Audio voice coil adaptor ring

A voice coil adaptor ring and loudspeaker system of the moving coil type including a cone diaphragm supported by a frame, a voice coil former for supporting a voice coil, and a lower suspension for securing and centering the voice coil former in a magnetic gap while it is displaced by a magnetic circuit. The voice coil adaptor ring is mounted over the voice coil former and comprises a substantially cylindrical sleeve having a ledge extending outward from said sleeve for supporting the cone and lower suspension; an inner glue flange projecting inward from the sleeve so as to define a diameter corresponding to an outer diameter of the voice coil former whereby the sleeve, inner glue flange and voice coil former define a gap for receiving epoxies; and a plurality of venting passages in fluid communication with a cap volume defined by the cone and dust cap for venting hot air from the cap volume.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the field of loudspeakers, and 
in particular, to a voice coil adaptor ring for mating the cone and spider 
for increased strength and efficiency. 
2. Description of the Prior Art 
With reference to FIG. 1, a conventional loudspeaker 20 generally comprises 
a support frame 22, a cone 24, a dust cap 26 bridging across the cone, a 
suspension system, a voice coil 40, a voice coil bobbin/former 43, and a 
vented pole piece 41. The voice coil 40 is wound about the voice coil 
former 43 such that an annular magnetic gap is defined between a top plate 
37 and the magnet and the voice coil 40. The magnetic circuit linearly 
cycles or displaces the voice coil former 43 in this gap. In the 
conventional speaker, the cone shaped diaphragm (cone 24) is attached to 
the voice coil former above the coil 40 at its lower end and to the frame 
at its upper end. A suspension system comprising two elements connects to 
the frame and upper end of the cone, and to the frame and voice coil 
former, respectively. 
The suspension system of the loudspeaker normally comprises two elements, 
the surround 28 (upper or outer suspension) and the spider 38 (lower or 
inner suspension). The surround 28 is a mechanical device which holds the 
outer edge of the diaphragm/cone of the loudspeaker and is often referred 
to as a "roll." Typically, the surround comprises a single, large, 
semi-circular corrugation constructed from either rubber, compressed foam 
rubber, or some similarly treated fabric. Surrounds may also be 
constructed from several other materials including corrugated cloth, 
paper, plastic, etc. One purpose of the surround is to help keep the cone 
24 centered and to provide a portion of the restoring force that keeps 
voice coil in the gap defined between the pole piece and the top plate of 
the loudspeaker. The surround also provides a damped termination for the 
edge of the cone. A choice of thickness and material type for surround 
construction can greatly alter the response of the loudspeaker. 
A spider 38 is commonly constructed from treated corrugated fabric. The 
spider 38 comprises a lower/inner suspension member that helps to keep the 
voice coil concentric to the pole piece. A portion of the restoring force 
that maintains the voice coil within the gap is also provided by the 
spider. Thus, the stiffness of the spider can greatly affect the 
loudspeaker's resonance. The spider also provides a barrier for keeping 
foreign particles away from the gap area. 
In addition to controlling the linear motion of the cone, the surround, 
like the spider, acts as a major centering force for the loudspeaker's 
voice coil. The voice coil generally comprises a winding concentrically 
supported by a cylindrical voice coil former. The centering force provided 
by the roll and spider prevents the voice coil and former from rocking and 
rubbing against the pole piece or top plate. Rocking is undesirable 
because it can cause audible noise and/or damage to the driver. 
Often a loudspeaker design can be best optimized by utilizing a voice coil 
with a smaller diameter. However, the smaller voice coil setup creates 
certain problems, especially when designing loudspeakers for low frequency 
reproduction. Thus, for larger diameter loudspeakers (typically 10 inches 
and above), small voice coil systems are not common. Accordingly, there 
are few, if any, existing cones tooled for the smaller diameter coil 
former. To incorporate a small voice coil system, the cone must be 
customized, adapted or re-tooled. 
One disadvantage of mating a cone directly to a smaller voice coil is that 
a relatively small adhesive joint is made. Since the voice coil's diameter 
is much smaller, the gluing circumference is drastically reduced. 
