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The present invention relates to a method of manufacturing a diaphragm for electroacoustic
transducers having partial areas of different thickness from a material of constant thickness
capable of thermoplastic deformation, said electroacoustic transducer Relates to the type that
operates according to the electrokinetic principle.
The behavior of the diaphragm has important implications for the mode of operation of any
electroacoustic transducer. This is because the transmission characteristics of the transducer are
significantly co-defined by the diaphragm. The behavior of the diaphragm, as well as the material
properties, is also significantly defined by the shape. As the shape of the electroacoustic
transducer diaphragm operating according to the electrokinetic principle, a shape as
schematically shown in FIG. 1 has been widely recognized as being suitable.
The center of the diaphragm is hemispherically shaped and is surrounded by a donut-like area.
The donut shaped area is provided with an edge for attachment to the magnet system. Attached
to the lower portion of the hemispherical section is a plunger coil which moves in a radially
extending magnetic field.
The purpose of all measures in the construction plane is to enable pistonic movement of the
plunger coil, for all frequencies and amplitudes. For that purpose, the individual diaphragm areas
have to be differently configured depending on the function.
In that case, the central hemispherical area should be as rigid as possible in order to prevent the
occurrence of vibration modes, even at high frequencies. Otherwise, the frequency response
would fall (Einbrueche).
The donut-like area is important for obtaining spring elasticity and often comprises recesses, socalled beads, which extend tangentially to the inner diameter. Thus, this part has been generally
referred to as the "bead area". The softer the bead area, the higher the sensitivity in the low
frequency transmission range.
These various requirements for the sub-areas of the diaphragm of the electroacoustic transducer
can be optimally met if the sub-areas are configured differently. However, these different
requirements are often not taken into consideration when manufacturing the diaphragm. For
example, diaphragm material, usually in the form of a sheet, is pressed into the mold while being
pressurized and heated. The sheet is taken out of the cooling stage and then the final diaphragm
is punched out. In this production form, no difference is formed between the hemispherical area
and the bead area, except for the point of shaping.
For this reason, methods have often been proposed to give stiffness to hemispherical areas. For
example, the hemispherical area can be stiffened by the addition of a second layer. For example,
EP-A-0446515 proposes the addition of a metallic fabric on the concave side of the
hemispherical area.
Another possibility to obtain a rigid hemispherical area is to configure the diaphragm to different
thicknesses. For example, in the case of loudspeaker structures, diaphragms with partial areas of
different thickness are used. For example, German Patent 38 38 853 describes a special
thickness distribution of the central area and the conical area in order to guarantee good
transmission properties.
Furthermore, as described in European Patent Publication No. 0 204 386, the diaphragm can be
divided into parts and the central part can be made of a thicker material.
A further possibility of increasing the stiffness of the central hemispherical area is to apply a
special form to this central hemispherical area, for example the central recess as described in EP
0 137 624 A1. To provide
Also, DE-A-43 29 637 describes the construction of the ribs. The central hemispherical area is
first manufactured to be larger than the target value, and then in the second deformation stage
optionally reinforcing ribs are formed in this hemispherical area.
These previously described methods are time consuming to implement and therefore expensive.
The object of the present invention is to eliminate these drawbacks and to provide a simple and
precisely definable method of manufacturing diaphragms of different partial area thickness that
can be advantageously used for electrokinetic transducers. is there.
SUMMARY OF THE INVENTION A diaphragm with partial areas of different thickness is produced
according to the invention from a material of constant thickness by means of a multistage
thermoplastic stamping process. In the first work phase, the diaphragm material area, which
needs to be thicker than the other areas when the diaphragm is completed, is held by the inner
fixing device, while the remaining area is additionally held by the outer fixing device. And, under
the action of tension and heat, are pre-stretched to a thinner thickness, and in a second working
step the whole diaphragm is thermoplastically stamped in the mould.
According to another feature of the invention, from the fixedly held diaphragm material area, the
hemispherical area is stamped and from the remaining pre-stretched diaphragm material area,
the bead area is stamped.
It is advantageous to carry out all the production steps with a single tool.
BRIEF DESCRIPTION OF THE DRAWINGS The process of the invention is explained in more detail
below with reference to the drawings.
