Patent Publication Number: US-8989410-B2

Title: Compact bone conduction audio transducer

Description:
BACKGROUND 
     Computing devices such as personal computers, laptop computers, tablet computers, cellular phones, and countless types of Internet-capable devices are increasingly prevalent in numerous aspects of modern life. Over time, the manner in which these devices are providing information to users is becoming more intelligent, more efficient, more intuitive, and/or less obtrusive. 
     The trend toward miniaturization of computing hardware, peripherals, as well as of sensors, detectors, and image and audio processors, among other technologies, has helped open up a field sometimes referred to as “wearable computing.” In the area of image and visual processing and production, in particular, it has become possible to consider wearable displays that place a “near-eye display” element close enough to a wearer&#39;s eye(s) such that a displayed image is perceived by the wearer. 
     Wearable computing systems can be configured to be worn proximate a wearer&#39;s head to allow for interfacing with the wearer&#39;s audible and/or visual senses. For example, a wearable computing system can be implemented as a helmet or a pair of glasses. To transmit audio signals to a wearer, a wearable computing system can function as a hands-free headset or as headphones, employing speakers to produce sound. Audio transducers are employed in microphones and speakers. A typical audio transducer converts electrical signals to acoustic waves by sending the electrical signals through a coil to produce a time-varying magnetic field which operates to move a small magnet connected to a membrane. The time-changing magnetic fields vibrate the magnet, which vibrates the membrane, and results in sound waves traveling through air. An acoustic transducer can also translate sound waves to electrical signals by a similar process using a pressure sensitive membrane to create a time-changing magnetic field that produces an electrical signal in a coil of wire, such as in a microphone. 
     Sound perception in the biological realm, such as in human ears, also involves converting acoustic waves to electrical signals. For conventional sound perception, incoming acoustic waves are directed by the outer ear toward the ear canal where the tympanic membrane (ear drum) is stimulated to vibrate in accordance with the received acoustic pressure wave. The pressure wave information is then translated and frequency shifted by three small ossicles bones in the middle ear. The ossicles bones mechanically stimulate another membrane separating the fluid-filled chamber of the inner ear, which includes the cochlea. Hairs lining the interior of the cochlea act as frequency-specific mechanotransducers when stimulated by the pressure wave transmitted through the fluid in the cochlea to activate neurons that send signals to the brain allowing for perception of sound. 
     Bone conduction transducers create sound perception by directly stimulating the ossicles bones in the middle ear and effectively bypassing the outer ear. Bone conduction transducers couple to a bony surface on the skull or jaw, such as the mastoid bone surface behind the ear, to create vibrations that propagate to the ossicles bones, and thereby allow for sound perception without directly vibrating the tympanic membrane. A bone conduction transducer transmits vibrations to the inner ear by a vibrating anvil placed on a bony structure of the skull or jaw. Such a bone conduction transducer can include an anvil suitable for making contact with a bony portion of the head can be mounted to a transducer, which can vibrate the anvil according to received electrical signals. 
     SUMMARY 
     A bone conduction transducer for a wearable computing system is disclosed. The bone conduction transducer can include a magnetic diaphragm configured to vibrate in response to a time-changing magnetic field generated by an electromagnetic coil operated according to electrical input signals. The magnetic diaphragm is elastically suspended over the electromagnetic coil to allow excursion toward and away from the coil by a pair of cantilevered leaf springs projected from opposing sides of the transducer to connect to opposing sides of the magnetic diaphragm. The bone conduction transducer is included in the wearable computing system to be arranged against a bony structure of a wearer&#39;s head. During operation, vibrations in the vibration transducer create vibrations that propagate through the wearer&#39;s jaw and/or skull to stimulate the wearer&#39;s inner ear and achieve sound perception in response to vibrations in the bone conduction transducer. 
     Some embodiments of the present disclosure provide a transducer including an electromagnet, a magnetic diaphragm, and a pair of cantilevered flexible support arms. The electromagnet can include a conductive coil surrounding a central core, wherein the conductive coil is configured to be driven by an electrical input signal to generate magnetic fields. The magnetic diaphragm can be configured to mechanically vibrate in response to the generated magnetic fields. The pair of cantilevered flexible support arms can elastically couple the magnetic diaphragm to a frame. The frame can be connected to the electromagnet such that the magnetic diaphragm vibrates with respect to the frame when the electromagnet is driven by the electrical input signal. The pair of cantilevered flexible support arms can be connected to opposing sides of the magnetic diaphragm and each of the pair of cantilevered flexible support arms can extend adjacent respective opposing sides of the magnetic diaphragm free of connection to either of the pair of cantilevered support arms. 
     Some embodiments of the present disclosure provide a wearable computing system including a support structure, an audio interface, and a vibration transducer. The support structure can include one or more portions configured to contact a wearer. The audio interface can be for receiving an audio signal. The vibration transducer can include an electromagnet, a magnetic diaphragm, and a pair of cantilevered flexible support arms. The electromagnet can include a conductive coil surrounding a central core, wherein the conductive coil is configured to be driven by an electrical input signal to generate magnetic fields. The magnetic diaphragm can be configured to mechanically vibrate in response to the generated magnetic fields. The pair of cantilevered flexible support arms can elastically couple the magnetic diaphragm to a frame. The frame can be connected to the electromagnet such that the magnetic diaphragm vibrates with respect to the frame when the electromagnet is driven by the electrical input signal. The pair of cantilevered flexible support arms can be connected to opposing sides of the magnetic diaphragm and each of the pair of cantilevered flexible support arms can extend adjacent respective opposing sides of the magnetic diaphragm free of connection to either of the pair of cantilevered support arms. The vibration transducer can be embedded in the support structure and configured to vibrate based on the audio signal so as to provide information indicative of the audio signal to the wearer via a bone structure of the wearer. 
     Some embodiments of the present disclosure provide a method of assembling a vibration transducer. The method can include arranging a first flexible support arm, arranging a second support arm, and laser welding the first and second flexible support arms. The first flexible support arm can have a first end and a second end. Arranging the first flexible support arm can be carried out such that: the first end is positioned over a first mounting surface of a magnetic diaphragm; and the second end is positioned over a first strut or sidewall of a frame of the vibration transducer. Overlapping regions of the first and second ends of the first flexible support arm can overlap the first mounting surface of the magnetic diaphragm and the first strut or sidewall of the frame, respectively. The second flexible support arm can have a first end and second end. Arranging the second flexible support arm can be carried out such that: the first end is positioned over a second mounting surface of the magnetic diaphragm; and the second end is positioned over a second strut or sidewall of the frame. The second mounting surface and the first mounting surface can be on opposing sides of the magnetic diaphragm. Overlapping regions of the first and second ends of the second flexible support arm can overlap the second mounting surface of the magnetic diaphragm and the second strut or sidewall of the frame, respectively. Laser welding the first and second flexible support arms can include directing a laser source sufficient to generate heat for laser welding to the respective overlapping regions of the first and second flexible support arms such that one or more laser spot welds are formed to connect the magnetic diaphragm and the frame via the first and second flexible support arms and thereby elastically suspend the magnetic diaphragm with respect to the frame. 
