Abstract:
The low frequency efficiency of a hearing instrument receiver can be improved by increasing the unoccupied rear volume. The receiver may be configured with one or more motor and diaphragm assemblies. The receiver may also be fabricated using multiple, conventional receivers with an added housing to create the increased, unoccupied rear volume.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to and claims the benefit of commonly-owned U.S. Provisional Patent Application Ser. No. 61/056,996, filed May 29, 2008, incorporated herein by reference. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    A conventional hearing instrument receiver has a motor that converts an input signal to mechanical energy that moves a diaphragm suspended within the receiver housing. The diaphragm divides the interior volume of the housing into volumes in front of and behind the diaphragm, i.e., the “front volume” and the “rear volume.” A receiver tube connected to the front volume conveys the sound pressure created by the movement of the diaphragm to the ear canal of the user. 
         [0003]    The efficiency of a hearing instrument receiver in a region of frequencies below 3 kHz, e.g., 500-1500 Hz, can be improved by increasing the unoccupied portion of the rear volume relative to the front volume, and providing a port in the rear volume and connecting a second receiver tube to that port. The diameter and length of the second receiver tube are chosen to achieve resonance at the frequencies of interest. 
         [0004]    The receiver may employ at least one, or two or more motor and diaphragm assemblies. This receiver may be used in open-fit hearing instruments, i.e., one where the ear canal is not occluded, as well as in other devices such as cellular telephones and earphones. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a cross-sectional drawing of a receiver with an increased unoccupied rear volume; 
           [0006]      FIG. 2  is a cross-sectional drawing of the receiver of  FIG. 1  with a second receiver tube located partially within the rear volume; 
           [0007]      FIG. 3  is a cross-sectional drawing of a receiver with a subdivided rear volume; 
           [0008]      FIGS. 4-7  are cross-sectional drawings of a receiver with two motors; 
           [0009]      FIGS. 8-10  are cross-sectional drawings of a receiver with two motors and subdivided front and rear volumes; and 
           [0010]      FIGS. 11-12  are cross-sectional drawings of a receiver with two motors, comprising individual single-motor receivers and an added housing rear volume. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0011]    A hearing instrument receiver comprising a single motor is shown in  FIG. 1 . A suitable motor is the electromagnetic motor illustrated in U.S. Pat. No. 7,362,878, incorporated by reference herein, and comprises magnets, coils, and an armature. Alternatively, the receiver could employ a piezoelectric or an electrostatic motor, or a motor using some other technology. 
         [0012]    A Receiver with an Increased Rear Volume 
         [0013]    The receiver in  FIG. 1  has a housing  10  which holds a motor  20 . Although not illustrated in the figures, the motor  20  is rigidly supported within the housing  10  and would typically have electrical connections on the outside of the housing  10 . 
         [0014]    The motor  20  imparts force to a drive rod  22  that moves a diaphragm  30 . The diaphragm  30  is supported within the housing  10  by a flexible support  32  such as a plastic film. One suitable material for the film is Mylar, a product of E. I. du Pont de Nemours and Company. 
         [0015]    Together, the diaphragm  30  and the flexible support  32  divide the interior volume of the housing into two volumes: a front volume  40  and a rear volume  42 . The rear volume  42  comprises the motor  20  and an unoccupied rear volume  44 . A first output port or spout  50  connects the front volume  40  to a first receiver tube  52  and a second output port or spout  60  connects the rear volume  42  to a second receiver tube  62 . 
         [0016]    Acoustic Resonance of the Receiver 
         [0017]    The unoccupied rear volume  44  and the second receiver tube  62  form an acoustic resonator, where the unoccupied rear volume  44  may be characterized as an acoustic compliance and the air in the second receiver tube  62  may be characterized as an acoustic mass. Since greater efficiency is sought in a band of low frequencies, i.e., below 3 kHz, the acoustic resonator (the unoccupied rear volume  44  of the receiver and the second receiver tube  62 ) are tuned for the center frequency of the desired band. Accordingly, the size of the unoccupied rear volume  44  relative to the front volume  40  and the length and inside diameter of the second receiver tube  62  are selected to achieve acoustic resonance at that center frequency. 
         [0018]    The frequency of an acoustic resonator is governed by the following equation: 
         [0000]    
       
         
           
             f 
             = 
             
               1 
               
                 2 
                  
                 
                     
