Method for avoiding an offset of a membrane of a electrodynamic acoustic transducer

Patent metadata

Field	Value
Publication number	US-10397706-B2
Application number	US-201815936909-A
Country	US
Kind code	B2
Filing date	Mar 27, 2018
Priority date	Mar 27, 2017
Publication date	Aug 27, 2019
Grant date	Aug 27, 2019

Abstract

A method for avoiding an offset of a membrane ( 3 ) of an electrodynamic acoustic transducer ( 1 ) having two voice coils ( 7, 8 ) is presented, wherein a control voltage (U CTRL ) is applied to at least one of the voice coils ( 7, 8 ) until the electromotive force (U emf1 ) of the first coil ( 7 ) or a parameter derived thereof and the electromotive force (U emf2 ) of the second coil ( 8 ) or a parameter derived thereof substantially reach a predetermined relation. Furthermore, an electronic offset compensation circuit ( 12 ) is presented, which performs the above application of a control voltage (U CTRL ). Finally, the invention relates to a transducer system with a transducer ( 1 ) and an electronic offset compensation circuit ( 12 ) connected to the transducer ( 1 ).

First claim

What is claimed is:

1. A method for avoiding an offset of a membrane of an electrodynamic acoustic transducer, wherein the electrodynamic acoustic transducer comprises a voice coil arrangement attached to the membrane, the voice coil arrangement having a first voice coil and a second voice coil, the method comprising:
applying a control voltage U CTRL to at least one of the first voice coil and the second voice coil; and
altering the control voltage U CTRL until a calculated value of the electromotive force U emf1 of the first voice coil or a parameter derived thereof and a calculated value of the electromotive force U emf2 of the second voice coil or said parameter derived thereof substantially reach a predetermined numeric relation.

2. The method as claimed in claim 1 , wherein the electromotive force U emf1 of the first voice coil and the electromotive force U emf2 of the second voice coil are calculated by the formulas:
U emf1 =U in1 ( t )− Z C1 ·I in ( t )

U emf2 =U in2 ( t )− Z C2 ·I in ( t )

wherein Z C1 is the coil resistance of the first voice coil, U in1 (t) is the input voltage to the first voice coil at the time t and I in (t) is the input current to the first voice coil at the time t and wherein Z C2 is the coil resistance of the second voice coil, U in2 ( t ) is the input voltage to the second voice coil at the time t and I in (t) is the input current to the second voice coil at the time t.

3. The method as claimed in claim 2 , wherein a parameter derived from the electromotive force U emf1 , U emf2 is an absolute value of the electromotive force U emf1 , U emf2 , a square value of the electromotive force U emf1 , U emf2 or a root mean square value of the electromotive force U emf1 , U emf2 .

4. The method as claimed in claim 3 , wherein the control voltage U CTRL is applied to at least one of the first and second voice coils and altered until the low pass filtered electromotive force U emf1 of the first voice coil or a parameter derived thereof and the low pass filtered electromotive force U emf2 of the second voice coil or said parameter derived thereof substantially reach a predetermined numeric relation.

5. The method as claimed in claim 4 , wherein a delta sigma modulation is used for applying a control voltage U CTRL to at least one of the first and second voice coils.

6. The method as claimed in claim 5 , wherein a signal output of the delta sigma modulator is filtered before it is applied to at least one of the first and second voice coils.

7. The method as claimed in claim 4 , wherein a control voltage U CTRL is applied to both the first voice coil and the second voice coil.

8. The method as claimed in claim 7 , wherein a sound signal is applied to the first voice coil and/or the second voice coil during application of a control voltage U CTRL .

9. The method as claimed in claim 8 , wherein the voice coil arrangement further comprises the first voice coil and the second voice coil being serially connected, and wherein the sound signal is only applied to an outer tap of one of the first or second voice coils.

