Abstract:
A CIC hearing instrument and appertaining method are provided that improve feedback stability. Accordingly, the microphone inlet is located on the faceplate of the instrument at a position of least vibration. Furthermore, the receiver is located in the device such that its vibrating membrane is parallel to a plane calculated to include a line of minimal vibration on the faceplate and a center of gravity for the instrument.

Description:
BACKGROUND 
       [0001]    The present invention is directed to a completely-in-canal (CIC) hearing aid constructed to have a robust feedback stability. 
         [0002]    A typical CIC instrument can operate normally when its acoustic gain does not exceed 40 dB. If the acoustic gain of a CIC instrument gets increased, the frequency response of the instrument develops sharp peaks. After the gain of a CIC instrument exceeds a certain threshold, the instrument becomes unstable and begins to oscillate at a frequency of the highest peak of the frequency response. A typical CIC instrument comprises a shell, a faceplate, a battery, a hybrid, a microphone, and a receiver. 
         [0003]    The purpose of the receiver is to convert the electrical signals into an acoustic sound pressure. As a by-product of its operation, a receiver creates mechanical vibrations. A typical CIC receiver is shown on  FIG. 1 . Its construction is described in related art publications (e.g., U.S. Pat. No. 6,078,677), in which its FIG. 2 (corresponding to  FIG. 1  in the present application), shows a longitudinal section of an electroacoustic transducer  1 . 100 , wherein an actuator comprises an electric coil  1 . 31  which is connected via an electric line  1 . 32  extending through the lower case  1 . 4  to terminals  1 . 33  mounted on the outer surface of the housing  1 . 2 . Placed within a magnet housing  1 . 34  is a magnetic member  1 . 35 . An air gap  1 . 36  of the magnetic member  1 . 35  is aligned with an air gap  1 . 37  of the coil  1 . 31 . A U-shaped armature  1 . 40  has a first leg  1 . 41  attached to the magnet housing  1 . 34  and a second leg  1 . 42  extending into the aligned air gaps  1 . 36  and  1 . 37 . Attached to the end of the second leg  1 . 42  is the fork  1 . 21 . 
         [0004]    If an externally generated current is presented to the coil  1 . 31 , a force is exerted on the armature  1 . 40  by the magnetic field generated by the magnetic member  1 . 35 . As a result thereof, a displacement is generated in the longitudinal direction of the fork, thereby moving the diaphragm to generate a pressure wave. The cover  1 . 3  has an opening  1 . 46  through which the interior of the housing  1 . 2  between the cover  1 . 3  and the diaphragm  1 . 10  communicates with the outside world. Attached to the housing is a substantially cylindrical nozzle  1 . 47  to which, if desired, a flexible tube can be fastened for guiding pressure waves. 
         [0005]    This figure shows that the diaphragm  1 . 10  may have a layered structure. More in particular, the diaphragm  1 . 10  comprises a thin flexible foil  1 . 51  and a reinforcement layer  1 . 52  attached thereto, e.g. by gluing. The reinforcement layer  1 . 52  has a thickness exceeding that of the foil  1 . 51  and has a surface defining the central diaphragm portion  1 . 11 . The part of the foil  1 . 51  projecting beyond the reinforcement layer  1 . 52  defines the edge portion  1 . 12 . 
         [0006]    A simplified vibration model of a CIC receiver is shown in  FIG. 2  of the present application. It comprises a case  20 , a U-shaped armature  30  and a membrane  40 . The motor (not shown for simplicity of illustration) creates various forces  50  that cause the membrane  40  to vibrate: the force applied to the U-shaped armature  30  and the reaction force applied to the case  20 . The major reason for an unstable operation of a CIC instrument is the receiver vibrations that cause the CIC faceplate to radiate the sound pressure into the microphone. 
         [0007]    Therefore the receiver has to be isolated from direct contact with the shell or other CIC components inside a CIC instrument. As  FIGS. 3 and 4  illustrate, the receiver  100  of a typical CIC instrument is placed inside the CIC shell  12  and attached to the shell tip  14  with a flexible tube  66 . The tube  66  feeds the sound pressure, generated by the receiver  100 , into the ear of the user. The tube  66  also isolates the vibrations that the receiver  100  creates, from spreading into the CIC instrument. A receiver in a conventional CIC instrument also has a soft boot or studs  60  that prevents the receiver walls from forming a direct contact with CIC elements inside the shell  12 . When such a direct contact occurs, the CIC becomes unstable or its frequency response begins to comprise many sharp and undesirable peaks. 
