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DESCRIPTION JP2016539562

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DESCRIPTION JP2016539562
Abstract: The present invention relates to an electrodynamic loudspeaker assembly comprising
an electrodynamic loudspeaker and first and second compensation filters. The electrokinetic
loudspeaker has a voice coil disposed in the air gap of the magnetically permeable structure and
a compensation coil wound around a portion of the magnetically permeable structure. The first
compensation filter of the assembly is configured to filter the audio input signal to the
loudspeaker assembly with the first frequency response to generate a voice coil compensation
signal for application to the voice coil. A second compensation filter of the assembly is
configured to filter 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 are time-variant or AC in the air gap generated by the voice
coil current across the predetermined audio frequency range so that flux modulation in the air
gap of the electrodynamic loudspeaker is suppressed. It is configured to suppress magnetic flux.
Loudspeaker assembly with flux modulation distortion suppression
[0001]
The present invention relates to an electrodynamic loudspeaker assembly comprising an
electrodynamic loudspeaker and first and second compensation filters. The electrokinetic
loudspeaker has a voice coil disposed in the air gap of the magnetically permeable structure and
a compensation coil wound around a portion of the magnetically permeable structure. The first
compensation filter of the assembly is configured to filter the audio input signal to the
loudspeaker assembly with the first frequency response to generate a voice coil compensation
signal for application to the voice coil. A second compensation filter of the assembly is
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configured to filter 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 are time-variant or AC in the air gap generated by the voice
coil current across the predetermined audio frequency range so that flux modulation in the air
gap of the electrodynamic loudspeaker is suppressed. It is configured to suppress magnetic flux.
[0002]
The present invention relates to an electrodynamic loudspeaker assembly having a compensation
coil that suppresses or eliminates flux modulation in the air gap of the electrodynamic
loudspeaker. One of the factors that can characterize the acoustic quality of electrokinetic
loudspeakers is their ability to produce undistorted sound. It is well known that the source of
distortion artifacts in the reproduced sound is due to the non-linearity of the loudspeaker system.
These non-linearities may be, for example, displacement dependence of force factor, compliance
of diaphragm, or inductance of voice coil. Of these non-linearities, flux modulation in the air gap
represents one of the major sources of distortion. The most common prior art technique to
reduce this effect is to attach several highly conductive rings in the iron structure of the
loudspeaker [1]. These conductive rings behave like a transformer coupled with a voice coil and
are capable of producing a magnetic flux which attempts to resist AC magnetic flux in the air gap
in which the voice coil is arranged, and Thereby, magnetic flux modulation can be reduced.
[0003]
U.S. Pat. No. 5,959,015 discloses an electrodynamic loudspeaker having a voice coil disposed in
the air gap of a magnetic circuit. The loudspeaker has a static compensation coil wound around
the central pole of the magnetic circuit and located outside the air gap. The compensation coil
attempts to generate a flux that resists the flux generated by the voice coil such that the net AC
flux generated by both is zero or substantially zero. The compensation coil is electrically
connected in series with the voice coil, but in opposite phase.
[0004]
The invention comprises an active method of suppressing or preferably completely eliminating
this type of flux distortion by means of an actively controlled additional fixed coil or
compensation coil. The use of additional coils for the suppression of flux modulation in
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electrodynamic loudspeakers is described in addition to the documents [2], [3] (non-patent
documents 2, 3) in addition to patent document 1 mentioned earlier. Is also disclosed. In these
references, the compensation coil is located in the air gap of the loudspeaker, which is in view of
the small dimensions of the normal air gap and the desire to produce high flux density in the air
gap. Not practical, for many reasons. On the other hand, the compensation coil disclosed by US
Pat. No. 6,075,067 is in particular due to a mismatch between the impedance of the displaceable
voice coil essentially having a moving impedance component and the impedance of the static
compensation coil And can not virtually cancel the flux modulation across any important audio
frequency range.
[0005]
It is very important to provide a more general loudspeaker assembly and flux modulation
suppression method that allows flexible selection of the placement of the compensation coil and
an accurate method of suppressing flux modulation across a predetermined audio frequency
range. Important and valuable.
[0006]
Specification of British Patent No. 2235350
[0007]
Knud Thorborg, Andrew D. Unruh, Electrical Equivalent Circuit Model for Dynamic Moving-Coil
Transducers Incorporating a Semiconductor, J. Audio Eng.