FIG. 1 is a cross-sectional view of a completed diaphragm with a plunger coil for an electrokinetic converter.
The central hemispherical area 1 is surrounded by a donut-like area.
For attachment to a magnet system not shown, the outer diaphragm edge 3 serves.
The plunger coil 4 is bonded to the diaphragm. The diameter of the plunger coil in this case
corresponds approximately to the outer diameter of the central hemispherical section 1.
The manufacturing method of the present invention will be described in detail with respect to the
details shown in each of the figures from FIG.
Usually, the sheet-shaped diaphragm material 5 is first introduced into a first device consisting of
inner and outer fasteners 6, 6 '; 7, 7', as schematically shown in FIG.
In that case, the inner fasteners 6, 6 'surround the central area 8 which needs to be thicker when
the diaphragm is completed. This central area 8 forms a hemispherical area 1 in the case of a
diaphragm of an electrokinetic converter. The outer fixings 7, 7 'enclose an area corresponding
to a diameter approximately twice the diameter of the finished diaphragm. The fixture consists of
two jaws 6, 6 '; 7, 7' respectively arranged above and below the diaphragm material 5. Both these
jaws 6, 6 '; 7, 7' are pressed together so that the diaphragm material 5 between them is held
stationary without displacement. In order to prevent damage to the diaphragm material during
this fixed holding, elastic sealing members 12, 12 '; 13, 13' can be added to both jaws.
By means of the relative movement between the inner and outer fixing devices 6, 6 '; 7, 7' and
the action of heat, the annular edge area 9 between the two fixing devices 6, 6 '; 7, 7' The
thickness can be reduced as shown schematically in FIG.
This reduction in material thickness is greater the greater the relative movement between the
inner and outer fasteners 6, 6 '; 7, 7'.
Thus, by appropriate selection of the motion parameters, an adequate means of forming the
annular edge area 9 to the target thickness is obtained.
The heat required for the pre-stretching of the diaphragm material 5 can be supplied by air or
radiation. In the case of air, the diaphragm material 5 is directly heated by hot air, and in the case
of radiation, the surrounding members, for example, solid members of the fixing device are
electrically heated to heat the diaphragm material 5.
In that case, the heat supply is advantageously performed in such a way that the partial area of
the diaphragm material which must be reduced in thickness is mainly heated. However, it is also
conceivable to use a cold-stretchable diaphragm material 5. In that case, no heating is required at
FIG. 4 shows the result of this first working phase, ie a diaphragm sheet in which the central area
8 is thicker than the edge area 9.
In a second operation stage, the diaphragm sheet is stamped and stamped using a conventional
diaphragm mold.
FIG. 5 shows the finished finished diaphragm punched out, the hemispherical area 10 being
significantly thicker than the bead area 11. The difference in thickness of about 50% between the
hemispherical area 10 and the bead area 11 can be realized as described above. This
manufacturing method can be used particularly effectively when carrying out the two work steps
with a single tool. The method according to the invention is carried out automatically by means
of a suitable control device by arranging the inner and outer fixing devices and the final
stamping die in combination with one another and axially movable relative to one another. can
This makes it possible to produce diaphragms with partial areas of different thickness, with a
production cost equal to that required to produce a conventional diaphragm. It also makes it
possible to inexpensively manufacture an electroacoustic transducer diaphragm having a thick
hemispherical area and a thinner bead area, which obviously improves the vibration behavior.
Brief description of the drawings
1 is a cross-sectional view of a complete diaphragm with a plunger coil for an electrokinetic
2 is a cross-sectional view of the inner and outer fixing device with the diaphragm material
3 is a cross-sectional view showing the diaphragm material is stretched by the relative movement
of the inner and outer fixing device.
FIG. 4 is a cross-sectional view of the diaphragm material in which the central area is clearly
thickened by pre-stretching.
5 is a cross-sectional view of the completed diaphragm for electrokinetic converter according to
the present invention.
Explanation of sign
1 hemispherical area, 2 donut-like area, 3 outer edge, 4 plunger coil, 5 diaphragm material, 6, 6
'inner fixing device, 7, 7' outer fixing device, 8 central area, 9 edge area , 10 hemispherical areas,
11 bead areas
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