DE102008050425A1 - Device for active reduction of external noise - Google Patents

Abstract

A device is provided for reducing external noise. The device has at least one sound transducer (3) for receiving a useful signal (u), for outputting a useful sound (7), which leads to the reduction with external noise (6) to reduce the external sound (6) in the superimposition, and for simultaneously outputting a first Signal which images the effect of the external sound (6) arriving at the sound transducer (3) in superposition with the effect of the useful signal (u) applied to the sound transducer (3). The first signal is processed to generate the useful signal (u). The device further comprises a first filter (FuiM) for receiving the useful signal (u), for simulating the behavior of the sound transducer (3) when operating without sound and for outputting a second signal (iuM). The device further comprises a subtraction unit for subtracting the second signal (iuM) from the first signal, so that the difference signal (idM) images the external sound (6) arriving at the sound transducer (3). The device further comprises a second filter (Fcomp) for receiving the difference signal (idM) and for generating the useful signal (u) which is supplied to the sound transducer (3) for generating counter-sound.

Description

The The present invention relates to a device for reducing of extraneous sound through a counter sound, with a contained sound transducer at the same time both for the detection of external noise and for Release of the counter sound is used. A preferred application is a headphone, the corresponding components to the active Contains reduction of ambient noise.

Around in a noisy environment the background noise, which reaches the ears of a person to reduce exists in addition to the use of passive noise protection devices the possibility to actively compensate the background noise. For this purpose, with an active sounder a counter sound to the background noise generated. At the ear of the person finds an overlay of the noise and the counter sound instead. The sounder is To control it so that the counter sound produced at the ear as possible exactly corresponds to the incoming at the ear portion of the noise, but has the opposite sign. A typical application for the implementation of this approach can be found in headphones.

1 shows the schematic representation of a headphone with a device for the active reduction of background noise according to the prior art. Here is just the listener cap 1 sketched for one of the two ears of a person. The headphone has at least one cap 1 , a sounder 3 , a microphone 4 , a regulator unit 9 and an amplifier 11 on. The cap 1 serves to record the sounder 3 and the microphone 4 , The cap 1 is worn so that the sounder 3 in front of the ear 2 a user is positioned. The microphone 4 is usually between the sounder 3 and the ear 2 positioned. The cap 1 May be circumaural or supraauricular. The cap 1 can also serve passive damping against external noise 5 provide so that only a reduced noise 6 inside the cap 1 arrives. Will the sounder 3 with an electrical voltage 12 activated, it generates a useful sound inside the cap 7 ,

At the entrance of the ear 2 finds an overlay of the passively damped noise 6 with the sounder 3 generated useful sound 7 instead of. The microphone 4 serves to detect this overlay and generates the measurement signal from it 8th , The measuring signal 8th becomes the controller unit 9 fed. The controller unit 9 generated based on the measurement signal 8th a control signal 10 , This control signal 10 becomes an amplifier 11 supplied, from which the electrical voltage 12 for the sounder 3 generated. The sounder 3 creates the useful sound from it 7 , The controller unit 9 is designed so that the resulting useful sound 7 at the entrance of the ear 2 to compensate for the incoming at the ear portion of the noise 6 suitable.

The principles of active noise cancellation are through SM Kuo and DR Morgan Active Noise Control Systems Algorithms and DSP Implementations. Wiley-Interscience Publication, New York, 1996 described.

A crucial feature of the previously known solutions is that one or more microphones 4 used to reduce the noise 5 or a portion of the noise 6 or to measure the superposition of background noise with a useful sound and additionally a sound generator 3 for generating the useful sound 7 is required.

US 5,862,234 shows a double use of a transducer as a transmitter and receiver for use for active noise compensation ( 5 in US 5,862,234 ). However, a concrete guide to the evaluation of the signal thus received for the sound compensation is missing. Also, no product is known which implements the dual use of the sound transducer for active noise cancellation described in the related patent family in 1992.