Soc, vol. 56, pp.
696- 709 (2008). Marco Carlisi, Mario Di Cola, Andrea Manzini, An Alternative Approach to
Minimizing Inductance and Related Distortions in Loudspeakers, presented at the 118th
Convention of the Audio Engineering Society, Barcelona Spain, (2005). Daniele Ponteggia, Marco
Carlisi, Andrea Manzini, Electrical Circuit Model for a Loudspeaker with an Additional Fixed Coil
in the Gap, presented at the 128th Convention of the Audio Engineering Society, London UK
(2010).
[0008]
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A first aspect of the invention relates to an electrodynamic loudspeaker assembly having an
electrodynamic loudspeaker. The electrodynamic loudspeaker comprises a magnetically
permeable structure and a magnetically permeable structure having an air gap disposed therein
and a magnetic circuit having a magnetic flux generator configured to generate a constant or DC
magnetic flux through the air gap, and a magnetic circuit within the air gap. A moveable
diaphragm assembly having a voice coil disposed, and a compensation coil wound around a
portion of the magnetically permeable structure to produce a compensating magnetic flux in the
air gap according to the compensating signal, and The electrodynamic loudspeaker assembly is
configured to filter an audio input signal to the loudspeaker assembly with a first frequency
response to generate a voice coil compensation signal for application to a voice coil. A
loudspeaker with a second frequency response to generate a compensation filter and a second
compensation signal for application to the compensation coil And a second compensation filter
configured to filter the audio input signal into the volume, wherein the first and second
frequency responses are such that the flux modulation in the air gap of the electrodynamic
loudspeaker is To be suppressed, it is configured to suppress time-varying or AC magnetic flux in
the air gap generated by the voice coil current over a predetermined audio frequency range.
[0009]
Those skilled in the art will appreciate that this electrodynamic loudspeaker assembly can range
from large woofers for Hi-Fi or loud-sounding applications to small broadband loudspeakers for
portable computing or communication devices such as mobile phones and laptop computers. It
will be appreciated that one may have different electrodynamic loudspeakers with different
impedances, sizes and power ratings.
[0010]
The application of the first and second compensation filters to adapt the frequency response of
the individual compensation signals of the voice coil and the compensation coil is accurate over a
wide audio frequency range such as the 20 Hz to 20 kHz range or the 100 Hz to 10 kHz range
Have the ability to provide good flux modulation suppression.
For example, by appropriate selection of the first and second frequency responses based on
specific calibration measurements detailed below with reference to the accompanying drawings,
various positions of the coils of the compensation coil and of the voice coil and The AC magnetic
flux in the air gap generated by the voice coil current in electrical characteristics can be
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effectively suppressed.
[0011]
The moveable diaphragm assembly, in certain embodiments of the present invention, includes a
diaphragm that can be attached to the frame of an electrodynamic loudspeaker via an elastic
edge suspension. In an alternative embodiment, the diaphragm may be mounted directly to the
frame of the electro-dynamic loudspeaker such that the diaphragm material forms a suspension.
The individual numbers of voice coil and compensation coil windings and DC resistance will vary
depending on the particular type of loudspeaker. In some useful embodiments, the DC resistance
of the voice coil is in the range of 1 ohm to 100 ohms, such as 2 ohms to 32 ohms, and the DC
resistance of the compensation coils is, for example, 1 ohms to 25 ohms, etc. In the range of
0.5Ω to 50Ω. The DC resistance of the voice coil may be identical to the DC resistance of the
compensation coil in some embodiments, as suggested by the above-described resistance range,
and different in other embodiments. It may be The number of voice coil and compensation coil
windings may be the same or different depending, for example, on the characteristics of the first
and second frequency responses of the first and second compensation filters, respectively. Good.
[0012]
The compensating coil may in principle be arranged anywhere in the magnetically permeable
structure, but due to various mechanical constraints determined by the dimensions of the
compensating coil, of course, more than others The specific position may be relatively practical.
In one embodiment, the compensation coil is wound around the central pole of the magnetically
permeable structure, which is why the central pole is often located in the arrangement of the
compensation coil in a normal loudspeaker design In order to be easily accessible.
[0013]
The audio input signal applied to the electrokinetic loudspeaker assembly for sound reproduction
in normal operation comprises speech and sourced from a suitable audio source such as a radio,
a CD player, a network player, an MP3 player, etc. And / or may have music. The audio source
may also have a microphone that generates a real time microphone signal in response to the
incoming sound.
