PATENT DOCUMENT

Publication Number: US-11206473-B2
Application Number: US-201916584929-A
Country: US
Kind Code: B2

Title: Magnet array for securing wireless listening devices

Abstract:
Embodiments describe a magnetic securing component including a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surfaces of each magnet in the set of magnets. The set of magnets includes: first and second magnets positioned laterally adjacent to one another, where the first and second magnets each have a polarity that is oriented parallel to a vertical dimension; and third and fourth magnets laterally positioned from the first and second magnets, where the third magnet is positioned adjacent to the first magnet and the fourth magnet is positioned adjacent to the second magnet, the third and fourth magnets each having a magnetic polarity that is oriented at an angle with respect to the vertical dimension.

Claims:
What is claimed is: 
     
       1. A magnetic securing component disposed within a case for electronic device, the magnetic securing component comprising:
 a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surfaces of each magnet in the set of magnets, the set of magnets comprising first, second, third and fourth magnets each of which has its polarity oriented in a different direction; 
 wherein the first and second magnets are positioned laterally adjacent to one another with polarities, oriented parallel to a vertical dimension in opposite directions; and 
 wherein the third and fourth magnets are laterally positioned from the first and second magnets with wherein the third magnet positioned adjacent to the first magnet, the fourth magnet positioned adjacent to the second magnet, and the third and fourth magnets each having a magnetic polarity that is oriented at a non-zero angle with respect to the vertical dimension. 
 
     
     
       2. The magnetic securing component of  claim 1 , wherein the non-zero angle is between 20 and 40 degrees with respect to the vertical dimension. 
     
     
       3. The magnetic securing component of  claim 1 , wherein the first magnet has a first magnetic polarity that is vertically downward, and the second magnet has a second magnetic polarity that is vertically upward. 
     
     
       4. The magnetic securing component of  claim 1 , further comprising a first shunt and a second shunt positioned below the set of magnets preventing stray magnetic fields from leaking to areas below the first and second shunts. 
     
     
       5. The magnetic securing component of  claim 4 , wherein the first shunt is positioned a distance away from the second shunt. 
     
     
       6. The magnetic securing component of  claim 4 , further comprising a third shunt positioned directly behind the set of magnets to hold the magnets together. 
     
     
       7. The magnetic securing component of  claim 6 , wherein first shunt, second shunt, and third shunt are formed of steel. 
     
     
       8. The magnetic securing component of  claim 1 , wherein the set of magnets further includes a curved front surface defined by individual curved front surface of each magnet in the set of magnets. 
     
     
       9. A magnetic securing component disposed within a case for electronic device, the magnetic securing component comprising:
 a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surfaces of each magnet in the set of magnets, the set of magnets comprising: 
 first and second magnets positioned laterally adjacent to one another with polarities oriented parallel to a first axis parallel to a vertical dimension and opposite directions; and 
 third and fourth magnets laterally positioned from the first and second magnets, wherein the third magnet is positioned adjacent to the first magnet and the fourth magnet is positioned adjacent to the second magnet, the third and fourth magnets each having a magnetic polarity that is oriented at a non-zero angle with respect to the vertical dimension; 
 wherein orientations of the magnetic polarities for the first and second magnets are oriented in different directions, and wherein orientations of the magnetic polarities for the third and fourth magnets are oriented in different directions, and wherein the third magnet has a third magnetic polarity that is angled downward and away from the first magnet, and the fourth magnet has a fourth magnetic polarity that is angled upward and toward the second magnet. 
 
     
     
       10. A case for a wireless listening device, comprising:
 a lid movable to open and close the case; 
 a hinge coupled to the lid to allow the lid to open and close the case; and 
 a body coupled to the lid by the hinge, the body comprising: 
 a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surface of each magnet in the set of magnets, the set of magnets comprising first, second, third and fourth magnets each of which has its polarity oriented in a different direction: 
 wherein the first and second magnets are positioned laterally adjacent to one another with the first magnet having a first magnetic polarity oriented vertically downward and parallel to a first axis, and the second magnet having a second magnetic polarity oriented vertically upward and parallel to the first axis; and 
 wherein the third and fourth magnets are laterally positioned from the first and second magnets with the third magnet positioned adjacent to the first magnet, the fourth magnet positioned adjacent to the second magnet, and the third and fourth magnets each having a magnetic polarity that is oriented at a non-zero angle with respect to the first axis. 
 
     
     
       11. The case of  claim 10 , wherein the case further comprises an inner frame comprising a curved surface for receiving the wireless listening device. 
     
     
       12. The case of  claim 10 , wherein orientations of the magnetic polarities for the third and fourth magnets are oriented at an angle between 20 and 40 degrees from the first axis. 
     
     
       13. The case of  claim 10 , further comprising a first shunt and a second shunt positioned below the set of magnets preventing stray magnetic fields from leaking to areas below the first and second shunts. 
     
     
       14. The case of  claim 13 , further comprising a third shunt positioned directly behind the set of magnets to hold the magnets together. 
     
     
       15. A wireless listening device system, comprising:
 a wireless listening device comprising: 
 a housing comprising an outer structure defining an acoustic opening and a nozzle disposed around the acoustic opening, the acoustic opening allowing sound to exit out of the outer structure; 
 a first communication system disposed within the housing and configured to send and receive data; 
 an eartip removably attached to the nozzle to direct sound outputted by the housing through the acoustic opening; and 
 an attachment mechanism removably attaching the eartip to the housing; and 
 a case, comprising: 
 a lid movable to open and close the case; 
 a hinge coupled to the lid to allow the lid to open and close the case; 
 a body coupled to the lid by the hinge, the body comprising: 
 a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surface of each magnet in the set of magnets, the set of magnets comprising first, second, third and fourth magnets each of which has its polarity oriented in a different direction: 
 wherein the first and second magnets are positioned laterally adjacent to one another with polarities oriented parallel to a vertical dimension in opposite directions; and 
 wherein the third and fourth magnets are laterally positioned from the first and second magnets with the third magnet positioned adjacent to the first magnet, the fourth magnet positioned adjacent to the second magnet, and the third and fourth magnets each having a magnetic polarity that is oriented at non-zero angle with respect to the vertical dimension; and 
 a second communication system disposed in the body and configured to exchange data with the first communication system. 
 
     
     
       16. The wireless listening device system of  claim 15 , wherein the non-zero angle is between 20 and 40 degrees with respect to the vertical dimension. 
     
     
       17. The wireless listening device system of  claim 16 , wherein orientations of the magnetic polarities of the first and second magnets are opposite in direction to one another. 
     
     
       18. The wireless listening device system of  claim 17 , wherein the first magnet has a first magnetic polarity that is vertically downward, and the second magnet has a second magnetic polarity that is vertically upward. 
     
     
       19. A wireless listening device system, comprising:
 a wireless listening device comprising: 
 a housing comprising an outer structure defining an acoustic opening and a nozzle disposed around the acoustic opening, the acoustic opening allowing sound to exit out of the outer structure; 
 a first communication system disposed within the housing and configured to send and receive data; 
 an eartip removably attached to the nozzle to direct sound outputted by the housing through the acoustic opening; and 
 an attachment mechanism removably attaching the eartip to the housing; and 
 a case, comprising: 
 a lid movable to open and close the case; 
 a hinge coupled to the lid to allow the lid to open and close the case; 
 a body coupled to the lid by the hinge, the body comprising: 
 a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surface of each magnet in the set of magnets, the set of magnets comprising first, second, third and fourth magnets each of which has its polarity oriented in a different direction: 
 wherein the first and second magnets are positioned laterally adjacent to one another with polarities oriented parallel to a vertical dimension in opposite directions; 
 wherein the third and fourth magnets are laterally positioned from the first and second magnets with the third magnet positioned adjacent to the first magnet, the fourth magnet positioned adjacent to the second magnet, and the third and fourth magnets each having a magnetic polarity that is oriented at a non-zero angle with respect to the vertical dimension; and 
 a second communication system disposed in the body and configured to exchange data with the first communication system; 
 wherein the third magnet has a third magnetic polarity that is angled downward and away from the first magnet, and the fourth magnet has a fourth magnetic polarity that is angled upward and toward the second magnet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/738,772 filed on Sep. 28, 2018, U.S. Provisional Patent Application No. 62/738,788 filed on Sep. 28, 2018, U.S. Provisional Patent Application No. 62/738,803 filed on Sep. 28, 2018, U.S. Provisional Patent Application No. 62/738,813 filed on Sep. 28, 2018, U.S. Provisional Patent Application No. 62/738,828 filed on Sep. 28, 2018, U.S. Provisional Patent Application No. 62/738,843 filed on Sep. 28, 2018, U.S. Provisional Patent Application No. 62/865,070 filed on Jun. 21, 2019, and U.S. Provisional Patent Application No. 62/900,307 filed on Sep. 13, 2019; the disclosures of which are hereby incorporated by reference in their entirety and for all purposes. 
    
