EP3026664B1 - Method and system for active noise suppression - Google Patents

Description

The present invention relates to a method for actively suppressing sound from a plurality of primary sound sources by means of sound from a plurality of secondary sound sources, wherein each secondary sound source is assigned exactly one primary sound source, and a system for active suppression of sound by a method according to the invention.

Active sound suppression systems and methods, also referred to as antinoise systems or noise reduction systems and methods, typically employ one or more secondary sound sources or secondary sound sources to reduce the primary sound radiated from one or more noise sources referred to as the primary sound source or sources Speakers, one or more sensors and a control device which is connected to the speakers and the sensors. The control device controls the loudspeakers on the basis of the signals supplied by the sensors in such a way that the entire sound field generated by the combination of the primary sound source (s) and the loudspeakers is favorably influenced in terms of the target of the sound reduction. In this case, one or more sensors can be used to generate reference signals, on the basis of which control signals for the secondary sound sources are determined, and one or more further sensors can serve as error sensors, with the aid of which the quality of the control signals is checked and their determination is adjusted as needed.

The desired influence of the sound field can be based on various physical mechanisms. In addition to the most well-known case of destructive interference, it is also possible for sound to be reflected at the locations of the secondary sound sources, for sound to be absorbed by the secondary sound sources and for the sound energy to be absorbed by the corresponding actuators is dissipated or that the primary sound sources and the secondary sound sources influence each other in such a way that the radiated from the combination of primary and secondary sound sources total sound power is minimized. For the latter case, the interference affects a reduction in the ability of sound sources to emit sound. This may for example be based on the fact that the secondary sound sources reduce the effective resistance of the primary sound source by acting on the acoustic modes of the sound field or act on the air molecules located in front of the primary sound source, that they less resistance to the movement of the radiation surface of the primary sound source , There is always the difficulty that the contribution of the secondary sound sources to the sound field must not overcompensate the benefits achieved in a negative way.

For example, one known type of active noise reduction employs one or more error microphones as sensors, each of which locally measures the sound pressure produced by all existing sound sources, including the primary sound source and one or more secondary sound sources. The measurement results are processed by the control device, which then controls the secondary sound sources in such a way that the sound pressure at the microphones is minimized as far as possible by destructive interference and / or sound reflection at the locations of the secondary sound sources. This can be a local noise reduction can be achieved at the microphone positions. This principle, which is an example of a sound pressure-based control, has the disadvantage that the local noise reduction at the microphone positions is generally accompanied by a noise amplification in other areas. Furthermore, only the local sound effect in the form of Sound pressure influenced without combating the cause in the form of sound power output by the primary sound source.

Further exemplary sound-pressure-based controls, which include, among others Elliot, SJ et al., In Flight Experiments on the Active Control of Propeller-induced Cabin Noise, Journal of Sound and Vibration (1990), No. 140 (2), pages 219-238 are known and have the goal of global noise reduction based on the mechanism of acting on the primary sound source via acoustic modes and have the disadvantage that the number and distribution of microphones must be chosen so that detection of the excited modes is possible. Furthermore, the scope is limited by the fact that for each application separately knowledge about the physical interaction of the speakers and sensors used and the primary sound field must be present.

Overall, for a global sound pressure minimization in cases of higher modal density, the microphones must also be distributed globally and the secondary sound sources must be arranged so that they can excite the same modes as the primary sound source. It is also problematic to take into account changing environmental influences in the implementation of the control. Further, because the microphones measure the overall sound pressure, these methods may fail in the presence of additional sources of noise since the controller can not account for the contribution of the various sound sources. Despite these drawbacks, controls based on sound pressure measurements are most commonly used because the necessary measurements are technically easy to implement.

In contrast, measurement of energy quantities of the sound field are in principle better suited to be used in the context of controllers which are intended to achieve a global reduction of noise by minimizing the radiated active power of all the sound sources in the room. There is the advantage that the corresponding error sensors can be arranged in the vicinity of the secondary sound sources, whereby the installation and optimization effort can be reduced. However, the corresponding prior art proposals have presented significant problems that have led them to abandon the academic trial stage. The problems arise in part because energy quantity sensors, such as sound intensity sensors, are more expensive than simple sound pressure sensors and the complexity of the controls due to a larger number of input variables (the sound intensity is determined for example by the sound pressure and the sound velocity) and associated multi-channel configurations ,

One approach to energy-based control, for example, is from the documents Elliott, SJ et al., Power output minimization and power absorption in the active control of sound, Journal of the Acoustic Society of America (1991), No. 90 (5), pages 2501 to 2512 and Bullmore, AJ et al, The active minimization of harmonic enclosed sound fields, Part I-III, Journal of Sound and Vibration (1987), 117, pages 1-58 known. There, it is described on the basis of theoretical derivations for the example of two point sound sources, that the radiated total active power of a pair of sound source from a primary source and a secondary source is minimal if and only if the secondary source is driven in phase or in phase, or with respect to the primary source oscillates in the same or opposite phase, and the secondary source does not radiate active sound power. The active sound power is the real part of the overall sound power usually represented by a complex size and corresponds to the actual net energy transport per second perpendicular to a surface, such as the emission surface of a sound source. In contrast, the dummy sound power represented by the imaginary part of the total sound power is due to the energy transport through the medium mass, which is merely moved, but not compressed. In these documents, however, no feasible proposals for the selection, design and arrangement of sensors and for the design of the control are made.

Experimental studies on this approach are in the two documents Tohyama, M., Suzuki, A, Sugiyama, K., Active Power Minimization of a Sound Source in a Reverberant Closed Space, IEEE Transactions on Signal Processing (1991), No. 39 (1), pages 246 to 248 and Kang, SW, Kim, YH, Active Global Noise Control by Sound Power, ACTIVE 95: Proceedings of the 1995 International Symposium on Active Control of Sound and Vibration, Newport Beach (USA), New York, Noise Control Foundation, 1995 described.

In both cases identical loudspeakers are used as primary and secondary source. In this case, the secondary source is driven either with a control signal for the primary source in the same or opposite phase (in the case of the former document) or an opposite in relation to the drive signal for the primary source drive signal (in the case of the latter document), so that The design uniformity can not be waived, and the amplitude of the drive signal for the secondary source is set manually. Furthermore, the sensors used are either a large number of microphones randomly distributed in space or a sound intensity sensor comprising two microphones spaced apart from each other. This means a relatively high amount of hardware. Finally, no feasible approaches for a suitable control are given overall.

From the EP 2 378 513 A1 For example, a system and method are known for actively suppressing sound from a primary sound source by means of a secondary sound source. In principle, the method described there can also be used for active sound suppression of a plurality of primary sound sources by a plurality of secondary sound sources, wherein each primary sound source is assigned exactly one secondary sound source. However, there is the problem that the interaction between the various primary and secondary sound sources is not taken into account and thus does not result in an effective minimization of the total radiated sound.

