Note: Descriptions are shown in the official language in which they were submitted.
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Active countersound system with special arrangement of the secondary actuators
for
reducing the passage of sound at an open boundary area of two volumes; active
countersound arrangement; method for actively reducing sound waves; and use of
an
active countersound system for actively reducing sound waves for a control
volume
that is at least partly open
Reference to related applications
This application claims the benefit of the filing date of German Patent
Application
No. 10 2005 016 021.2 filed April 7, 2005 and of United States Provisional
Patent
Application No. 60/669,061 filed April 7, 2005, the disclosure of which
applications
is hereby incorporated herein by reference.
Field of the invention
The invention relates to an active countersound system for actively reducing
sound
waves of at least one primary sound wave emanating from a primary actuator
that
emits primary sound waves, with a special arrangement of secondary actuators
to
reduce sound wave passage at or through an open boundary area of two volumes.
Moreover, the invention relates to an active countersound system arrangement,
a
method for actively reducing sound waves, and the use of an active
countersound
wave system for actively reducing sound waves for a control volume that is at
least
partly open.
Technological Background
Sound waves, in particular interfering souiid waves such as noise, may be
reduced
either passively with noise-absorbing devices, or actively by means of active
noise
control (ANC) as it is generally known.
A known ANC system in principle functions as follows:
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A primary actuator, such as for example a noise source, generates at least one
primary sound wave such as for example a sinusoidal sound wave. In order to
actively reduce or even eliminate this interfering primary sound wave, this
primary
sound wave has to be superimposed by a secondary sound wave or countersound
wave of at best the same amplitude and frequency but phase-shifted by 180 . To
this
effect an ANC regulator is provided. This regulator processes a reference
signal that
is synchronous in relation to the primary sound wave, which reference signal
is for
example acquired by means of a reference sensor, and an error signal that has
been
recorded by an error sensor, for example by an error microphone, and from this
calculates a secondary signal with the frequency of the reference signal but
with a
different amplitude and phase. This secondary signal is conveyed to secondary
actuators, for example loudspeakers, which convert the secondary signal to a
countersound wave or countersound waves. The superimposed waves are then again
acquired by the error sensor, and regulating or controlling is continued so as
to
achieve minimisation of the resulting sound wave.
It is known for example - as stated in the report "Current and Future
Industrial
Applications of Active Noise Control" on the occasion of ACTIVE 04 in
Williamsburg, Virginia of 20-22 September 2004 by Colin H Hansen, Active Noise
and Vibration Control Group, School of Mechanical Engineering, University of
Adelaide, SA 5005, Australia, chansen@mecheng.adelaide.edu.au - by means of an
ANC system to abate or reduce sound waves in a tube, i.e. a semi-open control
volume with two open passage areas. However, this is a simple overall system
with
one-dimensional sound wave propagation, in which system active sound wave
reduction can easily be implemented by arranging a secondary actuator within
the
tube.
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Furthermore, it is known to implement active sound wave reduction in closed
control
volumes.
From the report "Active Sound Control on the Flight Deck of a C 130 Hercules" -
also presented within the framework of ACTIVE 04 in Williamsburg, Virginia
from
20-22 September 2004 by Jon Gorman, Richard Hinchliffe and Ian Stothers, Ultra
Electronics Controls Division, Vitrum Building, St. John's Innovation Park,
Cowley
Road, Cambridge, CB4 OWS, England, jon.Gorman@ultracontrols.aero - an ANC
system has been disclosed which within a closed control volume, namely in an
aircraft fuselage, attenuates local areas, or reduces the primary sound wave
in local
areas.
The report "An actively controlled triple-glazed window" presented at "The
33rd
International Congress and Exposition on Noise Control Engineering" (inter-
noise
2004) from 22-25 August 2004 in Prague, Czech Republic, by A. Jakob, R.
Bauers,
M. Moser, Institute of Technical Acoustics, Technical University of Berlin,
Einsteinufer 25, D-10587 Berlin, Germany, andre.jakob@tu-berlin.de discloses
an
ANC system for a triple-glazed window. Here, too, in a closed control volume
in a
void between two glass panes of the triple glazing, active sound wave
reduction of
primary sound waves is effected. In this arrangement the secondary actuators
are
arranged at the margin of the interspace thus causing a reduction of the sound
waves
in the interior of the closed control volume. In this way the passage of sound
through
the closed window into the volume behind may be reduced.
The above illustrated systems are associated with a disadvantage in that
active sound
wave reduction is possible either only in closed control volunles or in simple
geometric control volumes with one-dimensional sound wave propagation in the
interior of the control volumes.
