Patent Abstract:
A wired or wireless earset assembly comprises an earset housing having a curved portion configured to fit to the top of an ear, a speaker driver contained in a speaker housing, a flexible tube having a first extension so as to be coupled with at least a part of the curved portion of the earset housing and a second extension coupled with the speaker housing, a rotatable cap containing a bud coupled with the speaker driver, a sound delivery port in the bud, a circuitry for processing an input signal in the case, and a wire in the flexible tube connecting the circuitry and the speaker driver. The structure of the assembly allows a user to wear it with great comfort and high quality acoustic performance for an extended period, enables the assembly to fit to both right and left ears by a simple rotation of the cap, and increases ease of manufacturability.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of prior U.S. patent application Ser. No. 10/757,796, entitled “Earset Assembly,” filed on Jan. 13, 2004. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an earset assembly for a hearing aid, a mobile phone, a communication device for a personal computer, a multimedia device, etc. More particularly, the present invention relates to a wired or wireless non-occluding earset assembly. 
       BACKGROUND OF THE INVENTION 
       [0003]    A sound delivery assembly for hearing aid, communication system or multimedia system is primarily configured to achieve high quality acoustic performance. It is also desired that the structure of the sound delivery assembly maintain in manufacture a designed user comfort in wearing it because he/she wants to use it for an extended time. 
         [0004]    High quality acoustic performance is achieved by high efficiency and high fidelity of the sound delivery system. Efficiency of a sound delivery system is determined by the size of a speaker element and the distance to the entrance of the ear canal from the end of the sound delivery assembly. Fidelity of a sound delivery system is determined by a number of factors including the size of the speaker element and the length of a sound tube to deliver sounds. 
         [0005]    So far, there are two primary types of sound delivery tools. One of them adopts an occluding earset structure such as an earmuff, an occluding earbud, or an occluding earmold. The other type adopts a non-occluding earset structure. 
         [0006]    An ear-occluding structure such as the earmuff type achieves high quality acoustic performance because the size of a speaker element can be relatively large. Other ear-occluding structures such as the earbud and the earmold sound delivery systems also achieve high quality acoustic performance because the sound is delivered into the ear canal at the entrance of the ear canal and because the sound pressure is sealed in by the occlusion, thereby easily producing good bass and high sound level. Thus, small speaker drivers can be used with occluding systems. However, it is not physically comfortable for a user to occlude the ear for an extended period for two reasons: the physical discomfort due to pressure on the tissue required to get a good seal as the jaw and jaw muscles move and change the canal shape, and due to the disturbing and uncomfortable nature of the sound of the user&#39;s own voice (bassy and too loud) and audibility of bodily sounds (heart beat, blood flow, chewing sounds, clearing throat, etc.). Another reason for the user&#39;s discomfort is that a user has difficulty in hearing sounds other than that delivered by the sound delivery assembly. Lack of hearing the background sounds makes a user feel isolated from his surroundings and uncomfortable. Particularly, when a user uses a mobile phone or communicates with a computer or multimedia, he/she needs to hear the surrounding sounds for safety or as a necessary part of the experience. 
         [0007]    Where the ear is not occluded, a user can hear surrounding sounds in addition to delivered sounds. Conventional non-occluding earsets are coupled with a relatively long sound tube for delivering sounds. They do not achieve high quality acoustic performance because their efficiency and fidelity are not high. Various structure of non-occluding earsets have been designed, however, they are not adjustable for each individual ear anatomy so that some users feel uncomfortable tension to the ear in wearing the earset or the earset provides compromised performance for some users due to the ill fit of the device. 
         [0008]    U.S. Pat. No. 6,009,183 by Taenzer presents an ambidextrous sound delivery system. This sound delivery system uses a tube for delivering sounds. It has an ambidextrous feature provided by rotating the tube at its axis. However, the long tube affects the sound fidelity so that substantial additional form elements need to be included. Additionally, the tube terminates in the ear canal so that the accommodation of different ear sizes has to be done by flexing the tube creating uncomfortable pressure on the canal wall. Further, since the entrance to the ear canal has hair, some users report that an unbearably uncomfortable tickling sensation is produced by the tube. 
