Abstract:
A hearing aid includes a speaker in a tip that is located in an ear canal. The tip includes a coupling, a retainer that mechanically engages the coupling, and a sleeve axially surrounding the retainer. The retainer attenuates lower frequencies than are attenuated by the sleeve. The sleeve is preferably a foam rubber and the retainer is preferably a composite material. A flange on the retainer reflects sound back into the sleeve for additional attenuation. It has been discovered that operation is improved if the outside diameter of the sleeve and the outside diameter of the retainer are in the ratio of approximately 1.75:1.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present patent application is a continuation of earlier-filed, non-provisional, co-pending parent patent application Ser. No. 12/001,247, filed Dec. 11, 2007, and the benefit of the Dec. 11, 2007 filing date of such earlier-filed patent application Ser. No. 12/001,247 is hereby claimed. 
     
    
       [0002]    This invention relates to hearing aids and, in particular, to a tip for insertion in the ear canal, wherein the tip significantly attenuates sound that would otherwise be transmitted through the canal. 
       BACKGROUND TO THE INVENTION 
       [0003]    A “speaker” generates sound from an electrical signal. In the hearing aid art, one often encounters the term “receiver” for such a device, which reads strangely to the uninitiated. “Electroacoustic transducer” is clumsy and pedantic. Thus, “speaker” is the term used for describing this invention. 
         [0004]    A human ear canal is a narrow, irregular, tubular structure, approximately 25 mm in length. Coupling amplified sound to the eardrum at the inner end of the canal is not as simple as it might seem. In a hearing aid, a microphone is connected to a speaker by a high gain (60-80 dB) amplifier and is relatively close to the speaker. An earpiece containing a speaker is assumed to fit the ear canal and the tissue of the ear canal is relied upon to isolate the speaker from the microphone. 
         [0005]    If the earpiece should move slightly and not seal the ear canal, an acoustic path is opened, coupling the speaker to the microphone, which permits sound from the speaker to be fed back to the microphone. Feedback typically occurs at high frequencies due to the higher gain at these frequencies, where most hearing loss occurs. The misalignment of the earpiece manifests itself as an unpleasant squeal that can be audible even to those several feet from the hearing aid. The squeal can be eliminated by reducing the gain of the amplifier by way of a volume control on the hearing aid. Often the wearer is obliged to adjust the gain frequently as the loudness of background sounds and the loudness of sounds of interest change. Feedback in a hearing aid can interfere with hearing and may cause the wearer not to use the hearing aid. High level feedback in a hearing aid may even damage the already impaired hearing of the wearer. 
         [0006]    Hearing aids can be divided into four groups: Behind-The-Ear (BTE), In-The-Ear (ITE), In-The-canal (ITC), and Completely-In-the-Canal (CIC). Some BTE hearing aids have an advantage over other types because the speaker is relatively far from any microphone in the body of the hearing aid. Before speakers became small enough to fit in an ear canal, it was known to add sound absorbing material to the earpiece of a BTE hearing aid; for example see U.S. Pat. No. 3,080,011. It has long been known that putting the speaker in the ear canal reduces feedback in a BTE hearing aid. See “Reducing Feedback in a Post-Auricular Hearing Aid by Implanting the Receiver in an Earmold”, Ross and Cirmo, The Volta Review, January 1980, pages 40-44. (Post auricular means behind the ear). See also U.S. Pat. No. 4,727,582 (de Vries et al.). Distance and dispersion provide some attenuation but, for those severely impaired, these are not enough. The high gain used for at least some frequencies assures that sufficient sound reaches a microphone for oscillation or squeal. 
         [0007]    A tip having a foam sleeve or jacket is known in the art and can be used with any type hearing aid but is primarily used with BTE hearing aids. The tip contains a speaker. The sleeve provides a resilient coupling to the wall of the ear canal and provides some attenuation of the sound traveling in either direction along the canal. 
         [0008]    It is known in the art to form the sleeve in the canal and it is known to pre-form the sleeve. In some cases, the sleeve is designed for comfort; e.g. U.S. Pat. No. 4,880,076 (Ahlberg et al.). It is alleged for other sleeves that feedback is prevented; e.g. U.S. Pat. No. 4,830,139 (Cirillo) and U.S. Pat. No. 6,724,902 (Shennib et al.). It is known in the art to make a sleeve from foam; e.g. U.S. Pat. No. 4,459,247 (Rothemund). Despite these disclosures, there remains a need in the art for a jacketed tip that is comfortable to wear and that prevents feedback even at high gain. That is, there is a need for a jacketed tip that attenuates sound a minimum of 40 dB and preferably 60 dB, particularly at and above 1,000 Hz. 