Furthermore, this requires from the EP 2 378 513 A1 known system of one-time pre-equalization for adjusting the acceleration or speed of the secondary sound sources. It is assumed that a time invariance of the primary sound sources and a sound transmission without external interference. In the long-term operation of the secondary sound sources, however, a phase relationship between the vibrations of the primary sound sources and the secondary sound sources, for example, by a vibro-acoustic interaction between the primary and secondary sound sources, change.

It is therefore an object of the present invention to provide a method and a system for active suppression of sound, with the sound emitted from a plurality of primary sound sources can be effectively suppressed. In a further aspect, the solution according to the invention is also intended to manage without primary equalization or tuning of the secondary sources to the respective primary sound sources and also a temporal change of the phase position between primary and secondary sound sources should be considered.

In a first aspect, the present invention achieves this object with a method of actively canceling sound from a plurality of primary sound sources by means of sound from a plurality of secondary sound sources, each secondary sound source being associated with exactly one primary sound source. To actively suppress the sound of the plurality of primary sound sources and to reduce a sound intensity of the sound of the secondary sound sources to or against zero, for each secondary sound source, a control amount of the secondary sound source is determined iteratively by the following steps: determining a sound velocity of each primary sound source Determining a sound velocity and a sound pressure of each secondary sound source, determining an effectively suppressing sound velocity for each secondary sound source, wherein the effectively suppressed sound velocity of a secondary sound source in addition to the sound velocity, which has been determined for the respective secondary sound source associated primary sound source, also which includes sound pressures and sound buffs determined for all secondary sound sources except for the secondary sound source concerned, and determining the manipulated variable for each sec undäre sound source such that a difference between the intended for a secondary sound source effectively suppressed sound velocity and that for the secondary Sound source is minimized certain speed of sound. The secondary sound sources are controlled with the respectively determined control variables.

For example, the plurality of primary sound sources may be different sound sources, each emitting separate sound. However, it is also conceivable that the plurality of primary sound sources are so-called elementary sound sources, into which a real sound source is thoughtfully decomposed, when the real sound source emits sound with different phases and / or in different directions.

By way of example, the secondary sound sources may be loudspeakers, and a secondary sound source may also be formed by a plurality of loudspeakers, which are all located at the same location and are controlled in the same way by the data processing device. Each of the secondary sound sources is assigned exactly one primary sound source. The number of primary sound sources whose sound is actively suppressed is thus less than or equal to the number of secondary sound sources. A primary sound source can thus also be assigned to a plurality of secondary sound sources. In principle, it is also possible that the number of primary sound sources is greater than the number of secondary sound sources. However, this presupposes that at least the sound radiated or generated by a part of the primary sound sources is not actively suppressed. For example, a primary sound source, which is not dominant in relation to the other primary sound sources, need not necessarily be suppressed. Nevertheless, every primary sound source is actively suppressed is to be assigned, at least one secondary sound source.

The secondary sound sources are controlled according to the invention with manipulated variables that are iterative, i. in several successive steps, it may be determined that the sound of the plurality of primary sound sources is actively suppressed, and the sound intensity of the sound emitted by the secondary sound sources becomes minimal, but not negative, i. is reduced to zero, and is preferably zero. If the sound intensity of the secondary sound sources becomes negative, the sound of the primary sound sources is absorbed and suppression of the sound of the primary sound sources can be achieved by maximizing the absorption.

Since in the following all calculations are carried out in the frequency domain, ie with measured signals that have been Fourier-transformed from the time domain into the frequency domain, the dependence of the different quantities is not given by the time t but by the frequency k .

berechnet werden, wobei der Index p für die primären Schallquellen und der Index s für die sekundären Schallquellen steht, q* das komplex konjugierte von q bezeichnet, diag{ v } einen Diagonalmatrix mit den Einträgen des Vektors v auf der Diagonalen ist, Im den Imaginärteil einer komplexen Zahl bezeichnet und ω = 2πk die Kreisfrequenz ist.The sound intensity i _s ( k ) of the secondary sound sources can be derived, for example, from the sound pressure p _s ( k ) and the speed or acceleration of the sound a _s ( k ), where the bold pressure on a vector a ( k ) = [ a ₁ ( k ) , a ₂ ( k ), ..., a _i ( k ), ..., a _n ( k )] with n entries for n secondary sound sources, according to $$i_{\mathrm{s}}\left(k\right)=-\frac{1}{2\omega }\cdot \mathrm{in\; the}\left(\mathrm{diag}\left\{p_{\mathrm{s}}\left(k\right)\right\}{a}_{\mathrm{s}}\left(k\right)*\right)$$

where the subscript p is the primary sound source and the subscript s is the secondary sound source, q * denotes the complex conjugate of q , diag { v } is a diagonal matrix with the entries of the vector v on the diagonal, Im denotes the imaginary part of a complex number and ω = 2 πk is the angular frequency.

In order to reach the zero point of the sound intensity of the secondary sources or to approach it as close as possible to positive sound intensities, a fast or sonic fast is determined for each sound source. The determination of a sound velocity does not necessarily mean that the actual sound velocity is actually determined. Depending on the configuration of the embodiment of the method according to the invention, it may also be sufficient if only the sound acceleration is determined. Thus, the term fast in the sense of the present patent application includes not only the actual sound velocity, but also directly with these related variables, such as acceleration or acceleration of sound. In order to determine the speed of a sound source, for example, an acceleration sensor can be used which is arranged directly on the oscillating sound source, for example a diaphragm of a loudspeaker. Alternatively, it is also possible to use a laser sensor, with which an oscillating movement of a surface of a sound source is detected, wherein from the detected movement an acceleration or a rapid of the sound can be determined.

Furthermore, a sound pressure is determined for each secondary sound source. When determining a sound pressure, for example, microphones can be used, which are arranged directly in front of the respective secondary sound sources.

wobei diag( κ (k)} a _p(k) die effektiv zu unterdrückende Schallschnelle ist. Dabei ist diag{ κ (k)} eine Diagonalmatrix mit reellwertigen Faktoren κ (k) = [κ ₁(k),κ ₂(k),...,κ _n(k)] auf der Diagonalen, wobei die Anzahl der reellwertigen Faktoren der Anzahl der sekundären Schallquellen entspricht. Der Vektor a _p( k ) umfasst die Schallschnellen oder Beschleunigungen, die für die primären Schallquellen bestimmt worden sind. Der i-te Eintrag des Vektors a _p( k ) ist die Schallschnelle oder Beschleunigung, die für die primäre Schallquelle bestimmt worden ist, die der i-ten sekundären Schallquelle zugeordnet worden ist. Somit enthält a _p(k) die für eine primäre Schallquelle bestimmte Schallschnelle oder Beschleunigung mehrfach, wenn die primäre Schallquelle mehreren sekundären Schallquellen zugeordnet ist. Die Bestimmung der effektiv zu unterdrückenden Schallschnelle, genauer gesagt der reellwertigen Faktoren κ (k), wird nachfolgend beispielhaft in Form von bevorzugten Ausführungsformen näher erläutert.From the specific sound buffs and sound pressures becomes an effectively suppressed speed of sound for each of the secondary Sound sources determined. The sound velocity to be effectively suppressed by a secondary sound source in a preferred embodiment corresponds exactly to the sound velocity that has been determined for the secondary sound source. This can be represented, for example, as follows: $$a_{\mathrm{s}}\left(k\right)=\mathrm{diag}\left\{\kappa \left(k\right)\right\}{a}_{\mathrm{p}}\left(k\right)$$