    
     BACKGROUND 
     Portable listening devices can be used with a wide variety of electronic devices such as portable media players, smart phones, tablet computers, laptop computers, stereo systems, and other types of devices. Portable listening devices have historically included one or more small speakers configured to be place on, in, or near a user&#39;s ear, structural components that hold the speakers in place, and a cable that electrically connects the portable listening device to an audio source. Other portable listening devices can be wireless devices that do not include a cable and instead, wirelessly receive a stream of audio data from a wireless audio source. Such portable listening devices can include, for instance, wireless earbud devices or in-ear hearing devices that operate in pairs (one for each ear) or individually for outputting sound to, and receiving sound from, the user. 
     While wireless listening devices have many advantages over wired portable listening devices, they also have some potential drawbacks. For example, it may be difficult to achieve high-end acoustic performance from the listening devices due to the limited amount of space available within each listening device. Also, some wireless listening devices that extend into the ear canal to achieve better performance can often have an improper seal between the portable listening device and the ear canal, causing the user to experience lower quality sound. Further, the small size of wireless listening devices often causes a compromise in user interface features, blockage of sensors and/or microphones, and lower overall user experience. 
     SUMMARY 
     Some embodiments of the disclosure provide a wireless listening device that achieves improved acoustic performance and functionality, which results in an enriched user experience. In some instances, the wireless listening device can include a housing and an eartip that can attach to the housing. The eartip can be configured to insert into a user&#39;s ear and provide an avenue through which sound generated by the housing can be outputted to the user. The housing can include various sensors that can work alone, or in conjunction with, the eartip to perform various functions, such as, but not limited to, detecting when the wireless listening device has been inserted into a user&#39;s ear canal, determining whether a proper seal has been made between the eartip and the ear canal, and determining whether an improper blocking of one or more sensors of the wireless listening device exists. The housing can also be configured to recognize user input through movement of anatomical parts of a user&#39;s ear proximate to the wireless listening device, as well as through the user&#39;s voice alone or in conjunction with additional sensing measurements. These additional features can improve the user experience as well as enhance the acoustic performance of the wireless listening device. 
     In some embodiments, a magnetic securing component includes a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surfaces of each magnet in the set of magnets. The set of magnets includes: first and second magnets positioned laterally adjacent to one another, where the first and second magnets each have a polarity that is oriented parallel to a vertical dimension; and third and fourth magnets laterally positioned from the first and second magnets, where the third magnet is positioned adjacent to the first magnet and the fourth magnet is positioned adjacent to the second magnet, the third and fourth magnets each having a magnetic polarity that is oriented at an angle with respect to the vertical dimension. 
     In some additional embodiments, a case for a wireless listening device includes a lid movable to open and close the case, a hinge coupled to the lid to allow the lid to open and close the case, and a body coupled to the lid by the hinge, where the body includes a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surface of each magnet in the set of magnets. The set of magnets includes: first and second magnets positioned laterally adjacent to one another, wherein the first magnet has a first magnetic polarity that is vertically downward, and the second magnet has a second magnetic polarity that is vertically upward; and third and fourth magnets laterally positioned from the first and second magnets, wherein the third magnet is positioned adjacent to the first magnet and the fourth magnet is positioned adjacent to the second magnet, the third and fourth magnets each having a magnetic polarity that is oriented at an angle with respect to the vertical dimension. 
     In some further embodiments, a wireless listening device system includes a wireless listening device and a case. The wireless listening device includes: a housing including an outer structure defining an acoustic opening and a nozzle disposed around the acoustic opening, the acoustic opening allowing sound to exit out of the outer structure; a first communication system disposed within the housing and configured to send and receive data; an eartip removably attached to the nozzle to direct sound outputted by the housing through the acoustic opening; and an attachment mechanism removably attaching the eartip to the housing. The case includes a lid movable to open and close the case; a hinge coupled to the lid to allow the lid to open and close the case; a body coupled to the lid by the hinge, and a second communication system disposed in the body and configured to exchange data with the first communication system. The body includes a set of magnets positioned laterally adjacent to one another and having a curved top surface defined by individual curved top surface of each magnet in the set of magnets, where the set of magnets includes: first and second magnets positioned laterally adjacent to one another, wherein the first and second magnets each have a polarity that is oriented parallel to a vertical dimension; and third and fourth magnets laterally positioned from the first and second magnets, wherein the third magnet is positioned adjacent to the first magnet and the fourth magnet is positioned adjacent to the second magnet, the third and fourth magnets each having a magnetic polarity that is oriented at an angle with respect to the vertical dimension. 
     A better understanding of the nature and advantages of embodiments of the present invention may be gained with reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram illustrating a portable electronic listening device system including an exemplary wireless listening device, according to some embodiments of the present disclosure. 
         FIG. 1B  is a simplified illustration of an exemplary portable electronic listening device system having a host device configured as a smart phone, a case, and a pair of wireless listening devices configured as earbuds, according to some embodiments of the present disclosure. 
         FIG. 2A  is a side-view illustration of an exemplary wireless listening device where an eartip is attached to a housing, according to some embodiments of the present disclosure. 
         FIG. 2B  is a side view illustration of a wireless listening device where an eartip is detached from a housing, according to some embodiments of the present disclosure. 
         FIG. 3A  is a cross-sectional view illustration of an eartip attached to an outer structure of a housing via an attachment mechanism, according to some embodiments of the present disclosure. 
         FIG. 3B  is a top-down view illustration of an eartip, according to some embodiments of the present disclosure. 
         FIG. 3C  is a close-up, cross-sectional view illustration of attachment mechanism attached to an outer structure via attachment features, according to some embodiments of the present disclosure. 
         FIG. 3D  is an exploded view illustration of an exemplary wireless listening device including a wireform attachment mechanism for attaching an eartip to a housing, according to some embodiments of the present disclosure. 
         FIG. 3E  is a cross-sectional view illustration of an eartip configured to attach to a housing by way of a wireform attachment mechanism, according to some embodiments of the present disclosure. 
         FIGS. 3F-3H  are illustrations of a wireform attachment mechanism that has an s-shaped profile configured to compress toward its center when engaging with an eartip, according to some embodiments of the present disclosure. 
         FIG. 3I  is a cross-sectional view illustration of an eartip attached to a housing via a wireform attachment mechanism, according to some embodiments of the present disclosure. 
         FIGS. 3J-3L  are a series of illustrations showing different points along the process of attaching an eartip to a nozzle, according to some embodiments of the present disclosure. 
         FIGS. 3M-3O  are illustrations of an exemplary wireform attachment mechanism that has a u-shaped profile configured to compress toward its center when engaging with an eartip, according to some embodiments of the present disclosure. 
         FIGS. 3P-3Q  are illustrations of an exemplary wireform attachment mechanism that has a u-shaped profile configured to rotate its end caps around an axis when engaging with an eartip, according to some embodiments of the present disclosure. 
         FIG. 4A  is a cross-sectional view illustration of an exemplary eartip configured as a capacitive sensor, according to some embodiments of the present disclosure. 
         FIGS. 4B and 4C  are cross-sectional view illustrations of eartip when it is inserted into an ear canal, according to some embodiments of the present disclosure. 
         FIG. 5A  is a bottom-up view illustration of an exemplary eartip configured with patterned lines separated by spaces on an inner surface of its outer eartip body, according to some embodiments of the present disclosure. 
         FIG. 5B  is a side-view illustration of an exemplary wireless listening device with an eartip and a housing having an optical sensor for observing the inner surface of the outer eartip body, according to some embodiments of the present disclosure. 
         FIG. 5C  is a bottom-up view of an eartip after deflection from being inserted into an ear canal, according to some embodiments of the present disclosure. 
         FIG. 6A  is a perspective view illustration of an exemplary wireless listening device having a control leak in its eartip, according to some embodiments of the present disclosure. 
         FIGS. 6B and 6C  are cross-sectional view illustrations of different eartips with different control leak configurations, according to some embodiments of the present disclosure. 
         FIG. 6D  is a cross-sectional view illustration of an eartip across a vertical cutting plane, according to some embodiments of the present disclosure. 
         FIG. 6E  is a cross-sectional view illustration of an eartip across a horizontal cutting plane, according to some embodiments of the present disclosure. 
         FIGS. 6F-6H  are perspective view illustrations of exemplary eartips having different modifications for mitigating the occlusion of a control leak when the outer eartip body is bent and deformed when inserted into an ear canal, according to some embodiments of the present disclosure. 
         FIG. 7  is a cross-sectional view of an exemplary wireless listening device showing further details of a housing, according to some embodiments of the present disclosure. 
         FIG. 8  is a cross-sectional view illustration of a wireless listening device when it is worn by a user to show the positioning of the wireless listening device with respect to an ear canal and the auricle of an ear, according to some embodiments of the present disclosure. 
         FIG. 9A  is a cross-sectional view illustration of a wireless listening device when a leakage is not present, according to some embodiments of the present disclosure. 
         FIG. 9B  is a cross-sectional illustration of a wireless listening device when a leakage is present, according to some embodiments of the present disclosure. 
         FIG. 10  is an exemplary side-view illustration of a wireless listening device worn by a user where one or more ports, control leaks, and/or microphones are occluded, according to some embodiments of the present disclosure. 
         FIGS. 11A and 11B  are cross-sectional view illustrations of exemplary configurations having different acoustic shielding components for microphones in a housing, according to some embodiments of the present disclosure. 
         FIG. 12  is an exploded view of an exemplary acoustic shielding component constructed as a multi-layer mesh, according to some embodiments of the present disclosure. 
         FIG. 13  is a side-view illustration of a wireless listening device whose battery and driver are uniquely positioned to decrease the size of the housing, according to some embodiments of the present disclosure. 
         FIG. 14  is a side-view illustration of a wireless listening device configured to display the user&#39;s listening status, according to some embodiments of the present disclosure. 
         FIG. 15  is a side-view illustration of a wireless listening device configured to receive user input through interactions with the anatomy of a user&#39;s ear, according to some embodiments of the present disclosure. 
         FIG. 16A  is a perspective view illustration of an exemplary wireless listening device that includes an eartip coupled to a housing that includes a stem, according to some embodiments of the present disclosure. 
         FIG. 16B  is a simplified cross-sectional view illustration of the electrical components within stem, according to some embodiments of the present disclosure. 
         FIG. 17A  is a perspective view illustration of an exemplary contact head configured with an alignment bar, according to some embodiments of the present disclosure. 
         FIG. 17B  is a perspective view illustration of an exemplary contact head configured with an alignment frame, according to some embodiments of the present disclosure. 
         FIG. 18A  is a cross-sectional view illustration of an exemplary bus bar having two conductive traces in a single layer, according to some embodiments of the present disclosure. 
         FIG. 18B  is a cross-sectional view illustration of an exemplary bus bar having two conductive traces in different layers, according to some embodiments of the present disclosure. 
         FIGS. 19A-19G  are simplified illustrations of an exemplary method of forming an eartip, according to some embodiments of the present disclosure. 
         FIG. 20A  is a front-view illustration of an exemplary case that is transparent to illustrate the configuration of the components inside of the case from the front, according to some embodiments of the present disclosure. 
         FIG. 20B  is a back-view illustration of an exemplary case that is transparent to illustrate the configuration of the components inside of the case from the back, according to some embodiments of the present disclosure. 
         FIG. 20C  is a cross-sectional view illustration of an exemplary case, according to some embodiments of the present disclosure. 
         FIG. 21A  is a simplified perspective view illustration of an internal frame for a case, according to some embodiments of the present disclosure. 
         FIG. 21B  is a simplified top-down view illustration of an internal frame for a case, according to some embodiments of the present disclosure. 
         FIG. 22A  is a simplified cross-sectional view illustration of the internal frame in  FIG. 21A , according to some embodiments of the present disclosure. 
         FIG. 22B  is a simplified zoomed-in view illustration of a portion of the cross-sectional view of  FIG. 22A , according to some embodiments of the present disclosure. 
         FIG. 23  is a simplified cross-sectional view illustration of a set of retaining magnets and a wireless listening device, according to some embodiments of the present disclosure. 
         FIG. 24A  is a front-view illustration of a set of retaining magnets, according to some embodiments of the present disclosure. 
         FIG. 24B  is a top-down view illustration of a set of retaining magnets, according to some embodiments of the present disclosure. 
         FIG. 25  is a simplified perspective view illustration of an exemplary visual indicator including a light emitter and a light tube for directing light emitted by the light emitter from within a body of a case to a region outside of the body of the case, according to some embodiments of the present disclosure. 
         FIGS. 26A-26B  are simplified cross-sectional views of an exemplary magnetic attachment and sensor system that includes a hybrid retention and sensor shunt, according to some embodiments of the present disclosure. 
         FIG. 27  is a perspective view illustration of an exemplary bistable hinge, according to some embodiments of the present disclosure. 
         FIGS. 28A-28C  are cross-sectional view illustrations of the different states of a bistable hinge, according to some embodiments of the present disclosure. 
         FIGS. 28D-28F  are simplified illustrations of an exemplary bistable hinge having a piston formed of a curved plate coupled to a rocker, according to some embodiments of the present disclosure. 
         FIGS. 29A-29C  are simplified illustrations of an exemplary straddle battery pack, according to some embodiments of the present disclosure. 
         FIG. 30  is a simplified plan view illustration of a case for a pair of wireless listening devices, according to some embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the disclosure describe a wireless listening device that achieves high-end acoustic performance and improved user experience. The wireless listening device can be one of a pair of wireless listening devices configured to fit in the left and right ears of a user for outputting sound to the user and for inputting sound from the user and/or the surrounding environment. In some instances, the wireless listening device can include a housing and an eartip that can attach to the housing. The housing can include a rigid outer structure that encloses various electrical components that operate the wireless listening device (e.g., a battery, a processor, a driver for generating sound, and the like). The outer structure can include an opening through which the generated sound can be outputted to the eartip, which can then direct the sound into the user&#39;s ear canal. The eartip can be substantially pliable in construction but include a stiff attachment structure that enables the eartip to easily attach to the housing by inserting into the opening of the outer structure. Details of example eartips are discussed herein with respect to  FIGS. 3A-3E . 
     In some instances, the eartip can be attached by way of a wireform attachment mechanism that enables the eartip to attach to the housing under application of a low insertion force while requiring a high extraction force to remove the eartip. The wireform attachment mechanism can have an s-shape profile that includes end caps for inserting into recesses of an attachment structure of the eartip. The end caps can have beveled upper corners to allow a vertical insertion force to translate into a horizontal force to compress the wireform attachment mechanism. Details of example wireform attachment mechanisms are discussed herein with respect to  FIGS. 3F-3Q . 
     In some additional or alternative embodiments, the wireless listening device can include a control leak for improved comfort. For example, the eartip can include a control leak in the form of a specifically designed opening through which the ear canal can be exposed to the atmosphere. The control leak can be defined by an attachment structure of the eartip. Without the control leak, pressure can be trapped in the ear canal and be uncomfortable to the user, and outputted sound may be muffled. Details of example control leaks are discussed herein with respect to  FIGS. 6A-6E . 
     In some embodiments, the wireless listening device can also include an acoustic shielding component to mitigate wind noise and improve sound capture quality. The acoustic shielding can be a multi-layered mesh structure that includes an acoustic mesh sandwiched between a cosmetic mesh and a stiffener. The outer surface of the cosmetic mesh can be flush with the outer contours of the housing so that wind noise can be mitigated. Details of example acoustic shielding components are discussed herein with respect to  FIGS. 11A-11B and 12 . 
     In some additional or alternative embodiments, the wireless listening device can include various sensors for performing various functions. For instance, the eartip can include a capacitive sensor for determining when the eartip has been inserted into an ear canal, as discussed herein with respect to  FIGS. 4A-4C . Or, in another instance, the housing can include an optical sensor that can work in conjunction with features of the eartip to determine when the eartip has been inserted into an ear canal, as discussed herein with respect to  FIGS. 5A-5C . The wireless listening device can also be configured to determine whether a proper seal has been made between the eartip and the ear canal, and whether one or more sensors of the housing is improperly blocked, as discussed herein with respect to  FIGS. 9A-9B . 
     The wireless listening device can also include various improved user interface features, such as a status light indicator, strategically positioned optical sensors, an outward facing microphone, and/or low-power accelerometers, as discussed herein with respect to  FIGS. 7-8, 10 , and  14 - 15 . The status light indicator can be configured to output different colors of light to indicate whether active noise cancelling (ANC) is activated. For instance, the status light indicator can output a red light when ANC is on and a green light when ANC is off so that people around the user can be made aware of the user&#39;s ability to communicate. The optical sensors can be strategically positioned to observe parts of the ear so that when the ear moves, e.g., pulls away from the wireless listening device when the user pulls on certain parts of his or her ear, the wireless listening device can associate that movement with a specific user input. The low-power accelerometer can be used in conjunction with the outward facing microphone to detect voice commands only from the user. For instance, the wireless listening device can determine that the user is speaking a command, as opposed to another person who happens to be speaking next to or directly to the user, by also measuring a degree of vibration with the low-power accelerometer. The low-power accelerometer may vibrate over a threshold when the user speaks. Thus, the wireless listening device can determine that the user is speaking a command when the command is spoken in conjunction with a threshold amount of vibration. These user interface features can improve the user experience of the wireless listening device, which are discussed further herein. 
     As used herein, the term “portable listening device” includes any portable device designed to play sound that can be heard by a user. Headphones are one type of portable listening device, portable speakers are another. The term “headphones” represents a pair of small, portable listening devices that are designed to be worn on or around a user&#39;s head. They convert an electrical signal to a corresponding sound that can be heard by the user. Headphones include traditional headphones that are worn over a user&#39;s head and include left and right listening devices connected to each other by a headband, headsets (a combination of a headphone and a microphone); and earbuds (very small headphones that are designed to be fitted directly in a user&#39;s ear). Traditional headphones include both over-ear headphones (sometimes referred to as either circumaural or full-size headphones) that have earpads that fully encompass a user&#39;s ears, and on-ear headphones (sometimes referred to as supra-aural headphones) that have earpads that press against a user&#39;s ear instead of surrounding the ear. 
     The term “earbuds”, which can also be referred to as earphones or ear-fitting headphones, includes both small headphones that fit within a user&#39;s outer ear facing the ear canal without being inserted into the ear canal, and in-ear headphones, sometimes referred to as canalphones, that are inserted in the ear canal itself. Thus, in-ear hearing devices can be another type of portable listening device that are configured to be positioned substantially within a user&#39;s ear. Other types of portable listening devices can also include hearing aids that augment sounds from the surrounding environment to the user. As used herein, the term “eartip”, which can also be referred to as earmold, includes pre-formed, post-formed, or custom-molded sound-directing structures that at least partially fit within an ear canal. Eartips can be formed to have a comfortable fit capable of being worn for long periods of time. They can have different sizes and shapes to achieve a better seal with a user&#39;s ear canal and/or ear cavity. 
     In addition to the wireless listening device aforementioned herein, embodiments also include a case for housing one or more wireless listening devices. The case can include a magnet array formed of a set of magnets laterally positioned with respect to one another. Each magnet can have a specific magnetic polarity that is positioned in a distinct direction to focus the magnetic force at a retention slab in the wireless listening device to generate high attractive forces in a small footprint. Details of example magnet arrays are discussed herein with respect to  FIGS. 23 and 24A-24B . 
     In some additional or alternative embodiments, the case can also include a bistable hinge that can have two stable states, one of which pulls the lid of the case closed, and the other one of which pushes the lid of the case opened. The bistable hinge can include three pivot points, as well as a spring and piston rod along which a piston guide can move. The relative direction of a force applied by the spring and a conversion axis defined by two pivot points can define which state the bistable hinge pushes or pulls into. The bistable hinge can provide a nice tactile feel when the lid for the case opens or closes, and can also minimize the number of magnets needed to keep the lid closed. Details of example bistable hinges are discussed herein with respect to  FIGS. 27 and 28A-28C . 
     In certain instances, the case can also include a hybrid retention and sensor shunt for detecting when the lid of the case is in the closed position. The hybrid shunt can allow a magnet in the lid to pull toward the body to keep the lid closed, while also providing a body through which magnetic fields from the magnet can traverse to a region below the shunt to be detected by a sensor. That way, the sensor can utilize the space provided for the hybrid shunt instead of being placed elsewhere around the case and occupying valuable real estate. Details of example hybrid retention and sensor shunts are discussed herein with respect to  FIGS. 26A-26B . 
     I. Wireless Listening Device 
       FIG. 1A  is a block diagram illustrating a portable electronic listening device system  100  including an exemplary wireless listening device  101 , according to some embodiments of the present disclosure. Wireless listening device  101 , as mentioned above, can include a housing  105 . Housing  105  can be an electronic device component that generates and receives sound to provide an enhanced user interface for a host device  130 . Housing  105  can include a computing system  102  coupled to a memory bank  104 . Computing system  102  can execute instructions stored in memory bank  104  for performing a plurality of functions for operating housing  105 . Computing system  102  can be one or more suitable computing devices, such as microprocessors, computer processing units (CPUs), graphics processing units (GPUs), field programmable gate arrays (FPGAs), and the like. 
     Computing system  102  can also be coupled to a user interface system  106 , communication system  108 , and a sensor system  110  for enabling housing  105  to perform one or more functions. For instance, user interface system  106  can include a driver (e.g., speaker) for outputting sound to a user, microphone for inputting sound from the environment or the user, and any other suitable input and output device. Communication system  108  can include Bluetooth components for enabling housing  105  to send and receive data/commands from host device  130 . Sensor system  110  can include optical sensors, accelerometers, microphones, and any other type of sensor that can measure a parameter of an external entity and/or environment. 
     Housing  105  can also include a battery  112 , which can be any suitable energy storage device, such as a lithium ion battery, capable of storing energy and discharging stored energy to operate housing  105 . The discharged energy can be used to power the electrical components of housing  105 . In some embodiments, battery  112  can also be charged to replenish its stored energy. For instance, battery  112  can be coupled to power receiving circuitry  114 , which can receive current from receiving element  116 . Receiving element  116  can electrically couple with a transmitting element  118  of an case  103  in embodiments where receiving element  116  and transmitting element  118  are configured as exposed electrical contacts. Case  103  can include a battery  122  that can store and discharge energy to power transmitting circuitry  120 , which can in turn provide power to transmitting element  118 . The provided power can transfer through an electrical connection  128  and be received by power receiving circuitry  114  for charging battery  112 . While case  103  can be a device that provides power to charge battery  112  through receiving element  116 , in some embodiments, case  103  can also be a device that houses wireless listening device  101  for storing and provide protection to wireless listening device  101  while it is stored in case  103 . 
     Case  103  can also include a case computing system  119  and a case communication system  121 . Case computing system  119  can be one or more processors, ASICs, FPGAs, microprocessors, and the like for operating case  103 . Case computing system  119  can be coupled to power transmitting circuitry  120  for operating the charging functionalities of case  103 , and case computing system  119  can also be coupled to case communication system  121  for operating the interactive functionalities of case  103  with other devices, e.g., housing  105 . In some embodiments, case communication system  121  is a Bluetooth component, or any other suitable communication component, that sends and receives data with communication system  108  of housing  105 , such as an antenna formed of a conductive body. That way, case  103  can be apprised of the status of wireless listening device  101  (e.g., charging status and the like). Case  103  can also include a speaker  123  coupled to case computing system  119  so that speaker  123  can emit audible noise capable of being heard by a user for notification purposes. 
     Host device  130 , to which housing  105  is an accessory, can be a portable electronic device, such as a smart phone, tablet, or laptop computer. Host device  130  can include a host computing system  132  coupled to a battery  135  and a host memory bank  134  containing lines of code executable by host computing system  132  for operating host device  130 . Host device  130  can also include a host sensor system  136 , e.g., accelerometer, gyroscope, light sensor, and the like, for allowing host device  130  to sense the environment, and a host user interface system  138 , e.g., display, speaker, buttons, touch screen, and the like, for outputting information to and receiving input from a user. Additionally, host device  130  can also include a host communication system  140  for allowing host device  130  to send and/or receive data from the Internet or cell towers via wireless communication, e.g., wireless fidelity (WIFI), long term evolution (LTE), code division multiple access (CDMA), global system for mobiles (GSM), Bluetooth, and the like. In some embodiments, host communication system  140  can also communicate with communication system  108  in housing  105  via wireless communication line  142  so that host device  130  can send sound data to housing  105  to output sound, and receive data from housing  105  to receive user inputs. Communication line  142  can be any suitable wireless communication line such as Bluetooth connection. By enabling communication between host device  130  and housing  105 , wireless listening device  101  can enhance the user interface of host device  130 . 
     An example of such portable electronic listening device system is shown in  FIG. 1B , which is a simplified illustration of an exemplary portable electronic listening device system  150  having a host device  152  configured as a smart phone, a case  154 , and a pair of wireless listening devices  156  configured as a pair of in-ear hearing devices, according to some embodiments of the present disclosure. Host device  152  can be wirelessly communicatively coupled with case  154  so that host device  152  can receive the charge level data for case  154  and/or the charge level data for wireless listening devices  156 . Host device  152  can also be wirelessly communicatively coupled with wireless listening devices  156  so that audio data can be transmitted to wireless listening devices  156  for play back to a user, and audio data can be received by host device  152  as recorded/inputted from microphones in wireless listening devices  156 . Wireless listening devices  156  can be wirelessly communicatively coupled with case  154  so that audio data from case  154  can be transmitted to wireless listening devices  156 . As an example, case  154  can be coupled to an audio source different than host device  152  via a physical connection, e.g., an auxiliary cable connection. The audio data from the audio source can be outputted to case  154 , which can then wirelessly transmit the data to wireless listening devices  156 . That way, a user can hear audio by way of wireless listening devices  156  even though the audio device does not have wireless audio output capabilities. 
