EP2684188B1 - Closed loop control system for active noise reduction and method for active noise reduction - Google Patents

Description

The present invention relates to a control system for active noise suppression, in particular for a mobile telephone, and to a method for active noise suppression.

In mobile telephony, ambient sounds on the ear of a user or listener often interfere with his or her acoustic reception at the ear, thereby reducing hearing. Therefore, there is an increasing demand for so-called active noise cancellation systems, also referred to as ANC "Active Noise Cancellation Systems". These have in common that they suppress interfering ambient noise in the range of the loudspeaker or at the ear of a listener in a given frequency band. Such an Active Noise Cancellation System is for example from the document GB 2449083 A known.

This shows similar to the FIG. 10 a so-called forward control. In a feedforward control, the noise is picked up in a path 2 via a microphone, and processed in a control network with filter 4 to output via a loudspeaker. The processing takes place in such a way that the noise is inverted with regard to its phase in a frequency range. The inverted signal thus output from the loudspeaker interferes with the sounds coming to the ear above the path 1 to cause the suppression of unwanted noise.

Alternatively, feedback control systems can also be used instead of a feedforward control. FIG. 11 shows such an example in which a microphone, which is part of a backward control, is mounted near a loudspeaker and receives the signal in the path 2. The loudspeaker also ideally reproduces a microphone signal which has been phase-rotated by 180 °, which with respect to its amplitude is adapted to the interference noise incident on the path 1.

In both cases, it comes through the inverse phase position in conjunction with a controlled amplitude of the speaker signal to a destructive interference with the original interference signal and thereby to a suppression of the same. It is essential here that the loudspeaker housing in both cases, as indicated, lies close to the ear, whereby a known, or easily comprehensible and thus stable acoustic ratio is established.

An essential factor for this are the transfer functions of the loudspeaker used, the microphones and the external parameters, since these can be reproduced by means of filters which are part of the control. In the cases shown here it is often a headphone system, which can be assumed to be relatively stable and unchangeable. As a result, a forward or backward control is adaptable to a known and well-defined acoustic ratio, whereby a good suppression is generally achieved.

However, this becomes problematic in cases where there are no stable acoustic conditions. This is the case, for example, in the field of mobile telephony, where a user of a mobile telephone uses it more or less evenly holds to his ear. As a result, there is no fixed and predetermined coupling of the speaker system to the ear of a user. Rather, the acoustic conditions and in particular the tightness between the speaker and ear are very variable. Moreover, since this tightness is an essential aspect in tuning a control system for active noise cancellation, these variable acoustic ratios regularly result in significant degradation. One possibility for counteracting these variable acoustic conditions is the development of adaptive control systems, for example with an adaptive filter. However, these are very expensive to implement in analog technology and correspondingly expensive in digital technology.

The document EP 1921602 A2 shows a digital system for active noise cancellation with an external microphone for a feedforward control and an internal microphone for a reverse control, which is placed in the vicinity of a speaker of the system. Compensation signals of both the feed forward control and the feed back control are provided to the loudspeaker. The feedforward control is tuned to a high bandwidth, while the feedforward control is tuned to a narrower bandwidth.

The document US 2001/0007907 shows another digital system for active noise cancellation with a forward control and a reverse control, which are active together. A co-ordination of the two regulations takes place adaptively on the basis of measured error signals.

Therefore, there is still a need to provide a control system for active noise cancellation, especially in mobile phones or other speaker systems, which achieve a sufficient good noise cancellation at the same time only low power and manufacturing costs, even with variable and changing acoustic conditions.

This need is met by the control system and active noise cancellation method.

According to the invention, it is provided to implement in a control system a forward and a reverse control, which are both tuned to different acoustic conditions. The two regulations are coupled to one another in such a way that at least one regulation compensates the other regulation with a corresponding change in the acoustic conditions.

Appropriately, the two regulations are tuned to one extreme of the possible acoustic conditions. Thus, it is appropriate to tune the backward control to a predetermined fixed acoustic ratio, which substantially corresponds to a tight closure of the speaker with an ear of a user. The backward control is therefore tuned to provide good noise cancellation over the frequency range with a tight termination and a fixed predetermined volume of air. The forward control, however, is tuned to a different acoustic ratio, which corresponds, for example, a completely leaky closure of the speaker with the user's ear. By matching the two regulations to these two extremes, a compensation of the one regulation can thus be achieved by means of the other regulation, if the acoustic conditions change from one extreme to the other extreme.

