Loudspeaker suitable for high-temperature use having a non-adhesive connection between the voice coil support and the loudspeaker diaphragm

In the state of the art, most loudspeaker diaphragms 10 and the voice coil supports 11 are joined by adhesives. However, even high-grade adhesives fail if such loudspeakers are subjected to continuous operating temperatures much above 120 degrees Celsius. The one-piece construction of loudspeaker diaphragm 10 and voice coil support 11 is also limited. It is particularly difficult to produce one-piece metal constructions by means of the deep-draw process. It is therefore the task of the invention to present a joint of loudspeaker diaphragm 10 and voice coil support 11, which is simple to produce, can be subjected to high temperatures and is free of adhesives. This task is fulfilled in that the upper rim 19 of the voice coil support 11 is flared together with the upper rim 16 of a neck 12 formed on the diaphragm 10. In addition the invention proposes to join the neck 12 of loudspeaker diaphragm 10 to the voice coil support 11 through the effect of a ring-shaped part 23. If the neck 12 of diaphragm 10 is located between the ring-shaped part 23 and the voice coil support 11, the latter has the function of opposing the pressure (force) exerted by the ring-shaped part 23 on the outside jacket of the neck 12.

TECHNICAL FIELD 
The invention concerns the connection of a loudspeaker diaphragm to a voice 
coil support. 
BACKGROUND OF THE INVENTION 
In the state of the art, the loudspeaker diaphragm is generally attached to 
the tube-shaped voice coil support with an adhesive. This technique was 
proven in loudspeakers subjected to a temperature of about 120 degrees 
Celsius. However, the above named adhesive bonds can no longer be used if 
loudspeakers must operate reliably at higher than the indicated operating 
temperatures. Even the use of adhesives that are resistant at higher 
temperatures is not enough to solve this problem of the mechanically 
highly stressed joints of voice coil support and loudspeaker diaphragm, 
since these adhesives are not suited for use above 200 degrees Celsius. 
Furthermore, the use of such improved, but sometimes also toxic, adhesives 
can presently no longer be justified for environmental protection reasons. 
Although one-piece construction of a loudspeaker diaphragm and a voice coil 
support are known, they can only be made of plastic or paper/cardboard 
because of the weight ratios required for this combination. One-piece 
constructions of light metal, which are accessible to higher operating 
temperatures as compared to plastic or paper constructions, are presently 
not available. Tests made by the applicant, to form one-piece aluminum 
construction of a loudspeaker diaphragm and a voice coil support, have 
shown that in deep-draw processes, the neck (which serves as voice coil 
support) with a wall thickness of about 200 .mu.m as required for the 
diaphragm cone, can only be manufactured to a length of about 10 mm. But 
such neck lengths are not suitable as voice coil supports. In addition, 
the 200 .mu.m wall thicknesses of the voice coil supports result in wide 
air gaps. This lowers the air gap induction and has a negative effect on 
the temperature stability of the magnet system. 
SUMMARY OF THE INVENTION 
It is therefore the task of the invention to present a connection of 
loudspeaker diaphragm and voice coil support that is simple to manufacture 
and can withstand temperatures to above 400 degrees Celsius. 
A common principle of the present invention is to exclude the use of 
adhesives to join a voice coil support and a loudspeaker diaphragm, and 
instead to join both named loudspeaker components by purely mechanical 
means. 
The loudspeaker diaphragm can be fabricated from metal and provided with a 
neck that extends into the space formed by the conical diaphragm, with the 
joint of neck and the upper rim of the voice coil support formed as a 
curled joint. This curled or flared joint permits manufacture of the 
loudspeaker diaphragm and the neck as a deep-drawn part, since the necks 
produced by the deep-draw process are long enough to create a curled joint 
between the voice coil support and the neck of the loudspeaker diaphragm. 
If the transition area between loudspeaker diaphragm and neck is in the 
form of a radius, breakage of the neck during the deep-draw process need 
not to be feared. 
The production of the curled or flared joint is further simplified if the 
upper rims of the voice coil support and neck are provided with notches 
running in the direction of the loudspeaker axis. 
Another mechanical, i.e. adhesive-free joint between voice coil support and 
loudspeaker diaphragm is created, if the neck of the loudspeaker diaphragm 
and the voice coil support telescope into each other, so that the two 
parts overlap, and if a ring-shaped (joint) area is available, which 
presses the neck of the loudspeaker diaphragm against the wall of the 
voice coil support, or presses the wall of the voice coil support against 
the neck of the loudspeaker diaphragm. If the neck of the loudspeaker 
diaphragm is located between the outside jacket of the voice coil support 
and the inner sleeve of the ring-shaped part, the required pressure effect 
can be achieved by heat-shrinking the ring-shaped part. 