         [0009]    U.S. Pat. No. 6,438,245 “Hearing Aid Communications Earpiece” shows an above-the-ear microphone for pickup of the user&#39;s own voice. U.S. Pat. No. 6,021,207 “Wireless Open Ear Canal Earpiece” and U.S. Pat. No. 6,181,801 “Wired Open Ear Canal Earpiece” show devices providing sound delivery to the ear canal in a non-occluding manner. 
         [0010]    U.S. Pat. No. 5,659,156 by Mauney presents an earmold for two-way communications devices. This earmold is a non-occluding one designed to securely hold the earmold in the ear and deliver sounds at the entrance of the ear canal. However, this earmold has to be configured to fit each individual and must also be configured to separately fit right and left ears. It is not adjustable for the anatomy of each individual or ear. 
         [0011]    An object of the present invention is to provide a earset assembly having a structure that easily fits to almost all people&#39;s either right or left ear and allows a user to wear it with great comfort on the ear for an extended period. 
         [0012]    Another object of the present invention its to provide an earset subassembly which creates and assures good sound performance for almost all ears. 
         [0013]    Another object of the present invention its to provide an earset subassembly which facilitates ease and flexibility in manufacturability of the assembly. 
         [0014]    Another object of the present invention its to provide an earset subassembly which facilitates ease of testing of the assembly during manufacture. 
       SUMMARY OF THE INVENTION 
       [0015]    An object of the present invention is to provide great comfort in the use of an earset assembly. A wired or wireless earset assembly comprises an earset housing having a curved portion configured to fit to a root of a top of an ear; a speaker driver having an input port, a speaker housing containing the speaker driver, a flexible neck tube having a first extension at a first end of the flexible neck so as to be coupled with at least a part of the curved portion of the earset housing and a second extension at a second end of the flexible tube coupled with the speaker housing, a rotatable cap containing a bud coupled with the speaker housing, circuitry for processing an input signal contained in the earset housing, having an input port and an output port, and a wire connecting the output port of the circuitry and an input port of the speaker driver. The wire is contained in the flexible neck tube. Because the structure of the non-occluding sound delivery assembly of the present invention does not give uncomfortable tension or pressure to the ear, a user can wear the sound delivery assembly with great comfort and high quality acoustic performance for an extended period. In addition, the present invention allows the sound delivery assembly to easily fit to almost all the person&#39;s either of right and left ears by an easy procedure. Furthermore, the present invention increases ease of manufacturability because the number of components in the assembly decreases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present invention and, together with the detailed description, serve to explain the principles and implementations of the invention. 
           [0017]    In the drawings: 
           [0018]      FIG. 1  is side view of an earset assembly in one embodiment of the present invention. 
           [0019]      FIG. 2  is an end view of the device of  FIG. 1 . 
           [0020]      FIG. 3  is a view of the opposite side of the device of  FIG. 1 . 
           [0021]      FIG. 4  is an end view of the device of  FIG. 1 . 
           [0022]      FIG. 5  is an exploded view of the device of  FIG. 1 . 
           [0023]      FIG. 6  is a view of the rotatable cap  104  of the device of  FIG. 1   
           [0024]      FIG. 7  is a side view of the rotatable cap  104  of the device of  FIG. 1   
           [0025]      FIG. 8  is an end view of the rotatable cap  104  of the device of  FIG. 1   
           [0026]      FIG. 9  is a bottom view of the rotatable cap  104  of the device of  FIG. 1   
           [0027]      FIG. 10  is a cross section view of the rotatable cap  104  of the device of  FIG. 1   
           [0028]      FIG. 11  is a cross section view of the rotatable cap  104  connected to the speaker housing  107 . 
           [0029]      FIG. 12  is a front view of the earset assembly of  FIG. 1  placed on a right ear. 
           [0030]      FIG. 13  is a front view of the earset assembly of  FIG. 1  placed on a left ear. 
           [0031]      FIG. 14  illustrates how a user mounts the assembly to the user&#39;s ear. 
           [0032]      FIG. 15  illustrates how a user mounts the assembly to the user&#39;s ear. 
           [0033]      FIG. 16  is a front view of another embodiment of a rotatable cap  104  of  FIG. 1 . 
