Loudspeaker assembly with suppression of magnetic flux modulation distortion

Patent metadata

Field	Value
Publication number	US-2016286301-A1
Application number	US-201415034075-A
Country	US
Kind code	A1
Filing date	Nov 4, 2014
Priority date	Nov 6, 2013
Publication date	Sep 29, 2016
Grant date	—

Abstract

An electrodynamic loudspeaker assembly having an electrodynamic loudspeaker and first and second compensation filters. The electrodynamic loudspeaker includes a voice coil arranged in an air gap of a magnetically permeable structure and a compensation coil wound around a portion of the magnetically permeable structure. The first compensation filter filters an audio input signal to the loudspeaker assembly with a first frequency response to generate a voice coil compensation signal for application to the voice coil. The second compensation filter filters the audio input signal to the loudspeaker assembly with a second frequency response to generate a second compensation signal for application to the compensation coil. The first and second frequency responses, across a predetermined audio frequency range, suppress a time-varying or AC magnetic flux in the air gap caused by voice coil current such that magnetic flux modulation in the air gap of the loudspeaker is suppressed.

First claim

1 . An electrodynamic loudspeaker assembly comprising:
an electrodynamic loudspeaker comprising: a magnetic circuit comprising a magnetically permeable structure having an air gap arranged therein and a magnetic flux generator configured to produce a constant or DC magnetic flux through the magnetically permeable structure and air gap, a movable diaphragm assembly comprising a voice coil arranged in the air gap, a compensation coil wound around a portion of the magnetically permeable structure to produce a compensation magnetic flux in the air gap in accordance with a compensation signal; and a first compensation filter configured to filtering an audio input signal to the loudspeaker assembly with a first frequency response to generate a voice coil compensation signal for application to the voice coil, a second compensation filter configured to filtering the audio input signal to the loudspeaker assembly with a second frequency response to generate a second compensation signal for application to the compensation coil, wherein the first and second frequency responses are configured to, across a predetermined audio frequency range, suppress a time-varying or AC magnetic flux in the air gap caused by voice coil current such that magnetic flux modulation in the air gap of the electrodynamic loudspeaker is suppressed.

2 . An electrodynamic loudspeaker assembly according to claim 1 , wherein each of the first and second frequency responses of the voice coil compensation filter and the second compensation filter, respectively, is substantially time invariant.

3 . An electrodynamic loudspeaker assembly according to claim 1 , wherein each of the first and second frequency responses of the first and second compensation filters, respectively, are adaptive or time-varying in accordance with instantaneous displacement of the diaphragm assembly from its rest position.

4 . An electrodynamic loudspeaker assembly according to claim 1 , wherein the first frequency response T VC of the first compensation filter and the second frequency response T FC of the second compensation filter have frequency responses conforming to:

T
VC

=

1
+

H
21



H

μ
,
1

H

μ
,
2



H
11

-

H

μ
,
1



H
21

,



T
FC

=

-

H
11



H

μ
,
1

H

μ
,
2



H
11

-

H

μ
,
1



H
21

,

wherein:
H 11 corresponds to a voice coil admittance transfer function across the predetermined audio frequency range;
H 21 corresponds to a transfer function between the second compensation signal, of the compensation coil, and the current in the voice coil across the predetermined audio frequency range;
H μ,1 corresponds to a transfer function between the voice coil compensation signal a magnetizing inductance representing the mutual inductance created by a magnetic flux in common with the voice coil and compensation coil across the predetermined audio frequency range;
H μ,2 corresponds to a transfer function between the second compensation signal, of the compensation coil, and the magnetizing inductance across the predetermined audio frequency range.

5 . An electrodynamic loudspeaker assembly according to claim 1 , further comprising:
a first power amplifier or buffer inserted between the voice coil compensation signal and the voice coil, a second power amplifier or buffer inserted between the output of the second compensation filter and the compensation coil.

6 . An electrodynamic loudspeaker assembly according to claim 1 , wherein the voice coil has a DC resistance between 1Ω and 100Ω and the compensation coil has a DC resistance between 0.5Ω and 50Ω.

7 . An electrodynamic loudspeaker assembly according to claim 1 , comprising a first analog-to-digital converter configured to convert the audio input signal into a digital audio input signal at a predetermined sample rate;
each of the first and second compensation filters comprising a digital filter.

8 . An electrodynamic loudspeaker assembly according to claim 1 , wherein the magnetic flux generator comprises at least one permanent magnet configured to produce the constant or DC magnetic flux through the magnetically permeable structure.

9 . A sound reproducing system comprising an electrodynamic loudspeaker assembly according to claim 1 .

10 . A method of suppressing magnetic flux modulation in an air gap of an electrodynamic loudspeaker, comprising steps of:
producing a magnetic flux in the air gap of the electrodynamic loudspeaker, coupling a first compensation filter having a first frequency response to a voice coil of the electrodynamic loudspeaker, coupling a second compensation filter having a second freq

Assignees

• Univ Danmarks Tekniske

Inventors

• Agerkvist Finn
• Antonello Niccolo
• Christensen Anders

Classifications

• H04R1/22 Primary

  for obtaining desired frequency characteristic only  {(circuit for combining transducers having different responses H04R3/00; for hearing aids H04R25/407)} · CPC title

• H04R9/025 Primary

  Magnetic circuit · CPC title

• H04R3/08

  of electromagnetic transducers · CPC title

• H04R29/003

  of the moving-coil type · CPC title

• H04R2201/028

  Structural combinations of loudspeakers with built-in power amplifiers, e.g. in the same acoustic enclosure (H04R2499/10 takes precedence; Single (sub)woofer with two or more satellite loudspeakers for mid- and high-frequency band reproduction driven via the (sub)woofer H04R2205/026) · CPC title