     These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an example wearable computing system. 
         FIG. 1B  illustrates an alternate view of the wearable computing system illustrated in  FIG. 1A . 
         FIG. 1C  illustrates another example wearable computing system. 
         FIG. 1D  illustrates another example wearable computing system. 
         FIG. 1E  is a simplified illustration of an example head-mountable device configured for bone-conduction audio 
         FIG. 2  is a simplified illustration of an example wearable system configured for bone-conduction audio. 
         FIG. 3A  is an exploded view of a bone conduction transducer including cantilevered support arms suspending a diaphragm. 
         FIG. 3B  is an assembled view of the bone conduction transducer in  FIG. 3A . 
         FIG. 4A  shows example spot welding locations to assemble the bone conduction transducer according to one embodiment. 
         FIG. 4B  shows example spot welding locations to assemble the bone conduction transducer according to another embodiment. 
         FIG. 5  shows an example process for assembling the bone conduction transducer according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     I. Overview 
     A bone conduction transducer is designed to receive audio signals and produce corresponding oscillations in the transducer&#39;s magnetic diaphragm. When placed against a bony structure of the head, the oscillating diaphragm creates vibrations in the skull that propagate to the inner ear and cause sound to be perceived. An electromagnet is formed by wire coiled around a core and operated according to the input signals to produce a time changing magnetic field sufficient to vibrate the diaphragm. Permanent magnets are located on opposing sides of the electromagnet to bias the diaphragm and/or magnetize ferromagnetic components of the diaphragm such that the diaphragm can be both attracted and repelled by the variations of the electromagnet. The diaphragm is elastically suspended over the electromagnet to allow for translation due to the combined magnetic forces acting on according to the input signals. In some embodiments disclosed herein, the diaphragm is elastically suspended by a pair of cantilevered support arms. 
     The present disclosure presents an example configuration for a bone conduction transducer in a compact form factor while maximizing the length of flexible components used to elastically suspend the diaphragm. An example embodiment is disclosed with cantilevered flexible support arms arranged to extend from one side of the transducer to an opposing side, across the longest the dimension of the bone conduction transducer. In comparison to a transducer that with flexible components connected to each corner of a suspended diaphragm, or with flexible components wound adjacent a shortened side of the diaphragm, the cantilevered support arms described herein maximize the available length of flexible materials used to elastically suspend the diaphragm. In other words, by suspending the diaphragm by flexible support arms that are cantilevered to extend adjacent the length of the diaphragm, the elasticity of the bone conduction transducer is increased without extending the length of the transducer significantly beyond the size of the diaphragm itself. The increased length of the flexible support arms is achieved within a relatively compact form factor by cantilevering the support arms from opposing sides of the transducer such that each cross opposing sides of the diaphragm and connect to opposing sides of the diaphragm. 
     A bone conduction transducer with cantilevered support arms as described herein provides a transducer designer with increased options for tuning the frequency and/or amplitude responsiveness of the transducer. The frequency and/or amplitude responsiveness of a transducer is influenced, at least in part, by the flexibility and/or frequency response of the flexible materials elastically suspending the diaphragm with respect to the electromagnet. Thus, increasing the length of the support arms also increases the ability of designers to tune the responsiveness of the transducer by adjusting the physical dimensions (e.g., width, thickness, etc.) and/or material selection (e.g., steel, aluminum, plastic, composite resins, etc.). Because longer support arms provide greater influence on the frequency and/or amplitude responsiveness of the transducer. Lengthy flexible supports were previously associated with large form factor transducers where flexible supports were connected to extend away from each side of a diaphragm, such that increased length of the flexible supports resulted in increased form factor length for the transducer. As a result of the present disclosure, a bone conduction transducer designer is no longer forced to choose between a small form factor design, and a broad selection of tunable frequency and/or amplitude responsiveness. 
     Further, because only two support arms are employed, as opposed to four supports, with one on each corner, the support arms are connected to opposing corners of the rectangular diaphragm. Connecting the support arms to opposing corners balance the torque on the diaphragm generated by one or the other of the support arms. 
     II. Examples of Wearable Computing Systems 
       FIG. 1A  illustrates an example wearable computing system. In  FIG. 1A , the wearable computing system takes the form of a head-mountable device (HMD)  102  (which may also be referred to as a head-mounted display). It is noted, however, that the present disclosure includes implementations of other wearable computing system form factors, such as helmets, hats, visors, headbands, adhesive patches, etc. As illustrated in  FIG. 1A , the head-mountable device  102  has lenses  110 ,  112  mounted in lens-frames  104 ,  106 . The lenses  110 ,  112  can optionally be vision-correcting lenses, for example. A center frame support  108  couples the lens-frames  104 ,  106  and can be configured to be compatible with a wearer&#39;s nose to allow the HMD  102  to be supported on a wearer&#39;s face. The HMD  102  also includes extending side-arms  114 ,  116  configured to be compatible with a wearer&#39;s ears to allow the HMD  102  to be supported on the wearer&#39;s face. The extending side-arms  114 ,  116  can be connected by a hinge to each of the lens-frames  104 ,  106  from a side opposite the center frame support  108 . 
     One or both of the lenses  110 ,  112  can be formed of a material suitable for displaying a projected image or graphic. The lenses  110 ,  112  can also be substantially transparent to allow a wearer to see through the lens element. Combining these features of the lenses  110 ,  112  can facilitate an augmented reality or heads-up display system where a projected image or graphic is superimposed over a real-world view, as perceived by the wearer through the lenses  110 ,  112 . 
     The HMD  102  can also include an on-board computing system  118 , a video camera  120 , a sensor  122 , and a finger-operable touch pad  124 . The on-board computing system  118  is shown to be positioned on the extending side-arm  114  of the head-mounted device  102 ; however, the on-board computing system  118  can be situated on other parts of the HMD  102  or can be positioned remote from the HMD  102  (e.g., a computing system can be wire-connected or wirelessly-connected to the HMD  102 ). The on-board computing system  118  can be configured to process signals from a content source to create driver signals to operate user-interface elements of the HMD  102  to portray information to the wearer, such as via the lenses  110 ,  112 . The on-board computing system  118  can be configured to receive and analyze data from the video camera  120 , the finger-operable touch pad  124 , and/or other sensory devices, user interfaces, etc. The on-board computing system  118  can include, for example, a processor executing instructions stored on a memory to implement the functions described. 
     The video camera  120  is positioned on the extending side-arm  114  of the head-mounted device  102 , but can also be situated in another location on the HMD  102 . The video camera  120  can be configured to capture images at various resolutions and/or frame rates. In some instances the video camera  120  can be similar in some respects to video cameras employed in other small form-factor environments, such as cameras used in cell phones, tablets, and webcams, for example. 
     Further, although  FIG. 1A  illustrates one video camera  120 , more video cameras can be included. For example, each can be configured to capture the same view, or to capture different views. For example, the video camera  120  can be forward-facing to capture at least a portion of the view perceived by the wearer. The forward-facing image captured by the video camera  120  can then be used to generate an augmented reality where computer generated images appear to interact with the real-world view perceived by the wearer. 