           [0034]      FIG. 17  is a side view of another example of rotatable cap  104  of  FIG. 1 . 
           [0035]      FIG. 18  is a front view of another example of rotatable cap  104  of  FIG. 1 . 
           [0036]      FIG. 19  is a side view of another example of rotatable cap  104  of  FIG. 1 . 
           [0037]      FIG. 20  is a front view of another example of rotatable cap  104  of  FIG. 1 . 
           [0038]      FIG. 21  is a side view of another example of rotatable cap  104  of  FIG. 1 . 
           [0039]      FIG. 21   a  is a front view of another example of rotatable cap  104  of  FIG. 1 . 
           [0040]      FIG. 21   b  is a side view of another example of rotatable cap  104  of  FIG. 1 . 
           [0041]      FIG. 22  is a cross-sectional view of an earset assembly according to one embodiment of the present invention. 
           [0042]      FIG. 23  is a perspective view of a wired type earset assembly in another embodiment of the present invention. 
           [0043]      FIG. 24  is a cross-sectional view of the earset assembly of  FIG. 23 . 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    Embodiments of the present invention are described herein in the context of an earset assembly. Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. 
         [0045]    As shown in  FIGS. 1-4 , the earset assembly  90  comprises earset housing  101 , neck member  103 , rotatable cap  104  having bud  105 , and speaker housing  107  for housing a speaker. Earset assembly  90  includes curved portion  102  configured to fit to the top of a user&#39;s ear and antenna enclosure portion  109 . Earset housing  101  includes four holes  110  so that a microphone  112  placed near holes  110  can receive sounds. Optionally, antenna enclosure portion  109  may be omitted. 
         [0046]    As shown in  FIG. 5 , neck member  103  comprises a neck tube  201  and a curved section  202 . The curved section  202  includes a U-shaped portion  203  coupled to earset housing  101 . The neck tube  201  and curved section  202  form substantially a U-shape or horseshoe shape to be hooked on the ear. Material of neck member  103  is elastic material such as rubber, urethane rubber or silicone rubber or the like. The neck tube  201  may contain a stiffening member  203   a , such as a length of copper wire, to allow the neck tube  201  to be formed by the user to the user&#39;s own anatomy, and to allow the neck member  103  to retain that shape, once it is formed. Further, the neck member can have embedded in it, a stiffening element, not shown, to enable the non-formable portions of the neck member  103  to retain their as-molded shapes, while still providing for the comfort of the elastic material against the user&#39;s skin. The neck member  103  includes a speaker housing  107  and a microphone housing  208 . A speaker  204  is located in the speaker housing  107 , and microphone  112  is located in the microphone housing  208 . A wireless radio  206 , such as a Bluetooth radio, FM radio, IEEE 802.11 radio or the like, is located in the earset housing  101 . 
         [0047]      FIGS. 6-10  show views of one embodiment of rotatable cap  104 . Rotatable cap  104  comprises body  301 , which is generally cylindrical, rotatably coupled to speaker housing  107  to cover and acoustically seal a speaker  204 , and bud  302  which is generally conical extending from the body  301 . The central axis  302   a  of bud  302  is located at an oblique angle to the central axis of generally cylindrical body  301 . Preferably, the angle between the axis  302   a  of bud  302  and the axis of body  301  is between 15 degrees and 90 degrees. A generally cylindrical port  306  is formed through the bud  302 , and the port  306  communicates with a cylindrical port  308  formed through the body  301 , and a flange  310  is formed around the periphery of the cylindrical port  308 . By rotating rotatable cap  104 , the distance between the bottom of the curved section  202  of neck member  103  and the opening end of bud  302  is adjusted to fit the distance between the top of the root of the ear and the entrance of the ear canal of each individual. Material of rotatable cap  104  is elastic material. Preferably, material of rotatable cap  104  is rubber, urethane rubber or silicone rubber or the like. 
         [0048]    The bud is preferably made non-occluding by a plurality of notches  310  on its surface, as shown, or by other means such as external longitudinal ridges, lateral piercings, an oval outer cross-sectional shape or the like. 
