Moving voice coil loudspeaker with heat dissipating enclosure

The dynamic loudspeaker is comprised of a speaker housing and a front sound panel. A diaphragm is mounted at the front of the speaker. A moving-coil unit is mounted in the speaker and includes a moving coil coupled to the diaphragm for transmitting oscillatory motion thereto. The moving-coil unit when in operation generates heat to such an extent as to tend to limit the rated steady power at which the loudspeaker can be operated without damage to the moving-coil unit. This limiting tendency is counteracted according to the invention by improving the dissipation of the heat generated by the moving-coil unit. The speaker housing or a surface portion thereof and/or the speaker sound panel or sound wall or a surface portion thereof is comprised of a material having a thermal conductivity W equal to or greater than 40 kcal/m-h-.degree. C. A heat-transmitting structure is comprised of a material likewise having a thermal conductivity W equal to or greater than 40 kcal/m-h-.degree. C., and it extends from the moving-coil unit to at least one of the aforementioned portions of the housing and/or sound wall, and is in thermally conductive engagement with both the latter and the moving-coil unit.

BACKGROUND OF THE INVENTION 
The invention relates to dynamic loudspeakers and in particular to the 
problem of increasing the rated steady power at which they can be driven. 
The performance of loudspeakers can be numerically described by a variety 
of measurable characteristics. Besides magnetic characteristics, the ones 
most often considered are the peak power at which the speaker can be 
driven, the natural resonant frequency of the speaker, the frequency range 
of the speaker, the operating power of the speaker, the sensitivity of the 
speaker, the frequency-dependence of the gain and phase of the speaker, 
and the nominal steady power at which the speaker can be driven. The 
latter signifies the input power at which the speaker can be steadily 
driven without undergoing permanent damage. 
With dynamic loudspeakers, the nominal steady power at which the speaker 
can be driven is limited by a number of factors, including the heat 
generated by the moving-coil unit of the speaker during operation. For 
this reason, high-powered moving-coil units are often comprised of moving 
coils wound on aluminum coil carriers and fabricated using 
highly-temperature resistant cement or glue. The moving coil principally 
transmit the heat which it generates to the central pole core and outer 
pole plates of the permanent magnet structure of the moving-coil unit, 
resulting in a heating-up of the entire magnet system. Contributing to 
this heat build-up is the fact that the magnet system of the moving-coil 
unit, for acoustical reasons, is often surrounded with mineral wool having 
heat-insulating characteristics. In some speakers, use is made of spider 
structures made of aluminum, a material of high thermal conductivity. 
However, the aluminum spider structures do not establish a 
heat-dissipating action. Typically, they are comprised of narrow radial 
arms leading to the front side of the speaker housing, with little or no 
transmission of heat from these spider arms to the housing. Most often, 
the ends of the spider arms are mounted on the spider housing by means of 
resilient material of extremely low thermal conductivity. 
SUMMARY OF THE INVENTION 
It is a general object of the invention to increase the nominal steady 
power at which such a speaker can be driven, by dissipating in a novel and 
highly effective manner the heat generated by the moving-coil unit of the 
speaker. 
According to one advantageous concept of the invention, this is achieved by 
making the speaker housing, or a part thereof, or one or more parts of the 
surface thereof, and/or the speaker sound panel or sound wall, or a part 
thereof, or one or more parts of the surface thereof, of a material having 
a thermal conductivity W equal to or greater than 40 kcal/m-h-.degree. C. 
There is then provided a heat-transmitting structure which is comprised of 
a material likewise having a thermal conductivity W equal to or greater 
than 40 kcal/m-h-.degree. C. The heat-transmitting structure extends from 
the moving coil unit to one or more of the aforementioned 
high-thermal-conductivity parts of the speaker housing or sound wall, and 
is in thermally conductive engagement with both the moving coil unit and 
such one or more high-thermal-conductivity parts. 