Therefore, the designer must be concerned with the possibility of 
mechanical failures since the stress distribution around the glue joint is 
high. Because the spider attaches at this critical junction as well, 
spider joint stress also increases, introducing yet another possible 
failure mode. 
Another problem associated with smaller voice coils occurs in the use of 
pole vents. Pole vents comprise holes bored directly through the pole 
piece within the motor structure. These vents are used to relieve air 
pressure that builds up beneath the dust cap. Without a pole vent, audible 
noise can be introduced as the trapped air tries to escape during large 
cone excursions. However, when using a small diameter voice coil, the 
amount of metal in the pole piece is very limited. This amount of steel 
can only support limited amount of magnetic flux. Consequently, using a 
pole piece with large amounts of metal removed for pole vents can 
radically alter the performance of the magnetic circuit. 
A vented pole piece further affects the thermal behavior of the speaker. 
The steel contained in the pole piece provides an effective thermal sink 
for the voice coil. Machining a pole vent in the pole piece increases 
thermal resistance of the sink, lowering the power handling capability of 
the loudspeaker. 
The mechanical integrity of the spider is also compromised when using a 
small voice coil. Spiders are typically made from resin treated cloth 
materials. When the inner diameter of the spider gets smaller, fewer 
strands of material intersect the cutout. Since the glue joint lies on 
this small circumference, very little spider material is captured. This 
places the spider material under greater stress than normal. This 
high-stress condition could cause the spider itself to fatigue 
prematurely. Since the spider is typically called on to center the moving 
assembly and limit cone motion at the extremes of excursion, a compromised 
spider could cause a catastrophic failure. 
Rocking resistance is also compromised when using a smaller inner diameter 
voice coil. Rocking in a loudspeaker describes the moving assembly 
rotating in the vertical plane about a point located along its axis of 
motion. As a spider's inner diameter gets larger, the material along the 
inner diameter is required to deflect more when the moving assembly 
rotates a given amount (as during rocking). Consequently, a spider with a 
larger inner diameter will be more resistant to rocking because more 
energy is required to invoke a given angular change. It follows that using 
a small voice coil, and hence a small inner diameter spider, makes a given 
loudspeaker more susceptible to rocking related problems. 
The smaller voice coil system further affects the cone's structural 
integrity. As a voice coil gets smaller, the cone angle increases (using a 
vertical axis as a reference), causing the cone to become flatter. As the 
cone begins to flatten, its mechanical strength drops. Increasing the cone 
angle increases the likelihood of audible degradation due to cone flexure. 
Normally, the only option available for preventing cone flexure is to 
increase the cone thickness and/or increase the cone depth. This decreases 
the cone angle and makes the cone wall more vertical. These solutions, 
however, are not desirable since increasing the cone depth requires a 
larger frame depth and using a thicker cone adds weight to the moving 
structure. Moreover, thicker cones and deeper frames require special 
tooling and make the speaker's mounting depth unattractive for certain 
applications. 
Several loudspeaker designs are contemplated in the background art for 
improving speaker performance, stabilizing the speaker cone/diaphragm, 
and/or simplifying the manufacturing process. However, none of these 
references solve the above-noted problems. For example, Mitobe (U.S. Pat. 
No. 5,111,510) discloses a speaker and manufacturing method therefor 
including a diaphragm integrally combined with a first frame piece and a 
driver unit integrally combined with a second frame piece. Saiki et al. 
(U.S. Pat. No. 5,371,805) discloses a speaker and speaker system employing 
the same, comprising a diaphragm secured to a first periphery of an edge 
member and a frame secured to a second periphery of the edge member. 
Scholz (U.S. Pat. No. 5,323,469) discloses a conical loudspeaker having a 
conical stabilizing element joined between an underside of a speaker 
membrane and an outside surface of a speaker moving coil carrier. 