A Object of the present invention is the acoustic / mechanical Construction of a device for active noise compensation opposite to simplify the prior art and the effect of the active Improve noise compensation.

These Task is achieved by a device according to claim 1 and solved according to claim 5.

Thus, a device for reducing external noise is provided. The device has at least one sound transducer for receiving a useful signal for outputting useful sound, which leads to the reduction of the extraneous sound when superimposed with existing external sound, and for simultaneously outputting a first signal which superimposes the effect of the extraneous sound arriving at the sound transducer with the effect of the applied to the sound transducer useful signal maps. The first signal is processed to generate the wanted signal. The device further comprises a first filter for receiving the useful signal, for simulating the behavior of the sound transducer when operating without external sound and for outputting a second signal. The device further comprises a subtraction unit for subtracting the second signal from the first signal so that the difference signal depicts the extraneous sound arriving at the sound transducer. The device further comprises a second filter for receiving the difference nals and for generating the useful signal, which is supplied to the sound transducer for generating counter-sound.

According to one Aspect of the present invention is the useful signal supplied to the sound transducer is designed so that the reduction of external noise their largest Effect unfolds in the ear canal of the user.

According to one Aspect of the present invention, the device may include a headphone, an in-ear earpiece or hearing protector.

The The invention also relates to a device with a sound transducer for receiving a useful signal, for outputting useful sound, in the overlay with existing external sound to Reduction of external noise leads. The device has a control unit for forming the desired signal, for receiving the signal of one or more microphones, to evaluate the signal one or more microphones, which reduce the noise to be reduced or a proportion thereof or an interference superposition and useful sound received and / or to evaluate one or more signals, The directly provided by a source of noise becomes. The control unit evaluates a first signal for generation from counter sound, which is detected at the transducer and the the effect of impinging on the transducer extraneous sound in overlay with the effect of the sound transducer applied Nutzschalls maps.

The Invention relates to the idea of the sounder used to produce the useful sound serves, at the same time to detect the noise and the thus detected signal for active noise compensation to use. In this case, an extinction of disturbance and counter sound especially in the ear canal of a wearer of the headphones. Basically, it is known that an acoustic transducer both as an actuator (sounder) and can be used as a sensor (microphone). As sounders are in Headphones mostly used so-called "dynamic transducers". The sound is emitted here by a membrane on which a Coil is applied. The coil is in a magnetic field. If an electrical voltage is applied to this coil, then flows a current in the coil. The magnetic field creates a force on the current-carrying coil, which the coil and thus also the membrane is set in motion, which leads to the sound emission. In this case, the transducer works as a sounder. Will, however the membrane is set in motion by an incoming sound, So this causes that in the coil that is in the magnetic field is moved, a voltage is induced. In this case works the transducer as a microphone. Also acoustic converters that follow other principles work, such as B. "electrostatic" transducer or piezo elements, can be used both as a sensor and as an actuator.

Further Embodiments of the invention are the subject of the dependent claims.

advantages and embodiments of the invention will be described below explained in more detail with reference to the drawings.

1 shows a schematic representation of a headphone with a device for the active reduction of background noise according to the prior art,

2 shows a schematic representation of a headphone with an interference sound detection based on a sound generator according to a first embodiment,

3 shows a schematic representation of an interference sound source and a headphone with the transfer functions to be considered,

4 shows a block diagram for determining an approximation of the Störschallsignals from the metrologically accessible signals according to a second embodiment,

5 shows a schematic representation of a headphone and a block diagram of an apparatus for the active reduction of noise according to a third embodiment, and

6 shows a schematic representation of a headphone and a control unit for the active reduction of background noise according to a fourth embodiment.