In this way, a sufficiently good noise suppression can be realized over a wide range of possible acoustic conditions. The control system according to the invention can thus be used in particular for the mobile radio sector, in which the acoustic conditions depend in particular on user behavior.

In one embodiment of the invention, a control system comprises a loudspeaker and an adder to which the loudspeaker is connected. The adder has a first and a second input. The control system further includes a feedforward control with a first microphone for receiving noise and a connected thereto control network with at least one filter to form a first controlled variable. On the output side is the first one Control network coupled to the adder for supplying the first controlled variable. The control system further comprises a reverse control with a second microphone for receiving a sound emitted by the loudspeaker. A second control network with at least one filter implemented in the reverse control serves to form a second controlled variable and is coupled on the input side to the second microphone. On the output side, the second control network is also connected to the adder.

According to the invention, it is now provided that the backward control is tuned for noise suppression based on a first, in particular a predetermined, fixed, acoustic ratio. The forward control, however, is tuned for a noise suppression, which is based on a second, in particular a non-fixed, acoustic ratio, in particular on an open ratio.

By the adder for adding the two control variables, it is possible to compensate for the first control variable at least partially, if changing current acoustic conditions in the direction of the first acoustic ratio.

Conveniently, the first acoustic ratio in one embodiment corresponds to a substantially tight closure of the loudspeaker with an ear of a user. Alternatively, the first acoustic ratio includes a substantially fixed volume of air, thereby facilitating tunability. In contrast, the second acoustic ratio corresponds to a leaking termination of the loudspeaker with an ear of a user. The thus existing between the speaker and the user's ear air column is at second, non-fixed acoustic ratio in contrast to the first, fixed acoustic ratio variable at least but significantly greater than the volume of air at the first, fixed acoustic ratio.

Alternatively, the first, fixed acoustic ratio also corresponds to a first distance between the loudspeaker and the eardrum of a user while the second, non-fixed acoustic ratio corresponds to a second distance and a second direction between the user's loudspeaker and ear. In particular, the second distance is greater than the first distance.

For example, it is provided that the first acoustic ratio corresponds to a first extreme value of possible acoustic conditions and the second acoustic ratio corresponds to a second extreme value of the possible acoustic conditions.

Preferably, the tuning of the feedforward control and the reverse control is invariable, at least during operation of the control system.

For example, the first and second control networks are based on a completely analog control.

In one embodiment, the first and / or the second control network has a control behavior coordinated with the respective acoustic ratio, in particular a coordinated control gain.

In a further development of the invention, the control system comprises a loudspeaker housing for receiving the loudspeaker, which essentially encloses a first volume of air. An additional housing with a substantially second volume of air is arranged in a preferred direction for sound radiation of the loudspeaker housing. In one embodiment, the fixed acoustic ratio is given by the first and second air volumes.

In addition, the second microphone may be arranged in the additional housing, which forms part of the backward regulation. The second control network may thus be tuned to a noise suppression based on the first and second air volumes. Accordingly, the first control network is tuned to a noise suppression based on an air volume which is significantly larger than the first and second air volumes.

In an active noise suppression method, backward control and forward control for noise suppression are provided. The backward control is adjusted to a first acoustic ratio, the forward control to a second acoustic ratio. For the active noise suppression, a control variable of the feedforward control is compensated by a controlled variable of the reverse control, if actual acoustic conditions change in the direction of the first acoustic ratio.

For example, the second and the first acoustic ratio may be predetermined by corresponding distances between the loudspeaker or a reference point and the ear of a user. In a change in the distance, for example, a reduction thus takes place a compensation of a Control gain of the feedforward control by the control gain of the feedback control.

Further aspects and embodiments of the invention will become apparent from the dependent claims. In the following the invention with reference to several embodiments with reference to the drawings will be explained in detail.