The improved dissipation of the heat generated by the moving-coil unit of 
the speaker increases considerably the steady power at which the speaker 
can be driven without undergoing permanent damage. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, numeral 1 denotes the loudspeaker housing, here made of a 
material having a thermal conductivity W equal to or greater than 40 
kcal/m-h-.degree. C., where kcal = kilocalories, m = meters, h = hours, 
and .degree. C. = degree celsius. One example of such a material is 
aluminum. The speaker is provided on its front side with a sound panel 2, 
which can be considered part of the speaker housing or a separate part, 
and which may or may not be integral therewith. In FIG. 1, the sound wall 
has the form of such a flat sound panel 2, but other configurations and 
shapes could likewise be utilized. An aluminum bar 3 has its left end in 
thermally conductive engagement with the back wall of the speaker housing 
1, and has its right end in thermally conductive engagement with the rear 
face of the permanent magnet structure 4 of the moving-coil unit of the 
speaker. The aluminum bar 3 is connected to the back wall of the housing 
and to the permanent magnet structure by means of a long screw 5 which 
passes through the back wall of the housing, through an interior bore 6 in 
the bar 3 and has a threaded end screwed into a threaded bore in the 
permanent magnet structure 4. 
Mounted on the permanent magnet structure 4 is the moving coil 7 of the 
moving-coil unit. Coil 7 is wound on an aluminum coil carrier structure 
and is fabricated using a cement of high temperature resistance and of 
high thermal conductivity, so that the heat generated within coil 7 will 
be readily transmitted to the permanent magnet structure 4. A spider 
structure 8 has its outer ends connected to the sound panel 2, to which is 
also connected the edge suspension 9 for the speaker diaphragm 10. The 
speaker additionally includes a centering or positioning diaphragm 11 
which is connected with the permanent magnet structure 4 by means of 
screws 12. 
During operation of the moving coil 7, the heat which it generates is 
mainly transmitted to the central core portions of the permanent magnet 
structure 4. This results in a heating-up of the entire magnet system. The 
aluminum bar 3, because its thermal conductivity W is likewise equal to or 
greater than 40 kcal/m-h-.degree. C., transmits this generated heat very 
efficiently to the aluminum rear wall of the speaker housing 1, where it 
is readily dissipated into the ambient air. 
In the embodiment of FIG. 2, the one-piece heat-transmitting structure of 
FIG. 1 is replaced by a two-piece heat-transmitting structure 13, 15 which 
permits back-and-forth movement of the permanent magnet structure 4. The 
heat-transmitting structure 13, 15 is comprised of a first component 13 
which is connected to the permanent magnet structure 4 by means of a screw 
14 and is in thermally conductive engagement with the permanent magnet 
structure 4. The heat-transmitting structure 13, 15 includes a second 
component 15 which is connected to the back wall of the aluminum housing 
of the speaker by means of a screw 16 and is in thermally conductive 
engagement with the aluminum back wall. The first and second components 
13, 15 have the form of cylindrical pipes, of which pipe 13 is slidably 
received within and guided by pipe 15, the outer diameter of pipe 13 being 
just slightly smaller than the inner diameter of pipe 15. This makes it 
possible for the component 13, fixedly secured to the permanent magnet 
structure 4, to respond to back-and-forth movement of the latter by 
sliding back and forth within the component 15. To ensure that the 
thermally conductive engagement between first and second components 13 and 
15 is sufficiently good, it is advantageous to provide a paste 17 of high 
thermal conductivity between the two components. 
FIG. 3 depicts a modification of the embodiment of FIG. 2, requiring no 
thermally conductive paste 17, and of inherently simpler construction, and 
also somewhat easier to assemble. In FIG. 3, the heat-transmitting 
structure is comprised of a sheet-metal strip 18, bent to have an S-shape. 