2 shows a schematic representation of a headphone with a noise detection using a sounder according to a first embodiment. The headphone has a cap 1 and a sounder 3 on. The cap 1 is used for passive acoustic damping of external noise 5 , so that only a reduced noise 6 inside the cap 1 arrives. The sounder 3 comes with an electrical voltage 12a supplies and gives a useful signal 7 from. At the sounder 3 is a resistance 15 connected. At the resistance 15 can be a voltage u _i 14 be recorded. The sounder 3 is intended here as a "dynamic converter". To the sounder 3 In addition to the useful sound generation according to the invention to use in addition to the detection of noise, here is the measurement of the current 13a necessary in the sound generator 3 flows and which is here also marked with i _a . The electrical voltage 12a , which is also referred to here as u _a , is according to the representation in 1 from an amplifier (not shown here) 11 made available. However, it does not go directly to the sounder here 3 but to a series circuit of the sounder 3 with the resistance 15 , The amplifier 11 is designed so that the reaction of the connected series circuit of sounder 3 and resistance 15 on the value of tension 12a negligible is small. Is now the voltage 12a on the series circuit of sound generator 3 and resistance 15 on, so becomes a stream 13a flow. The current 13a is partly an effect of tension 12a connected to the series circuit of sound generator 3 and resistance 15 is applied. In addition, there is a further proportion resulting from movements of the membrane, which by one on the sounder 3 incoming noise 6 be generated. From the stream 13a can by further processing of background noise 6 be determined. For evaluation according to the invention in this embodiment, therefore, the measurement of the current 13a required.

In 2 is an example of a way to measure the current 13a shown. The resistance is used to measure the current 15 standing in line with the sounder 3 is switched. The voltage 12a is here at the series connection from the sounder 3 and the resistance 15 at. At the resistance 15 then creates a tension 14 , which is also referred to here as u _i and proportional to the current 13a is. With the detection of tension 14 So is a measurement of the current 13a who is in the sounder 3 flows, available.

The further task now is to measure the measured current 13a to process so that a control signal 10 is generated, which via an amplifier 11 and the sounder 3 to a useful sound 7 leads, as a counter sound to the background noise 6 suitable is.

3 shows a schematic representation of an interfering sound source 16 and a headphone with the transfer functions to be considered, in which case the headset is not worn by a person but is mounted on a dummy head. The artificial head contains an artificial ear 17 , which serves to simulate the acoustic conditions of a real ear, and a microphone 18 , The noise source 16 a disturbance signal d is supplied, so that it emits a noise. The sound transducer included in the headphones 3 an electrical voltage signal u is supplied so that it emits a useful sound. The microphone 18 detects the microphone 18 incoming sound and generates the measurable microphone signal e. Another measure is the sound transducer 3 the current signal i detected.

• • Fdi(f) beschreibt das Übertragungsverhalten nach Betrag und Phase als Funktion der Anregungsfrequenz f, welches sich bei diesem Aufbau von dem Störanregungssignal d zu dem Stromsignal i ergibt.
• • Fde(f) beschreibt das Übertragungsverhalten nach Betrag und Phase als Funktion der Anregungsfrequenz f, welches sich bei diesem Aufbau von dem Störanregungssignal d zu dem Mikrofonsignal e ergibt.
• • Fui(f) beschreibt das Übertragungsverhalten nach Betrag und Phase als Funktion der Anregungsfrequenz f, welches sich bei diesem Aufbau von dem Spannungssignal u zu dem Stromsignal i ergibt.
• • Fue(f) beschreibt das Übertragungsverhalten nach Betrag und Phase als Funktion der Anregungsfrequenz f, welches sich bei diesem Aufbau von dem Spannungssignal u zu dem Mikrofonsignal e ergibt.

In 3 In addition, the four transfer functions Fdi (f), Fde (f), Fui (f) and Fue (f) are entered:

• • Fdi (f) describes the transfer behavior in terms of magnitude and phase as a function of the excitation frequency f, which results from the disturbance excitation signal d to the current signal i in this structure.
• • Fde (f) describes the transfer behavior in terms of magnitude and phase as a function of the excitation frequency f, which in this structure results from the interference signal d to the microphone signal e.
• • Fui (f) describes the transfer behavior in terms of magnitude and phase as a function of the excitation frequency f, which results in this structure from the voltage signal u to the current signal i.
• • Fue (f) describes the transfer behavior in terms of magnitude and phase as a function of the excitation frequency f, which in this structure results from the voltage signal u to the microphone signal e.

