Electrodynamic actuator for a speaker or a sound transducer with improved damping

1. An electrodynamic actuator ( 1 a . . . 1 c ), which is designed to be connected to a backside of a plate like structure ( 25 ) or membrane ( 2 ) opposite to a sound emanating surface (S) of the plate like structure ( 25 ) or the membrane ( 2 ) and which comprises

at least one voice coil ( 7 , 7 a , 7 b ), which has an electrical conductor in the shape of loops running around a coil axis (A) in a loop section;

a magnet system ( 8 ) being designed to generate a magnetic field (B) transverse to the conductor in the loop section; and

an arm arrangement ( 14 a . . . 14 j ) of a plurality of arms ( 17 a . . . 17 t ) coupling the at least one voice coil ( 7 , 7 a , 7 b ) and

a) the magnet system ( 8 ) and allowing a relative movement between the voice coil ( 7 , 7 a , 7 b ) and said magnet system ( 8 ) in an excursion direction (C) parallel to the coil axis (A); or

b) a movable part ( 28 ) of the magnet system ( 8 ) and allowing a relative movement between the voice coil ( 7 , 7 a , 7 b ) and said movable part ( 28 ) of the magnet system ( 8 ) in an excursion direction (C) parallel to the coil axis (A),

wherein

the arms ( 17 a . . . 17 t ) 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 and wherein

each of the arms ( 17 a . . . 17 t ) comprises at least two arm sections (s, s 1 , s 2 ), which are arranged movable to each other and which are connected to each other by means of a damping material ( 18 a . . . 18 g ) with a tensile storage modulus of 0.1-6000 MPa and a tensile loss factor of at least 0.1, each measured at room temperature of 20° C.

2. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the arms ( 17 a . . . 17 t ) comprise more than two arm sections (s, s 1 , s 2 ), wherein each two of them are connected to each other by means of the damping material ( 18 a . . . 18 g ).

3. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the at least two arm sections (s, s 1 , s 2 ) run next to each other forming a longitudinal gap in-between, in which the damping material ( 18 a . . . 18 g ) is arranged.

4. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that a ratio between a length of said gap to its width is >20.

5. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the at least two arm sections (s, s 1 , s 2 ) are arranged at a distance (b 1 . . . b 4 ) measured in the direction of the coil axis (A).

6. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 5 , characterized in that the distance (b 1 . . . b 4 ) between the at least two arm sections (s, s 1 , s 2 ) being connected by means of the damping material ( 18 a . . . 18 g ) is in a range of 5 μm≤d≤100 μm.

7. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the at least two arm sections (s, s 1 , s 2 ) are arranged at a distance (b 1 . . . b 4 ) measured perpendicularly to the direction of the coil axis (A).

8. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 7 , characterized in that the distance (b 1 . . . b 4 ) between the at least two arm sections (s, s 1 , s 2 ) being connected by means of the damping material ( 18 a . . . 18 g ) is in a range of 20 μm≤d≤100 μm.

9. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the gap is made by etching and/or by use of a laser.

10. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the arms ( 17 a . . . 17 t ) are L-shaped, U-shaped, S-shaped, shaped like a bow or shaped like a meander when viewed in a direction parallel to the coil axis (A).

11. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 10 , characterized in that the at least two arm sections (s, s 1 , s 2 ) are concatenated in a longitudinal direction of the respective arm ( 17 a . . . 17 t ) and

alternatingly are bent in a different sense of direction or

alternatingly are straight and bent.

12. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 11 , characterized in that a distance (b 1 . . . b 4 ) between the at least two arm sections (s, s 1 , s 2 ) being connected by means of a damping material ( 18 a . . . 18 g ), which is measured perpendicularly to the direction of the coil axis (A), is in a range of 50 μm≤d≤400 μm.

13. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the at least two arm sections (s, s 1 , s 2 ) consist of different materials.

14. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the arms ( 17 a . . . 17 t ) are coated.

15. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the arms ( 17 a . . . 17 t ) are coated with the damping material ( 18 a . . . 18 g ).

16. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 10 , characterized in that the at least one of the plurality of arms ( 17 a . . . 17 t ) is encompassed by or embedded in the damping material ( 18 a . . . 18 g ).

17. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 16 , characterized in that a thickness of the damping material ( 18 a . . . 18 g ), which is measured in the direction of the coil axis (A), is in a range of 20 μm≤d≤200 μm.

18. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 14 , characterized in that the coating consist of or contains sprayed silicone.

19. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the arms ( 17 a . . . 17 t ) together with the damping material ( 18 a . . . 18 g ) are coated.

20. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the at least two arm sections (s, s 1 , s 2 ) have a different stiffness.

21. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that the arms ( 17 a . . . 17 t ) are made of or comprise steel, brass, bronze, molybdenum or tungsten.

22. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 21 , characterized in that the arms ( 17 a . . . 17 t ) are made of a stainless steel.

23. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 22 , characterized in that the arms ( 17 a . . . 17 t ) are 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 .

24. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 , characterized in that at least some of said arms ( 17 a . . . 17 t ) are electrically connected to the at least one voice coil ( 7 , 7 a , 7 b ).

25. A speaker ( 5 ), characterized by an electrodynamic actuator ( 1 a . . . 1 c ) as claimed in claim 1 and a membrane ( 2 ), which is fixed to the at least one coil ( 7 , 7 a , 7 b ) and to the magnet system ( 8 ).

26. The electrodynamic actuator ( 1 a . . . 1 c ) as claimed in to claim 1 , wherein the at least one voice coil ( 7 , 7 a , 7 b ) or the magnet system ( 8 ) comprises a flat mounting surface, which is intended to be connected to the backside of the plate like structure ( 25 ) opposite to a sound emanating surface (S) of the plate like structure ( 25 ), wherein said backside is oriented perpendicularly to the coil axis (A).

27. An electrodynamic transducer ( 26 a , 26 b ), comprising a plate like structure ( 25 ) with a sound emanating surface (S) and a backside opposite to the sound emanating surface (S) and comprising an electrodynamic actuator ( 1 a . . . 1 c ) connected to said backside, characterized in that the electrodynamic actuator ( 1 a . . . 1 c ) is designed according to claim 1 .

28. An electrodynamic transducer ( 26 a , 26 b ) as claimed in claim 27 characterized in that an average sound pressure level of the electrodynamic transducer ( 26 a , 26 b ) measured in an orthogonal distance of 10 cm from the sound emanating surface (S) is at least 50 dB_SPL in a frequency range from 100 Hz to 15 kHz.

29. An output device characterized in that the plate like structure ( 25 ) as claimed in claim 27 is embodied as a display and that the electrodynamic actuator ( 1 a . . . 1 c ) is connected to the backside of the display.

30. A method of manufacturing an intermediate product for an electrodynamic actuator ( 1 a . . . 1 c ), comprising the steps of:

providing at least one voice coil ( 7 , 7 a , 7 b ), which has an electrical conductor in the shape of loops running around a coil axis (A) in a loop section;

providing a magnet system ( 8 ), which is designed to generate a magnetic field (B) transverse to the conductor in the loop section;

manufacturing an arm arrangement ( 14 a . . . 14 j ) of a plurality of arms ( 17 a . . . 17 t ), wherein

the arms ( 17 a . . . 17 t ) 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 and wherein

the arms ( 17 a . . . 17 t ) are L-shaped, U-shaped, S-shaped, shaped like a bow or shaped like a meander when viewed into a direction parallel to the coil axis (A),

embedding at least one of the plurality of arms ( 17 a . . . 17 t ) in silicone, which is sprayed onto the at least one of the plurality of arms ( 17 a . . . 17 t ) and which forms a damping material ( 18 a . . . 18 g ) for the at least one of the plurality of arms ( 17 a . . . 17 t ), and

coupling the at least one voice coil ( 7 , 7 a , 7 b ) and

a) the magnet system ( 8 ) by use of the arm arrangement ( 14 a . . . 14 j ) and allowing a relative movement between the voice coil ( 7 , 7 a , 7 b ) and said magnet system ( 8 ) in an excursion direction (C) parallel to the coil axis (A), or

b) a movable part ( 28 ) of the magnet system ( 8 ) by use of the arm arrangement ( 14 a . . . 14 j ) and allowing a relative movement between the voice coil ( 7 , 7 a , 7 b ) and said movable part ( 28 ) of the magnet system ( 8 ) in an excursion direction (C) parallel to the coil axis (A).