     According to some embodiments of the present disclosure, each wireless listening device  156  can include a housing  158  formed of a body  160  and a stem  162  extending from body  160 , where housing  158  is formed of a monolithic outer structure. Body  160  can include an internally facing microphone  164  and an externally facing microphone  166  for purposes discussed herein with respect to  FIGS. 7-10 . Externally facing microphone  166  can be positioned within an opening defined by portions of body  160  and stem  162  as shown in FIG.  1 B. By extending into both body  160  and stem  162 , microphone  166  can be large enough to receive sounds from a broader area around the user. In some embodiments, housing  158  can be attached to an eartip  174  that can direct sound from an internal audio driver out of housing  158  and into a user&#39;s ear canal. Thus, wireless listening devices  156  can be configured as in-ear hearing devices. Stem  162  can be substantially cylindrical in construction, but it can include a planar region  168  that does not follow the curvature of the cylindrical construction. Planar region  168  can indicate an area where the wireless listening device is capable of receiving user input. For instance, a user input can be inputted by squeezing stem  162  at planar region  168 . Stem  162  can also include electrical contacts  170  and  172  for making contact with corresponding electrical contacts in case  154 , as will be discussed further herein with respect to  FIG. 20A . 
     As will be appreciated herein, wireless listening devices  156  can include several features can enable them to be worn by a user all day. Its eartip can be soft and pliable, and can include control leaks to release trapped pressure in an ear canal so that it is comfortable to wear. Its functionality can also enable wireless listening devices  156  to provide an audio interface to host device  152  so that the user may not need to utilize a graphical interface of host device  152 . In other words, wireless listening devices  156  can be so sophisticated that it can enable the user to perform day-to-day operations from host device  152  solely through interactions with wireless listening devices  156 . This can create further independence from host device  152  by not requiring the user to physically interact with, and/or look at the display screen of, host device  152 , especially when the functionality of wireless listening devices  156  is combined with the voice control capabilities of host device  152 . Furthermore, wireless listening devices  156  can function in transparent mode where audible sounds from the surrounding environment can be recorded by externally facing microphone  166  and immediately replicated to the user by outputting the sound through eartip  174  to be heard by the user. Additionally, for those users that are hard of hearing, wireless listening devices  156  can increase the volume of the sounds in the surrounding environment for the user to hear. Moreover, for those users that are in an extremely loud environment, such as a user at a music concert, wireless listening devices  156  can decrease the volume of the sounds in the surrounding environment to a more acceptable level. This adjustment between increasing and decreasing volume can occur automatically to maintain a certain decibel range, in some embodiments. Thus, wireless listening devices  156  can enable a true hands free experience for the user. 
     According to some embodiments of the present disclosure, eartip  124  can attach to, and detach from, housing  105 , as shown in  FIGS. 2A and 2B .  FIG. 2A  is a side-view illustration of an exemplary wireless listening device  200  including an eartip  204  and a housing  202 , where eartip  204  is attached to housing  202 , according to some embodiments of the present disclosure; and  FIG. 2B  is a side view illustration of wireless listening device  200  where eartip  204  is detached from housing  202 , according to some embodiments of the present disclosure. As shown in  FIG. 2A , eartip  204  can include a tip region  206  and a base region  208  that together form a monolithic structure, and a sound channel  210  that extends through both tip region  206  and base region  208 . Tip region  206  can include a curved, annular surface  207  that inserts into an ear canal for directing sound from housing  202  to the user, and can be formed of a pliable material that can easily bend to conform to the inner surfaces of the ear canal for forming an acoustic seal. 
     Eartip  124  can attach to housing  105  in various ways. For instance, eartip  124  can be magnetically attached to housing using magnets to magnetically attract eartip  124  to housing  105 . Eartip  124  can also be attached to housing  105  using mechanical means, such as a screw and threaded hole attachment. In such instances, an opening of housing  105  can be threaded and base region  208  can be correspondingly threaded so that eartip  124  can be screwed into housing  105 . Furthermore, eartip  124  can be simply adhered to housing  105  using an adhesive or any other chemical bonding. In certain embodiments, eartip  124  can have features that hook onto housing  105 , or a separate wireform attachment mechanism can be implemented in housing  105  to latch onto eartip  124 . Further details of the construction of eartip  204  will be discussed further herein with respect to  FIGS. 3A-3C and 3E . Eartip  204  can be detached from housing  202 , as shown in  FIG. 2B , so that damaged eartips can be easily replaced or so that different types and/or sizes of eartips can be used to more comfortably fit in ear canals of different anatomical shapes and sizes. 
     It is to be appreciated that eartip  204  and housing  202  can have different configuration and functionality that result in improved sound quality and user experience. The details of such configurations and functionalities are discussed further herein. 
     II. Eartip 
     As mentioned above, an eartip can be attached to, and detached from, the housing of a wireless listening device. When configured as an in-ear hearing device or a hearing aid, the eartip can be positioned inside the ear canal of a user and direct sound outputted by the housing into the ear canal. In some embodiments, an attachment mechanism can be implemented in the base of the eartip to enable the eartip to attach to, and detach from, the housing as discussed herein with respect to  FIGS. 3A-3C . 
     A. Construction of an Eartip and an Attachment Mechanism 
       FIG. 3A  is a cross-sectional view  300  of an eartip  302  attached to an outer structure  304  of a housing via an attachment structure  308 , according to some embodiments of the present disclosure. It is to be appreciated that discussion of  FIG. 3A  may refer to  FIG. 3B  for a better understanding of the structure of eartip  302 .  FIG. 3B  is a top-down view  301  of eartip  302 , according to some embodiments of the present disclosure. 
     With reference to  FIG. 3A , eartip  302  can include an eartip body formed of an inner eartip body  316  and an outer eartip body  322  that together form a monolithic structure. Outer eartip body  322  can extend around a perimeter/circumference of inner eartip body  316  and during manufacturing, can initially be formed together as a deformable tube that is later folded over so that outer eartip body  322  is positioned outside of inner eartip body  316  as shown. Inner eartip body  316  can be centered along a central axis  313  and define a sound channel  310  that extends through eartip  302  between an interfacing end  312  and an attachment end  314  of the eartip body. Sound channel  310  can be vacant space through which sound can travel from attachment end  314  to interfacing end  312 . In some embodiments, attachment end  314  can be an end of eartip  302  that is configured to attach to outer structure  304  of the housing so that sound generated by the housing can pass into sound channel  310  through an acoustic opening  311  of outer structure  304 ; and, interfacing end  312  can be an end of eartip  302  opposite from attachment end  314  where outer eartip body  324  begins to extend from inner eartip body  316  (such as at the top end of eartip  302 ) and that is configured to interface with (e.g., insert into) an ear canal of a user. When eartip  302  is attached to outer structure  304 , sound channel  310  can be substantially aligned with acoustic opening  311  of outer structure  304  so that sound the from the housing can easily propagate into sound channel  310 . 
     Inner eartip body  316 , in certain embodiments, can be substantially cylindrical and can define a cylindrical sound channel  310 . Thus, as shown in the top-down view  301  of  FIG. 3B , sound channel  310  can be substantially circular. It is to be appreciated that a circular profile is merely exemplary and that the top-down profile of sound channel  310  can have other profiles, such as ovular, triangular, rectangular, oblong, and the like without departing from the spirit and scope of the present disclosure. 
     With reference back to  FIG. 3A , in some embodiments, eartip  302  can include a tip region  318  and a base region  320  (e.g., tip region  206  and base region  208  in  FIG. 2 ). Tip region  318  can be a part of eartip  302  that inserts into the ear canal of the user while base region  320  can be a part of eartip  302  that extends toward and attaches to outer structure  304  of the housing. Base region  320  can be configured so that eartip  302  minimally protrudes from outer structure  304 . For instance, base region  320  can be configured so that tip region  318  is positioned a distance D away from a non-protruding surface of outer structure  304  that is less than 3 mm, particularly less than 2 mm in some embodiments. By having eartip  302  protrude a minimal distance away from outer structure  304  of the housing, eartip  302  may better resist inadvertent separation forces to minimize accidental detachment, as well as minimally protrude from the user&#39;s ear when worn for a pleasing appearance. 
     In some embodiments, outer eartip body  322  can be a part of tip region  318  that extends from, and is coupled to, inner eartip body  316  at interface end  312  of eartip  302  toward attachment end  314 . Outer eartip body  322  can bend and conform to the contours of the ear canal to form an acoustic seal to prevent sound from leaking out of the ear canal. Thus, according to some embodiments of the present disclosure, outer eartip body  322  can be formed of a thin, compliant material, e.g., silicone, thermoplastic urethane, thermoplastic elastomer, or the like, that can easily bend and deflect inward and outward to conform to various contours of the ear canal. To allow outer eartip body  322  to deflect inward and outward, outer eartip body  322  can be like a cantilever where its end closest to attachment end  314  is positioned a distance away from inner eartip body  316  to define a deflection zone  323  formed of vacant space within which outer eartip body  322  can freely deflect. In some additional and alternative embodiments, inner eartip body  316  can also be formed of the same material as outer eartip body  322  but of a different, e.g., larger, thickness so that a substantial portion of eartip  300  as a whole can be formed of the compliant material. Inner eartip body  316  can have a larger thickness than outer eartip body  322  because it does not contact the ear canal and provides some structural integrity to eartip  300 ; thus, it does not need to be as compliant as outer eartip body  322  for conforming to the ear canal. 
     Outer eartip body  322  can include a curved interface surface  324  that is sized and shaped to make contact with the inner surfaces of the ear canal for forming an acoustic seal when the wireless listening device is worn by the user. Outer eartip body  322  can taper toward interfacing end  312  to make it easier for the user to insert eartip  302  into his or her ear canal. In some embodiments, a part of outer eartip body  322  closest to attachment end  314  can bend back toward inner eartip body  316  to reduce the chances of outer eartip body  322  flipping inside-out. 
     According to some embodiments of the present disclosure, eartip  302  can include attachment structure  308  for securely attaching to outer structure  304 . As mentioned herein, eartip  302  can be formed of a compliant material such as silicone. Compliant materials may not easily attach to stiff structures alone. Thus, attachment structure  308  can be implemented to provide some rigidity for certain parts of eartip  302  to enable eartip  302  to securely attach to outer structure  304 . In some embodiments, attachment structure  308  is positioned within base portion  320  and may extend into a portion of tip portion  318  closest to attachment end  314  so that attachment structure  308  can help attach eartip  302  to outer structure  304  of the housing. Attachment structure  308  can be formed of a stiff, rigid material such as plastic or thermal plastic urethane (TPU) that is strong enough to achieve the desired attachment characteristics suitable for attaching eartip  302  with outer structure  304 . In some embodiments, attachment structure  308  is formed to be more rigid than inner eartip body  316  and outer eartip body  322 . 
     Attachment structure  308  can include a mesh  309  for preventing debris and other unwanted particles from falling into the housing through acoustic opening  311 . Mesh  309  can be an interlaced structure formed of a network of wire that allows sound to propagate through but prevents debris from passing through. In some embodiments, mesh  309  extends into a portion of attachment structure  308  so that mesh  309  can be securely fixed within eartip  302  by the rigid structure of attachment structure  308 . Attachment structure  308  can also include a plurality of attachment features  326  that protrude out of attachment end  304  and are configured to physically couple with outer structure  304 . In some instances, attachment features  326  can be separately positioned around a perimeter of attachment structure  308  so that attachment features  326  can attach to discrete locations of outer structure  304 . Each attachment feature  326  can include an arm and a hook that secures to outer structure  304 , as better shown in  FIG. 3C . 
       FIG. 3C  is a close-up, cross-sectional view illustration of attachment structure  308  attached to outer structure  304  via attachment features  326 , according to some embodiments of the present disclosure. Attachment structure  308  can include a frame portion  328  and attachment features  326  that together form a monolithic structure. Frame portion  328  can be a ring positioned around central axis  313 , and can include a groove  330  extending around an outer circumference of frame portion  328 . Groove  330  can increase the surface area that contacts inner eartip body  316  to enhance the structural coupling between inner eartip body  316  and attachment structure  308 . In some embodiments, attachment features  326  can extend from frame portion  328  in a direction that is parallel to the central axis  313  so that attachment features  326  can attach to outer structure  304  and position central axis  313  at an angle that is substantially perpendicular to the plane in which outer structure  304  is oriented at the attachment location (which is shown to be horizontal in  FIG. 3A ). Each attachment feature  326  can include an arm  332  and a hook  334  for attaching to outer structure  304 . Hook  334  can be a portion of attachment feature  326  that bends away from central axis  313  of attachment structure  308  so that hook  334  can grab onto a lip  336  of outer structure  304  that protrudes into acoustic opening  311  of outer structure  304 . In some embodiments, lip  336  extends into acoustic opening  311  and includes an attachment surface  335  to which hook  334  can attach. Arm  332  can be a cantilevered structure that applies outward force when hook  334  is engaged with lip  336  to secure eartip  302  to outer structure  304  of the housing. In some embodiments, lip  336  can extend a short distance away from outer structure  304  and provide a slanted surface upon which base portion  320  of eartip  302  can rest as shown in  FIG. 3C  to further secure a robust attachment. 
     In some embodiments, the plurality of attachment features  326  can secure eartip  302  to outer structure  304  with a force that is strong enough to withstand inadvertent detachment (e.g., when the listening device is repositioned in an ear canal or is being held in a user&#39;s hand), but weak enough to allow intentional detachment by the user (e.g., when the user wants to change eartip types or when the user wants to clean eartip  302 ). The plurality of attachment features  326  can also provide tactile feedback when engaged, such as a snapping sensation, when hooks  334  engage with lip  336 . Furthermore, as can be appreciated herein, attachment structure  308  allows eartip  302  to attach to outer structure  304  by inserting into an opening of outer structure  304 , instead of wrapping around a rigid protrusion of outer structure  304  as is conventionally done. Accordingly, when attached, a portion of eartip  302  may be positioned within outer structure  304  of the housing. In such embodiments, attachment structure  308  requires less total space to securely attach eartip  302  with outer structure  304 , and moves the failure point in the event of a drop/bend/pinch event to base region  320  of eartip  302  as opposed to outer structure  304  of the housing. This substantially reduces the cost of replacement/repair of the wireless listening device/in-ear hearing device. 
     Constructing eartip  302  with a circular profile as shown in the top-down view in  FIG. 3B  simplifies alignment with acoustic opening  311  of outer structure  304 . However, alignment may be more difficult to achieve when eartip  302  is intended to be oriented a certain way when attached to outer structure  304 , even more so when eartip  302  is non-circular. Thus, in some embodiments, alignment magnets can be implemented in eartip  302  and outer structure  304  to guide them into proper alignment when they are placed proximate to one another. For instance, a first magnet  338  can be positioned within bottom region  320  of eartip  302  adjacent to a surface that makes contact with outer structure  304 , and a second magnet  340  can be positioned within lip  336  of outer structure  304  adjacent to a surface that makes contact with eartip  302  so that magnet  338  can attract magnet  340  to properly orient eartip  302  with outer structure  304  during attachment. Implementing magnets  338  and  340  into both eartip  302  and outer structure  304  of the housing, respectively, can ease the way in which the two components achieve alignment when attaching together. 
     Although  FIGS. 3A-3C  illustrate attachment structure  308  as having a plurality of discrete attachment features  326 , embodiments are not limited to such configurations. For instance, instead of having a plurality of attachment features that each have an individual arm and hook, some embodiments can have a single, annular attachment feature that attaches to an entire perimeter of acoustic opening  311  of outer structure  304 . It is to be appreciated that attachment features having a variety of other types of hooks that extend into acoustic opening  311  for attaching to outer structure  304  can be envisioned herein. For example, various attachment feature designs incorporating wireform attachment mechanisms for attaching an eartip with a housing according to some embodiments of the present disclosure are further discussed and illustrated herein with respect to  FIGS. 3D-3Q . 
       FIG. 3D  is an exploded view illustration of an exemplary wireless listening device  350  including a wireform attachment mechanism  351  for attaching an eartip  352  to a housing  353 , according to some embodiments of the present disclosure. In some instances, eartip  352  can be attached to a nozzle  359 , and nozzle  359  can be securely attached to, or be a portion of, housing  353 . When configured to be securely attached to housing  353 , nozzle  359  can be a separate structure from housing  353  that is attached via welding or adhesive so that nozzle  359  cannot separate from housing  353 . Alternatively, when configured to be a portion of housing  353 , nozzle  359  can be a monolithic portion of housing  353  that protrudes outward away from housing  353 . Nozzle  359  can include openings  361  through which portions of wireform attachment mechanism  351  can extend to latch eartip  352  to housing  353 , and nozzle  359  can include a mesh  303  to cover the opening of nozzle  359  and prevent dust and debris from entering housing  353 , as will be discussed further herein with respect to  FIG. 3I . Wireform attachment mechanism  351  can be an independent and separate structure from nozzle  359  and housing  353  that makes contact with both components. Because eartip  352  attaches to housing  353  by way of wireform attachment mechanism  351 , eartip  352  may be configured to complement the design of wireform attachment mechanism  351 , as will be discussed further herein. 
       FIG. 3E  is a cross-sectional view illustration of eartip  352  configured to attach to a housing by way of a wireform attachment mechanism, according to some embodiments of the present disclosure. Like eartip  302  in  FIG. 3A , eartip  352  can include an eartip body formed of an inner eartip body  325  and an outer eartip body  327  that together form a monolithic structure. Outer eartip body  327  can extend around a perimeter/circumference of inner eartip body  325  and during manufacturing, can initially be formed together as a deformable tube that is later folded over so that outer eartip body  327  is positioned outside of inner eartip body  325  as shown in  FIG. 3E . Inner eartip body  325  can be centered along a central axis  329  and define a sound channel  331  that extends through inner eartip body  325  between an interfacing end  333  and an attachment end  337  of the eartip body. In some embodiments, attachment end  337  can be an end of the eartip body that is configured to attach to the housing via a nozzle and a wireform attachment feature so that sound generated by the housing can pass into sound channel  331  through an acoustic opening of the housing; and, interfacing end  333  can be an end of eartip  352  opposite from attachment end  337  where outer eartip body  327  begins to extend from inner eartip body  325 , such as at the top end of the eartip body. 
     Inner eartip body  325 , in certain embodiments, can be substantially ovular and can define a sound channel  331 ; thus, the top-down outer profile of eartip  352  can also be substantially ovular or oblong in some instances. However, embodiments are not limited to such configurations and can have other profiles, such as circular, triangular, rectangular, and the like without departing from the spirit and scope of the present disclosure. 
     Like eartip  302  in  FIG. 3A , eartip  352  can also include a tip region  339  and a base region  341 . Tip region  339  can be a part of eartip  352  that inserts into the ear canal of the user while base region  341  can be a part of eartip  352  that extends toward and attaches to the housing. Base region  341  can be configured so that eartip  352  minimally protrudes from the outer structure of the housing, e.g., distance D in  FIG. 3A , thereby enabling eartip  352  to better resist inadvertent separation forces to minimize accidental detachment, as well as minimally protrude from the user&#39;s ear when worn for a pleasing appearance. 
     In some embodiments, eartip  352  can include an attachment structure  343  that is formed of a different and stiffer material than what is used to construct the eartip body. Attachment structure  343  can be formed of a stiffer material so that its rigidity can be more suitable for attaching to the housing. Attachment structure  343  can include an upper region  378  and a lower region  399  that extends from upper region  373 . Upper region  378  can have a more horizontal disposition than lower region  399 , which may be more vertical than upper region  378 , thereby being an inverted u-shaped profile as shown. Unlike attachment structure  308  in  FIG. 3A  which has features that actively grip onto the housing, attachment structure  343  instead includes recesses  345   a - b  around lower region  399  for providing latching points for wireform attachment mechanism  351  for attachment. Recesses  345   a - b  can be cavities defined by an inner surface  344  of lower region  399  of attachment structure  343  that passively allow a wireform attachment mechanism to secure eartip  352  to a housing. For instance, portions of the lower region below recesses  345   a - b  can form an inverted overhang structure that hooks onto an external structure, such as an end cap of a wireform attachment structure, as will be discussed further herein with respect to  FIGS. 3J-3L . Inner eartip body  325  can interface with attachment structure  343  at a boundary  376  where inner eartip body  325  initially makes contact with attachment structure  343  as shown by a dashed and dotted line. Boundary  376  can be defined by an imaginary horizontal line positioned between interfacing end  333  and attachment end  337 , as shown in  FIG. 3E . 
     According to some embodiments of the present disclosure, the thickness of a sidewall of inner eartip body  325  can gradually change from one end to the other. The sidewall of inner eartip body  325  can be defined by a portion of inner eartip body  325  disposed between boundary  376  and interfacing end  333 . As an example, inner eartip body  325  can have a first sidewall thickness T 1  closest to boundary  376  and a second sidewall thickness T 2  closest to interfacing end  333  that is smaller than the first sidewall thickness T 1 . In some instances, the thickness of the sidewall gradually decreases from first sidewall thickness T 1  to second sidewall thickness T 2 , as shown in  FIG. 3E . Furthermore, in some embodiments, the inner surface of inner eartip body  325  may be substantially vertical while the outer surface of inner eartip body  325  may be sloped so that the gradual change in thickness is created by the sloped surface of the outer surface of inner eartip body  325 . Having a thinner sidewall thickness at interfacing end  333  enables the eartip body to be more pliable at interfacing end  333  so that eartip  352  can be more comfortable to the user when worn. In certain embodiments, the thickness of outer eartip body  327  can be the same as the second sidewall thickness T 2  of inner eartip body  325 . 
     Although  FIG. 3E  illustrates the eartip body that includes inner eartip body  325  separated from outer eartip body  327  by a deflection zone, embodiments are not so limited. In some embodiments, inner eartip body  325  and outer eartip body  327  can be one solid, compliant structure formed of silicone. Thus, a deflection zone may not be defined between inner eartip body  325  and outer eartip body  327 . Any other type of configuration is envisioned herein without departing from the spirit and scope of the present disclosure. 
     Eartip  352  can also include a mesh  303  for preventing debris and other unwanted particles from falling completely through sound channel  331 . Mesh  303  can be a soft, porous fabric that allows sound to propagate through but prevents debris from passing through. For instance, mesh  303  can be formed of a polyester fabric. In some embodiments, mesh  303  extends into upper region  378  of attachment structure  343  so that mesh  303  can be securely fixed within eartip  352  by the rigid structure of attachment structure  343 . 
     As can be appreciated from the illustration of  FIG. 3E , the structure of the eartip body (i.e., inner eartip body  325  and outer eartip body  327 ) can be formed of a different, more pliable material than what is used for forming attachment structure  343 . For instance, inner eartip body  325  and outer eartip body  327  can be formed of silicone, while attachment structure  343  is formed of a stiff polymer, such as polycarbonate. Thus, to form eartip  352 , the soft pliable structure of inner eartip body  325  may be securely attached to attachment structure  343 . In some embodiments, inner eartip body  325  and outer eartip body  327  are molded over attachment structure  343  so that a degree of chemical bonding is achieved at the interface between the two structures during the manufacturing process. However, in some additional embodiments, several through-holes  349  can be positioned around an upper region of attachment structure  343  to allow the soft material of which inner eartip body  325  is formed to pass from an outer surface  342  of attachment structure  343  to an inner surface  344  of attachment structure  343 . In some instances, the amount of material that passes through through-holes  349  can result in a formation of a thin, annular structure  346  that extends across a part of inner surface  344  of attachment feature  343  near through-holes  349 . The combination of annular structure  346  and structural pass-throughs between inner eartip body  325  and attachment structure  343  creates a mechanical interlocking feature that further strengthens the bond between inner eartip body  325  and attachment structure  343 . In some instances, annular structure  346  can be an extension of inner eartip body  325  that covers at least part of inner surface  344  of attachment structure  343 . Thus, annular structure  346 , material within pass-throughs  349 , inner eartip body  325 , and outer eartip body  327  can all be part of a same monolithic structure. 
     In some embodiments, attachment structure  343  also includes a control leak  348  set in a cavity region  307 , as will be discussed further herein with respect to  FIG. 6D . Control leak  348  can provide an atmospheric pass-through between an outside environment and sound channel  331  so that eartip  352  does not completely seal the ear canal and trap pressure within the ear canal. This can allow for a more comfortable user experience and can also improve the acoustic performance of the listening device. Cavity region  307  can be a shallow cavity defined by inner surface  344  of attachment structure  343  to mitigate the chances of control leak  348  from being occluded from the inside of inner eartip body  325 , as will be discussed further herein with respect to  FIG. 6E . In some embodiments, outer eartip body  327  can be modified to mitigate the changes of control leak  348  from being occluded from the outside of inner eartip body  325 , as will be discussed further here with respect to  FIGS. 6F-6H . 
     In some instances, inner eartip body  325  can further include an annular attachment flange  360  extending around a perimeter of attachment structure  343  at attachment end  337 . Attachment flange  360  can form an acoustic seal by pressing against an inner side surface of a housing, e.g., housing  353  in  FIG. 3D . Attachment flange  360  can extend away from center line  329  of inner eartip body  325  and in an upward and lateral direction as shown in  FIG. 3E . By configuring attachment flange  360  to extend upward and laterally, the directionality of the collapse of attachment flange  360  when it makes contact with the housing can be controlled. Because attachment flange  360  is part of inner eartip body  325 , attachment flange  360  can be formed of the same material as inner eartip body  325 , such as silicone. In some instances, attachment flange  360  can be an extension of inner eartip body  325  that covers at least part of outer surface  342  of attachment structure  343 . Thus, attachment flange  360 , inner eartip body  325 , and outer eartip body  327  can all be part of a same monolithic structure. 
     With reference back to  FIG. 3D , according to some embodiments of the present disclosure, wireform attachment mechanism  351  can attach eartip  352  to nozzle  359 , and thus to housing  353 . Wireform attachment mechanism  351  can be configured to enable eartip  352  to mechanically attach to and detach from housing  353 . In some embodiments, wireform attachment mechanism  351  can enable eartip  352  to latch onto nozzle  359  with application of low insertion force and resist separation from housing  353  once eartip  352  is latched onto nozzle  359 . Once eartip  352  is attached to nozzle  359 , wireform attachment mechanism  351  does not have to apply active force to maintain attachment. Rather, the physical structure of wireform attachment mechanism  351  can allow eartip  352  to remain attached to nozzle  359 . That way, wireform attachment mechanism  351  does not have to apply a high amount of active force to keep eartip  352  attached to nozzle  359  and allow attachment by application of a low insertion force, as will be discussed further herein with respect to  FIG. 3I . 