     A sensor  122  is shown on the extending side-arm  116  of the HMD  102 ; however, the sensor  122  can be positioned on other parts of the HMD  102 . The sensor  122  can include, for example, a gyroscope and/or an accelerometer to provide inertial motion sensitivity as an input to the computing system  118 . The sensor  122  can additionally or alternatively include sensors configured to detect environmental features and/or aspects of a wearer such as a microphone, a thermometer, an air monitor, solar detector, perspiration sensor, etc. 
     The finger-operable touch pad  124  is shown on the extending side-arm  114  of the HMD  102 . However, the finger-operable touch pad  124  can be positioned on other parts of the HMD  102 . Further, more than one finger-operable touch pad can be included on the HMD  102 . The finger-operable touch pad  124  can be used by a wearer to input commands. The finger-operable touch pad  124  can sense a presence, position, and/or movement of a finger in contact with, or at least proximate, the finger-operable touch pad  124 . The finger-operable touch pad  124  can operate via capacitive sensing, resistance sensing, or a surface acoustic wave process, among other possibilities. The finger-operable touch pad  124  can be capable of sensing finger movement in a direction parallel or planar to the pad surface, in a direction normal to the pad surface, or both, and can also be capable of sensing a level of pressure applied to the pad surface. The finger-operable touch pad  124  can be formed of one or more translucent or transparent insulating layers and one or more translucent or transparent conducting layers. Edges of the finger-operable touch pad  124  can be formed to have a raised, indented, or roughened surface, so as to provide tactile feedback to a user when the user&#39;s finger reaches the edge, or other area, of the finger-operable touch pad  124 . If more than one finger-operable touch pad is present, each finger-operable touch pad can be operated independently, and can provide a different function. 
     A vibration transducer  126  is embedded in the right extending side-arm  114 . The vibration transducer  126  functions as a bone-conduction transducer (BCT), which can be arranged such that when the HMD  102  is worn, the vibration transducer  126  is positioned to contact the wearer behind the wearer&#39;s ear. Additionally or alternatively, the vibration transducer  126  can be arranged such that the vibration transducer  126  is positioned to contact a front of the wearer&#39;s ear. In an example embodiment, the vibration transducer  126  can be positioned to couple to a specific location of the wearer&#39;s ear and/or skull, such as the tragus of the ear and/or the mastoid region of the skull. 
     The HMD  102  includes an audio interface (not shown) that is configured to receive an audio signal from a source of audio content and provide suitable electrical signals to the vibration transducer  126  to drive the vibration transducer  126 . For instance, in an example embodiment, the HMD  102  can include a microphone, an internal audio playback device such as an on-board computing system that is configured to play digital audio files, and/or an audio interface to an auxiliary audio playback device, such as a portable digital audio player, smartphone, home stereo, car stereo, and/or personal computer. The connection to such an auxiliary audio playback device can be a tip, ring, sleeve (TRS) connector, or can take another form. Other audio sources and/or audio interfaces can also be employed to generate electrical driver signals to the vibration transducer  126 . 
       FIG. 1B  illustrates an alternate view of the wearable computing device illustrated in  FIG. 1A . As shown in  FIG. 1B , the lens elements  110 ,  112  can act as display elements. The HMD  102  can include a projector  128  coupled to an inside surface of the extending side-arm  116  and configured to project a display  130  onto an inside surface of the lens element  112 . Additionally or alternatively, a second projector  132  can be coupled to an inside surface of the extending side-arm  114  and configured to project a display  134  onto an inside surface of the lens element  110 . 
     The lens elements  110 ,  112  can be configured to act as a combiner in a light projection system and can include a coating that reflects light projected onto them from the projectors  128 ,  132 . In some embodiments, a reflective coating is not used (e.g., when the projectors  128 ,  132  are scanning laser devices). 
     In alternative embodiments, other types of display elements can also be used. For example, the lens elements  110 ,  112  themselves may include: a transparent or semi-transparent matrix display, such as an electroluminescent display or a liquid crystal display. One or more optical waveguides or other optical elements can be incorporated in the lens elements  110 ,  112  or otherwise situated on the HMD  102  to deliver an in focus near-to-eye image to the wearer. A corresponding display driver can be disposed within the frame elements  104 ,  106  for driving such a matrix display (e.g., for providing electrical signals suitable for operating the projectors  128 ,  132  and/or electroluminescent display, etc.). Alternatively or additionally, a laser or LED source and scanning system can be used to draw a matrix display directly onto the retina of the wearer&#39;s eye(s). 
     The HMD  102  can optionally include vibration transducers  136   a ,  136   b , embedded in the left side-arm  116  and the right side-arm  114 , respectively. The vibration transducers  136   a ,  136   b  can be an alternative to, or in addition to, the vibration transducer  126 . The vibration transducers  136   a ,  136   b  can be situated on the HMD  102  to contact the wearer near the wearer&#39;s temple. 
       FIG. 1C  illustrates another example wearable computing system which takes the form of a head-mountable device (“HMD”)  138 . The HMD  138  can include frame elements and side-arms similar to the frame and extending side arms described in connection with  FIGS. 1A and 1B  above. The HMD  138  can additionally include an on-board computing system  140  and a video camera  142 , similar to the computing system and video camera(s) described in connection with  FIGS. 1A and 1B  above. The video camera  142  is shown mounted on a frame of the HMD  138 . However, the video camera  142  can be mounted at other positions on the HMD  138  as well. 
     As shown in  FIG. 1C , the HMD  138  can include a single display  144  which can be coupled to the device. The display  144  can be formed on one of the lens elements of the HMD  138 , which can be similar to the lens elements described in connection with  FIGS. 1A and 1B  above. The lenses in the HMD  138  can be configured to overlay computer-generated visually perceivable graphics in the wearer&#39;s view of the physical world. The display  144  is shown to be situated near the center of the lens of the HMD  138 , however, the display  144  can be situated in other positions, such as near a periphery of the lens(es), for example. The display  144  can be controlled (“driven”) via the computing system  140 . An optical waveguide  146  can optionally convey optical content to the display  144  from an image-generating region included in the frame of the HMD  138 . 
     The HMD  138  includes vibration transducers  148   a - b  embedded in the left and right side-arms of the HMD  138 . Each vibration transducer  148   a - b  functions as a bone-conduction transducer, and is arranged such that when the HMD  138  is worn, the vibration transducer is positioned to contact a wearer at a location behind the wearer&#39;s ear. Additionally or alternatively, the vibration transducers  148   a - b  can be situated on the HMD  138  such that the vibration transducers  148   a - b  are positioned to contact the front of the wearer&#39;s ear. 
     Further, in an embodiment with two vibration transducers  148   a - b , the vibration transducers can be separately driven to provide stereo audio (e.g., left and right stereo channels are conveyed via the two vibration transducers  148   b  and  148   a , respectively). As such, the HMD  138  can include at least one audio interface (not shown) for receiving audio signals from a source of audio content and providing suitable electrical driver signals to the vibration transducers  148   a - b.    
