Patent Publication Number: US-9900676-B2

Title: Wearable computing device with indirect bone-conduction speaker

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 13/269,935, filed on Oct. 10, 2011, which claims priority to U.S. Provisional Patent Application No. 61/509,997, filed Jul. 20, 2011, both of which are incorporated herein by reference in their entirety and for all purposes. 
    
    
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     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 very small image display element close enough to a wearer&#39;s (or user&#39;s) eye(s) such that the displayed image fills or nearly fills the field of view, and appears as a normal sized image, such as might be displayed on a traditional image display device. The relevant technology may be referred to as “near-eye displays.” 
     Near-eye displays are fundamental components of wearable displays, also sometimes called “head-mounted displays” (HMDs). A head-mounted display places a graphic display or displays close to one or both eyes of a wearer. To generate the images on a display, a computer processing system may be used. Such displays may occupy a wearer&#39;s entire field of view, or only occupy part of wearer&#39;s field of view. Further, head-mounted displays may be as small as a pair of glasses or as large as a helmet. 
     SUMMARY 
     In one aspect, an exemplary wearable-computing system may include: (a) one or more optical elements; (b) a support structure comprising a front section and at least one side section, wherein the support structure is configured to support the one or more optical elements; (c) an audio interface configured to receive an audio signal; and (d) at least one vibration transducer located on the at least one side section, wherein the at least one vibration transducer is configured to vibrate at least a portion of the support structure based on the audio signal. In this exemplary wearable-computing system, the vibration transducer is configured such that when the support structure is worn, the vibration transducer vibrates the support structure without directly vibrating a wearer. Further, the support structure is configured such that when worn, the support structure vibrationally couples to a bone structure of the wearer. 
     In another aspect, an exemplary wearable-computing system may include: (a) a support structure comprising a front section and at least one side section, wherein the support structure is configured to support the one or more optical elements; (b) a means for receiving an audio signal; and (c) a means for vibrating at least a portion of the support structure based on the audio signal, wherein the means for vibrating is located on the at least one side section. In this exemplary wearable-computing system, the means for vibrating is configured such that when the support structure is worn, the means for vibrating vibrates the support structure without directly vibrating a wearer. Further, the support structure is configured such that when worn, the support structure vibrationally couples to a bone structure of the wearer. 
     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. 1  illustrates a wearable computing system according to an exemplary embodiment. 
         FIG. 2  illustrates an alternate view of the wearable computing system of  FIG. 1 . 
         FIG. 3  illustrates an exemplary schematic drawing of a wearable computing system. 
         FIG. 4  is a simplified illustration of a head-mounted display configured for indirect bone-conduction audio, according to an exemplary embodiment. 
         FIG. 5  is another block diagram illustrating an HMD configured for indirect bone-conduction audio, according to an exemplary embodiment. 
         FIG. 6  is another block diagram illustrating an HMD configured for indirect bone-conduction audio, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary methods and systems are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or features. The exemplary embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. 
     I. Overview 
     The disclosure generally involves a wearable computing system with a head-mounted display (HMD), and in particular, an HMD having at least one vibration transducer that functions as a speaker. An exemplary HMD may employ vibration transducers that are commonly referred to as bone-conduction transducers. However, standard applications of bone-conduction transducers involve direct transfer of sound to the inner ear by attaching the transducer directly to the bone (or a pad that is adjacent to the bone). An exemplary HMD, on the other hand, may include a bone-conduction transducer (or another type of vibration transducer) that transfers sound to the wearer&#39;s ear via “indirect bone conduction.” 
     More specifically, an exemplary HMD may include a vibration transducer that does not vibrationally couple to wearer&#39;s bone structure (e.g., a vibration transducer that is located so as to avoid substantial contact with the wearer when the HMD is worn). Instead, the vibration transducer is configured to vibrate the frame of the HMD. The HMD frame is in turn vibrationally coupled to the wearer&#39;s bone structure. As such, the HMD frame transfers vibration to the wearer&#39;s bone structure such that sound is perceived in the wearer&#39;s inner ear. In this arrangement, the vibration transducer does not directly vibrate the wearer, and thus may be said to function as an “indirect” bone conduction speaker. 