Figur 1

ein Übersichtsdiagramm zur Erläuterung des erfindungsgemäßen Prinzips,

Figur 2

eine Systemdarstellung einer ersten Ausführungsform des erfindungsgemäßen Prinzips,

Figur 3

ein Frequenzleistungsdiagramm einer aktiven Geräuschunterdrückung zur Erläuterung der Verbesserung bei einem Verfahren nach dem vorgeschlagenen Prinzip,

Figur 4

eine schematische Darstellung einer zweiten Ausgestaltung der Erfindung,

Figur 5

eine schematische Darstellung der Erfindung in einem Mobilfunktelefon in einer ersten Benutzerkonfiguration,

Figur 6

eine schematische Darstellung der Erfindung in einer zweiten Benutzerkonfiguration,

Figur 7

eine schematische Darstellung der Erfindung in einem Mobilfunkgerät in einer weiteren Benutzerkonfiguration,

Figur 8

eine Ausgestaltung eines Gehäuses mit einigen Elementen des Regelsystems nach dem erfindungsgemäßen Prinzip,

Figur 9

eine Ausgestaltung einer Vorwärts- beziehungsweise einer Rückwärtsregelung nach dem vorgeschlagenen Prinzip,

Figur 10

eine Darstellung mit einer Vorwärtsregelung bei einem festen akustischen Verhältnis,

Figur 11

eine Darstellung einer Rückwärtsregelung bei einem festen akustischen Verhältnis.

Show it:

FIG. 1

an overview diagram for explaining the principle according to the invention,

FIG. 2

a system representation of a first embodiment of the principle according to the invention,

FIG. 3

a frequency power diagram of an active noise suppression to explain the improvement in a method according to the proposed principle,

FIG. 4

a schematic representation of a second embodiment of the invention,

FIG. 5

a schematic representation of the invention in a mobile phone in a first user configuration,

FIG. 6

a schematic representation of the invention in a second user configuration,

FIG. 7

a schematic representation of the invention in a mobile device in another user configuration,

FIG. 8

an embodiment of a housing with some elements of the control system according to the principle of the invention,

FIG. 9

an embodiment of a forward or a reverse control according to the proposed principle,

FIG. 10

a representation with a forward control at a fixed acoustic ratio,

FIG. 11

a representation of a backward control at a fixed acoustic ratio.

FIG. 1 shows a first embodiment of the inventive principle. The control system shown is part of a mobile device or a headset and comprises a loudspeaker housing 700 shown schematically here. The loudspeaker housing 700 may be designed in the form of a headphone housing with a padding 701. In addition, however, other housing for the speaker 300 are conceivable that can be held on the ear of a user. Ear clips with corresponding ear mounts that are inserted into the ear of a user also form possible speaker housing 700. These housings have in common that they ensure depending on their design a more or less tight closure to the ear of a user. The term "tight conclusion" and its meaning will be explained in more detail below.

In addition to the loudspeaker housing 700, the control system also includes a microphone 200 in the vicinity of the speaker. The microphone 200 is part of a feedback control from the control network 400 and the adder 600. The control network 400 is connected to an input of the adder 600. A second input of the adder 600 is connected to a second control network 500. The second control network 500 forms part of a feedforward control and is connected on the input side to the microphone 100.

The forward control microphone 100 is mounted on the outside of the speaker cabinet 700 while the backward control microphone 200 is mounted near the speaker 300. The microphone 200 thus detects the signal output from the speaker and supplies it to the feedback control and the control network 400.

The following is with reference to FIG. 1 the forward and reverse controls are explained separately with the two control networks 500 and 400, respectively. The feedforward function works such that the microphone 100 picks up external noise that also passes through the speaker housing to a user's ear. The recorded interference signal is fed to the control network 500, which performs phase and amplitude compensation. This is done so that the recorded signal is rotated over a relatively wide frequency range to the original noise with respect to its phase position by 180 °. This now inverted noise signal is additionally amplified in the control network 500 and then supplied to the speaker. In an inverse phase position and a corresponding same amplitude to the original noise signal occurs at the ear of a user to a destructive interference and thus to a suppression of the noise signal.