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[0014]
Those skilled in the art will appreciate that each of the first and second compensation filters may
comprise an analog filter or a digital filter, or a combination of both. If each of the first and
second compensation filters comprises a digital filter, the audio input signal may be provided in
digital format from an audio signal source. The digital audio input signal may have a format that
can be applied directly to the first and second compensation filters, or may require format
conversion. The digital audio input signal may, for example, be formatted according to a
standardized serial data communication protocol such as IIC or SPI or may be formatted
according to a digital audio protocol such as I <2> S, SPDIF, etc. In this alternative, the audio
input signal may be provided in analog format and sampled by an analog-to-digital converter of
the assembly prior to application to the first and second digital compensation filters. It may be
converted to a suitable digital format. Those skilled in the art will understand that the first and
second digital compensation filters may be implemented as a filter routine or program on a
software programmable microprocessor or DSP integrated on or operably coupled to the
loudspeaker assembly. It will be understood that it may be done. The filter routine or program
comprises a set of executable program instructions stored in a microprocessor or DSP program
memory.
[0015]
According to a preferred embodiment, each of the first and second frequency responses of the
first and second compensation filters, respectively, is substantially unchanged with time. This
embodiment simplifies the design and minimizes the complexity of the compensation filter.
Alternatively, respectively, the first and second frequency responses of the first and second
compensation filters, respectively, may for example be timed according to the momentary
displacement of the diaphragm assembly from its rest position or unbiased position And may be
adaptive or time-variant.
[0016]
According to a preferred embodiment of the electrokinetic loudspeaker assembly, the first
frequency response T VC of the first compensation filter and the second frequency response T FC
of the second compensation filter have individual frequency responses according to Are selected,
and T VC = 1 + (H 21 H μ, 1) / (H μ, 2 H 11 -H μ, 1 H 21) (11a) T FC =-(H 11 Hμ, 1 / (H μ, 2
H 11 −H μ, 1 H 21) (11b) where H 11 is the voice coil admittance transfer function across the
predefined audio frequency range and H 21 is the predefined audio frequency The transfer
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function between the second compensation signal of the compensation coil across the range and
the current in the voice coil, where H μ, 1 is the voice coil compensation signal of the voice coil
across the predefined audio frequency range, the voice coil and the compensation Mutual
generated by magnetic flux common to coils H.sub..mu., 2 is the transfer function between the
second compensation signal of the compensation coil and the magnetizing inductance over the
predetermined audio frequency range.
[0017]
The outputs of the first and second compensation filters are output to the voice and
compensation coils if the output impedance of the respective one of these filters is properly
matched to the individual impedances of the voice and compensation coils. It may be directly
coupled.
Alternatively, the first power amplifier or buffer may be inserted between the voice coil
compensation signal and the voice coil, and the second power amplifier or buffer is the output of
the second compensation filter and the compensation coil. And may be inserted between. Each of
the first and second power amplifiers or buffers is, for example, a switching type or D such as a
pulse density modulation (PDM) or a pulse width modulation (PWM) output amplifier having
high power conversion efficiency. May have a class amplifier. This is a particularly advantageous
feature used in portable communication devices powered by batteries. In this alternative, each of
the first and second power amplifiers may have a conventional non-switching power amplifier
topology, such as class A or class AB. These embodiments with a power amplifier or buffer will
often allow flexible selection of the individual impedances of the voice coil and the compensation
coil, because of the output impedance of a normal power amplifier or buffer. Is small in
comparison with the actual coil impedance. The output impedance of each power amplifier or
buffer of the power amplifier or buffer may be, for example, less than 0.1Ω.
[0018]
The voice coil may have a DC resistance of 1 Ω to 100 Ω, and the compensation coil may have a
DC resistance of 0.5 Ω to 50 Ω. The voice coil impedance range will cover various practical
loudspeaker designs.
[0019]
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If each of the first and second compensation filters, as described above, comprises a digital filter,
the electro-dynamic loudspeaker assembly converts the audio input signal to a digital audio input
signal at a predetermined sample rate And the first analog-to-digital converter configured. The
sample rate or sampling frequency may be a standardized digital audio frequency, such as 16
kHz, 32 kHz, 44.1 kHz, 48 kHz, 96 kHz, etc. In this alternative, the audio input signal may be
provided in digital format with a predetermined sample rate, such that a first analog-to-digital
converter is not required.