       FIG. 1D  illustrates another example wearable computing system which takes the form of a head-mountable device (“HMD”)  150 . The HMD  150  can include side-arms  152   a - b , a center frame support  154 , and a nose bridge  156 . The center frame support  154  connects the side-arms  152   a - b . The nose bridge  156  and the side-arms  152   a - b  can be configured to rest upon a wearer&#39;s nose and ears, respectively, to allow the HMD  150  to be mountable on a wearer&#39;s face. The HMD  150  does not include lens-frames containing lens elements. The HMD  150  can include an on-board computing system  158  and a video camera  160 , such as the computing systems and video camera(s) described in connection with  FIGS. 1A-1C  above. 
     The HMD  150  can include a display device  162  that can be coupled to one of the side-arms  152   a - b  or the center frame support  154 . The display device  162  is shown in  FIG. 1D  coupled to the side-arm  152   a  for purposes of illustration. The display device  162  can be similar to the display described in connection with  FIG. 1C  above, and can include, for example, electroluminescent and/or liquid crystal components to provide a matrix display of individually programmable pixels. In some examples, the display device  162  is configured to overlay computer-generated graphics on the wearer&#39;s view of the physical world. In one example, the display device  162  can be coupled to the inner side of the extending side-arm  152   a  (i.e., the side exposed to a portion of a wearer&#39;s head). The display device  162  can be positioned in front of or proximate to a wearer&#39;s eye when the HMD  150  is worn. For example, the display device  162  can be positioned below the center frame support  154 , as shown in  FIG. 1D , such that the display device  162  is situated in a line of sight of a wearer&#39;s eye while the nose bridge  156  rests on the wearer&#39;s nose. 
     Vibration transducers  164   a - b  are located on the left and right side-arms of HMD  150 . The vibration transducers  164   a - b  can be situated in the side-arms  152   a - b  of the HMD  150  similarly to the vibration transducers  148   a - b  on HMD  138  discussed in connection with  FIG. 1D  above. 
     The arrangements of the vibration transducers of  FIGS. 1A-1D  are not limited to those that are described and shown with respect to  FIGS. 1A-1D . Additional or alternative vibration transducers can be embedded in a head-mountable device or other wearable computing system. In some embodiments of the present disclosure, a wearable computing system includes vibration transducers positioned at one or more locations at which the wearable computing system contacts the wearer&#39;s head. In some examples, vibration transducers are situated on the wearable computing system to provide vibrational coupling to a bony structure of the wearer&#39;s head to allow acoustic signals to propagate through the wearer&#39;s jaw and/or skull to stimulate the wearer&#39;s inner ear and thereby allow for sound perception based on the operation of the vibration transducers. 
       FIG. 1E  is a simplified illustration of an example head-mountable device (“HMD”)  170  configured for bone-conduction audio. As shown, the HMD  170  includes an eyeglass-style frame comprising two side-arms  172   a - b , a center frame support  174 , and a nose bridge  176 . The side-arms  172   a - b  are connected by the center frame support  174  and arranged to fit behind a wearer&#39;s ears. The HMD  170  includes vibration transducers  178   a - e  that are configured to function as bone-conduction transducers. In some examples, one or more of the vibration transducers  178   a - e  vibrate anvils configured to interface with a bony portion of the wearer&#39;s head to thereby convey acoustic signals through the wearer&#39;s jaw and/or skull when the vibration transducers  178   a - e  vibrate with respect to the frame of the HMD  170 . Additionally or alternatively, it is noted that bone conduction audio can be conveyed to a wearer through vibration of any portion of the HMD  170  that contacts the wearer so as to transmit vibrations to the wearer&#39;s bone structure. For example, in some embodiments of the present disclosure, one or more of the vibration transducers  178   a - e  can operate without driving an anvil, and instead couple to the frame of the HMD  170  to cause the side-arms  172   a - b , center frame support  174 , and/or nose bridge  176  to vibrate against the wearer&#39;s head. 
     The vibration transducers  178   a - e  are securely connected to the HMD  170  and can optionally be wholly or partially embedded in the frame elements of the HMD  170  (e.g., the side-arms  172   a - b , center frame support  174 , and/or nose bridge  176 ). For example, vibration transducers  178   a ,  178   b  can be embedded in the side-arms  172   a - b  of HMD  170 . In an example embodiment, the side-arms  172   a - b  are configured such that when a wearer wears HMD  170 , one or more portions of the eyeglass-style frame are configured to contact the wearer at one or more locations on the side of the wearer&#39;s head. For example, side-arms  172   a - b  can contact the wearer at or near the wearer&#39;s ear and the side of the wearer&#39;s head. Accordingly, vibration transducers  178   a ,  178   b  can be embedded on the inward-facing side (toward the wearer&#39;s head) of the side-arms  172   a - b  to vibrate the wearer&#39;s bone structure and transfer vibration to the wearer via contact points on the wearer&#39;s ear, the wearer&#39;s temple, or any other point where the side-arms  172   a - b  contact the wearer. 
     Vibration transducers  178   c ,  178   d  are embedded in the center frame support  174  of HMD  170 . In an example embodiment, the center frame support  174  is configured such that when a wearer wears HMD  170 , one or more portions of the eyeglass-style frame are configured to contact the wearer at one or more locations on the front of the wearer&#39;s head. Vibration transducers  178   c ,  178   d  can vibrate the wearer&#39;s bone structure, transferring vibration via contact points on the wearer&#39;s eyebrows or any other point where the center frame support  404  contacts the wearer. Other points of contact are also possible. 
     In some examples, the vibration transducer  178   e  is embedded in the nose bridge  176  of the HMD  170 . The nose bridge  176  is configured such that when a user wears the HMD  170 , one or more portions of the eyeglass-style frame are configured to contact the wearer at one or more locations at or near the wearer&#39;s nose. Vibration transducer  178   e  can vibrate the wearer&#39;s bone structure, transferring vibration via contact points between the wearer&#39;s nose and the nose bridge  176 , such as points where the nose bridge  176  rests on the wearer&#39;s face while the HMD  170  is mounted to the wearer&#39;s head. 
     When there is space between one or more of the vibration transducers  178   a - e  and the wearer, some vibrations from the vibration transducer can also be transmitted through air, and thus may be received by the wearer over the air. That is, in addition to sound perceived due to bone conduction, the wearer may also perceive sound resulting from acoustic waves generated in the air surrounding the vibration transducers  178   a - e  which reach the wearer&#39;s outer ear and stimulate the wearer&#39;s tympanic membrane. In such an example, the sound that is transmitted through air and perceived using tympanic hearing can complement sound perceived via bone-conduction hearing. Furthermore, while the sound transmitted through air can enhance the sound perceived by the wearer, the sound transmitted through air can be sufficiently discreet as to be unintelligible to others located nearby, which can be due in part to a volume setting. 
     In some embodiments, the vibration transducers  178   a - e  are embedded in the HMD  170  along with a vibration isolating layer (not shown) in the support structure of the HMD  170  (e.g., the frame components). For example, the vibration transducer  178   a  can be attached to a vibration isolation layer, and the vibration isolation layer can be connected to the HMD  170  frame (e.g., the side-arms  172   a - b , center frame support  174 , and/or nose bridge  176 ). In some examples, the vibration isolating layer is configured to reduce audio leakage to a wearer&#39;s surrounding environment by reducing the amplitude of vibrations transferred from the vibration transducers to air in the surrounding environment, either directly or through vibration of the HMD  170  frame components. 