In the complex representation of the transfer functions, the measurable signals i (f) and e (f) thus result as a function of the excitation signals d (f) and u (f): i (f) = Fdi (f) * d (f) + Fui (f) * u (f) (1) e (f) = Fde (f) * d (f) + Fue (f) * u (f) (2)

The current signal i (f) from equation (1) thus consists of one component i d (f) = Fdi (f) * d (f) (3) and one share i u (f) = Fui (f) · u (f) (4) together. The proportion i _d (f) is due to external sound, which at the sound transducer 3 arrives. The signal i _d thus represents an image of the interfering sound to be compensated. For normal measurement, however, only the superimposition i = i _d + i _u , in which the contribution i _u additionally the reaction of the sound transducer, is accessible 3 on the applied voltage u maps.

4 shows a block diagram for determining an approximation of the Störschallsignals i _d from the metrologically accessible signals u and i according to a second embodiment. The disturbance excitation signal d generates the component i _d via the transfer function Fdi (f) and the voltage signal u generates the component i via the transfer function Fui (f). These two components result in their superposition the measurable current signal i. In 4 the voltage signal u is additionally a Filter supplied, which has the transfer function FuiM (f). The filter FuiM (f) is designed so that it simulates the transmission behavior Fui (f) as much as possible in terms of magnitude and phase as a function of the frequency f. As an output, the filter FuiM (f) delivers a signal i _uM which represents a simulation of the portion i _{u of} the current signal i which can not be measured alone in normal operation. The signal i _uM is in 4 subtracted from the measurable signal i. The result of this subtraction is the signal i _dM . Overall, i _dM is therefore too i dm = i - i around = i d + i u - i around ≈ i d (5)

Since the signal i _{uM represents} an approximation of the signal i, the components i _u and i _{uM are} removed from the signal i _dM , so that the signal i _{dM is} a good approximation for the component i _{d that} can not be measured alone in normal operation Available.

For the design of the filter FuiM (f) in 4 it is necessary to measure the transmission behavior of Fui (f) over the frequency f by magnitude and phase. The frequency response of Fui (f) can be measured directly by looking at the construction 3 the disturbance excitation d = 0 is selected, so that the proportion i _d = 0. Consequently, an excitation signal u to the sound transducer 3 applied and the resulting current signal i are measured, which under this condition consists only of the share i _u . The desired transmission behavior for FuiM (f) is known from this measurement and the associated filter circuit can be designed accordingly. Any included filter circuits as well as summation or subtraction points can be realized either analog or digital.

For the active noise compensation now a transmission behavior must be determined, which must have a filter so that it generates from the approximation for i _d a signal u, which leads to a counter sound, which leads to the ear of the user to reduce the noise. The determination of this target transmission behavior is based on the in 3 Registered transfer functions Fdi (f), Fde (f) and Fue (f).

For the arrangement in 3 These three transfer functions can be measured in terms of amount and phase as a function of the excitation frequency f, with the respective excitation signals d and u and the response signals of the structure i and e, respectively. Unlike the build out 3 However, the noise in a real environment does not normally arise from a single source at a particular location, but is composed of multiple sources in different locations. In particular, there is no disturbance excitation signal d that could be used to generate a compensation signal.