where diag ( κ ( k )} a _p ( k ) is the sound velocity to be effectively suppressed, where diag { κ ( k )} is a diagonal matrix with real-valued factors κ ( k ) = [ κ ₁ ( k ), κ ₂ ( k ), ..., κ _n ( k )] on the diagonal, where the number of real-valued factors corresponds to the number of secondary sound sources The vector a _p ( k ) comprises the sound beats or accelerations determined for the primary sound sources . the i-th entry of the vector a _p (k) is the particle velocity or acceleration, which has been determined for the primary sound source that has been assigned to the i th secondary sound source. Thus, contains a _p (k) is the primary of a Sound source determines certain speed of sound or acceleration several times if the primary sound source is assigned to several secondary sound sources The determination of the effectively suppressed sound velocity, more precisely the real-valued factors κ ( k ), is given below haft explained in more detail in the form of preferred embodiments.

The effectively suppressing sound velocity of a secondary sound source according to the invention comprises, in addition to the sound velocity, which has been generated by the primary sound source, which is associated with the relevant secondary sound source, other contributions that are generated by the remaining secondary sound sources. In other words, the sound velocity effectively suppressed by a secondary sound source the sound velocity of the primary sound source associated with the secondary sound source concerned, and contributions from any other secondary sound source that can be determined from the sound buffs and sound pressures determined for all other secondary sound sources. Thus, the interaction of the various secondary sound sources can be taken into account in an advantageous manner, so that in fact as complete as possible active suppression of the sound of a plurality of primary sound sources is possible.

zu minimieren, wird daher in einem weiteren Schritt eine neue Stellgröße für jede sekundäre Quelle oder Schallquelle bestimmt. Dabei kennzeichnet der obere Index m einen gemessenen oder bestimmten Wert. Um die Schallintensität der sekundären Schallquellen gegen oder auf null zu reduzieren, wird erfindungsgemäß dabei die Stellgröße so gewählt, dass der Unterschied bzw. die Differenz zwischen den effektiv zu unterdrückenden Schallschnellen und den für die sekundären Schallquellen bestimmten Schallschnellen kleiner oder minimiert wird. Dabei umfasst die Minimierung einer Differenz nicht nur ein Auffinden eines absoluten Minimums der Differenz, das in der Praxis kaum oder zumindest nur schwer zu erreichen ist, sondern bereits ein Auffinden eines relativen Minimums einer Differenz, d.h. eine Verkleinerung gegenüber einer anderen Differenz. Die Minimierung kann beispielsweise mit einem aus dem Stand der Technik bekannten Optimierungsverfahren erfolgen. Ein mögliches, erfindungsgemäßes Verfahren zur Minimierung der Differenz wird nachfolgend als bevorzugte Ausführungsform der Erfindung näher erläutert.Initially, in order to determine the effective speed of sound to be suppressed, it was assumed that the effectively suppressed sound velocity of a secondary sound source and the sound velocity determined for the secondary sound source are the same. In fact, however, the specific sound beats of the secondary sound sources and the effectively suppressing sound beats differ from each other. To the difference or deviation $$e\left(k\right)=a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)-\mathrm{diag}\left\{\kappa \left(k\right)\right\}{a}_{\mathrm{p}}^{\mathrm{m}}\left(k\right)$$

Therefore, in a further step, a new manipulated variable is determined for each secondary source or sound source. In this case, the upper index m denotes a measured or determined value. In order to reduce the sound intensity of the secondary sound sources against or to zero, the manipulated variable is inventively chosen so that the difference or the difference between the effectively suppressed sound beats and the sound beats intended for the secondary sound sources is smaller or minimized. In this case, minimizing a difference does not only involve finding an absolute minimum of the difference that exists in the Practice is hardly or at least difficult to achieve, but already finding a relative minimum of a difference, ie a reduction compared to another difference. The minimization can be done, for example, with an optimization method known from the prior art. A possible method according to the invention for minimizing the difference is explained in more detail below as a preferred embodiment of the invention.

According to the invention, the secondary sound sources are controlled with the control variables determined in this way. By controlling the secondary sound sources with the newly determined control variable, the difference between the sound velocity of the secondary sound sources and the sound velocity to be effectively suppressed is advantageously reduced and thus the sound emitted by the primary sound sources is suppressed. At the same time, the sound intensity of the secondary sound sources is also reduced to zero. Thus, the sound of the primary sound sources is actively suppressed in an advantageous manner while avoiding that the secondary sound sources themselves generate new noise. In addition, the interaction of the sound sources with one another is taken into account by the calculation of a sound velocity to be effectively suppressed by the respective secondary sound sources taking into account the remaining secondary sound sources.

In a preferred embodiment, the sound buffs to be effectively suppressed are determined on the assumption that the sound intensity of each secondary sound source is zero. This assumption has proven to be particularly advantageous for taking into account interactions between the various secondary sound sources and at the same time the overall to minimize radiated sound energy to zero. This creates an altogether less loud procedure.

Furthermore, it is preferred that a transmission path matrix is used for determining the sound buffs to be effectively suppressed, wherein a portion of the one secondary sound source at the sound pressures determined for the secondary sound sources can be determined with the transmission path matrix from a sound bounce determined for a secondary sound source.

The use according to the invention of a transmission path matrix enables the calculation of the sound pressure of the secondary sound sources from the sound beats determined for the secondary sound sources. The transmission path matrix H _pa ( k ) takes into account that sound velocity and sound pressure of the secondary sound source are not measured at the same location. For example, the sound velocity of a secondary sound source is measured directly on a membrane of a loudspeaker, for example by means of a laser sensor or a Hall probe, while the sound pressure is measured by means of a microphone which is arranged at a distance from the membrane. The transmission path matrix is thus an empirical quantity which describes a system of secondary sound sources and measuring devices and which, once measured, can be stored permanently in a device for carrying out the method according to the invention.

bestimmt werden, wobei p _s(k) der bestimmte sekundäre Schalldruck ist. Eine gemessene und nicht nur am theoretischen Modell bestimmte Übertragungsstreckenmatrix wird im Folgenden mit ${\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}$

bezeichnet wird. Der am Messort von den primären Schallquellen erzeugte Schalldruck $p_{\mathrm{ps}}^{\mathrm{m}}\left(k\right)$

ergibt sich auf Grundlage der mit realen Sensoren gemessenen oder bestimmten Größen aus $$p_{\mathrm{ps}}^{\mathrm{m}}\left(k\right)=p_{\mathrm{s}}^{\mathrm{m}}\left(k\right)-{\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}\left(k\right)a_{\mathrm{s}}^{\mathrm{m}}\left(k\right).$$