Its right end is secured to the permanent magnet structure 4 by means of a 
screw 19 and is in thermally conductive engagement with the permanent 
magnet structure 4. Its left end is secured to the aluminum back wall of 
the speaker housing by means of a screw 20 and is in thermally conductive 
engagement with the aluminum back wall. The embodiment of FIG. 3, compared 
to that of FIG. 2, does not create manufacturing tolerance problems. It is 
possible to use resilient heat-transmitting bodies, embodying the concept 
of FIG. 3, but of different configuration, i.e., not sheet-metal strips. 
FIG. 4 depicts an embodiment in which the second panel 2 is made of 
aluminum and the heat generated by the moving-coil unit is transmitted to 
the sound panel for dissipation into the ambient air. In this embodiment, 
the spider structure 8 of the speaker is of one piece with the sound panel 
2, and accordingly transmits thereto, quite directly, the heat being 
generated in moving coil 7, to some extent also through the intermediary 
of the outer pole plate part 21 of the permanent magnet structure. The 
integration of the second panel 2 and the spider structure 8 has the 
additional advantage that the total number of speaker parts is reduced. 
For reasons well known in the art, the axial length of the moving coil 7 
exceeds the thickness of the pole plate section 21 of the permanent magnet 
structure 4. The inner end of the spider structure 8 is provided with an 
opening whose diameter corresponds to that of the annular gap in the 
permanent magnet structure in which the moving coil 7 is mounted. Here the 
diameter of the opening in the center of the spider structure 8 is equal 
to the outer diameter of the annular gap in the permanent magnet structure 
4, and is carefully assembled to be in exact register therewith. The 
central core portion of the permanent magnet structure 4 is provided with 
an extension 22 having a thickness equal to that of the inner part of the 
spider structure 8. The inner part of the spider structure 8 has a 
thickness comparable to that of the pole plate section 21 and forms a 
structural continuation of section 21. The heat generated by the moving 
coil 7 is transmitted to the pole plate section 21, to the extension 22, 
and in that way to the spider structure 8, and from there to the aluminum 
sound panel 2. 
FIG. 5 depicts a modification of the embodiment shown in FIG. 4. Here, in 
addition to the low-frequency-range speaker unit 23, the sound wall 22 of 
the speaker is large enough to also mount a middle- or 
high-frequency-range speaker unit 24. Accordingly, both speaker units are 
located in a single radiation plane. Advantageously, the housing 1 and the 
front wall panel 2 are cast as a one-piece casting. 
In general, with respect to the embodiments of FIGS. 1-5, the following 
should be noted. The housing 1 can be made of a material of the high 
thermal conductivity in question (e.g., aluminum) in its entirety. 
Alternatively, it can be comprised of a portion made of such material, or 
of a plurality of such portions. The highly thermally conductive portion 
could be provided on the external surface of the housing 1, and a 
plurality of such surface portions could be provided. The 
heat-transmitting structure could then extend to each of the plurality of 
heat-dissipating portions. This likewise applies to the sound panel 2. All 
of sound panel 2, or just a part thereof, or a plurality of discrete parts 
thereof, or one or more surface portions thereof, can be made of the 
highly thermally conductive material. Advantageously, the sound panel 2 is 
of one piece with the spider structure and/or with the housing, in all 
embodiments. Also, whereas in FIGS. 1-5 a speaker of rectangular geometry, 
having a planar sound panel 2 at its front is shown, the invention is 
equally applicable to speakers of non-rectangular geometry, having 
non-planar sound walls 2. In general, the inventive concept is applicable 
to dynamic speakers of any design, wherever the problem of heat 
dissipation is encountered. The heat generated by the moving coil of the 
moving-coil unit can be transmitted to the ambient air via a 
heat-transmitting structure provided in addition to the anyway present 
structural parts of the speaker, or the anyway present parts of the 
speaker can be made of such materials and designed for thermally 
conductive engagement with one another, to effect the desired heat 
transmission and dissipation without the addition of a distinct 
heat-transmitting structure. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in 
speakers of particular design, it is not intended to be limited to the 
details shown, since various modifications and structural changes may be 
made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.