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SummM of the invention
Amongst other things, it may be an object of the present invention to
implement
effective active sound wave reduction of primary sound waves that propagate in
several directions in a control volume or space that is at least partly open,
wherein
sound wave reduction takes place not only locally but in relation to the
entire space
or the entire control vohune.
This object may be met by an active countersound system with a special
arrangement
of secondary actuators for reducing the passage of sound at an open boundary
area of
two volumes with the characteristics according to the independent claim 1;
moreover
the object of the present invention may be met by an active countersound
system
arrangement, a method for actively reducing sound waves, and the use of an
active
countersound system for actively reducing sound waves for a control volume
that is
at least partly open, with the characteristics according to the remaining
independent
claims.
The active countersound system according to the invention comprises at least
one
regulator unit, at least one error sensor, at least one reference sensor and
one or
several secondary actuators. The secondary actuators are designed to emit
countersound waves. The error sensor, which is coupled to the regulator unit,
acquires the superimposed sound waves and, if they are acquirable, conveys
them as
an error signal to the regulator unit by way of the coupling. The reference
sensor,
which is coupled to the regulator unit, acquires the primary sound wave, of
which
there is at least one, and conveys a corresponding reference signal to the
regulator
unit by way of the coupling. The regulator unit, which is coupled to the
secondary
actuators, processes the error signal and the reference signal and from them
generates
a secondary signal that is conveyed to the secondary actuators by way of the
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coupling so as to control the secondary actuators by means of the secondary
signal,
dependent on the error signal, such that said secondary actuators generate
countersound waves that reduce the error signal so that optimum sound wave
abatement may be achieved.
In this setup the secondary actuators are arranged such that they are located
on the
margin of a passage area that is at least partly open, which passage area
comprises a
margin and is to be penetrated by the primary sound waves, in order to ensure
active
sound wave abatement of at least part of the space arranged behind the passage
area,
which space is at least partly open, of the countersound waves in the manner
of a
curtain.
Furthermore, according to the invention an active countersound arrangement
with a
control volume and with an active countersound system with the above-described
characteristics is created for actively reducing sound waves of the primary
sound
waves in the control volume..
In the method according to the invention for active abatement of sound waves
of at
least one primary sound wave emanating from a primary actuator that emits
primary
sound waves, by means of a reference sensor a reference signal of a primary
sound
wave is acquired. Furthermore, by means of an error sensor an error signal is
acquired by superimposed sound waves. By means of couplings the error signal
and
the reference signal are transmitted to a regulator unit. Furthermore, the
regulator
unit evaluates the transmitted signals, and a secondary signal is generated.
The
secondary signal is transmitted by means of coupling to secondary actuators.
The
secondary actuators are arranged on the margin of an open passage area for the
primary sound waves. Furthermore, by means of the secondary actuators,
secondary
waves are generated from the transmitted secondary signal, which secondary
waves
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in the manner of a curtain are superimposed on the open passage area so that
the
primary sound wave that propagates through the open passage area is at least
reduced
and/or eliminated, wherein the steps are repeated and/or continuously carried
out in
the active countersound system that is designed as a control circuit.
Furthermore, according to the invention the use of an active countersound
system for
actively reducing sound waves in an at least partly open control volume is
provided.
A fundamental idea of the invention comprises the fitting of an active
countersound
system with secondary actuators, wherein the secondary actuators are arranged
such
that they are arranged so as to be marginal, i.e. along the margin of an open
passage
area for primary sound waves, and so that they generate secondary sound waves
or
countersound waves that in the open passage area are superimposed on the
primary
sound waves, thus reducing or eliminating the primary sound waves. In this way
a
kind of "acoustic curtain" may be created through which all primary sound
waves in
their direction of propagation behind the passage area may at least be
reduced.
Generally speaking, primary waves are noise waves. Accordingly, secondary
waves
or countersound waves are corresponding (phase-shifted) noise waves.
Correspondingly, secondary actuators for generating these noise waves are
loudspeakers.
An open passage area is an area surrounded by a closed margin, through which
area
the primary sound wave(s) reache(s) the space or the control volume.
The margin can have any closed geometric shape. In particular, however, the
margin
may be arranged in one plane. For example, the margin can be designed as a
circumference of a simple geometric figure comprising triangles, circles,
ovals,
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ellipses, quadrangles, polygons, squares, rectangles, trapeziums, lozenge
shapes or
the like.