By means of the transmission path matrix, it is possible to solve the problem that, at the location of the measurement or determination of the sound pressure of the secondary sound sources, influences of all primary and secondary sound sources act on the sensor. In contrast to measuring the speed of sound, which is directly At the source of sound, and thus should be free of contributions from other sound sources, the measurement of the sound pressure always includes parts of other sound sources. According to the invention, the transmission path matrix is used to subtract, from a sound pressure determined for a secondary sound source, the proportion due to the secondary sound sources in order to obtain the proportion of the sound pressure generated by the primary sound sources. The proportion of the primary sound pressure p _ps ( k ), that is to say the sound pressure generated by the primary sound sources at the measuring location, can be determined, for example, according to FIG $$p_{\mathrm{ps}}\left(k\right)=p_{\mathrm{s}}\left(k\right)-H_{\mathrm{pa}}\left(k\right)a_{\mathrm{s}}\left(k\right)$$

where p _s ( k ) is the determined secondary sound pressure. A measured transmission distance matrix, which is not determined solely by the theoretical model, is described below ${\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}$

referred to as. The sound pressure generated at the site by the primary sound sources $p_{\mathrm{ps}}^{\mathrm{m}}\left(k\right)$

is based on the measured or determined with real sensors sizes $$p_{\mathrm{ps}}^{\mathrm{m}}\left(k\right)=p_{\mathrm{s}}^{\mathrm{m}}\left(k\right)-{\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}\left(k\right)a_{\mathrm{s}}^{\mathrm{m}}\left(k\right),$$

In a preferred embodiment, the transmission link matrix for each secondary sound source comprises a factor for correcting a phase difference between the sound pressure determined for a secondary sound source and the speed determined for the relevant secondary sound source. The factor according to the invention can advantageously be used, for example, for a transit time difference from a sound source to the different sensors, phase differences due to deviating quality of the sensors or phase differences due to different measuring methods in the determination of a Compensate sound pressure and a speed of sound. The use of a factor for correcting a phase difference has been found to be particularly advantageous in the practical implementation of the method in order to actively actively suppress the sound generated by the primary sound source.

in der die Phasenunterschiede nicht behoben sind, gemäß $${\widehat{H}}_{\mathrm{pa}}\left(k\right)=\mathrm{diag}\left\{{\mathrm{e}}^{-j{\varphi }_1\left(k\right)},e^{-j{\varphi }_2\left(k\right)},\dots ,{\mathrm{e}}^{-j{\varphi }_{\mathrm{n}}\left(k\right)}\right\}{\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}\left(k\right)$$

in eine Übertragungsstreckenmatrix Ĥ _pa(k) überführt werden, in der die Phasenunterschiede berücksichtigt werden, wobei j die imaginäre Einheit und ϕ ein frequenzabhängiger Phasenunterschied ist. Entsprechend kann auch der Anteil am gemessenen Schalldruck aufgrund der primären Schallquellen in einen Schalldruck der Form $${\widehat{p}}_{\mathrm{ps}}\left(k\right)=\mathrm{diag}\left\{{\mathrm{e}}^{-j{\varphi }_1\left(k\right)},e^{-j{\varphi }_2\left(k\right)},\dots ,{\mathrm{e}}^{-j{\varphi }_{\mathrm{n}}\left(k\right)}\right\}{p}_{\mathrm{ps}}^{\mathrm{m}}\left(k\right)$$

überführt werden, welcher die Phasenunterschiede zwischen den verschiedenen Sensoren berücksichtigt.For example, a measured transmission link matrix ${\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}.$

in which the phase differences are not resolved, according to $${\widehat{H}}_{\mathrm{pa}}\left(k\right)=\mathrm{diag}\left\{{\mathrm{e}}^{-j{\phi }_1\left(k\right)}.e^{-j{\phi }_2\left(k\right)}.....{\mathrm{e}}^{-j{\phi }_{\mathrm{n}}\left(k\right)}\right\}{\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}\left(k\right)$$

into a transmission link matrix Ĥ _pa ( k ) in which the phase differences are taken into account, where j is the imaginary unit and φ is a frequency-dependent phase difference. Accordingly, the proportion of the measured sound pressure due to the primary sound sources in a sound pressure of the form $${\widehat{p}}_{\mathrm{ps}}\left(k\right)=\mathrm{diag}\left\{{\mathrm{e}}^{-j{\phi }_1\left(k\right)}.e^{-j{\phi }_2\left(k\right)}.....{\mathrm{e}}^{-j{\phi }_{\mathrm{n}}\left(k\right)}\right\}{p}_{\mathrm{ps}}^{\mathrm{m}}\left(k\right)$$

be converted, which takes into account the phase differences between the various sensors.

gesetzt werden. Sollten allerdings bei der Bestimmung der Schallschnellen der primären und der sekundären Schallquellen Sensoren mit unterschiedlichen Messprinzipien verwendet werden, so wäre eine Phasenkorrektur entsprechend zu Gleichung (6b) notwendig.In an exemplary, preferred embodiment, acceleration sensors with the same measuring principle are used to detect the sound beats of the primary and secondary sound sources. Therefore, it is not necessary to compensate for the particular sound beats a phase difference, as between the sensors no phase difference occurs. Thus, in the exemplary embodiment $$a_{\mathrm{p}}^{\mathrm{m}}\left(k\right)=a_{\mathrm{p}}\left(k\right)\mathrm{and}{a}_{\mathrm{s}}^{\mathrm{m}}\left(k\right)=a_{\mathrm{s}}\left(k\right)$$

be set. However, if sensors with different measurement principles are used in the determination of the sound beats of the primary and secondary sound sources, a phase correction corresponding to equation (6b) would be necessary.

berechnen, wobei der Index sol die Lösung eines Gleichungssystems bezeichnet und der obere Index c die Korrektur um den Phasenfehler kennzeichnet. Dabei ist allerdings zu beachten, dass Gleichung 7 nur zu einer eindeutigen Lösung für κ (k) führt, wenn - wie in einer bevorzugten Ausführungsform - die Anzahl der sekundären Schallquellen gleich der Anzahl der primären Schallquellen ist. Sind mehrere sekundäre Schallquellen hingegen einer primären Schallquelle zugeordnet, so ist das Gleichungssystem (7) überbestimmt, sofern sich die sekundären Quellen, welche genau einer primären Quelle zugeordnet sind, am selben Ort befinden und eine Lösung für den Faktor κ (k) kann beispielsweise über ein Optimierungsverfahren gefunden werden. Lösungsmöglichkeiten für überbestimmte Gleichungssysteme sind dem Fachmann aus dem Stand der Technik hinlänglich bekannt.Using the equations 1, 2, 5 and 6a-c mentioned above, the factor κ used to determine the sound velocity to be effectively suppressed can be determined in an exemplary embodiment according to FIG $$\begin{array}{l}{\kappa }_{\mathrm{Sol}}^{\mathrm{c}}\left(k\right)=-\mathrm{in\; the}{\left[\mathrm{diag}\left\{a_{\mathrm{p}}^{\mathrm{m}}\left(k\right)*\right\}{\widehat{H}}_{\mathrm{pa}}\left(k\right)\mathrm{diag}\left\{a_{\mathrm{p}}^{\mathrm{m}}\left(k\right)\right\}\right]}^{-1},\\ \mathrm{in\; the}\left[\mathrm{diag}\left\{{\widehat{p}}_{\mathrm{ps}}\left(k\right)\right\}{a}_{\mathrm{p}}^{\mathrm{m}}\left(k\right)*\right]\end{array}$$

where the sol sol denotes the solution of a system of equations and the upper index c denotes the correction around the phase error. It should be noted, however, that equation 7 only leads to a unique solution for κ ( k ) if, as in a preferred embodiment, the number of secondary sound sources is equal to the number of primary sound sources. On the other hand, if a plurality of secondary sound sources are assigned to a primary sound source, then the system of equations (7) is overdetermined, provided that the secondary sources, which are assigned to exactly one primary source, are located at the same location and a solution for the factor κ ( k ) can be used, for example an optimization process can be found. Possible solutions for overdetermined equation systems are well known to the person skilled in the art.

