is connected to the main cone 1 and to the treble cone 2 by means of a tapering member 22 of non-magnetic material, e.g. aluminum. In the shown embodiment the member 22 is given the shape of a cone, but other shapes are also possible provided that the member ends in a tip or rather in a small area forming the driving point 3 common to the main cone 1 and the treble cone 2. The main cone 1 is folded in order to improve the rigidity. The folds 25 run closer at the driving point 3. The folds laid together in said point, are designated by 24.

The voice coil works like a piston which via the connection member 22 transfers the oscillations onto the main cone 1 and the treble cone 2. As the driving point 3 is offset far from the centre of the speaker, and in case no compensating counter-measures were taken, the oscillations would dominate in the treble zone 2 and in the upper left-hand quadrant in Fig. 1. In order to stimulate oscillations also in the base zone B the same is suspended more flexibly in the chassis 5 than the treble zone D. This has been accomplished by making the cone support 4 a great deal wider in the region remote from the driving point 3 than in the region close thereto, as is shown in the drawings. Therefore, in the base zone B the diaphragm is movable quite more easily than the diaphragm in the treble zone D. Moreover, the centre axis 25 of the voice coil 7 is inclined towards the centre of the speaker, i.e. in the same direction of the base zone, which also enhances the propagation of vibrations to the base zone B.

Claims

1. Arrangement in loud speakers comprising a driving means (7) for transforming electrical oscillations into mechanical ones, said driving means being connected to at least one acoustical first diaphragm (1), so that its kinetic energy is propagated to the diaphragm and transformed into sound energy, ch ara c t e r i s e d in that the edge (6) of the diaphragm (1) is of an oblond rounded shape, and in that the driving means (7) is connected to the diaphragm at a driving area (3) which, projected perpendicularly to the edge plane of the diaphragm, is situated laterally of a first reference line (13) connecting the maximally distant points (11, 12) of the edge line, and also laterally of a second reference line (16) which perpendicularly intersectes said first reference line midway between said points, so that said two lines (13, 16) divide the edge plane into four quadrants, one of which comprises said driving area (3).

2. Arrangement as claimed in claim 1, c h ar a c t er i s e d in that the driving means (7) is attached to the diaphragm (1) via a non-magnetic member (22) tapering into a tip, so that the transfer of oscillations to the diaphragm takes place at a driving point (3) consisting of a very small area at the apex of the cone, and in that the driving point and the area of contact between the diaphragm and the tapering member connecting the voice coil to the diaphragm are of a maximum extension not exceeding 10 per cent and preferably not exceeding 5 per cent of the maximum extension of the diaphragm in the edge plane.

3. Arrangement as claimed in any of the claims 1 or 2, c h a r a c t er i s e d in that the shape of the diaphragm essentially is that of an inclined cone (1), the cone angle of which is at least 130 degrees in a plane coinciding with the first reference line (13).

4. Arrangement as claimed in any of the claims 1 to 3, c h a r a c t e r i s e d in that the diaphragm Is stiffened by folds (23) extending from the driving point (3) to the edge (6).

5. Arrangement as claimed in any of the claims 1 to 4, c h a r a c t e r i s e d in that a treble cone (2) is provided within the first-mentioned cone (1) constituting the main cone of the loud speaker, the treble cone being connected to the main cone at the driving point (3) common to the two cones.

6. Arrangement as claimed in claim 5, c h a r a c t e r i s e d in that the edge of the treble cone, projected perpendicularly to the edge plan of the main cone, reaches substantially up to and beyond the edge (6) of the main cone.

7. Arrangement as claimed in any of the claims 5 or 6, c h a r a c t e r i s e d in that the main cone in a zone (D) close to driving point and of an extension such that at least a substantial part thereof corresponds to that of the treble cone (2), is made of a material essentially not able of reproducing sound in the treble frequency range. but able to transferring the oscillations of the diaphragm (1) to parts of the diaphragm remote from the driving point.

8. Arrangment as claimed in claim 7, c h a r a c t e r i s e d in that the main cone (1) consists of materials being different in at least the zones for treble frequency reproduction and for bass frequency reproduction and preferably also in a zone for intermediate frequency reproduction.

9. Arrangement as claimed in any of the claims 5 to 8, c h a r a c t e r i s e d in that the diaphragm of the main cone is perforated.

10. Arrangment in any of the claims 1 to 8, c h a r a c t e r i s e d in that the centre axis (25) of the voice cone is inclined to said edge plane in a direction towards those parts (B) of the main cone situated most remote from the driving point (3), and/or in that the suspension means (4) of the cone is of a greater flexibility at a range remote from the driving point than at a range close thereto, in order to make the diaphragm more mobile in the first-mentioned range than in the latter.