The margin can also be designed as a so-called envelope so that encapsulation
of a
primary actuator that is designed as a noise source can be achieved. In this
way the
entire surroundings behind this envelope would undergo primary sound wave
reduction.
The secondary actuators are preferably arranged so as to be equidistant along
the
margin of the passage area. In this way, optimum primary sound wave reduction
can
be achieved. Equidistant distribution along the margin makes it possible to
design
simpler computing models with simpler algorithms for regulating or controlling
the
active countersound system, thus ensuring more effective primary sound wave
reduction.
The number of secondary actuators for effective primary sound wave reduction
depends on a multitude of parameters comprising the geometry of the space to
be
shielded, or on the control volume, geometry of the passage area, spectral
composition of the primary sound wave(s), amplitude and/or frequency of the
primary sound wave(s), bandwidth of the primary sound wave(s), degree of the
desired sound wave reduction and the like.
The term "space to be shielded" refers to the space or the control volume in
which
active (primary) sound wave reduction is to take place.
Generally speaking, the denser the countersound wave curtain and the better,
i.e.
among other things the faster and more accurate, the regulator unit, the
higher the
primary sound wave reduction. This means that in order to achieve effective
primary
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sound wave reduction, corresponding quality and/or quantity of the secondary
actuators and corresponding quality of the regulator unit or, generally
speaking, of
regulation, should be ensured.
In the case of a narrow-band primary sound wave only narrow-band secondary
actuators are necessary. In the case of primary sound waves with a large
amplitude,
for example more powerful secondary actuators or a correspondingly greater
number
of secondary actuators are necessary. Due to the host of possible applications
it is
however not possible to state all the option of the various designs, depending
on the
combination of paraineters.
The same applies to the type of secondary actuators. Here, too, for effective
reduction of primary sound waves the type of secondary actuators depends on
many
parameters comprising the geometry of the space to be shielded or the control
volume, geometry of the passage area, spectral composition of the primary
sound
wave(s), amplitude and/or frequency of the primary sound wave(s), bandwidth of
the
primary sound wave(s), degree of the desired sound wave reduction and the
like.
Analogous to the above example of a primary sound wave of large amplitude,
either
a larger number of secondary actuators or the same number of secondary
actuators
with means to generate a countersound wave also of larger amplitude may be
required. If the frequency of the primary sound wave is in a low frequency
range,
only secondary actuators to generate a low frequency range may be necessary.
Also on the basis of the correlation of the paraineters among each other, it
is not
possible in the present document to list all the combinations and/or
embodiments.
However, in particular some combinations, for example a large number of high-
quality secondary actuators and fast higli-quality regulation, result in
effective
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primary sound wave reduction, wherein the design size, in particular of the
secondary actuators, also always should be talcen into account.
In addition, the position of the error sensors may have an influence on the
effectiveness of the active countersound system.
Just like the type and number of secondary actuators, the number and/or type
of error
sensors also depends on parameters such as the geometry of the space to be
shielded,
the control volume, geometry of the passage area, spectral composition of the
primary sound wave(s), amplitude and/or frequency of the primary sound
wave(s),
degree of the desired sound wave abatement and the like.
Furthermore, the reference sensor and the error sensor may be designed so as
to be
integrated in one sensor. In this way both so-called feedforward systems and
feedback systems can be designed. Thus from a reference signal that is
otherwise
obtained by means of a reference sensor, said reference signal can also be
obtained
from the error sensors and reference sensors that have been combined and
integrated
in one sensor.
The use of the active countersound system according to the invention, with the
special marginal arrangement of the secondary actuators for actively reducing
sound
waves for an at least partly open control volume, is manifold. For example,
the active
countersound system can be arranged in entrance regions of noise-attenuated
spaces
in order to achieve effective noise reduction. In particular primary actuators
designed
as noise sources can effectively be encapsulated with this system. Similarly,
for
example in workshop halls, certain areas, in which for example due to legal
requirements noise reduction is mandatory, can be effectively protected
against the
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effects of noise, without the need to meet noise protection measures for the
entire
workshop hall.
This results in a multitude of application options of active countersound
arrangements with an at least partly open control volume, with an open passage
area
with a margin, and with an active countersound system according to the
invention.
For example, with the arrangement of secondary actuators along a plane
rectangle
with several of these arrangements, individual regions can quasi be designed
in the
manner of an acoustic partition or barrier as a noise-attenuated zone. Also
imaginable
are embodiments on airfields, along highways or railway lines, construction
sites and
the like.