It is particularly advantageous if the ring-shaped part and the voice coil 
support or the neck of the loudspeaker diaphragm have different 
coefficients of thermal expansion. In that event, the different expansion 
of ring-shaped part and voice coil support or loudspeaker diaphragm neck 
can be used to further increase the pressure on the joined parts at higher 
operating temperatures. 
If the wall thickness of voice coil support or loudspeaker diaphragm should 
not have sufficient stability to withstand the pressure exerted by the 
ring-shaped part, it is advantageous to provide a reinforcing ring on the 
side of the loudspeaker diaphragm or the voice coil support that faces 
away from the ring-shaped part. 
The pressure between the ring-shaped part and the reinforcing ring can be 
increased with rising operating temperature, if the thermal expansion 
coefficients of ring-shaped part and reinforcing ring are different. 
It should be pointed out that the pressure of the ring-shaped part can also 
be used to join the centering diaphragm of the loudspeaker to the voice 
coil support or the loudspeaker diaphragm.

BEST MODE FOR CARRYING OUT THE INVENTION 
The invention will now be explained in more detail by means of the figures. 
The top part of the schematic cross sectional illustration of FIG. 1 
depicts a loudspeaker diaphragm 10 and the bottom part a voice coil 
support 11. In this configuration example, both parts 10, 11 are made of 
aluminum. This does not mean that the loudspeaker diaphragm 10, the voice 
coil support 11 or even both parts 10, 11 cannot be made of a different 
metal. 
The approximately conical loudspeaker diaphragm 10 is provided with a 
formed neck 12. This neck 12 extends into the space 14, which is limited 
by the inner sleeve of the conical diaphragm 10. The transition area 15 of 
loudspeaker diaphragm 10 and neck 12 has a rounded shape. The upper rim 16 
of neck 12 is equipped with notches 17, to simplify the curling process 
described later in more detail. These notches 17 run parallel to the 
loudspeaker axis 18. 
The voice coil support 11 is tube-shaped and also has notches 17 in its 
upper rim 19, which run parallel to the loudspeaker axis 18. These notches 
17 in the upper rim 19 of voice coil support 11 also serve to improve the 
curling process that will be described later. 
To form a unit of loudspeaker diaphragm 10 and voice coil support 11, the 
voice coil support 11 is inserted, for example in the direction of the 
arrow, into the neck opening 20 of loudspeaker diaphragm 10. 
This condition is schematically illustrated in FIG. 2a. It can clearly be 
seen in this illustration that, once the voice coil support 11 has reached 
its final position in the neck opening 20, the upper rim 19 of voice coil 
support 11 extends beyond the upper rim 16 of neck 12. It should be 
pointed out in this connection that the notches of FIG. 1 have been 
omitted in the illustrations of FIGS. 2a to c. 
To join the loudspeaker diaphragm 10 to the voice coil support 11, the 
upper rim 16 of the voice coil support 11 is bent outward around the upper 
rim 19 of the neck 12 (shown by the curved arrows in FIG. 2a). 
Once this curling process has been completed, the voice coil 
support-loudspeaker diaphragm combination looks as shown in FIG. 2b. To 
make the first curl explained in conjunction with FIG. 2a visible, the 
narrow joint between rims 16, 19 was not shown in the illustration of FIG. 
2b. 
Once the condition according to FIG. 2b is achieved, the upper rim 21 
formed by the first curl is again bent outward (indicated by the arrows in 
FIG. 2b). 
After the second curling is completed, a condition as shown in FIG. 2c 
occurs. The curled joint 22 securely connects the coil support 11 and the 
loudspeaker diaphragm 10 to each other, since after the second curling the 
bent rim areas are superimposed on each other without any separation. The 
latter is not illustrated in FIG. 2c to better clarify the curling 
process. 
If the static friction of the folded joint 22, shown in FIG. 2c, between 
the two contacting parts of neck 12 and voice coil support 11 is to be 
increased with rising operating temperatures, the part that is only curled 
once (like the neck 12 in FIGS. 2a to c), should have a higher coefficient 
of thermal expansion than the part that is curled several times (in this 
case the upper rim of the voice coil support 11). 
The notches 17 in the upper rim 16 of the neck 12 and the upper rim 19 of 
the voice coil support 11 facilitate bending over the upper rims 16, 19 as 
described to thereby simplify and improve the first and second curling 
processes. 
