GB2186761A

GB2186761A - Cone loudspeakers

Info

Publication number: GB2186761A
Application number: GB08703315A
Authority: GB
Inventors: Ian Stanley White
Original assignee: CELESTION INT Ltd
Current assignee: CELESTION INT Ltd
Priority date: 1986-02-14
Filing date: 1987-02-13
Publication date: 1987-08-19
Also published as: EP0235991A3; ATE98081T1; ES2048733T3; GB2186761B; CA1292307C; DE3788293D1; GB8703315D0; GB8603645D0; EP0235991A2; JPS62248398A; DE3788293T2; EP0235991B1

Abstract

In a cone loudspeaker having a central dome (14), an annular cone (10) around the dome, and a voice coil (18), the central dome (14) is made mechanically strong and axially stiff and is an acoustic radiator in its own right. The dome (14) is preferably also radially stiff and its radial stiffness may be enhanced by a circumferential reinforcing ring. The dome is preferably hemispherical and may be made of aluminium, titanium or fibre-reinforced plastics materials. <IMAGE>

Description

1 GB 2 186 761 A 1 SPECIFICATION and the material or materials from which

it is made, are chosen to optimise the behaviour of the dome, and Cone loudspeakers 65 in particularto minimise misbehaviour in the upper end of the audio range. It is desirable that the material This invention relates to cone loudspeakers, and is of the dome should have a very high stiffness to particularly concerned with improving the acoustic weight ratio.

behaviour of such loudspeakers. One wayto achieve the desired axial stiffness of the It is already known to produce a one-piece metal 70 dome, coupled with it acting as a clean radiator, is to dome and voice coil formerfor cone loudspeakers. shape the dome with relatively steep sides. Preferably, This known product uses a metal dome primarily for the outside wall of the dome as it falls awayfrom the heat sink purposes and the dome is a shallow, apex is at least as steep- sided as a hemisphere. It has generally "flat" dome with only a small amount of been found that a dome of substantially hemispherical curvature. With this known product, due to misbe- 75 shape is particularly suitable.

haviour of the dome, and also of the cone, one So far as materials are concerned, although the encounters break-up of the acoustic response at choice of materials is determined by a wide range of relatively lowfrequencies. Roli-off due to this misbe- different considerations, it has been found that haviour can start at as low as 2 to 3 kHz. aluminium and titanium are particularly suitable Starting from the basis of a cone loudspeaker 80 materialsforthe central dome. Non-metallic materials having a central dome, the following are among the such as plastics materials reinforced with carbon fibre objects of the present invention: or glass fibre may also be used. Such materials have a 1. To achieve an accurate response atthe higher particularly high stiffness to weight ratio.

frequency end of the audio range; Within the context of the present invention, the 2. To drive the point atwhich the audio response 85 central dome of the loudspeaker may be made as one breaks up eitherfuily above the audio range or at east with the voice coil former, orthe dome and voice coil intothe upper region of that range; formercould be separate, possiblywith an intermedi- 3. Substantiallyto preventthe occurrence of vibrat- ate stiffe n i n g ri n g.

ing modes; A numberof embodiments of cone loudspeaker in 4. Substantiallyto prevent parasitic resonance of 90 accordance with the invention will now be described the dome; by way of example and with reference to the 5. Substantiallyto preventthe occurrence of selfaccompanying drawings, in which:

resonant modes overthe full audio band; Fig. 1 is a schematic partial representation of a first 6. To use a dome which is designed for its acoustic embodiment of cone loudspeaker in accordance with behaviour, and notjust as a heat sink; 95 the present invention; 7. To make the central dome "behave" through at least Fig. 2 is a partial viewof a slightly modified dome the greater partof the audio range; construction; 8. To provide a central domewhich is a clean Fig. 3 is a partial view of an alternative modified radiator in its own right and which is mechanically dome construction; and strong. 100 Fig. 4 is a schematic illustration of a dome having an Thefulfilment of these objects gives riseto a alternative shape.

number of advantages which are achieved bythe As shown in the drawings, the loudspeakercom loudspeaker of the present invention. Among these prises a conventional annular cone 10 with a corn advantages arethe following: pliantsurround 12 around its periphery.Adome 14is 1. A more stable acoustic response; 105 positioned centrally within the cone. In Figs. 1 to 3 the 2. The prevention of break-up in the audio band; central dome 14 is a substantially hemispherical 3. It is easierto achieve smooth cross-overs in element. In Fig. 1 an integral cylindrical skirt portion 16 multi-way systems; extends axially of the open end of the dome. The cone 4. One achieves a more realistic response at 10 isfixed to the outside of the central dome at cross-overfrequencies; 110 approximately the position wherethe hemispherical 5. The high frequency output of the loudspeaker dome element 14 and the skirt portion 16 meet. The sounds subjectively like a tweeter; apex of the central dome 14 here lies substantially in 6. It is then feasible to use electronic equalisation to the plane of the outer perimeter of the cone 10.

make it possible to produce an accurate full-range However, in other embodiments, the dome apex loudspeaker. Electronic equalisation use with conven- 115 could lie above or belowthis plane.