         [0009]    In view of the foregoing, it is therefore an object of the invention to provide a jacketed tip for a hearing aid that provides at least 40-60 dB of attenuation and is comfortable to wear. 
         [0010]    Another object of the invention is to provide a jacketed tip for a hearing aid that provides at least 40 dB of attenuation even at low frequencies 
         [0011]    A further object of the invention is to provide a pre-formed, high attenuation sleeve for a hearing aid. 
         [0012]    Another object of the invention is to provide a high gain, BTE hearing aid with a speaker in the ear canal surrounded by sound absorbing, resilient material. 
       SUMMARY OF THE INVENTION 
       [0013]    The foregoing objects are achieved by this invention in which a hearing aid includes a speaker in a tip that is located in an ear canal. The tip includes a coupling, a retainer that mechanically engages the coupling, and a sleeve axially surrounding the retainer. The retainer attenuates lower frequencies than are attenuated by the sleeve. The sleeve is preferably foam and the retainer is preferably a composite material. A flange on the retainer reflects sound back into the sleeve for additional attenuation. It has been discovered that operation is improved if the outside diameter of the sleeve and the outside diameter of the retainer are in the ratio of approximately 1.75:1. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a perspective view of a behind-the-ear hearing aid; 
           [0016]      FIG. 2  is a cross-section taken along line  2 - 2  in  FIG. 1 ; 
           [0017]      FIG. 3  is a perspective view of an in-the-canal hearing aid including an attenuating tip constructed in accordance with the invention; 
           [0018]      FIG. 4  is a cross-section taken along line  4 - 4  in  FIG. 1 ; 
           [0019]      FIG. 5  is a chart comparing an earpiece constructed in accordance with a preferred embodiment of the invention with a commercially available earpiece; and 
           [0020]      FIG. 6  is a chart of the attenuation of an earpiece constructed in accordance with an alternative embodiment the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  is a perspective view of a behind-the-ear hearing aid having an earpiece containing a speaker and surrounded by a sound absorbing sleeve constructed in accordance with the invention. The drawing is not necessarily to scale. 
         [0022]    Hearing aid  10  includes a sculptured body  11  that contains one or more microphones, a battery, and audio processing circuitry that provides correction for impaired hearing. Earpiece  12  preferably contains at least one speaker coupled to the audio processing circuitry in body  11  by cable  14 . The speaker (not shown) is suitably supported on coupling  16  which is surrounded by tip  17 . Tip  17  resiliently supports earpiece  12  in an ear canal, acoustically seals the canal, and absorbs sound generated by the speaker. 
         [0023]    A tip constructed with the invention can be located anywhere in the ear canal. That is, the tip need not be “completely-in-canal” (touching the bony portion of the ear canal) but is inserted a sufficient distance for the tip to engage the canal about the circumference of the tip. 
         [0024]      FIG. 2  is a cross-section of earpiece  12  taken along line  2 - 2  in  FIG. 1 . In accordance with one aspect of the invention, tip  17  includes two parts, each designed to absorb sound in different parts of the audio spectrum. Retainer  21  is a composite, specifically a filled rubber, that absorbs low frequencies; e.g. frequencies below 1,000 Hz. Sleeve  23  axially surrounds retainer  21  and is made from a foam rubber that has high density and slow recovery time and absorbs high frequencies (above 1,000 Hz) better than retainer  21 . Retainer  21  has an interior shape complementary to the shape of coupling  16  ( FIG. 1 ) to which it is attached, preferably by interference fit. A frequency of 1,000 Hz is not a hard boundary but is used for the sake of description. The ranges of frequencies necessarily overlap because the retainer and the sleeve are not sharp cut-off filters. In accordance with another aspect of the invention, it has been found that retainer  21  is preferably a composite material, specifically an organic carrier containing inorganic filler. Fine (e.g. 10-3-10-4 mm) particles of barium sulphate (BaSO4) is preferred as the filler. In general, the more dense the filler, the better the acoustical performance. For example, barium sulphate is more dense than “Mistron® vapor” (fine particles of talc—magnesium silicate) and performs better than talc. As used herein, “density” refers to the density of the material relative to water, not the amount of filler per unit volume of rubber. A mixture of 5 weight percent of filler in rubber has been found suitable. The retainer is less resilient than the sleeve. The preferred organic carrier is butyl rubber. The sleeve is preferably made by reacting MDI (methylene diphenyl diisocyanate) with polyol, producing a dense foam. This material is known in the art as a thermal insulator. Preferably the foam has a specific gravity of 0.1 or higher. 
