Patent Abstract:
There is provided a method for monitoring a hearing device having an electroacoustic output transducer worn at a user&#39;s ear or in a user&#39;s ear canal, the method includes the steps of measuring the electrical impedance of the output transducer; analyzing the measured electrical impedance of the output transducer in order to evaluate the status of the output transducer and/or of an acoustical system cooperating with the output transducer; and outputting a status signal representative of the status of the output transducer and/or of the acoustical system cooperating with the output transducer.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for monitoring a hearing device comprising an electro-acoustic output transducer worn at a user&#39;s ear or in a user&#39;s ear canal. The invention also relates to such a hearing device having self-monitoring function. According to another aspect, the invention relates to a method for adjusting a behind-the-ear hearing device and also to such an adjustable behind-the-ear hearing device. 
     2. Description of Related Art 
     Ear-worn hearing devices, such as hearing aids (which have an integrated microphone system) or wireless systems (which comprise a remote audio signal source, such as a remote microphone, and an ear-piece receiver) usually comprise an electro-acoustic output transducer (loudspeaker) which is located in or at least close to the ear canal. This applies particularly to in-the-ear (ITE) or completely in-the-canal (CIC) systems. However, also behind-the-ear (BTE) systems have a tubing extending from the loudspeaker (which in this case is located behind the ear) into the ear canal. A frequent problem of such ear-worn hearing devices is that the performance of the loudspeaker may be significantly deteriorated due to blocking with ear wax (cerumen) from the ear canal. 
     It is known to use special wax filters in order to protect the loudspeaker for preventing the loudspeaker from getting blocked by wax. However, none of these wax filters is capable of providing for a full protection from wax blocking. 
     If the loudspeaker performance is deteriorated by wax blocking, the user may not immediately notice this. This may be particularly true for systems used by children, since they usually have much more difficulty in noticing and communicating problems regarding the hearing device. 
     EP 1 276 349 B1 relates to a hearing aid with a self-test capability, wherein the hearing-aid automatically undergoes a self-test procedure for determining whether the hearing aid comprises a defect. The hearing aid is capable to indicate the presence and the type of defect to the user, for example, on the display of a programming device connected to the hearing aid for service purposes. During the self-test procedure it is checked whether each of the hearing aid microphones produces a signal. From the absence of such signal it is concluded that the input port to the respective microphone has been occluded by ear wax. 
     It is one object of the invention to provide for a method for monitoring a hearing device comprising an electio-acoustic output transducer worn at a user&#39;s ear or in a user&#39;s ear canal, by which method it should be enabled to monitor the acoustic performance of the output transducer in a simple and efficient manner. In addition, such hearing device having a monitoring function should be provided. 
     It is a further object of the invention to provide for a method for adjusting a behind-the-ear hearing device comprising an electroacoustic output transducer connected to a tubing ( 26 ) extending into a user&#39;s ear canal. In addition, such a hearing device should be provided. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided a method comprising the steps of measuring an electrical impedance of said output transducer; analyzing the measured electrical impedance of the output transducer in order to evaluate a status of the output transducer and/or an acoustical system cooperating with the output transducer; and outputting a status signal representative of the status of the output transducer and/or the acoustical system cooperating with said output transducer. Also, in accordance with first aspect, a hearing device is provided with self-monitoring function, comprising an electroacoustic output transducer to be worn at or in a user&#39;s ear canal, means for measuring an electrical impedance of said output transducer, means for analyzing said measured electrical impedance of said output transducer in order to evaluate the status of the output transducer and/or an acoustical system cooperating with the output transducer, and means for outputting a status signal representative of the status of the output transducer and/or the acoustical system cooperating with said output transducer. 