tional loudspeakers of this type will boostthe flaws in As shown in Fig. 1, a voice coil 18 is wound around the acoustic characteristic. the outside of the outer end of the skirt portion 16 of These objects and advantages are acheived in the central dome. A central pole-piece 19 is fitted into accordance with the present invention by a cone the skirt portion 16. Front and rear plates 21 a and 21 b loudspeaker comprising an annular cone and a central 120 which sandwich an annular magnet 23 are positioned dome which is mechanically strong, which is axially outwardly of the coil.

stiff and which is an acoustic radiator in its own right. In Fig. 2the voice coil 18 isshown wound on a Preferably the dome is also radial ly stiff. voice-coil former 20 which is separated from the The shape and configuration of the central dome, central dome 14, with thetwo components held The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a later filed formal copy.

2 GB 2 186 761 A 2 togetherbyan intermediate stiffening ring 22which is which thecone is fixed adjacent to the junction ofthe of T-shaped cross-section with the leg of the T lying dome and the former.

within the gap between the dome 14 and the former 11. A cone loudspeaker as claimed in any of claims 20. In this case the dome 14 and coil former 20 would 1 to 8, which includes a voice coil former made be manufactured as separate items. The coil former 20 70 separately from the dome, and means to enhance the may be of metal or may be non-metallic. radial stiffness of the dome connecting the dome and The stiffening ring 22 provided around the dome 14 formertogether.

preferably lies approximately atthe equator of the 12. A cone loudspeaker as claimed in claim 11, in hemisphere, and either internally or externally of the which the meansto enhance the radial stiffness of the dome. Fig. 2 shows an arrangementwith a T-shaped 75 dome comprising a ring member positioned around ring having the head of theTexternally ofthe dome, the dome and former at their junction.

whereas Fig. 3 shows the ring internally of the dome 13. A cone loudspeaker as claimed in claim 12, in and bridging the gap between the dome and the which the reinforcing ring member is of metal, former. This reinforcing ring 22 is preferably of metal, preferably aluminium or magnesium.

for example aluminium or magnesium, and is pro- 80 14. A cone loudspeaker as claimed in claim 12 or vided to enhance the radial stiffness of the dome. 13, in which the dome is hemispherical and the The central dome 14 of the loudspeaker of the reinforcing ring member is positioned substantially at present invention is a "hard" dome, designed for the equator of the dome.

good behaviour acoustically. Although a wide range 15. A cone loudspeaker comprising a cone, and a of materials could be used forthe dome 14, it has been 85 central dome which is mechanically strong, which is found thattitanium and aluminium are particularly axially and radially stiff and which is an acoustic good materials forthis purpose. Although the need to radiator in its own right, the shape and configuration provide relatively steep sides forthe dome has been of the dome and the material of which it is made being shown in Figs. 1 to 3 as being achieved bythe use of a such that break-up of the audio response does not hemispherical dome, other shapes and configurations 90 occur below a frequency of the order of 17 kHz.

of dome could be used. For example, as shown in Fig. 16. A cone loudspeaker as claimed in claim 15, in 4, a more elongate dome W, tending towards a which break-up of the audio response does not occur semi-ovoid shape, could alternatively be used. In each below a frequency of the order of 20 kHz.

case,the dome 14 is axially stiff and mechanically 17. A cone loudspeaker substantially as hereinbe strong and the dome acts as a clean radiator in its own 95 fore described with reference to the accompanying right, without misbehaving in the upperfrequency drawings.

range of the audio band, for example up to about 17 kHz and preferably up to in excess of 20 kHz. Printed in the United Kingdom for Her Majesty's Stationery Office by the Tweeddale Press Group, 8991685, 8187 18996. Published at the Patent Office, The term "radiaV as used herein is to be understood 25 Southampton Buildings, London WC2A lAY, from which copies may be as meaning a direction across the equator of the obtained.

dome, whereas the term "axial " as used herein is to be understood as meaning the direction in which the dome vibrates in use.

Claims

1. A cone loudspeaker comprising an annular cone and a central dome which is mechanically strong, which is axially stiff and which is an acoustic radiator in its own right.

2. A cone loudspeaker as claimed in claim 1, in which the dome is radially stiff.

3. A cone loudspeaker as claimed in claim 1 or 2, in which the dome has a high stiffness to weight ratio.

4. A cone loudspeaker as claimed in any preceding claim, in which the dome is of titanium or aluminium.

5. A cone loudspeaker as claimed in any of claims 1 to 3, in which the dome is of fibre-reinforced plastics material.

6. A cone loudspaker as claimed in any preceding claim, in which the outside wall of the dome as itfalls away from the apex is at least as steep-sided as a hemisphere.

7. A cone loudspeaker as claimed in claim 6, in which the dome is substantially hemispherical.

8. A cone loudspeaker as claimed in any of claims 1 to 6, in which the dome issemi-ovoid in shape.

9. A cone loudspeaker as claimed in any preceding claim, in which the central dome is integral with a voice coil former which comprises a skirt portion extending axially of the open end of the dome.

10. Acone loudspeaker as claimed in claim 9, in