     In an exemplary embodiment, the vibration transducer may be placed at a location on the HMD that does not contact the wearer. For example, on a glasses-style HMD, a vibration transducer may be located on a side-arm of the HMD, near where the side-arm connects to the front of the HMD. Further, in an exemplary embodiment, the HMD may be configured such that when worn, there is space (e.g., air) between the portion of the HMD where the vibration transducer is located and the wearer. As such, the portion of the HMD that contacts and vibrationally couples to the wearer may be located away from the vibration transducer. 
     In another aspect, because the vibration transducer vibrates the frame of the HMD instead of directly vibrating a wearer, the frame may transmit the audio signal through the air as well. In some embodiments, the airborne audio signal may be heard by the wearer, and may actually enhance the sound perceived via indirect bone conduction. At the same time, this airborne audio signal may be much quieter than airborne audio signals emanating by traditional diaphragm speakers, and thus may provide more privacy to the wearer. 
     In a further aspect, one or more couplers may be attached to the HMD frame to enhance the fit of the HMD to the wearer and help transfer of vibrations from the frame to the wearer&#39;s bone structure. For example, a fitting piece, which may be moldable and/or made of rubber or silicone gel, for example, may be attached to the HMD frame. The fitting piece may be attached to the HMD frame in various ways. For instance, a fitting piece may be located behind the wearer&#39;s temple and directly above their ear, or in the pit behind the wearer&#39;s ear lobe, among other locations. 
     II. Exemplary Wearable Computing Devices 
     Systems and devices in which exemplary embodiments may be implemented will now be described in greater detail. In general, an exemplary system may be implemented in or may take the form of a wearable computer (i.e., a wearable-computing device). In an exemplary embodiment, a wearable computer takes the form of or includes an HMD. However, an exemplary system may also be implemented in or take the form of other devices, such as a mobile phone, among others. Further, an exemplary system may take the form of non-transitory computer readable medium, which has program instructions stored thereon that are executable by at a processor to provide the functionality described herein. An exemplary, system may also take the form of a device such as a wearable computer or mobile phone, or a subsystem of such a device, which includes such a non-transitory computer readable medium having such program instructions stored thereon. 
     In a further aspect, an HMD may generally be any display device that is worn on the head and places a display in front of one or both eyes of the wearer. An HMD may take various forms such as a helmet or eyeglasses. As such, references to “eyeglasses” herein should be understood to refer to an HMD that generally takes the form of eyeglasses. Further, features and functions described in reference to “eyeglasses” herein may apply equally to any other kind of HMD. 
       FIG. 1  illustrates a wearable computing system according to an exemplary embodiment. The wearable computing system is shown in the form of eyeglass  102 . However, other types of wearable computing devices could additionally or alternatively be used. The eyeglasses  102  include a support structure that is configured to support the one or more optical elements. 
     In general, the support structure of an exemplary HMD may include a front section and at least one side section. In  FIG. 1 , the support structure has a front section that includes lens-frames  104  and  106  and a center frame support  108 . Further, in the illustrated embodiment, side-arms  114  and  116  serve as a first and a second side section of the support structure for eyeglasses  102 . It should be understood that the front section and the at least one side section may vary in form, depending upon the implementation. 
     Herein, the support structure of an exemplary HMD may also be referred to as the “frame” of the HMD. For example, the support structure of eyeglasses  102 , which includes lens-frames  104  and  106 , center frame support  108 , and side-arms  114  and  116 , may also be referred to as the “frame” of eyeglasses  102 . 
     The frame of the eyeglasses  102  may function to secure eyeglasses  102  to a user&#39;s face via a user&#39;s nose and ears. More specifically, the side-arms  114  and  116  are each projections that extend away from the frame elements  104  and  106 , respectively, and are positioned behind a user&#39;s ears to secure the eyeglasses  102  to the user. The side-arms  114  and  116  may further secure the eyeglasses  102  to the user by extending around a rear portion of the user&#39;s head. Additionally or alternatively, for example, the system  100  may connect to or be affixed within a head-mounted helmet structure. Other possibilities exist as well. 
     In an exemplary embodiment, each of the frame elements  104 ,  106 , and  108  and the side-arms  114  and  116  may be formed of a solid structure of plastic or metal, or may be formed of a hollow structure of similar material so as to allow wiring and component interconnects to be internally routed through the eyeglasses  102 . Other materials or combinations of materials are also possible. Further, the size, shape, and structure of eyeglasses  102 , and the components thereof, may vary depending upon the implementation. 