[0020]
The flux generator may have at least one permanent magnet configured to generate a constant or
DC flux through the magnetically permeable structure.
[0021]
A second aspect of the invention relates to a sound reproduction system comprising an
electrodynamic loudspeaker assembly according to any one of the preceding claims.
The sound reproduction system may have an active loudspeaker with an integrated power supply
and one or more power amplifiers coupled to the individual electrodynamic loudspeakers.
[0022]
A third aspect of the invention relates to a method of suppressing flux modulation in an air gap
of an electrodynamic loudspeaker, the method comprising the steps of: generating magnetic flux
in the air gap of the electrodynamic loudspeaker; Coupling a first compensation filter having a
second frequency response to the voice coil of the electrodynamic loudspeaker; and a second
compensation filter having a second frequency response wound around a portion of the
permeable structure of the electrodynamic loudspeaker Combining an audio input signal from an
audio signal source with a voice coil compensation filter and a second compensation to couple a
voice coil compensation signal to the voice coil and a second compensation signal to the
compensation coil; Applying to each of the filters and generated by the voice coil current across
the predetermined audio frequency range Suppressing varying or AC magnetic flux when the air
gap, thereby, in order to suppress the magnetic flux modulation in the gap has a step of adjusting
the first and second frequency response, the.
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[0023]
The adjustment of the first and second frequency responses preferably comprises determining a
voice coil admittance function H 11 across the predefined audio frequency range, and a second
compensation signal of the compensation coil across the predefined audio frequency range and
the voice coil Determining a transfer function H 21 between the currents in the current source
and the voice coil compensation signal across the predetermined audio frequency range and the
magnetizing inductance representing the mutual inductance generated by the flux common to
the voice coil and the compensation coil Determining the transfer function H.sub..mu., 1 between
them, determining the transfer function H.sub..mu., 2 between the second compensation signal of
the compensation coil and the magnetizing inductance across the predetermined audio frequency
range, and , First frequency response T VC of the first compensation filter and second frequency
response of the second compensation filter Adjusting FC and T VC = 1 + (H 21 H μ, 1) / (H μ, 2
H 11 -H μ, 1 H 21) (11a) T FC = − (H 11 H μ, 1) It is carried out by or in a calibration
procedure having / (H μ, 2 H 11 -H μ, 1 H 21) (11 b).
[0024]
The determination of the transfer functions H μ, 1 and H μ, 2 in the calibration procedure may
be performed by several different methods.
According to one embodiment, the transfer functions H μ, 1 and H μ, 2 insert a magnetic field
pickup coil and an inductor with known inductance into the air gap, and the first of the magnetic
field pickup coils for the voice coil compensation signal Determining the transfer function H μ, 1
by measuring the response signal, inserting the magnetic field pickup coil or inductor into the air
gap, and measuring the second response signal of the magnetic field pickup coil to the second
compensation signal Thus, the step of determining the transfer function Hμ, 2 is determined.
[0025]
An alternative embodiment of the calibration procedure comprises coupling a force transducer to
a voice coil to measure multiple force values on the voice coil in response to individual
combinations of voice coil current and compensation coil current; Voice coil and compensation to
determine the transfer functions H μ, 1 and H μ, 2 by separating the contribution of the voice
coil current and the compensation coil current to the measured force value on the voice coil
according to In the step of changing the coil current independently, the transfer function H μ, 1
and the step of changing F L = B l · i = b L μ i μ i = b L μ (i H μ, 2 is determined.
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[0026]
A method of suppressing flux modulation may include first and second compensation filters of
the first and second compensation filters over time, respectively, according to the instantaneous
displacement of the diaphragm assembly from its centered or unbiased position. There may be
the step of optimally adjusting each of the frequency responses.
[0027]
The preferred embodiments of the present invention will be described in further detail in
connection with the attached drawings.
[0028]
FIG. 1 is an equivalent electrical schematic of an electrodynamic loudspeaker having a
compensation coil suitable for use as a component of a loudspeaker assembly according to a first
embodiment of the present invention.
A) shows a schematic block diagram of a loudspeaker assembly according to a first embodiment
of the invention, and B) shows a schematic block diagram of a loudspeaker assembly according to
a second embodiment of the invention.
