Patent Publication Number: US-10313778-B2

Title: Method for operating an electroacoustic system and electroacoustic system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a United States National Phase Application of International Application PCT/EP2016/056232, filed Mar. 22, 2016, and claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2015 003 855.9, filed Mar. 26, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to a method for operating an electroacoustic system, in which an electroacoustic device for at least partially occluding an ear canal is arranged at least partially on an ear, in which a signal processing device is used to process a signal incoming to the device, and in which at least one correction unit of the signal processing device is intended and/or used to modify the signal incoming to the device. Furthermore, the present invention pertains to an electroacoustic system, which is operated according to such a method. 
     BACKGROUND OF THE INVENTION 
     Such a method and such an electroacoustic system are known from US 2014/0321657 A1. According to this, an incoming acoustic signal can be modified taking into account the acoustic properties of the ear canal in an area between the device at least partially occluding the ear canal and the eardrum. 
     Using electroacoustic systems and/or an electroacoustic device that at least partially or completely occlude, fill up, shut and/or close an ear and/or an ear canal, for example, in the area of consumer electronics and/or hearing aids is known. In this case, it is disadvantageous that the occlusion of the ear canal causes a change in the perception of ambient noises. This changed perception of ambient noises, and especially natural ambient noises, may comprise a muffling, a spectral modification, a change in the color tone, a change in the sound spectrum and/or a change in spatial perception. It is especially disadvantageous that ambient noises are not perceived and/or are perceived as unnatural in case of an ear canal at least partially occluded by means of the electroacoustic device. This may lead to a danger to the person using the electroacoustic device, especially in traffic. In addition, the wearing and/or use of the electroacoustic device may be felt to be uncomfortable. 
     SUMMARY OF THE INVENTION 
     A basic object of the present invention is to further develop a method and electroacoustic system of the type mentioned in the introduction such that an interfering and/or undesired change in the perception of ambient noises during the use of an electroacoustic device at least partially occluding the ear canal is reduced, avoided and/or at least partially compensated. 
     The basic object of the present invention is accomplished by means of a method and by means of an electroacoustic system of the type mentioned in the introduction, wherein a signal outgoing from the device by means of the at least one correction unit is generated to achieve acoustic transparency, in which, on the basis of the outgoing signal, a received signal is generated at the eardrum, which is adapted to correspond to a free-ear received signal at the eardrum in case of a free ear canal without the device. 
     It is advantageous here that ambient noises can be perceived in sufficient quality despite an at least partial occluding of the ear canal. In particular, the method and/or the electroacoustic system makes possible a checking, control and/or manipulation of the received signals, preferably of a frequency response, at the eardrum. The electroacoustic system can be operated in an acoustic transparency mode as a result of this. The perception of ambient noises of a person using the electroacoustic system is preferably not disturbed or changed because of the acoustic transparency, or is disturbed or changed slightly at most and/or to a non-disturbing extent. The person using the electroacoustic system preferably experiences a perception of noises, especially approximately as with a free ear canal. Thus, the method and/or the electroacoustic system makes possible a pleasant, especially natural, perception of ambient noises in case of a partially and/or completely occluded ear canal. The electroacoustic system here may make possible a plurality of additional functions, for example, in conjunction with a consumer electronic device, with a hearing protection device, with a hearing aid and/or with a communication device, in particular a mobile phone and/or a smartphone. In particular, a hearing aid may be additionally provided, preferably when needed. The received signal generated at the eardrum may be amplified and/or muffled in comparison to the signal incoming to the device. 
     Within the framework of the present application, acoustic transparency is preferably configured as a perceptive acoustic transparency. In particular, a perceptive and/or acoustic transparency means that there is no audible distinction from a free-ear signal or free-ear received signal. A perceptive and/or acoustic transparency can thus be achieved, without having to achieve an absolute physical agreement of the received signal generated at the eardrum with a free-ear received signal in case of a free ear canal without the device. It is preferably sufficient when a person using the device has the perception that the received signal generated with the device agrees, in terms of perception, with the free-ear received signal in case of a free ear canal without the device. 
     According to another embodiment, the correction unit has a first correction filter and a second correction filter. The first correction filter of the signal processing device may be intended and/or used to achieve acoustic transparency. The second correction filter of the signal processing device is preferably intended and/or used to modify the especially acoustic signal outgoing from the device. In particular, the acoustic properties of an ear canal section from the device to an eardrum of the ear are taken into account by means of the second correction filter. The first correction filter and/or the second correction filter may be configured as especially digital, electrical circuits. The correction unit, the first correction filter and/or the second correction filter may have at least one analog-to-digital converter and/or at least one digital-to-analog converter. 