Nevertheless, can be based on the structure 3 determine a transmission behavior that is valid for many cases of noise sources and that allows the generation of the compensation signal without knowledge of a disturbance excitation signal d. For this purpose, a measurement must first be carried out in which the signal u = 0 is selected. This means that the two supply lines of the sound transducer 3 be connected to each other. The measurable current signal i then only consists of the component i _d , since the component i _u here becomes zero. For the measurement, the excitation of the structure with a disturbance excitation signal d occurs. However, the signal d itself is not taken into account as a measured variable in this measurement. Rather, the resulting relationship between the signal i _d and the signal e is detected in terms of magnitude and phase as a function of the excitation frequency f. With u = 0 it can be deduced from the equations ( 1 ) and (2) derive the following relationship between the signals i _d and e: e (f) = (Fde (f) / Fdi (f)) * i d (f) at u = 0 (6)

For the resulting transfer function (Fde (f) / Fdi (f)), therefore, the signal i _{d is} regarded as the input signal and the signal e as the output signal, and the measurement directly yields the quotient (Fde (f) / Fdi (f) ) by magnitude and phase as a function of the excitation frequency f.

Clearly, the equation (6) can be interpreted such that 1 / Fdi (f) * i _d (f) is used to determine a "virtual" signal d, which in the arrangement of FIG 3 would belong to the measured signal i _d . However, in the same step, the signal e resulting from the virtual signal d is determined directly from the virtual signal d by multiplication with the transfer function Fde (f). Since this process is performed in one step, the actual determination of the signal d is not required. It should be noted at this point that the transmission behavior of the signal i _d to the signal e due to the defined acoustic conditions between the transducer 3 and the microphone 18 does not depend on whether the background noise is actually from an interfering sound source 16 according to 3 is produced. For example, the transmission behavior of the signal i _d to the signal e does not change when the distance of the noise source 16 is varied to the listener. Even a superposition of background noise from a plurality of noise sources at different distances to the listener does not change the relationship between the signal i _d and the signal e. With increasing frequency, however, an increasing dependence of this transmission behavior on the direction of the incident noise is to be observed. This side effect is not considered in the other versions.

By merging equation (2) and (6) the signal e of the microphone 18 can be in normal operation - ie under the influence of noise and when applying a signal u to the transducer 3 - specify as follows: e (f) = (Fde (f) / Fdi (f)) * i d (f) + Fue (f) · u (f) (7)

The transmission behavior Fue (f) can be measured directly by magnitude and phase as a function of the excitation frequency f, by in the construction 3 the disturbance excitation d = 0 is selected.

The signal e, which is the microphone 18 in the artificial ear 17 detects, represents the sound that results in the ear canal of a user of the device. The goal for the active noise compensation is therefore to make the signal e to zero for as wide a frequency range as possible. With e = 0, equation (7) can be changed so that a desired transfer function Fset (f) can be specified, which would have to have a filter with the signal i _d as input and the voltage signal u as output, so that an optimal compensation of the noise in the user's ear canal results in: u (f) = - (Fde (f) / Fdi (f)) * 1 / Fue (f) * i d (f) = Fsoll (f) · i d (f) (8)

According to the arrangement 4 is the signal i _dM an approximation for the signal i _d available, which can be used as an input for the compensation _filter . From the measured transfer functions (Fde (f) / Fdi (f)) and Fue (f), the nominal transfer function can be calculated for each measured frequency point f Fsoll (f) = - (Fde (f) / Fdi (f)) · 1 / Fue (f) (9) state according to amount and phase.

5 shows a schematic representation of a headphone and a block diagram of an inventively constructed device for the active reduction of background noise according to a third embodiment. The signal processing for generating the useful signal u is carried out according to the approach given in equation (8). The useful signal u is in 5 the sound transducer 3 supplied, so that this the useful sound 7 emits. The cap 1 May be circumaural or supraauricular. The cap 1 can serve a passive damping against the external noise 5 to offer, so only a reduced noise 6 inside the cap 1 arrives. Alternatively, the handset may be provided as an in-ear earphone without a cap. At the ear 2 the user of the listener meets the superposition of background noise 6 and useful sound 7 one. The useful signal u is also fed to a filter FuiM (f), which generates the signal i _uM . In the sound converter 3 arises in response to the useful signal u and the noise 6 the current signal i. From the measured signal i, the signal i _{uM is} subtracted, which is a simulation of the response of the transducer 3 represents the useful signal u. The result of this subtraction is the signal i _dM , which approximates the response of the transducer 3 on the background noise 6 represents. The signal i _dM is fed to a filter Fcomp (f), which generates the useful signal u from it. In 5 In addition, an audio signal a is shown, which can be added to the useful signal u to produce a desired sound signal.