Similarly, the backward control also works with the microphone 200 and the control network 400. The microphone 200 picks up the loudspeaker signal from the loudspeaker 300 and the noise signal passing through the loudspeaker cabinet and feeds it to the control network 400. The rules network 400 is constructed in a manner similar to the rules network 500 and includes means for phase inversion and control gain. Accordingly, an inverted signal is emitted by the loudspeaker, which is destructively superimposed with the interference signals coming via the loudspeaker housing 700.

The backward control corresponds to a so-called open loop in which the amplitude and phase of the output loudspeaker signal are measured. The inverse of the filter transfer function calculated from this corresponds to the ideal filter of the control network. Because of the dead time between the output speaker signal and the microphone is often not complete phase inversion, so that the one control gain to high frequencies must be weakened to ensure the stability of the system.

According to the invention, it is now provided to feed the control signal of the feedforward control and the control signal of the feedforward control jointly to an adder 600 which forms a summation signal therefrom. This sum signal is supplied to the speaker 300.

The backward control in this way also detects the first control signal of the feedforward control as a disturbance variable and can compensate for this under certain circumstances. Thus, as a result, the adder 600 compensates by the backward control not only of noise that couple through the housing 700 in the microphone 200, but also a compensation of the controlled variable of the feedforward control and thus the control network 500, which is discharged through the speaker 300.

For this purpose, the backward control and the feedforward control are tuned to different acoustic conditions. In other words, the backward control operates optimally at a predetermined acoustic ratio at which the feedforward control substantially no longer works, or at least significantly less. For the noise suppression, especially the backward regulation is decisive with this acoustic ratio. Accordingly, the feedforward control is optimally tuned to a second acoustic ratio and results in this to a good noise suppression. In contrast, with this second acoustic ratio, the backward control no longer functions sufficiently, so that the noise suppression in the second acoustic ratio only determines the first controlled variable of the feedforward control.

The optimal tuning of the individual control networks as well as the forward and the reverse control to the two different acoustic conditions is in the FIGS. 5 to 7 shown.

An acoustic ratio is essentially the influence of external parameters on the noise suppression. In a fixed predetermined speaker housing, the acoustic ratio and in particular the quality of a noise suppression, especially of the tightness or the stability of an air volume between the speaker and the eardrum of a user dependent.

This circumstance is characterized by the term of so-called termination between the speaker cabinet and the ear of a user. In a "tight seal" stable acoustic conditions are present, for example, the speaker housing is arranged around the ear or on the ear of a user, so that no exchange of air between an outer volume and the volume of air in the housing and the ear of a user takes place. A "close seal" is given, for example, in headphones whose earpieces have a predetermined shape and snuggle tightly around the ear of a user.

Like in the FIG. 5 now indicated are for interference noise essentially two different paths 1 and 2 decisive. The first path 1 couples via the loudspeaker housing and the ear into the air volume located between the loudspeaker housing and the ear and thus reaches the eardrum of a user. The second path 2 of the noise is passed directly to the microphone 100 of the feed forward control. It is processed there in the control network 500 of the forward control and fed to the adder 600. The adder 600 outputs this signal as a first controlled variable to the loudspeaker 300. The loudspeaker 300 radiates the noise signal into a predetermined and fixed but at the same time stable air volume, which is ensured by the tight closure to the ear.

The microphone 100 of the feedback control now takes the output from the speaker signal noise including the first controlled variable together with the einkoppelnden over the path 1 Interference signal on and leads it to the second control network of the backward control. The tuning of the backward control is designed so that it is optimal in the case of tight closure. Thus, in this close termination, the feedback control and the control gain in the control network 400 completely compensates for a control gain of the feedforward control. In addition, there is an inversion of the interference signal that is coupled in via the path 1 and recorded, that is to say that the loudspeaker 300 as a total signal reduces a phase-inverted and, in its amplitude, a noise signal that couples in via the path 1 by means of destructive interference.

The case of the very tight conclusion of the FIG. 5 thus represents an extreme case and is used to vote the reverse control, so that at this conclusion a maximum noise suppression by the backward control is done. The control gain of the forward control not adapted for this case is compensated by the backward control.