     A first correction filter of the correction unit is preferably arranged upstream of a second correction filter of the correction unit. In particular, the incoming signal is first modified by means of the first correction filter to achieve acoustic transparency. The changed incoming and/or received signal is subsequently modified by means of the second correction filter to filter out transmission effects in the area from the device to the eardrum because of the at least partial occlusion of the ear canal by means of the device. A received signal, which corresponds to the free-ear received signal in case of a free ear canal without the device, is generated by means of the especially acoustic signal outgoing from the device. Thus, an interfering effect of the device at least partially occluding the ear canal on the perception of ambient noises can be reduced and/or compensated. In particular, a received signal, which is adapted to correspond and/or corresponds to a free-ear received signal in this area of the ear canal section in case of a free ear canal without the device, is generated to achieve acoustic transparency on the basis of the outgoing signal in the area of the ear canal section from the device to the eardrum. 
     According to a variant, the incoming, especially acoustic, signal is fed as an incoming electrical signal to the signal processing device by means of an external sound receiver associated with the device and directed away from the eardrum and outwards. At least one additional, external acoustic and/or electrical signal is preferably fed to the signal processing device, especially by means of an additional external sound receiver and/or a direct wired connection to an additional external signal source. In particular, the external sound receiver and/or the additional external sound receiver is each configured as a microphone. The additional external signal may likewise be modified by means of the correction unit. 
     A negative feedback loop can especially be achieved by means of the electroacoustic system. The external sound receiver and the additional external sound receiver are preferably used to achieve the negative feedback loop. 
     According to another embodiment, a calibration is carried out before using the electroacoustic system. A first correction filter and/or a second correction filter is especially determined within the framework of the calibration. The calibration is preferably carried out after each use of the device for at least partially occluding the ear canal. The calibration is especially preferably carried out by means of an external sound source and/or a calibration control unit. As an alternative, a starting calibration may first be carried out to determine the first correction filter and the second correction filter, especially by means of an external sound source. After the starting calibration has been carried out and a new use of the device for at least partially occluding the ear canal, only a single calibration filter, in particular the first correction filter or the second correction filter, is recalibrated within the framework of a partial calibration. A headphone, which is placed onto an auricle with an inserted electroacoustic device, may be used as an external sound source for calibration. The use of a signal hitting the ear from outside is especially advantageous for detecting the spatial resolution of an incoming signal. The calibration control unit may be in the device, in an earpiece, a computer and/or smartphone. The calibration control unit especially has a processor. The calibration control unit may be connected to the electroacoustic device by means of a cable, a wireless connection, a near field communication and/or Bluetooth. 
     An individual calibration is preferably carried out for the respective person using the device and/or after each use of the device in the ear canal. A calibration and/or setting of the first and/or second correction filter is especially carried out during the current operation. A readjustment can be carried out as a result of this. A readjustment is preferably carried out if at least one predefined triggering parameter is present. For example, a readjustment may be carried out at predefined times or at predefined time intervals. As an alternative or in addition, a readjustment can be initialized when at least one predefined and monitored triggering parameter is reached, fallen below or exceeded. 
     The correction unit, first correction filter and/or second correction filter are especially recalibrated and/or repositioned in the current operation. A continuous and/or intermittent calibration can thus be carried out especially in conjunction with a starting and/or first calibration. 
     A first correction filter of the correction unit is preferably determined on the basis of a first model and/or a second correction filter of the correction unit is determined on the basis of a second model. The first model and/or the second model is preferably based on the Thevenin equivalent and/or on the Norton equivalent. These models are tried and tested and make possible a sufficiently accurate estimation of the relevant parameters. 
     According to a variant, a total pressure P tot  of an external acoustic signal within the ear canal at least partially occluded by the device is composed of two parts to determine a first correction filter A of the correction unit. A first part of the total pressure P tot  is preferably a passage pressure P HT  that is measured by means of an internal sound receiver, which is associated with the device and faces an eardrum of the ear. The internal sound receiver maybe configured as a microphone. The passage pressure P HT  is especially a sound pressure of an external acoustic signal after the passage through the ear canal at least partially occluded by the device. A second part of the total pressure P tot  is preferably an outgoing pressure P EP  measured by means of a sound generator, which is associated with the device and faces the eardrum. The sound generator may be configured as a loudspeaker and/or receiver. At least one other and/or additional sound generator may be provided. The at least one additional sound generator may be arranged at an end of the device facing the eardrum or at an end of the device facing away from the eardrum. 
     A pressure is preferably defined as a pressure frequency within the scope of the present invention. In particular, a pressure frequency response is obtained at a sound receiver and/or at an eardrum on the basis of a pressure frequency of a signal source, a noise source and/or a sound generator. 
     According to another embodiment, to determine a first correction filter A of the correction unit, a total pressure P tot  of an external acoustic signal within the ear canal at least partially occluded by the device is compared with a target pressure P T,E  to be expected. The first correction filter A is preferably determined with the following equation, taking into consideration a passage pressure P HT  measured by means of an internal sound receiver, which is associated with the device and faces an eardrum of the ear: 
     
