Electromagnetic actuator for a speaker or a sound transducer with a multimetal layer connection between the voice coil and the magnet system
An electrodynamic actuator for a speaker or an electrodynamic acoustic transducer in general is disclosed, which comprises at least one voice coil, a magnet system and an arm arrangement of a plurality of arms connecting the at least one voice coil and the magnet system or at least a movable part thereof so that a relative movement between these parts is allowed. The arms are made of a metal core, which at least partly is coated with a coating structure having at least one coating metal layer consisting of a different material than the metal core.
1. Electrodynamic actuator, which is designed to be connected to a backside of a plate like structure or membrane opposite to a sound emanating surface of the plate like structure or the membrane and which comprises
at least one voice coil, which has an electrical conductor in the shape of loops running around a coil axis in a loop section, and
a magnet system being designed to generate a magnetic field transverse to the conductor in the loop section and
an arm arrangement of a plurality of arms connecting the at least one voice coil and
a) the magnet system and allowing a relative movement between the voice coil and said magnet system in an excursion direction parallel to the coil axis or
b) a movable part of the magnet system and allowing a relative movement between the voice coil and said movable part of the magnet system in an excursion direction parallel to the coil axis,
wherein
the arms are made of a metal core, which at least partly is coated with a coating structure having at least one coating metal layer consisting of a different material than the metal core, and
wherein the bending stress within the metal core is below its fatigue strength, whereas the bending stress within the at least one coating metal layer is above its fatigue strength, or the bending stress within the metal core is below its ultimate tensile strength, whereas the bending stress within the at least one coating metal layer is above its bending ultimate tensile strength when the excursion of the voice coil relative to the magnet system or its movable part in a direction parallel to the coil axis reaches its nominal maximum of the electrodynamic actuator or is above 0.4 mm with respect to the idle position of the voice coil.
2. Electrodynamic actuator as claimed in claim 1 , characterized in that the material of the at least one coating metal layer has a higher electrical conductivity than the material of the metal core, but a lower bending fatigue strength or ultimate tensile strength.
3. Electrodynamic actuator as claimed in claim 1 , characterized in that at least one coating metal layer comprises or consists of copper, silver, gold or aluminum.
4. Electrodynamic actuator as claimed in claim 1 , characterized in that the coating structure comprises at least two coating metal layers, wherein a first coating metal layer comprises copper, silver, aluminum or gold and wherein a different second coating metal layer, which is located between the metal core and the first coating metal layer, comprises nickel, titanium or chromium.
5. Electrodynamic actuator as claimed in claim 4 , characterized in that the first coating metal layer and the second coating metal layer are chosen from the pairs of Cu/Ni, Au/Ni, Ag/Ni, Al/Ti, Al/Cr, wherein the first cited metal refers to the first coating metal layer and the second cited metal refers to the second coating metal layer and wherein said metals are the main components of the respective coating metal layers or the coating metal layers consist of the respective metals.
6. Electrodynamic actuator as claimed in claim 1 , characterized in that the coating structure comprises an outer coating layer made of a polymer, which at least partly covers the at least one coating metal layer.
7. Electrodynamic actuator as claimed in claim 1 , characterized in that at least some of said arms are electrically connected to the at least one voice coil.
8. Electrodynamic actuator as claimed in claim 1 , characterized in that the metal core is made of or comprises steel, brass, bronze, molybdenum or tungsten.
9. Electrodynamic actuator as claimed in claim 8 , characterized in that the metal core is made of a stainless steel.
10. Electrodynamic actuator as claimed in claim 9 , characterized in that the metal core is made of a cold-rolled stainless steel with a fatigue strength in a range of 370 to 670 N/mm 2 or an ultimate tensile strength in a range of 1100 to 2000 N/mm 2 .
11. Electrodynamic actuator as claimed in claim 1 , characterized in that the cross section of the metal core is rectangular wherein a ratio between the width of the cross section, which is its extension in a direction perpendicular to the coil axis, divided by the height of the cross section, which is its extension in a direction parallel to the coil axis, is above 3.0.