         [0049]      FIG. 11  shows a cross-sectional view of rotatable cap  104  and speaker housing  107 . Speaker driver  204  is contained in speaker housing  107 . The front face  402  of speaker driver  204  touches a part of the bottom of body  301  of rotatable cap  104 . This allows the elastic material of rotatable cap  103  to form a circular, rotatable seal  403   a  to the front face  402  of the speaker driver  204 , preventing the cancellation of sound that would occur if the sound wave from the front of the speaker driver  204  were allowed to mingle with the wave from the back of speaker driver  204 . This cancellation would occur because the wave from the front of the speaker driver  204  is exactly 180 degrees out of phase with the wave from the back of speaker driver  204 . 
         [0050]    There is a contained space between the back of the speaker  204  and the speaker housing  107 , and this space is called “back volume”  403 . According to well known methods in the art, the back volume and speaker vent  406  form an acoustic Helmholz resonator that is tuned to work with the electro-acoustic parameters of speaker driver  204  to allow the assembly to create high fidelity sound to the ear of the user. 
         [0051]    The front sound wave pressure created by the drive of speaker driver  204  is captured by body  301  of rotatable cap  104  and delivered through port  306  toward a user&#39;s ear canal. Here it should be understood that the sound tube for delivering sounds created by speaker, consisting of the port  306  formed through the bud  302 , is short and speaker driver  204  is located in the speaker housing  107 . Since the length of the sound tube is relatively short the earset assembly achieves high efficiency and high fidelity despite a relatively small speaker driver. Also, due to high efficiency and high fidelity, the power consumption of the earset sound assembly decreases. Accordingly, a user can continue to use the earset sound assembly for a longer period without replacing a battery with a new one or recharging a battery. On the other hand, the speaker is relatively large compared to the restricted size of an ear canal located speaker, such as are used in In-The-Canal (ITC) and Completely-In-The-Canal (CIC) hearing aids, allowing for improved bass response fidelity and efficiency as compared to those designs. 
         [0052]      FIGS. 12 and 13  are a front view of the earset assembly of  FIG. 1  placed on a right ear  500  and a left ear  501 , respectively. It should be noted that the axis of the speaker is oriented substantially perpendicular to the axis of the ear canal  504  of the user with the front face  402  of the speaker directed forward, in the direction the user is facing. 
         [0053]    A user can wear the earset assembly of the present embodiment according to the following steps, illustrated in  FIGS. 14 and 15 . First, a user rotates the rotatable cap  104  so as to direct bud  302  toward the ear on which the user wants to wear the assembly. The user puts bud  302  at entrance  502  of ear  500  (or  501 ), and then places earset housing  101  above ear  500  (or  501 ) as seen in  FIG. 14 . Then, the user rotates earset housing  101  rearward behind the auricle so as to securely hook the assembly on the ear, as shown in  FIG. 15 . If the bud  302  is not directed toward the user&#39;s ear entrance  502 , the user can remove the device and adjust the angle of rotatable cap  104  to make the assembly secure, yet comfortable. This adjustment only needs to be made once for a new user. It should be noted that the ports  110  are located symmetrically on each side of the device to allow for use of the device on either ear. 
         [0054]    Further, neck tube  201  is adjustable as described above by forming the neck tube  201  into any comfortable shape, for example by forming the neck tube  201  in a lateral curve to increase or decrease the distance of the end of bud  104  from the entrance of the ear  502 . Such adjustment is retained by the stiffening member  203   a , even when the device is off the ear. 
         [0055]    The structure of the earset assembly of the present invention allows a user to wear the earset assembly on either of right and left ear, placing the ear bud very close to the entrance of the ear  502  and securely hooking the earset assembly on the ear according to the above described procedure. Because neck member  103  is primarily elastic material such as rubber, urethane rubber or silicone rubber, which is flexible and adjustable to fit the individual user, a user does not feel uncomfortable tension and a user does not feel irritated in wearing the earset assembly. Consequently, the user can use the earset assembly with great comfort for an extended period. 