     According to a second aspect of the invention there is provided a method for adjusting a behind-the-ear hearing device having an electroacoustic output transducer connected to a tubing extending into a user&#39;s ear canal, involving the steps of measuring an electrical impedance of said output transducer, analyzing the measured electrical impedance of the output transducer to determine at least one parameter selected from a length of the tubing and a diameter of the tubing, and adjusting operation parameters of the hearing device according to the at least one parameter determined to optimize an acoustical performance of said hearing device. Also, in accordance with second aspect, a hearing device is provided having an electroacoustic output transducer connected to a tubing adapted for extending into a user&#39;s ear canal, means for measuring an electrical impedance of the output transducer, means for analyzing the measured electrical impedance of the output transducer in order to determine at least one parameter selected from a length of said tubing and a diameter of said tubing, and means for providing a signal representative of the at least one parameter for adjusting operation parameters of the hearing device to optimize acoustical performance of the hearing device. 
     The invention is generally beneficial in that, by measuring and analyzing the electrical impedance of the output transducer, the status of the output transducer and/or of an acoustical system cooperating with the output transducer, such as a tubing of a BTE hearing device, may be evaluated in a simple and efficient manner. According to one aspect, thereby it is enabled to automatically and immediately recognize when the output transducer or an acoustical system cooperating with the output transducer is blocked by ear wax or when the output transducer is damaged. According to another aspect, thereby the length and/or diameter of the tubing of a BTE hearing device can be automatically determined in a simple manner, and the thus determined length and/or diameter of the tubing can be used to optimize the operation parameters of the hearing device according the determined length and/or diameter of the tubing in order to optimize the acoustical performance of the hearing device. 
     These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a first embodiment of a hearing device according to the invention; 
         FIG. 2  is a block diagram of a second embodiment of a hearing device according to the invention; 
         FIG. 3  is an example of how the electrical impedance of the output transducer of a hearing device according to the invention may be measured; 
         FIG. 4  shows schematically the set-up for the test measurements of  FIGS. 5 and 6 ; 
         FIG. 5  is a plot of the voltage measured at the resistor of  FIG. 4  as a function of frequency obtained in test measurements with the set-up of  FIG. 4  for different obstruction levels of the loudspeaker; and 
         FIG. 6  is a plot of the acoustic output level curve of the loudspeaker measured with the set-up of  FIG. 4  in a 1.4 cc coupler for different loudspeaker obstruction levels. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram of a first example of a hearing device for which the invention can be used, wherein the hearing device is a hearing aid  10  which comprises a microphone arrangement  12  (which may consist of two spaced-apart microphones for enabling acoustic beam forming capability), a central processing unit  14  for processing the audio signals produced by the microphone arrangement  12 , a power amplifier  16  for amplifying the processed audio signals from the central processing unit  14 , and a loudspeaker  18  for stimulating the user&#39;s hearing with the processed amplified audio signals from the microphone arrangement  12 . The hearing aid  10  could be of the ITE or CIC type, in which cases the loudspeaker  18  would be located in the ear canal of the user. 
     The loudspeaker  18  may cooperate with an acoustical system  20  located downstream of the loudspeaker  18 , which may comprise, for example, a wax filter  22 , acoustical filters  24  and some kind of tubing  26 . Such tubing  26  will have a significant length if the hearing aid  10  is of the BTE type, in which case the loudspeaker, together with the hearing aid  10 , will be located behind the ear, while the tubing  26  extends into the ear canal. 
       FIG. 2  is a block diagram of an alternative embodiment of a hearing device, wherein the hearing device is a wireless ear-piece  110  which represents the receiver unit of a wireless audio system and which receives audio signals from a remote transmission unit  143  via a wireless audio link  145 . 
     The transmission unit comprises a microphone arrangement  144  (which may consist of two or more spaced-apart microphones for enabling acoustic beam forming capability), an audio signal processing unit  146  for processing the audio signals from the microphone arrangement  144 , a transmitter  148  and an antenna  150 . Usually the audio link  145  will be an FM link. 