The other extreme case is in FIG. 6 represented by a leaky conclusion. In this, a more or less variable distance is provided between the ear of a user and the housing of the speaker. The air volume is therefore undefined. At the same time, due to the lack of closure between the ear and the loudspeaker housing, there is only slight attenuation for interfering noise which reaches the user's ear via path 1. Since the termination to the ear is very leaking, much of the sound energy of the speaker is lost here, without being detected by the microphone 200 of the backward control. Accordingly, a controlled variable of the backward control is very small and has hardly any effect.

In this case, a completely leaky conclusion between a speaker housing and the ear of a user, the feedforward control is tuned. This detects the noise over the path 2 with its microphone 100 and supplies it to a control network 500. The control network 500 generates therefrom the first control variable, which is supplied to the adder 600 together with a very small second controlled variable of the feedback control. The tuning of the filter function of the feedforward control is done in this case, so that when a leaking conclusion of the speaker housing, the forward control for noise reduction works optimally. Due to the sound losses due to the leaky finish, the effect of the reverse control is very low.

The in the Figures 5 and 6 Terminals shown represent the extreme cases of the application for the control system according to the invention. In a completely tight closure, which is ensured for example by a firm contact pressure of the speaker to the ear of a user or by a special headphone shape, the backward control shows the maximum effect, while the feedforward is mismatched for this application. At a leaky conclusion, that is, a large distance and a more or less variable volume of air between the speaker cabinet and the ear of a user due to the sound losses, the backward control has no effect and the noise compensation is achieved by the tuned for this case, forward control.

The standard case, however, lies between the two extremes and will be as in FIG. 7 represented as normal completion.

In this both control networks and regulations are active. The conclusion to the ear is in this embodiment of the FIG. 7 not completely tight, but not as leaky as in the extreme case of FIG. 6 , It is considered a kind of intermediate state. The control gain and any filters in the control network 500 of a forward control lead to an increased sound pressure in the path 3, that is in the speaker cabinet. The reason for this is the lower sound losses due to the now reduced leakage at the ear. This results in the forward control to a small mismatch, which is expressed by an overcompensation of noise that couple through the path 1. This reduces noise rejection and may even result in noise enhancement with increasingly denser termination. This overcompensation is now compensated by the backward control. By the denser conclusion than that in the FIG. 6 More sound energy reaches the arranged in the speaker cabinet microphone 200. The recorded signal, which in addition to the noise in the path 1 and the overcompensation by the feed forward control is supplied to the control network 400. The control network now generates a second disturbance, which counteracts the overcompensation of the forward control. This is possible because the backward control does not distinguish between the externally entering noise and the overcompensated signal coming from the loudspeaker. As a result, the second control variable of the backward control increases with increasing tightness and compensates for the first controlled variable of the feedforward control. Due to the suitable combination of forward and reverse regulation and tuning The two regulations for different acoustic conditions, preferably a very dense and a very leaky conclusion can thus achieve a sufficient noise compensation over a wide variable range of acoustic conditions.

FIG. 2 again shows the system representation of the forward and reverse control in another view. The feedforward control comprises a control network 500 with three components shown schematically here. The control network 500 of the feedforward control 10 receives the noise picked up by the microphone 100. The control network 500 includes one or more filters that substantially cause an inversion of the phase of the received signal by 180 °. The second element 502 schematically shows the frequency response of the feedforward control. Finally, the control network 500 also comprises one or more control amplifiers, which are designed in such a way that the control gain increases as a function of increasing leakage. This is an inherent property of the feedforward control since it does not include information regarding tightness and acoustics. The feedforward control 10 thus has to be tuned to a predetermined acoustic ratio, for example an open or leaky end.

The output of the feedforward control 10 is connected to an adder 600 which is coupled on the output side to the loudspeaker 300. A second microphone 200 is disposed in the vicinity of the speaker 300 and thus detects passively attenuated noises as well as the signals emitted by the loudspeaker 300. The microphone 200 is connected to the second control network 400, which forms part of the feedback control. The second rule network also includes several Elements that are shown schematically. These include filter elements for an inversion of the phase position, which have a certain frequency response. The control network 400 also includes a control gain 401 that depicts a dependence on the tightness of the termination of the speaker at an ear of a user. The output signal of the feedback control is fed to a second input of the adder 600. In the operation of the feedback control, this now also sees the output signal of the feedforward control as a disturbance variable. Accordingly, it should compensate for this disturbance variable signal, especially when the feedforward control causes overcompensation due to a mismatch. This is the case, for example, when the feedforward control is tuned for a leaky finish and the feedforward control for a tight cut. In this case, in the feedforward control overcompensation occurs due to the predetermined control gain compensated by the feedback control.