FIG. 7 is a schematic diagram of a simple magnetic circuit used for experimental verification of
flux modulation suppression.
4 shows four graphs of the measured transfer function of an electrodynamic loudspeaker with a
compensation coil.
4 shows four further graphs of the measured transfer function of an electrodynamic loudspeaker
with a compensation coil. Fig. 6 shows the determined frequency response of a first
compensation filter for a voice coil and the determined frequency response of a second
compensation filter for a compensation coil.
[0029]
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FIG. 1 is an equivalent electrical schematic 100 of an electrodynamic loudspeaker having fixed or
compensating coils suitable as a component of a loudspeaker assembly described below
according to a first embodiment of the invention. In the following description, for the sake of
clarity, the permanent magnet of the loudspeaker is replaced by supplying a compensating or
fixed coil with a DC current representing the magnetomotive force of the permanent magnet in
the loudspeaker's magnetic circuit. Please note. As shown in the drawing, the voice coil
impedance of the voice coil equivalent circuit 103 is the back electromotive force caused by the
resistor R, the inductance L 1, and the mechanical system in series with the transformer
connecting the voice coil to the compensation coil. It is modeled by BI * u (which is a regular
model of a conventional regular loudspeaker). Compensating Coil The compensating coil of
equivalent circuit 105 has a similar impedance with resistor R 2 and inductor L 2. An equivalent
circuit of the mechanical system 107 is shown above the equivalent circuits 103, 105 of the
voice coil and the compensation coil. The transformer is modeled by an ideal transformer
denoted by u 1 and u 2 arranged in parallel with the inductance L u. The ideal transformers u 1
and u 2 combine the voltages and currents at their inputs and outputs according to the following
relationship: u 1 / u 2 = K (1a) i 1 / i 2 = -1 / K (1b) where K is the transformer gain, which is
ideally given by the ratio of the number of primary and secondary coil windings, K = N1 = N2. L
μ is referred to as the magnetizing inductance and represents the mutual inductance generated
by the voice coil and the compensation coil, that is, the magnetic flux in common with both coils.
On the other hand, L 1 and L 2 are the leakage inductances of the voice coil and the
compensation coil, respectively. These represent the flux leakage of both coils, i.e. the noncommon flux. Thus, the flux is mutual flux by assuming that no fringe field is present. Since the
flux leakage of the voice coil and the compensation coil is already taken into account in the
electrical circuit by L 1 and L 2, Hopkinson's law may be expressed as follows for this magnetic
circuit, N 1 i = N 2 i 2 = Rφ (2) where R is the reluctance of the magnetic circuit.
This would include the effects of both the magnetic core and air gap reluctance and the
reluctance of any permanent magnet in the loudspeaker's magnetic circuit. When focusing on the
voice coil circuit 103 of FIG. 1, Kirchhoff's current law is defined as i = i 1 + i μ.
[0030]
Using this equation with (2) and (1b) gives the following equation: φ = (N 1 i μ) / R magnetic
flux density is easily obtained by dividing the cross-sectional area Ag of the air gap in which the
voice coil is arranged under the assumption that the effect of the fringe magnetic field is
negligible can do. Therefore, by knowing that the force coefficient of the loudspeaker is L μ = N
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1 <2> / R, it can be expressed as the following equation in terms of i μ and L μ, and B l = ((L μ i
μ) / (N 1 A g)) l = i μL μ b where b is only dependent on the geometric values that are often
difficult to obtain (force Consider the effective length l of the factor equation). Since i μ depends
on the current in the voice coil, using this equation of force factor will introduce nonlinearity in
the system. This non-linearity represents flux modulation, i.e. the mechanism that the B-field
through the entire air gap is not constant but has an AC field component generated by the voice
coil current.
[0031]
As a result, by focusing on the Lorentz force equation acting on the voice coil, the following
equation is obtained. F L = B l · i = b L μ i μ i = b L μ (i <2> + (1 / K) i 2 i) In this equation, the
first term on the right hand side is caused by nonlinear distortion caused by magnetic flux
modulation The second term is a constant force to be sought. It is clear that the effect of this
non-linear distortion will be removed if i μ is constant.
[0032]
This circuit does not take into account the effects of eddy currents, and references [1] and [2]
(non-patent documents) for improved models of the circuit to further generate the equivalent
circuit of the loudspeaker. It can be found in 1 and 2).