     III. Remotely-Controlled Wearable Computing Systems 
       FIG. 2  illustrates a schematic drawing of an example computing system. In system  200 , a device  202  communicates using a communication link  212  (e.g., a wired or wireless connection) to a remote device  214 . The device  202  can be any type of device that can receive data and display information corresponding to or associated with the data. For example, the device  202  can be a wearable computing system, such as the head-mountable devices  102 ,  138 ,  150 , and/or  170  described with reference to  FIGS. 1A-1E . 
     The device  202  can include a bone conduction audio system  204  for delivering audio content to a wearer of the device  202 . The bone conduction audio system  204  includes a processor  206  and a bone conduction transducer (“BCT”)  208 . The BCT  208  can be, for example, an embedded device including a vibrating diaphragm configured to vibrate according to input signals. In some examples, the bone conduction audio system  204  includes more than one bone conduction transducer. The BCT  208  (or group of BCTs) can be mounted to a frame portion of the device  202  and situated to convey vibrations to a bony portion of the wearer&#39;s head such that vibrations propagate through the wearer&#39;s skull and/or jaw to the wearer&#39;s inner ear. The memory  210  can include executable instructions to be carried out via the processor  206 . The processor  206  and/or memory  210  can include hardware and/or software implemented functions to interface with a source of audio content and provide suitable electrical driver signals to the BCT  208  (or group of BCTs). 
     The processor  206  and/or memory  210  can be configured to receive data from a remote device  214  via wired and/or wireless signals  212 . The processor  206  and/or memory  210  can be configured to generate driver signals for the BCT  208  based on the received data signals  212 . The processor  206  can be, for example, a micro-processor, a digital signal processor, etc. 
     The remote device  214  can be a computing device or transmitter configured to transmit data  212  to the device  202 . For example, the remote device  214  can be a laptop computer, a mobile telephone, a tablet computing device, etc. The remote device  214  and the device  202  can each include appropriate hardware to allow for generating and receiving the communication signals  212 , such as processors, transmitters, receivers, antennas, etc. 
     In  FIG. 2 , the communication link between the device  202  and the remote device  214  is illustrated as a wireless connection; however, wired connections can also be used. For example, the communication link providing the signals  212  can be achieved by a wired serial bus such as a universal serial bus or a parallel bus. A wired connection can be a proprietary connection as well. The communication link  212  can additionally or alternatively be a wireless connection using, e.g., Bluetooth® radio technology, communication protocols described in IEEE 802.11 (including any IEEE 802.11 revisions), Cellular technology (such as GSM, CDMA, UMTS, EV-DO, WiMAX, or LTE), or Zigbee® technology, among other possibilities. The remote device  214  can be accessible via the Internet and may include a server associated with a particular web service (e.g., social-networking, photo sharing, audio streaming, etc.). 
     IV. Bone Conduction Transducer with Cantilevered Support Arms 
       FIG. 3A  is an exploded view of a bone conduction transducer (“BCT”)  300  including cantilevered support arms  340  suspending a diaphragm  330 .  FIG. 3B  is an assembled view of the BCT  330  shown in  FIG. 3A . The BCT  300  includes a frame  310  providing a support structure for an electromagnet with a wire coil  322  and permanent magnets  320   a - b . A diaphragm  330  is elastically suspended over the wire coil  322  by a pair of cantilevered support arms  340 . The support arms  340   a - b  are arranged as leaf springs that each extend adjacent a long side of the diaphragm  330 . The support arms  340   a - b  flex to allow the diaphragm  330  to travel toward and away from the electromagnetic wire coil  322  in response to time-changing magnetic fields generated by the wire coil  322 . 
     The frame  310  includes a base platform with a top surface  311   a  and a bottom surface  311   b  opposite the top surface  311   a . A core  314  extends normal to the top surface  311   a  from a central portion of the base platform to pass through the center of the wire coil  322 . The core  314  (and the rest of the frame  310 ) can be formed of nickel-plated steel or another ferromagnetic material to respond to the time-varying magnetic field created by current in the wire coil  322 . The diaphragm  330  can also be formed of a ferromagnetic material (e.g., nickel-plated steel) such that the diaphragm  330  moves under the combined forces of the electromagnetic wire coil  322  and the permanent magnets  320   a - b.    
     The permanent magnets  320   a - b  combine to provide a magnetic bias on the diaphragm  330 . The permanent magnets  320   a - b  can be arranged with their magnetic fields commonly aligned and oriented in parallel with the axis of the electromagnet coil  322  (i.e., along the direction of the core  314 ). The permanent magnets  320   a - b  can be situated approximately axially symmetric with respect to the axis of the wire coil  322  (i.e., the core  314 ) such that the magnetic field contributions provided by each of the permanent magnets  320   a - b  are approximately equal at the center of the wire coil  322 . For example, the permanent magnets  320   a - b  can be situated on the top surface  311   a  of the base platform of the frame  310  on opposing sides of the wire coil  322 . Where the diaphragm  330  is a ferromagnetic material, such as, for example, nickel-plated steel, the bias from the permanent magnets  320   a - b  magnetizes diaphragm  330  with an opposite (attractive) magnetic field roughly aligned along the core  314  (at the mid-point of the two permanent magnets  320   a - b ). The induced magnetization of the diaphragm  330  due to the permanent magnets  320   a - b  allows the diaphragm  330  to react to time varying magnetic fields generated via the electromagnetic wire coil  322 . 
     It is noted that the present disclosure describes an arrangement of the BCT  300  with two permanent magnets (e.g., the permanent magnets  320   a - b ), however the magnetic bias of the diaphragm  330  can be provided by one or more permanent magnets connected to the frame  310 . For example, in some embodiments, a magnetic bias can be provided by three permanent magnets arranged approximately axially symmetrically around the core  314  of the electromagnetic wire coil  322 . Moreover, the permanent magnets need not be mounted to the top surface  311   a  of the frame platform, and can be additionally or alternatively mounted to the bottom surface  311   b , for example. 
     In addition to the core  314 , the frame  310  includes two struts  312   a - b  that extend normal to the top surface  311   a  of the base platform. The struts  312   a - b  can be situated so as to originate from opposing ends of the base platform of the frame  310 . Where the base platform is rectangular in shape with four corners, the first strut  312   a  extends perpendicular to the top surface  311   a  from one corner of the rectangle while the second strut  312   b  extends from an opposite corner (i.e., a non-adjacent corner). The struts  312   a - b  each provide a secure mounting point for one of the flexible support arms  340   a - b . In combination, the struts  312   a - b  anchor one end of each of the flexible support arms  340   a - b  to the frame  310 . The opposite end of each of the support arms  340   a - b  is connected to the diaphragm  330  to allow the diaphragm  330  to vibrate under force of the time-changing magnetic field generated by the electromagnetic coil  322 . 