     Wireform attachment mechanism  351  can include a body formed of a single, contiguous strip of wire that is bent in various directions to create a compressible spring that can apply pressure in a lateral direction to attach eartip  352  to nozzle  359 .  FIGS. 3F-3H  are illustrations of wireform attachment mechanism  351  that has an s-shaped profile configured to compress toward its center when engaging with an eartip, according to some embodiments of the present disclosure. Specifically,  FIG. 3F  is a top-down view illustration of wireform attachment mechanism  351  in its uncompressed state,  FIG. 3G  is a top-down view illustration of uncompressed wireform attachment mechanism  351  superimposed over its compressed state, and  FIG. 3H  is a side-view illustration of wireform attachment mechanism  351  superimposed over its release state, according to some embodiments of the present disclosure. 
     As shown in  FIG. 3F , the strip of wire forming wireform attachment mechanism  351  can have an s-shape profile that includes a center segment  354  having opposing ends from which two wireform features extend. The two wireform features can include a first wireform feature  355   a  and a second wireform feature  355   b  that each includes respective intermediate segments  356   a - b , u-shaped segments  357   a - b , and end segments  358   a - b . U-shaped segments  357   a - b  can be positioned between intermediate segments  356   a - b  and end segments  358   a - b  as shown in  FIG. 3F . U-shaped segments  357   a - b  may not appear to have a u-shaped profile from the top-down view in  FIG. 3F  because the u-shaped profile of the bent wire extends into/out of the page, but its u-shaped profile may be more apparent in  FIG. 3D  which shows a perspective view of wireform attachment mechanism  351 . With reference back to  FIG. 3F , in some embodiments, center segment  354  can have a substantially straight profile/construction, and intermediate segments  356   a - b  extending from center segment  354  can have an arcuate profile/construction. The curvature of intermediate segments  356   a - b  can conform to a segment of a corresponding outer profile of nozzle  359  so that intermediate segments  356   a - b  can achieve a better fit with nozzle  359 . Wireform attachment mechanism  351  can also include end caps  366   a - b  that cover respective lateral bend portions  375   a - b  of u-shaped segments  357   a - b . As shown in the side-view illustration in  FIG. 3H , end caps  366   a - b  can have a beveled top corner  377   a - b  and a flat bottom surface  379   b . Beveled top corner  377   a - b  can transition vertical insertion force into lateral force to bend wireform attachment mechanism  380  during attachment, and flat bottom surface  379   b  can resist separation of the eartip once attached and lock onto respective portions of an attachment structure (e.g., portions of the lower region of the attachment structure below recesses  345   a - b  discussed herein with respect to  FIG. 3E ). 
     In some embodiments, center segment  354 , intermediate segments  356   a - b  and end segments  358   a - b  can be substantially positioned in a same first plane, while u-shaped segments  357   a - b  can be substantially positioned in different but parallel second and third planes. The first plane can be positioned at an angle from the second and third planes. For instance, the first plane can be substantially perpendicular to the second and third planes, or at any other suitable angle without departing from the spirit and scope of the present disclosure. In some embodiments, wireform features  355   a - b  can each include respective end caps  366   a - b  that cover the center portion of u-shaped segments  357   a - b  to provide a better fit with nozzle  359  and eartip  352  when eartip  352  is attached to housing  353  via wireform attachment mechanism  351 . 
     During attachment, the eartip can press against end caps  366   a - b  until end caps  366   a - b  snap into the recesses in the nozzle, as will be discussed further herein with respect to  FIGS. 3J-3L . When pressing against end caps  366   a - b , wireform attachment mechanism  351  can bend into a compressed state  315 , as shown in  FIG. 3G  represented by a dotted silhouette of parts of wireform attachment mechanism  351 , to allow the attachment structure of the eartip to slide over the nozzle. In some embodiments, opposite halves of wireform attachment mechanism  351  can be cantilever beams that bend from a midpoint  317  of center segment  354 . Each half of wireform attachment mechanism  351  can have a long beam length so that they bend at a lower insertion forces than other configurations with shorter beam lengths. The beam length can be defined by the length of wireform attachment mechanism  351  from midpoint  317  to one of its ends. 
     During extraction, the eartip can be pulled away from the housing to release end caps  366   a - b  from the recesses of the eartip. Instead of resulting in a bending motion as shown in  FIG. 3G  to release end caps  366   a - b  from the recesses, extraction can result in a torsional motion as shown in  FIG. 3H . During the torsional motion, wireform attachment mechanism  351  can rotate the u-shaped segments  357   a - b  around axes defined by a line perpendicular to the page that intersects the two points where the end segments  358   a - b  and intermediate segment  356   a - b  meet u-shaped segments  357   a - b , as shown by axes  319   a - b  in  FIG. 3H . That way, when u-shaped segments  357   a - b  rotate along curves  321   a - b  around axes  319   a - b , end caps  366   a - b  can move inwards to allow the eartip to be released from the housing and separated. The direction of curves  321   a - b  along which u-shaped segments  357   a - b  rotate can be opposite from one another. For instance, curve  321   a  can be clockwise while curve  321   b  can be counter-clockwise, as shown in  FIG. 3H . 
     According to some embodiments of the present disclosure, wireform attachment mechanism  351  may be easier to bend than it is to move in a torsional rotation, and thus have a high torsional force to bending force ratio. This characteristic can be attributed in part to the long beam length resulting from the s-shape profile, as well as the properties of the wire itself, which can have a torsional rigidity that is higher than its bending rigidity due to the nature of a long and thin wire. This high ratio can allow wireform attachment mechanism  351  to allow an eartip to attach to a housing with a low insertion force while requiring a higher extraction force to release the eartip from the housing. This force profile enhances user experience because it enables the eartip to be easily yet robustly connected to the housing. In some embodiments, the force at which end caps  366   a - b  set into recesses of the eartip can generate an audible noise that can give the user another degree of feedback to confirm that the eartip has been attached. 
     To attach eartip  352  and nozzle  359  to housing  353 , wireform attachment mechanism  351  can apply lateral force at the end caps  366   a - b  in the horizontal direction away from center segment  354 . End caps  366   a - b  can fit through openings  361  of nozzle  359  and within respective recesses in eartip  352  to attach eartip  352  to housing  353 , which is better illustrated in  FIG. 3I . 
       FIG. 3I  is a cross-sectional view illustration of eartip  352  attached to housing  353  via wireform attachment mechanism  351 , according to some embodiments of the present disclosure. Eartip  352  can be directly attached to nozzle  359 , which can be (1) a separate structure that is securely attached to housing  353  as shown in  FIG. 3I , or (2) a protruding monolithic portion of housing  353  (not shown). Nozzle  359  can include mesh  303  that covers the opening of nozzle  359  to prevent dust and debris from entering housing  353 . Mesh  303  can be formed as a multi-layered structure including a cosmetic mesh  305   a  and an acoustic mesh  305   b  adhered to the cosmetic mesh, where cosmetic mesh  305   a  forms an outer surface of nozzle  359  and is formed of an interlaced network of stiff wire, while acoustic mesh  305   b  is adhered to an inner surface of cosmetic mesh  305   a  and is formed of a porous fabric. For instance, cosmetic mesh  305   a  can be formed of interlaced stainless steel and acoustic mesh  305   b  can be formed of polyester. To securely attach nozzle  359  to housing  353 , a welding ring  363  can be used to securely attach housing  353  to nozzle  359 . Welding ring  363  can be a stiff structure in the shape of a flat ring having a top surface  364  and bottom surface  365  opposite from top surface  364 . In some embodiments, housing  353  and nozzle  359  can be welded to top surface  364  of welding ring  363  so that housing  353  and nozzle  359  are securely attached to one another. Welding ring  363  can be formed of any suitable material, such as a metal. It is to be understood that  FIG. 3I  is a close-up view of how wireform attachment mechanism  351  attaches eartip  352  housing  353  and nozzle  359 , so only portions of eartip  352  and housing  353  are shown. 
     As shown in  FIG. 3I , wireform attachment mechanism  351  can include u-shaped segments  357   a - b  whose center portions are covered by end caps  366   a - b . End caps  366   a - b  can extend through openings  361  in nozzle  359  and into eartip  352 . In some embodiments, end caps  366   a - b  can extend into respective recesses  368   a - b  in eartip  352 . Recesses  368   a - b  can be formed in a frame portion  362  of eartip  352 . As mentioned herein, eartip  352  can be formed of a compliant material such as silicone, which may not easily attach to stiff structures, e.g., end caps  366   a - b , alone. Thus, frame portion  362  can be implemented in eartip  352  to provide some rigidity for securely attaching eartip  352  to nozzle  359  via wireform attachment mechanism  351 . Frame portion  362  can be formed of a stiff, rigid material such as plastic or thermal plastic urethane (TPU) that is strong enough to achieve the desired attachment characteristics suitable for attaching eartip  352  with nozzle  359 . In some embodiments, frame portion  362  is formed to be more rigid than the inner eartip body and outer eartip body, e.g., inner eartip body  316  and outer eartip body  322  in  FIG. 3A , of eartip  352 . 
       FIGS. 3J-3L  are a series of illustrations showing different points along the process of attaching eartip  352  to nozzle  359 , according to some embodiments of the present disclosure. To attach eartip  352  to nozzle  359  (and thus to housing  353 ), eartip  352  can be pressed into housing  353  in a downward direction  369  as shown in  FIG. 3J . Pressing eartip  352  downward causes frame portion  362  of eartip  352  to press against end caps  366   a - b  of wireform attachment mechanism  351 , as shown in  FIG. 3K . In some instances, frame portion  362  of eartip  352  presses against end caps  366   a - b  with a force in a lateral inward direction  370  toward center segment  354  such that end caps  366   a - b  deflect inward as it slides along frame portion  362 . Center segment  354  of wireform attachment mechanism  351  can allow each wireform feature to shift laterally toward center segment  354 . In some embodiments, u-shaped segments  357   a - b  can move horizontally toward center segment  354  as a whole, as shown in  FIG. 3K . End caps  366   a - b  can include respective beveled corners  373   a - b  so that end caps  366   a - b  can transition vertical downward force into lateral inward force that presses end caps  366   a - b  inward toward center segment  354  when force in downward direction  369  is applied to attach eartip  352  to nozzle  359 . Once end caps  366   a - b  reach recesses  368   a - b  as shown in  FIG. 3L , end caps  366   a - b  can click into place as the spring forces generated by the s-shape profile of wireform attachment mechanism  351  press in a lateral outward direction  371  away from center segment  354 . When end caps  366   a - b  are clicked into place, eartip  352  can be successfully attached to nozzle  359  and housing  353 , and an acoustic seal can be formed by attachment flange  360  at interface  374 . Attachment flange  360  can press against the inner surface of housing  353  in a lateral direction; thus, attachment flange  360  can form a radial seal with housing  353 . In some embodiments, clicking end caps  366   a - b  into recesses  368   a  provides a tactile feel that gives the user feedback to indicate when successful attachment has occurred, which can result in an enhanced user experience. 
     With reference back to  FIG. 3I , when eartip  352  is attached to nozzle  359  and housing  353 , wireform attachment mechanism  351  can resist separation forces in an upward direction  372  by blocking the upward movement of eartip  352  with end caps  366   a - b . In some embodiments, end caps  366   a - b  are positioned to interfere with the vertical movement of frame portion  362  so that their structure passively resists separation of eartip  352  from housing  353 . Thus, wireform attachment mechanism does not need to apply active clamping force to hold eartip  352  in place. This design is robust and reliable and does not lose resistance strength over time. In certain embodiments, the slope of beveled corners  373   a - b  allow end caps  366   a - b  to easily press inward toward center segment  354  when force in downward direction  369  is applied to attach eartip  352  to nozzle  359 . Conversely, the bottom corner of end cap  366   a - b  may not include beveled corners so that end caps  366   a - b  can resist substantially greater separation forces in upward direction  372 . Thus, eartip  352  can be attached under the application of low insertion force in downward direction  367  and separated under the application of high force in upward direction  372 . This force profile enabled by wireform attachment mechanism  351  can provide improved user experience and attachment reliability. In some embodiments, the attachment force sufficient to attach eartip  352  to nozzle  359  can be applied by a set of magnets (not shown). The magnets can be placed at regions in eartip  532  and nozzle  359  near interface  374  or any other interface where eartip  532  and nozzle  359  meet so that attractive magnetic forces can draw eartip  532  to nozzle  359  with enough force to effectuate attachment. 
     In some embodiments, u-shaped segments  357   a - b  can include respective lateral bend portions  367   a - b  to which end caps  366   a - b  are attached, as shown in  FIG. 3I . Lateral bend portions  367   a - b  can extend in a horizontal plane parallel to the plane in which center segment  351  and intermediate segments  356   a - b  are positioned in a non-overlapping manner. Thus, lateral bend portions  367   a - b  can be positioned at an angle with respect to the rest of the u-shaped segment  357   a - b , such as at a 90 degree angle. Lateral bend portions can improve the structural strength of end caps  366   a - b  and provide a stiff frame to which it can attach. 
     Although  FIGS. 3D-3L  discuss wireform attachment mechanisms configured with s-shape profiles, embodiments are not limited to such configurations. It is to be appreciated that any wireform shape can be used to attach eartips to housings without departing from the spirit and scope of the present disclosure. Examples of some suitable variations of wireform attachment mechansims are discussed herein with respect to  FIGS. 3M-3O  and  FIGS. 3P-3Q . 
       FIGS. 3M-3O  illustrate an exemplary wireform attachment mechanism  380  that has a u-shaped profile configured to compress toward its center when engaging with an eartip, according to some embodiments of the present disclosure. Specifically,  FIG. 3M  is a top-down view illustration of wireform attachment mechanism  380  in its uncompressed state,  FIG. 3N  is a top-down view illustration of uncompressed wireform attachment mechanism  380  superimposed over its compressed state, and  FIG. 3O  is a bottom-up perspective view illustration of wireform attachment mechanism  380  positioned in a nozzle, according to some embodiments of the present disclosure. 
     As shown in  FIG. 3M , wireform attachment mechanism  380  can be constructed of a single, contiguous strip of wire that is bent to have a u-shaped profile that includes u-shaped segments (not seen from this view) having respective lateral bend portions  381   a - b  coupled to respective end segments  382   a - b . Each end segment  382   a - b  can have a first end coupled to a respective u-shaped segment and an opposite second end that is dangling, e.g., not connected to any other part of wireform attachment mechanism  380 . Unlike wireform attachment mechanism  351  in  FIG. 3D , wireform attachment mechanism  380  may not include a center segment, but instead may just have an connecting segment  383  formed of a single curve of wire having an arcuate profile. Thus, according to some embodiments of the present disclosure, wireform attachment mechanism  380  can include two wireform features that are delineated by a center line  386  and configured as mirror images of one another where each wireform feature includes an intermediate segment formed by a respective half of connecting segment  383 . Connecting segment  383  can be coupled to ends of lateral bend portions  381   a - b  opposite from the ends to which lateral bend portion  381   a - b  are attached. In some embodiments, end caps  384   a - b  can be attached over lateral bend portions  381   a - b , similar to end caps  366   a - b  and lateral bend portions  375   a - b  discussed herein with respect to  FIG. 3I , for inserting into respective openings in the nozzle for attaching an eartip to the nozzle. 
     During attachment, as discussed herein with respect to  FIGS. 3J-3L , the eartip can press against end caps  384   a - b  until a certain point at which end caps  384   a - b  snap into the recesses in the nozzle. When pressing against end caps  384   a - b , wireform attachment mechanism  380  can bend into a compressed state  385 , as shown in  FIG. 3N  represented by a dotted silhouette of parts of wireform attachment mechanism  380 , to allow the frame portion of the eartip to slide over the nozzle. In some embodiments, opposite halves of wireform attachment mechanism  380  (when divided by a center line  386 ) can be cantilever beams that are fixed at a joint region  387  of connecting segment  383 . During compression, in some instances, each entire half can move toward center line  386  in a horizontal direction while bending at joint region  387 . In the compressed state, opposite halves of wireform attachment mechanism  380  divided by a center line  381  can be positioned closer to center line  381  than when wireform attachment mechanism  380  is in an uncompressed state. Furthermore parts of wireform attachment mechanism  380  positioned farther away from joint region  387  may move more during compression than parts of wireform attachment mechanism  380  positioned closer to joint region  387 . 
     As shown in  FIG. 3O , nozzle  359  can have an inner surface  388  that matches the curvature of wireform attachment mechanism  380 . Inner surface  388  can include a recess  389  that provides space for end segments  382   a - b  to be positioned, as well as to provide clearance space for allowing end segments  382   a - b  to move when wireform attachment mechanism  380  transitions from an uncompressed state to a compressed state, as discussed herein with respect to  FIG. 3N . In some embodiments, joint region  387  of wireform attachment mechanism  380  can be freely resting on inner surface  388 , or joint region  387  can be securely attached to inner surface  388  via an adhesive, welding, or any other suitable attachment method. Joint region  387  can be relatively small to allow a substantial majority of wireform attachment mechanism  380  move during compression, as shown in  FIG. 3N . However, in some embodiments, joint region  387  can be relatively large to allow only a small portion of wireform attachment mechanism  380  move during compression, as discussed herein with respect to  FIGS. 3P-3Q . 
       FIGS. 3P-3Q  illustrate an exemplary wireform attachment mechanism  390  that has a u-shaped profile configured to rotate its end caps around an axis when engaging with an eartip, according to some embodiments of the present disclosure. Specifically,  FIG. 3P  is a side view illustration of uncompressed wireform attachment mechanism  390  superimposed over its compressed state, and  FIG. 3Q  is a bottom-up perspective view illustration of wireform attachment mechanism  390  positioned in a nozzle, according to some embodiments of the present disclosure. 
     Similar to wireform attachment mechanism  380 , wireform attachment mechanism  390  shown in  FIG. 3P  can be constructed of a single, contiguous strip of wire that is bent to have a u-shaped profile substantially similar to that shown in  FIG. 3M . Accordingly, wireform attachment mechanism  390  can include a pair of lateral bend portions  391   a - b  coupled to respective u-shaped segments  392   a - b  that are coupled together via a connecting segment  393  formed of a single curve of wire. According to some embodiments of the present disclosure, wireform attachment mechanism  390  can include two wireform features that are delineated by a center line  396  and configured as mirror images of one another. Each wireform feature can include an end segment, a u-shaped segment including a lateral bend portion, and an intermediate segment formed by a respective half of connecting segment  393 . Connecting segment  393  can be coupled to ends of lateral bend portions  391   a - b  opposite from the ends to which lateral bend portion  391   a - b  are attached. End caps  394   a - b  can be attached over lateral bend portions  391   a - b  for inserting into respective openings in the nozzle for attaching an eartip to the nozzle. 
     When the eartip presses against end caps  394   a - b  during attachment, wireform attachment mechanism  390  can bend into a compressed state  395 , as shown in  FIG. 3P  and represented by a dotted silhouette of parts of wireform attachment mechanism  390 , to allow the frame portion of the eartip to slide over the nozzle. Unlike wireform attachment mechanism  380  where the entire halves compresses laterally during attachment, wireform attachment mechanism  390  can instead rotate only the u-shaped segments  392   a - b  around an axis. The axis can be defined by a line that intersects the two points where the end segments and intermediate segment meet u-shaped segments  392   a - b , as shown by axes  396   a - b  in  FIG. 3M . That way, when u-shaped segments  392   a - b  rotate along curves  397   a - b  around axes  396   a - b , end caps  394   a - b  can move inwards to allow the eartip to move toward the nozzle until end caps  394   a - b  snap into recesses of the eartip, as discussed herein with respect to  FIG. 3L . The direction of curves  397   a - b  along which u-shaped segments  392   a - b  rotate can be opposite from one another. For instance, curve  397   a  can be clockwise while curve  397   b  can be counter-clockwise, as shown in  FIG. 3P . 
     As shown in  FIG. 3Q , wireform attachment mechanism  390  can rest on inner surface  388  of nozzle  359 . In some embodiments, connecting segment  393  can be freely resting on inner surface  388 , or connecting segment  393  can be securely attached to inner surface  388  via an adhesive, welding, or any other suitable attachment method. In certain embodiments, a vast majority of connecting segment  393 , such as the entire length of connecting segment  393 , can be securely attached to inner surface  388 . Furthermore, end segments  398   a - b  can also be securely attached to inner surface  388  of nozzle  359 . That way, only u-shaped segments  392   a - b  can rotate around axes  396   a - b  during compression, as discussed herein with respect to  FIGS. 3P-3N . 
     B. Capacitive Eartip 
     According to some embodiments of the present disclosure, an eartip can be configured as a sensor for detecting when the wireless listening device is worn by a user. For instance, the eartip can be configured as a capacitive sensor that changes in capacitance when the eartip is inserted in an ear canal. 
       FIG. 4A  is an exemplary eartip  400  configured as a capacitive sensor, according to some embodiments of the present disclosure. As a capacitive sensor, eartip  400  can include a first conductive structure  402  and a second conductive structure  404  positioned within tip region  318  of eartip  400  and separated by deflection zone  323 . First conductive structure  402  can be a metal plate bent into a inner eartip body-like shape that can be positioned on an outer surface of inner eartip body  316  in some embodiments, or a conductive inner eartip body  316  by doping inner eartip body  316  with conductive material to convert inner eartip body  316  into a conductive structure. Similarly, second conductive structure  404  can be a metal plate bent and curved to conform to an inner surface of outer eartip body  322 , or be a conductive outer eartip body  322  by doping outer eartip body  322  with conductive material to convert outer eartip body  322  into a conductive structure. With this construction, the two conductive structures  402  and  404  and deflection zone  323  can define a first capacitance when eartip  300  is not inserted into an ear canal, but change in capacitance (e.g., increase in capacitance) when eartip  300  is inserted into an ear canal due to the deflection of outer eartip body  322  toward inner eartip body  316  when eartip  300  is inserted into the ear canal, as shown in  FIGS. 4B and 4C . In some embodiments, each conductive structure  402  and  404  extends around the entire circumference of eartip  400 . However, in some other embodiments, each conductive structure  402  and  404  may extend around only a portion of the entire circumference of eartip  400 . In such instances, each conductive structure  402  and  404  can be configured as a strip of conductive plating that are positioned directly across from one another to form a capacitor. 
       FIGS. 4B and 4C  are cross-sectional views of eartip  400  when it is inserted into an ear canal, according to some embodiments of the present disclosure. As shown in  FIG. 4B , eartip  400  can bend and conform to the inner surfaces of ear canal  406  when eartip  400  is inserted into ear canal  406 . Housing  202  may not bend or conform when the wireless listening device, e.g., in-ear hearing device, is worn by the user. As shown in  FIG. 4C , outer eartip body  322  may bend into deflection zone  323  when the wireless listening device is worn, thereby causing some parts of first and second conductive structures  402  and  404  to be positioned closer to one another. As such, the capacitance created by conductive structures  402  and  404  and the smaller separation distance between them may be different from, e.g., greater than, the capacitance when eartip  400  is not inserted into an ear canal, which is shown in  FIG. 4A  for instance. Thus, eartip  400  can be configured to have a first capacitance when it is not inserted into an ear canal, and a second capacitance when it is inserted into an ear canal. By modifying eartip  400  to be a capacitive sensor, additional, bulkier sensors are not needed in the housing, thereby helping the housing achieve a smaller form factor. 
     The wireless listening device can be configured to measure the difference in capacitance and determine that the wireless listening device has been worn by the user. This determination can be made when the capacitance of eartip  400  changes past a threshold value. By being able to determine when the device is worn, the wireless listening device can enhance user experience by automatically initiating specific, targeted UI controls related to the wireless listening device when it detects that it is worn, such as automatically providing play/pause options for music, answering/ending phone calls, and the like. 
     C. Patterned Eartip 
     Instead of, or in addition to, configuring the eartip as a capacitive sensor, some embodiments can configuring the eartip as an optical indicator that changes when the eartip is inserted into an ear canal. For instance, the eartip can include a pattern of lines and spaces on an inner surface of the outer eartip body that can be observed by an optical sensor in the housing to determine if the wireless listening device is worn by a user, as discussed further herein with respect to  FIGS. 5A-5C . Specifically,  FIG. 5A  is a bottom-up view of an exemplary eartip  500  configured with patterned lines  502  separated by spaces  504  on an inner surface of its outer eartip body  506 ,  FIG. 5B  is a side-view of an exemplary wireless listening device  501  with eartip  500  and a housing  510  with an optical sensor  508  for observing the inner surface of outer eartip body  506 , and  FIG. 5C  is a bottom-up view of eartip  500  after deflection from being inserted into an ear canal, according to some embodiments of the present disclosure. 
     As shown in  FIG. 5A , the inner surface of outer eartip body  506  can have a series of patterned lines  502  separated by gaps  504 . Lines  502  can extend along the entire circumference of outer eartip body  506  and thus can have a substantially circular shape. The thickness of each line can be the same as or different from other patterned lines, and the size of each gap can similarly be the same as or different from the size of other gaps. The series of patterned lines  502  can be observed by an optical sensor  508  that faces eartip  500 . In some embodiments, optical sensor  508  can detect changes in patterned lines  502  when eartip  500  is inserted into an ear canal. For instance, as shown in  FIG. 5C , patterned lines  502  and gaps  504  can alter in shape due to outer eartip body  506  deflecting and conforming to an inner surface of an ear canal. In certain embodiments, optical sensor  508  can observe pattern lines  502  and gaps  504  as a whole, or observe a portion  510  of patterned lines  502  and gaps  504 . Optical sensor  508  can, in some embodiments, observe only a portion of the series of patterned lines  502  and gaps  504  in front of optical sensor  508 . And, in some embodiments, more than one optical sensor can be implemented to observe the entire patterned lines  502  and gaps  504  around the circumference of eartip  500 . When more than one optical sensor is used, they can be positioned axially symmetrical around the opening in housing to which eartip  500  is attached. 
     Wireless listening device  501  can determine that it is worn by a user when patterned lines  502  and gaps  504  deflect a threshold distance away from its initial position when it is not inserted into an ear canal, e.g., as shown in  FIG. 5A . Thus, eartip  500  can be configured to have a first line pattern when it is not inserted into an ear canal, and a second line pattern different from the first line pattern when it is inserted into an ear canal. Each line pattern can be substantially circular and extend around a circumference of eartip  500 . By modifying eartip  500  to have patterned lines  502  and gaps  504  and configuring housing  510  to have an optical sensor for observing patterned lines  502  and gaps  504 , eartip  500  may not have conductive structures, thereby making it simpler to manufacture and having less avenues for failure. 
     Being able to determine when the device is worn by measuring a deflection of patterned lines and gaps, the wireless listening device can, enhance user experience by automatically initiating specific, targeted UI controls related to the wireless listening device when it detects that it is worn, such as automatically providing play/pause options for music, answering/ending phone calls, and the like. Additionally, the wireless listening device can be configured to detect unique deflection patterns and associate those unique deflection patterns with individual users. By doing this, the wireless listening device can automatically set its operational settings to reflect specific predefined preferences of that user. Furthermore, being able to detect unique patterns can allow the wireless listening device to be able to identify which eartip type is attached to the housing. For instance, different sizes of eartips can have different, unique patterns of lines and gaps. The housing can be configured to observe the unique patterns of lines and gaps when the eartips are not inserted into an ear canal and automatically determine which eartip is attached to the housing by matching the observed patterns of lines and gaps with a list of known patterns of lines and gaps for the different types of eartips. In some embodiments, instead of observing the individual line and gap patterns, optical sensor  508  can measure the observed color of the inner surface of eartip  500  as a whole. That way, a less expensive optical sensor can still be used to detect the identity of eartip  500 . 
     D. Control Leak for Eartip 