       
         
           
             A 
             = 
             
               
                 
                   
                     P 
                     
                       T 
                       , 
                       E 
                     
                   
                   - 
                   
                     P 
                     HT 
                   
                 
                 
                   
                     P 
                     tot 
                   
                   - 
                   
                     P 
                     HT 
                   
                 
               
               . 
             
           
         
       
     
     In particular, after a first determination of a first correction filter A of the correction unit, especially within the framework of a calibration, a fine adjustment of the first correction filter A is carried out. At least one predefined calibration signal and/or a predefined noise is preferably used. The calibration signal may be configured as white noise. In particular, a pressure P E  measured by means of an internal sound receiver, which is associated with the device and faces an eardrum of the ear, is compared with a target pressure P T,E  during the fine adjustment. The first correction filter A in this case is iteratively adapted until a predefined convergence criterion is reached in case of a deviation of the measured pressure P E  from the target pressure P T,E . 
     To determine a first correction filter A of the correction unit, a pressure P E  measured by means of an internal sound receiver, which is associated with the device and is facing an eardrum of the ear, is preferably compared with a target pressure P T,E  to be expected at the internal sound receiver, and the target pressure P T,E  to be expected at the internal sound receiver is estimated to be a pressure at the location of the internal sound receiver in case of a free ear canal without the device. 
     The target pressure P T,E  to be expected at the internal sound receiver in case of a free ear canal can be estimated by means of an electroacoustic model, in particular with a Thevenin pressure source model and/or a source impedance model. The target pressure P T,E  to be expected at the internal sound receiver is preferably estimated by means of a source pressure P S , an ear canal impedance Z L  and a radiation impedance Z RAD  especially with the following equation: 
     
       
         
           
             
               P 
               
                 T 
                 , 
                 E 
               
             
             = 
             
               
                 P 
                 S 
               
               ⁢ 
               
                 
                   Z 
                   L 
                 
                 
                   
                     Z 
                     L 
                   
                   + 
                   
                     Z 
                     RAD 
                   
                 
               
             
           
         
       
     
     According to a variant, to determine a second correction filter B of the correction unit by means of an internal sound receiver, which is associated with the device and is facing an eardrum of the ear, an estimation of the acoustic received signal at the eardrum is carried out. An identical frequency response and/or an identical pressure at the internal sound receiver and at the eardrum is especially assumed for the estimation. The pressure at the eardrum P D  is preferably estimated by means of the pressure P E  which is measured at the internal sound receiver by using an electroacoustic model of the ear canal. 
     A pressure at the eardrum P D  is preferably determined by means of a pressure P E  measured at the internal sound receiver and by means of the correction filter B with the following equation:
 
 P   D   =P   E   B.  
 