     The receiver unit  110  comprises an antenna  152 , a receiver  154  for recovering the audio signals from the signal received at the antenna  152 , a central processing unit  114  for processing the received audio signals, a power amplifier  116  for amplifying the processed audio signals, and a loudspeaker  118 . As in the example of  FIG. 1 , the loudspeaker  118  may cooperate with an acoustical system located downstream of the loudspeaker  118 , for example, a wax filter  22 . As in the case of  FIG. 1 , the loudspeaker  118  will be located in or at the ear canal. The loudspeaker  118  may be integrated into the receiver unit  110 , as shown in  FIG. 2 , or it may be mechanically and electrically connected thereto. 
     Both in the embodiment of  FIG. 1  and the embodiment of  FIG. 2  an analyzer unit  30  is provided which may be activated by the central processing unit  14 ,  114  and which serves to measure the electrical impedance as a function of frequency of the loudspeaker  18 ,  118  and to provide the corresponding measurement result to the central processing unit  14 ,  114  in order to enable the central processing  14 ,  114  to produce a status signal representative of the status of the loudspeaker  18 ,  118  and/or the acoustical system  20 ,  120  cooperating with the loudspeaker  18 ,  118 . The measured electrical impedance as a function of frequency of the loudspeaker  18 ,  118  provided by the analyzer unit  30  is evaluated in the central processing unit  14 ,  114  in order to generate the respective status signal. 
     According to one embodiment, an acoustic alarm signal may be produced by the central processing unit  14 ,  114  with the help of the loudspeaker  18 ,  118  in order to provide the user with an acoustic alarm. Such acoustic alarm may comprise an alarm tone and/or a voice message. 
     According to an alternative embodiment, the status signal may be transmitted from the central processing unit  14 ,  114  to a remote device  32  via a wireless link  34  which possibly is an inductive link utilizing an inductive antenna  38  included in the remote device  32  and an inductive antenna  36  connected to the central processing unit  14 ,  114 . The remote device  32  further includes a signal processing unit  40  for processing the signals received by the antenna  38  and a display  40  for displaying the alarm signal received via the inductive link  34 , which in this embodiment will be an optical alarm signal rather than an acoustic alarm signal. 
     The remote device  32  could be used by the user of the hearing device  10 ,  110 , or, in particular in the case of  FIG. 2 , it could be used by the person using the transmission unit  143 , for example, the teacher in a classroom of pupils using the receiver unit  110 . In this case, the remote device  32  could be functionally integrated within the transmission unit  143 . 
     The inductive link  34  may be bidirectional link. In this case, transmission of the status signal from the hearing device  10 ,  110  may be initiated by receipt of a polling command at the hearing device  10 ,  110  transmitted from the remote device  32 . Thereby, for example, the teacher in the classroom may check whether the loudspeaker  118  used by each pupil works properly. In addition, the bidirectional link  34  may serve to monitor also other components of the system, such as battery status, status of the audio link  145 , etc. 
     According to an alternative embodiment, rather than being initiated by receipt of a polling signal, measurement of the electrical impedance of the loudspeaker  18 ,  118  and the subsequent analysis of the measured electrical impedance will be repeated in regular intervals. 
     Preferably, the measured electrical impedance as a function of frequency will be analyzed by comparing the measured electrical impedance to reference data stored in the hearing device  10 ,  110 . Such reference data may be generated in the manufacturing process of the hearing device  10 ,  110 . Preferably the resonance frequency and/or the quality factor of the loudspeaker  18 ,  118  are analyzed by measuring the electrical impedance as a function of frequency. Preferably the status signal will be provided as all alarm signal if the difference between the actually measured electrical impedance data and the stored reference data exceeds a predetermined threshold, wherein the magnitude of the difference between the measured data and the stored reference data may be taken as a measure of the degree of disturbance of the loudspeaker  18 ,  118 , for example of the degree of the mechanical obstruction of the loudspeaker  18 ,  118  by ear wax. 
     The evaluation of the status of loudspeaker  18 ,  118  and/or the acoustical system  20 ,  120  cooperating with the loudspeaker  18 ,  118  may include an evaluation of whether the loudspeaker  18 ,  118  is working according to specification. 
     Preferably such evaluation will include a check of whether the loudspeaker is still working properly or whether it is out of order. 