     As can be appreciated herein, the outer eartip body of an eartip according to some embodiments of the present disclosure can press against an inner surface of an ear canal to form an acoustic seal. This acoustic seal can enhance the quality of sound experience by the user, but it can also sometimes trap pressure in the ear canal, potentially causing an unpleasant sensation to the user. Thus, in some embodiments, the eartip can include a control leak for preventing the trapping of pressure in the ear canal while still enabling the outer eartip body to form an acoustic seal. 
       FIG. 6A  is a perspective view of an exemplary wireless listening device  600  having a control leak  602  in eartip  604 , according to some embodiments of the present disclosure. Control leak  602  can be positioned in an inner eartip body of eartip  604 . In some embodiments, control leak  602  is an opening that provides an avenue through which pressure built up in the ear canal can be released to atmosphere, thereby relieving the ear canal of any trapped pressure and preventing the user from experiencing any unpleasant sensation from trapped pressure. Control leak  602  can be a circular hole or be configured with any other shape, such as an ovular, oblong, rectangular, square-like, triangular, octagonal, and the like without departing from the spirit and scope of the present disclosure. 
     As shown in  FIG. 6A , control leaks positioned in eartip  604  can be located closer to the ear drum than control leaks implemented in housing  606 . Locating control leak  602  close to the ear drum can improve the effectiveness of control leak  602  by virtue of their close proximity to the ear drum alone. Furthermore, implementing control leaks in the eartip avoids the formation of an additional opening in the outer structure of housing  606 , thereby resulting in a housing that has fewer debris ingress points for better product reliability. Moreover, implementing control leaks in the inner eartip body of eartip  604  mitigates the chances of the control leaks from being blocked by the physical contours and protrusions of a user&#39;s ear because the outer eartip body can shield them from those surfaces. Additionally, moving the control leak into eartip  604  allows the control leak to be easily accessed by the user by merely removing eartip  604  from housing  606 . Thus, the control leak can be regularly cleaned and easily replaced. 
     Control leaks of different shapes and sizes can have more or less resistance to occlusion. For instance, elongated control leaks that are in the shape of ovals, rectangles, or oblong openings can be more resistant to occlusion from debris than control leaks that are in the shape of circles or squares because elongated control leaks have greater opening areas than non-elongated control leaks. In some embodiments, eartip  604  includes a single control leak  602 , while other embodiments can have more than one control leak, as shown in  FIGS. 6B and 6C . 
       FIGS. 6B and 6C  are cross-sectional view illustrations of different eartips with different control leak configurations. As shown in  FIG. 6B , eartip  601  can have a control leak configuration that includes at least two control leaks: a first control leak  608   a  and a second control leak  608   b . First and second control leaks  608   a  and  608   b  can be positioned in the same plane but in opposite hemispheres of the inner eartip body so that pressure can be released from the ear canal through pressure release pathways  609   a  and  609   b  through opening  612 . Having a larger number of control leaks decreases the chances of complete occlusion because having more control leaks means greater redundancy, where even if one control leak is occluded, the other control leaks may not be occluded and still enable trapped pressure to be released. In certain embodiments, both control leaks  608   a  and  608   b  can be configured to have the same size and shape. However, in some embodiments, control leaks  608   a  and  608   b  can be configured to have different sizes and shapes, as shown in  FIG. 6C . That is, eartip  603  in  FIG. 6C  can have a first control leak  610   a  that is elongated and a second control leak  610   b  that is not elongated, or a first control leak  610  that is the same shape as second control leak  610   b  but just larger in size. It is to be appreciated that any number, shape, and size of control leak(s) implemented in the inner eartip body of an eartip are envisioned herein, without departing from the spirit and scope of the present disclosure. 
     Although  FIGS. 6A-6C  illustrate control leaks being formed by the inner eartip body of an eartip, embodiments are not limited to such embodiments. Rather, one or more control leaks can be formed in the attachment structure of an eartip, as further discussed herein with respect to  FIGS. 6D-6E . 
       FIGS. 6D-6E  are cross-sectional views of an exemplary eartip  612  having control leaks  614   a - b  formed in its attachment mechanism, according to some embodiments of the present disclosure. Specifically,  FIG. 6D  is a cross-sectional view across a vertical cutting plane of eartip  612 , and  FIG. 6E  is a cross-sectional view across a horizontal cutting plane of eartip  612 . Eartip  612  is shown to be configured as eartip  352  in  FIG. 3E . Thus, similar features discussed herein with respect to eartip  352  apply to eartip  612  and are not discussed here for brevity. 
     Like control leaks  602 ,  608   a - b , and  610   a - b  in  FIGS. 6A-6C , each control leak  614   a - b  is an opening that opens sound channel  632  to the atmosphere. Thus, control leaks  614   a - b  provide avenues through which pressure built up in the ear canal/sound channel  632  can passively release into the atmosphere, thereby relieving the ear canal of any trapped pressure and preventing the user from experiencing any unpleasant sensation from trapped pressure. Each control leak  614   a - b  can extend from an inner surface  620  to an outer surface  622  of a sidewall of attachment structure  618 . The sidewall of attachment structure  618  can extend around a periphery of attachment structure  618 . Regions of outer surface  622  proximate to control leaks  614   a - b  can protrude outward to form respective lips  624   a - b  so that those regions of outer surface  622  are coplanar/flush with an outer surface  626  of inner eartip body  628  of eartip  612 . Lips  624   a - b  can provide structural rigidity and integrity for control leaks  614   a - b . In some embodiments, control leak  614   a - b  can be an oblong hole or be configured with any other shape, such as an circular, ovular, rectangular, square-like, triangular, octagonal, and the like without departing from the spirit and scope of the present disclosure. In particular embodiments, control leaks  614   a - b  are oblong openings that are arranged horizontally, e.g., arranged so that their long axis extends along a perimeter of attachment structure  618  around center line  630 . 
     As shown in  FIG. 6E , eartip  312  can include two control leaks  614   a - b  and two recesses  632   a - b . Control leaks  614   a - b  can be positioned on opposite sides of attachment structure  618  along a first axis  634 , while the recesses  632   a - b  are positioned on opposite sides of attachment structure  618  along a second axis  636 . In some instances where eartip  312  has an ovular cross-sectional shape, as shown in  FIG. 6E , first axis  634  can be the long axis of the ovular eartip while second axis  636  can be the short axis of the ovular eartip. Positioning recesses  632   a - b  on the long axis of the eartip allows end caps for a wireform attachment mechanism to make greater surface area contact with eartip  312  so that a more secure attachment can be achieved as well as a louder snapping sound can be emitted when the end caps snap into recesses  632   a - b . While  FIG. 6E  illustrates two control leaks  614   a - b  and two recesses  632   a - b  positioned along axes that are perpendicular to one another, it is to be appreciated that any number of control leaks and recesses can be positioned along any location around attachment structure  618  without departing from the spirit and scope of the present disclosure. 
     In some embodiments, cavity regions  638   a - b  can be formed around respective control leaks  614   a - b . Cavity regions  638   a - b  can be shallow cavities formed by inner surface  620  of attachment structure  618  to mitigate the chances of occlusion of control leaks  614   a - b  from inside eartip  612 . For instance, if an object presses against inner surface  620  of eartip  612 , cavity regions  638   a - b  can still provide an opening through which pressure can be released from sound channel  632 . 
     In some embodiments, as shown in  FIGS. 6D and 6E , meshes  616   a - b  can be positioned within respective control leaks  614   a - b  to prevent ingress of debris. Meshes  616   a - b  can be an interlaced structure formed of a network of wire that allows air to pass through but resists debris from passing through. In some embodiments, meshes  616   a - b  are each attached to inner surface  620  of attachment structure  618 , or extend into attachment structure  618 , so that meshes  616   a - b  can be securely fixed within eartip  612 . 
     As can be appreciated herein, when eartip  612  is inserted into the ear canal, outer eartip body  640  can bend and deform when it presses against the ear canal. The bending and deforming of outer eartip body  640  can potentially cause it to occlude one or more control leaks  614   a - b . Thus, to mitigate such occlusion, outer eartip body  640  can be modified to maintain an air pathway for control leaks  614   a - b  even when outer eartip body  640  bends and deforms when eartip  612  is inserted into an ear canal, as will be discussed further herein with respect to  FIGS. 6F-H . 
       FIGS. 6F-6H  are perspective view illustrations of exemplary eartips having different modifications for mitigating the occlusion of a control leak when the outer eartip body is bent and deformed when inserted into an ear canal, according to some embodiments of the present disclosure. As shown in  FIG. 6F , eartip  650  can have an outer eartip body  652  that is modified to include a slit  654  at an end of outer eartip body  652  closest to the attachment end of eartip  650 . Slit  654  can extend all the way through to the end of outer eartip body  652  and can be positioned over control leak  656  so that when outer eartip body  652  is bent and presses against attachment structure  658 , slit  654  can provide an opening through which air can pass to enable the functionality of control leak  656  as discussed herein with respect to  FIGS. 6A-6E . As can be appreciated herein, many other types of modification to enable an opening through which air can pass for the control leak are envisioned herein. 
     As an example shown in  FIG. 6G , eartip  660  can have an outer eartip body  662  that is modified to include a hole  664  positioned near the attachment end of eartip  660  and positioned over control leak  666 . Although hole  664  is shown as a circular hole, any other shape can be used to form hole  664 , such as an ovular, oblong, rectangular, square, triangular, and the like. 
     As another example shown in  FIG. 6H , eartip  670  can have an outer eartip body  672  that is modified to include one or more bumps  674   a - b  positioned at an end of outer eartip body  672  closest to the attachment end of eartip  670  and positioned over control leak  676 . Bumps  674   a - b  can be protrusions that extend from an inner surface of outer eartip body  672  toward control leak  676 . That way, when outer eartip body  672  is bent and presses against attachment structure  678 , bumps  674   a - b  can prevent sealing flange  672  from completely sealing control leak  676  so that an opening through which air can pass to enable the functionality of control leak  656  as discussed herein with respect to  FIGS. 6A-6E  can be maintained. 
     III. Housing 
     As can be understood by the disclosures herein, a wireless listening device also includes a housing to which the eartip couples. The housing can be an electronic device that can be configured to communicate with a host device, such as a smart phone, tablet, laptop, and the like. As an example, a housing can receive digitized sound data/commands for outputting sound to a user. Furthermore, the housing can also send digitized sound data received from a microphone, and/or send commands from a user input to the host device. Thus, the housing can include one or more processors, memory, communication systems, sensor systems, user interface systems, power sources, and power receiving circuitry, as discussed herein with respect to  FIG. 1A . As will be appreciated herein, various additional features and configurations of the housing can be implemented to enhance the user experience of the wireless listening device. For instance, one or more sound ports, control leaks, and microphones can be implemented in the housing to improve output sound quality, comfort, and user interface methods of the wireless listening device, as will be discussed further herein. 
       FIG. 7  is a cross-sectional view of an exemplary wireless listening device  700  showing further details of a housing  702 , according to some embodiments of the present disclosure. As shown, housing  702  can include a plurality of internal components and an outer structure  704  formed of a rigid material, e.g., plastic, that defines an internal cavity within which internal components can be housed and protected from the environment and physical damage during drop events. Outer structure  704  can also include an acoustic opening  719  through which sound can exit outer structure  704  into sound channel  717  of eartip  703 . The internal components can include a battery  706 , interconnection structure  708 , electronic devices  710 , and a driver  715 . Battery  706  can be any suitable energy storage device that can store and discharge stored energy, such as a lithium ion battery, and the like. Battery  706  can be electrically coupled to electronic devices  710  and driver  715  through interconnection structure  708  so that when discharging, the discharged energy can be used to power electronic devices  710  and driver  715 . Interconnection structure  708  can be any suitable component that can route signals and power between electronic devices, such as a printed circuit board (PCB) or a flexible PCB. Electronic devices  710  can be any suitable semiconductor devices for operating wireless listening device  700 , such as microcontrollers, processors, field programmable gate arrays (FPGA), application specific integrated circuits (ASIC), dynamic random-access memory (DRAM) and the like. Electronic devices  710  can be configured to interact with one another and various other internal components to perform various functions that improve the user experience as well as the sound quality of wireless listening device  700 , as will be discussed in detail further herein. Driver  715  can be an electrical device that generates sound waves, such as a speaker and/or a subwoofer. Driver  715  can be coupled to, and operated by, the one or more electronic devices  710 . When wireless listening device  700  is worn by a user, wireless listening device  700  can provide sound to an ear canal through eartip  703 , which is better shown in  FIG. 8 . 
       FIG. 8  is a cross-sectional view  800  of wireless listening device  700  when it is worn by a user to show the positioning of wireless listening device  700  with respect to an ear canal  804  and the auricle of ear  801 , according to some embodiments of the present disclosure. Wireless listening device  700  is shown as an in-ear hearing device. When wireless listening device  700  is worn, outer eartip body  705  of eartip  703  can press into the inner surfaces of ear canal  804  to form an acoustic seal so that sounds outputted by wireless listening device  700  can be heard by the user in a sealed environment, which improves sound quality of wireless listening device  700 . 
     According to some embodiments of the present disclosure, wireless listening device  700  can also include one or more sound ports, control leaks, and microphones for improving the functionality and usability of wireless listening device  700  while still enabling wireless listening device  700  to achieve a small form factor. 
     A. Control Leak and Sound Port 
     For example, as further shown in  FIG. 7 , outer structure  704  of housing  702  can include, in some embodiments, a tuned bass port  711  and a tuned control leak  713 . Tuned bass port  711  and tuned control leak  713  can be openings that are specifically designed and positioned within outer structure  704  to enable wireless listening device  700  to achieve certain functionalities. For instance, tuned bass port  711  can be an opening positioned beside acoustic opening  719  and coupled to an acoustic pathway  723  via port pathway  724  from driver  715  and allows air to flow easier within the acoustic pathway for low frequency sounds, e.g., bass sound waves that are lower than 20 Hz. For low frequency sounds, a driver may move a large volume of air as it generates sound waves. When it is easier for a driver to move air, the driver can achieve better sound quality. Thus, tuned bass port  711  can provide an opening for the air to easily move out to, and be drawn in from, the atmosphere, thereby allowing wireless listening device  700  to provide higher quality bass notes. Tuned bass port  711  can be configured to achieve a certain rate of airflow when driver  715  is operating. This rate of air flow can be altered by the shape and size of tuned bass port  711 , which can be tuned in various ways according to design. 
     Similar to tuned bass port  711 , tuned control leak  713  can be an opening within outer structure  704  for allowing air to flow out of housing  702 . However, the result achieved by releasing the air out of housing  702  may be different from the result achieved by tuned bass port  711 . For instance, instead of improving bass sound quality, tuned control leak  713  can be configured to relieve pressure trapped the ear canal when a seal is formed between outer eartip body  705  and ear canal  804 , such as when wireless listening device  700  is worn by a user. In some embodiments, pressure from the ear canal can flow through a pressure release pathway  726  that flows from opening  717  into outer structure  704  and then out into the atmosphere through tuned control leak  713 . Thus, tuned control leak  713  may be similar in function to control leak  602  in eartip  604  discussed herein with respect to  FIG. 6A . By relieving trapped pressure in ear canal  804 , wireless listening device  700  may be comfortable to wear. In some embodiments, tuned control leak  713  extends from an acoustic pathway from opening  717  of inner eartip body  707  so that pressure trapped in the ear canal can be vented to the atmosphere. Like tuned bass port  711 , tuned control leak  713  can be configured to achieve a certain rate of airflow when pressure is built up in the ear canal. This rate of air flow can be altered by the shape and size of tuned control leak  713 , which can be tuned in various ways according to design. For instance, tuned control leak  713  can be an opening that is substantially circular in profile, or any other shape and size, such as ovular, oblong, rectangular, hexagonal, and the like without departing from the spirit and scope of the present disclosure. 
     It is to be appreciated that the specific positions of tuned bass port  711  and tuned control leak  713  may be specifically chosen to minimize occlusion and acoustic coupling with other internal components, as will be discussed further herein with respect to section III, subsection C below. 
     B. Externally and Internally Facing Microphones 
     With continued reference to  FIGS. 7 and 8 , the plurality of internal components in housing  702  can further include one or more externally facing microphones  712  and  714  and one or more internally facing microphones  716 . Externally facing microphones  712  and  714  can be configured to receive sounds from the environment outside of housing  702  that are propagating toward the user from regions outside of the user&#39;s ear canal while internally facing microphone  716  can be configured to receive sounds from the environment outside of housing  702  that are propagating away from the user from regions in or around the user&#39;s ear canal. 
     Positioning externally facing microphones  712  and  714  and internally facing microphone  716  on opposite sides of housing  702  allows each microphone to receive sound from two different environments for achieving different functionalities. For instance, by receiving sounds from outside of the ear canal with externally facing microphones  712  and  714 , wireless listening device  700  can operate in transparency mode where sounds received from outside of the ear canal can be reproduced with or without augmentation by wireless listening device  700  so that the user can hear sounds from the outside environment. This enables the user to still hear sounds from his environment, such as spoken words from a person with which the user is conversing, even though the user&#39;s ear canal may be sealed by outer eartip body  705  of eartip  703 . Furthermore, receiving sounds outside of the ear canal also enables wireless listening device  700  to perform active noise reduction to selectively minimize distracting noise from the environment. That is, wireless listening device  700  can output sound that specifically negates the sound received from externally facing microphones  712  and/or  714  of the external environment. 
     By receiving sounds  904  from inside of the ear canal with internally facing microphone  716 , wireless listening device  700  can measure sounds within ear canal  804  to determine if sound is leaking across outer eartip body  705 . A complete in-ear seal between outer eartip body  705  and ear canal  804  creates a much better acoustic performance for products designed based on an assumption of that seal. In such products, loss of a complete seal can reduce the volume of low frequency sounds experienced by the user and can increase the amount of ambient noise. The loss of complete seal can sometimes be attributed to a mismatch between the user&#39;s ear anatomy and the size of the eartip used. Thus, by being able to determine if an improper seal is made between outer eartip body  705  and ear canal  804 , wireless listening device  700  can be configured to send the user an alert indicating such and possibly instruct the user to make certain adjustments to the fit of the wireless listening device  700 . 
     In some embodiments, an externally facing speaker  723  can also be implemented within outer structure  704  of housing  702 . Externally facing speaker  723  can be an electronic device that generates sound. Externally facing speaker  723  can be positioned beside externally facing microphones  712  and  714  so that externally facing speaker  723  can output sound into an environment outside of the wireless listening device through opening  725  in outer structure  704 . The sound can be outputted away from the ear canal of the user so that people beside the user can hear the sounds generated by externally facing speaker  723 . The sounds can be music or a conversation that the user intends to share with someone beside him or her. 
       FIGS. 9A and 9B  are cross-sectional illustrations of wireless listening device  700  configured to detect an improper seal with an ear canal when it is worn by a user, according to some embodiments of the present disclosure. Specifically,  FIG. 9A  is a cross-sectional view illustration  900  of wireless listening device  700  when a leakage is not present, and  FIG. 9B  is a cross-sectional illustration  901  of wireless listening device  700  when a leakage is present. 
     As shown in  FIG. 9A , wireless listening device  700  can be an in-ear hearing device that is configured to use internally facing microphone  716  to detect a loss of a complete seal. For instance, wireless listening device  700  can generate a test sound  902  into ear canal  804 , and internally facing microphone  716  can be activated to receive sound from outside of the seal with ear canal  804 . When no leakage is present and a complete seal is made with ear canal  804 , internally facing microphone  716  may not detect test sound  902 . However, as shown in  FIG. 9B , when leakage is present and an improper, leaky seal is made with ear canal  804 , internally facing microphone  716  may detect test sound  902  to a certain degree and determine whether the detected sound is caused by a leak in the seal. For instance, wireless listening device  700  can be configured to measure the decibel level of sound resonating within ear canal  804  induced by a control sound tone or pulse, and compare that measured decibel level to an expected decibel level. If the measured decibel level is greater than the expected decibel level, then wireless listening device  700  can determine that an improper seal exists and an alert can be sent to the user to correct the positioning of listening device  700 . Having a proper seal can improve attenuation of outside noise, enabling the operation of active noise cancellation to use less power. Furthermore, having a proper seal can imply that the eartip has a solid contact with the ear canal, which can result in improved in-ear stability. 
     As can be appreciated herein, being in such close proximity to a user&#39;s ear often invites the opportunity for occlusions of one or more ports, control leaks, and/or microphones. Occluded bass ports often exhibit an overall decrease in bass/low frequency response; and occluded controlled leaks often exhibit an abnormal increase in bass/low frequency response and a reduction in measurable ambient noise inside the ear canal. Thus, according to some embodiments of the present disclosure, internally facing microphone  716  can also enable wireless listening device  700  to perform acoustic self-testing to determine the presence of occluded ports, control leaks, and/or external microphones, and to inform the user of improper fit or how to change the positioning/use of wireless listening device  700  when occlusion is detected to ensure the best possible acoustic performance. 
       FIG. 10  is an exemplary side-view illustration  1000  of wireless listening device  1001  worn by a user where one or more ports, control leaks, and/or microphones are occluded. When worn, eartip  1006  can be positioned inside of the ear canal and housing  1008  can be positioned within cavity  1002  defined by the auricle of the user&#39;s ear  1004 . In some cases, wireless listening device  1001  can be improperly positioned in ear  1004  where the contours of ear  1004  occlude, i.e., cover up, one or more ports, control leaks, and/or microphones, e.g., externally facing microphone  1012 , as shown in  FIG. 10 . Externally facing microphone  1012  may not be able to properly function when it is occluded by ear  1004 . Thus, wireless listening device  1001  can be configured to determine that externally facing microphone  1012  is occluded and alert the user and/or instruct the user to move wireless listening device  1001  to the correct position where microphone  1012  is not occluded. 
     In some embodiments, wireless listening device  1001  can determine that one or more ports, control leaks, and/or microphones are occluded by comparing the current operation of the ports, control leaks, and/or microphones with their expected operation. As an example, wireless listening device  1001  can be configured to define an expected operation of externally facing microphone  1012  by measuring the operation of externally facing microphone  1012  when it is stored in an case. Wireless listening device  1001  can emit a sound in the case and measure the received sound by externally facing microphone  1012 . In some embodiments, the case can be configured with one or more cavities that ensure externally facing microphone  1012  is un-occluded and provide a controlled and sealed environment with which wireless listening device  1001  can perform its measurement of the operation of externally facing microphone  1012 . The measured operation of externally facing microphone  1012  can be stored in the memory of wireless listening device  1001  or the host device, e.g., a smart phone to which wireless listening device  1001  is wirelessly coupled. 
     Thus, when wireless listening device  1001  is worn by a user, wireless listening device  1001  can measure the operation of externally facing microphone  1012  and compare the measured operation of externally facing microphone  1012  with the expected operation of externally facing microphone  1012 . If the measured operation is different from the expected operation by greater than a threshold amount, wireless listening device  1001  and/or the host device can determine that externally facing microphone  1012  is occluded and send the necessary alerts/instructions to the user to correct the positon of wireless listening device  1001 . If, however, the measured operation is only different from the expected operation by less than the threshold amount, then wireless listening device  1001  and/or the host device can use that information as another factor in determining that wireless listening device  1001  is worn by the user in conjunction with other factors, such as capacitive sensing or patterned lines in the eartip, as discussed herein with respect to  FIGS. 4A-4C and 5A-5C . The same process can be performed for each port, control leak, and microphone for enabling wireless listening device  1001  to determine occlusions. By being able to determine occlusions of one or more ports, control leaks, and/or microphones, wireless listening device  1001  can better ensure that the full potential of the sound quality and usability of wireless listening device  1001  is experienced by the user. 
     C. Positioning of Microphones, Ports, and Control Leaks 
     With reference back to  FIGS. 7 and 8 , the positioning of the microphones, ports, and control leaks are important because they are each designed to receive sound from, and/or output sound to, specific regions around the ear and the ear canal. According to some embodiments of the present disclosure, externally facing microphones  712  and  714  can be positioned in housing  702  so that when wireless listening device  700  configured as an in-ear hearing device is worn, externally facing microphones  712  and  714  face away from the ear canal and internally facing microphone  716  faces toward the ear canal, an example of which is shown in  FIG. 8 . 
       FIG. 8  shows the positioning of externally and internally facing microphones  712 ,  714 , and  716 , tuned bass port  711 , and tuned control leak  713  of wireless listening device  700 , according to some embodiments of the present disclosure. As shown, externally facing microphones  712  and  714  are positioned inside of ear cavity  802  and face away from ear canal  804 , while internally facing microphone  716  is positioned inside of ear cavity  802  and face toward ear canal  804 . Ear cavity  802  can be a cavity defined by the auricle of ear  801 , and can abut ear canal  804 . 
     In some embodiments, externally facing microphones  712  and  714  and internally facing microphone  716  are positioned on opposing halves of housing  702  when divided in half by dividing line  806 . Dividing line  806  can be a line that divides housing  702  in two halves, where one half is positioned closer to ear canal  804  than the other half. In some embodiments, with reference back to  FIG. 7 , dividing line  806  can be perpendicular to axis  709  of acoustic opening  719  and inner eartip body  707 . And, dividing line  806  can be positioned so that housing  702  is divided into two halves. Thus, as shown in  FIG. 7 , dividing line  806  can be diagonally oriented when housing  702  is laid on its side, where externally facing microphones  712  and  714  are positioned on one half of housing  702  and internally facing microphone  716  is positioned on the other half of housing  702 . In some embodiments, internally facing microphone  716  and eartip  703  are positioned in the same half of housing  702  when halved by dividing line  806 . 
     As can be appreciated from disclosures herein, tuned bass port  711  and tuned control leak  713  are openings through which channels within housing  702  are coupled to the atmosphere. Thus, in order for tuned bass port  711  and tuned control leak  713  to operate properly, port  711  and control leak  713  should be free of occlusion. Thus, tuned bass port  711  and tuned control leak  713  can be positioned at locations that are least likely to be occluded by surface features of the user&#39;s ear. As an example, as shown in  FIG. 7 , tuned bass port  711  and tuned control leak  713  can be positioned in outer structure  704  at areas that are directly below the umbrella covering of outer eartip body  705 . That way, outer eartip body  705  can provide clearance for space around tuned bass port  711  and tuned control leak  713 . 
     When placed close to externally facing microphones  712  and  714 , tuned bass port  711  and tuned control leak  713  can cause echo and feedback distortion. Thus, in some embodiments, tuned bass port  711  and tuned control leak  713  can be positioned away from externally facing microphones  712  and  714 . For instance, where dividing line  806  divides housing  702  in half and externally facing microphones  712  and  714  are positioned on one half of housing  702 , tuned bass port  711  and tuned control leak  713  can be positioned on the other half of housing  702  next to eartip  703 . 