     Thus, the second correction filter B can be determined with knowledge of the pressure at the eardrum P D  and the pressure P E  measured at the internal sound receiver. 
     The electroacoustic system comprising the electroacoustic device for at least partially occluding an ear canal, especially for carrying out the method according to the present invention, preferably has the signal processing device to process a signal incoming to the device. Here, the signal processing device has at least one correction unit to modify the signal incoming to the device. Furthermore, the correction unit is used to provide and/or generate a signal outgoing from the device. The correction unit has a first correction filter and a second correction filter, wherein the first correction filter of the signal processing device is configured to achieve acoustic transparency, in which, on the basis of the outgoing signal, a received signal can be generated at the eardrum, which is adapted to correspond to a free-ear received signal at the eardrum in case of a free ear canal without the device. The second correction filter of the signal processing device is preferably configured to modify the especially acoustic signal outgoing from the device. 
     The use of a method according to the present invention and/or an electroacoustic system according to the present invention, especially in connection with a hearing protection device, with an in-ear headphone and/or a hearing aid, is especially advantageous. The method and/or the electroacoustic system according to the present invention can be used in conjunction with a consumer electronic device and/or a communication device, especially with a mobile phone and/or with a smartphone. In particular, the method and/or the electroacoustic system is especially integrated in an existing system and/or an existing device, for example, in a hearing aid, a behind-the-ear device and/or a communication device. An external and/or additional, especially acoustic, signal can be mixed with an ambient signal of an ambient noise. In particular, the mixing is carried out after the application of the first correction filter to the incoming signal and/or to the ambient signal. 
     The signal processing device may be integrated in an in-ear device, a behind-the-hear device, a computer and/or a communication device, especially in a mobile phone and/or smartphone. The internal sound receiver, the external sound receiver and/or the sound generator are preferably connected by means of a wire to an in-ear device, a behind-the-ear device, a computer and/or a communication device, especially in a mobile phone and/or smartphone. 
     The acoustic transparency can make possible a perception of ambient noises that is at least largely familiar for a person and/or a spatial hearing in case of a partially occluded ear canal. 
     The electroacoustic system, the correction unit, the first correction filter and/or second correction filter are configured according to another embodiment to attenuate and/or suppress a sound radiation outwards, especially away from the person using the device and/or from the eardrum. 
     The electroacoustic device may have a venting device. The venting device may be configured as a venting channel in order to make possible an equalization of pressure in case of a device used in an ear canal. The wearing comfort can be further improved as a result of this. The device and/or an earpiece may comprise an air-permeable material. An internal sound receiver, an external sound receiver and/or a sound generator may be arranged at least partially or completely within the venting device. 
     The present invention is described in detail below with reference to the attached figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic view of an electroacoustic device for an electroacoustic system according to the present invention; 
         FIG. 2  is a schematic view of an electroacoustic model of the electroacoustic device according to  FIG. 1 ; 
         FIG. 3  is a schematic view of a logic circuit of a signal processing device with the electroacoustic device according to  FIG. 1  during a calibration; and 
         FIG. 4  is a schematic view of a logic circuit of a signal processing device of the electroacoustic device according to  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings,  FIG. 1  shows a schematic view of an electroacoustic device  10  for an electroacoustic system  11  according to the present invention. The device  10  has an earpiece  12 . The earpiece  12  is adapted, with respect to its shape, to an individual ear canal of a person, not shown in detail here, in this exemplary embodiment. As an alternative, at least one external coating of the earpiece  12  may have an elastic configuration, as a result of which at least a partial adaptation of the surface of the earpiece  12  to the shape of an ear canal is made possible. The earpiece  12  may be arranged in an inner auricle shell and/or an ear canal entrance. The ear canal is at least partially, i.e., partially or completely, occluded by means of the earpiece  12 . 
     The device  10  has an external sound generator  13 . The external sound generator  13  is configured as an external microphone in this exemplary embodiment. When the earpiece  12  is used in an ear and/or an ear canal, the external sound generator  13  is directed away from an eardrum, which is not shown in detail here. The external sound generator  13  is directed outwards to receive an incoming signal, namely from acoustic ambient noises. The external sound generator  13  is arranged here, for example, on the surface of the earpiece  12 . The position of the external sound generator  13  makes it possible for the incoming signal to contain all spatial monaural information. Incoming acoustic signals are converted into electrical signals by means of the external sound generator  13 . 
