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JP2000151782

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DESCRIPTION JP2000151782
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
plastic capsules for acoustic transducers, and to encapsulated acoustic transducers, in particular
for incorporation in the housing of a communication device, and to a method of manufacturing
encapsulated acoustic transducers.
[0002]
2. Description of the Related Art Acoustic transducers such as microphones, loudspeakers etc. are
often pushed into or attached to plastic moldings, for example as a unit in the housing of a
communication installation. Plastic moldings are necessary to optimize the special acoustic
performance characteristics of the acoustic transducer, such as sound quality, bass or higher
frequency response, background noise, etc., depending on the application. For this purpose,
plastic moldings are usually made of soft plastic or rubber and define the mounting space of the
acoustic transducer, in which the dimensions of the mounting space are such that the acoustic
transducer fits snugly onto the plastic molding. Be The plastic molding thus forms the capsule of
the acoustic transducer.
[0003]
Such plastic capsules have one or more sound pressure openings through which sound can reach
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the acoustic input of the acoustic transducer contained in the plastic capsule. The number of
sound pressure openings and the position of the acoustic transducer in the plastic capsule have a
great influence on the acoustic nature of the device. In the case of a "unidirectional" microphone,
there is only one sound pressure aperture and the acoustic input of the transducer is relatively
far from this pressure aperture so that only the sound directed to it reaches the transducer. do
not do. On the other hand, in the case of an "omnidirectional" microphone, the acoustic input of
the transducer is close to the sound pressure aperture so that sounds from different directions
can reach the acoustic input of the transducer. In a "bi-directional" microphone, the two inputs
are arranged at an angle of 90 ° in the preferred form. In this way background noise or nondirectional sound fragments can be eliminated and sound pressure entering through the sound
pressure aperture is directed to the opposite side of the membrane acting as an acoustic
transducer, so that background noise non-direction can be achieved. Sound pressure levels are
mutually offset.
[0004]
However, the acoustic performance characteristics of the acoustic transducer are not only
determined by the type and structure of the plastic capsule, but also acoustically transparent
friction elements with an inherent acoustic impedance are used in the acoustic transducer in the
form of flat fabrics or membranes . As such, this type of friction element is often porous and air
permeable to obtain this acoustical impedance. That is, although the sound pressure reaches the
sound input of the acoustic transducer due to the air permeability of the friction element as
before, but with a characteristic friction or sound pressure loss, such an acoustically transparent
friction element A target sound effect can be obtained. Thus, in addition to plastic or rubber
capsules, acoustically transparent friction elements form another damping element independent
of the type and structure of the plastic capsules. The properties of the porous damping element
depend on the thickness of the material, the porosity and the nominal pore size. Here, "sound
transmissive" means that the acoustic energy is affected by the friction factor from 0 to 20 dB
depending on the desired properties.
[0005]
Heretofore, acoustically transparent friction elements have been mounted, for example, directly
attached to acoustic transducers, such as microphones. The microphone thus prepared was
inserted into a plastic capsule and then mounted as a unit, for example at a suitable position in
the housing of a mobile telephone.
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[0006]
Devices according to the prior art are shown in FIGS. 4a and 4b by way of example of a bidirectional converter. The plastic capsule (10) has two openings (3a, 3b). A bi-directional
transducer is inserted into the plastic capsule (10) such that its acoustic input falls behind the
openings (3a, 3b). The acoustic input is covered with a self-adhesive film (4), which is attached to
the transducer before it is inserted into the plastic capsule (10). A corresponding membrane
cutout (4) with two parts (4a and 4b) for covering the opposite openings (3a and 3b) of the
acoustic input is shown by way of example in FIG. 4b. Plastic capsules of this type are usually of
the order of a few millimeters in the field of communications, for example, about 6 to 8 mm wide
or deep and about 5 to 6 mm high. The opening may be round or square, for example, 3.5 mm in
diameter, or 2 mm × 2.8 mm in side length.