     In the case of a BTE hearing aid the system will include a tubing  26  extending from the loudspeaker  18  into the user&#39;s ear canal. The length and/or the diameter of such tubing  26  can be selected individually by the fitter. If the length/diameter of the tubing  26  is known, the acoustical performance of the BTE hearing aid can be optimized. Due to the acoustical coupling of the tubing  26  to the loudspeaker  18  it is possible to estimate from the measured electrical impedance of the loudspeaker  18  the length/diameter of the tubing  26  used for each BTE hearing aid  10 . With this knowledge, it is possible to optimize the acoustical performance of the hearing device automatically by optimizing the setting the operation parameters of the hearing aid according to the determined length/diameter of the tubing  26 , eliminating therefore the need for the fitter to enter the length/diameter data into the computer (not shown) for a fine tuning procedure, thus saving time and avoiding possible errors. To this end, the central processing unit  14  of the hearing aid  10  may provide for a signal representative of the determined length/diameter of the tubing  26 , which signal is supplied to the fitting computer. 
     In addition to evaluating the length/diameter of the tubing  26  from the measured electrical impedance of the loudspeaker  18  it is also possible to evaluate whether the end of the tubing  26  suffers from a mechanical obstruction, for example by ear wax. 
     An example of how the measurement of the electrical impedance of the loudspeaker  18 ,  118  can be done by the analyzer unit  30  as given in  FIG. 3 . According to  FIG. 3 , the voltage on a serial resistor  60  located between the ground and the loudspeaker  18  is measured by voltmeter  62 . For such an arrangement the voltage curve (i.e. the voltage as a function of frequency) on the resistor  60  becomes the image of the impedance curve of the loudspeaker  18 . The electric impedance—and hence the voltage measured by the voltmeter  62 —will be different depending on whether the loudspeaker is open or blocked. Even if the loudspeaker  18  is only partly blocked (resulting in a relatively small acoustic attenuation), a change in voltage will be observed. 
     Test measurements have been performed with the set-up of  FIG. 4 , wherein the resistor  60  had a resistance of 22 Ohms, the loudspeaker  18  had a resistance of 260 Ohms and the acoustic output level measurements were performed in a 1.4 cc coupler with perfect sealing. 
       FIG. 5  shows the voltage measured at the resistor  60  as a function of frequency for different levels of obstruction, namely for totally closed filter (close acoustic output, labeled “close”), different intermediate levels of obstruction (partly closed acoustic output, labeled “Half  1 ” to “Half  4 ”, measurement without filter (open acoustic output, labeled “Nofilter”) and measurement with filter (open acoustic output, labeled “Wsfilter”). The loudspeaker  18  was fluid damped. 
     According to  FIG. 5 , different voltage levels are obtained for different obstruction levels of the loudspeaker  18 ,  118 . The voltage difference is obviously the largest at the resonance frequency of the loudspeaker  18 ,  118  (in the present case about 3,200 Hz). In the case of small obstruction the quality factor decreases due to the parasitic acoustical resistance. For a totally blocked filter, the air volume between the loudspeaker  18  and the “stopper” creates a compliance (acoustic capacitor) in parallel with the standard compliance of the loudspeaker diaphragm. If the acoustic resistor is replaced by a compliance, the quality factor increases, but the resonance frequency also increase to about 4,000 Hz. 
       FIG. 6  shows the acoustic output level of the loudspeaker  18  measured in a 1.4 cc coupler as a function of frequency for the various obstruction levels of  FIG. 5 . 
     According to one embodiment, the resonance frequency of the loudspeaker in free space is stored in the hearing device  10 ,  110  during the manufacturing process. Later, when the hearing device  10 ,  110  is operated, the analyzer unit  30  generates the stored resonance frequency and measures the voltage on the resistor  60  at this frequency. If the measurement shows too much of a difference, an alarm signal is created, as already explained above, for example, telling the user that the loudspeaker is blocked and should be cleaned. 
     While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.

Technology Classification (CPC): 7