         [0025]      FIG. 3  is a perspective view of in-the-canal hearing aid  30  including an attenuating tip constructed in accordance with the invention. Hearing aid  30  includes body  31  housing the necessary electronics, battery, and microphone (not shown). The earpiece includes foam sleeve  33  axially surrounding a retainer (not shown in  FIG. 3 ), which is joined internally to coupling  35 . The construction and performance of the foam sleeve and the retainer is the same as the embodiment of  FIG. 1 . 
         [0026]    In accordance with another aspect of the invention, it has been found that the geometry of the tip affects performance. Specifically, sleeve  23  preferably has a thickness of at least 0.25 mm. The outside diameter of the tip can vary from 6.5 mm to 13.5 mm, depending upon the particular patient, but is typically about 10.5 mm. It has been found that the outside diameter of sleeve  23 , represented by the letter a in  FIG. 4 , and the outside diameter of retainer  21 , represented by the letter b in  FIG. 4 , should be in the ratio (a:b) of approximately 1.75.05:1. 
         [0027]    As illustrated in  FIG. 4 , retainer  21  has an interior shape that provides an interference fit with coupling  16  ( FIG. 1 ), which contains a speaker (not shown). Specifically, retainer  21  defines interior shoulder  41  for engaging the coupling. The shoulder resists removal of the coupling. Sleeve  23  and retainer  21  are joined by adhesive (not shown). Thus, the components are securely joined for normal use. In the event a coupling is accidentally pulled out, a pull tab or stem  42  is optionally provided for removing the earpiece from the ear canal. 
         [0028]    Dash-dot line  44  represents the center line and longitudinal axis of the tip. In accordance with another aspect of the invention, flange  45  is located near the longitudinal middle of retainer  21  and extends radially into sleeve  45  further than other portions of the retainer. Flange  44  has been found to facilitate attenuation by reflecting sound, particularly high frequencies, from within the canal back through a portion of foam sleeve  45 , as indicated by arrows  47 . Flange  45  provides a large surface area, relative to diameter b of retainer  21 , for reflecting sound. That is, distal end  48  has an outside diameter less than b. The longitudinal location of the flange can be changed to adjust the acoustic characteristics of the earpiece. 
         [0029]      FIG. 5  is a chart comparing an earpiece constructed in accordance with a preferred embodiment of the invention with an earpiece having a solid silicone tip from Phonak AG. The tip is considered a quality component in the art. The sound level of the input signals was +74 dB SPL. The amplitudes of attenuated sounds were subtracted from the amplitudes of non-attenuated sounds and the differences plotted for  FIG. 5 . The chart is a plot of attenuation (dB) vs. frequency (Hz). In  FIG. 5 , curve 51 represents the attenuation of an earpiece constructed in accordance with a preferred embodiment of the invention and deeply inserted into an ear canal. Curve 52 represents the attenuation of the earpiece loosely inserted into an ear canal. The pronounced dip at approximately 4 kHz. is believed to be an artifact of the test equipment. Curve 55 represents the attenuation of an earpiece having a Phonak tip and deeply inserted into an ear canal. Curve 52 represents the attenuation of the earpiece having a Phonak tip loosely inserted into an ear canal. The pronounced dip at approximately 8 kHz. is believed to be an artifact of the test equipment. 
         [0030]      FIG. 6  is a chart of the attenuation of an earpiece constructed in accordance with an alternative embodiment the invention. For  FIG. 6 , the sleeve had a heat shrinkable covering. Curve 61 represents the attenuation of a tip deeply inserted into an ear canal. Curve 63 represents the attenuation of a tip near the outer end of an ear canal but fully engaging the canal. For a substantial portion of the audio spectrum, attenuation was greater than 60 dB. Although insertion depth has some effect on attenuation, the tip is relatively immune to variation in insertion depth. 
         [0031]    The invention thus provides a jacketed tip for a hearing aid that provides at, least 40-60 dB of attenuation and is comfortable to wear. The tip provides at least 40 dB of attenuation at low frequencies and 60 dB of attenuation at high frequencies. The retainer and sleeve are pre-formed and is suitable for use in a BTE hearing aid capable of high gain (greater than 60 dB). 
         [0032]    Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, retainer  21  can be held in place by interference fit, frictional engagement, a fractional turn locking mechanism, or other technique.