[0007]
However, attaching an acoustically transparent membrane to an acoustic transducer is
problematic in several respects. On the one hand, as mentioned earlier, especially in the field of
communication, the size of the acoustic transducer is only a few millimeters, which tends to be
smaller. Because of this, targeted membrane attachment is difficult, laborious and therefore
costly. On the other hand, although the acoustic transducer thus prepared has to be inserted into
a plastic capsule, as mentioned earlier, the internal dimensions of the plastic capsule exactly
match the external dimensions of the acoustic transducer. During the insertion of the acoustic
transducer, the glued membrane can get jammed at the edge or loose from the acoustic
transducer due to friction, which is a particularly serious problem in bi-directional microphones.
This is because, with this type of microphone, when inserting the transducer into a plastic
capsule, one of the membranes must be pushed uniformly along the inner wall of the plastic
capsule. For mass production, simpler and more reliable manufacturing methods are desirable,
while guaranteeing comparable high quality.
[0008]
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a
encapsulated acoustic transducer which can be produced in a cost-effective and reliable manner,
in particular with an acoustically transparent friction element for incorporation in the housing of
a communication device. To provide.
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[0009]
The problem is solved according to the invention by the features of the independent claims.
The center of the solution does not fix the acoustically transparent friction elements directly to
the acoustic transducer, but instead mold on (bond one side to the plastic during injection
molding of the plastic capsule preferably in or on the sound pressure opening of the plastic
capsule) Or mold around (wrap on both sides with plastic) and fix it.
[0010]
Bonding of the acoustically transparent friction elements according to the invention, ie flat
fabrics or membranes, with plastic capsules can be carried out by geometrical engagement or by
friction. A snap-in connection is a form-engagement connection in which the snap element can be
molded directly into a plastic capsule, which is usually injection molded. In this case, the friction
element only has to be arranged in front of the sound pressure opening and fitted in by means of
a snap connection. Accidental movement of the friction element upon insertion of the acoustic
transducer is prevented, and the risk of attaching the friction element is much smaller than
directly bonding the membrane to the acoustic transducer.
[0011]
However, according to the invention, plastic capsules are preferred in which the acoustically
transparent friction elements are already fixed during production of the plastic capsules by "mold
around" or "mold on". Here too, a connection by means of a geometrical engagement of the
friction element and the plastic capsule is involved. In the case of "mold on", the shape
engagement occurs when the plastic material of the plastic capsule engages the pores and
irregularities of at least part of the surface of the fabric or membrane, while the opposite surface
remains free of plastic. A connection by means of this formally engagement has proved to be
sufficiently adequate. However, if the edge portion of the friction element is continuously "moldaround" with plastic material from one side of the friction element to the opposite side, a more
stable connection is obtained.
[0012]
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The friction connection between the friction element and the plastic capsule is possible, for
example, by means of adhesion with an adhesive.
[0013]
Further preferred embodiments are given in the dependent claims and below as a description of
preferred embodiments.
[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the figures, the different forms
of the same components are indicated by the same reference numerals.
[0015]
The acoustic transducer plastic capsules (10) according to the invention are shown in FIGS. 1 to
3, which are used in the manner shown or similar for incorporation in the housing of a
communication device. Used in the method.
The plastic capsule (10) defines by its wall (1) a mounting space (2) for mounting the acoustic
transducer (20), which is only shown by way of example in FIG. 1a.
Sound pressure openings (3 or 3a and 3b) are provided in the wall (1) through which sound from
the surroundings reaches the sound input of the sound transducer (20) provided in the mounting
space (2) Can.
In the case of an omnidirectional or unidirectional transducer, one sound pressure aperture (3) is
sufficient, but in the case of a bi-directional transducer two sound pressure apertures (3a and 3b)
are provided, It is desirable for this to be arranged at right angles to each other as shown in FIG.
Each sound pressure aperture is plugged with an acoustically transparent friction element, which
is preferably a fabric or a membrane that transmits the sound pressure and at the same time
influences the sound pressure by the acoustic impedance specific to the friction element.
However, a version is also conceivable in which one sound pressure opening is designed without
friction elements. In other versions, it is possible to plug the sound pressure openings with
friction elements of different acoustic impedance (e.g. 100 ohms and 500 ohms) or with friction
elements of the same impedance.