     Further, each of the optical elements  110  and  112  may be formed of any material that can suitably display a projected image or graphic. Each of the optical elements  110  and  112  may also be sufficiently transparent to allow a user to see through the optical element. Combining these features of the optical elements can facilitate an augmented reality or heads-up display where the projected image or graphic is superimposed over a real-world view as perceived by the user through the optical elements. 
     The system  100  may also include an on-board computing system  118 , a video camera  120 , a sensor  122 , and finger-operable touchpads  124 ,  126 . The on-board computing system  118  is shown to be positioned on the side-arm  114  of the eyeglasses  102 ; however, the on-board computing system  118  may be provided on other parts of the eyeglasses  102 . The on-board computing system  118  may include a processor and memory, for example. The on-board computing system  118  may be configured to receive and analyze data from the video camera  120  and the finger-operable touchpads  124 ,  126  (and possibly from other sensory devices, user interfaces, or both) and generate images for output from the optical elements  110  and  112 . 
     The video camera  120  is shown to be positioned on the side-arm  114  of the eyeglasses  102 ; however, the video camera  120  may be provided on other parts of the eyeglasses  102 . The video camera  120  may be configured to capture images at various resolutions or at different frame rates. Many video cameras with a small form-factor, such as those used in cell phones or webcams, for example, may be incorporated into an example of the system  100 . Although  FIG. 1  illustrates one video camera  120 , more video cameras may be used, and each may be configured to capture the same view, or to capture different views. For example, the video camera  120  may be forward facing to capture at least a portion of the real-world view perceived by the user. This forward facing image captured by the video camera  120  may then be used to generate an augmented reality where computer generated images appear to interact with the real-world view perceived by the user. 
     The sensor  122  is shown mounted on the side-arm  116  of the eyeglasses  102 ; however, the sensor  122  may be provided on other parts of the eyeglasses  102 . The sensor  122  may include one or more of a gyroscope or an accelerometer, for example. Other sensing devices may be included within the sensor  122  or other sensing functions may be performed by the sensor  122 . 
     In an exemplary embodiment, sensors such as sensor  122  may be configured to detect head movement by a wearer of eyeglasses  102 . For instance, a gyroscope and/or accelerometer may be arranged to detect head movements, and may be configured to output head-movement data. This head-movement data may then be used to carry out functions of an exemplary method, such as method  100 , for instance. 
     The finger-operable touchpads  124 ,  126  are shown mounted on the side-arms  114 ,  116  of the eyeglasses  102 . Each of finger-operable touchpads  124 ,  126  may be used by a user to input commands. The finger-operable touchpads  124 ,  126  may sense at least one of a position and a movement of a finger via capacitive sensing, resistance sensing, or a surface acoustic wave process, among other possibilities. The finger-operable touchpads  124 ,  126  may 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 may also be capable of sensing a level of pressure applied. The finger-operable touchpads  124 ,  126  may be formed of one or more transparent or transparent insulating layers and one or more transparent or transparent conducting layers. Edges of the finger-operable touchpads  124 ,  126  may 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 of the finger-operable touchpads  124 ,  126 . Each of the finger-operable touchpads  124 ,  126  may be operated independently, and may provide a different function. 
       FIG. 2  illustrates an alternate view of the wearable computing system of  FIG. 1 . As shown in  FIG. 2 , the optical elements  110  and  112  may act as display elements. The eyeglasses  102  may include a first projector  128  coupled to an inside surface of the side-arm  116  and configured to project a display  130  onto an inside surface of the optical element  112 . Additionally or alternatively, a second projector  132  may be coupled to an inside surface of the side-arm  114  and configured to project a display  134  onto an inside surface of the optical element  110 . 
     The optical elements  110  and  112  may act as a combiner in a light projection system and may include a coating that reflects the light projected onto them from the projectors  128  and  132 . In some embodiments, a special coating may not be used (e.g., when the projectors  128  and  132  are scanning laser devices). 
     In alternative embodiments, other types of display elements may also be used. For example, the optical 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 waveguides for delivering an image to the user&#39;s eyes, or other optical elements capable of delivering an in focus near-to-eye image to the user. A corresponding display driver may be disposed within the frame elements  104  and  106  for driving such a matrix display. Alternatively or additionally, a laser or LED source and scanning system could be used to draw a raster display directly onto the retina of one or more of the user&#39;s eyes. Other possibilities exist as well. 