10. The method as claimed in claim 1 , comprising the steps of:
a) calculating a velocity of the membrane based on an input voltage U in and an input current I in to at least one of the first or second voice coils of the transducer and based on an idle driving force factor of the transducer when the membrane is in an idle position;
b) calculating a position of the membrane by integrating said velocity;
c) calculating the velocity of the membrane based on the input voltage U in and the input current I in to the at least one of the first or second voice coils of the transducer and based on a driving force factor of the transducer at the position of the membrane calculated in step b); and
d) recursively repeating steps b) and c).

11. The method as claimed in claim 10 , characterized in that the velocity, the input voltage U in , the input current I in , the idle driving force factor, the driving force factor and the position are related to the same point in time.

12. The method as claimed in claim 10 , characterized in that the velocity, the input voltage U in , the input current I in , the idle driving force factor, the driving force factor and the position are related to different points in time.

13. The method as claimed in claim 12 , comprising the steps of:
a) calculating a velocity v(t) of the membrane based on an input voltage U in (t) and an input current I in (t) to at least one of the first or second voice coils of the transducer and based on an idle driving force factor of the transducer when the membrane is in an idle position;
b) calculating a position x(t) of the membrane by integrating said velocity v(t);
c) calculating the velocity v(t+1) of the membrane based on the input voltage U in (t+1) and the input current I in (t+1) to the at least one of the first or second voice coils of the transducer and based on a driving force factor BL(x(t) of the transducer at the position x(t) of the membrane calculated in step b); and
d) recursively repeating steps b) and c) wherein t gets t+1.

14. The method as claimed in claim 10 , wherein the position x(t) of the membrane is calculated by the formula:
x ( t )= x ( t− 1)+ v ( t )·Δ t.

15. The method as claimed in claim 14 , wherein the velocity v(t) of the membrane is calculated by the formula:
v ( t )=( U in ( t )− Z C ·I in ( t ))/ BL (0) in step a ) or by

v ( t+ 1)=( U in ( t+ 1)− Z C ·I in ( t+ 1))/ BL ( x ( t )) in step c )

16. The method as claimed in claim 14 , wherein the velocity v−(t) of the membrane is calculated by the formula:
v ( t+ 1)= v ˜ ( t+ 1)· BL (0)/ BL ( x ( t )) in step c ) wherein

v ˜ ( t+ 1)=( U in ( t+ 1)− Z C ·I in ( t+ 1))/ BL (0)

17. The method as claimed in claim 14 , wherein the velocity v−(t) of the membrane is calculated by use of
the electromotive force U emf1 of the first voice coil, or
the electromotive force U emf2 of the second voice coil, or
the sum of the electromotive force U emf1 of the first voice coil and the electromotive force U emf2 of the second voice coil.

18. An electronic offset compensation circuit configured to be connected to a voice coil arrangement of an electrodynamic acoustic transducer, wherein the electrodynamic acoustic transducer comprises a membrane attached to the voice coil arrangement and a magnet system configured to generate a magnetic field transverse to a longitudinal direction of a wound wire of the voice coil arrangement, wherein the voice coil arrangement comprises a first voice coil and a second voice coil, and wherein the electronic offset compensation circuit is further configured to apply a control voltage U CTRL to at least one of the first and second voice coils and to alter said control voltage U CTRL until a calculated value of the electromotive force U emf1 of the first voice coil or a parameter derived thereof and a calculated value of the electromotive force U emf2 of the second voice coil or a parameter derived thereof substantially reach a predetermined numeric relation.

19. The electronic offset compensation circuit as claimed in claim 18 , wherein the electronic offset compensation circuit is further configured to:
a) calculate a velocity of the membrane based on an input voltage U in and an input current I in to at least one of the first and second voice coils and based on an idle driving force factor of the transducer when the membr

Assignees

• Sound Solutions Int Co Ltd

Inventors

• Reining Friedrich

Classifications

• H04R9/025

  Magnetic circuit · CPC title

• H04R29/003

  of the moving-coil type · CPC title

• H04R3/04

  for correcting frequency response · CPC title

• H04R9/04

  Construction, mounting, or centering of coil · CPC title

• H04R9/08

  Microphones · CPC title