In the overall result, the efficiency of an active noise suppression in the diagram of FIG. 3 demonstrate. The noise suppression itself is effective only over a predetermined frequency range. In addition, there are differences in the forward and reverse control in the frequency domain. In particular, the backward control shows a slightly lower frequency range, in which a good noise compensation is feasible. Especially at higher frequencies, the control gain of the feedback control must be mitigated to ensure the stability of the system because of the deadtime of the path between the compensating loudspeaker and the microphone of the feedback control. The curve KFF shows the frequency dependence of a feed forward control, the curve KFB a feedforward control individually considered. Although the forward control over a wider range is suitable for noise suppression, the reverse control shows significantly better results in a narrower frequency band. A combination of the two rules results in the curve KK, which essentially represents a superimposition of the two curves. By combining a significantly better noise suppression is thus achieved in a frequency band, at the same time in a wider frequency space at least a noise suppression similar to a forward control is feasible.

The invention is therefore particularly suitable for the mobile radio sector, in which there are substantially variable acoustic conditions. For this purpose it is possible as in FIG. 4 additionally shown in the reverse control to couple a useful signal. This can be, for example, a voice signal, music signal or the like. This coupling, which takes place, for example, in the control network of the feedback control in a control amplifier allows it to deliver useful signal through the speaker while minimizing from the outside einkoppelnde noise. In addition to a direct coupling of a useful signal, moreover, this can also be filtered or specially processed in order to minimize disturbance of the useful signal due to the backward or forward control. At the same time a good noise suppression is ensured even with a variable distance of the speaker housing to the ear through the two schemes.

An exemplary control network for the forward or reverse control shows FIG. 9 , On the input side, the control network is connected to the corresponding microphone. It includes a preamplifier that over the illustrated two RC network groups is coupled to a power amplifier arranged on the output side. The network groups each comprise RC networks with parallel-connected operational amplifiers and serve for an amplitude adjustment and a phase inversion of the applied and preamplified input signal. The RC network groups are adjustable in terms of their transfer characteristic, the gain of the operational amplifier as well. This allows a predetermined characteristic, which results from the speaker housing and / or the microphone mimic well and thus achieve the desired phase inversion.

In order to tune the backward regulation to a predetermined acoustic ratio, it is conceivable in one embodiment to carry out a tuning only in relation to the loudspeaker housing or the corresponding mobile radio part. FIG. 8 shows a corresponding realization. In this case, a first microphone 100 is arranged in a mobile radio part housing on a side facing away from the loudspeaker. This forms the part of the feedforward control. The speaker 300 itself is mounted in a speaker housing having a predefined first fixed volume of air. In the emission direction of the loudspeaker, a second air volume 210 is arranged, which likewise forms part of the mobile radio housing. This additional housing 210 comprises, in addition to an optional compensation opening 220 and the central opening for outputting the loudspeaker signal 230, the microphone 200.

For tuning the backward control, for example, the central opening 230 can now be covered so that a predefined and fixed air volume results from the loudspeaker housing 301 and the additional housing 210. On this Fixed air volume, which also represents a very stable acoustic ratio, the backward control can now be tuned by the filters within the control network and the amplification factors of the amplifiers are chosen so that the maximum extinction results in the desired frequency range. Accordingly, the feedforward control is adjusted by removing the cover from the central opening 230.

If the central opening is now held in the vicinity of the ear of a user in an operation of the mobile telephone, or pressed against this, an acoustic ratio results, which adjusts depending on the position between the two extremes. This ensures sufficiently good noise suppression over a wide range.