         [0056]    Moreover, it should be understood that the rotatable cap  104  can be rotated to any angle to fit a wide variety of users. This is best understood with reference to  FIGS. 12 and 13 . As shown in  FIG. 12  the distance between the top of the user&#39;s ear and the entrance  502  to ear canal is relatively short, so the rotatable cap is located with the axis of port  306  oriented at an angle upward from the horizontal. On the other hand, as shown in  FIG. 13  the distance between the top of the user&#39;s ear and the entrance  502  to ear canal is relatively long, so the rotatable cap is located with the axis of port  306  oriented at an angle downward from the horizontal. 
         [0057]      FIGS. 16 and 17  show a top view and a side view of another example of rotatable cap  104 , respectively. Bud  701  extending from the surface of body  702  has a cylindrical shape. The diameter of bud  701  is selected to fit opening end  703  of bud  701  to an entrance of the ear canal. 
         [0058]      FIGS. 18 and 19  show a top view and a side view of another example of rotatable cap  104 , respectively. Bud  801  is extended from the side surface of body  802 , and directs in a direction parallel to front face  402  of speaker driver  401 . 
         [0059]      FIGS. 20 and 21  show a top view and a side view of another example of rotatable cap  104 , respectively. A bud comprises cylinder  901  extended from body  903  and mushroom shaped part  902  coupled with the ear end of cylinder  901 . The bud directs in an oblique direction to the plane parallel to the bottom of body  903  so as to just enter the opening of the ear canal. Preferably, the angle between the axis of the bud and the axis of generally cylindrical body  903  is between 15 degrees and 90 degrees. The mushroom shaped part is of relatively thin and resilient material and includes a plurality of port piercings  904 . The port piercings  904  prevent occlusion by preventing a complete seal of the mushroom shaped part  902  with the inside of the ear canal. When the mushroom shaped part is inserted into the ear canal it deforms slightly and tends to be captured and not easily fall out or be jarred loose. Therefore this design is useful for sport models of the device. 
         [0060]      FIGS. 21   a  and  21   b  show a top view and a side view of another example of rotatable cap  104 , respectively. In this embodiment the bud includes three sound ports  906 . When viewed in  FIG. 21   a  the vertical dimension “a” of the end of the bud can be seen to be longer than its horizontal dimension “b”. Accordingly when the bud is inserted in the ear canal the long axis contacts the ear canal while the short axis does not, so that the bud is prevented from being occluding. 
         [0061]      FIG. 22  shows a cross-sectional view of an earset assembly in one embodiment of the present invention. As shown in  FIG. 22 , the earset assembly comprises antenna  1001 , circuitry  1002  for processing a signal received by antenna  1001 , and wire  1003  contained in neck member  103  which connects between output port  1004  of circuitry  1002  and input port  1005  of speaker driver  401 , and battery  1006 . Circuitry  1002  and battery  1006  are contained in earset housing  101 . Battery  1006  supplies the electrical power to speaker driver  401  and circuitry  1002 . Battery  1006  may be rechargeable so that the assembly may comprise a port for recharging battery  1006 . Alternatively, an external power source may supply the electrical power to speaker driver  401  and circuitry  1002  through a cable so that battery  1006  need not be contained in earset housing  101 . Antenna  1001  is contained in antenna enclosure portion  109 . Alternatively, antenna  1001  may be covered by another cover or uncovered. A signal received by antenna  1001  is processed by circuitry  1002 , and then transmitted to speaker driver  401  through wire  1003  in neck member  103 . Speaker driver  401  transduces the transmitted electrical signal to a sound, and then the sound is delivered to an ear of the user through a hollow in bud  105 . 
         [0062]    An earset assembly further comprises microphone  1010  as shown in  FIG. 22 . Preferably, microphone  1010  is placed near the end of curved portion in earset housing  101 , that is the bottom of U-shape configured by the coupling of earset housing  101  and neck member  103 . Earset housing  101  has one or more holes called microphone sound ports near microphone  1010 . A sound received by microphone  1010  via the microphone sound ports is transduced to an electrical signal. The electrical signal is processed by a circuitry  1007  contained in earset housing  101 , and communicated with an external communication device or multimedia device through antenna  1001 . 