     Furthermore, the device  10  has an internal sound generator  14 . In this exemplary embodiment, the internal sound receiver  14  is configured as an inner microphone. When the earpiece  12  is used in an ear and/or in an ear canal, the internal sound receiver  14  is facing an eardrum, which is not shown in detail here. The internal sound receiver  14  is directed inwards to detect a sound field in an ear canal section from the device  10  or from the earpiece  12  to the eardrum. The internal sound receiver  14  is arranged, for example, on the surface of the earpiece  12  here. Incoming acoustic signals are then converted into electrical signals by means of the internal sound receiver  14 . 
     The device  10  has a sound generator  15 . The sound generator  15  is arranged in the area of the internal sound receiver  14 . Furthermore, the sound generator  15  faces an eardrum, which is not shown in detail here, when the earpiece  12  is used in an ear and/or in an ear canal. The sound generator  15  is arranged, for example, on the surface of the earpiece  12  here. The sound generator  15  is directed inwards to radiate the outgoing signal in the ear canal section between the device  10  or the earpiece  12  and the eardrum. The sound generator  15  is configured to convert an electrical signal into an acoustic signal. 
     The device  10  has a signal processing device  16 . The external sound receiver  13 , the internal sound receiver  14  and the sound generator  15  are each connected to the signal processing device  16  by means of a wire. The signal processing device  16  is integrated into the earpiece  12  in this exemplary embodiment. As an alternative, the signal processing device  16  may also be arranged outside of the earpiece  12 , for example, in a housing for arranging behind an ear or in an auricle. Here, the signal processing device  16  is configured, for example, as a digital signal processing device  16 . The signal processing device  16  has analog-digital converters and digital-analog converters, which are connected to electroacoustic sound converters, especially to the external sound receiver  13 , to the internal sound receiver  14  and to the sound generator  15 . Calculations, modifications and/or corrections in relation to a signal incoming to the external sound receiver  13  and a signal outgoing from the sound generator  15  are carried out by means of the signal processing device  16 . 
     The signal processing device  16  has a correction unit  17 . A signal incoming to the device  10  or to the external sound receiver  13  is corrected and/or modified by means of the correction unit  17  in order to generate a signal outgoing from the device  10  or from the sound generator  15 . The correction unit  17  has a first correction filter A and a second correction filter B. 
     In this exemplary embodiment the signal processing device  16  is connected to an additional external signal source  18  by means of a wire. An additional external, especially acoustic, signal can be fed to the signal processing device  16  by means of the additional signal source  18 . The additional signal source may be configured as a consumer electronic unit, as a music source and/or as a communication device. 
     The device  10  or the earpiece  12  has a venting device  19 . The venting device  19  is configured as a venting channel in this exemplary embodiment. The venting device  19  makes possible a pressure equalization in case of a device  10  used in an ear canal. An air volume of an ear canal section between the earpiece  12  and the eardrum is connected to the surrounding area outside of the ear canal or ear by means of the venting device  19 . 
     The internal sound receiver  14  makes possible an estimation of a received signal and/or an acoustic signal at the eardrum, especially of a frequency response at the eardrum on the basis of any noise source in case of an ear canal at least partially occluded by the device  10  or the earpiece  12 . This estimation can be carried out by the mechanical-acoustic properties of the device  10  being assumed such that the frequency response at the position of the internal sound receiver  14  and the eardrum are identical. In this exemplary embodiment, the pressure at the eardrum is estimated by means of the pressure measured at the position of the internal sound receiver  14  using an electroacoustic model of the ear canal P. 
       FIG. 2  shows a schematic view of an electroacoustic model  20  of the electroacoustic device  10  according to  FIG. 1 . The device  10  or the earpiece  12  according to  FIG. 1  is modeled as a Norton- and/or Thevenin-equivalent electroacoustic velocity and/or pressure model, which is connected to the ear canal impedance according to the view in  FIG. 2 . 
     The source parameters are applied to an electroacoustic circuit model, which has a voltage source for the pressure or a current source for the velocity, an inner source impedance, the ear canal as a two-port network and the eardrum as the terminating impedance of the circuit. The source terms P S  for the pressure, Q S  for the velocity and Z S  for the impedance can be determined by means of measurements of the pulse responses, which are induced by the sources, when these are connected to various loads of known theoretical impedances. Therefore, these sources are assumed to be known and are part of the electroacoustic ear canal model P, which is dependent on the individual configuration of the device  10 . The abbreviation P L  in  FIG. 2  denotes the load pressure and the abbreviation Z L  denotes the load impedance. 
     The load impedance Z L  is determined with the following formula by means of the pressure P E  measured at the position of the internal sound receiver  14  and using the electroacoustic circuit model according to  FIG. 2   
     