     It is noted that the struts  312   a - b  illustrate one example configuration to mechanically connect the support arms  340   a - b  to the frame  310  such that the diaphragm  330  is elastically suspended with respect to the frame  310 . However, other configurations can be employed to elastically suspend the diaphragm  330  with respect to the frame  310 . For example, the frame  310  can additionally or alternatively include sidewalls that extend perpendicularly from the top surface  311   a  of the base platform and terminate with a top surface suitable for mounting the support arms  340   a - b . In some examples, sidewalls can be integrally formed to form sides adjacent each of the magnets  320   a - b . In some examples, support arms for elastically suspending the diaphragm  330  can be formed with a transverse mounting surface to overlap with respective top surfaces of such sidewalls. 
     A. Cantilevered Flexible Support Arms 
     Each of the support arms  340   a - b  includes a leaf spring extension  344   a - b  terminating at one end with a frame mount end  346   a - b , and terminating at the opposite end with an overlapping diaphragm connection  342   a - b . On the first support arm  340   a , the leaf spring extension  344   a  can be formed of a metal, plastic, and/or composite material and has an approximately rectangular cross-section with a height smaller than its width. For example, the approximately rectangular cross section can have rounded corners between substantially straight edges, or can be a shape that lacks straight edges, such as an ellipse or oval with a height smaller than its width. Due to the smaller height, the support arm  340   a  flexes more readily in a direction transverse to its cross-sectional height than its width, such that the support arm  340   a  provides flexion (i.e., movement) in a direction substantially transverse to its cross-sectional height, without allowing significant movement in a direction transverse to its cross-sectional width. 
     In some embodiments, the cross-sectional height and/or width of the support arms  340   a - b  can vary along the length of the support arms  340   a - b  in a continuous or non-continuous manner such that the support arms  340   a - b  provide desired flexion. For example, the cross-sectional height and/or width of the support arms  340   a - b  can be gradually tapered across their respectively lengths to provide a change in thickness from one end to the other (e.g., a variation in thickness of 10%, 25%, 50%, etc.). In another example, the cross-sectional height and/or width of the support arms  340   a - b  can be relatively small near their respective mid-sections in comparison to their respective ends (e.g., a mid-section with a thickness and/or width of 10%, 25%, 50%, etc. less than the ends). Changes in thickness (i.e., cross-sectional height) and/or width adjust the flexibility of the support arms  340   a - b  and thereby change the frequency and/or amplitude response of the diaphragm  330 . 
     Thus, the leaf spring extension  344   a  can allow the diaphragm  330  to travel toward and away from the wire coil  322  (e.g., parallel to the orientation of the core  314 ), without moving substantially side-to-side (e.g., perpendicular to the orientation of the core  314 ). The leaf spring extension  344   b  similarly allows the diaphragm  330  to elastically travel toward and away from the wire coil  322 . The frame mount ends  346   a - b  can be a terminal portion of the leaf spring extensions  340   a - b  that overlaps the struts  312   a - b  when the BCT  330  is assembled. The frame mount ends  346   a - b  are securely connected to the respective top surfaces  313   a - b  of the struts  312   a - b  to anchor the support arms  340   a - b  to the frame  310 . The opposite ends of the support arms  340   a - b  extend transverse to the length of the leaf spring extensions  344   a - b  to form the overlapping diaphragm mounts  342   a - b . In some embodiments, the leaf spring extensions  344   a - b  can resemble the height of an upper-case letter “L” while the respective transverse-extended overlapping diaphragm mounts  342   a - b  resemble the base. In some embodiments, such as where the frame  310  additionally or alternatively includes sidewalls for mounting the support arms  340   a - b , the support arms  340   a - b  can resemble an upper-case letter “C,” with leaf spring extensions formed from the mid-section of the “C” and the bottom and top transverse portions providing mounting surfaces to the diaphragm  330  and the side walls, respectively. 
     The diaphragm  330  is situated as a rectangular plate situated perpendicular to the orientation of the electromagnet core  314  with extending mounting surfaces  332   a - b . The diaphragm  330  includes an outward vibrating surface  334  and opposite coil-facing surface  336 , and mounting surfaces  332   a - b  extending outward from the vibrating surface  334 . The mounting surfaces  332   a - b  can be in a parallel plane to the vibrating surface  334 , with both in a plane approximately perpendicular to the orientation of the core  314 . The mounting surfaces  332   a - b  interface with the overlapping diaphragm mounts  342   a - b  to elastically suspend the diaphragm  330  over the electromagnetic coil  322 . 
     In some embodiments, the vibrating surface  334  is rectangular and oriented in approximately the same direction as the base platform of the frame  310 . The mounting surfaces  332   a - b  can optionally project along the length of the rectangular diaphragm  330  to underlap the transverse-extended overlapping diaphragm mounts  342   a - b  of the support arms  340   a - b . The mounting surfaces  332   a - b  can optionally project along the width of the rectangular diaphragm  330  to allow the support arms  340   a - b  to overlap the mounting surfaces  332   a - b  on a portion of the leaf-spring extensions  344   a - b  in addition to the transverse-extended overlapping diaphragm mounts  342   a - b.    
     Furthermore, the two support arms  340   a - b  are connected to opposite ends of the diaphragm  330  (via the overlapping diaphragm mounts  342   a - b ) so as to balance torque generated on the diaphragm  330  by the individual support arms  340   a - b . That is, each of the support arms  340   a - b  are connected to the diaphragm  330  away from its center-point, but at opposing locations of the diaphragm  330  so as to balance the resulting torque on the diaphragm  330 . 
     When assembled, the first support arm  340   a  is connected to the frame  310  at one end ( 346   a ) via the first strut  312   a , and the leaf spring extension  344   a  is projected adjacent the length of the diaphragm  330 . The overlapping diaphragm mount  342   a  of the first support arm  340   a  connects to the diaphragm  330  at the mounting surface  332   a . One edge of the mounting surface  332   a  is situated adjacent the second strut  312   b , but the opposite end can extend along the width of the diaphragm  330  to underlap the overlapping diaphragm mount  342   a . Similarly, the second support arm  340   b  is connected to the frame  310  at one end ( 346   b ) via the second strut  312   b , and the leaf spring extension  344   b  is projected adjacent the length of the diaphragm  330 . The overlapping diaphragm mount  342   a  of the first support arm  340   a  connects to the diaphragm  330  at the mounting surface  332   a . One edge of the mounting surface  332   b  is situated adjacent the first strut  312   a , but the opposite end can extend along the width of the diaphragm  330  to underlap the overlapping diaphragm mount  342   b . To allow for movement of the diaphragm  330  via flexion of the leaf spring extensions  344   a - b  of the support arms  340   a - b , each of the support arms  340   a - b  and the diaphragm  330  are free of motion-impeding obstructions with the frame  310 , wire coil  322  and/or permanent magnets  320   a - b.    