If the secondary sources, which are assigned to a primary sound source, are not in the same place, the transmission matrix Ĥ _pa ( k ) results in other entries in the secondary ones Sound pressures at the location of the secondary sound sources and also in the vector of the primary sound pressure p _ps ( k ), the values at the locations of the secondary sound sources, which are assigned exactly to a primary sound source, different. Thus, the coefficients in the equation system and the right sides are different. It thus again results in a clear solution.

It is further preferred to use a Filtered-Reference-Least-Mean-Square algorithm for the iterative determination of the manipulated variables. Preferably, as a reference in the Filtered-Reference least mean square algorithm, an image of a sound velocity determined for one of the primary sound sources is used. The imaging takes place by means of a manipulated variable transmission matrix with which it can be determined which sound beats are generated by the secondary sound sources as a function of the control variables.

bestimmt werden, wobei w _u die im vorausgehenden Schritt u bestimmt Stellgröße ist, µ(k) ein Gewicht ist, mit dem die Konvergenzgeschwindigkeit des Filters eingestellt werden kann, X(k) eine Referenz, beispielsweise eine Schallschnelle einer der Primärquellen, ist, der hochgestellte Index H eine adjungierte, d.h. komplex konjugierte und transponierte, Matrix bezeichnet und ${\widehat{H}}_{\mathrm{a}}^{\mathrm{m}}$

die Stellgrößenübertragungsmatrix bezeichnet.Filtered-Reference Least-Mean Square (FxLMS) algorithms are well known to those skilled in the art. They allow a simple yet robust minimization of an error quantity, in this case the difference e ( k ) between the sound velocity to be effectively suppressed and the sound velocity determined for the secondary sources according to equation (3). For example, the manipulated variable w _{u +1} ( k ) according to $$w_{u+1}\left(k\right)=w_u\left(k\right)-\mu \left(k\right)X\left(k\right)*{\left({\widehat{H}}_{\mathrm{a}}^{\mathrm{m}}\left(k\right)\right)}^{H}e\left(k\right)$$

where w _{u is} the manipulated variable determined in the preceding step u , μ ( k ) is a weight with which the convergence speed of the filter can be set, X ( k ) is a reference, for example a sound velocity of one of the primary sources superscript index H one adjoint, ie complex conjugated and transposed, called matrix and ${\widehat{H}}_{\mathrm{a}}^{\mathrm{m}}$

denotes the manipulated variable transmission matrix.

In a preferred embodiment, each primary sound source is assigned exactly one secondary sound source. This preferred embodiment of the method according to the invention is particularly economical, since the number of secondary sound sources and sensors required is minimal.

In another aspect, the object underlying the invention is achieved by a system for active suppression of sound with a method according to one of the preceding embodiments. The system includes a plurality of sound pressure sensors, a plurality of primary sound velocity sensors, a plurality of secondary sound velocity sensors, a plurality of secondary sound sources, and a data processing device. The sound pressure sensors, the sound velocity sensors and the secondary sound sources are functionally connected to the data processing device. The system is designed to determine the sound velocity of the primary sound sources using the primary sound velocity sensors. The system is further adapted to determine the sound pressure of the secondary sound sources by means of the sound pressure sensors. Furthermore, the system is configured to determine the sound velocity of the secondary sound sources by means of the secondary sound velocity sensors. The data processing device is set up to determine from the determined sound buffs and sound pressure correcting variables for the secondary sound sources with a method according to one of the preceding preferred embodiments and to control the secondary sound sources with the determined actuating variables.

The system according to the invention comprises the means necessary for carrying out the inventive method. Insofar as the system is set up to determine, for example, a sound velocity or a sound pressure, the step of determining can already be carried out directly by the sensors, which measure a quantity on the basis of which the respective value is determined. However, it is also conceivable that the sensors send only one measured value to a data processing device, which is evaluated in this to determine the required value or the required size. The data processing device may be, for example, a conventional computer or an integrated circuit. A data processing device can be set up for carrying out method steps, for example by uploading software, but also by means of corresponding hardware-related measures. Also, the data processing device can be formed by a plurality of separate data processing devices.

The advantages of the system according to the invention correspond to the advantages which result for the embodiments of a method according to the invention carried out with the system and have already been presented in the preceding sections.

In a preferred embodiment, one of the sound velocity sensors is a laser sensor. Laser sensors enable an essentially instantaneous measurement of the acceleration of a sound source and thus of the sound velocity of the sound generated by the sound source, without the need for a sensor to be attached directly to the sound source. In particular, a laser sensor for measuring a sound velocity a primary sound source in a housing of a system according to the invention and measure the acceleration from a distance to the primary sound source. This eliminates the need for modifications to the primary sound source for mounting sensors.

It is particularly preferred to form at least one primary and one secondary sound velocity sensor from a laser sensor, the one laser sensor used both for determining a sound velocity of a primary sound source and for determining a sound velocity of the secondary sound source, which has been assigned to the relevant primary sound source can be. In other words, in the preferred embodiment, the same laser sensor is used to determine a sound velocity of a primary sound source and a secondary sound source. This ensures that the same measurement method is used to determine the sound beats of secondary and primary sound sources and that there is no need to compensate for phase differences between measurement methods. This makes the implementation of the calculation method easier. Furthermore, can be dispensed with an additional Schallschnellesensor, which reduces the cost of a system according to the invention.

In a further preferred embodiment, at least one of the sonic velocity sensors is a Hall probe. A Hall probe is a particularly inexpensive embodiment of an acceleration sensor that can be used to determine a sound velocity of a sound source.

It is further preferred that at least one of the sound pressure sensors is a microphone. It is further preferred that in a memory of the data processing device, the transmission path matrix and / or the manipulated variable transmission matrix are permanently stored. Thus, with a permanent arrangement of the system, this can be operated at any time without the need for previous measurements for adjusting the system. Finally, it is preferred if a number of the sound pressure sensors, the primary sound velocity sensors, the secondary sound velocity sensors and the secondary sound sources are the same.

Unless expressly deviated from in the description of the various embodiments of the inventive system of statements that have already been made in relation to the inventive method in the preceding paragraphs, so are the embodiments of the method according to the invention and the advantages of the method according to the invention shown on the various embodiments of the system according to the invention applicable.

