[0001] The invention relates to loudspeakers and more particularly to drive units for loudspeakers.
[0002] It is known to make the cones of loudspeakers from materials such as paper, plastics
and metal sheet, although increasingly the chosen material is a plastics material
such as polypropylene since this material has good characteristics for this particular
use.
[0003] Conventional polymer cones are vacuum-moulded from sheet by a process using heat
to soften the plastics. Drawn down over a shaped mould, the material is thinnest at
the apex or peak of the cone, with the highest tension at this position. This is the
converse of what is desired, namely a stronger, thicker section at the cone neck for
good termination to the driving coil, and a thinner, low mass region at the marginal
edge. Preferably the cone section should be gently tapered to provide a well-ordered
break-up behaviour, while the join to the flexible surround should be imperceptible
to minimise standing wave reflections at the boundary between the surround and cone.
[0004] The most basic loudspeaker cone is formed about its periphery with a corrugation
which forms a suspension or surround by which the cone is able to move under the influence
of its drive means which is usually a moving coil motor. More advanced speaker cones
are provided with a peripheral suspension in the form of a corrugated member of flexible
rubber or other elastomeric material and which is sometimes known as a roll surround.
Such elastomeric suspensions are normally compression moulded from thermosetting elastomeric
materials and are secured to the material of the cone with the aid of an adhesive.
This requires skilled hand assembly to ensure concentricity and a reliable bond and
is thus slow and expensive. This form of assembly is however usually justified by
the improved acoustic performance which results from the provision of a compliant
suspension for the cone.
[0005] It is an object of the invention to provide a loudspeaker cone and suspension or
surround assembly which can be made without the need for hand assembly so that variations
in manufacture and thus in performance, which have previously been commonplace, can
be avoided or at least mitigated.
[0006] In the following description the term cone will be used to describe any kind of air
moving device whether flat or conical or of other shape and whether or not it is driven
by a moving coil or other mechanism.
[0007] According to the invention there is provided a loudspeaker cone and surround assembly
wherein the surround is an injection moulding formed directly onto the cone.
[0008] From another aspect the invention is a loudspeaker cone and surround assembly wherein
the cone is an injection moulding formed directly onto the surround. In this way the
cross-sectional thickness of the cone can be tailored as desired, e.g from relatively
thick near the centre to relatively thin near its margin.
[0009] Preferably the cone is of a plastics material and the surround is of an elastomer.
Preferably both cone and surround are injection moulded. Advantageously, the cone
comprises a polypropylene polymer and the surround comprises a styrene-ethylene butylene-styrene
polymer. This combination of materials results in the materials of the cone and the
surround becoming chemically bonded together during the injection moulding step. This
chemical bonding largely obviates the problem of de-lamination which frequently occurs
with hand assembled loudspeaker cone and surround assemblies when using adhesives.
[0010] In assembling a loudspeaker drive unit it is conventional to attach the cone and
surround assembly to a chassis member with the aid of an adhesive applied to the outer
marginal edge of the surround. Since the chassis is usually of metal, it is necessary
to employ special adhesives such as cyanoacrylates to bond the elastomeric surround
to the metal chassis. Such adhesives can be harmful and are prohibited in some countries.
As an alternative an annular paper ring or gasket can be fixed to the margin of the
surround using non-harmful adhesives and again non-harmful adhesives can be used to
fix the paper ring or gasket to the drive unit chassis. This procedure involves extra
work.
[0011] In accordance with the present invention and to obviate the extra production step
while avoiding the need for harmful adhesives, a paper or the like gasket may be directly
moulded onto the surround when the surround is made. Thus the paper gasket can be
placed in the mould before the elastomer is injected to form the surround.
[0012] The junction between the material of the cone and the material of the surround preferably
comprises an overlapping portion to lend strength to the joint. If desired the material
of the surround can overlap both sides of the outer peripheral margin of the cone.
Where the external appearance of the loudspeaker is important, it may be desirable
that the overlap is invisible, in which case it can be situated only on the rear surface
of the cone. Preferably the junction between the cone and the surround is situated
close to the edge of the active portion of the surround, that is to say the portion
designed to move in use, so that the material of the surround does not form part of
the air driving activity of the cone since this might adversely influence the acoustic
characteristics of the cone.
[0013] From a further aspect the invention is a method of making a loudspeaker cone and
flexible surround assembly comprising arranging a cone in the mould cavity of an injection
moulding apparatus and injection moulding a surround material onto the periphery of
the cone under heat and pressure to form a surround or suspension which is chemically
bonded to the material of the cone.
[0014] Preferably the cone comprises polypropylene and is injection moulded and preferably
the surround comprises an elastomeric material.
[0015] From yet another aspect the invention is a method of making a loudspeaker cone and
flexible surround assembly comprising arranging a surround in a mould cavity of an
injection moulding apparatus and injection moulding a cone material onto the surround
under heat and pressure to form a cone which is chemically bonded to the material
of the surround.
[0016] Preferably the cone comprises polypropylene and preferably the surround comprises
an elastomeric material and is injection moulded.
[0017] One method of making the loudspeaker cone and flexible surround assembly comprises
injection moulding a polypropylene cone in a first cavity in an injection moulding
machine and thereafter altering the shape of the cavity to define a peripheral surround
cavity into which the peripheral edge of the cone extends and injection moulding an
elastomer into the surround cavity whereby it chemically bonds to the edge of the
cone. Alternatively the cone can be moulded first in one mould cavity and then transferred
to another mould cavity in which the surround is injection moulded onto the cone.
[0018] The polypropylene used for the cone may be a homopolymer or co-polymer and may comprise
a proportion of a filler such as mica. The plastic material will have a high melt
flow index to allow the material to be moulded in a cavity having a thin section.