     D. Acoustic Shielding Component of Microphones 
     To enable microphones  712 ,  714 , and  716  to accurately measure sound, microphones  712 ,  714 , and  716  can be positioned adjacent to outer structure  704 , and outer structure  704  can include openings  718 ,  720 , and  722  for providing an avenue through which sound can travel from outside of outer structure  704  to microphones  712 ,  714 , and  716 , respectively. The open cavities defined by openings  718 ,  720 , and  722  form step differentials between an outer surface of housing  704  and the outermost surface of respective microphones  712 ,  714 , and  716 . When air blows across each of these step differentials (such as when the wireless listening device is being used outside, wind noise can be generated and cause audible interference. Thus, each opening can include an acoustic shielding component that is configured to be flush with the outer surface of housing  704  to remove the aforementioned step differential and mitigate wind noise, as discussed herein with respect to  FIGS. 11A-11B . 
       FIGS. 11A and 11B  are cross-sectional view illustrations of exemplary listening device configurations across the cut-line shown in side image  1103  that have different acoustic shielding components for microphones in a housing, according to some embodiments of the present disclosure. Specifically,  FIG. 11A  is a cross-sectional view illustration of a first configuration  1100  including acoustic shielding component  1102  for protecting microphone  1104  of a housing  1106 , and  FIG. 11B  is a cross-sectional view illustration of a second configuration  1101  including a multi-layer mesh  1122  for protecting microphone  1124  of a housing  1126 . 
     As shown in  FIG. 11A , acoustic shielding component  1102  can be formed of a porous plastic material constructed of a solid matrix defining a plurality of pores that allows the microphone to be exposed to the atmosphere but resists liquid and debris from entering housing  1106 . According to some embodiments of the present disclosure, acoustic shielding component  1102  can be a three-dimensional porous structure that extends at least partially between externally facing microphone  1104  and an outer surface  1108  of housing  1106 . In some instances, acoustic shielding component  1102  can completely fill in opening  1110  so that acoustic shielding component  1102  extends from an inner surface  1112  of housing  1106  to outer surface  1108  of housing  1106 . External surface  1114  of acoustic shielding component  1102  can face outside of housing  1106  and be substantially planar with the immediately adjacent regions of external surface  1108  of housing  1106 . In some embodiments, external surface  1114  of acoustic shielding component  1102  is curved to seamlessly integrate with the curvature/profile of outer surface  1108  of housing  1106 . The substantial planarity and seamless integration between external surface  1114  and outer surface  1108  can avoid any structural step formations and recesses at their interface, thereby substantially mitigating the formation of acoustic turbulence as air  1116  moves quickly past opening  1110  while still enabling external noise to filter through to microphone  1104 . Mitigating acoustic turbulence increases microphone performance in outdoor environments. 
     It is to be appreciated that, using acoustic shielding component to protect microphones in a housing can achieve additional benefits. For instance, acoustic shielding component can improve the congruency of housing aesthetics by blending in with the appearance of housing  1106 , especially when acoustic shielding component is formed of similar material used to form outer housing  1106 . Furthermore, using porous plastic can achieve better protection from liquid and debris ingress because of its array of small openings in a three-dimensional structure. 
     Alternative to the porous plastic embodiment shown in  FIG. 11A , an acoustic shielding component can be configured as a multi-layer mesh structure in some embodiments for mitigating wind noise and improving sound capture, as shown in  FIG. 11B . An acoustic shielding component  1122  can be constructed as a multi-layer mesh structure that extends at least partially between externally facing microphone  1104  and an outer surface  1128  of housing  1126 . For instance, like acoustic shielding component  1102  in  FIG. 11A , an external surface  1130  of acoustic shielding component  1122  can face outside of housing  1126  and be substantially planar with the immediately adjacent regions of external surface  1128  of housing  1126 . External surface  1130  of acoustic shielding component  1112  can be curved to seamlessly integrate with (i.e., be flush with) the curvature/profile of outer surface  1128  of housing  1126  so that structural step formations and recesses at their interface can be avoided, thereby substantially mitigating the generation of acoustic turbulence as air  1132  moves quickly past opening  1134  while still enabling external noise to filter through to microphone  1124 . 
     Unlike acoustic shielding component  1102  in  FIG. 11A , however, acoustic shielding component  1122  can be formed of more than one distinct layers. For instance, acoustic shielding component  1122  can include a cosmetic mesh and an acoustic mesh, as will be discussed in detail further herein with respect to  FIG. 12 . In some instances, the multi-layer mesh structure of acoustic shielding component  1122  is relatively thin compared to the depth of opening  1134 . Thus, because external surface  1130  of acoustic shielding component  1122  is positioned planar with external surface  1128  of housing  1126 , a cavity  1136  within opening  1134  and below external surface  1130  of acoustic shielding component  1122  can be defined by the structure of acoustic shielding component  1122 . The relatively large surface area of external surface  1130  of acoustic shielding component  1122  along with its thin construction and position relative to cavity  1136 , acoustic shielding component  1122  may be particularly vulnerable to deformation during drop events. Thus, to resist such deformation, a support post  1138  can be abutted against an inner surface  1140  of acoustic shielding component  1122  opposite from external surface  1130 . Support post  1138  can be an extension of housing  1126  that extends toward, and in some instances makes contact with, acoustic shielding component  1122 . Support post  1138  can be positioned so that it makes contact with a central region of acoustic shielding component  1122 . In addition to support post  1138 , a stiffener can be implemented to provide structural rigidity to acoustic shielding component  1122 , and a grounding tab  1142  can couple acoustic shielding component  1122  to ground, as will be discussed further herein with respect to  FIG. 12 . 
       FIG. 12  is an exploded view of an exemplary acoustic shielding component  1200  constructed as a multi-layer mesh, according to some embodiments of the present disclosure. Acoustic shielding component  1200  can include an acoustic mesh  1202  positioned between a cosmetic mesh  1204  and a stiffener  1206 . Acoustic mesh  1202  can be constructed as a single layer with contours that conform to a topography of an external surface of a housing. In some instances, acoustic mesh  1202  can be a porous layer that is tuned to a specific acoustic impedance to enable proper operation of an underlying microphone. In some embodiments, acoustic mesh  1202  is formed of a pliable, porous material, such as a porous polyester. Acoustic mesh  1202  can be covered with a hydrophobic coating that enables acoustic mesh  1202  to resist ingress of water into the housing of the wireless listening device. 
     Cosmetic mesh  1204  can be an interlaced structure formed of a network of stiff wire for providing a visible mesh texture to acoustic shielding component  1200  when the wireless listening device is viewed from the outside. A mesh cover  1208  of cosmetic mesh  1204  may be positioned external to the housing of the wireless listening device. Thus, an outer surface of mesh cover  1208  can form an external surface of acoustic shielding component  1200 , such as external surface  1130  of acoustic shielding component  1101  in  FIG. 11B . Accordingly, mesh cover  1208  can be constructed as a single layer with contours that conform to a topography of an external surface of a housing. The porosity of cosmetic mesh  1204  may lend itself to have negligible acoustic impact on the sounds passing through porous shield  1200 , while having a degree of aesthetic appeal so that its design complements the appearance of the wireless listening device. In some embodiments, cosmetic mesh  1204  is formed of a stainless steel mesh. Acoustic mesh  1202  can be adhered to cosmetic mesh  1204  via any suitable adhesive, such as pressure sensitive adhesive (PSA). 
     In some embodiments, an outer periphery of an inner surface of mesh cover  1208  can extend upward to form a mesh wall  1210 , which can make contact with the housing to improve stability when installed in the housing. Mesh wall  1210  can be substantially perpendicular to mesh cover  1208 . In certain embodiments, mesh wall  1210  can define a tab  1212  that extends from a portion of mesh wall  1210 . Tab  1212  can extend away from mesh cover  1208  so that when installed, tab  1212  can couple to an internal grounding feature, such as a grounding plane for an antenna. This may be better shown with brief reference to  FIG. 11B , where tab  1142  of acoustic shielding component  1122  extends away from external surface  1130  and past microphone  1124  to couple to an internal grounding component. By grounding cosmetic mesh  1204 , damage to the device from electric static discharge can be avoided. In some embodiments, mesh cover  1208 , mesh wall  1210 , and tab  1212  can together be a monolithic structure that forms cosmetic mesh  1204 . 
     Stiffener  1206  can be a solid, instead of porous, structure that has high rigidity for providing structural integrity to acoustic shielding component  1200  to resist deformation during drop events. Stiffener  1206  can include a plurality of ribs  1214  positioned between stiffener walls  1216   a  and  1216   b . Ribs  1214  can follow a contour of cosmetic mesh  1204 ; thus, ribs  1214  can also include contours that conform to the topography of the external surface of the housing. Ribs  1214  can be evenly spaced apart from one another and be distributed across a length of acoustic shielding component  1200  to provide structural rigidity across the length of acoustic shielding component  1200 . In some embodiments, a distance between ribs  1214  near the center of stiffener  1206  can be greater than the distances between other pairs of ribs so that a gap  1220  can be formed to allow space for a support post, e.g., support post  1138  in  FIG. 11B , to be positioned to provide additional support to acoustic shielding component  1200 . Although gap  1220  is shown to be formed by stiffener  1206 , other stiffeners may not have a gap and can instead have ribs in position of gap  1220  in the equally-spaced apart configuration. Stiffener  1206  can be formed of any suitable stiff material, such as stainless steel, and can be attached to cosmetic mesh  1204  via a plurality of laser welding points  1218  on stiffener walls  1216   a - b . Stiffener walls  1216   a - b  can be portions of stiffener  1206  that bend upward for increasing surface area contact with cosmetic mesh  1204  housing to improve mechanical coupling with cosmetic mesh  1204 . When attached, stiffener  1206  can be surrounded by mesh wall  1210 . 
     E. Positioning of Battery and Driver for Defining Acoustic Path 
     According to some embodiments of the present disclosure, the battery and driver for a wireless listening device can be specifically positioned to decrease the size of its housing.  FIG. 13  is a side-view illustration of a wireless listening device  1300  whose battery  1302  and driver  1304  are uniquely positioned to decrease the size of housing  1306 , according to some embodiments of the present disclosure. When wireless listening device  1300  is worn by a user, eartip  1310  can be inserted into the ear canal. This allows housing  1306  to extend farther into the opening of the ear, and thus opens up more space for housing  1306  to occupy in the ear concha. To take advantage of this enlarged space, larger components can be positioned next to eartip  1310 . As an example, battery  1302  can be positioned adjacent to eartip  1310  such that its longest dimension, e.g., its width, is oriented along axis  1311  of eartip  1310 . 
     Furthermore, other larger internal devices can be positioned close to battery  1302  so that larger components can be concentrated in one region of housing  1306  to maximize the larger space immediately outside of the ear canal. For instance, driver  1304  can be positioned immediately beside battery  1302  and oriented so that its longest dimension, e.g., its width can take full advantage of the extra space provided by the ear concha, as shown in  FIG. 13 . When oriented in this way, an acoustic path  1316  of driver  1304  can be initially directed toward a flat, side surface of battery  1302 , but then be redirected by the side surface toward opening  1312  of housing  1306  and ultimately out of opening  1312  and into the ear canal through eartip  1310 . Thus, even though battery  1302  is positioned adjacent to opening  1312 , battery  1302  can be positioned so that an acoustic pathway can still be provided into opening  1312  beside battery  1302 . 
     By arranging battery  1302  in the largest open area of the ear (e.g., the concha), the size of battery  1302 , and thus the product battery life of wireless listening device  1300 , can be maximized. Furthermore, by arranging battery  1302  and driver  1304  in this configuration, an antenna  1314  of wireless listening device  1300  can be positioned as far away from the user&#39;s body as possible, which can optimize antenna performance. Furthermore, smaller components can be more compactly arranged in the other regions of housing  1306 , thereby allowing those regions of housing  1306  to be smaller, which thus reduces the overall size of housing  1306 . Having a smaller size can improve the comfort and appearance of wireless listening device  1300  when it is worn. 
     IV. User Interface for a Wireless Listening Device 
     According to some embodiments of the present disclosure, one or more processors of a wireless listening device can be configured to display the user&#39;s listening status and to interact with one or more sensors of the wireless listening device and execute commands stored in its memory to provide a variety of unique user interface methods for allowing the user to operate the wireless listening device, as will be discussed further herein. 
     A. Noise Cancelling Status Indicator 
       FIG. 14  is a side-view illustration  1400  of a wireless listening device  1402  configured to display the user&#39;s listening status, according to some embodiments of the present disclosure. As can be appreciated herein, wireless listening device  1402  can perform active noise cancellation functions, which can cancel out external sounds, and can perform transparency functions, which can amplify the external noise to the user. Thus, it may be useful for wireless listening device  1402  to be able to indicate whether the wireless listening device  1402  is in active noise canceling mode where the user and cannot hear external sounds or in transparency mode where the user can hear external sounds. 
     According to some embodiments of the present disclosure, a dynamic visual indicator  1404  can be implemented by wireless listening device  1402  to display the user&#39;s listening status. For instance, visual indicator  1404  can be a light emitting diode that can display different colors of light and be positioned in housing  1406  where it can be seen when wireless listening device  1402  is worn by the user. In some embodiments, visual indicator  1404  can display different colors of light depending on the particular operating mode of wireless listening device  1402 . As an example, wireless listening device  1402  can be configured to output red light with visual indicator  1404  when wireless listening device  1402  is in the active noise cancelling mode, green light when wireless listening device  1402  is in the transparency mode, and/or orange light when wireless listening device  1402  is outputting sound, e.g., when the user is on a phone call or is listening to music. That way, people who may want to speak with the user can be apprised of the listening status of the user without needing the user to tell them him or herself. 
     Other than changing the color of visual indicator  1404 , wireless listening device  1402  can be configured to output varied flashing patterns with visual indicator  1404  to show which mode is active. For instance, visual indicator  1404  can blink at a high frequency when wireless listening device  1402  is in the active noise cancelling mode, can output a steady light when wireless listening device  1402  is in the transparency mode, and can blink at a low frequency when wireless listening device  1402  is outputting sound when the user is on a phone call or listening to music. Alternatively, wireless listening device  1402  can be configured to output varied intensity of light with visual indicator  1404  to show which mode is active. For instance, visual indicator  1404  can emit bright light when wireless listening device  1402  is in the active noise cancelling mode, no light when wireless listening device  1402  is in the transparency mode, and dim light when the user is on a phone call or listening to music. Although  FIG. 14  shows an embodiments where wireless listening device  1402  only has one visual indicator, embodiments are not so limited. Other embodiments can have more than one visual indicator where different combinations of visual indicators can output light based on which mode is active, without departing from the sprit and scope of the present disclosure. 
     Furthermore, it is to be appreciated that other types of indicators can be used instead of visual indicator  1404 . For instance, an audio indicator can be used to indicate the user&#39;s listening status. As an example, the wireless listening device&#39;s externally facing speaker can be used as an audio indicator to output sound indicative of the user&#39;s listening status. That is, the audio indicator can output be chirping sounds and/or beeping sounds that are outputted at specific frequencies and/or intervals to indicate the user&#39;s listening status. 
     B. User Input by Interacting with User Anatomy 
     According to some embodiments of the present disclosure, a wireless listening device can also be configured to interact with the anatomy of a user&#39;s ear to receive various user inputs. For instance, different parts of an ear can be pulled to effectuate a user input.  FIG. 15  is a side-view illustration  1500  of a wireless listening device  1502  configured to receive user input through interactions with the anatomy of a user&#39;s ear  1501 , according to some embodiments of the present disclosure. In certain instances, wireless listening device  1500  can be configured to receive a user input when the user pulls certain parts of ear  1501 . 
     For example, wireless listening device  1502  can associate a downward pull  1504  of earlobe  1506  as a specific user input. When earlobe  1506  is pulled downward, antitragus  1508  of ear  1501  can also move downward by a lesser degree. This downward motion of antitragus  1508  can be detected by one or more optical sensors or microphones of wireless listening device  1502  to identify that earlobe  1506  has been pulled and thus in turn receive the specific user input associated with downward pull  1504 . 
     In another example, wireless listening device  1502  can associate an outward pull  1510  of the side of helix  1512  as a specific user input. When the side of helix  1512  is pulled outward, antihelix  1514  of ear  1501  can also move outward by a lesser degree. This outward motion of antihelix  1514  can be detected by one or more optical sensors or microphones of wireless listening device  1502  to identify that side of helix  1512  has been pulled outward and thus in turn receive the specific user input associated with outward pull  1510 . 
     In yet another example, wireless listening device  1502  can associate an upward pull  1504  of the top of helix  1512  as a specific user input. When the top of helix  1512  is pulled upward, antihelix  1514  of ear  1501  can also move upward by a lesser degree. This upward motion of antihelix  1514  can be detected by one or more optical sensors or microphones of wireless listening device  1502  to identify that top of helix  1512  has been pulled upward and thus in turn receive the specific user input associated with upward pull  1516 . 
     Although  FIG. 15  discusses pulling the ear for various user inputs, embodiments are not so limited. As an example, wireless listening device  1502  can be configured to associate any type of interaction with the ear as a specific user input, such as a flicking of earlobe  1506 . When earlobe  1506  is flicked, a vibrating force can be detected by wireless listening device  1502  and a specific input can be received. In addition to the ear, other parts of a user&#39;s anatomy can also be used for user input. For instance, the user&#39;s teeth can be used to indicate a user input when the teeth are “clicked”, e.g., bitten together to generate a clicking or tapping sound. The sound of the teeth clicking can be picked up by one or more microphones, and/or the specific reverberations through skull caused by the teeth clicking can be picked up by one or more sensors, e.g., accelerometers, in wireless listening device  1502 . Such flicking vibrations and/or teeth clicking sounds can be learned or set up ahead of time when the user pairs wireless listening device  1502  with a host device for the first time. Furthermore, wireless listening device  1502  can be configured to measure vibrations and/or other signals created by a finger touching and moving along a surface of the wireless listening device  1502 . The direction of motion and position of the finger as it touches wireless listening device  1502  can be received as an input by wireless listening device  1502 . For instance, a user can run his finger up or down a stem (not shown in  FIG. 15 , but shown in  FIG. 16  as stem  1606 ) of wireless listening device  1502  to effectuate an input such as increasing volume when the finger is run up the stem and decreasing volume when the finger is run down the stem. 
     C. User Input by Voice Control 
     Other than using physical interactions with the user&#39;s anatomy, specific user inputs can be effectuated using voice control. For instance, a spoken phrase including one or more words can be received as a user input, e.g., a voice command. Often, electronic devices that enable voice control require the use of a trigger phrase in order for it to receive a user input. A trigger phrase can be a default phrase that is spoken by the user and recognized by the host device. Once the trigger phase is recognized, the host device can treat the next spoken phrase as a user input. Using a trigger phrase to recognize user inputs is a two-step process that can be cumbersome to use because the user has to speak two phrases instead of one. Furthermore, electronic devices may not be able to recognize when a specific user is speaking the command. Often times, an electronic device may mistakenly interpret a phrase spoken by a nearby non-user (e.g., someone who is not authorized to control the device) during the normal course of a conversation as a trigger phrase or a voice command. As a result, the electronic device may inaccurately interpret parts of a conversation as unintentional voice commands. Or, unauthorized users may inappropriately operate the electronic device by simply speaking the trigger phrase followed by a voice command. 
     According to some embodiments of the present disclosure, a wireless listening device can enable a host device, e.g., smart phone, tablet, laptop, and the like, to identify a spoken phrase as a user input without the need for a trigger phrase, and perform authentication of the spoken phrase before receiving the spoken phrase as a user input by verifying that the spoken phrase is indeed spoken by the user (e.g., a user authorized to control the host device). As an example, the host device can receive a spoken phrase and then cross reference that spoken phrase with a list of predetermined spoken phrases. If the spoken phrase matches with any one of the spoken phrases in the list of predetermined spoken phrases, then the host device can authenticate the spoken phrase by verifying whether the spoken phrase was spoken by the user. 
     In some embodiments, the host device can authenticate the spoken phrase by comparing the sounds (i.e., frequencies) of the spoken phrase with known sounds of the user&#39;s voice. If the sounds match, then the host device can determine that the spoken phrase is an input; otherwise, if the sounds do not match, then the host device can disregard the spoken phrase as not a user input. To further authenticate the spoken phrase, in some embodiments, the host device can utilize an accelerometer of the wireless listening device. For instance, the host device can receive a measurement of vibrational force experienced by an accelerometer in the wireless listening device when the phrase was spoken. If the vibrational force is greater than a threshold value, then the authentication of the spoken phrase can be confirmed, or independently determined. Even further authentication can be performed by the host device by utilizing one or more microphones of the wireless listening device. As an example, the host device can determine a directionality of the sound by analyzing the temporal movement of sound across two microphones. If the direction of the sound is moving away from the wireless listening device, then the authentication of the spoken phrase can be confirmed, or independently determined. 
     Sometimes, a phrase spoken by the user during a conversation (i.e., a spoken phrase that is not intended to be a user input) may match with a spoken phrase in the list of predetermined spoken phrases. To minimize the chances of the host device determining that a spoken phrase not intended to be a user input is interpreted to be a user input, the host device can be configured to measure temporal spacing before and after the spoken phrase, and compare the measured temporal space with a delay threshold. If the measured temporal spacing is greater than the delay threshold, then the host device can determine that the spoken phrase is a user input; otherwise, if the measured temporal spacing is less than the delay threshold, then the host device can determine that the spoken phrase is not a user input. 
     In some embodiments, the list of predetermined spoken phrases and the sound of the user&#39;s voice can be set during a one-time initialization protocol. During the initialization protocol, the host device can follow a script to walk the user through various functions that can be initiated by voice command, such as turning on active noise cancellation mode, turning on transparency mode, adjusting the volume, playing/pausing music, and various other functions. The host device can also be configured to allow the user to define what the spoken phrases should be, thereby enhancing personal connection to the host device. 
     V. Stem with Bus Bar and Method of Forming an Eartip 
     Although embodiments discussed herein have shown housings that are substantially ovular/oblong (see  FIGS. 2A-2B, 5B, 6A, 7, 11A-11B ), and/or amorphous (see  FIG. 13 ), embodiments are not limited to such configurations. Rather, some embodiments can include a stem that can be an extension of the outer structure, e.g., outer structure  704  in  FIG. 7 , that protrudes from the body of the housing. As an extension of the outer structure, the stem can also enclose one or more electrical components within it. In some embodiments, the stem can be a tubular structure that has electrical contacts at its far end for interacting with a power source to charge the wireless listening device. 
       FIG. 16A  is a perspective view illustration of an exemplary wireless listening device  1600  that includes an eartip  1602  coupled to a housing  1604  that includes a body  1605  and a stem  1606 , according to some embodiments of the present disclosure. Housing  1604  can be formed of a monolithic outer structure that forms both body  1605  and stem  1606 . Thus, the outer structure can include a body portion  1608  and a stem portion  1610  that extends from body portion  1608 . The elongated structure of stem  1606  can be used as an alignment feature for aligning wireless listening device  1606  to a charging device, such as an case, as will be discussed further herein with respect to  FIG. 20 . Stem  1606  can also house electrical components and allow them to be positioned away from housing  1604  for coupling with the charging device. The different components within stem  1606  are further discussed in detail herein with respect to  FIG. 16B . 
       FIG. 16B  is a simplified illustration of the electrical components within stem  1606 , according to some embodiments of the present disclosure. As shown, stem  1606  can include two external contacts  1612  and  1614  positioned at the very bottom of an outer structure  1607  of stem  1606 . External contacts  1612  and  1614  can be conductive structures configured to make contact with leads of an external charging device, such as an case in which wireless listening device  1600  is stored when not used by a user. Contacts  1612  can be securely coupled to an insert mold  1616  that holds contacts  1612  and  1614  in place at the bottom of stem  1606  (e.g., attaches contacts  1612  and  1614  to stem  1606  at the point farthest away from housing  1604 ). Insert mold  1616  can be a cosmetic piece that has similar aesthetics to outer structure  1607  of stem  1606  to provide an aesthetically pleasing seamless transition between insert mold  1616  and outer structure  1607 . In some embodiments, insert mold  1616  and contact  1614  can define an opening  1618  that extends through insert mold  1616  and contact  1614  from an outer surface of contact  1614  to an inner surface of insert mold  1616 . Opening  1618  can be an acoustic port that can enable sound waves outside of stem  1606  to enter into stem  1606  so that an internal component, such as a microphone (not shown), can receive the sound waves. Although not shown in  FIG. 16B , a gasket can be implemented between insert mold  1616  and outer structure  1607  of stem  1607 . That way, a quality seal can be formed between them to prevent intrusion of moisture and/or debris. 
     Stem  1606  can also include an interconnection structure  1620 , e.g., interconnection structure  708  in  FIG. 7 , that can be any suitable interconnection structure for coupling electronic devices to one another, such as a printed circuit board (PCB). In some embodiments, interconnection structure  1620  is a part of interconnection structure  708  in  FIG. 7  that extends into stem outer structure  1607 , or a completely separate interconnection structure positioned in stem outer structure  1607 . Interconnection structure  1620  can have various electrical components (not shown) mounted on it, such as electronic devices  710  discussed herein with respect to  FIG. 7 . In some embodiments, external contacts  1612  and  1614  are electrically coupled to interconnection structure  1620 . Some ways in which external contacts  1612  and  1614  can be coupled to interconnection structure  1620  can include extending interconnection structure  1620  downward through stem outer structure  1607  so that interconnection structure  1620  can directly attach to external contacts  1612  and  1614  by soldering, hot bar processing, or any other means. In such cases, however, the high heat temperatures from soldering during final assembly, test and pack (FATP) can warp and/or discolor insert mold  1616 , which can negatively impact the aesthetics of insert mold  1616  and its seamless aesthetic integration with outer structure  1607 . 
     Thus, according to some embodiments of the present disclosure, a bus bar assembly  1622  can be implemented in stem  1606  to move high-heat processes, such as soldering or hot bar processes, away from insert mold  1616  during FATP. Bus bar assembly  1622  can include a bus bar  1624 , two leads  1626  and  1628  at the bottom of bus bar  1624 , and a contact head  1630  at the top of bus bar  1624 . Bus bar  1624  can be formed of one or more layers of copper traces coated with a protective insulating film, leads  1626  and  1628  can be exposed ends of the one or more layers of copper traces for making contact with external structures, and contact head  1630  can include exposed ends of the one or more layers of copper traces coupled to an alignment frame. Further details of bus bar  1624  and contact head  1630  are discussed further herein with respect to  FIGS. 17A-17B and 18A-18B . 