The use of the arrangement according to the invention is associated with an
advantage in that said arrangement does not visually block out the open
passage area,
as is for example the case in passive noise protection barriers. The use as a
noise
protection barrier or noise protection barrier element may also provide an
advantage
in that essentially only the acoustic perception is altered.
Preferably, the arrangement of the secondary actuators or of the margin of the
open
passage area is designed as a simple geometric figure. In this way several of
these
arrangements can be arranged together in a modular way, also in order to
generate
large-area noise protection.
When compared to the ANC system relating to a triple-glazed window, as stated
above, the system proposed in the present invention is effective also with the
window
open. In this application the use or the function as an "acoustic curtain"
becomes
particularly clear.
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Short description of the drawing
One exemplary embodiment of the invention is shown in the figure and is
explained
in more detail below.
The figure shows an in-principle diagram of an active countersound system
according to the invention.
The illustrations in the figure are diagrammatic and not to scale.
Detailed description of an exemplM embodiment .
Below, with reference to the figure, an active countersound system arrangement
30
according to one embodiment of the invention is described.
The active countersound system arrangement 30 comprises an active countersound
system 10 and a control volume 20. The active countersound system 10 comprises
a
regulator unit 11, two error sensors 12, a reference sensor 13 and four
secondary
actuators 14. The secondary actuators 14 are designed as loudspeakers with
which
countersound waves 15 can be generated. These countersound waves 15 are
sinusoidal sound waves and are acquired by means of the two error sensors 12,
which
in the present embodiment are correspondingly designed as microphones. The
error
sensors 12 are coupled to the regulator unit 11 by means of lines. By way of
this line
the error signal F acquired by the error sensors 12 is transmitted to the
regulator unit
11. A primary sound wave 16, generated by a primary actuator (not shown) is
acquired by the reference sensor 13 as a reference signal R. In this
embodiment the
primary sound wave 16 is shown in the shape of a sinusoidal noise wave or
sound
wave. Correspondingly, in this embodiment the reference sensor 13 is a
microphone.
The reference sensor is also coupled to the regulator unit 11 by way of a
coupling
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designed as a line. By way of this line the reference signal R is transmitted
to the
regulator unit 11. The regulator unit 11 evaluates the two transmitted signals
R, F
and from them calculates a secondary signal S. The regulator unit 11 is
coupled to
the secondary actuators 14 by way of lines. By way of this coupling the
secondary
signal S generated by the regulator unit is transmitted from the regulator
unit 11 to
the secondary actuators 14. Correspondingly, the secondary actuators 14
convert the
secondary signal S to countersound waves 15 onto which the primary sound wave
16
is superimposed. This superimposed sound wave or these superimposed sound
waves
is/are again acquired by the error sensors 12, and regulating is continuously
carried
out or repeated.
The control volume 20 is designed as a partly open control volume, which in
the
figure is diagrammatically illustrated as a right parallelepiped whose one
side is
designed as an open passage area 21. Through this open passage area 21 the
primary
sound wave 16, or the primary sound wave 16' or sound waves onto which the
countersound wave(s) has/have been superimposed, or which primary sound wave
16' has been attenuated by the countersound wave(s), reaches/reach the
interior.of
the control volunle 20.
The open passage area 21 is surrounded by a margin. Along this margin, which
in the
embodiment shown is rectangular in shape, the secondary actuators 14 are
arranged.
In this arrangement the secondary actuators 14 are spaced apart from each
other so as
to be equidistant. The countersound waves 15 emitted by the secondary
actuators 14
along the open passage area 21 form a type of "acoustic curtain" so that no
primary
sound wave 16 can pass the open passage area 21 towards the interior of the
control
volume 20 without these countersound waves 15 being superimposed on it. The
superimposition generates an attenuated primary sound wave 16', wherein the
degree
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of attenuation is to be equated with the reduction in noise or reduction in
the primary
sound wave.
In addition it should be pointed out that "comprising" does not exclude other
elements or steps, and "a" or "one" does not exclude a plural number.
Furthermore, it
should be pointed out that characteristics or steps which have been described
with
reference to one of the above embodiments can also be used in combination with
other characteristics or steps of other embodiments described above. Reference
characters in the claims are not to be interpreted as limitations.
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Reference List
Active countersound system
11 Regulator unit
12 Error sensor
13 Reference sensor
14 Secondary actuator
Countersound wave
16 Primary sound wave
16' Superimposed/attenuated primary sound wave
Control volume
21 Open passage area
F Error signal
R Reference signal
S Secondary signal