An optimal reduction of noise at the entrance of the ear 2 results when the filter Fcomp (f) maps the transfer behavior of Fsoll (f) from equation (9) by magnitude and phase as a function of the frequency f. From the measurements described, a complete description of the desired transmission behavior of Fcomp (f) is thus available. Because the entire transmission behavior of the sound transducer 3 to the ear of the user both for the external sound 6 as well as for the useful sound 7 For the design specification for the filter Fcomp (f) described here according to the invention, the result is a device which transmits the useful signal u to the sound transducer 3 is supplied, so generated that the reduction of the extraneous sound exerts its greatest effect in the ear canal of the user.

Since Fsoll (f) is not the direct result of the measurement of a real system, but the course has developed by offsetting different shares, it is generally not to be assumed that the complete course of magnitude and phase with a feasible filter Fcomp (f ). A real filter is always "causal" (it can not show a response before a stimulus hits), and for a real application, the filter itself must be "stable" (in the absence of excitation, the output must aim for a finite constant end value). From these two conditions, there are compelling relationships between the course of the magnitude and the phase of the transfer function of the filter as a function of the frequency f. Thus, since the magnitude and phase history of Fcomp (f) can not be independently set, Fcomp (f) will generally only approximate Fsoll (f). For a limited frequency range, it is usually possible with a causal stable filter to approximate a given course in terms of magnitude and phase. A reasonable approximation is thus obtained by selecting a frequency range in which Fcomp (f) can well follow the course of Fsoll (f) in terms of magnitude and phase. In this frequency range, ultimately, the desired noise compensation effect, since the counter sound in the ear canal is generated correctly according to amount and phase. Outside of the selected frequency range, the amount of Fcomp (f) should be chosen as low as possible, because due to the undefined phase relationship between noise and compensation sound otherwise even increases in noise can occur. If this condition is adhered to, the phase characteristic of Fcomp (f) outside the selected frequency range is not subject to any restrictions, which results in the necessary degrees of freedom permitting the design of a causally stable filter.

Optionally, the in 5 shown possibility to add the useful signal u an audio signal a. The at the entrance of the ear 2 incoming useful sound 7 is then a combination of the antinoise signal and a desired according to the audio signal a sound signal. The generation of the antinoise signal is not impaired by adding the audio signal a to the useful signal u. The audio signal a is in 5 Component of the useful signal u, both the sound transducer 3 as well as the filter FuiM (f) is supplied. Consequently, the audio signal a becomes both in the sound transducer 3 reflected signal measured i as well as in the filter _output i _uM in the same way. Since the signal i _{uM is subtracted} from the measured signal i, the components attributable to the audio signal a cancel out, so that the audio signal a is not reflected in the thus generated signal i _dM , which serves as the input for the filter Fcomp (f) , Consequently, the audio signal has no influence on the generation of the antinoise signal. Accordingly, the device for generating the antinoise signal has no influence on the desired reproduction of the audio signal a.

Another object of the present invention is to improve the effect of active noise cancellation devices having a prior art acoustic / mechanical structure. A decisive feature of the previously known solutions is that one or more microphones are used to measure the background noise or a portion of the noise or the superposition of background noise with a useful sound and additionally at least one sounder for generating the counter sound is included. As an alternative or in addition to the microphone signals, according to the prior art, in some cases signals are used to generate the antinoise signal, which signals are provided directly by an interfering sound source. The generation of the antinoise signal is based on the prior art on a processing of the signal from the microphone (s) contained or on signals which are provided by an interfering sound source or a combination of said signals. According to the invention, the noise compensation effect of such devices can be improved by additionally detecting a signal at the sounder which maps the effect of the sound impinging on the sounder into superposition with the effect of the useful signal applied to the sounder, and processes this signal in addition to producing the counter sound becomes. As an example of a corresponding acoustic / mechanical device according to the prior art is used in 6 a headphone.

