Electromagnetic actuator for a speaker or a sound transducer with a high-strength metal 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 metal with a fatigue strength of at least 370 N/mm 2 or an ultimate tensile strength of at least 1100 N/mm 2 .
1. Electrodynamic actuator, which is designed to be connected to a backside of a plate structure or membrane opposite to a sound emanating surface of the plate structure or the membrane and which comprises
at least one voice coil, which has an electrical conductor in a 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 electrical 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 at least one 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 at least one voice coil and said movable part of the magnet system in an excursion direction parallel to the coil axis,
wherein
the plurality of arms are made of a metal with a fatigue strength of at least 370 N/mm 2 or an ultimate tensile strength of at least 1100 N/mm 2 .
2. Electrodynamic actuator as claimed in claim 1 , characterized in that the plurality of 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, wherein the metal core has a fatigue strength of at least 370 N/mm 2 or an ultimate tensile strength of at least 1100 N/mm 2 .
3. Electrodynamic actuator as claimed in claim 1 , characterized in that the plurality of arms and in particular a metal core is made of or comprises steel, brass, bronze, molybdenum or tungsten.
4. Electrodynamic actuator as claimed in claim 3 , characterized in that the plurality of arms and in particular the metal core is made of a stainless steel.
5. Electrodynamic actuator as claimed in claim 4 , characterized in that the plurality of arms and in particular 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 .
6. Electrodynamic actuator as claimed in claim 1 , characterized in that a cross section of the plurality of arms and in particular a metal core is rectangular wherein a ratio between a width of the cross section, which is its extension in a direction perpendicular to the coil axis, divided by a height of the cross section, which is its extension in a direction parallel to the coil axis, is above 3.0.
7. Electrodynamic actuator as claimed in claim 1 , characterized in that a width of a cross section of the plurality of arms and in particular a metal core is in a range of 200 to 800 μm.
8. Electrodynamic actuator as claimed in claim 1 , characterized in that a height of the cross section of the plurality of arms and in particular a metal core is in a range of 10 to 100 μm.
9. Electrodynamic actuator as claimed in claim 1 , characterized in that the width and/or height of a cross section of the plurality of arms and in particular a metal core varies over a length of the plurality of arms.
10. Electrodynamic actuator as claimed in claim 1 , characterized in that a cross section of the plurality of arms and in particular a metal core has rounded corners with a radius of at least 3 μm or chamfers, wherein a smallest length of a side of a rectangular triangle defining a chamfer is at least 3 μm.
11. Electrodynamic actuator as claimed in claim 1 , characterized in that a 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 a 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.
12. Electrodynamic actuator as claimed in claim 1 , characterized in that a material of at least one coating metal layer has a higher electrical conductivity than a material of a metal core, but a lower bending fatigue strength or ultimate tensile strength.
13. Electrodynamic actuator as claimed in claim 1 , characterized in that a bending stress within a metal core is below its fatigue strength, whereas a bending stress within at least one coating metal layer is above its fatigue strength, or a bending stress within a 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 at least one 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 an idle position of the at least one voice coil.
14. 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.
15. Electrodynamic actuator as claimed in claim 1 , characterized in that at least some of the plurality of arms are electrically connected to the at least one voice coil.
16. Electrodynamic actuator as claimed in claim 1 , characterized in that the plurality of arms are shaped like a bow, like a meander or L-shaped when viewed into a direction parallel to the coil axis.
17. Electrodynamic actuator as claimed in claim 16 , characterized in that the plurality of 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 a corner of the L-shape.
18. Electrodynamic actuator as claimed in claim 17 , characterized in that a distance between the bow or corner and the at least one contacting pad is less than 0.2 mm.
19. Electrodynamic actuator as claimed in claim 16 , 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 plurality of arms is arranged within at least one bow of the two bows.
20. Electrodynamic actuator as claimed in claim 1 , characterized in that a coating structure is arranged on a metal core over a length of at least 90% of a longitudinal extension of at least one arm of the plurality of arms.
21. 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.
22. Speaker, characterized by the electrodynamic actuator as claimed in claim 1 and the membrane, which is fixed to the at least one coil and to the magnet system.
23. Speaker as claimed in claim 22 , characterized in that a ratio of a stiffness of the plurality of arms arrangement to a stiffness of the membrane in direction of the coil axis is below 2.7.
24. Speaker as claimed in claim 22 , characterized in that a ratio of a stiffness of the plurality of arms arrangement to a stiffness of the membrane in direction transverse to the coil axis is below 5.0.
25. Speaker as claimed in claim 22 , characterized in that an 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 .