       
         
           
             
               Z 
               L 
             
             = 
             
               
                 
                   Z 
                   S 
                 
                 ⁢ 
                 
                   P 
                   E 
                 
               
               
                 
                   P 
                   S 
                 
                 - 
                 
                   P 
                   E 
                 
               
             
           
         
       
     
     When the source impedance Z S , the load impedance of the ear canal Z L , especially in an area from the device  10  or the earpiece  12  to the eardrum, and the pressure P E  present in the interior of the ear canal and/or a pressure frequency response are known, the particle velocity U E  at the position of the internal sound receiver  14  is determined using the load impedance Z L  according to 
               U   E     =       P   E       Z   L             
and/or using the source impedance Z S  according to
 
     
       
         
           
             
               U 
               E 
             
             = 
             
               
                 
                   P 
                   S 
                 
                 - 
                 
                   P 
                   E 
                 
               
               
                 Z 
                 S 
               
             
           
         
       
     
     The relationship of a pressure at the eardrum P D  to the pressure P E  at the position of the internal sound receiver  14  is given according to estimation methods based on the energy density, as it is described, for example, in the following document:
     M. Hiipakka, M. Karjalainen and V. Pulkki, “ Estimating pressure at eardrum with pressure - velocity measurements from ear canal entrance ,” Application of Signal Processing to Audio and Acoustics, 2009. WASPAA &#39;09. IEEE Workshop on., 2009.   

     The pressure P E  measured at the position of the internal sound receiver  14  and the estimated particle velocity U E  are used to obtain the following estimation:
 
 P   D =√{square root over (| P   E | 2   +|U   E   ρc|   2 )}
 
ρ is the air density and c is the sound velocity here.
 
     The ratio of P E  to P D  is converted into the linear filter B, as a result of which the following equation is obtained:
 
 P   D   =P   EB .
 
     The acoustic properties of the ear canal, especially in an area between the device  10  at least partially occluding the ear canal and the end of the earpiece  12  facing the eardrum, are taken into account by means of the filter B during the modification or correction by means of the signal processing device  16  and the correction unit  17 , respectively. 
       FIG. 3  shows a schematic view of a logic circuit  21  of a signal processing device with the electroacoustic device  10  according to  FIG. 1  during a calibration. 
     The electroacoustic system  11 , the device  10  or the earpiece  12  can be calibrated in situ, i.e., in case of an at least partially occluded ear canal. The goal of the calibration is to obtain a predefined pressure and/or a predefined frequency response at the eardrum using a calibration routine. The filter A is intended for this. A signal outgoing from the device  10  or from the sound generator  15  can be generated by means of the filter A by modification of the incoming signal, which signal generates a target pressure and/or a target frequency response at the position of the internal sound receiver  14 . 
     Thus, the pressure P E  at the position of the internal sound receiver  14  corresponds to the target pressure P T,E  at the position of the internal sound receiver  14 :
 