6 shows the schematic representation of a headphone and a control unit for the active reduction of background noise according to a fourth embodiment. The cap 1 contains a sound transducer 3 and a microphone 4 , The cap 1 is worn so that the sound transducer 3 in front of the ear 2 is positioned. The microphone 4 is here between the sound transducer 3 and the ear 2 positioned. The cap 1 can serve a passive damping against the external noise 5 to offer, so only a reduced noise 6 inside the cap 1 arrives. Will the sound transducer 3 driven by a useful signal u, it generates a useful sound inside the cap 7 , At the entrance of the ear 2 finds an overlay of the passively damped noise 6 with the sound transducer 3 generated useful sound 7 instead of. The microphone 4 serves to detect this overlay and generates the measurement signal from it 8th , At the sound converter 3 the signal i is detected, which is the effect of the sound transducer 3 incoming foreign sound 6 in overlay with the effect of the sound transducer 3 applied useful signal u maps. The signal i becomes common with the signal 8th a control unit 19 fed. In addition, the control unit 19 an audio signal a is supplied, which represents a desired sound signal. The control unit 19 generated from the three input signals 8th and a the useful signal u, the sound transducer 3 is supplied.

According to the invention, in contrast to the prior art in 6 in addition to the signal 8th the signal i evaluated to generate the antinoise signal. From this approach there are numerous possibilities to improve the effect of the active noise compensation of known acoustic / mechanical devices according to the prior art:
In the construction off 6 is the microphone 4 mounted inside the cap, so that it is the superposition of the noise 6 with the useful sound 7 detected. The incoming background noise 6 reached in 6 first the sound transducer 3 and hits due to the sound propagation in air only with a slight delay on the microphone 4 one. From this delay, the generation of the antinoise signal according to the prior art results in restrictions on the maximum frequency up to which a noise compensation effect is achieved. Since the background noise 6 first the sound transducer 3 and only then the microphone 4 reached, stands with the signal i an input to the control unit 19 available that does not have this delay. According to the invention, therefore, the additional evaluation of the signal i offers the possibility of widening the frequency range of the noise compensation effect compared to the prior art.

In a headphone according to the prior art according to 1 caused by head movements of the user of the headphone pressure fluctuations inside the cap 1 , These are from the microphone 4 detected and can have significant amplitudes. In the processing according to the prior art 1 This can lead to overdrives in the generation of the antinoise signal. To prevent this, usually limiting measures are taken in the associated circuit, but affect the effect of active noise compensation. Since the mentioned pressure fluctuations are predominantly in a frequency range below the human audible range, a reaction of the circuit to these pressure fluctuations is not desired. In order to counteract the problem of overdriving, therefore, the signal i, in which the mentioned pressure fluctuations also reflect, according to the invention and according to 6 used to determine the head movements based parts of the signal 8th to recognize and from the signal 8th to subtract, so that it does not come in the signal chain to overdrive and thus not to affect the noise compensation effect.

Unlike in 6 it is also known in the prior art known the microphone 4 outside on the cap 1 to install. In such systems, the effect of active noise cancellation often depends to a considerable extent on the direction of the incoming noise. According to the invention here the sounder 3 be used via the signal i as an additional sensor for detecting the noise. By the Störschallerfassung in different places information about the direction of the Störschalls are available in the thus available signals. By suitably processing the additional signal, the frequency range in which a noise compensation effect is achieved can be broadened and the directionality can be reduced.

Furthermore, according to the prior art, "adaptive" methods are known in which the transmission behavior of the filters for generating the antinoise signal during operation is adapted to changing conditions of the acoustic structures and the noise. Even with such structures can according to the invention, the signal i, the sound transducer 3 can be taken into account as an additional measurement signal for improving the noise compensation effect or the adaptive behavior of the adaptive algorithms.