                 
                  
                 π 
                  
                 
                   
                     
                       M 
                       A 
                     
                     · 
                     
                       C 
                       A 
                     
                   
                 
               
             
           
         
       
     
         [0000]    where: 
         [0019]    f is the frequency of the acoustic resonator; 
         [0020]    M A  is the acoustic mass; and 
         [0021]    C A  is the acoustic compliance. 
         [0000]    (See, U.S. Pat. No. 5,261,006, incorporated herein by reference, col. 3, line 35, through col. 4 line 6.) 
         [0022]    The product of acoustic mass and acoustic compliance can be determined given the desired center frequency. The necessary volume of the unoccupied rear volume  44  of the receiver and the dimensions of the second receiver tube  62  to achieve the product of acoustic mass and compliance that yields a center frequency of f may then be derived utilizing the formulas for acoustic compliance and mass. (See, e.g., Leo L. Beranek, “Acoustics,” pp. 128-33 (Acoustical Soc. of America 1954) (1986)). In practice, the unoccupied rear volume  44  may be sized to approximately six times the size of the front volume  40 , and possibly fifteen to twenty times that volume. 
         [0023]    For example, the low frequency band of interest may be 500-1500 Hz and therefore the center frequency of that band would be 1000 Hz. Once the size of the unoccupied rear volume  44  is fixed, the acoustic compliance can be determined and this in turn will dictate the required acoustic mass to achieve acoustic resonance at 1000 Hz. The variables of length and inside diameter of the second receiver tube  62  are then chosen to provide the necessary acoustic mass. Typically, for a receiver employed in an open-fit hearing instrument and the size of its unoccupied rear volume, the inside diameter of the second receiver tube will be 0.5-2.0 mm and its length will be 5-20 mm. 
         [0024]    Where space is at a premium and the required length of the second receiver tube exceeds the available space, the second receiver tube may be partially insert into rear volume. The receiver in  FIG. 2  has a port  160  and a second receiver tube  162  partially located within the rear volume  42 . A flange  164  may be provided for structural support for the second receiver tube  162  in this configuration. 
         [0025]    A Receiver with a Subdivided Rear Volume 
         [0026]    A second hearing instrument receiver comprising a single motor is shown in  FIG. 3 . In addition to the components described with respect to the receiver of  FIG. 1 , this device has a barrier or dividing wall  12  with a passageway  14 , subdividing the rear volume  42 . Such a configuration may be created by taking a conventional hearing instrument receiver and adding a separate housing  16  (the portion of the housing  10  above the dashed line). A passageway  14  or opening is then made in the conventional receiver housing to allow the sound pressure to travel into the separate housing  16 . 
         [0027]    Dual Motors 
         [0028]    A receiver employing two motors  120  and  220  is shown in  FIGS. 4-7 . The motors  120  and  220  drive two diaphragms  130  and  230  with drive rods  122  and  222 , respectively. The diaphragms  130  and  230  together with a barrier  210  delineate the front volume  140 , while the rear volume  142  is behind the diaphragms  130  and  230  and the barrier  210 . The unoccupied rear volume  144  can be seen in the cross-sectional end view of  FIG. 5  and the external end view of  FIG. 7 . 
         [0029]    In  FIG. 4 , the diaphragms  130  and  230  are positioned in opposition. Alternatively, the motors could be positioned side-by-side, with the two diaphragms in the same plane. Depending on the space available, the rear volume could be positioned above, below, around, or to the side of the motors. 
         [0030]    Subdivided Front and Rear Volumes 
         [0031]    The receiver illustrated in  FIGS. 8-10  employ barriers in the front and rear volumes  140  and  142 . In  FIG. 8 , a horizontal barrier  210  between the diaphragms  130  and  230  subdivides the front volume  140 . A vertical barrier  212 , having passageways  214 , subdivides the rear volume  142  creating an unoccupied rear volume  144 . As desired, the receiver may use either or both of the horizontal and vertical barriers  210  and  212 . 
         [0032]    The receiver of  FIGS. 8-10  may be fabricated from two conventional receivers  300  and  310 , positioned together as shown in  FIGS. 11 and 12 . A housing  400  is attached to the two receivers  300  and  310  to create a rear volume  402 . Passageways  302  and  312  are provided in the receivers  300  and  310 , respectively, to allow the passage of sound.