FIGS. 3a-g refer to the joint between loudspeaker diaphragm 10 and voice 
coil support 11 of an alternative embodiment of the present invention. As 
shown by schematic illustrations in FIGS. 3a, c, e and g, the tube-shaped 
voice coil support 11 is inserted into an opening enclosed by the neck 12 
of loudspeaker diaphragm 10, and extends into the space 14 formed by the 
inner sleeve of the conical diaphragm surface. The fact that the neck 12 
of loudspeaker diaphragm 10 extends downward in FIGS. 3a-g, in contrast to 
the illustrations of FIGS. 1 and 2, is only significant for the 
configuration of the invention in FIGS. 3b, d and f, since the 
configuration of the invention according to FIGS. 3a, c, e and g is also 
given when the neck 12 of diaphragm 10 extends into the space 14. It 
should be pointed out for the latter, which is not a separately 
illustrated configuration, that in addition to the ring-shaped part 23 
which produces the joint, the upper rims of neck 12 and voice coil support 
11 can be curled as depicted in conjunction with FIGS. 1 and 2. 
According to the illustrations of FIGS. 3b, d and f, the neck 12 of 
loudspeaker diaphragm 10 is inserted into the tube-shaped voice coil 
support 11. 
In the illustration of FIG. 3a, the outside jacket of neck 12 is surrounded 
by a ring-shaped part 23, which presses the neck 12 against the wall of 
voice coil support 11. For reasons of better visibility, the 
superimposition of the respective parts in the joint area of FIGS. 3a-g 
was omitted. 
To achieve the required pressure effect from the ring-shaped part 23 
depicted in FIG. 3a, this part 23 was heat- shrunk over the neck 12. To 
improve the pressure effect, the ring-shaped part 23 has a lower 
coefficient of thermal expansion than the voice coil support 11. This has 
the effect that with rising operating temperature, the ring-shaped part 23 
exerts greater pressure force on the neck 12 and the voice coil support 
it. To further improve the joint of voice coil support 11 and loudspeaker 
diaphragm 10, the areas of these components that come in contact with each 
other may be roughened on the sides facing each other. 
In the illustration of FIG. 3b, the ring-shaped part 23 is located on the 
outside jacket of voice coil support 12. In this illustration, the neck 12 
of loudspeaker diaphragm 10 serves to oppose the pressure force exerted by 
the ring-shaped part 23. For that reason, the illustration of FIG. 3b 
depicts the loudspeaker diaphragm 10 and therefore also the neck 12 to be 
made of metal. The voice coil support 11 is clamped between the outside 
jacket of neck 12 and the ring-shaped part 23. In the illustration 
according to FIG. 3b, the ring-shaped part 23 was heat-shrunk as well. To 
improve the pressure effect of the ring-shaped part 23 during operation of 
the loudspeaker, in this illustration as well, the ring-shaped part 23 has 
a lower coefficient of thermal expansion than the neck 12. 
According to the illustrations in FIGS. 3c and d, the ring-shaped part 23 
is located inside the voice coil support 11 (FIG. 3c), or inside the neck 
12 (FIG. 3d). In order for the ring-shaped part 23 to exert sufficient 
pressure force on the parts 12 or 11 that oppose it, the ring-shaped part 
23 was inserted in a supercooled condition. If the ring-shaped part 23 is 
to exert a greater pressure force on the respective opposing parts with 
rising operating temperature according to FIGS. 3c and d, the ring-shaped 
part 23 must have a higher coefficient of thermal expansion than the 
respective opposing parts. 
The illustration in FIG. 3e and f has a reinforcing ring 24 in addition to 
the ring-shaped part 23, which is located on the side of the neck 12 or 
the voice coil support 11 that faces away from the ring-shaped part 23. 
The use of the reinforcing ring 24 is necessary, if the neck 12 or the 
voice coil support 11 does not have sufficient stability by itself to 
oppose the pressure force exerted by the ring-shaped part 23. Whether the 
ring-shaped part 23 is located outside or inside, and the reinforcing ring 
24 inside or outside of the loudspeaker diaphragm-voice coil support 
combination, is left to the will of the technician. It is only important 
for the respective inside part to have a higher coefficient of thermal 
expansion than the respective outside part. 
In addition to the neck 12 of loudspeaker diaphragm 10 and the voice coil 
support 11, FIG. 3g also depicts a centering loudspeaker diaphragm 25 
between the ring-shaped part 23 and the reinforcing ring 24. 
FIG. 3g furthermore contains a dust protection cap 26, which is partially 
inserted into the inner cross section of the ring-shaped voice coil 
support 11. This cap 26 is connected to the voice coil support 11 in the 
manner shown in FIGS. 2a-c, wherein the upper rim 27 is bent in the arrow 
direction. As already explained in conjunction with FIGS. 1 and 2a-2c, the 
rims 19, 27 may contain notches along the loudspeaker axis (not 
illustrated), to simplify the curling process. If the curled joint is 
located between the cap 26 and the voice coil support 11, the bottom 28 of 
cap 16 seals the inside cross section of the voice coil support 11, thus 
preventing dust from entering into the air gap of the magnet system. The 
fact that the outside jacket of the cap 26 in FIG. 3c is not located 
against the inside sleeve of the voice coil support 11, is only for 
reasons of better visibility.