[0019] The elastomer of the suspension is preferably a styrene-ethylene butylene-styrene
polymer such as that sold by Evode Plastics Limited under their registered trademark
Evoprene G. Preferably the elastomer has a shore A hardness below 40.
[0020] A preferred injection moulding apparatus will have two injection units and barrels
one of which injects the material of the cone into the mould cavity and the other
of which injects the material of the suspension into the mould cavity.
[0021] The cone could be moulded from other plastics such as ABS, polystyrene, PVC, nylon
or polyethylene or any other rigid polymer. The surround is preferably of styreneethylene
butylene-styrene but could be of flexible PVC or of a thermoplastic rubber alloy compound.
[0022] The invention is diagrammatically illustrated by way of example in the accompanying
drawings in which:-
Figure 1 is a perspective view of a loudspeaker cone and surround assembly made in
accordance with the present invention;
Figure 2 is a scrap cross section of part of the loudspeaker cone and suspension assembly
of Figure 1, and taken on the line II - II of Figure 1, and
Figure 3 is a scrap cross-sectional view corresponding to Figure 2 of a modified arrangement.
[0023] In the drawings there is shown a loudspeaker drive cone and surround assembly of
generally conventional appearance and comprising a frusto-conical drive cone 1 which,
in use, is attached at its inner margin 11 in any convenient manner to a loudspeaker
drive motor, e.g. a moving coil, not shown, the outer margin 3 of the cone 1 being
attached to a compliant surround or suspension 2 which in turn is secured in any convenient
fashion to a loudspeaker drive unit chassis (not shown). In the present case the peripheral
margin 3 of the loudspeaker drive cone 1 has been injection moulded from polypropylene
and the flexible elastomeric surround or suspension 2, which is of generally conventional
configuration, has been injection moulded thereon. The surround is annular in shape
and comprises an outer flange 5 by which it is attached to the loudspeaker drive unit
chassis (not shown), a part circular roll or bellows 6 which is the active part of
the cone suspension and an inner flange 7, which is moulded onto the rear face 9 of
the cone 1 so as to overlap the outer margin 3 of the cone to some extent. The overlapping
join is thus invisible in use. The outer edge 8 of the cone 1 is preferably positioned
closely adjacent to the roll or bellows 6 of the surround 2 so that the surround does
not adversely affect the acoustic properties of the cone.
[0024] The material of the surround 2 is a styrene-ethylene butylene-styrene which bonds
chemically under the heat and pressure of the injection moulding process to the polypropylene
cone to form an integral unit therewith, thereby obviating the need to glue the cone
and surround together as has been necessary heretofore. In this way the alignment
between the cone and surround can be controlled more predictably than is the case
with hand assembly, and the connection between the cone and surround can be achieved
consistently.
[0025] In the arrangement of Figure 3, a paper gasket 10 is arranged in the mould prior
to the injection moulding of the surround 2, whereby the gasket 10 is bonded to the
flange 5. In this way the cone and surround unit can be secured to the chassis (not
shown) of a drive unit using conventional, that is, non-harmful, adhesives.
[0026] The invention thus provides a novel drive cone and surround assembly which can be
manufactured more efficiently than was previously the case.
1. A loudspeaker cone and surround assembly (1,2) characterised in that the surround
(2) is an injection moulding formed directly onto the cone (1).
2. A loudspeaker cone and surround assembly (1,2) characterised in that the cone (1)
is an injection moulding formed directly onto the surround (2).
3. A loudspeaker cone and surround assembly according to claim 1 or claim 2, characterised
in that the cone (1) comprises a plastics material, the surround (2) comprises an
elastomeric material, and in that the cone and the surround (1,2) are injection mouldings.
4. A loudspeaker cone and surround assembly according to claim 3, characterised in that
the cone (1) comprises a polypropylene polymer and the surround (2) comprises a styrene-ethylene
butylene-styrene polymer.
5. A loudspeaker cone and surround assembly according to any preceding claim, characterised
in that a paper gasket (10) is moulded onto a peripheral margin (5) of the surround
(2).
6. A loudspeaker drive unit incorporating a loudspeaker cone and surround assembly (1,2)
as claimed in any preceding claim.
7. A loudspeaker incorporating a loudspeaker cone and surround assembly (1,2) as claimed
in any of claims 1 to 5.
8. A method of making a loudspeaker cone and flexible surround assembly (1,2) characterised
by arranging a cone (1) in the mould cavity of an injection moulding apparatus and
injection moulding a surround material onto the periphery (3) of the cone (1) under
heat and pressure to form a surround (2) which is chemically bonded to the material
of the cone (1).
9. A method according to claim 8, characterised in that the cone (1) is formed by injection
moulding.
10. A method of making a loudspeaker cone and flexible surround assembly (1,2) characterised
by arranging an elastomeric surround (2) in a mould cavity of an injection moulding
apparatus and injection moulding a cone material onto the surround (2) under heat
and pressure to form a cone (1) which is chemically bonded to the material of the
surround (2).
11. A method according to claim 10, characterised in that the surround (2) is formed by
injection moulding.
12. A method according to any one of claims 8 to 11, characterised in that the cone (1)
comprises a plastics material and the surround (2) comprises an elastomeric material.
13. A method according to any one of claims 8 to 12, characterised in that the cone (1)
comprises a polypropylene polymer.
14. A method according to any one of claims 8 to 13, characterised in that the surround
(2) comprises a styreneethylene butylene-styrene polymer.
15. A method according to any one of claims 8 to 14, characterised by arranging a paper
gasket (10) in a portion of the mould cavity in which the surround (2) is to be formed,
such that on injection moulding the surround (2), the paper gasket (10) is bonded
thereto.