[0033]
Having described the implementation of the circuit of the speaker with the additional coil and the
description of the flux modulation distortion, we can now introduce a technique for flux
modulation compensation.
The “hat (^)” notation in the following indicates complex notation. This assumes that the
modeled electrodynamic loudspeaker is essentially linear, which can be realized at least for small
level audio input signals. This condition is also satisfied by the magnetic circuit when not
saturated. Therefore, the loudspeaker can be regarded as a system of the following equation, ^ i =
^ E in H 11 + ^ E f H 21 (7a) ^ i 2 = ^ E in H 12 + ^ E f H 22 (7 b) ^ i μ = ^ E in H μ, 1 + ^ E f H
μ, 2 (7 c) where the transfer function H is the current and the input voltage ^ E in (H Represents
an alternative representation of (^). same as below. Represents the ratio between) and ^ E f. For
example, H 11 can be obtained by the ratio H 11 = ^ i / ^ E in when ^ E f is set to zero. This is
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simply the inverse of the voice coil impedance H 11 = Z VC <−1> and H 22 will be the inverse of
the compensation coil impedance. The transfer functions H 21 and H 12 are due to the operation
of the transformer, ie a generator in one of the voice coil and the compensation coil induces a
current in the other coil The reason is that it is
[0034]
By assuming that ^ e is the electrical audio signal to be played by the device, in equation (7b) ^
Ein is chosen to be equal to: ^ Ein = ^ e-^ E f (H 21 / H 11) (8) The current on the primary side is
the equation ^ i 1 = ^ e multiplied by H 11. Therefore, the influence of the secondary current is
canceled. Now, the magnetizing current may be forced to zero, i.e. ii μ = 0, which means that the
AC flux component is not desirable in the magnetic circuit and the air gap to avoid flux
modulation. It means that.
[0035]
By combining equation (8) with equation (7c), the necessary compensation in the compensation
coil can be calculated as in the following equation. ^ E f = E f, DC-((H 11 H μ, 1) / (H μ, 2 H 11H μ, 1 H 21)) ^ e (9) In this formula, the DC component E f, Note that DC has been reintroduced,
which may simply represent the DC flux generated by the loudspeaker's permanent magnet.
Finally, equation (8) can be expressed again as the following equation. ^ E in = ^ e + (H 21 H μ,
1) / (H μ, 2 H 11-H μ, 1 H 21) ^ e (10)
[0036]
Equations (10) and (9) represent the total compensation system used to cancel the AC flux in the
air gap while avoiding interference between the coils. Thus, equations (10) and (9) represent a
total compensation system or mechanism that is applied to cancel the AC flux in the air gap while
avoiding interference between the compensation coil and the voice coil. Thus, this mechanism
according to the first embodiment of the invention voice coil the first compensation filter 206 as
schematically illustrated on the electrokinetic loudspeaker assembly shown in FIG. 2A). Placing
the second compensation filter 204 in series with the compensation coil 202. The individual
transfer functions of the voice coil compensation filter and the second compensation filter 206,
204 can be expressed as the following equation: T VC = 1 + (H 21 H μ, 1) / (H μ, 2 H 11 −H μ,
1 H 21) (11 a) T FC = − (H 11 H μ, 1) / (H μ, 2 H 11 − H μ, 1 H 21) (11 b) where T VC is , T
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FC is the transfer function of the second compensation filter 204.
[0037]
The simplified electrodynamic loudspeaker assembly 200 shown in FIG. 2A) has a magnetic
circuit with a magnetically permeable structure 201 with an air gap 203 disposed therein. A flux
generator is schematically represented by a DC voltage source E f, DC, which generates a DC
current in the compensation coil 202 wound around the legs of the magnetically permeable
structure 201, and This induces a constant DC flux through the magnetically permeable structure
201 and in the air gap 203. The electrodynamic loudspeaker also includes a moveable
diaphragm assembly (not shown) having a voice coil 208 disposed within the air gap 203. The
movable diaphragm assembly may be mechanically connected to the electrodynamic loudspeaker
frame (not shown) via a suitable edge suspension in a conventional manner. The electrodynamic
loudspeaker assembly is configured such that the first compensation filter 206 described above
is configured to filter the audio input signal ^ e applied to the loudspeaker assembly by the
frequency response T VC of the first compensation filter 206 Have. As a result, a voice coil
compensation signal E in is derived from the audio input signal and applied to the voice coil 208.