         [0008]    A conventional CIC instrument performance is not consistent. Even if the same assembly worker builds two “identical” instruments, their performance would be quite different because the position of a receiver inside the shell is not fixed. The receiver can be moved and turned before it is fixed to its final position, and the worker can not replicate such a position even if the shell of the second instrument is exactly the same as that of the first instrument. 
         [0009]    A construction of a receiver and a hearing instrument is described in the related art U.S. Patent Publication No. 2005/0074138; this reference teaches how to build instruments with a higher consistency of performance. In the instrument disclosed, the virtual receiver position is chosen by using custom 3-D software before the shell is manufactured. Then, the real shell is produced by a stereo lithographic apparatus (SLA) process with all necessary features that will support the receiver in a designated place. The construction of the receiver and the supporting structures guarantee that the CIC instrument will operate without the feedback with the acoustic gain up to 40 dB. 
         [0010]    A typical construction of a CIC instrument  10  with an RSA receiver  100  is shown in  FIG. 5 , that comprises a faceplate  11 , shell  12 , microphone  13 , battery door  15  with battery  16 , hybrid  17 , and vent  18 . Such an instrument has a maximum gain limitation of 40 dB. However, a CIC instrument with an RSA receiver can be built with higher maximum stable gain by following special rules during its virtual assembly. 
       SUMMARY 
       [0011]    The present invention provides a superior construction of a CIC instrument with at least 10 dB higher feedback threshold than typical conventional CIC instruments. Accordingly, a CIC hearing instrument is provided, comprising: a shell; a microphone internal to the shell; a receiver that is suspended inside of the shell, the receiver having a membrane; and a faceplate having a microphone inlet hole whose center is located along a line of minimal vibrational sound pressure on the faceplate. 
         [0012]    Additionally, a method is provided for producing a CIC hearing instrument, comprising: providing a receiver and microphone within a hearing aid shell and a faceplate on top of the shell; determining a line of minimal vibrational sound pressure on the faceplate; and producing a microphone inlet hole within the faceplate, the hole having a center located along the line of minimal vibrational sound pressure. 
         [0013]    According to an embodiment, the receiver is arranged within the shell by first calculating a plane that passes through a line of minimal vibration on the shell and a calculated center of mass of the device. Then the receiver is placed so that its membrane is parallel to this calculated plane 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention is explained with respect to various preferred embodiments illustrated in the following drawings and described below. 
           [0015]      FIG. 1  is a pictorial illustration of a known CIC receiver; 
           [0016]      FIG. 2  is a pictorial illustration of a simple vibrational model of a CIC receiver; 
           [0017]      FIG. 3  is a pictorial illustration of a known CIC receiver with suspension elements; 
           [0018]      FIG. 4  is a pictorial illustration of a CIC receiver suspended inside of a CIC shell; 
           [0019]      FIG. 5  is a pictorial illustration of a construction of a CIC instrument; 
           [0020]      FIG. 6  is a pictorial illustration of a typical receiver vibration pattern caused by reaction forces of the receiver moving elements; 
           [0021]      FIG. 7  is a further pictorial illustration of a typical receiver vibration pattern caused by reaction forces of the receiver moving elements; 
           [0022]      FIG. 8  is a pictorial illustration of a typical vibration pattern of a CIC instrument caused by reaction forces of the receiver moving elements; 
           [0023]      FIG. 9  is a pictorial illustration of a typical distribution of a sound pressure, generated on a surface of a CIC faceplate, caused by the instrument vibrations; and 
           [0024]      FIG. 10  is a pictorial illustration of a preferred receiver orientation that minimizes the vibration-related sound pressure near the microphone inlet. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]      FIGS. 6 and 7  show a typical pattern of RSA receiver vibrations, which is caused by the vibrating U-shaped armature and a membrane. In these figures, the receiver  100  vibrates between a first  100  and second  100 ′ position. The vibrating receiver  100  causes the whole CIC instrument  10  to vibrate between a first  10  and second  10 ′ position, as is illustrated in  FIG. 8 . A typical CIC instrument will vibrate about its center of mass C. Putting such an instrument into the user&#39;s ear will affect the vibration pattern, but not a great deal, since the ear tissues are soft. 
