Abstract:
A hearing aid has a directional receiving system with a more efficient direction into the patient&#39;s ear than away from the patient&#39;s ear.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from Provisional Serial No. 60/279,163, filed Mar. 27, 2001, which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Hearing aids are typically designed to fit snugly into the outer ear with a custom-molded earmold or shell. This snug fit achieves two goals. First, a device that is custom-fitted to the ear remains securely in the ear and is less prone to coming loose than one that is not custom fitted. Second, a tight fit decreases acoustic feedback, which is the cause of whistling in hearing aids. There are drawbacks, however, to such a tight fitting hearing aid. A tight fit leads to the uncomfortable feeling of a plugged ear, and leads to an undesirable “occlusion effect,” i.e., the amplification of one&#39;s own voice caused by plugging the ear. Although some hearing aids have been designed so as not to occlude the ear, such aids are limited by acoustic feedback and the amount of amplification that they can provide to the user.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention includes a hearing aid with a directional receiver system to increase the amount of amplification that can be provided to a hearing-aid user without providing whistling. Unlike current hearing aids that use receivers (i.e., miniature loudspeakers that provide the amplified acoustic signals to the user) that are omnidirectional in that they radiate sound approximately equally well in all directions, the hearing aid of the present invention uses a directional receiver that radiates more sound power in one direction than in other directions.  
           [0004]    By arranging a directional receiver so that the most efficient direction points into the ear, increased sound power is delivered to the ear without a proportional increase in the amount of acoustic feedback. Other features and advantages become apparent from the following detailed description, drawings, and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a side view of a behind-the-ear hearing aid showing two displaced sound tubes.  
         [0006]    [0006]FIG. 2 is a block diagram showing processing of a signal received from a hearing aid microphone.  
         [0007]    [0007]FIG. 3 is a diagram illustrating a normalized acoustic radiation pattern. 
     
    
     DETAILED DESCRIPTION  
       [0008]    In one implementation of the present invention, as shown in FIG. 1, a behind-the-ear style hearing aid  10  has a housing  20  and two attached acoustic tubes  12 ,  14  extending away from housing  20  for transmitting sound to a patient&#39;s ear canal. At the end, away from the housing, acoustic tubes  12 ,  14  are connected to respective receivers  16 ,  18  that can be driven by independent electrical signals. Housing  20  houses a microphone and acoustic signal processing. Tubes  12 ,  14  have equal length but are displaced relative to one another so that the ends at the entrance to the ear canal and the ends at the hearing aid housing are each spaced apart by a distance d (not zero or substantially zero).  
         [0009]    A microphone  24  (located in housing  20 ) provides a signal that is processed as indicated in the block diagram in FIG. 2. The microphone provides a signal to known hearing aid signal processing that includes frequency shaping, amplification, compression, and other known processing techniques, which are lumped together in a “Hearing Aid Processing” block  26 . The processed signal  28  is then split into two components at a node  30 . A first component  32  drives receiver  18  directly. A second component  34  is delayed in a delay block  36  and inverted by an inverter  38  before driving receiver  16 .  
         [0010]    With this arrangement of receivers, sound tubes, and signal processing, and with an internal delay equal to d/c (where c is the speed of sound), the resulting normalized acoustic radiation pattern will be similar in shape to that shown in FIG. 3. There will be an on-axis direction (0°) in which radiation will be strongest due to the reinforcement of acoustic signals, while in the direction 180° opposite there is a null due to cancellation of the acoustic signals. The arrangement that delivers maximal power into the ear has the tips of the two tubes on a line pointing into the ear with tube  12  proximal and tube  14  distal.  
         [0011]    Due both to the termination of the tubes into the open ear canal and to the gradient nature of the processing, the signal that reaches the eardrum from this hearing aid will be strongly high-passed. This effect can be compensated to some extent by prior linear filtering (which can be included as part of the hearing aid processing in the block).  
         [0012]    Other configurations that make use of the same principles can be envisioned. For example, it is possible to increase the degree of directionality by employing more than two receiver/sound tube combinations. In addition, frequency-dependent processing can be used to replace the wide band delay and inversion described above.  
         [0013]    Having described an embodiment of the present invention, modifications can be made without departing from the scope of the invention as defined by the appended claims. For example, the hearing aid can be occluding or non-occluding.