Kreitmeier (U.S. Pat. No. 5,424,496) discloses an electromagnetic 
converter comprising an internal magnet system, a moving coil and tubular 
segment. Kreitmeier (U.S. Pat. No. 4,764,968) discloses a disk-like 
diaphragm made from a conical plastic film and provided with vacuum formed 
support members which extend up to the disk-like radiating layer. Finally, 
Kobayashi (U.S. Pat. No. 4,118,605) discloses a coil mount structure 
comprising a cylindrical member, around one end portion of which a 
diaphragm edge is fixed, an inner peripheral edge portion where a damper 
is removably fixed, and an opposite end portion around which a coil is 
provided. Kobayashi, however, does not provide any structure for 
ventilating air pressure from beneath the dust cap or a structure for 
creating a secure joint between the diaphragm/cone, spider, and/or voice 
coil. The present invention, by way of contrast, is directed to an adaptor 
ring, the structure of which facilitates a stronger adhesive joint between 
the cone, spider, and voice coil bobbin or former, and a means for venting 
air pressure buildup. 
The above-noted background art neither solves or addresses the problems 
contemplated by the present invention. Accordingly, there remains a need 
for a loudspeaker capable of providing improved structural joints between 
the speaker cone, spider, and voice coil former, allowing the use of 
smaller voice coil systems and providing ventilation in the speaker 
without forfeiting performance. The instant invention addresses the needs 
in the art by providing a voice coil adaptor ring that provides increased 
stability to the speaker cone, spider, and voice coil former, and that 
facilitates the reliable use of smaller voice coils in loudspeaker 
designs, including low frequency speakers. The instant invention also 
addresses the need for improved ventilation. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a structure that 
facilitates the secure attachment of a cone edge, spider, and voice coil 
for improved loud speaker performance. 
Another object of the invention to provide a voice coil adaptor ring that 
allows for a stronger joint between the cone/diaphragm, spider/lower 
suspension and voice coil. 
It is also an object of the invention to provide a voice coil adaptor ring 
that makes it possible to use relatively small voice coils in low 
frequency speakers. 
It is a further object of the invention to provide a voice coil adaptor 
ring that eliminates the need for machining pole vents in the pole pieces 
of loud speakers. 
It is an additional object of the invention to provide a voice coil adaptor 
ring that facilitates use of a larger inner diameter spider that is more 
resistant to rocking. 
It is another object of the invention to provide a voice coil adaptor ring 
that makes it possible to reduce the cone angle for a given voice coil 
size to strengthen the cone. 
It is still an additional object of the invention to provide a voice coil 
adaptor ring that provides a structure that eliminates the need for 
adhering the spider and cone to the voice coil former. 
It is still a further object of the invention to provide a structure that 
allows the cone to mechanically lock and secure the spider suspension. 
It is yet another object of the instant invention to reduce the number of 
failure points in a loudspeaker and the probability of loud speaker 
failure. 
Another object of the instant invention is to reduce stress in the joints 
securing the spider and cone. 
A further object of the instant invention is to provide a voice coil 
adaptor ring that allows the cone to be attached further out from the 
voice coil former to increase the vertical angle of the cone and hence the 
cone's strength. 
According to these and other objects, the present invention comprises a 
voice coil adaptor ring and a loudspeaker with a moving coil that 
incorporates the adaptor ring. The loudspeaker comprises a cone, a dust 
cap, a frame supporting the cone's upper end, a voice coil former, a voice 
coil wound around the former, the adaptor ring mounted to the former, a 
lower suspension (spider) connected at one end to the frame and at the 
other end to the adaptor ring for centering the voice coil system, and a 
magnetic circuit including at least one magnet, front plate, a back plate 
and a pole piece. The adaptor ring comprises a substantially cylindrical 
sleeve adapted for mating over the voice coil former and for securing and 
attaching the speaker cone/diaphragm and spider suspension. The adaptor 
ring of the instant invention defines a ledge around its lower peripheral 
edge having sufficient surface area for receiving, supporting and adhering 
the speaker cone and spider. Accordingly, this ledge is also referenced as 
a spider plateau since it provides a horizontal platform for supporting 
the spider. The spider plateau stabilizes and increases the structural 
integrity of the cone for minimizing deflection and providing an overall 
improved performance and strength. This plateau/edge provides a larger 
surface area for adhering the spider which is superior to gluing it 
directly to the vertical wall of the voice coil former, as shown in U.S. 