 P   E   =P   T,E  
 
     The pressure P E  or target pressure P T,E  at the position of the internal sound receiver  14  is obtained on the basis of an ambient noise signal from a noise source  22 . The noise source  22  is outside of the ear and causes common ambient noises. 
     As is shown according to  FIG. 3 , the acoustic signal outgoing from the noise source  22  within the ear canal and in case of an ear canal at least partially occluded by means of the device  10  or the earpiece  12  is split into two partial signals  23 ,  24 . 
     The first partial signal  23  is a passage signal. A pressure frequency response and/or a passage pressure P HT , which is measured at the position of the internal sound receiver  14 , are associated with the first partial signal  23 . The second partial signal  24  is a device-released signal. The second partial signal  24  is generated and released by means of the sound generator  15  from the earpiece  12  in the direction of the eardrum. The second partial signal  24  is obtained by the signal incoming to the external sound receiver  13 , which is modified by means of the filtering by means of the first filter A and the second filter B and is subsequently released by means of the sound generator  15 . An outgoing pressure frequency and/or an outgoing pressure P EP  is associated with the second partial signal  24 . 
     The passage pressure P HT  and the outgoing pressure P EE  are measured for the calibration by means of the sound receivers  13 ,  14  using the noise source  22 , which is configured as a headphone in this exemplary embodiment, when the filters A and B are not applied. However, since the outgoing pressure P EP  cannot be measured independently of the passage pressure P HT , a total frequency response and/or a total pressure P tot  is introduced:
 
 P   tot   =P   EP   +P   HT .
 
     The total pressure P tot  is compared to the target pressure P T,E , taking the correction filter A into consideration:
 
 P   T,E   =P   HT   +P   EP   A=P   HT +( P   tot   −P   HT ) A.  
 
     After the first determination described above, a first correction filter A is thus calculated by means of the measured frequency responses and/or pressures P T,E , P HT  and P tot  as follows: 
     
       
         
           
             A 
             = 
             
               
                 
                   P 
                   
                     T 
                     , 
                     E 
                   
                 
                 - 
                 
                   P 
                   HT 
                 
               
               
                 
                   P 
                   tot 
                 
                 - 
                 
                   P 
                   HT 
                 
               
             
           
         
       
     
     This first correction filter A is determined within the framework of a first calibration. 
     A fine adjustment of the correction filter A can then be carried out. A predefined calibration signal is used to adapt the actual frequency response and/or the pressure P E  at the internal sound receiver  14  to the target pressure P T,E . In this exemplary embodiment, the calibration signal is configured as white noise. The calibration signal is released by the noise source  22 . The frequency response and/or the pressure P E  are measured by means of the internal sound receiver  14 . The correction filter A is adapted correspondingly on the basis of a deviation of the measured pressure P E  from the target pressure P T,E . The first correction filter A is adapted iteratively in case of a deviation of the measured pressure P E  from the target pressure P T,E  until a predefined convergence criterion is reached. 
     The target pressure P T,E  at the position of the internal sound receiver  14  must be known for the determination of the correction filter A or for achieving the acoustic transparency. Furthermore, the generated frequency response and/or the pressure P D  at the eardrum for a free ear canal and an at least partially occluded ear canal with an active and calibrated device  10  must be identical. The pressure P D  at the eardrum is consequently equated with the target pressure P T,D  at the eardrum:
 
 P   D   =P   T,D .
 