     While  FIGS. 1 and 2  show two touchpads and two display elements, it should be understood that many exemplary methods and systems may be implemented in wearable computing devices with only one touchpad and/or with only one optical element having a display element. It is also possible that exemplary methods and systems may be implemented in wearable computing devices with more than two touchpads. 
       FIG. 3  illustrates an exemplary schematic drawing of a wearable computing system. In particular, a computing device  138  communicates using a communication link  140  (e.g., a wired or wireless connection) to a remote device  142 . The computing device  138  may be any type of device that can receive data and display information corresponding to or associated with the data. For example, the computing device  138  may be a heads-up display system, such as the eyeglasses  102  described with reference to  FIGS. 1 and 5 . 
     Thus, the computing device  138  may include a display system  144  comprising a processor  146  and a display  148 . The display  148  may be, for example, an optical see-through display, an optical see-around display, or a video see-through display. The processor  146  may receive data from the remote device  142 , and configure the data for display on the display  148 . The processor  146  may be any type of processor, such as a micro-processor or a digital signal processor, for example. 
     The computing device  138  may further include on-board data storage, such as memory  150  coupled to the processor  146 . The memory  150  may store software that can be accessed and executed by the processor  146 , for example. 
     The remote device  142  may be any type of computing device or transmitter including a laptop computer, a mobile telephone, etc., that is configured to transmit data to the device  138 . The remote device  142  and the device  138  may contain hardware to enable the communication link  140 , such as processors, transmitters, receivers, antennas, etc. 
     In  FIG. 3 , the communication link  140  is illustrated as a wireless connection; however, wired connections may also be used. For example, the communication link  140  may be a wired link via a serial bus such as a universal serial bus or a parallel bus. A wired connection may be a proprietary connection as well. The communication link  140  may also 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  142  may be accessible via the Internet and may comprise a computing cluster associated with a particular web service (e.g., social-networking, photo sharing, address book, etc.). 
     II. Exemplary HMDs Configured for Indirect Bone Conduction 
     A. Exemplary HMD with Vibration Transducer 
       FIG. 4  is a simplified illustration of an HMD configured for indirect bone-conduction audio, according to an exemplary embodiment. As shown, HMD  400  includes two optical elements  402 ,  404 . The frame of HMD  400  includes two side arms  408 -L and  408 -R, two lens-frames  409 -L and  409 -R, and a nose bridge  407 . The nose bridge  407  and side arms  408 -L and  408 -R are arranged to fit behind a wearer&#39;s ears and hold the optical elements  402  and  404  in front of the wearer&#39;s eyes via attachments to the lens-frames  409 -L and  409 -R. 
     Further, HMD  400  may include various audio sources, from which audio signals may be acquired. For example, HMD  400  includes a microphone  410 . Further, HMD  400  may additionally or alternatively an internal audio playback device. For example, an on-board computing system (not shown) may be configured to play digital audio files. Yet further, HMD  400  may be configured to acquire an audio signal from an auxiliary audio playback device  412 , such as a portable digital audio player, smartphone, home stereo, car stereo, and/or personal computer. Other audio sources are also possible. 
     An exemplary HMD may also include one or more audio interfaces for receiving audio signals from various audio sources, such as those described above. For example, HMD  400  may include an interface for receiving an audio signal from microphone  410 . Further, HMD  400  may include an interface  411  for receiving an audio signal from auxiliary audio playback device  412  (e.g., an “aux in” input). The interface to the auxiliary audio playback device  412  may be a tip, ring, sleeve (TRS) connector, or may take another form. HMD  412  may additionally or alternatively include an interface to an internal audio playback device. For example, an on-board computing system (not shown) may be configured to process digital audio files and output audio signals to a speaker or speakers. Other audio interfaces are also possible. 
     HMD  400  also includes a vibration transducer  414  located on side arm  408 -R, which functions as an indirect bone-conduction speaker. Various types of bone-conduction transducers (BCTs) may be implemented, depending upon the implementation. Further, it should be understood that any component that is arranged to vibrate the HMD  400  may be incorporated as a vibration transducer, without departing from the scope of the invention. 