Pat. No. 4,764,968. By providing a substantially horizontal plateau for 
securing the spider suspension, adhesives may be applied to both the upper 
and lower sides of the spider for increasing the adhesive contact area. 
The extra adhesive contact area defined by the plateau provide for a 
strengthened spider attachment so as to greatly reduce the possibility of 
failure. 
The plateau also benefits the cone in that it provides a mechanical stop 
for receiving the cone's lower edge and adhering it to the adaptor. This 
enhances the joint between the cone and adaptor for increased reliability 
and reduced likelihood of failure. Once the cone is attached to the top of 
the spider, the spider is completely locked and secured in place so as to 
virtually eliminate this joint as a possible failure point in the 
loudspeaker. A substantial decrease in stress on the glue joints is 
realized by the structure and method of the instant invention. In short, 
there is better stress distribution across the joint and increased 
stability provided by the spider plateau. 
The adaptor ring of the instant invention further comprises venting 
passages vertically bored through the wall of the adaptor ring from top to 
bottom for releasing air pressure build up in the volume defined by the 
cap and cone. These venting passages of the instant invention eliminate 
the need for providing a pole vent in the pole piece. Eliminating the pole 
vent reduces manufacturing time and costs. A solid pole piece also offers 
an increase in magnetic circuit efficiency as well as a less resistant 
thermal path for heat transfer from the voice coil. An improvement in the 
heat transfer from the voice coil increases the power rating of the driver 
making the speaker more reliable. It has been determined that when a 
fairly porous spider is paired with the venting passages, air may exit 
noiselessly from the arena area under the cap. 
The adaptor ring of the instant invention defines an inner diameter adapted 
to receive the voice coil former for mounting the adaptor ring on the 
speaker. Accordingly, the cylinder is dimensioned to correspond to the 
voice coil former. An inner glue flange is defined along the inner wall 
and floor of the adaptor ring. When the adaptor ring is installed over the 
voice coil former a gap remains between the interior wall of the ring and 
the voice coil former. This gap is filled with glue to adhere the adaptor 
ring to the voice coil former. In the alternative, the voice coil former 
may have a stop projecting from the former for locking the adaptor ring in 
place. 
The spider plateau of the adaptor ring may also include at least one wire 
channel, or slots in the inner glue flange along its circumferential edge 
to form channels when the adaptor is mounted to the former, for running 
speaker wires, such as the lead out wire. In the alternative, the wire may 
be passed through one of the venting passages. The ring may also include a 
textured or ribbed surface for increased surface tension when applying 
adhesives. 
While the instant invention is described with reference to loudspeakers 
having small voice coils, the voice coil adaptor ring may be incorporated 
with other loudspeakers for improved performance and strength. 
The invention is described in detail below with reference to the 
accompanying drawings, in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the drawings, FIGS. 2-9, depict the preferred embodiment 
of the voice coil adaptor ring 51 and loudspeaker system 50 incorporating 
the adaptor ring 51 in accord with the preferred embodiment of the instant 
invention. The loudspeaker 50 of the instant invention incorporates the 
voice coil adaptor ring 51 and comprises a cone-shaped diaphragm 24' 
(cone), a frame 22' supporting the upper end of the cone 24', a voice coil 
40' wound around a voice coil former 43', the voice coil adaptor ring 51 
mounted over the former 43', an upper suspension 28', a spider 38' and a 
magnetic circuit. The spider 38' is attached and adhered to the adaptor 
ring 51 to provide a centering force for the former 43' and voice coil 
40'. The magnetic circuit comprises at least one magnet 35', a pole piece 
41', a front plate 37' and a back plate 33'. A magnetic gap exists between 
the top plate 37' and the pole piece 41. Together, the adaptor ring 51 and 
spider suspension center the voice coil system and former in this gap. 
