FIG. 1 shows a schematic drawing of a conventional electrodynamic sound transducer. The transducer 100 comprises a diaphragm 110, a coil 120 and a magnet system 101 consisting of a pole piece 130, a magnet 140 and a yoke 150. The magnet system 101 together with the diaphragm 110 and the coil 120 can be placed and glued in a chassis 160. Further, the elements of the magnet system 101, namely pole piece 130, magnet 140 and yoke 150, can be glued together. Alternatively, the connection can be made by rivets. The coil 120 is a voice coil and coupled to the vibratory diaphragm 110.
The electrodynamic transducer described above is usually manufactured by first gluing together the pole piece 130, the magnet 140 and the yoke 150. This must be done very precisely, since a magnetic gap 170 for the coil 120 to vibrate is very narrow. Here it is to be considered that meeting the magnetic gap 170 exactly has a very big impact to the transducer's acoustic quality. The magnet system 101 consisting of the pole piece 130, the magnet 140 and the yoke 150 is glued into the chassis 160. Then the coil 120 that is fixed to the vibratory diaphragm 110 can be inserted into the magnetic gap, and the diaphragm can be glued at its edge for example to the chassis 160.
Both when assembling the magnet system 101, consisting of the pole piece 130, the magnet 140 and the yoke 150, and when inserting the magnet system into the chassis, extreme precision of execution is important. It is of high importance that the assembly is performed concentrically (i.e. that all—usually rotationally symmetrical—components are assembled with a common center), and that the resulting magnetic gap 170 has constant width at every point of the circumference and the coil is centric therein. Even smallest deviations that may occur during assembly will lead to hearable distortion in acoustic reproduction, e.g. due to staggering of the diaphragm when being driven.
Especially for gluing the edge of the diaphragm to the chassis it must be ensured that the coil is centered in the magnetic gap.
The manufacturing of an electrodynamic transducer as describe above is unfavorable, since all method steps need to be executed in an extremely accurate way, and since an exactly accurate arrangement of the single components is required. Nevertheless, a certain amount of scrap during manufacturing cannot be avoided.
Joining the magnet system by rivets can lead to mechanical abrasion of the material or the riveter, which may pollute the tools used. This attrition material may also accumulate during assembly at places in the product where it may lead to malfunction.
When the elements of the magnet system are glued together, surplus glue may pollute the centering tool. This leads to a high amount of scrap and a high maintenance effort. When the magnet system is inserted into the chassis, the yoke must fit exactly into the chassis. Therefore low tolerances of the outer diameter of the yoke and the inner diameter of a recess in the chassis are required. Thus, manufacturing of the chassis may be very cost-intensive. Moreover, adhesion between the yoke and the inner side of the chassis must be good for the yoke not to slip.
In the German patent application which is the priority application for the present application, the German Patent and Trademark Office has cited the following documents: DE 10 2011 080 606 A1, DE 102014 114 713A1 and U.S. Pat. No. 6,236,733 B1.
U.S. Pat. No. 7,433,478 B2 describes an electroacoustic transducer and a method for its manufacturing.
DE 2901223 describes a method for manufacturing a magnet system for electrodynamic transducers. Herein, components of the magnet system can be fixed in their position by thermoplastic material.
DE 1974072 U describes a coil connection for a dynamic electroacoustic transducer. The electrodynamic transducer has a plastic yoke that encloses fully or partially a magnet system of the transducer.