12. Electrodynamic actuator as claimed in claim 1 , characterized in that the width of the cross section of the metal core is in a range of 200 to 800 μm.
13. Electrodynamic actuator as claimed in claim 1 , characterized in that the height of the cross section of the metal core is in a range of 10 to 100 μm.
14. Electrodynamic actuator as claimed in claim 1 , characterized in that the width and/or height of the cross section of the metal core varies over the length of the arms.
15. Electrodynamic actuator as claimed in claim 1 , characterized in that the cross section of the metal core has rounded corners with a radius of at least 3 μm or chamfers, wherein the smallest length of a side of a rectangular triangle defining the chamfer is at least 3 μm.
16. Electrodynamic actuator as claimed in claim 1 , characterized in that the thickness (s) of the at least one coating metal layer is in a range of 0.5 to 10 μm, wherein the thickness (s) of the at least one coating metal layer is its extension in a direction parallel to the coil axis in case that a contacting area to the metal core lies in a plane perpendicular to the coil axis and its extension in a direction perpendicular to the coil axis in case that a contacting area to the metal core lies in a plane parallel to the coil axis.
17. Electrodynamic actuator as claimed in claim 1 , characterized in that the arms are shaped like a bow, like a meander or L-shaped when viewed into a direction parallel to the coil axis.
18. Electrodynamic actuator as claimed in claim 17 , characterized in that the arms are shaped like a bow or L-shaped when viewed into a direction parallel to the coil axis, wherein at least a contacting pad of the arms is arranged within the bow or within the corner of the L-shape.
19. Electrodynamic actuator as claimed in claim 17 , characterized in that the arms are shaped like a meander when viewed into a direction parallel to the coil axis, wherein the meander has two bows at most and wherein at least one contacting pad of the arms is arranged within the at least one bow.
20. Electrodynamic actuator as claimed in claim 18 , characterized in that a distance between the bow or corner and the at least one contacting pad is less than 0.2 mm.
21. Electrodynamic actuator as claimed in claim 1 , characterized in that the coating structure is arranged on the metal core over a length of at least 90% of the longitudinal extension of an arm.
22. Electrodynamic actuator as claimed in claim 1 , characterized in that a diameter of a metal core of the electrical conductor of the at least one voice coil is ≤110 μm.
23. Speaker, characterized by an electrodynamic actuator as claimed in claim 1 and a membrane, which is fixed to the at least one coil and to the magnet system.
24. Speaker as claimed in claim 23 , characterized in that a ratio of a stiffness of the arm arrangement to a stiffness of the membrane in direction of the coil axis is below 2.7.
25. Speaker as claimed in claim 23 , characterized in that a ratio of a stiffness of the arm arrangement to a stiffness of the membrane in direction transverse to the coil axis is below 5.0.
26. Speaker as claimed in claim 23 , characterized in that the area of the membrane seen in a direction parallel to the coil axis is smaller than 600 mm 2 and/or a back volume of the speaker is in a range from 200 mm 3 to 2 cm 3 .
27. Electrodynamic actuator as claimed in to claim 1 , wherein the at least one voice coil or the magnet system comprises a flat mounting surface, which is intended to be connected to the backside of the plate like structure opposite to a sound emanating surface of the plate like structure, wherein said backside is oriented perpendicularly to the coil axis.
28. Electrodynamic transducer, comprising a plate like structure with a sound emanating surface and a backside opposite to the sound emanating surface and comprising an electrodynamic actuator connected to said backside, characterized in that the electrodynamic actuator is designed according to claim 1 .
29. Electrodynamic transducer as claimed in claim 28 characterized in that an average sound pressure level of the electrodynamic transducer measured in an orthogonal distance of 10 cm from the sound emanating surface is at least 50 dB_SPL in a frequency range from 100 Hz to 15 kHz.
30. Output device characterized in that the plate like structure as claimed in claim 28 is embodied as a display and that the electrodynamic actuator is connected to the backside of the display.