         [0026]    The vibration of a CIC instrument  10  will cause the faceplate  11  to vibrate as well. The faceplate  11  has a microphone inlet  19  which picks up the sound pressure and feeds it into the microphone  13 . In addition to a useful sound pressure (speech, music, etc), the microphone  13  will pick-up the vibrational sound pressure that the faceplate  11  creates due to its own mechanical vibrations. A possible distribution of a vibrational sound pressure on the faceplate  11  is shown in  FIG. 9 , which indicates two areas of maximum vibrational sound pressure—for positive normal displacements and for negative normal displacements. Also lines of equal sound pressure  11   a  are shown: the sound pressure will be the highest at the centers of the areas. The line of a minimal vibrational sound pressure divides the areas of maximum sound pressure for positive and negative normal displacements. 
         [0027]    If the microphone inlet  19  is positioned close to the center of areas of maximum vibrational sound pressure, the feedback performance of a CIC instrument would be the worst, as is illustrated by  FIG. 9 . As shown in this figure, the faceplate  11  comprises lines of equal vibrational sound pressure  11   a,  different halves of the faceplate  11  are vibrating 180° out of phase with each other, where an area a has a maximum vibrational sound pressure for positive normal displacement, and area b has a maximum sound pressure for negative normal displacement. As can be seen, in this worst placement configuration, the microphone inlet  19  is located at precisely the area b at which the vibrational sound pressure is the greatest. An axis  11   b  is defined which is a line of minimal vibration sound pressure. Although it is illustrated in  FIGS. 9 and 10  as a straight line, it could, in fact, be a curved line, depending on the particular geometry and materials used (e.g., if flexible). In the preferred embodiment, the faceplate is rigid and thus the axis  11   b  is generally straight. A straight line can be calculated from the curved line, if need be. 
         [0028]      FIG. 10  illustrates the placement of the microphone inlet  19  on the axis of minimal vibration  11   b,  which therefore creates a substantial improvement in the feedback stability of a CIC instrument. According to an embodiment of the invention, the placement of the microphone inlet  19  on the faceplate  11  is determined as follows. An ellipse  11   d  is determined that approximates the oval shape of the faceplate  11 , and its major axis  11   b  is calculated. The center of gravity C of the device is then determined, and a plane  11   c  is calculated that includes the major axis  11   b  of the ellipse as well as the calculated center of gravity C. Once the center of gravity C and the plane  11   c  is calculated, the receiver  100  can be positioned so that its membrane  40  is parallel to the plane  11   c.  This helps to minimize the vibrational effect at the microphone inlet  19 . It is also possible to perform the calculation of the center of gravity C in an iterative manner in the situation where the receiver is included in the center of gravity calculations. 
         [0029]    The above-described conditions produce an optimal balance for feedback performance, and although modifications can be made, it will generally result in tradeoffs in device performance. Although theoretically the above analysis could be applied one time to an entire family based on a design, variations in CIC instruments are significant enough so that, ideally, the analysis is performed for each instrument. It could be possible to classify CIC instruments into various groups by shape, and then to specify a typical position for the receiver and microphone inlet. The resultant improvements can improve the feedback effects by up to 10 dB. 
         [0030]    For the purposes of promoting an understanding of the principles of the invention, reference has been made to the preferred embodiments illustrated in the drawings, and specific language has been used to describe these embodiments. However, no limitation of the scope of the invention is intended by this specific language, and the invention should be construed to encompass all embodiments that would normally occur to one of ordinary skill in the art. 
         [0031]    The present invention may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of hardware components configured to perform the specified functions. The particular implementations shown and described herein are illustrative examples of the invention and are not intended to otherwise limit the scope of the invention in any way. For the sake of brevity, conventional structural and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent exemplary functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. Moreover, no item or component is essential to the practice of the invention unless the element is specifically described as “essential” or “critical”. Numerous modifications and adaptations will be readily apparent to those skilled in this art without departing from the spirit and scope of the present invention. 
       TABLE OF REFERENCE CHARACTERS 
       [0000]    
       
           1 .xx related art patent reference characters 
           10  CIC hearing aid/instrument 
           11  faceplate 
           11   a  lines of equal vibrational sound pressure 
           12  CIC shell 
           13  microphone 
           14  CIC shell tip 
           15  battery door 
           16  battery 
           17  hybrid 
           18  vent 
           19  microphone inlet 
           20  case 
           30  u-shaped armature 
           40  membrane 
           50  motor forces 
           60  stud 
           62  stopper ring 
           64  spline 
           66  tube 
           100  receiver