The voice coil adaptor ring 51 comprises a sleeve having substantially 
cylindrical walls 52 adapted for snugly mating and conforming to the outer 
peripheral edges of the voice coil former 43'. With reference to FIG. 9, 
the adapter ring in the alternative may comprise other shapes, such as 
conical, without departing from the scope and spirit of the instant 
invention. As seen in FIG. 4, the adaptor ring 51 defines a first inner 
diameter D1 which corresponds to the diameter/dimensions of the voice coil 
former 43'. The first inner diameter D1 of the adaptor ring 51 is defined 
by an inner glue flange 58. A second inner diameter D2, larger than the 
first, is defined by the interior of wall 52a. Thus, a gap exists between 
the interior wall 52a and the exterior wall of voice coil former 43' when 
the ring 51 is installed. This gap is filled with epoxy 60 to secure the 
adaptor ring 51 to the voice coil former 43'. 
In the alternative, the former 43' may be manufactured with a projecting 
shelf on which the adaptor ring would sit and lock in place. In this 
alternative embodiment, the inner glue flange 58 would define grooves 59 
which would interlock with the projecting shelf where the adaptor ring is 
rotated, locking it in place. 
The adaptor ring 51 further comprises venting passages 56 which are bored 
vertically through the cylindrical walls 52 to provide a complete 
passageway for venting air from the dust cap volume of the speaker. The 
dust cap volume is defined by the cone walls 24' and dust cap 26'. The 
venting passages 56 prevent pressure build up in this volume for improved 
sound quality. In the preferred embodiment, an annular gap or pocket is 
defined by the adaptor ring walls 52, inner glue flange 58, and voice coil 
former 43' for filling with epoxy 60. This adheres the ring 51 to the 
former 43'. 
With reference to FIG. 6-7, a cross-section of the adaptor ring is shown to 
illustrate the venting passages 56 and the inner glue flange 58. The 
passages 56 are divided by partitions 57. The partitions 57 may be sloped, 
tapered, planar or otherwise. Selected partitions 57' may be sloped, as 
shown in FIG. 7, to reduce stress on lead out wires when they are run 
through the adaptor 51. Lead out wires are typically fragile, so bending 
the wires at right angles would increase the risk of fractures. Referring 
to FIGS. 2-7, the adapter ring 51 includes a means for running lead out 
wires. This wire running means preferably comprises slots 59 defined at 
selected locations around the inner peripheral edge of the inner glue 
flange 58 so that wire running channels are formed when the adapter ring 
51 is mounted to the voice coil former 43'. The slots 59 should be in 
alignment with the sloped partitions 57' so that lead out wires may be 
passed through the wire channels and over the sloped partitions. In the 
alternative, wire channels may be bored through the adapter ring walls 52, 
plateau 54 or inner glue flange 58. The adaptor ring 51 may be 
manufactured by any plastic, thermoplastic, polymer plastic, metal or 
other acceptable material. An injection molding process is preferred to 
make the ring 51. It should be noted, however, that any embodiment of the 
adapter ring may be manufactured integrally with the voice coil former 43' 
such that the adapter ring would be metallic. At least one wire channel 55 
may also be provided by the ring 51 for running wires. 
The venting passages 56 eliminate the need for a pole vent 42, as shown in 
FIG. 1. The conventional pole vent 42 is required in the background art to 
vent heat and air pressure build up in the cap volume, as defined by the 
dust cap 26 and the cone 24. The voice coil adaptor ring 51 of the instant 
invention eliminates the pole vent 42 by including venting passages 56 in 
the adaptor ring 51, as discussed above. The venting passages 56 comprise 
channels bored completely through the cylindrical wall 52 from the top end 
to the bottom end. Replacing the conventional pole vent 42 with the 
adaptor ring vent passages 56 saves machining in the pole piece structure 
41 so as to reduce costs. A solid pole piece 41 also increases magnetic 
circuit efficiency and provides an improved thermal path for heat transfer 
from the voice coil. By allowing for improved heat transfer from the voice 
coil, the driver may be operated at a higher power rating. 