Fig. 1

schematisch den prinzipiellen Aufbau eines erfindungsgemäßen Systems zur aktiven Unterdrückung von Schall,

Fig. 2

ein Flussdiagramm einer bevorzugten Ausführungsform eines erfindungsgemäßen Verfahrens und

Fig. 3

eine schematische Darstellung einer Ausführungsform einer sekundären Schallquelle.

In the following the invention will be further explained by means of exemplary embodiments on the basis of the drawings. The drawings show in

Fig. 1

schematically the basic structure of a system according to the invention for active suppression of sound,

Fig. 2

a flowchart of a preferred embodiment of a method according to the invention and

Fig. 3

a schematic representation of an embodiment of a secondary sound source.

FIG. 1 1 shows a system 1 according to the invention for the active suppression of sound from a plurality of primary sound sources 3. The system 1 comprises two secondary sound sources 5 in the form of loudspeakers, two primary sound velocity sensors 7 in the form of Hall probes, two secondary sound velocity sensors 9 also in the form of Hall probes, two Sound pressure sensors 11 in the form of microphones and a data processing device 13. Each secondary sound source 5 is assigned to exactly one primary sound source 3, wherein in the in Fig. 1 illustrated embodiment, each primary sound source 3 is associated with exactly one secondary sound source 5. In principle, however, it is also conceivable that each primary sound source 3 is assigned more than one secondary sound source 5.

The various sensors 7, 9, 11 are functionally connected to the data processing device 13. Also with the data processing device 13, the secondary sound sources 5 are functionally connected in such a way that the data processing device 13 can control the secondary sound sources 5 by means of manipulated variables. How to do the presentation in Fig. 1 can be seen, the secondary Schallschnellesensoren 9 are arranged directly on a membrane 15 of the secondary sound sources 5. Thus, the acceleration of the secondary sound sources 5 can be measured without delay and undisturbed by the influences of other sound sources, and the sound velocity can be determined therefrom or used as sound velocity in the further process.

Also shown in Fig. 1 is a real sound source 17 that emits sound that is to be actively suppressed by the system 1. The sound generation by the real sound source 17 is due to the vibrating surface of the Sound source 17 indicated. This real sound source 17 generates sound with two different phase responses. Therefore, as indicated by the arrow 19, the real sound source 17 is decomposed into two elementary primary sound sources 3, each of which oscillates constantly in one phase. However, the two primary sound sources 3 emit sound with different phase responses compared to each other. Thus, the primary sound velocity sensors 7 are actually not arranged directly on a surface of one of the two primary sound sources 3, but on the surface of the real sound source 17. In the following, however, reference will be made only to the separate primary sound sources 3 for simplicity of illustration.

Even if that is in Fig. 1 As illustrated embodiment of a system 1 according to the invention is limited to two primary sound sources 3, it is obvious that the system can be extended to a larger number of primary sound sources 3 using corresponding number of sensors 7, 9, 11 and secondary sound sources 5. It is also possible to use a plurality of secondary sound sources 5 for suppressing the sound of a primary sound source 3.

In Fig. 3 an alternative construction of a secondary sound source 21 is shown, which is also in the system 1 according to Fig. 1 can be used. The secondary sound source 21 comprises in a single housing 23 a sound pressure sensor 11 in the form of a microphone and a combined primary and secondary sound velocity sensor 25 in the form of a laser sensor with which both a rapid or acceleration of the secondary sound source 21, ie a movement of the membrane 15 of the secondary Sound source 21, as well as a sound velocity of a primary sound source 3 can be measured. In Fig. 3 is in the housing 23 of the secondary sound source 21 and a data processing device 13 arranged with. This results in a particularly compact device, in which advantageously the sound velocity of the primary and secondary sound sources 3, 21 can be measured without contact and with the same sensor 25. This saves the effort for an additional sensor. In addition, it is ensured that the sound beats of the primary sound source 3 and the secondary sound source 21 are measured with the same delay. Also, in a non-contact measurement of the sound velocity of the primary sound source 3, it is not necessary to arrange 3 sensors on the surface of this sound source. Thus, the inventive system 1 using the in Fig. 3 shown secondary sound sources 21 are used particularly flexible. In order to provide a clear presentation, is in Fig. 3 has been dispensed with the representation of functional connections between the individual elements.

Also a combination of in the FIGS. 1 and 3 illustrated embodiments of the secondary sound sources 5, 21 according to the invention is possible. In particular, for example, a laser sensor can be used to measure the speed of sound of the primary sound source 3, while a Hall probe is used in the determination of the sound velocity of the secondary sound source 5, 21.

Hereinafter, referring to Fig. 2 a method according to the invention for the active suppression of sound from a plurality of primary sound sources by means of sound from a plurality of secondary sound sources, as could be performed, for example, with a system 1 according to the invention. However, the inventive method according to FIG. 2 be carried out with other devices, provided that they provide the necessary means for the implementation of the method.

einer Mehrzahl von primären Schallquellen 3, eine Schallschnelle $a_{\mathrm{s}}^{\mathrm{m}}\left(t\right)$

einer Mehrzahl von sekundären Schallquellen 5, 21 sowie einen Schalldruck $p_{\mathrm{s}}^{\mathrm{m}}\left(t\right)$

einer Mehrzahl von sekundären Schallquellen 5, 21. Die Eingangsgrößen sind zuvor aus den mit den jeweiligen Sensoren 7, 9, 11, 25 gemessenen Signalen bestimmt worden. Sämtliche Eingangsgrößen werden vor Durchführung der weiteren Verfahrensschritte in den Frequenzraum fouriertransformiert, wie durch die mit dem Bezugszeichen 27 gekennzeichneten Symbole angedeutet wird. In dem in Fig. 1 dargestellten System 1 entspricht die Anzahl der primären Schallquellen 3 der Anzahl der sekundären Schallquellen 5, 21. Werden hingegen mehr sekundäre Schallquellen 5, 21 als primäre Schallquellen 3 verwendet, so ist zu beachten, dass der i-te Eintrag des Vektors $a_{\mathrm{p}}^{\mathrm{m}}\left(t\right)$

die Schallschnelle ist, die für die primäre Schallquelle 3 bestimmt worden ist, die der sekundären Schallquelle 5, 21 zugeordnet worden ist, deren Schallschnelle den i-ten Eintrag im Vektor $a_{\mathrm{s}}^{\mathrm{m}}\left(t\right)$

bildet.This in Fig. 2 The method described requires three different input variables: a sonic velocity $a_{\mathrm{p}}^{\mathrm{m}}\left(t\right)$

a plurality of primary sound sources 3, a sound velocity $a_{\mathrm{s}}^{\mathrm{m}}\left(t\right)$

a plurality of secondary sound sources 5, 21 and a sound pressure $p_{\mathrm{s}}^{\mathrm{m}}\left(t\right)$

a plurality of secondary sound sources 5, 21. The input quantities have previously been determined from the signals measured with the respective sensors 7, 9, 11, 25. All input variables are Fourier-transformed before performing the further method steps in the frequency domain, as indicated by the symbols indicated by the reference numeral 27. In the in Fig. 1 system 1 shown corresponds to the number of primary sound source 3 to the number of secondary sound sources 5, 21. If, however, more secondary sound sources 5, 21 is used as a primary sound source 3, it should be noted that the i-th entry of the vector $a_{\mathrm{p}}^{\mathrm{m}}\left(t\right)$

is the sound velocity, which has been determined for the primary sound source 3, which has been assigned to the secondary sound source 5, 21, the sound particle velocity of the i th entry in the vector $a_{\mathrm{s}}^{\mathrm{m}}\left(t\right)$

forms.