     Vibration transducer  414  is configured to vibrate at least a portion of the eyeglass frame  406  based on an audio signal received via one of the audio interfaces. In an exemplary embodiment, the side arm  408 -R is configured such that when a user wears HMD  400 , an inner wall of a first portion of side arm  408 -R contacts the wearer so as to vibrationally couple to a bone structure of the wearer. For example, side arm  408 -R may contact the wearer at or near where the side-arm is placed between the wearer&#39;s ear and the side of the wearer&#39;s head, such as at the wearer&#39;s mastoid. Other points of contact are also possible. 
     Eyeglass frame  406  may be arranged such that when a user wears HMD  400 , the eyeglass frame contacts the wearer. As such, when the vibration transducer  414  vibrates the eyeglass frame  406 , the eyeglass frame can transfer vibration to the bone structure of the wearer. In particular, vibration of the eyeglass frame  406  can be transferred at areas where the eyeglass frame contacts the wearer directly. For instance, the eyeglass frame  406  may transfer vibration, via contact points on the wearer&#39;s ear, the wearer&#39;s nose, the wearer&#39;s temple, the wearer&#39;s eyebrow, or any other point where the eyeglass frame  406  directly contacts the wearer. 
     In an exemplary embodiment, vibration transducer  414  is located on a second portion of the side-arm  408 -R, away from the first portion of the side-arm  408 -R that vibrationally couples to wearer. Further, in an exemplary embodiment, vibration transducer  414  vibrates the support structure without directly vibrating the wearer. To achieve this result, the second portion of the side-arm  408 -R, at which vibration transducer  414  is located, may have an inner wall that does not contact the wearer. This configuration may leave a space between the second portion of the side-arm  408 -R and the wearer, such that the vibration transducer indirectly vibrates the wearer by transferring vibration from the second portion to the first portion of the side-arm  408 -R, which in turn is vibrationally coupled to the wearer. 
     In practice, the spacing of the vibration transducer may be accomplished by housing the transducer in or attaching the transducer to the side-arm in various ways. For instance, as shown, the vibration transducer  414  is attached to and protruding from the exterior wall of side arm  408 -R. Other arrangements are possible as well. For example, a vibration transducer may be attached to an inner wall of the side arm (while still configured to leave space between the vibration transducer and the wearer). As another example, a vibration transducer may be enclosed within a side arm having the vibration transducer. As yet another example, a vibration transducer may be partially or wholly embedded in an exterior or interior wall of a side arm. Furthermore, vibration transducers may be arranged in other locations on or within side-arm  408 -L and/or  408 -R. Additionally, vibration transducers may be arranged on or within other parts of the frame, such as the nose bridge sensor  407  and/or lens frames  409 -L and  409 -R. 
     In a further aspect of the illustrated arrangement, the location of the vibration transducer may enhance the vibration of the side-arm  408 -R. In particular, side-arm  408 -R may contact and be held in place by the lens-frame  408 -R on one end, and may contact and be held in place by the wearer&#39;s ear on the other end (e.g., at the wearer&#39;s mastoid), allowing the portion of the side-arm between these points of contact to vibrate more freely. Therefore, placing vibration transducer  414  between these points of contact may help the transducer vibrate the side-arm  408 -R more efficiently. This in turn may result in more efficient transfer of vibration from the eyeglass frame to the wearer&#39;s bone structure. 
     Further, when there is space between vibration transducer  414  and the wearer, some vibrations from the vibration transducer may also be transmitted through the air, and thus may be heard by the wearer over the air. In other words, the user may perceive the sound from vibration transducer  414  using both tympanic hearing and bone-conduction hearing. In such an embodiment, the sound that is transmitted through the air and perceived using tympanic hearing may complement the sound perceived via bone-conduction hearing. Furthermore, while the sound transmitted through the air may enhance the sound perceived by the wearer, the sound transmitted through the air may be unintelligible to others nearby. Further, in some arrangements, the sound transmitted through the air by the vibration transducer may be inaudible (possibly depending upon the volume level). 
     B. Other Arrangements of Vibration Transducers on an HMD 
     Other arrangements of a vibration transducer or transducers on a side-arm and elsewhere on the HMD frame are also possible. For example,  FIG. 5  is another block diagram illustrating an HMD configured for indirect bone-conduction audio, according to an exemplary embodiment. In particular,  FIG. 5  shows an HMD  500 , in which a vibration transducer  514  is arranged on an outer wall of side-arm  508 -R. As such, when HMD  500  is worn, a portion of side-arm  508 -R on which vibration transducer  514  is located is proximate to the pit behind the ear lobe of the wearer. 