     In some embodiments, bus bar  1624  can be a flexible cable that electrically couples leads  1626  and  1628  to contact head  1630 , so that structures contacting leads  1626  and  1628  can be electrically coupled to structures contacting contact head  1630 . As an example, external contacts  1612  and  1614  can be coupled to leads  1626  and  1628 , and interconnection structure  1620  can be coupled to contact head  1630  so that external contacts  1612  and  1614  can be electrically coupled to interconnection structure  1620  (or any other electronic components mounted on interconnection structure  1620 ) via bus bar  1624 . By using bus bar  1624 , stem  1606  can be constructed without subjecting insert mold  1616  to high temperature processes. For instance, during manufacturing, leads  1626  and  1628  can first be laser welded to external contacts  1612  and  1614  when insert mold  1616  is not present. Then, contacts  1612  and  1614  can be overmolded to form insert mold  1616 . Afterwards, at FATP, contact head  1630  of bus bar assembly  1622  can be hot barred or soldered to interconnection structure  1620 . Accordingly, the hot temperature process step of hot barring/soldering is moved away from insert mold  1616 , and the laser welding process can be performed when insert mold is not present. That way, the cosmetic and structural integrity of insert mold  1616  can be maintained, thereby forming a more aesthetically pleasing and structurally sound product, as well as improving manufacturing yield. Using bus bar assembly  1622  also allows insert mold  1616  along with contacts  1612  and  1614  to move around so that an adhesive can easily be applied to the entire interface surface between insert mold  1616  and outer structure  1607 . This eases manufacturing and provides a better seal between them. 
       FIGS. 17A and 17B  are perspective view illustrations of different contact heads for a bus bar assembly, according to some embodiments of the present disclosure. Specifically,  FIG. 17A  is a perspective view illustration of an exemplary contact head  1700  configured with an alignment bar, and  FIG. 17B  is a perspective view illustration of an exemplary contact head  1700  configured with an alignment frame. 
     As shown in  FIG. 17A , conductive head  1700  can include contacts  1704  and  1706 . Contacts  1704  and  1706  can be exposed ends of copper traces  1703  and  1705  in bus bar  1624  that are formed to include contact features  1704  and  1706 . Contact features  1704  and  1706  can be in the shape of circles as shown in  FIG. 17A  to increase the surface area of copper traces  1703  and  1705  to enable a more robust coupling with an interconnection structure, e.g., interconnection structure  1620  in  FIG. 16B . Conductive head  1700  can also include an alignment bar  1702  for aligning contact features  1704  and  1706  to specific contact locations on the interconnection structure. Alignment bar  1702  can be positioned at ends of copper traces  1703  and  1705  opposite from bus bar  1624 . In some embodiments, alignment bar  1702  can include alignment features  1708  and  1710  positioned on laterally opposite ends of alignment bar  1702 . Alignment features  1708  and  1710  can be in the shape of crescents that are configured to align with complementary alignment posts, which can be positioned on the interconnection structure. Although alignment bar  1702  is shown as a single horizontal piece, alignment bar  1702  can be reinforced to prevent bending during FATP, as discussed in  FIG. 17B . 
     With reference to  FIG. 17B , conductive head  1701  can include an alignment frame  1712  positioned around contact features  1704  and  1706 . Alignment frame  1712  can be in the shape of a picture frame that includes four parts: a top part  1714 , a bottom part  1716 , and two side parts  1718  and  1720 , which together form a monolithic structure. Side parts  1718  and  1720  can include alignment features  1708  and  1710  for helping align contact features  1704  and  1706  to specific contact locations on the interconnection structure. The four parts of alignment frame  1712  can better resist bending and/or buckling during FATP to ease manufacturing. 
       FIGS. 18A and 18B  are cross-sectional view illustrations of different bus bars for a bus bar assembly, according to some embodiments of the present disclosure. Specifically  FIG. 18A  is a cross-sectional view illustration of an exemplary bus bar  1800  having two conductive traces in a single layer, and  FIG. 18B  is a cross-sectional view illustration of an exemplary bus bar  1801  having two conductive traces in different layers. 
     As shown in  FIG. 18A , bus bar  1800  can include a first copper trace  1802  and a second copper trace  1804  that are both insulated from one another by insulating film  1806 . First copper trace  1802  can be coupled to ground, and second copper trace  1804  can be coupled to power, or vice versa. First and second copper traces  1802  and  1804  can be formed in a single layer such that copper traces  1802  and  1804  are coplanar. Insulating film  1806  can be formed of any suitable insulating material, such as polyimide (PI) or any other polymer material. Although first and second copper traces  1802  and  1804  are shown to be arranged in a single layer in  FIG. 18A , embodiments are not limited to such configurations. In some embodiments, the copper traces can be arranged in different layers, as shown in  FIG. 18B . 
     With reference to  FIG. 18B , bus bar  1801  can include a first copper trace  1808  and a second copper trace  1810  that are both disposed within an insulating film  1812 . First copper trace  1808  can be coupled to power, and second copper trace  1810  can be coupled to ground, or vice versa. First and second copper traces  1808  and  1810  can be formed in different layers that are separated by an insulating layer  1814 . Insulating film  1812  and insulating layer  1814  can be formed of any suitable insulating material, such as polyimide (PI) or any other non-conductive polymer material. By arranging first and second copper traces  1808  and  1810  in different layers, each trace can take advantage of the entire width of bus bar  1801 . Thus, any of copper traces, e.g., second copper trace  1810 , can have a width that extends across the entire width of bus bar  1810 . Having a greater width increases the cross-sectional area of second copper trace  1810 , thereby allowing second copper trace  1810  to have less resistance, which improves the conductivity of bus bar  1801 . 
     VI. Method of Forming an Eartip 
       FIGS. 19A-19G  are simplified illustrations of an exemplary method of forming an eartip, according to some embodiments of the present disclosure. The eartip can be eartip  300  discussed herein with respect to  FIG. 3 . As shown in  FIG. 19A , a first mold  1900  can be patterned over a first side  1901  of wire mesh  1902 . Wire mesh  1902  can be a circular disk cut from a sheet of wire cloth formed of a network of wire suitable for allowing sound to pass through but preventing dust from passing through, e.g., 50 mesh wire cloth. In some embodiments, wire mesh  1902  can have a lip  1904  that is bent at a 90 degree angle around the entire perimeter of wire mesh  1902 , as illustrated by the dotted lines representing structures that are behind the cut line. Lip  1904  can be used as an alignment feature for later processes. In certain embodiments, first mold  1900  can include a flat layer  1905  and a protrusion  1906  extending from the center of flat layer  1905 . Flat layer  1905  can cover a surface of wire mesh  1902  bordered by lip  1904 , and protrusion  1906  can be a tapered structure that narrows as it extends away from wire mesh  1902 . Protrusion  1906  can act as an alignment feature that can work alone or in conjunction with lip  1905  for alignment purposes in later processing. 
     In some embodiments, a second mold  1910  can be formed on a second side  1903  of wire mesh  1902  opposite of first side  1901 . Second mold  1910  can be formed as a mirror image of first mold  1900  and positioned to be vertically aligned with first mold  1900 . Thus, second mold  1910  can also include a flat layer  1912  and a protrusion  1914  extending from the center of flat layer  1912 . Protrusion  1914  can be a tapered structure that narrows as it extends away from wire mesh  1902  and first mold  1900 . Protrusion  1914  can act as an alignment feature for later processing, e.g., injection molding. In some embodiments, first and second molds  1900  and  1910  can be formed of a material that resists bonding with certain materials and can function as a mask that prevents those certain materials from forming on regions of wire mesh  1902  covered by first and second molds  1900  and  1910 , as will be discussed further herein. Although  FIGS. 19A and 19B  are ordered such that first mold  1900  is formed before second mold  1910 , it is to be appreciated that this is merely exemplary and that other embodiments can form second mold  1910  before first mold  1900  without departing from the spirit and scope of the present disclosure. 
     Once second mold  1910  is formed, then the resulting structure can be positioned on a tool fixture  1916  as shown in  FIG. 19C . Tool fixture  1916  can be a fixture of a processing tool, e.g., a silicon molding tool, having a recess  1918  designed to receive and position the structure including wire mesh  1902  and first and second molds  1900  and  1910  in the correct position for processing. In some embodiments, protrusion  1906  of first mold  1900  can correctly align the structure to tool fixture  1916  by resting in recess  1918 . Furthermore, lip  1904  can also help align the structure with tool fixture  1916  by wrapping around the outer edges of fixture  1916 . 
     After the structure is properly aligned, energy can be applied to melt portions of first and second molds  1900  and  1910 . For instance, ultrasonic energy can be applied to the structure and cause first and second molds  1900  and  1910  to melt over a portion of wire mesh  1902  disposed between first and second molds  1900  and  1910 , thereby forming combined mold  1920 . By melting first and second molds  1900  and  1910  to cover a portion of wire mesh  1902 , air gaps between first and second molds  1900  and  1910  can be removed and wire mesh  1902  can thus be better coated and protected by molds  1900  and  1910  so that formation of structures using injection molding in later processing steps, such as an attachment mechanism and a inner eartip body of the eartip, can be prevented from leaking and/or flashing/spreading into portions of wire mesh  1902  covered by molds  1900  and  1910 , as discussed herein with respect to  FIGS. 19E and 19F . 
     As shown in  FIG. 19E , an attachment mechanism  1922  can be formed by injection molding. Attachment mechanism  1922  can be substantially similar in structure to attachment structure  308  discussed herein with respect to  FIGS. 3A and 3C . Attachment structure  308  can, in some embodiments, be molded over lip  1904  of wire mesh  1902 . Molding over lip  1904  can provide sufficient surface area for attachment mechanism  1922  to securely couple with wire mesh  1902 . In some embodiments, attachment structure  308  can be formed of a stiff polymer, such as polycarbonate. As can be appreciated herein, molds  1900  and  1910  (and thus combined mold  1920 ) can be formed of a material that resists forming a chemical bond with polycarbonate (PC) materials, e.g., a synthetic polymer like polyvynl alcohol (PVA). By forming molds  1900  and  1910  with PVA, combined mold  1920  can act as a mask that prevents flashing of PC materials into inner regions of wire mesh  1902 . As will be appreciated further herein with respect to  FIG. 19G , molds  1900  and  1910  can be formed of a soluble material so that it can be cleanly removed to leave wire mesh  1902  intact. 
     Then, as shown in  FIG. 19F , the rest of the eartip can be formed. For instance, a single, monolithic structure  1924  including inner eartip body  1926  and outer eartip body  1928  can be formed. The structure and purpose of inner eartip body  1926  and outer eartip body  1928  can be similar to inner eartip body  316  and outer eartip body  322  discussed herein with respect to  FIGS. 3A-4C . Monolithic structure  1924  can be formed of a soft, compliant material that can easily bend and deform to fit within an ear canal. As an example, monolithic structure  1924 , and thus inner eartip body  1926  and outer eartip body  1928  by association, can be formed of silicone. Structure  1924  can be formed over portions of attachment mechanism  1922  so that attachment mechanism  1922  can provide a stiff stopper with which structure  1924  can attach to the eartip. 
     Once structure  1924  including inner eartip body  1926  and outer eartip body  1928  is formed, combined mold  1920  can be removed to form the completed eartip, according to some embodiments of the present disclosure as shown in  FIG. 19G . For instance, mold  1920  can be dissolved and washed away using a solvent compatible for removing PVA, such as hot water. Removing mold  1920  can expose the once-covered portions of wire mesh  1902  and leave it intact. That way, wire mesh  1902  can remain as a barrier for debris and an avenue through which sound can pass through, such as sound generated by a housing, e.g., housing  702  in  FIG. 7 . 
     VII. Case for Wireless Listening Devices 
     As mentioned herein, a wireless listening device can be one of a pair of wireless listening devices that are designed to fit in the ears of a user and to fit within an case when not in use. The case can protect the wireless listening devices from physical damage as well as provide a source of power for charging the wireless listening devices. 
       FIGS. 20A-20C  are different views of an exemplary case for a pair of wireless listening devices, according to some embodiments of the present disclosure. Specifically,  FIG. 20A  is a front-view illustration of a case  2000  that is transparent to illustrate the configuration of the components inside of case  2000  from the front,  FIG. 20B  is a back-view illustration of case  2000  that is also transparent to illustrate the configuration of the components inside of case  2000  from the back, and  FIG. 20C  is a cross-sectional view illustration of case  2000 . 
     As shown in  FIG. 20A , case  2000  can include a lid  2002  and a body  2004  that forms an internal cavity for housing a pair of wireless listening devices  2006   a - b . Lid  2002  and body  2004  can meet at interface  2005 . In some embodiments, case  2000  can include an internal frame  2008  formed of a monolithic structure including portions  2008   a - d  designed to provide contours and surface features against which wireless listening devices  2006   a - b  can rest in the strategic positions discussed herein to minimize the size of case  2000 . Portion  2008   a  can be a part of the internal frame that makes contact with body  2004  to seal areas inside case  2000  below portion  2008   a  from the outside environment. Portions  2008   b - c  can be parts upon which stems  2010   a - b  can rest, and portions  2008   d - e  can be parts upon which eartips  2012   a - b  and housings  2014   a - b  can rest. Details of internal frame  2008  are further shown and discussed herein with respect to  FIGS. 21A-21B, and 22A-22B . 
     To minimize the overall size of case  2000 , wireless listening devices  2006   a - b  can be positioned at strategic angles when placed in case  2000 . In some embodiments, each stem  2010   a - b  of respective wireless listening devices  2006   a - b  are positioned at an angle with respect to two axis: an x-axis and a y-axis, instead of being positioned substantially vertical where the stem is not positioned at any angle in the x- and y-axes. For purposes of description, the x-axis runs between wireless listening devices  2006   a - b , the y-axis runs between the front and the back of the case, and the z-axis runs between the bottom of body  2004  and the top of lid  2002 . 
     Case  2000  can be configured to charge wireless listening devices  2006   a - b  when they are housed in case  2000 . Thus, case  2000  can include two pairs of contacts  2016   a - b  and  2018   a - b  for making electrical contact with respective pins on stems  2010   a - b  so that charge can flow from an internal battery of case  2000  to internal batteries of wireless listening devices  2006   a - b . In some embodiments, the contacts of each pair of contacts are positioned on axes  2020   a - b  that are oriented at 90 degree angles with respect to one another. That way, the amount of space needed to implement contacts  2016   a - b  is smaller when compared to other contact arrangements, such as some contact arrangements where the two contacts are positioned at 180 degree angles with respect to one another. Utilizing less space results in more space for other components within case  2000  and/or helps reduce the overall size of case  2000 . 
     In some embodiments, contacts  2016   a - b  and  2018   a - b  can be sealed from the outside environment to protect them from moisture. For instance, sealing rings  2022   a ,  2022   b , and  2022   c  can be strategically positioned at interface regions that are entry points to contacts  2016   a - b  and  2018   a - b . As an example, sealing ring  2022   a  and  2022   b  can be positioned on opposite ends of each contact  2016   a - b  and  2018   a - b , and sealing ring  2022   c  can be positioned on a portion of the interior frame around portion  2008   b.    
     Case  2000  can also include a visual indicator  2024  configured to emit different colors of light. Visual indicator  2024  can change colors depending on the charge status of the case, e.g., emit green light when the case is charged, emit orange light when the case battery is charging and/or when the case battery has less than a full charge, and red light when the battery is depleted. When viewed from outside of case  2000 , visual indicator  2024  can have a circular shape, or any other suitable shape, such as square-like, rectangular, oval, and the like. With brief reference to  FIG. 20C , visual indicator  2024  can include a light emitter  2025  and a light tube  2027 . Light emitted from emitter  2024  can be projected into light tube  2027 , which can direct the light out of case  2000 . According to some embodiments of the present disclosure, an input end of light tube  2027  and an output end of light tube  2027  can have different shapes, as will be discussed further herein with respect to  FIG. 25 . 
     As shown in the back-view illustration of case  2000  in  FIG. 20B , case  2000  can include two sets of retaining magnets  2030   a - b  positioned below portions of housing bodies of respective wireless listening devices  2006   a - b . Each set of retaining magnets can be specifically configured to attract and hold respective wireless listening devices  2006   a - b  in place when devices  2006   a - b  are placed in case  2000 . For example, each set of retaining magnets  2030   a - b  can include a plurality of magnets and shunts that are uniquely designed and arranged to generate highly concentrated magnetic attraction on ferrous retention slabs in wireless listening devices  2006   a - b , as discussed herein with respect to  FIGS. 23 and 24A-24B . 
     Case  2000  can further include a button  2032  mounted on a button substrate  2034 , such as a PCB, that includes conductive traces for routing electrical signals when button  2032  is pressed by a user. Button  2032  can be configured to initiate different commands when pressed, such as a reset command or a pairing command with an external device, such as a smart phone. In some embodiments, case  2000  can also include a wireless power receiving coil  2036  formed of a wire arranged in a plurality of turns between an outer diameter  2038  and an inner diameter  2040 . Receiving coil  2036  can wind around button  2032  so that button  2032  is positioned at a center of receiving coil  2036  within inner diameter  2040 . Receiving coil  2036  can interact with time-varying magnetic flux to generate current that can be used to charge an internal battery of case  2000 . To minimize the height and width of receiving coil  2036 , a portion of receiving coil  2036  can overlap with a portion of button substrate  2034  so that inner diameter  2040  is positioned over substrate  2034 . Another view of this configuration can be seen in the cross-sectional view of  FIG. 20C . As shown, portions of coil  2036  can overlap the outer regions of button substrate  2034 , and button  2032  can be positioned within the inner diameter of coil  2036 . In some embodiments, button  2032  can include an o-ring  2035  that can act as a dynamic seal that moves with the movement of button  2032 . O-ring  2035  can seal the internal components of case  2000  from the outside environment around button  2032 . By using o-ring  2035 , space utilized by button  2032  can be minimized, thereby allowing coil  2036  to overlap with portions of button substrate  2034 , which helps decrease the size of case  2000  as a whole. 
     With reference back to  FIG. 20B , in some embodiments, case  2000  can also include, a speaker  2041  configured to emit audible sound. Speaker  2041  can be configured to emit sound to indicate different states of the device. For instance, speaker  2041  can emit a beep when case  2000  is successfully paired with an external device, such as a smart phone, and/or emit sound when case  2000  drops out of connection with the external device. Furthermore, speaker  2041  can be configured to emit a repetitive pinging noise when it is in a find-me mode, such as when the case is lost and the user is looking for the case. 
     Case  2000  can also include an antenna  2042  for sending and receiving radio frequency (RF) signals. Antenna  2042  can be a conductive body formed on a case substrate  2044  and can be positioned a distance away from other electrical components to mitigate interference of antenna operation. For instance, a clearance zone  2046  can be imposed around antenna  2042  where other electrical components are not allowed to be positioned. By having an antenna, case  2000  can wirelessly communicate with other devices to send and receive data and commands. For instance, if the case is lost, the user can access his or her smart phone to which case  2000  is paired and initiate the find-me sequence where speaker  2041  is activated to emit the repetitive pinging noise. Antenna  2042  can be positioned at one of two bottom corners of case  2000  within body  2004  and away from lid  2002 . In some instances, speaker  2041  can be positioned in the other of two bottom corners of case  2000  within body  2004  and away from lid  2002 , as shown in  FIG. 20B . 
     As shown in  FIG. 20C , case  2000  can include a hinge  2048  for opening and closing lid  2002 . Hinge  2048  can be a bistable hinge that has two stable states: an open state and a closed state. Having a bistable hinge can allow for case  2000  to close without needing many magnets to generate a high magnetic attraction force to draw lid  2002  toward body  2004  to close lid  2002 . Accordingly, only a single magnet  2050  may be sufficient to keep lid  2002  closed. Thus, in the stable closed state, hinge  2048  can cause lid  2002  to press on body  2004  and magnet  2050  may need to have just enough force to help it stay closed to resist inadvertent opening of lid  2002 . Details of bistable hinge  2048  is discussed further herein with respect to  FIGS. 27 and 28A-28C . 
     To help keep lid  2002  closed, magnet  2050  can be attracted to a magnetic component in body  2004 . For instance, a shunt  2052  formed of a ferrous block of material, such as steel, can be positioned within body  2004  immediately below a top surface of body  2004  and aligned with magnet  2050  when lid  2002  is in the closed position. Magnet  2050  can be attracted to shunt  2052  when the magnetic fields from magnet  2050  interact with the ferrous properties of shunt  2052 . According to some embodiments of the present disclosure, shunt  2052  can operate as a hybrid retention and sensor shunt that can not only help lid  2002  stay closed by attracting magnet  2050 , but also be used as a sensor component so that a sensor  2054  positioned below shunt  2052  can detect when lid  2002  is opened or closed by way of shunt  2052 , as will be discussed further herein with respect to  FIGS. 26A-26B . Sensor  2052  can be any suitable sensor that can detect the presence of a magnetic field, such as a hall-effect sensor. 
     In some embodiments, case  2000  can further include one or more energy storage devices  2056   a - b , upon which a plurality of electrical devices can be mounted. Energy storage devices  2056  can store power that can be discharged to operate case  2000 . In some embodiments, case  2000  can include two energy storage devices  2056   a - b  that are positioned on opposite sides of a vertically oriented case substrate  2044 , as will be discussed further herein with respect to  FIGS. 29A-29C . In addition to including an antenna, e.g., antenna  2042  discussed herein with respect to  FIG. 20B , case substrate  2044  can operate as the motherboard for operating case  2000 , and can thus include communication systems, computing systems, and circuities, e.g., case communication system  121 , case computing system  119 , and power transmitting circuitry  120  in  FIG. 1 . 
     A. Internal Frame 
     As discussed herein with respect to  FIG. 20A , an internal frame can be formed of a monolithic structure designed to provide contours and surface features against which electronic components within the case can rest and/or attach.  FIGS. 21A-21B  illustrate different views of an exemplary internal frame  2100 , according to some embodiments of the present disclosure. Specifically,  FIG. 21A  is a simplified perspective view illustration of internal frame  2100 , and  FIG. 21B  is a simplified top-down view illustration of internal frame  2100 . 
     Internal frame  2100  is substantially similar to internal frame  2008  in  FIG. 20A , and can provide the structural backbone for the internal components of a case. As discussed herein with respect to  FIG. 20A , the internal frame can provide a structure upon which electrical devices can be mounted and compartmentalized, such as wireless listening devices, a printed circuit board, batteries, speakers, and the like. Thus, internal frame  2100  can define two bowl regions  2102   a - b  for accepting each wireless listening device, a center region  2105  defined by flaps  2017   a - b  for holding battery packs and a printed circuit board with electrical devices, and various other contours for other electronic devices discussed herein. 
     In some embodiments, internal frame  2100  can be configured to seal the internal components of a case from the outside environment through the top of the case body. Thus, internal frame  2100  can include a sealing structure  2104  that is formed of a pliable material suitable for sealing purposes. Sealing structure  2104  can follow the contours of the top ridges of internal frame  2100 . For instance, sealing structure  2104  can extend around the perimeter of the top ridge of internal frame  2100 , as shown in  FIG. 21A . To seal off regions around a hinge (not shown) for the case, sealing structure  2104  can diverge at a first point  2018 , extend around a clearance region  2106  in which a portion of the hinge could be positioned, and then converge back together past clearance region  2106  at a second point  2020 , which then continues as part of sealing structure  2104 . Thus, sealing structure  2104  can include a first diverged portion  2023  and a second diverged portion  2024 . 
     As shown in  FIG. 21A , first diverged portion  2023  can be positioned a distance away from second diverged portion  2024 . In some embodiments, first diverged portion  2023  can be positioned a vertical distance away from second diverged portion  2024 . And, as shown in  FIG. 21B , first diverged portion  2023  can also be positioned a lateral distance away from second diverged portion  2024 . In some instances, first diverged portion  2023  can be positioned at the outer perimeter of internal frame  2100 , while second diverged portion  2024  can be positioned within the outer perimeter of internal frame  2100 . As will be appreciated further herein with respect to  FIGS. 22A-22B , second diverged portion  2024  can be constructed differently than the rest of sealing structure  2104 , including first diverged portion  2023 , so that when internal frame  2100  is positioned within a body of a case and an insert is positioned over internal frame  2100 , sealing structures  2014  can seal the electrical components within the case body from the outside environment. 
       FIGS. 22A-22B  illustrate cross-sectional views of internal frame  2100  implemented in a body  2200  of a case with an insert  2203  attached on the top of body  2200 , according to some embodiments of the present disclosure. Specifically,  FIG. 22A  is a simplified cross-sectional view illustration  2200  of internal frame  2100 , and  FIG. 22B  is a simplified zoomed-in view illustration  2201  of a portion of the cross-sectional view of  FIG. 22A . The cross-sectional views can be from a perspective across the cut line shown in  FIG. 21B   
     Insert  2203  can be a structure that is pressed over internal frame  2100  and functions as part of the outer top structure of body  2200  of the case. As can be seen in the cross-sectional view illustration  2200  of internal frame  2100 , sealing structure  2104  and first diverged portion  2023  can make contact with both insert  2203  and body  2200 , while second diverged portion  2024  can make contact with only insert  2203  and not body  2200 . Thus, second diverged portion  2024  can be configured to make a face seal with internal frame  2100 , while the rest of sealing structure  2104  including first diverged portion  2023  can be configured to make both a face seal with insert  2203  and a radial seal with body  2200 . 
     As shown in the close-up cross-sectional view illustration  2201  of sealing structure  2104  in  FIG. 22B , sealing structure  2104  can include a horizontal portion  2204  and a vertical portion  2206  such that the combination of horizontal portion  2204  and vertical portion  2206  forms a monolithic structure having an “L” shape profile. Horizontal portion  2204  can interface with an inner side surface of case  2200  while vertical portion  2206  can interface with a bottom surface of insert  2203 . Thus, regions beside and below sealing structure  2104  may be sealed from the outside environment. Configuring sealing structure  2104  in this manner allows sealing structure  2104  to achieve two sealing points in different axis with only one structure instead of two. It is to be appreciated that first diverged portion  2023  can have the same structure and function as the portion of sealing structure  2104  shown in  FIG. 22B , but first diverged portion  2023  can just be arranged as a mirror image of the portion of sealing structure  2104  because it seals with an opposite side of body  2200 , as can be seen in  FIG. 21B . 
     B. Magnetic Retention System 
     As discussed herein, a case can include two sets of retaining magnets, each of which can be specifically configured to attract and hold respective wireless listening devices in place when the devices are placed in the case.  FIG. 23  is a simplified cross-sectional view illustration  2300  of a set of retaining magnets  2302  and a wireless listening device  2304  aside from any other component within device  2304  and the case in which both magnets  2302  and device  2304  are positioned. Set of retaining magnets  2302  can attract a retention slab  2306  within a housing of wireless listening device  2304 . Retention slab  2306  can have a curved surface that complements the curved surface of the housing of wireless listening device  2304 . Retention slab  2306  can be formed of any suitable ferrous material, such as an iron and silicon alloy. In some embodiments, retention slab  2306  is positioned at a bottom region of the housing and above a stem  2308  of wireless listening device  2304 . That way, the distance between retention slab  2306  and set of retaining magnets  2302  is small to increase the potential magnetic force achieved by set of retaining magnets  2302 . In some embodiments, the amount of attractive magnetic force achieved along a direction, e.g. along an axis  2309  of stem  2308 , is approximately 1 to 1.5 N, particularly 1.2 N in some embodiments. Because the direction of the targeted attractive magnetic force is at an angle, the actual amount of force that set of retaining magnets  2302  achieves in the vertical direction may be greater than 1.2 N, such as 1.5 N. 
     To achieve sufficient attractive magnetic force within certain size constraints, set of retaining magnets  2302  can be specifically designed to augment its magnetic field in one direction. And, in some instances, set of retaining magnets  2302  can be further designed to concentrate its magnetic field toward a small region within the general augmented direction. An example of this is shown more detail in  FIGS. 24A and 24B , which are simplified illustrations of an exemplary set of retaining magnets  2400 , according to some embodiments of the present disclosure. Specifically,  FIG. 24A  is a front-view illustration of set of retaining magnets  2400 , and  FIG. 24B  is a top-down view illustration of set of retaining magnets  2400 . 