Claims (14)

1. Closed loop system for active noise cancellation, comprising:

   - a loudspeaker (300) for outputting sound;

   - an adding device (600) to which the loudspeaker (300) is connected, and which has a first and a second input;

   - a feedforward control (10) with

   - a first microphone (100) for receiving interfering noise;

   - a first control network (500) with at least one filter for forming a first control variable, wherein the first control network (500) is coupled to the first microphone (100) on its input side and to the adding device (600) on its output side in order to supply the first control variable;

   - a feedback control (20) with

   - a second microphone (200) for receiving sound that is output by the loudspeaker (300);

   - a second control network (400) with at least one filter for forming a second control variable, wherein the second control network (400) is coupled to the second microphone (200) on its input side and to the adding device (600) on its output side;
   characterized in that

   - the feedback control (20) is adapted for a noise suppression based on a first acoustic ratio, the feedforward control (10) is adapted for a noise suppression based on a second acoustic ratio;

   - the first acoustic ratio corresponds to a first distance between the loudspeaker (300) and an eardrum of a user, and the second acoustic ratio corresponds to a second distance between the loudspeaker (300) and the eardrum, wherein the second distance is greater than the first distance; and

   - the adaptation of the feedforward control (10) and the feedback control (20) is invariable at least during the operation of the closed loop system.
2. Closed loop system according to claim 1, in which the first acoustic ratio corresponds to an essentially tight sealing of the loudspeaker (300) to an ear of a user, and the second acoustic ratio corresponds to a leaky sealing of the loudspeaker (300) to the ear.
3. Closed loop system according to anyone of claims 1 or 2, in which the first and/or the second control network (400) have (has) a control amplification adapted to the respective acoustic ratio.
4. Closed loop system according to anyone of claims 1 to 3, in which the first and/or the second control network (400, 500) comprise(s) a series connection of a control amplifier and an RC filter.
5. Closed loop system according to anyone of claims 1 to 4, in which the first and the second control network (400, 500) are based on an entirely analog control.
6. Closed loop system according to anyone of claims 1 to 5, further comprising:

   - a loudspeaker housing (700, 300) for accommodating the loudspeaker (301), which essentially encloses a first air volume, and

   - an auxiliary housing (210) which essentially encloses a second air volume and is disposed in a preferred direction for sound radiation of the loudspeaker housing (301).
7. Closed loop system according to claim 6, in which the auxiliary housing (210) is arranged to receive the second microphone (200).
8. Closed loop system according to claim 6 or 7, in which the second control network (500) is adapted for a noise suppression which is based on the first and the second air volume.
9. Closed loop system according to anyone of claims 1 to 8, in which the feedforward control has a higher control bandwidth than the feedback control.
10. Method for the active noise cancellation for a loudspeaker (300) for the output of sound, the method comprising:

    - providing a feedback control for noise suppression adapted to a first acoustic ratio;

    - providing a feedforward control for noise suppression adapted to a second acoustic ratio;

    wherein the first acoustic ratio corresponds to a first distance between the loudspeaker (300) and an eardrum of a user, and the second acoustic ratio corresponds to a second distance between the loudspeaker (300) and the eardrum, wherein the second distance is greater than the first distance; and
    wherein the adaptation of the feedforward control and the feedback control is invariable at least during the operation of the closed loop system.
11. Method according to claim 10, in which the first acoustic ratio corresponds to an essentially tight sealing of the loudspeaker (300) to an ear of a user, and the second acoustic ratio corresponds to a leaky sealing of the loudspeaker (300) to the ear.
12. Method according to anyone of claims 10 or 11, in which the step of compensating comprises:
    detecting the control variable of the feedforward control as an interfering variable by the feedback control.
13. Method according to anyone of claims 10 to 12, in which the providing of the feedforward control comprises:

    - receiving interfering noise;

    - amplifying the received interfering noise;

    - filtering the received interfering noise;

    - outputting the filtered interfering noise;

    wherein the filtering is performed such that a cancellation of the interfering noise by the filtered and amplified interfering noise is caused at least in part in a first area in front of the loudspeaker.
14. Method according to anyone of claims 10 to 13, in which the providing of the feedback control comprises:

    - receiving interfering noise in the area of the loudspeaker;

    - amplifying the received interfering noise;

    - filtering the received interfering noise such that a cancellation of the interfering noise by the filtered and amplified interfering noise is caused at least in part in a second area in front of the loudspeaker;

    - outputting the interfering noise.

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