     B. Operation of the Bone Conduction Transducer 
     In operation, electrical signals are provided to the BCT  300  that are based on a source of audio content. The BCT  300  is situated in a wearable computing device such that the vibrations of the diaphragm  330  are conveyed to a bony structure of a wearer&#39;s head (to provide vibrational propagation to the wearer&#39;s inner ear). For example, with reference to  FIG. 2 , the processor  206  can interpret signals  212  from the remote device  214  communicating a data indicative of audio content (e.g., a digitized audio stream). The processor  206  can generate electrical signals to the wire coil  322  to create a time-changing magnetic field sufficient to vibrate the diaphragm  330  to create vibrations in the wearer&#39;s inner ear corresponding to the original audio content communicated via the signals  212 . For example, the electrical signals can drive currents in alternating directions through the wire coil  322  so as to create a time-changing magnetic field with a frequency and/or amplitude sufficient to create the desired vibrations for perception in the inner ear. 
     The vibrating surface  334  of the diaphragm  330  can optionally include mounting points, such as, for example, threaded holes, to allow for securing an anvil to the BCT  300 . For example, an anvil with suitable dimensions and/or shape for coupling to a bony portion of a head can be mounted to the vibrating surface  334  of the diaphragm  330 . The mounting points thereby allow for a single BCT design to be used with multiple different anvils, such as some anvils configured to contact a wearer&#39;s temple, and others configured to contact a wearer&#39;s mastoid bone, etc. It is noted that other techniques may be used to connect the diaphragm  330  to an anvil, such as adhesives, heat staking, interference fit (“press fit”), insert molding, welding, etc. Such connection techniques can be employed to provide a rigid bond between an anvil and the vibrating surface  334  such that vibrations are readily transferred from the vibrating surface  334  to the anvil and not absorbed in such bonds. In some examples, the diaphragm  330  can be integrally formed with a suitable anvil, such as where a vibrating surface of the diaphragm  330  is exposed to be employed as an anvil for vibrating against a bony portion of the wearer&#39;s head. 
     In some embodiments of the present disclosure, the support arms  340   a - b  are cantilevered along the length of the diaphragm  330  (i.e., along the longest dimension of the approximately rectangular plate forming the vibrating surface  334 ). One end of the cantilevered support arm  340   a  is connected to the frame  310  via the strut  312   a  (at the connection point  346   a ) near one side of the diaphragm  330 , and the opposite end of the support arm  340   a  is connected to the diaphragm  330  near the opposite end of the diaphragm  330  via the support surface  332   a  and the overlapping diaphragm mount  342   a . Similarly, one end of the cantilevered support arm  340   b  is connected to the frame  310  via the strut  312   b  (at the connection point  346   b ) near one side of the diaphragm  330 , and the opposite end of the support arm  340   b  is connected to the diaphragm  330  near the opposite end of the diaphragm  330  via the support surface  332   b  and the overlapping diaphragm mount  342   b . Thus, the two support arms  340   a - b  cross one another on opposite sides of the diaphragm  330  to balance the torque on the diaphragm  330 , with one extending adjacent one side of the diaphragm  330 , the other extending along the opposite side of the diaphragm  330 . 
     It is noted that the BCT  330  shows the connection between the support arms  340   a - b  and the diaphragm  330  with the support arms  340   a - b  overlapping the diaphragm  330  (e.g., at the overlapping diaphragm mounts  340   a - b ). However, a secure mechanical connection between the support arms  340   a - b  and the diaphragm  330  can also be provided by arranging the diaphragm  330  to overlap the support arms  340   a - b . In such case, the struts  312   a - b  can optionally be lowered by an amount approximately equal to the thickness of the diaphragm mounting surfaces  332   a - b  to achieve a comparable separation between the diaphragm lower surface  336  and the electromagnetic coil  314 . 
     Some embodiments of the present disclosure provide a compact form factor for a bone conduction transducer while maximizing the length of the elastic components (e.g., the leaf spring extensions  344   a - b  of the support arms  340   a - b ). The performance of the BCT  300  can accordingly be tuned by adjusting the parameters of the support arms  340   a - b  contributing to the elasticity of the diaphragm  330 . Generally, materials selection of the support arms  340   a - b  can be chosen to achieve different frequency and/or amplitude responses for the BCT  300 . For example, the support arms  340   a - b  can be formed of steel (including a variety of grades of stainless steel), aluminum, other metals and alloys, plastics, carbon composites, etc. to provide varying frequency and/or amplitude responses. Furthermore, even for a particular material, such as stainless steel, for example, frequency and/or amplitude response can be adjusted by modifying the grade (e.g., purity) and/or manufacturing processes (e.g., tempering) of such material. The thickness of the support arms (i.e., the cross-sectional height) and/or the width of the support arms can be adjusted to provide varying frequency and/or amplitude responses. For example, an increased cross-sectional height of the support arms  340   a - b  results in a “stiffer” response, that is, less amplitude variations for a given time-varying magnetic field generated by the wire coil  322 . Selecting from among available materials and dimensions allows for tuning the BCT  300  to achieve a desired amplitude and/or frequency response. 
     In some embodiments, the support arms  340   a - b  are themselves non-magnetic to prevent the support arms  340   a - b  from contributing to the response of the time-varying magnetic fields produced at the electromagnetic coil  322 . For example, the support arms  340   a - b  can be formed of a non-magnetic stainless steel, carbon fiber, plastic, and/or glass-fiber composites, etc. 
     C. Laser Spot Weld Assembly of the Bone Conduction Transducer 
       FIG. 4A  shows example spot welding locations to assemble a bone conduction transducer  400  according to one embodiment. The bone conduction transducer  400  is assembled by laser welding the support arms  340   a - b  to the struts  312   a - b  of the frame  310  and the diaphragm  330  at a series of spots along the exposed edges of the interface between the support arms  340   a - b  and the struts  312   a - b  and diaphragm  330 . For illustrative purposes, the second support arm  340   b  is shown with three laser weld spots  410 ,  411 ,  412  along the outer edge where the second support arm end  346   b  meets the top surface  313   b  of the second strut  312   b . Laser spot welds  413 ,  414  are indicated along the exposed edges of the interface between the first support arm end  346   a  meets the top surface  313   a  of the first strut  312   a . Similarly, laser spot welds  420 ,  421 ,  422 , etc. are indicated along the exposed edges of the interface between the overlapping diaphragm mount  342   b  and the diaphragm mounting surface  332   b . During assembly of the BCT  400 , a laser sufficient to generate heat for laser welding is directed to the regions indicated as laser weld spots  410 - 422 , etc. It is noted that the view provided in  FIG. 4A  illustrates one visible side of the BCT  400 , and that an edge laser weld assembly would include applying laser welds along all exposed edges of interfaces between the support arms  340   a - b , the struts  312   a - b , and the diaphragm  330 , including edges not visible in  FIG. 4A . 
       FIG. 4B  shows example spot welding locations to assemble a bone conduction transducer  401  according to another embodiment. The bone conduction transducer  401  is assembled by laser welding the support arms  340   a - b  to the struts  312   a - b  and the diaphragm  330  by laser welding the top exposed surface of the support arms  340   a - b . The support arms  340   a - b  are sufficiently thin that a laser weld spot applied to the top surface can effectively securely connect the support arms  340   a - b  to the diaphragm  330  and/or struts  312   a - b  located below. For illustrative purposes, the second support arm  340   b  is shown with two laser weld spots  430 ,  431  where the second support arm end  346   b  meets the top surface  313   b  of the second strut  312   b . The laser weld spots  430 ,  431  are generated by directing a laser source to the side of the second support arm end  346   b  opposite the side facing the top surface  313   b  of the second strut  312   b . Heat generated at the laser weld spots  430 ,  431  welds the second support arm end  346   b  to the second strut  312   b . Similarly, laser spot welds  440 ,  441 , etc. are indicated along the exposed top surface of the overlapping diaphragm mount  342   b  opposite the side facing the diaphragm mounting surface  332   b . Heat generated at the laser weld spots  440 ,  441  welds the second support arm  340   b  to the diaphragm  330 . Similarly, laser weld spots are indicated to connect the first support arm  340   a  to the first strut  312   a  and diaphragm mounting surface  332   a.    