     As shown in  FIG. 24A , set of retaining magnets  2400  can include several magnets arranged beside one another like a Halbach array. For instance, set of retaining magnets  2400  can include four magnets  2402   a - d  where pair of magnets  2402   b - c  are positioned directly beside one another, and magnets  2402   a  and  2402   d  are positioned on opposite sides of magnets  2402   b - c . To concentrate magnetic field to a specific area, e.g., an area  2404  above magnets  2402   b  and  2402   c , the polarity of each magnet in set of retaining magnets  2400  can have its polarity oriented in a different way. As an example, the polarity of magnet  2402   a  can be oriented downward and at an angle  2408  tilted away from magnet  2402   b  with respect to a vertical dimension, the polarity of magnet  2402   b  can be oriented vertically downward with no tilt angle, the polarity of magnet  2402   c  can be oriented vertically upward with no tilt angle, and the polarity of magnet  2402   d  can be oriented upward and at an angle  2410  tilted toward magnet  2402   c  with respect to the vertical dimension. By arranging the magnets of set of retaining magnets  2400  in this manner, magnetic fields can be concentrated toward area  2404  where retention slab  2306  may be positioned so that set of retaining magnets  2400  can generate a sufficiently high attractive magnetic force to retain the wireless listening device with strenuous size constraints. For reference, the orientation of the polarities of magnets  2402   a - d  are represented by arrows where the north pole is represented by an arrowhead and the south pole is represented by the tail, or vice versa. 
     Although both magnets  2402   a  and  2402   d  have polarities whose orientations are positioned at an angle with respect to a vertical axis, the degree of their tilt angle can depend on the position of area  2404 . If area  2404  is to be positioned along the center of set of retaining magnets  2400 , then angles  2408  and  2410  may be the same. However, if area  2404  is to be positioned a little to the left of center, then angles  2408  and  2410  can be adjusted accordingly, e.g., angle  2408  can be decreased and angle  2410  can be increased. In some embodiments, the degree of tilt for angles  2408  and  2410  can range between 20 and 40 degrees, such as 28 degrees for angle  2408  and 34 degrees for angle  2410 , in certain particular instances. Furthermore, although magnets  2402   b - c  are shown as having polarities oriented in only one dimension (the z-dimension) and magnets  2402   a  and  2402   d  are shown as having polarities oriented in two dimensions (the z- and x-dimensions) for pulling shunt  2306  vertically downward, embodiments are not so limited. Other embodiments can include magnets  2402   b - c  that have polarities in two dimensions (the z-dimension and the y-dimension) and magnets  2402   a  and  2402   d  that have polarities in three dimensions. That way, the resulting magnetic force does not only have a vertical downward component, but also has a lateral y-dimension component to more efficiently direct an attractive force along axis  2309  of stem  2308  by more closely aligning the direction of magnetic force to axis  2309  of stem  2308 . 
     Although  FIG. 24A  shows a set of retaining magnets as having four magnets, is to be appreciated that embodiments are not so limited and that any other number and configuration of magnets are envisioned herein without departing from the spirit and scope of the present disclosure. For instance, a set of retaining magnets can have six magnets where the two central magnets have vertical magnetic polarities, while the immediately adjacent two magnets straddling the two central magnets have angled magnetic polarities, and the final outer two magnets straddling the inner four magnets have magnetic polarities that are even more angled than the immediately adjacent two magnets. It can be appreciated that any number of magnets can be used and with different polarities to focus the magnetic force at a certain region above the set of retaining magnets, as discussed herein. 
     In some embodiments, set of retaining magnets  2400  can have a top surface  2406  that is curved to follow the curve of an interface surface upon which the housing of wireless listening device  2304  may rest. Thus, the curvature of top surface  2406  of set of retaining magnets  2400  can follow the curvature of the bottom of the housing of wireless listening device  2304  where retention slab  2306  may be positioned. While top surface  2406  is curved, each magnet  2402   a - d  in set of retaining magnets  2400  may be substantially vertical structures. For instance, each magnet  2402   a - d  in set of retaining magnets  2400  can have vertical sidewalls and horizontal bottom surfaces, while its top surface is curved. As can be further appreciated in  FIG. 24A , even though the structure of magnets  2402   a  and  2402   d  are substantially vertical, the orientation of their polarity may be angled as shown by the arrows. 
     While use of magnets can result in a concentration of magnetic fields in a specific location, the magnetic properties of such magnets can also result in a leakage of magnetic fields that are propagating in undesirable directions. For instance, while magnetic fields are intended to be concentrated upwards, some magnetic fields may propagate downwards or into and out of the page. Thus, in some embodiments, one or more magnetic shunts may be implemented in addition to set of retaining magnets  2400  to control the leakage of magnetic fields. As an example, magnetic shunts  2412  and  2414  can be positioned at the bottom of set of retaining magnets  2400  to prevent magnetic fields from leaking downward. In some instances, shunts  2412  and  2414  can be positioned a distance away from one another to form a gap  2416 , which can provide clearance space for positioning the stem of the wireless listening device. Magnetic shunts  2412  and  2414  can be configured to redirect stray magnetic fields to prevent them from propagating downward past shunts  2412  and  2414 . Thus, magnetic shunts  2412  and  2414  can be formed of any material having high magnetic permeability, such as steel. Shunts  2412  and  2414  can be formed of a simple steel plate configured as shown in  FIG. 24A . 
     In addition to shunts  2412  and  2414 , an additional shunt can also be positioned on a back surface of set of retaining magnets  2400 , as better shown in the top-down view perspective of  FIG. 24B . As shown in  FIG. 24B , a third shunt, shunt  2418 , can be attached to a back surface  2420  of set of retaining magnets  2400  so that shunt  2418  makes contact with each magnet  2402   a - d . Shunt  2418  can adhere to magnets  2402   a - d  of set of retaining magnets  2400  to hold them together as a single structure. That way, adhesives or other attachment methods may not need to be implemented between adjacent magnets, thereby further decreasing the footprint of set of retaining magnets  2400 . A shunt may not need to be placed on a front surface  2422  of set of retaining magnets  2400  because that may be an area where the wireless listening device is positioned. 
     Although  FIG. 24A  illustrates set of retaining magnets  2400  as only having a curved top surface, embodiments are not limited to such configurations. As an example, from the top-down view perspective in  FIG. 24B , set of retaining magnets  2400  can also have a curved front surface  2422 . The curvature of front surface  2422  can follow a contour of the wireless listening device so that set of retaining magnets  2400  can maximize its presence around wireless listening device to increase its magnetic forces while providing clearance space for the wireless listening device to be positioned. 
     C. Visual Indicator 
       FIG. 25  is a simplified perspective view illustration of an exemplary visual indicator  2500  including a light emitter  2504  and a light tube  2501  for directing light  2502  emitted by light emitter  2504  from within a body of a case to a region outside of the body of the case, according to some embodiments of the present disclosure. Light tube  2501  can have an input end  2506  and an output end  2508 , where input end  2506  receives light  2502  from light emitter  2504  and outputs the received light out of output end  2508 . Input end  2506  can have a profile that is substantially similar to the profile of light emitter  2504  so that light tube  2501  can efficiently capture a large amount of the emitted light from light emitter  2504 . Depending on the design as to how visual indicator  2500  is to appear from outside of the case, output end  2508  can have that specific profile, e.g., circular as shown in  FIG. 20A . Thus, the profile of input end  2506  can be different from the profile of output end  2508 . 
     In some embodiments, light emitter  2504  can be a light emitting device (LED) that has a square-like profile. Thus, in embodiments where visual indicator  2024  has a circular profile when viewed from outside of the case, light tube  2501  can be have an input end  2506  that has a square-like profile, and an output end  2508  that has a circular profile. A middle region  2510  between input end  2506  and output end  2508  can be formed of a structure that gradually transitions from a square-like profile at input end  2506  to a circular profile at output end  2508 . Thus, middle region  2510  can have four surfaces  2512 , each extending from input end  2506  and tapering, e.g., having a gradual decreasing width, toward output end  2508 , so that the structure of light tube  2501  gradually changes from a square-like profile to a circular profile. Although  FIG. 25  shows light emitter  2504  being positioned far away from light tube  2501 , embodiments are not so limited. In some embodiments, light emitter  2504  can be placed adjacent to, or in contact with, light tube  2501  so that there is a minimal distance between light emitter  2504  and input end  2506  of light tube  2501 . 
     It is to be appreciated that input end  2506  and output end  2508  can have any other profile and does not necessarily have to be square-like and circular, respectively. Rather, the profile of input end  2506  can depend on the shape of light emitter  2504 , and the profile of output end  2508  can depend on design. Thus, input end  2506  and output end  2508  can be any other suitable shape, such as rectangular, triangular, oblong, and the like. In some embodiments, light tube  2501  can include a flange  2514  for securing light tube  2501  to a body of the case, as shown in  FIG. 20C . Flange  2514  can extend outward from a center axis  2503  of inner eartip body  2501  and along the same plane as input end  2506  of light tube  2501 . 
     D. Hybrid Retention and Sensor Shunt 
     As discussed herein with respect to  FIG. 20C , a shunt can operate as a hybrid retention and sensor shunt that can not only help the lid stay closed by allowing a magnet in the lid to attract to it, but it can also be used as a sensor component so that a sensor positioned below the shunt can detect when the lid is opened or closed by way of the shunt.  FIGS. 26A-26B  are simplified cross-sectional views of an exemplary magnetic attachment and sensor system  2600  that includes a hybrid retention and sensor shunt  2602 , according to some embodiments of the present disclosure. Specifically,  FIG. 26A  is a simplified cross-sectional view of magnetic attachment and sensor system  2600  when a lid  2610  is opened, and  FIG. 26B  is a simplified cross-sectional view of magnetic attachment and sensor system  2600  when a lid  2610  is closed. Hybrid retention and sensor shunt  2602  and a sensor  2604  can be positioned within a body  2606  of a case, and a magnet  2050  can be positioned within a lid  2610  of the case. 
     As shown in  FIG. 26A , when lid  2610  is opened, lid  2610  is positioned away from body  2606  of the case. When lid  2610  is positioned away from body  2606 , magnetic fields  2612  generated by magnet  2608  may propagate around magnet  2608  but may be so far from sensor  2604  that sensor  2604  may not detect the presence of magnetic fields  2612 . In this case, sensor  2604  may generate a signal indicating that lid  2610  is open. 
     However, when lid  2610  is closed, as shown in  FIG. 26B , lid  2610  can contact body  2606 . When lid  2610  is in contact with body  2606 , magnetic fields  2612  can propagate through hybrid retention and sensor shunt  2602  so that a magnetic attractive force can be generated to assist the bistable hinge in pulling lid  2610  shut. In addition, magnetic fields  2612  can propagate through hybrid retention and sensor shunt  2602  by entering a top surface of hybrid retention and sensor shunt  2602  and exiting a bottom surface of hybrid retention and sensor shunt  2602 . Because hybrid retention and sensor shunt  2602  is formed of a ferrous material, such as steel, magnetic fields  2612  can easily pass through hybrid retention and sensor shunt  2602 , which causes the propagation of magnetic fields  2612  to extend below hybrid retention and sensor shunt  2602 . In this case, sensor  2604  can detect the presence of magnetic fields  2612  and generate a signal indicating that lid  2610  is closed. In some embodiments, sensor  2604  can detect the presence of magnetic fields  2612  when lid  2610  is in near contact with body  2606 . For instance, if lid  2610  is at an angle of 0° when it is in contact with body  2606 , sensor  2604  can detect the presence of magnetic fields  2612  when lid  2610  is at an angle of less than 10°. That way, there is a greater tolerance for detecting when lid  2610  is closed. By using hybrid retention and sensor shunt  2602 , sensor  2604  can be placed vertically below shunt  2602  to detect the presence of a magnet that is positioned at a far distance that otherwise would not have been possible. This allows sensor  2604  to efficiently utilize the space already provided for hybrid retention and sensor shunt  2602 , without requiring the need for space elsewhere around body  2606  to be reserved for sensor  2604 . This configuration provides a more simple and elegant solution to a complex sensing and retention system. 
     E. Lid Hinge Design 
     As discussed herein with respect to  FIG. 20C , a case can include a spring-loaded hinge for opening and closing the lid. In some embodiments, the hinge can be a bistable hinge that has two stable states: an open state and a closed state. This means that the bistable hinge can have a neutral position where it does not pull to open or close the lid, but once the lid moves in one direction past the neutral position, the bistable hinge can either pull the lid open or pull the lid closed. Thus, the lid can close without requiring a large number of magnets to generate a high magnetic attraction force to close the lid.  FIGS. 27 and 28A-28C  illustrate an exemplary bistable hinge  2700 , according to some embodiments of the present disclosure. Specifically,  FIG. 27  is a perspective view illustration of bistable hinge  2700 , and  FIGS. 28A-28C  are cross-sectional view illustrations of the different states of bistable hinge  2700 . 
     As shown in  FIG. 27 , bistable hinge  2700  can be formed as part of a lid  2702  of a case. Bistable hinge  2700  can include several pivot points about which bistable hinge  2700  can move to effectuate bistable opening and closing of lid  2702 . As an example, bistable hinge  2700  can include a first pivot point  2704  along a first shaft  2706  that forms a first hinge about which bistable hinge  2700  rotates and a second pivot point  2708  along a second shaft  2710  that forms a second hinge about which bistable hinge  2700  rotates. The relative position between first shaft  2706  and second shaft  2710  can be fixed so that first shaft  2706  and second shaft  2710  are positioned a distance away from one another. An axis intersecting the first and second pivot points  2704  and  2708  can define the neutral position where bistable hinge  2700  does not pull in either direction to open or close lid  2702 , as will be discussed further herein with respect to  FIGS. 28A-28C . 
     In addition to first and second pivot points  2704  and  2708 , bistable hinge  2700  can also include a third pivot point  2712  along a third shaft  2714  that forms a third hinge about which a piston guide  2716  can rotate. Piston guide  2716  can rotate around third shaft  2714  to maintain a concentric alignment with a piston rod  2718  while piston guide  2716  moves up and down piston rod  2718 . Piston guide  2716  can have an inner diameter that is shaped as a tube to conform to the cylindrical shape of piston rod  2718 . A first end of piston rod  2718  can be coupled to second shaft  2710  so that piston rod  2718  can pivot around second pivot point  2704  as bistable hinge  2700  transitions between open and closed positions, and a second end of piston rod  2718  opposite from its first end can be attached to a stopper  2720 . Stopper  2720  can include a flange region  2722  that is annular in construction and is positioned around a portion of piston rod  2718  and perpendicular to an outer surface of piston rod  2718 . Stopper  2720  can make contact with a part of lid  2702  to prevent lid  2702  from moving past the open position, as will be discussed herein with respect to  FIG. 28C . 
     To generate the spring-loaded forces for the operation of bistable hinge  2700 , a spring  2721  can be implemented between piston guide  2716  and second pivot point  2708 . Spring  2721  can be a coil spring that is wound about a portion of piston rod  2718  so that it can apply force against piston guide  2716 . In certain instances, spring  2721  is conical where it is wider in one end and narrower in the opposite end so that spring  2721  can provide a linear force profile during transition between compressed and extended states. Strictly cylindrical springs can buckle when compressed to a certain extent, which would result in a non-linear force profile. In some embodiments, third shaft  2714  is fixed in position so that piston guide  2716  cannot move relative to lid  2702 . Thus, spring  2721  can generate force in a direction that is along an axis of piston rod  2718  but directed away from piston guide  2716 . The direction of this force, when compared to the axis formed by the first and second pivot points  2704  and  2708  can effectuate the bistable operation of hinge  2700 , as will be discussed further herein with respect to  FIGS. 28A-28C . 
       FIGS. 28A-28C  are simplified illustrations of the different positions of bistable hinge  2700 , according to some embodiments of the present disclosure. As discussed herein, bistable hinge  2700  can be in two stable states: an open state and a closed state. In the closed state, bistable hinge  2700  applies a pushing torsional force that presses the lid closed, whereas in the open state, bistable hinge  2700  applies a pulling torsional force that pulls the lid open. Between the open state and the closed state is a neutral position, where bistable hinge  2700  does not push or pull into either one of the open state or the closed state. Once the lid is nudged to the right or left, bistable hinge  2700  will then begin to push or pull the lid into one of the two states. In some embodiments, the farther the hinge is in each state, the greater the torsional force is applied to keep it in that state. 
       FIG. 28A  shows bistable hinge  2700  in a neutral position. The neutral position may be a position where bistable hinge  2700  does not push toward or pull into the closed or open state. The neutral position may be achieved when a direction of force  2802  (represented by an arrow) is aligned with a conversion axis  2804  (represented by a dashed line) defined by a line that intersects centers of first and second pivot points  2704  and  2708  where first and second shafts  2706  and  2710  are positioned, respectively as shown in  FIG. 28A . In this position, spring  2721  may be compressed  2813  while providing force  2802 , and lid  2702  may be at an angle of between 20° to 40°, such as 30°, with respect to horizontal. The direction of force  2802  is in-line with the axis of piston rod  2718  because spring  2721  is concentric to piston rod  2718 . Conversion axis  2804  may define the angle at which bistable hinge  2700  moves between the closed state and the opened state. 
     For instance, once bistable hinge  2700  tilts out of alignment with conversion axis  2804 , bistable hinge  2700  may begin to apply torsional force toward the direction in which it begins to tilt with increasing amounts of force as the angle between direction of force  2802  and conversion axis  2804  increases. As an example, if the lid begins to close, direction of force  2802  begins to angle away from conversion axis  2804  towards the left side of conversion axis  2804 , and bistable hinge  2700  begins to apply increasing amounts of torsional force  2806  to push the lid toward the closed state until bistable hinge  2700  reaches the closed state, as shown in  FIG. 28B . At this time, spring  2721  also begins to expand  2814  as it applies force  2802  to the left side of conversion axis  2804 . Bistable hinge  2700  may stop pushing once lid  2702  presses against the body of the case, such as when the lid is parallel (e.g., at an angle of 0°) with respect to a horizontal dimension. In this case, bistable hinge  2700  may be completely in the closed state. 
     Alternatively, if the lid begins to open from the neutral position, direction of force  2802  begins to angle away from conversion axis  2804  towards the right side of conversion axis  2804 , and bistable hinge  2700  begins to apply increasing amounts of torsional force  2808  to pull the lid toward the open state until bistable hinge  2700  reaches the opened state, as shown in  FIG. 28C . At this time, spring  2721  also begins to expand  2816  as it applies force  2802  to the right side of conversion axis  2804 . Bistable hinge  2700  may stop pulling once stopper  2720  presses against a seat  2810  formed in lid  2702 , e.g. when the lid is at an angle between 100° and 130°, such as 115°, with respect to the horizontal dimension. In this case, bistable hinge  2700  may be completely in the open state. 
     As can be appreciated herein, bistable hinge  2700  can include a pivot guiding structure  2812  coupled to the first shaft  2706  or both first and second shafts  2706  and  2710 . Pivot guiding structure  2812  can move independently from lid  2702  so that it can guide the bistable movement of hinge  2700 . For instance, pivot guiding structure  2812  can pivot around first shaft  2706  while second shaft  2710  slides along an outer surface of pivot guiding structure  2812  as bistable hinge  2700  transitions between opened and closed states, as shown in  FIGS. 28A-28C . 
     In some embodiments, bistable hinge  2700  may apply maximum amount of force when it is completely in the closed state or the open state, and gradually less amounts of force when approaching the neutral position. This may be because of the large angle between direction of force  2802  and conversion axis  2804  when in either of the states, and the smaller angles between force  2802  and conversion axis  2804  when approaching the neutral position. Thus, the most amount of resistance may be felt when pressing the lid to move out of either the closed state or the opened state, which achieves high quality user experience. 
       FIGS. 28D-28F  are simplified illustrations of an exemplary bistable hinge  2820  different from hinge  2700  in  FIG. 27  in that bistable hinge  2820  has a piston formed of a curved plate coupled to a rocker, according to some embodiments of the present disclosure. Specifically,  FIG. 28D  is a perspective view illustration of an exemplary bistable hinge  2820 . As shown, bistable hinge  2820  can include a pushplate  2826  and a rocker  2828  coupled between a first shaft  2822  and a second shaft  2824 . A first end of pushplate  2826  can be coupled to first shaft  2822  within a hinge block  2830 , which can protect the coupling joint between pushplate  2826  and first shaft  2822 , while a second end of pushplate  2826  opposite from the first end can be coupled to a first end of rocker  2828  via a third shaft  2832 . A second end of rocker  2828  opposite from its first end can then be coupled to second shaft  2824 . The combined movement of pushplate  2826  and rocker  2828  can effectuate the movement of bistable hinge  2820 . In some embodiments, pushplate  2826  can be constructed as a curved plate to provide clearance space for other components within the case, and can be coupled to a spring  2834  that provides the spring forces for opening and closing the bistable hinge. Pushplate  2826  can be a single structure that is pressed against spring  2834  such that spring  2834  moves in conjunction with pushplate  2826  for guiding the movement of bistable hinge  2820 . However, embodiments are not so limited. For instance, pushplate  2826  can be separated into two structures to allow spring  2834  to pivot freely with respect to pushplate  2826 , as shown in  FIG. 28E . 
       FIG. 28E  is a perspective view illustration of an exemplary pushplate  2836  constructed of a primary structure  2838  and a secondary structure  2840 . Third shaft  2832  can thread through both primary structure  2838  and secondary structure  2840  as shown. In some embodiments, secondary structure  2840  is set within a cutout region  2842  of primary structure  2838  so that portions of primary structure  2838  are positioned on opposite sides of secondary structure  2840 . In certain embodiments, secondary structure  2840  can move independently from primary structure  2838  so that spring  2834  can be decoupled from primary structure  2838 , thereby allowing spring  2834  to move independently from primary structure  2838 . This movement allows a modified torque curve that can provide a better user feel when opening and closing the lid. 
       FIG. 28F  is a cross-sectional view illustration of a case  2844  implemented with bistable hinge  2820  that includes pushplate  2826  and rocker  2828 , according to some embodiments of the present disclosure. Pushplate  2826  can be coupled to a body  2844  of case  2820  by way of hinge block  2830 . The curvature of pushplate  2826  can bend around internal components of case  2820  as shown in  FIG. 28F  before coupling to rocker  2828  via third shaft  2832 . Rocker  2828  can be positioned at an angle with respect to pushplate  2826  and can be coupled to a mounting structure  2846  that is affixed to a lid  2848  of case  2820 . Spring  2834  can contact, and be positioned between, pushplate  2826  and mounting structure  2846  so that forces applied by spring  2834  can press against pushplate  2826  to alter the angle between pushplate  2826  and rocker  2828  to open lid  2848 . Protrusions  2850  and  2852  extending from mounting structure  2846  and pushplate  2826 , respectively, can retain spring  2834  in position. 
     F. Straddle Battery Pack 
     As discussed herein, a case can include more than one battery pack for storing energy that can be later discharged to operate the case. For instance, the case can have two battery packs that are coupled together to provide twice as much energy storage than a single battery pack. In such instances, the two battery packs can be arranged to minimize occupied space so that the case can have a smaller size and/or more space can be utilized by other internal components. For instance, two battery packs can be positioned side-by-side and separated by a case substrate, such as a PCB, to minimize space. 
       FIGS. 29A-29C  illustrate configurations of an exemplary straddle battery pack  2900 , according to some embodiments of the present disclosure. Straddle battery pack  2900  can include two battery packs: a first battery pack  2902   a  and a second battery pack  2902   b , that can be oriented vertically and positioned side-by-side. To operate together, battery packs  2902   a - b  can be electrically coupled together via connection cables  2904  that can couple with a case substrate for providing power to operate the case. In some embodiments, battery packs  2902   a - b  can be separated by a gap  2906 , within which one or more components can be strategically positioned to minimize the footprint of battery packs  2902   a - b.    
     As an example, as shown in  FIG. 29B , a case substrate  2908  mounted with a plurality of electronic devices  2910  can be positioned between first and second battery packs  2902   a - b  within gap  2906 . To provide power to operate the case, connection cables  2904  can couple battery packs  2902   a - b  to case substrate  2908 . By sandwiching case substrate  2908  between two battery packs, the overall footprint of the module can be small enough to be tucked away in a small region of the case. As an example shown in  FIG. 29C , battery packs  2902   a - b  can be tucked in the space between bowls  2912   a - b  of an inner frame  2914  for a case. That way, battery packs  2902   a - b  can provide ample power storage while taking up minimal space within the case. 
     G. Case as a One-Handed Applicator 
       FIG. 30  depicts a simplified plan view of a case  3000  for a pair of wireless listening devices according to some embodiments of the disclosure. As shown in  FIG. 30 , case  3000  includes a housing  3005  having one or more cavities  3010   a  and  3010   b  configured to receive a pair of wireless listening devices  3015   a  and  3015   b . In some embodiments, cavities  3010   a  and  3010   b  can be positioned adjacent to each other on opposite sides of a center plane of case  3000 . Each cavity  3010   a  and  3010   b  can be sized and shaped to match that of its respective listening device  3015   a  and  3015   b . Each cavity can include a stem section  3016   a  and  3016   b  and a bud section  3017   a  and  3017   b . Each stem section  3016   a  and  3016   b  can be an elongated generally cylindrical cavity that extends from its respective bud section  3017   a  and  3017   b  towards a bottom  3006  of case  3000 . Each bud section  3017   a  and  3017   b  can be offset from its respective stem section  3016   a  and  3016   b  and open at an upper surface  3008  of housing  3005 . Embodiments of the disclosure are not limited to any particular shape, configuration or number of cavities  3010   a  and  3010   b  and in other embodiments cavities  3010   a  and  3010   b  can have different shapes to accommodate different types of listening devices, different configurations and/or can be a single cavity or more than two cavities. 
     Case  3000  further includes a lid  3020  attached to housing  3005 . Lid  3020  is operable between a closed position where lid  3020  is aligned over one or more cavities  3010   a  and  3010   b  fully enclosing pair of listening devices  3015   a  and  3015   b  within the housing, and an open position where the lid is displaced from the housing and cavities  3010   a  and  3010   b  such that a user can remove the listening devices from the cavities or replace the listening devices within the cavities. Lid  3020  can be pivotably attached to housing  3005  and can include a magnetic or mechanical system (not shown in  FIG. 30 ) that provides lid  3020  with a bi-stable operation, as described more fully below. Case  3000  can also include a charging system  3025  configured to charge pair of listening devices  3015   a  and  3015   b . Charging system  3025  can make electrical contact with external contacts of pair of listening devices  3015   a  and  3015   b  to provide power to listening devices  3015   a  and  3015   b.    
     According to some embodiments of the present disclosure, case  3000  can be configured as a one-handed applicator that can eject one or both listening devices  3015   a  and  3015   b  with one hand without having to have one hand hold the case and the other hand pull listening devices  3015   a  and  3015   b  out of case  3000 . As an example, case  3000  can include an ejection feature  3022  that can be configured to slide upwards to eject one or both listening devices  3015   a  and  3015   b . In some embodiments, ejection feature  3022  can be formed of a frame that includes an engaging portion  3026  that is positioned below listening devices  3015   a  and  3015   b  so that when ejection feature  3022  is slid upwards, engaging portion  3026  can press upward against one or both listening devices  3015   a  and  3015   b  to eject one or both simultaneously. Ejection feature  3022  can also include an activation portion  3028  that is exposed on a side surface of case  3000  so that a user can use his or her finger to activate ejection feature  3022 . In some embodiments, activation portion  3028  can include two parts, one positioned on opposite sides of case  3000  to allow flexibility in activating ejection feature  3022 . Case  3000  can also include tracks (not shown) on the side surfaces of case  3000  to allow activation portion  3028  to move up and down. In some additional and alternative embodiments, activation portion  3028  can be a button that is pressed or a switch that is flipped instead of a sliding feature to activate ejection feature  3022 . It is to be appreciated that any suitable type of activation feature can be envisioned herein without departing from the spirit and scope of the present disclosure. 
     Although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.

Metadata:
Filing Date: 20190926
Publication Date: 20211221
Grant Date: 20211221
Priority Date: 20180928
Inventors: Ji, Qigen
ZHU, HAO
SANG, Haochuan
COUSINS, Benjamin A.
WU, Meiting
Assignee: APPLE INC
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Family ID: 69945307