Loudspeaker with a heat resistant two-part diaphragm

A loudspeaker is disclosed in which the frustoconical diaphragm is formed in two parts, including a first or outer part made of synthetic material e.g. polypropylene or polystyrene, and a second or inner part of paper or plastic material having higher heat resistance than the first part. The second part is therefore able to withstand the high temperatures of the moving coil support to which it is attached while affording advantages of synthetic material diaphragms.

FIELD OF THE INVENTION 
The present invention relates to loudspeakers, and more particularly to 
loudspeakers having a vibrating diaphragm actuated by means of a moving 
coil carried by a support. 
BACKGROUND OF THE INVENTION 
The advantages of loudspeakers provided with diaphragms of plastic material 
are already known and include their vibration response uniformity in the 
different zones of the diaphragm and their physical uniformity in 
comparison to paper diaphragms. This uniformity of the diaphragm produces 
a reduction in the number of resonant frequences which results in less 
"coloration" for the listener. 
Nevertheless, plastic diaphragms which have low mechanical characteristics 
because of the low heat resistance of the plastic sheet material of which 
they are made (of the order of 100.degree.-150.degree. C. in general) 
limit the permissible power of the loudspeakers. 
SUMMARY OF THE INVENTION 
An object of the present invention is to overcome such drawbacks with 
plastic diaphragms. 
According to the invention there is provided a loudspeaker of the type 
comprising a vibrating diaphragm actuated by a moving coil carried by a 
support. The loudspeaker is characterized in that the diaphragm comprises 
at least two parts made of different materials including a first or outer 
part of synthetic material and a second or inner part extending from the 
first part of synthetic material to the support for the moving coil, the 
second part being made of a material having greater heat resistance than 
that of the synthetic material of the first part. 
Owing to the fact that the support for the moving coil is separated from 
the first part made of synthetic material by a second part having a heat 
resistance greater than that of the first part, it is possible to choose a 
good heat conducting material for the support and therefore increase heat 
dissipation of the moving coil. 
These and other features and advantages of the invention will be brought 
out in the description which follows given by way of example with 
reference to the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a loudspeaker diaphragm of two-part construction including 
parts 1 and 2 each of generally frustoconical configuration. The first 
part 1 generally connected by a peripheral suspension member to the basket 
support (not shown in FIG. 1) is made of synthetic polymeric or 
copolymeric material, such as polypropylene, but may be of any other 
suitable material, for example polystyrene, and have any desired cross 
section. 
The second part 2 attached to the support for the moving coil (not 
illustrated in FIG. 1) has its large diameter end or connecting zone 21 
attached in a corresponding smaller diameter end or connecting zone 11 of 
the first part 1. The small diameter end zone of the second part 2 is 
extended by a connecting or fastening zone 22 to the support for the 
moving coil. The fastening zone 22 at the moving coil support has a 
generally cylindrical configuration here. In order that the moving coil 
support may be made of good heat conducting material to increase the heat 
dissipation potential of the moving coil, e.g., aluminum, the second part 
2 is made of paper or a plastic such as a high temperature aromatic 
polyamide sold under the mark "Nomex" by Dupont de Nemours, or a high 
temperature polyimide sold under the trade mark "Kapton" also by Dupont de 
Nemours, or the like, so that it is possible to obtain good operating 
characteristics with a support reaching temperatures greater than 
150.degree. C. (for example 220.degree. C.) even if the material of which 
the first part 1 is made is resistant to temperatures less than 
150.degree. C. 
In the present case the connecting zone 11 on the first part 1 is disposed 
inside the connecting zone 21 of the second part 2. The connecting zones 
11 and 21 which are attached to each other and overlie each other along a 
length selected for each loudspeaker as a function of its use so that 
taking account of the speed of sound propagation in the respective 
materials in contact, the wavelengths at which there may be reflections of 
the transverse waves when passing from one material to another, 
corresponds to frequencies outside the operative frequency range of the 
loudspeaker. 
The second part 2 of the diaphragm comprising the fastening zone 22 for the 
moving coil support and also to the internal fixing member or spider (not 
shown in FIG. 1) and at the output lead is a height of the order of one 
quarter of the total height of the diaphragm cone. 
The attachment of the various parts and members together may be effected by 
bonding or any other appropriate means. 
Tests carried out with loudspeakers having a diameter of twenty centimeters 
show that, all other things being equal, a two-part diaphragm of 
polypropylene and paper associated with a moving coil on an aluminum 
support permits a power output about 20% greater than that of a 
polypropylene diaphragm associated with a coil on a paper support and 40% 
greater than a polypropylene diaphragm associated with a moving coil on an 
aluminum support. Other technical characteristics of loudspeakers such as 
the response curves, impedance curves and distortion showed no significant 
differences. 
FIG. 2 shows a loudspeaker designated by general reference numeral 30 
incorporating a modified diaphragm 32 according to the invention. The 
diaphragm 32 is also of two-part construction in this embodiment and 
includes a first or outer generally frustoconical part 33 connected at its 
larger diameter end to a peripheral suspension member 31 which in turn is 
attached to the outer peripheral zone of the basket support 36 of the 
loudspeaker. The second or inner part 34 of the two-part diaphragm 32 is 
attached to a generally cylindrical support 37 for a moving coil by a 
corresponding generally cylindrical portion 39 at the small diameter end 
of the second or inner diaphragm part 34. The large diameter end of the 
second or inner part 34 of the diaphragm 32 is bonded to the small 
diameter end of the first or outer diameter diaphragm part 33 along the 
outwardly facing surface thereof. This arrangement is in contrast to that 
shown in the embodiment of FIG. 1 where the connecting zone 22 of the 
first or outer diaphragm part 1 is attached along its inwardly facing 
surface. The outer and inner diaphragm parts 33 and 34, respectively, are 
constructed of the materials disclosed with respect to the embodiment of 
FIG. 1. And in accordance with the invention the inner part 34 is made of 
a material having a greater heat resistance that that of the synthetic 
material of which the outer part 33 of the diaphragm is made, whereby the 
inner part is adapted to withstand the heat dissapated by the moving coil 
support or cylindrical support 37. 
The loudspeaker shown in FIG. 2 is in other respects of conventional 
construction and further comprises a conventional part spherical dust cap 
40 attached to the large diameter end of the inner part 34 opposite the 
small diameter end of the outer part 33. A conventional spider 35 is 
likewise attached between the outer surface of the cylindrical portion 39 
of the inner part 34 and the base part of the basket support 36. 
The loudspeaker 30 further comprises a moving coil 38 mounted on the coil 
support 37. Directly behind the moving coil 38 and coaxial thereto is a 
pole piece 41. A ferrite ring 43 is disposed radially outwardly of the 
pole piece 41 and sandwiched between a front plate 44 and a rear plate 42 
both of ferromagnetic material. 
Of course the invention is not limited to the embodiment described and 
illustrated herein. Various alternatives, modifications and expedients may 
be resorted to without departing from the spirit and scope of the 
invention.