The Abnormal noise reduction device described above in a headphone, in an in-ear listener or be implemented in an ear protection. An in-ear listener according to the invention has a smaller footprint on, as an additional microphone for recording the interference signal can be omitted.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 5862234 [0007, 0007]

Cited non-patent literature

• - SM Kuo and DR Morgan's Active Noise Control Systems Algorithms and DSP Implementations. Wiley-Interscience Publication, New York, 1996 [0005]

Claims (8)

Device for reducing extraneous sound with at least one sound transducer ( 3 ) for receiving a useful signal (u), for outputting a useful sound ( 7 ), which in the overlay with existing external sound ( 6 ) for reducing the external noise ( 6 ) and for simultaneously outputting a first signal (i), which effects the effect on the transducer ( 3 ) incoming foreign sound ( 6 ) in superposition with the effect of the sound transducer ( 3 ) is applied, wherein the first signal (i) for generating the useful signal (u) is processed, a first filter (FuiM) for receiving the useful signal (u), for simulating the behavior of the sound transducer ( 3 ) in operation without external _sound and for outputting a second signal (i _uM ), a subtraction unit for subtracting the second signal (i _uM ) from the first signal (i), so that the difference signal (i _dM ) the external _sound ( 6 ), which at the sound transducer ( 3 ), and a second filter (Fcomp) for receiving the difference signal (i _dM ) and for generating the useful signal (u), which the sound transducer ( 3 ) is supplied to generate counter-sound. Apparatus according to claim 1, wherein the useful signal (u), the the sound transducer ( 3 ) is designed so that the reduction of the external sound ( 6 ) unfolds its greatest effect in the ear canal of a user. Device according to one of the preceding claims, the device being a headphone, an in-ear earpiece or hearing protection. Device according to one of the preceding claims, wherein the useful signal (u) additionally a portion of a Audio signal source (a) is added. Device with at least one sound transducer ( 3 ) for receiving a useful signal (u), and for outputting the useful sound ( 7 ), which in the overlay with existing external sound ( 6 ) for reducing the external noise ( 6 ), and a control unit (CU) for forming the useful signal (u), for receiving the signal of one or more microphones, for evaluating the signal of one or more microphones, which reduces the noise to be reduced or a portion thereof or a superimposition of interference. and useful sound received and / or for evaluating one or more signals that are provided directly by an interfering sound source, wherein the control unit (CU) for generating counter sound additionally evaluates a first signal (i), which at the sound transducer ( 3 ) and that the effect of the sound transducer ( 3 ) incoming foreign sound ( 6 ) in superposition with the effect of the sound transducer ( 3 ) applied useful signal (u) maps. Apparatus according to claim 5, wherein the device a headphone, an in-ear earpiece or hearing protection is. Apparatus according to claim 5 or 6, wherein the control unit additionally a signal from an audio signal source (a) supplied becomes. Method for reducing extraneous sound in a headphone, in-ear earpiece or hearing protector with at least one sound transducer ( 3 ), with the steps: receiving a useful signal (u), outputting a useful sound ( 7 ), which leads to the reduction of the external noise when superimposed with existing external sound, and at the same time outputting a first signal by the sound transducer, wherein the first signal is the effect of the sound arriving at the sound transducer ( 6 ) in superposition with the effect of the sound transducer ( 3 ) is applied, the first signal for generating the useful signal (u) is processed, receiving the useful signal, emulating the behavior of the transducer during operation without extraneous sound and outputting a second signal (i _uM ) by a first filter (FuiM ), Subtracting the second signal (i _uM ) from the first signal (i), so that the difference signal is the extraneous sound ( 6 ), which at the sound transducer ( 3 ), and receiving the difference signal and generating the useful signal (u) which the sound transducer ( 3 ) is supplied to generate counter-sound.