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[0016]
In the version shown in FIGS. 1 and 2, the acoustically transparent friction element (4 or 4a and
4b) is a wall so that the wall material extends continuously from the top of the friction element to
the opposite back side of the friction element. It is surrounded by (3). This is possible as a
process by inserting the friction element into the injection mold of the plastic capsule (10) before
starting the injection molding. Thereafter, the friction element (4) is mold-around during injection
molding so that it is rigidly connected to the wall (1) by means of a geometric engagement.
[0017]
FIG. 1 shows two orthogonal cross sections of a plastic capsule (10) for a bi-directional
transducer (20), and FIG. 2 has only one acoustically transparent friction element (4) Fig. 1
shows a cross-sectional view of a plastic capsule (10) for an omnidirectional transducer. In the
embodiment shown in FIG. 2, the lid cover (5) has a film hinge (6) in the embodiment shown in
FIG. 2 so that the lid cover (5) can be snapped behind the tabs (7) and the plastic capsule can be
closed safely. Are molded directly into plastic capsules.
[0018]
FIG. 3 shows a plastic capsule of another embodiment of the present invention. In the versions
shown in FIGS. 1 and 2, the acoustically transparent friction element (4b) is "mold-around" with
the wall (1) of the plastic material, whereas in this case the friction element (4a) It will only be
mold on. In the case of "mold on", during injection molding the plastic material penetrates into
the pores and irregularities of the surface of the friction element (4) and causes sticking, so that
the geometrical engagement between the friction element (4a) and the wall (1) With connection
by.
[0019]
However, alternatively, an acoustically transparent friction element is attached to the wall by
means of a snap-on lid similar to the snap-on lid shown in FIG. 2 together with the lid cover (5) or
alternatively on the surface of the wall (1) Direct bonding is also possible.
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[0020]
Depending on the requirements, it may be beneficial to block only one of the several sound
pressure openings with an acoustically transparent friction element.
[0021]
Porous materials which transmit sound pressure but which have a specific influence on sound
pressure due to the unique acoustic impedance are suitable as acoustically transparent friction
elements.
Thus, polypropylene, polyester, polyamide, polyether, polytetrafluoroethylene (PTFE),
polysulfone, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene propylene copolymer
(FEP) and tetrafluoroethylene / perfluoro (propyl vinyl) ) Porous films made of sintered or nonsintered synthetic polymers such as ether copolymers (PFA) or membranes are suitable.
The above fluoropolymers are desirable in terms of their processing properties, temperature
resistance and chemical inertness. Porous membranes made of polytetrafluoroethylene are
particularly desirable. Films of this type may contain dark pigments or dyes for aesthetic reasons.
[0022]
Porous polytetrafluoroethylene films suitable for use in the present invention may incorporate
the filler into the PTFE resin according to known methods, for example by drawing or squeeze, by
a papermaking process, and then be removed for a porous structure Or by powder sintering. Use
of a porous expanded PTFE film of bonded nodes and fibrils as porous PTFE, as described in US
Pat. Nos. 3,959,566 and 4,187,390, which illustrate desirable materials and desirable steps of
film production It is desirable to do. The nodes and fibrils form an internal structure of a threedimensional network of interconnecting pathways and openings extending from one surface
perpendicular to the other surface and from one edge through the membrane to the other edge
laterally Do. The thickness of the porous PTFE film should be in the range of 0.5 to 1000 μm,
preferably in the range of 5 to 100 μm, and the porosity should be in the range of 20 to 98%,
80% to A range of up to 90% is desirable, and the air permeability should be in the range of 0.05
to 30 Gurley seconds, preferably from 0.5 to 30 Gurley seconds, and the nominal pore size is in
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the range of 0.05 to 50 μm, from 3 to 20 μm The range of is desirable.
[0023]
However, instead of a membrane, it is also possible to use a fabric having the corresponding
properties. Woven, knitted or non-woven and microfiber fabrics of synthetic or natural origin are
suitable as fabrics.
[0024]
In order to increase the stability of the porous structure, the friction element is attached to at
least one support material, such as a non-woven fabric, woven fabric, knitted fabric, perforated
board, mesh layer or non-woven layer of various plastic or organic materials. Suitable support
materials are polyesters, polyamides, aramids or fluoropolymers, among which dark non-woven
polyester materials are preferred. Support materials made of cellulose are also particularly
suitable. The thickness of such a desirable support material is in the range of 40 to 1000 μm,
preferably 50 to 200 μm.