         [0063]    In accordance with another embodiment of the present invention,  FIG. 23  shows a perspective view of a wired type earset assembly. As shown in  FIG. 23 , the earset assembly comprises housing  1101  having curved portion  1102  configured to fit to the top of an ear, flexible tube  1103 , rotatable cap  1104  having bud  1105 , and speaker housing  1107  coupled with rotatable cap  1104 . The flexible tube  1103  and curved portion  1102  are substantially U-shaped to be hooked on the ear.  FIG. 24  shows a cross-sectional view of the earset assembly of  FIG. 23 . As shown in  FIG. 24 , the earset assembly further comprises circuitry  1301  coupling with external signal source  1302  such as communication device and multimedia device through a cable  1303 , wire  1304  contained in flexible tube  1203  which connects between output port  1305  of circuitry  1301  and input port  1306  of speaker driver  1307 . Circuitry  1301  processes a signal transmitted through cable  1303  and then processed signal is further transmitted to speaker driver  1307  through wire  1308  in flexible tube  1203 . Electrical power is supplied to circuitry  1301  through cable  1303  and also supplied to speaker driver  1307 . Speaker driver  1307  transduces the transmitted electrical signal to a sound, and then the sound is delivered to an ear of the user through a hollow in bud  1205 . 
         [0064]    An earset assembly further comprises microphone  1310  as shown in  FIG. 24 . Preferably, microphone  1310  is placed near the end of curved portion in housing  1201 , that is the bottom of the U-shape configured by the coupling of housing  1201  and flexible tube  1203 . Housing  1201  has one or more holes called microphone sound ports near microphone  1310 . A sound received by microphone  1310  via the microphone port(s) is transduced to an electrical signal. The electrical signal is processed by a circuitry  1311  contained in housing  1201 , and communicated with external communication device or multimedia device  1302 . 
         [0065]    It should be understood that the design of neck member  103  is an important feature. As designed, all the critical electro-acoustic and ergonomic (human fit) elements of the device are captured in this one neck member sub-assembly. Accordingly, the neck member sub-assembly controls the delivered sound frequency response, loudness, loudness/distortion trade-off, mic pickup directionality, mic sensitivity, mic SNR, top-of-ear comfort, ear variation adjustability (one size fits all), ear occlusion, microphone wind noise rejection, and even the product&#39;s as-worn appearance (Hair, the ear and head coverings usually “camouflage” the back of the instrument, i.e. the earset housing  101  when worn so the neck member sub-assembly becomes the most visible element of the earset). 
         [0066]    Thus, the neck member  103  sub-assembly is designed so that it can be pre-built and pre-tested, thereby controlling the quality of the product. The remainder of the device, which is housed in earset housing  101 , consists of highly reliable and consistent parts (i.e. the radio, battery and housings), so later assembly of these parts to the neck member  103  sub-assembly is routine. Yet, all product differentiation can readily be done in the earset housing  101 . For example, the Bluetooth radio can be changed to 802.11 radio (for VoIP applications), or to low-power FM radio for low cost applications, without affecting the customer&#39;s product perception (It looks and works the same to them). As another example, the battery can be changed from Lilon to NiCd to LiP to NiMH without any change to the perceived product or its audio performance. Yet another example, housing colors, logo printing, shape and size, can all be changed while the acoustics and ergonomics do not change. Thus, how the product feels and acts remains captured in the neck member  103  sub-assembly. Despite this product flexibility, it is unnecessary to redesign and qualify another electro-acoustic solution every time it is desired to make a product change. 
         [0067]    Furthermore, the special neck member  103  simplifies the testability of the device. The neck member  103  sub-assembly can be tested for acoustic performance by installing the speaker and microphone in the neck member  103  and then connecting the tester signal leads to the speaker and microphone leads. After testing is completed satisfactorily, the neck member  103  is affixed to the earset housing  101  with its included components. 
         [0068]    Another important point to note about the neck member  103  is that it is single part that houses both a speaker and a microphone without feedback between them. Usually, such an assembly is undesirable, since audio frequency mechanical vibrations created by the speaker travel directly to the microphone creating feedback “echo”, in other words the listener at the other end of the communication hears his own voice returning to him/her with a two-way delay. This can be very disturbing and prevent easy communication. However, the neck member  103  overcomes this since the use of elastomeric material allows this single sub-assembly to avoid the feedback problem. 
         [0069]    While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.

Technology Classification (CPC): 7