The electrokinetic loudspeaker assembly 200 further comprises the above-described second
compensation filter 204 configured to filter the audio input signal e according to the frequency
response T FC of the second compensation filter 204. As a result, a second compensation signal
is derived from the audio input signal and applied to the compensation coil 202. As detailed
above, the first and second frequency responses of the first and second compensation filters 206,
206, respectively, are time-variant or AC magnetic flux within the air gap 203 generated by the
voice coil current. It is designed or configured to be suppressed or preferably substantially
eliminated over the audio frequency range. Thereby, the magnetic flux modulation in the air gap
is suppressed. The audio frequency range may vary depending on the application specific
requirements of the loudspeaker assembly of interest. The audio frequency range may be in the
range of 20 Hz to 20 kHz in some applications and in relatively small ranges such as 100 Hz to
10 kHz or 100 Hz to 1 kHz in other applications It is also good.
[0038]
FIG. 2B) shows another embodiment of this electrodynamic loudspeaker assembly 250. This
simplified schematic of the electrokinetic loudspeaker assembly 250 comprises a magnetic
circuit having a magnetically permeable structure 251 having an air gap 253 disposed therein.
The permanent magnets 255 of the magnetic circuit 251 generate a constant DC flux through
the magnetically permeable structure 251 and in the air gap 253. The electrodynamic
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loudspeaker also includes a moveable diaphragm assembly (not shown) having a voice coil 258
disposed within the air gap 253. The movable diaphragm assembly may be mechanically
connected to the electrodynamic loudspeaker frame (not shown) via a suitable edge suspension
in a conventional manner. In addition to the contents described above for the first and second
compensation filters 256, 254, respectively, this embodiment comprises a first power amplifier
or buffer A1 and a second power amplifier or buffer A2. A first power amplifier or buffer A 1 is
inserted between the first (or voice coil) compensation signal E in and the voice coil 258. A
second power amplifier or buffer A 2 is inserted between the second compensation signal E f and
the compensation coil 252. With the addition of the first and second power amplifiers, the first
and second power amplifiers are connected to the signal source or generator supplying the audio
input signal ee, with many of the respective coils of these coils. Sufficient drive current can be
supplied to the individual coils so that no load is applied in some cases with relatively low
impedance. The DC impedance of voice coil 258 may be in the range of 1 to 100 ohms for a
typical loudspeaker design, and the DC impedance of compensation coil 252 may be in the range
of 0.5 to 100 ohms. Good. The DC impedance of voice coil 258 may be substantially equal to the
DC impedance of compensation coil 252 or may be higher, such as, for example, twice as large.
[0039]
We suppress the flux modulation in the magnetic circuit by using the experimental magnetic
circuit 300 shown in FIG. 3 which shows the magnetic circuit used to test the flux modulation
suppression or compensation technique. The above-described electrodynamic loudspeaker
assembly and method were verified by experiments. The magnetic circuit has a permeable core
350 which may be of ferromagnetic material such as an untreated iron bar 8 mm thick and 2 cm
wide. An aluminum frame (not shown) is used to avoid any movement of the steel bar. The
magnetic circuit further comprises permanent magnets 355 for generating a DC flux. There are
two fixed coils arranged on a magnetically permeable core 350 formed by a compensation coil
manufactured from 500 winding turns and a fixed voice coil with 300 winding turns. There is. A
magnetic field pickup coil 354 is disposed inside the air gap 353. Since i μ can not be measured
directly, but has been found to be directly proportional to B * I, instead, the magnetic flux is
measured by the pick-up coil 354 via a test voltage induced therein It is measured. This test
voltage is applied to the measurement system for recording and processing. The pickup coil 354
was calibrated by a Helmholtz coil that produces a known B field. A properly configured
computerized measurement system such as the Bruel & Kjaer PULSE measurement system was
used to measure all of the transfer functions H 11, H 21, H μ, 1, and H μ, 2 described above. A
collection of voice coil admittance transfer functions H 11 is shown on the graphs 401 a, b of
FIG. 4 across a frequency range of approximately 3 Hz to 3 kHz. As mentioned above, this is just
the reciprocal of the voice coil impedance, so that the transfer function is determined by the DC
resistance of the voice coil in the low frequency case and the voice in the high frequency case. It
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demonstrates the well-known behavior of being determined by the coil inductance.