     When located as such, a gap may exist between the wearer and the portion of side-arm  508 -R to which vibration transducer  514  is attached. As a result, driving vibration transducer  514  with an audio signal vibrates side-arm  508 -R. While the portion of side-arm  508 - to which vibration transducer  514  is attached does not contact the wearer, side-arm  508 -R may contact the wearer elsewhere. In particular, side-arm  508 -R may contact the wearer in between the ear and the head, such as at location  516 , for example. Accordingly, vibrations of side-arm  508 -L may be transferred to a wearer&#39;s bone structure at location  516 . Therefore, by vibrating side-arm  508 -R, which in turn vibrates the wearer&#39;s bone structure, vibration transducer  514  may serve as an indirect bone conduction speaker. 
     In a further aspect, some embodiments may include two or more vibration transducers in various locations on the eyeglass frame. For example,  FIG. 6  is another block diagram illustrating an HMD configured for indirect bone-conduction audio, according to an exemplary embodiment. In particular,  FIG. 6  shows an HMD  600 , which includes two vibration transducers  614  and  615 . As shown vibration transducers  614  and  615  are arranged on the side arms  608 -L and  608 -R, respectively. Arranged as such, when HMD  600  is worn, vibration transducers  614  and  615  are typically located on portions of side-arm  608 -L and  608 -R, respectively, which are proximate to a wearer&#39;s left and right temple, respectively. For example, vibration transducer  614  may be located on the outer wall of side-arm  608 -L, in between the wearer&#39;s left eye and left ear. Similarly, vibration transducer  615  may be located on the outer wall of side-arm  608 -R, in between the wearer&#39;s right eye and right ear. 
     C. Fitting Pieces 
     In a further aspect, an exemplary HMD may include one or more couplers arranged on the HMD. These couplers may help to enhance the fit of the HMD frame to the wearer, such that the HMD fits in a more secure and/or a more comfortable manner. Further, in an exemplary embodiment, these couplers may help to more efficiently transfer vibration of the HMD frame to the bone structure of the wearer. 
     As an example of such couplers, HMD  600  includes two fitting pieces  616 -L and  616 -R. As shown, fitting piece  616 -L is located on an inner wall of side-arm  608 -L and extends from a portion of the inner wall that is proximate to the pit behind the left ear lobe of the wearer. Configured as such, fitting piece  616 -L may serve to fill any gap between the wearer&#39;s body and the side-arm  608 -L. Further, fitting piece  616 -R may be configured in a similar manner as fitting piece  616 -L, but with respect to the right side of the wearer&#39;s body. 
     In exemplary embodiments, the fitting pieces or any type of couplers may be attached to, embedded in, and/or enclosed in the HMD frame at various locations. For example, fitting pieces may be located in various locations so as to fill space between an HMD frame and wearer&#39;s body, and thus help the HMD frame vibrate the wearer&#39;s bone structure. For instance, a fitting piece may be configured to contact a wearer&#39;s ear, nose, temple, eyebrow, nose (e.g., at the bridge of the nose), or neck (e.g., at the pit behind the ear lobe), among other locations. 
     Generally, it should be understood that an exemplary embodiment may include only one coupler, or may include two or more couplers. Further, it should be understood that an exemplary embodiment need not include any couplers. 
     D. Additional Features of an HMD with Vibration Transducer Speaker 
     In some embodiments, an HMD may be configured with multiple vibration transducers, which may be individually customizable. For instance, as the fit of an HMD may vary from user-to-user, the volume of speakers may be adjusted individually to better suit a particular user. As an example, an HMD frame may contact different users in different locations, such that a behind-ear vibration transducer (e.g., vibration transducer  514  of  FIG. 5 ) may provide more-efficient indirect bone conduction for a first user, while a vibration transducer located near the temple (e.g., vibration transducer  414  of  FIG. 4 ) may provide more-efficient indirect bone conduction for a second user. Accordingly, an HMD may be configured with one or more behind-ear vibration transducers and one or more vibration transducers near the temple, which are individually adjustable. As such, the first user may choose to lower the volume or turn off the vibration transducers near the temple, while the second user may choose to lower the volume or turn off the behind-ear vibration transducers. Other examples are also possible. 