[0025]
The structure of the acoustically transparent friction element is usually very thin in order to have
the following characteristics: The acoustic resistance should be in the range of 0 to 10,000 ohms
and the sound pressure loss should be in the range of 0 to 20 decibels. GORE-TEX laminates
EV22209 or EV22210 supplied by the applicant are suitable as laminates for this application.
[0026]
Curable plastics such as silicone or natural rubber and thermoplastics such as polypropylene,
polyethylene, polycarbonate or polyamide, and as desired Santoprene® (available from
Montsanto, Italy) or Hytrel® (registered trademark) Thermoplastic elastomers such as those
available from DuPont) are particularly suitable as materials for plastic capsules. All the abovementioned plastics can be used in the so-called insert molding injection molding process and
have the great advantage that the injection molding of the plastic capsule and the coupling of the
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acoustically transparent friction element with the plastic capsule can be carried out in one
process step. In particular, thermoplastic elastomers have the property that they can be
processed in an insert molding injection molding process and maintain their elastomeric
properties in this processing.
[0027]
The production of plastic capsules according to the invention, incorporating acoustically
transparent friction elements in the insert molding injection molding process, takes place as
follows. First, the friction element is fixed in the injection molding die. This is possible by
pressing the friction element against the wall of one side of the injection molding die such that
the edge portion of the friction element projects into the injection molding die. The plastic is then
molded on so that the surface of the friction element is sealed on the surface of the wall of the
finished plastic capsule, ie at least one side of the friction element remains free of plastic. On the
other hand, if the friction element is pressed against the ridge of the wall of the injection mold so
that its edge portion projects laterally above this ridge, the edge portion of the friction element
can be molded around, The friction element is tightly enclosed in the wall (1), as shown in FIGS.
For example, with a 5 mm diameter opening, it is sufficient to laterally enclose about 0.5 mm of
the edge portion of the friction element. In special cases, it is necessary to fix the friction element
between the two punches so that during the injection process the friction element protrudes
laterally above the punch so that the edge part of the friction element can be molded around with
the injection molding material There is a possibility. Subsequent production is preferably
performed using two moveable punches in accordance with the manufacturing method described
in Sumitomo Electric Industries Limited EP 0 350 813 A2.
[0028]
After the plastic capsule has been removed from the injection molding die, the acoustic
transducer can be inserted into the plastic capsule without any harm and without the risk of the
membrane loosening.
[0029]
The production of plastic capsules by means of an insert molding injection molding process also
has the added advantage of precisely locating the friction elements in the desired position.
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This is a problem in known processes.
[0030]
The plastic capsule according to the invention has the advantage that the electronic components
of the acoustic transducer are completely protected from environmental influences, in particular
dust, salt and liquid, if all sound pressure openings are closed with friction elements. There is
also. This is especially true for ePRFE membranes. This is because the ePRFE membrane is
permeable to air, and at the same time, it is also watertight and dustproof. The hydraulic pressure
of this type of friction element must be at least 1 bar.
[0031]
The thickness of the test method membrane employed was determined using a thickness gauge
and the mean value was determined from four measurements.
[0032]
The porosity was determined from the equation below.
In the above equation, ρ is the apparent density obtained as a ratio of weight to volume
including air content and bubbles, spec spec is the specific density of the material, and ρ spec
for PTFE is about 2.2 g / m 3 .
[0033]
Air permeability was determined according to ASTM test method D726-84 using a Gurley
densitometer from W. & L. E. Gurley & Sons.
[0034]
The hydraulic pressure was measured with reference to an ePTFE membrane stretched between
two test plates.
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Water pressure can be applied to the membrane above the lower test plate. A pH paper was
placed between the upper test plate and the membrane to detect water permeation through the
membrane. The water pressure was raised little by little and each time the water pressure was
raised, it waited for 10 seconds before checking the pH paper. The hydraulic pressure is the
water pressure when the pH paper is colored due to the penetration of water, and the test results
were taken from the center of the membrane to eliminate the effect of edge damage.
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