[0040]
The assembly of the transfer function H 21 between the second compensation signal of the
compensation coil and the current in the voice coil is shown on the graph 411 a, b of FIG. 4.
These graphs show the operation of the transformer acting as a band pass filter. The main effect
associated with changing the inductance is again the shift in amplitude. Although relatively less
pronounced, another effect is the increase of the cut-off frequency on the high frequency side.
[0041]
All of the measured transfer functions described above are individual curves obtained for a voice
coil displacement of "0 mm" at zero, ie with the voice coil centered in the air gap.
[0042]
A measured collection of transfer functions H μ, 1 between the voice coil compensation signal of
the voice coil and the magnetization inductance representing the mutual inductance generated
by the voice coil and the compensation coil in common is about 3 Hz to 3 kHz. Over the
frequency range is shown on the graphs 501a, b of FIG.
The measured transfer function H μ, 2 between the second compensation signal applied to the
compensation coil and the magnetizing inductance is shown on the graph 511 a, b of FIG. 5
across the frequency range of approximately 3 Hz to 3 kHz. ing. Both of these transfer functions
are individual curves obtained for voice coil displacement of zero, which is indicated by the "0
mm" notation.
[0043]
Finally, the graph 601a, b of FIG. 6 shows the determined or calculated frequency response T VC
of the first compensation filter for the voice coil over a frequency range of approximately 3 Hz to
3 kHz. Graphs 611a, b of FIG. 6 illustrate the determined or calculated frequency response T FC
of the second compensation filter for the compensation coil, over a frequency range of
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approximately 3 Hz to 3 kHz. It is apparent that at relatively high frequencies, the amplitude of
the second compensation signal applied to the compensation coil is increasing above the 0 dB
line of graph 611 a to reach more than 10 dB. This can represent, in particular, the potential
problem of reproducing at high acoustic pressure levels on the loudspeaker, because the level of
the second compensation signal applied to the compensation coil is the desired flux This is
because it is necessary to exceed the compensation signal applied to the voice coil by about 10
dB in order to make full use of the suppression. However, this task can be overcome by the
design of a relatively small compensation coil, because the compensation coil used in this
experimental measurement is 500 windings and 5 It is because it has a resistance of 5 Ω. It is
possible to reduce the number of windings of the compensation coil, which reduces the
impedance of the compensation coil at high frequencies and thus requires a relatively low level
compensation signal for magnetic flux compensation It will be Furthermore, it is possible to use
relatively thick wires to form the compensation coil, so that the best trade-off between these two
factors will be found.
[0044]
It also measures the dependence of the position or displacement of the voice coil in the air gap
on the transfer functions H 11, H 21, H μ, 1 and H μ, 2 and the individual frequencies of the
first and second compensation filters The resulting effects on the responses T VC and T FC were
investigated. The pickup coil was moved within the air gap with the voice coil to obtain these
measurements. Therefore, these transfer functions are all in the state where the voice coil is
positioned at a displacement of 0 mm as described above, and then the graphs 401a, b, 411a, b,
501a, b, 511a, b, Measured repeatedly at voice coil displacements of -3 mm, -1 mm, +1 mm, and
+3 mm, as shown by the individual sets of curves on the respective graphs of 601 a, b and 611 a,
b The Examination of the computed frequency responses T VC and T FC of the first and second
compensation filters on graphs 601 a, b and 611 a, b reveals that their transfer functions are
changing as a function of voice coil displacement It is. As a result, in the further optimized
suppression of the flux modulation in the air gap as the frequency response of these changes
according to the instantaneous displacement of the voice coil and diaphragm assembly from its
rest position, The adaptive frequency response of a bicompensation filter could be used.
[0045]
Finally, each of the compensation and voice coils is supplied with a sine wave input having the
phase and amplitude provided by the first and second compensation filters, which can be
calculated from the transfer function using equations 11a and 11b above. Thus, suppression of
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magnetic flux modulation in the air gap was verified. Some of the suppression of flux modulation
with and without a compensation filter to filter the audio input signal prior to application to the
coil at three different test frequencies: 20 Hz, 220 Hz and 2 kHz Measurement was performed. At
these test frequencies, a very large reduction in flux modulation measurement of 23 dB to 53.5
dB was obtained.
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