bestimmt, der dort von den primären Schallquellen 3 erzeugt wird. Hierzu wird von dem bestimmten sekundären Schalldruck $p_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

gemäß Gleichung (5) der Anteil ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

der sekundären Schallquellen 5, 21 abgezogen. Der Anteil ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

der sekundären Schallquellen 5, 21 wird durch Abbildung der bestimmten Schnelle oder Beschleunigung $a_s^m\left(k\right)$

der sekundären Schallquellen 5, 21 mittels einer vor Verwendung des Systems 1 bestimmten Übertragungsstreckenmatrix ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)$

ermittelt. Die Übertragungsstreckenmatrix ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)$

ist vorzugsweise dauerhaft in einem Speicher der Datenverarbeitungseinrichtung 13 abgelegt.First, in an addition step 29, the proportion p _ps ( k ) of the sound pressure measured at the respective sound pressure sensors 11 $p_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

determined there generated by the primary sound sources 3. This is determined by the specific secondary sound pressure $p_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

according to equation (5) the proportion ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

the secondary sound sources 5, 21 subtracted. The amount ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

of the secondary sound sources 5, 21 is determined by mapping the particular speed or acceleration $a_s^m\left(k\right)$

the secondary sound sources 5, 21 by means of a before using the system. 1 certain transmission link matrix ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)$

determined. The transmission link matrix ${\widehat{H}}_{\mathrm{pa}}^m\left(k\right)$

is preferably stored permanently in a memory of the data processing device 13.

der Übertragungsstreckenmatrix ${\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}\left(k\right)$

sowie einem Vektor ϕ _e (k) = [e^{-jϕ 1(k)},e^{-jϕ 2(k)},...,e^{-jϕ n(k)}] von Faktoren zur Kompensierung eines Phasenunterschieds bei der Messung der Schallschnellen und der Schalldrücke einem Berechnungsschritt 31 zugeführt, in dem gemäß Gleichung (7) der Faktor $\mathrm{diag}\left\{{\kappa }_{\mathrm{sol}}^{\mathrm{c}}\left(k\right)\right\}$

bestimmt wird. Der Vektor ϕ _e (k) wird ebenfalls einmal vor Verwendung des Systems 1 bestimmt und dann dauerhaft im Speicher der Datenverarbeitungseinrichtung 13 abgelegt.The thus determined proportion p _ps ( k ) becomes common with the sound beats determined for the primary sound sources 3 $a_{\mathrm{p}}^{\mathrm{m}}\left(k\right).$

the transmission link matrix ${\widehat{H}}_{\mathrm{pa}}^{\mathrm{m}}\left(k\right)$

and a vector φ _e ( k ) = [e ^{- jφ 1 ( k )} , e ^{- jφ 2 ( k )} , ..., e ^{- jφ n ( k )} ] of factors for compensating a phase difference in the measurement of the sound buffs and the sound pressure is supplied to a calculation step 31, wherein according to equation (7) the factor $\mathrm{diag}\left\{{\kappa }_{\mathrm{Sol}}^{\mathrm{c}}\left(k\right)\right\}$

is determined. The vector φ _e ( k ) is also determined once before using the system 1 and then stored permanently in the memory of the data processing device 13.

und den für die primären Schallquellen 3 bestimmten Schallschnellen $a_{\mathrm{p}}^{\mathrm{m}}\left(k\right)$

in einem Multiplikationsschritt 33 die effektiv zu unterdrückenden Schallschnellen $\mathrm{diag}\left\{{\kappa }_{\mathrm{sol}}^{\mathrm{c}}\left(k\right)\right\}{a}_p^m\left(k\right)$

berechnet. Die effektiv zu unterdrückenden Schallschnellen werden in einem weiteren Additionsschritt 35 von für die sekundären Schallquellen 5, 21 bestimmten Schallschnellen $a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

abgezogen, um das zur Minimierung vorgesehene Fehlersignal e (k) gemäß Gleichung (3) zu bestimmen. Dieses Signal dient als Eingangsgröße für einen Minimierungsschritt 37 mit einem FxLMS Algorithmus.The following are from the factor $\mathrm{diag}\left\{{\kappa }_{\mathrm{Sol}}^{\mathrm{c}}\left(k\right)\right\}$

and the sound beats intended for the primary sound sources 3 $a_{\mathrm{p}}^{\mathrm{m}}\left(k\right)$

in a multiplication step 33 the sound beats to be effectively suppressed $\mathrm{diag}\left\{{\kappa }_{\mathrm{Sol}}^{\mathrm{c}}\left(k\right)\right\}{a}_p^m\left(k\right)$

calculated. In a further addition step 35, the sound buffs to be effectively suppressed are sound beats determined for the secondary sound sources 5, 21 $a_{\mathrm{s}}^{\mathrm{m}}\left(k\right)$

deducted to determine the error signal e ( k ) to be minimized according to equation (3). This signal serves as an input to a minimization step 37 with a FxLMS algorithm.

als Referenzwert X(k) ausgewählt, die für die primären Schallquellen bestimmt worden sind. Von dem Referenzwert wird in einem ersten Schritt 41 die komplex Konjugierte gebildet. Der komplex konjugierte Referenzwert wird in einem Abbildungsschritt 43 mittels einer adjungierten Stellgrößenübertragungsmatrix ${\left({\widehat{H}}_{\mathrm{a}}^{\mathrm{m}}\left(k\right)\right)}^H,$

die den Zusammenhang zwischen den Stellgrößen und den von den sekundären Quellen 5, 21 erzeugten Schnallschnellen beschreibt, abgebildet. Das Ergebnis der Abbildung ist der gefilterte Referenzwert, der die weitere Eingangsgröße für den Minimierungsschritt 37 ist.As further input variables for the minimization step 37, a weight μ ( k ), which in Fig. 2 not shown, and uses a filtered reference value. To determine the filtered reference value, first in a selection step 39, a sound velocity is determined from the sound beats determined for the primary sound sources $a_{\mathrm{p}}^{\mathrm{m}}\left(k\right)$

selected as the reference value X ( k ), which has been determined for the primary sound sources are. From the reference value, the complex conjugate is formed in a first step 41. The complex conjugate reference value is determined in an imaging step 43 by means of an adjoint manipulated variable transmission matrix ${\left({\widehat{H}}_{\mathrm{a}}^{\mathrm{m}}\left(k\right)\right)}^H.$

which depicts the relationship between the manipulated variables and the buckling speeds generated by the secondary sources 5, 21. The result of the mapping is the filtered reference value, which is the further input to the minimization step 37.