     In some embodiments, different vibration transducers may be driven by different audio signals. For example, in an embodiment with two vibration transducers, a first vibration transducer may be configured to vibrate a left side-arm of an HMD based on a first audio signal, and a second vibration transducer may be configured to vibrate a second portion of the support structure based on a second audio signal. 
     In some embodiments, the above configuration may be used to deliver stereo sound. In particular, two individual vibration transducers (or possibly two groups of vibration transducers) may be driven by separate left and right audio signals. As a specific example, referring to  FIG. 6 , vibration transducer  614 -L may vibrate side-arm  608 -L based on a “left” audio signal, while vibration transducer  614 -R may vibrate side-arm  608 -R based on a “right” audio signal. Other examples of vibration transducers configured for stereo sound are also possible. 
     Furthermore, an HMD may include more than two vibration transducers (or possibly more than two groups of vibration transducers), which each are driven by a different audio signal. For example, multiple vibration transducers may be individually driven by different audio signals in order to provide a surround sound experience. 
     Further, in some embodiments, different vibrations transducers may be configured for different purposes, and thus driven by different audio signals. For example, one or more vibrations transducers may be configured to deliver music, while another vibration transducer may be configured for voice (e.g., for phone calls, speech-based system messages, etc.). Other examples are also possible. 
     E. Vibration Dampeners 
     In a further aspect, an exemplary HMD may include one or more vibration dampeners that are configured to substantially isolate vibration of a particular vibration transducer or transducers. For example, when two vibration transducers are arranged to provide stereo sound, a first vibration transducer may be configured to vibrate a left side-arm based on a “left” audio signal, while a second vibration transducer may be configured to vibrate a right side-arm based on a second audio signal. In such an embodiment, one or more vibration transducers may be configured to (a) substantially reduce vibration of the right arm by the first vibration transducer and (b) substantially reduce vibration of the left arm by the second vibration transducer. By doing so, the left audio signal may be substantially isolated on the left arm, while the right audio signal may be substantially isolated on the right arm. 
     Vibration dampeners may vary in location on an HMD. For instance, continuing the above example, a first vibration dampener may be coupled to the left side-arm and a second vibration dampener may be coupled to the right side-arm, so as to substantially isolate the vibrational coupling of the first vibration transducer to the left side-arm and vibrational coupling of the second vibration transducer to the second right side-arm. To do so, the vibration dampener or dampeners on a given side-arm may be attached at various locations along the side-arm. For instance, referring to  FIG. 4 , vibration dampeners may be attached at or near where side-arms  408 -L and  408 -R are attached to lens-frames  409 -L and  409 -R, respectively. 
     As another example, vibration transducers may be located on the left and right lens-frames, as illustrated in  FIG. 6  by vibration transducers  618 -L and  618 -R. In such an embodiment, HMD  600  may include vibration dampeners (not shown) that help to isolate vibration of the left side of HMD  600  from the right side of HMD  600 . For instance, to help vibrationally isolate vibration transducers  618 -L and  618 -R, vibration dampeners may be attached at or near to where lens-frames  609 -L and  609 -R couple to nose bridge  607 . Additionally or alternatively, a vibration dampener (not shown) may be located or attached to nose bridge  607 , in order to help prevent: (a) vibration transducer  618 -L from vibrating the right side of HMD  600  (e.g., lens frame  609 -R and/or side-arm  608 -R) and (b) vibration transducer  618 -R from vibrating the left side of HMD  600  (e.g., lens frame  609 -L and/or side-arm  608 -R). 
     In an exemplary embodiment, vibration dampeners may vary in size and/or shape, depending upon the particular implementation. Further, vibration dampeners may be attached to, partially or wholly embedded in, and/or enclosed within the frame of an exemplary HMD. Yet further, vibration dampeners may be made of various different types of materials. For instance, vibration dampeners may be made of silicon, rubber, and/or foam, among other materials. More generally, a vibration dampener may be constructed from any material suitable for absorbing and/or dampening vibration. Furthermore, in some embodiments, a simple air gap between the parts of the HMD may function as a vibration dampener (e.g., an air gap where a side arm connects to a lens frame). 
     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 and spirit being indicated by the following claims.