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

Abstract

An active countersound system for actively reducing the sound waves of primary sound waves, with a regulator unit, an error sensor, a reference sensor and several secondary actuators. The secondary actuators are designed to emit countersound waves, wherein the regulator unit, which is coupled to the secondary actuators, processes an error signal and a reference signal, and generates a secondary signal, which by way of the coupling is conveyed to the secondary actuators in order to control the secondary actuators by means of the secondary signal such that said secondary actuators generate countersound waves that reduce the error signal so that optimal sound wave abatement is implemented, wherein the secondary actuators are arranged such that they are located on the margin of an open passage area, 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 the open space that in the direction of passage is arranged behind the open passage area, of the countersound waves in the manner of a curtain.

Description

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of German Patent Application No. 10 2005 016 021.2 filed Apr. 7, 2005 and of U.S. Provisional Patent Application No. 60/669,061 filed Apr. 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 sound 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:

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, Va. of 20-22 Sep. 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.

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 C130 Hercules”—also presented within the framework of ACTIVE 04 in Williamsburg, Va. from 20-22 Sep. 2004 by Jon Gorman, Richard Hinchliffe and Ian Stothers, Ultra Electronics Controls Division, Vitrum Building, St. John's Innovation Park, Cowley Road, Cambridge, CB4 0WS, 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 Aug. 2004 in Prague, Czech Republic, by A. Jakob, R. Bauers, M. Möser, Institute of Technical Acoustics, Technical University of Berlin, Einsteinufer 25, D-10587 Berlin, Germany, andrejakob@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 volumes or in simple geometric control volumes with one-dimensional sound wave propagation in the interior of the control volumes.

SUMMARY 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 volume.

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 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 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, 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 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 parameters.

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 parameters 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 high-quality regulation, result in effective primary sound wave reduction, wherein the design size, in particular of the secondary actuators, also always should be taken 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 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.

SHORT DESCRIPTION OF THE DRAWINGS

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 EXEMPLARY 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 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 volume 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 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.

REFERENCE LIST

• 10 Active countersound system
• 11 Regulator unit
• 12 Error sensor
• 13 Reference sensor
• 14 Secondary actuator
• 15 Countersound wave
• 16 Primary sound wave
• 16′ Superimposed/attenuated primary sound wave
• 20 Control volume
• 21 Open passage area
• F Error signal
• R Reference signal
• S Secondary signal

Claims

1. An active countersound system for actively reducing the sound waves of at least one primary sound wave emanating from a primary actuator that emits primary sound waves,

with at least one regulator unit;

with at least one error sensor;

with at least one reference sensor;

with several secondary actuators;

wherein the secondary actuators are designed to emit countersound waves;

wherein the error sensor, which is coupled to the regulator unit, acquires the superimposed sound waves, which are conveyed as an error signal to the regulator unit by way of the coupling;

wherein the reference sensor, which is coupled to the regulator unit, acquires the primary sound wave, of which there is at least one, which is conveyed to the regulator unit by way of the coupling;

wherein the reference sensor and the error sensor are designed so as to be integrated in one sensor;

wherein the regulator unit, which is coupled to the secondary actuators, processes the error signal and the reference signal, and generates a secondary signal, which is conveyed to the secondary actuators by way of the coupling in order to control the secondary actuators, depending on the error signal, by means of the secondary signal such that said secondary actuators generate countersound waves that reduce the error signal so that optimum sound wave abatement is implemented;

wherein 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 open passage area, which space is at least partly open, of the countersound waves in the manner of a curtain.

2. The active countersound system of claim 1, in which the secondary actuators are equidistant along the margin of the open passage area.

3. The active countersound system of claim 1, in which the number of secondary actuators has been selected depending on parameters such as the geometry of the space to be shielded, geometry of the open passage areas, 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.

4. The active countersound system claim 1, in which the type of secondary actuators has been selected depending on parameters such as the geometry of the space to be shielded, geometry of the open 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.

5. The active countersound system claim 1, in which several error sensors are in place, wherein the number and/or the positioning of the error sensors have/has been selected depending on parameters such as the geometry of the space to be shielded, geometry of the open 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.

6. A method for actively abating sound waves of at least one primary sound wave emanating from a primary actuator that emits primary sound waves,

in which method

by means of a reference sensor a reference signal of a primary sound wave is acquired;

by means of an error sensor an error signal of superimposed sound waves is acquired;

wherein the reference sensor and the error sensor are designed so as to be integrated in one sensor;

by means of couplings the error signal and the reference signal are transmitted to a regulator unit;

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; and

the secondary actuators from the transmitted secondary signal generate countersound waves which 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 reduced or eliminated, wherein the steps are carried out repeatedly in a control circuit.

7. An active countersound system arrangement, comprising an at least partly open control volume with an open passage area with a margin;

comprising an active countersound system of claim 1 for actively reducing the sound waves of the primary sound waves in the control volume.

8. The use of an active countersound system for actively reducing sound waves for a control volume that is at least partly open.

9. An active countersound system arrangement, comprising an at least partly open control volume with an open passage area with a margin;

comprising an active countersound system of claim 2 for actively reducing the sound waves of the primary sound waves in the control volume.

10. An active countersound system arrangement, comprising an at least partly open control volume with an open passage area with a margin;

comprising an active countersound system of claim 3 for actively reducing the sound waves of the primary sound waves in the control volume.

11. An active countersound system arrangement, comprising an at least partly open control volume with an open passage area with a margin;

comprising an active countersound system of claim 4 for actively reducing the sound waves of the primary sound waves in the control volume.

12. An active countersound system arrangement, comprising an at least partly open control volume with an open passage area with a margin;

comprising an active countersound system of claim 5 for actively reducing the sound waves of the primary sound waves in the control volume.