     In some embodiments, the support arms  340   a - b  can be securely connected to the struts  312   a - b  and/or diaphragm  330  with a combination of laser welds along exposed edges, on the surface of the support arms  340   a - b  or a combination thereof. Furthermore, some embodiments of the present disclosure provide for the support arms  340   a - b  to be securely connected to the struts  312   a - b  and/or diaphragm  330  without employing a laser weld connection (e.g., by adhesives, heat staking, interference fit (“press fit”), insert molding, other forms of welding, etc.). 
     In some embodiments, the connection between the support arms  340   a - b  and the struts  312   a - b  can optionally be non-uniform across the top surfaces  313   a - b  of the struts  312   a - b . For example, to adjust (“tune”) the frequency and/or amplitude response of the support arms  340   a - b , the support arms  340   a - b  can be connected only near the far end of the support arm ends  346   a - b  (e.g., near the laser weld point  410  in  FIG. 4A ) and the remainder of the interfaces with the top surfaces  313   a - b  can be left unconnected to allow for additional travel of the diaphragm  330 . Alternatively, the support arms  340   a - b  can be connected only nearest the edge of the struts  312   a - b  further from the far end of the support arm ends  346   a - b  (e.g., near the laser weld point  412  in  FIG. 4A ) and the remainder of the interfaces with the top surfaces  313   a - b  can be left unconnected to allow for additional spring in the diaphragm  330 . 
       FIG. 5  shows an example process  500  for assembling the bone conduction transducer according to an embodiment. A first flexible support arm is arranged with one end overlapping a mounting surface on a magnetic diaphragm and another end overlapping a frame element ( 502 ). A second flexible support arm is arranged with one end overlapping a mounting surface on a magnetic diaphragm and another end overlapping a frame element ( 504 ). The frame element on which the flexible support arms are overlaid can be, for example, a strut feature similar to the struts  312   a - b , an integrally formed sidewall similar to the discussion of sidewalls in connection with  FIG. 3  above, etc. The two support arms can be connected to opposing sides of the magnetic diaphragm (e.g., the diaphragm mounting surfaces  332   a ,  332   b ). The support arms can be situated with their respective ends overlaid on the magnetic diaphragm and the frame elements at overlapping regions of the support arms. It is noted that the support arms (e.g., the support arms  340   a - b ) can be arranged in any order (e.g., first arm, then second arm; second arm, then first arm; or simultaneously). 
     Once arranged, the support arms can be laser welded to both the magnetic diaphragm and the frame such that the magnetic diaphragm is elastically suspended with respect to the frame via the flexible support arms ( 506 ). A laser source sufficient to generate heat for laser welding can be directed to the overlapping regions of the flexible support arms to form one or more laser weld spots that couple the support arms to the magnetic diaphragm and the frame. For example, laser weld spots can be created by directing the laser source to an exposed top surface of the flexible support arms (e.g., a surface opposite the surface facing the magnetic diaphragm and/or frame elements) to form weld spots by heating through the overlapping regions of the flexible support arms, such as the laser weld spots described in connection with  FIG. 4B  above. Additionally or alternatively, laser weld spots can be created by directing the laser source to an exposed edge of the flexible support arms (e.g., a side edge immediately adjacent a surface facing the magnetic diaphragm and/or frame elements) to form weld spots by side heating the edges of the overlapping regions of the flexible support arms, such as the laser weld spots described in connection with  FIG. 4A  above. 
     As noted above, in some embodiments, the support arms can be arranged according to blocks  502 ,  504  simultaneously. For example, with reference to the example support arms in  FIGS. 3A and 3B , the pair of support arms  340   a - b  can be joined, during alignment, by one or more removable tabs integrally formed with the support arms, such that the pair of support arms is moved into position as a single unit to overlap the mounting surfaces  332   a - b  of the magnetic diaphragm  330  and the frame elements. For example, the pair of support arms  340   a - b  can be formed by stamping a piece of sheet metal (or other metal) to cut out both support arms  340   a - b  simultaneously while leaving one or more tabs connecting the two support arms. For example, tabs can be cut out such that respective opposing ends of the support arms  340   a - b  are connected together to maintain the geometry of the support arm configuration (e.g., the spacing between the support arms, the co-planar relationship of the support arms, etc.). Thus, in one example, the support arm end  346   a  of the first support arm  340   a  can be connected to the overlapping diaphragm mount  346   b  of the second support arm  340   b  through an integrally formed tab, and the support arm end  346   b  of the second support arm  340   b  can be connected to the overlapping diaphragm mount  346   a  of the first support arm  340   a  through an integrally formed tab. In such an example, the integrally formed tabs can complete a four-sided frame formed by the two support arms  340   a - b  to rigidly hold the configuration of the two support arms  340   a - b  relative to one another while they are positioned (“arranged”) and laser welded in place. Once the support arms  340   a - b  are laser welded in place, such as in block  506  above, the alignment tabs, if present, can be removed (e.g., by breaking the tabs along score lines, by cutting the tabs with an appropriate tool, etc.). For example, score lines can be formed by an appropriate relief in the die that stamps the pair of support arms and the alignment tabs. 
     In some embodiments, such tabs can be stamped from the same sheet of metal (or other material) as the support arms. In comparison to forming the first support arm from one sheet of metal and the second support arm from another sheet of metal, forming the pair of support arms from adjacent regions of the same sheet of metal. (e.g., by stamping the sheet of metal to form support arms in the configuration and alignment desired once assembled) results in pairs of support arms with matched properties, such as thickness, material chemistry, flexibility, etc. Creating support arms with matched properties ensures that the assembled bone conduction transducer is balanced and the magnetic diaphragm vibrates back and forth without biasing one side or the other. 
     In some embodiments, such alignment tabs are situated to protrude from the body of the assembled bone conduction transducer without interfering with other features in the transducer (such as sidewalls and/or struts of the frame, the magnetic diaphragm, the permanent magnets, etc.). Such alignment tabs can protrude, for example, transverse to the direction of the leaf spring extensions  344   a - b  (i.e., the “long” dimension of the respective support arms), and outward from the transducer  300  (i.e., away from the middle of the transducer  300 . Such a configuration may be employed, for example, when the support arms are implemented in a C-shaped configuration and connect to the frame along a base of the C that is transverse to the leaf-spring section and overlaps a sidewall of the frame. In such an example, an alignment tab can emerge from the end of the C-shaped base of one support arm and join the other support arm along the middle portion of the C shape, near the end overlapping the magnetic diaphragm. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.