Using the described input variables, a next manipulated variable w _{u + 1} ( k ) is calculated in the minimization step 37 by means of equation (8) from a current manipulated variable w _u ( k ). The manipulated variable w _{u + 1} ( k ) thus determined reduces the value of the error signal e ( k ) by taking into account an overall reduction of the sound intensity emitted by the secondary sound sources to zero or to zero.

In order to control the secondary sound sources 5, 21 with the specific manipulated variables w _{u + 1} ( k ), these are multiplied by the reference value X ( k ) in a multiplication step 45 and output y ^m ( k ) in a remaining step 47 from FIG Frequency domain transformed into the time domain. The manipulated variables y ^m ( t ) thus obtained can either be used directly for controlling the secondary sound sources 5, 21 or subjected to further processing steps.

The inventive method according to Fig. 2 thus has all the advantages that have been described in the general description with reference to embodiments of the method according to the invention. In particular, in the active suppression of the sound of a plurality of primary sound sources 3, the Considered interaction between the various secondary sound sources 5, 21 and possible phase differences due to different maturities in the system or different measuring methods or different sensors.

Claims (15)

1. Method for active suppression of sound from a plurality of primary sound sources (3) by means of sound from a plurality of secondary sound sources (5, 21),
   wherein to each secondary sound source (5, 21) exactly one primary sound source (3) is assigned,
   wherein for active suppression of sound of the plurality of primary sound sources and for reducing a sound intensity of the sound of the secondary sound sources (5, 21) to zero or to a value approaching zero, for each secondary sound source (5, 21) a controlled variable for controlling the secondary sound source (5, 21) is iteratively determined by the following steps:

   determining a sound particle velocity of each primary sound source (3),

   determining a sound particle velocity and a sound pressure of each secondary sound source (5, 21),

   determining for each secondary sound source (5, 21) a sound particle velocity effectively to be suppressed, wherein the sound particle velocity effectively to be suppressed of a secondary sound source (5, 21) comprises, besides the sound particle velocity which has been determined for the primary sound source (3) assigned to the respective secondary sound source, also the determined sound pressures and the sound particle velocities of all secondary sound sources (5, 21) except the respective secondary sound source (5, 21), and

   determining the controlled variable of each secondary sound source (5, 21) in such a manner that a difference between the sound particle velocity determined as effectively to be suppressed for a second sound source (5, 21) and the sound particle velocity determined for the secondary sound source (5, 21) is minimized, and

   wherein the secondary sound sources (5, 21) are controlled with the respectively determined controlled variables.
2. Method for active suppression of sound according to claim 1, wherein the sound particle velocities effectively to be suppressed are determined under the assumption that the sound intensity of each secondary sound source (5, 21) is zero.
3. Method for active suppression of sound according to claim 1 or 2, wherein the sound particle velocities effectively be suppressed are determined under the assumption that the effectively to be suppressed sound particle velocity by a secondary sound source (5, 21) corresponds to the sound particle velocity that has been determined for the respective secondary sound source (5, 21).
4. Method for active suppression of sound according to any of the preceding claims, wherein for determining the sound particle velocities effectively to be suppress a transmission path matrix is used, wherein from a sound particle velocity determined for a secondary sound source (5, 21) a contribution of a secondary sound source (5, 21) to the sound pressures determined for the secondary sound sources (5, 21) can be determined by the transmission path matrix.
5. Method for active suppression of sound according to claim 4, characterized in that the transmission path matrix comprises for each secondary sound source (5, 21) a factor for correcting a phase difference between the sound pressure determined for a secondary sound source (5, 21) and the sound particle velocity determined for the secondary sound source (5, 21).
6. Method for active suppression of sound according to claim 4 or 5, wherein during the determination of the sound particle velocities effectively to be suppressed first the sound pressures of the primary sound sources are determined by correcting the sound pressures determined for the secondary sound sources (5, 21) for the contributions of the secondary sound sources (5, 21) which can be determined by means of the transmission path matrix from the sound particle velocities determined for the secondary sound sources (5, 21).
7. Method for active suppression of sound according to any of the preceding claims, wherein for iteratively determining the controlled variables a Filtered-Reference-Least-Mean-Square algorithm is utilized.
8. Method according to claims 7, characterized in that as a reference in the Filtered-Reference-Least-Mean- Square algorithm a mapping for a sound particle velocity determined for a primary sound source (3) is used, wherein the mapping is performed by means of a controlled variable transfer matrix, wherein by means of the controlled variable transfer matrix sound particle velocities generated by the secondary sound sources (5, 21) in dependence on the controlled variables can be determined.
9. Method according to any of the preceding claims, wherein exactly one secondary sound source is assigned to each primary sound source.
10. System (1) for active suppression of sound using a method according to any of the preceding claims, wherein the system (1) comprises a plurality of primary sound particle velocity sensors (7, 25), a plurality of secondary sound particle velocity sensors (9, 25), a plurality of secondary sound sources (5, 21) and a data processing device (13),
    wherein the sound pressure sensors (11), the sound particle velocity sensors (7, 9, 25) and the secondary sound sources (5, 21) are functionally connected to the data processing device (13),
    wherein the system (1) is arranged to determine the sound particle velocity of the primary sound source (3) by means of the primary sound particle velocity sensors (7, 25),
    wherein the system (1) is arranged to determine the sound pressure of the secondary sound sources (5, 21) by means of the sound pressure sensors (11),
    wherein the system (1) is arranged to the determine the sound particle velocity of the secondary sound sources (5, 21) by means of the secondary sound particle velocity sensors (9, 25), and
    wherein the data processing device (13) is arranged to determine from the determined sound particle velocities and sound pressures controlled variables for the secondary sound sources (5, 21) using a method according to any of the claims 1 to 8, and to control the secondary sound sources (5, 21) with the controlled variables determined.
11. System (1) for active suppression of sound according to claim 10, wherein at least one of the sound particle velocity sensors (25) is a laser sensor (25),
    wherein preferably at least one of the primary sound particle velocity sensors (25) and at least one secondary sound particle velocity sensor (25) is formed by a laser sensor, wherein this laser sensor can be utilized for determining the sound particle velocity of a primary sound source (3) as well as for determining the sound particle velocity of a secondary sound source (5, 21) to which the respective primary sound source (3) is assigned.
12. System for active suppression of sound according to claim 10 or 11, wherein at least one of the sound particle velocity sensors (7, 9) comprises a Hall probe.
13. System (1) for active suppression of sound according to any of the claims 10 to 12, wherein at least one of the sounds pressure sensors (11) is a microphone.
14. System (1) for active suppression of sound according to any of the claims 10 to 13, wherein in a memory of the data processing device (13) the transmission path matrix and/or the controlled variable transfer matrix are permanently stored.
15. System (1) for active suppression of sound according to any of the claims 10 to 14, wherein the numbers of sound pressure sensors (11), of primary sound particle velocity sensors (9, 25), of secondary sound particle velocity sensors (7, 25) and of the secondary sound sources (5, 21) are equal.

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