     A target model T is introduced in order to provide the frequency response and/or the pressure at the eardrum as an individual estimation for each person using the device  10 . 
     In this case, however, the frequency response and/or the target pressure P T,D  at the eardrum are not determined or estimated. Instead, the target frequency response and/or the target pressure P T,E  at the position of the internal sound receiver  14  in case of a free ear canal are estimated. 
     An electroacoustic circuit model, which has a Thevenin pressure source model P S  and a source impedance model Z S , is used for this. The source pressure P S  is estimated by means of the frequency response measured at the external sound receiver  13  and/or the pressure measured there, when an incoming signal is generated by the noise source  22 . The radiation of the source pressure P S  in the ear canal in the case of a free ear canal is estimated by means of the radiation impedance Z RAD  and the ear canal impedance Z L . 
     The individual ear canal impedance Z L , depending on the respective person, is determined by means of the above-mentioned measurements and calculations. However, no individual measurements and/or determinations are possible for the radiation impedance Z RAD . Therefore, an estimated value is used, which is based on a theoretical model and measurements with trial subjects, as is described, for example, in the following document:
     M. Hiipakka, T. Kinnari and V. Pulkki, “ Estimating head - related transfer functions of human subjects from pressure - velocity measurements ,” The Journal of the Acoustical Society of America, 2012.   

     Thus, the target frequency response and/or the target pressure P T,E  at the position of the internal sound receiver  14  in case of a free ear canal are obtained as follows: 
     
       
         
           
             
               P 
               
                 T 
                 , 
                 E 
               
             
             = 
             
               
                 P 
                 S 
               
               ⁢ 
               
                 
                   Z 
                   L 
                 
                 
                   
                     Z 
                     L 
                   
                   + 
                   
                     Z 
                     RAD 
                   
                 
               
             
           
         
       
     
     In this exemplary embodiment, the above-described calibration for determining the first correction filter A and the second correction filter B is carried out after each use of the device  10  or earpiece  12  in the ear or the ear canal. Changes on the basis of a deviating position of the device  10  or of the earpiece  12  in the ear canal or on the ear are taken into consideration as a result of this. An acoustic transparency with an especially high quality can be achieved as a result of this. After the calibration or during normal operation of the device  10  or of the earpiece  12 , the correction filters A and B remain unchanged according to this exemplary embodiment. As an alternative, an adaptive repositioning and/or recalibration of the correction filter A and/or B can be carried out, especially during the normal operation. 
     After the calibration, the first correction filter A is used to modify the incoming signal, as a result of which the outgoing signal or the outgoing pressure P E,P  is modified. Information about the path of transmission from the position of the internal sound receiver to the eardrum is taken into account by means of the second correction filter B during the modification of the signal incoming to the device  10  or during the generation of the outgoing signal. 
       FIG. 4  shows a schematic view of a logic circuit  25  with a signal processing device  16  of the electroacoustic device  10  according to  FIG. 1 . 
     During normal operation an ambient noise is received as an incoming acoustic signal by the external sound receiver  13 , converted into an incoming electrical signal and sent to the signal processing device  16 . The signal processing device  16  corrects and modifies the signal by means of the two correction filters A and B in order to adapt the frequency response and/or the pressure at the eardrum to the frequency response and/or the pressure at the eardrum in case of a free ear canal. In this exemplary embodiment, the same frequency response and/or the same pressure at the eardrum are generated as in case of a free ear canal because of the two correction filters A and B. 
     Such an acoustic transparency is made possible, since the incoming signal at the external sound receiver  13  contains all direction information. By contrast, the path of transmission from the inner auricle to the eardrum is independent of the incoming signal direction or sound direction both for the free and the at least partially occluded ear canal. 
     According to  FIG. 1  and  FIG. 4  a signal of an additional signal source in addition to the ambient noise, for example, from the noise source  22  according to  FIG. 3 , is fed to the device  10 . For example, the additional signal source  18  is configured as a consumer electronic unit and/or as an additional sound receiver for the device  10 . Depending on the purpose and/or type of signal source  18 , the additional signal is used to transmit information and/or to amplify the signal incoming to the device  10 . The frequency response and/or the pressure at the eardrum on the basis of the additional signal or the additional signal source  18  is modified by means of the correction filters A and/or B determined beforehand in this exemplary embodiment. On the basis of a correction by means of the correction filter B, the additional signal is modified such that undesired transmission effects of the ear canal in an area between an end of the device  10  or of the earpiece  12  facing the eardrum and the eardrum are attenuated and/or avoided. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.