With reference to FIGS. 2-8, the adaptor ring 51 of the instant invention 
preferably has cylindrical walls 52 that define an exterior spider plateau 
54. The spider plateau 54 is preferably planar, or substantially 
horizontal, such that it provides a ledge for receiving and securing the 
spider/lower suspension 38' and the neck/lower edge of the speaker cone 
24'. The spider plateau 54 preferably supports the inner edge of the 
spider 38' and provides enough surface area for applying adhesives between 
the spider 38' and the ledge 54 so as to firmly secure the spider in 
place. Adhesives are also applied to the upper surface of the spider 38' 
for adhering the neck of the cone 24'. The instant invention is superior 
to the background art, whereby the ledge 54 of the adaptor ring 51 
provides a more stable securing structure than the vertical surface of the 
voice coil former 43'. In addition, it provides a structure that enables 
the joining of the cone 22' and spider 38' for a stronger joint. 
Accordingly, attaching the spider 38' and cone 24' to the voice coil 
adaptor ring 51 along a larger circumferential planar surface provides 
more contact area for applying epoxy. This additional contact area 
alleviates stress on the glue joints via improved stress distribution for 
increased reliability. In the alternative, the surface of the spider 
plateau 54 and/or the entire adaptor ring 51, can be textured or ribbed to 
enhance adhesion. The adaptor ring 51 and spider plateau 54 also provide a 
mechanical stop for the cone's 24' lower edge providing a more reliable 
joint. Once the cone 24' is attached to the top of the spider 38', the 
spider 38' is completely locked in place. Consequently, the 
spider/cone/voice coil joint is virtually eliminated as a possible point 
of failure in the loudspeaker. 
Referring to FIG. 4, the voice coil adaptor ring 51 provides extra coil 
attachment height allowing for a larger adhesive contact area, especially 
in small diameter voice coils. In addition, the inner glue flange 58, aids 
in the gluing process by catching and holding the glue in contact with the 
coil former surface allowing a larger amount of adhesive to be used. This 
large joint provides a more favorable stress distribution around the coil 
former 43' making the attachment more reliable. 
The voice coil adaptor 51 facilitates use of a corrugated spider 38' having 
a larger inner diameter in the area of its mid section. A spider with a 
large inner diameter is amenable with the instant invention because of the 
additional security provided by the voice coil adaptor ring 51 and spider 
plateau 54. That is, because more spider material is adjacent to the glue 
joint in a loudspeaker using the voice coil adaptor in 51, spider fatigue 
is less of a concern. As noted, a larger inner diameter spider 38' is more 
resistant to rocking that may incur in a loudspeaker. With the use of the 
adaptor ring 51, the acceptable spider material deflection is increased 
for a given degree of coil rotation making the spider more resistant to 
fatigue. The additional stability provided by the adaptor ring 51 and 
corrugated spider 38', make the speaker stronger and more reliable. The 
improved centering force allows for tightened tolerances in the magnetic 
gap as defined between the top plate 37' and pole piece for improved 
speaker performance. Maintaining a smaller magnetic gap increases the 
motor strength and enhances the thermal power handling of the loudspeaker. 
The adaptor ring 51 moves the contact point of the lower cone edge outward. 
As a result, the cone angle is decreased, with reference to a vertical 
axis, for higher strength and rigidity. As a result, the cone 24' is not 
only more reliably stabilized, but may be manufactured from a thinner 
material reducing the cone's weight and audible coloration. 
With reference to FIG. 8, the voice coil former 43' may have grooves 72 and 
74' formed along the interior wall, preferably from top to bottom. The 
grooves 72 and 74 provide a means and structure for breaking any 
conductive loop in the former 43' that may result. These grooves 72, 73 
may be especially necessary when the adaptor ring is formed integrally 
with the former 43' and the former-adaptor ring assembly is electrically 
conductive. An alternative embodiment of the adaptor ring is shown in FIG. 
9, where the adaptor is conical in shape. The conical adapter 51' performs 
the same functions as the preferred adapter 51 and likewise comprises a 
spider plateau 54', a sloped wall 52', and vent passages 56'. A vertical 
stop 55 is also included in the alternative embodiment for receiving the 
cone and spider and facilitating an improved adhesion surface. 
The instant invention has been shown and described herein in what is 
considered to be the most practical and preferred embodiment. It is 
recognized, however, that departures may be made therefrom within the 
scope of the invention and that obvious modifications will occur to a 
person skilled in the art.