Patent Publication Number: US-2022217463-A1

Title: Wireless listening device

Description:
This application is claims the benefit of U.S. Provisional Patent Application No. 63/134,922, filed Jan. 7, 2021, entitled “WIRELESS LISTENING DEVICE,” and claims the benefit of U.S. Provisional Patent Application No. 63/165,991, filed Mar. 25, 2021, entitled “WIRELESS LISTENING DEVICE.” Each of the &#39;922 and &#39;991 applications are hereby incorporated by reference herein in their entirety for all purposes. 
     This application is related to concurrently filed U.S. Non-provisional patent application Ser. No. ______, “WIRELESS LISTENING DEVICE”, (Attorney Docket No. 090911-P52724US2-1267809), which is incorporated herein by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     Portable listening devices, such as headphones, 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. Relatively recently, wireless portable listening devices that do not include a cable and instead, wirelessly receive a stream of audio data from a wireless audio source, have become ubiquitous. Such wireless portable listening devices can include, for instance, wireless earbud devices or wireless 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 portable listening devices have many advantages over wired portable listening devices and have become a very popular with consumers, improved wireless portable listening devices are desirable. 
     BRIEF SUMMARY 
     The present disclosure describes various embodiments of portable listening devices that can enable a user to experience high-end acoustic performance and a pleasant, positive user experience. 
     In some embodiments an earphone comprises: a device housing that defines an internal cavity within the device housing; an acoustic port formed through a wall of the device housing and having an opening at an exterior surface of the device housing; an audio driver disposed within the device housing and aligned to emit sound through the acoustic port; and a mesh disposed within the acoustic port and having an outer periphery spaced apart from the device housing wall, wherein the mesh forms a portion of an exterior surface of the earphone that is recessed from the opening at the exterior surface of the device housing. 
     In some embodiments, a portable acoustic device is provided that comprises: a device housing that defines an internal cavity within the device housing, the device housing comprising a speaker housing portion and a stem portion extending away from the speaker housing portion, wherein the speaker housing portion and stem portion combine to define the internal cavity within the device housing; an acoustic port formed through a wall of the device housing and having an opening at an exterior surface of the device housing, wherein the wall includes first and second edges separated by a shelf that extends fully around a perimeter of the acoustic port; an audio driver disposed within the device housing and aligned to emit sound through the acoustic port; and a mesh disposed within the acoustic port and having an outer periphery spaced apart from the device housing wall, wherein the mesh forms a portion of an exterior surface of the portable acoustic device that is recessed from the opening at the exterior surface of the speaker housing. 
     In still further embodiments a portable acoustic device is provided that comprises: a device housing that defines an internal cavity within the device housing, the device housing comprising a speaker housing portion and a stem portion extending away from the speaker housing portion, wherein the speaker housing portion and stem portion combine to define the internal cavity within the device housing; a wireless antenna disposed within the housing; an acoustic port formed through a wall of the device housing and having an opening at an exterior surface of the device housing, wherein the wall includes first and second edges separated by a shelf that extends fully around a perimeter of the acoustic port; an audio driver disposed within the device housing and aligned to emit sound through the acoustic port; a battery disposed within the housing; and a mesh disposed within the acoustic port and having an outer periphery spaced apart from the device housing wall, wherein the mesh forms a portion of an exterior surface of the portable wireless acoustic device that is recessed from the opening at the exterior surface of the device housing. 
     In some embodiments, a portable wireless acoustic device comprises: a device housing that defines an internal cavity, the device housing comprising a speaker housing portion and a stem portion extending away from the speaker housing portion; a first acoustic port formed through a wall of the speaker housing; an audio driver disposed within the speaker housing portion and aligned to emit sound through the acoustic first port; a battery disposed within the speaker housing portion and positioned an opposite side of the audio driver than the acoustic port; an antenna disposed in the stem; a user input region disposed along the stem; and a system in a chip disposed in the stem, the system in a chip comprising: a processor that controls operation of the portable wireless acoustic device, charging circuitry, an accelerometer, a wireless communication controller, support components for the antenna and support components for the user input region. 
     In some further embodiments a portable wireless acoustic device includes: a device housing defining an internal cavity; an acoustic port formed through the device housing; an audio driver disposed within the device housing and aligned to emit sound through the acoustic port; one or more electronic components that require power to operate; a battery disposed within the device housing and operable to provide power to the one or more electronic components, the battery having an exterior surface and including first and second electrical interconnects extending away from the exterior surface and configured to enable the battery to be operatively coupled to the one or more electronic components; and a hydrophobic coating deposited over an entire exterior surface of the battery except for the first and second electrical interconnects. 
     In still further embodiments, an earphone comprises: a device housing including a speaker housing that defines an internal cavity within the device housing; an acoustic port formed through the device housing; an audio driver disposed within the device housing and aligned to emit sound through the acoustic port, wherein the audio driver cooperates with an inner surface of the speaker housing to define a front volume within the device housing for the audio driver that is sealed to an ambient environment except for a free flowing air path to the ambient environment through the acoustic port; a microphone disposed within the front volume of the device housing; and a processor operatively coupled to receive output from the microphone, the processor configured to change an audio profile of the audio driver based on output from the microphone. 
     Various implementations of an earphone or portable acoustic device described herein can include one or more of the following features. The mesh can be recessed within the acoustic port between 0.5 to 2.0 mm from an opening at the exterior surface of the device housing. The mesh can have a convex profile in which outer edges of the mesh are recessed further from the opening at the exterior surface of the housing than a center of the mesh. The wall can include first and second edges separated by a shelf that extends fully around a perimeter of the acoustic port. The shelf can define an acoustic dead zone that surrounds an outer periphery of acoustic port and the outer periphery of the mesh is disposed within the acoustic dead zone. The mesh can be a multi-layer mesh that includes an outer cosmetic mesh and an inner acoustic mesh. The device housing can include a speaker housing and a stem extending away from the speaker housing. The speaker housing and the stem can combine to define the internal cavity within the device housing. The earphone or portable acoustic device can include a user input region along a portion of the stem. The earphone or portable acoustic device can include a force sensor disposed within the stem adjacent to the user input region. The earphone or portable acoustic device can include an antenna disposed within the stem. The earphone or portable acoustic device can further include a bass port formed through the housing and configured to provide an acoustic pathway from the driver that allows air to flow easier within the acoustic pathway for low frequency sounds, and a control leak formed through the housing and configured to provide an atmospheric pass-through between an outside environment and the acoustic port such that, when the earphone or portable acoustic device is worn by a user, the housing does not completely seal a user&#39;s ear canal and trap pressure within the ear canal. 
     Various implementations of an earphone or acoustic device described herein can include one or more of the following features. The device can include a second port formed through a surface of the device housing that faces a user&#39;s ear when the portable wireless acoustic device is worn by the user. The device can include an optical sensor operatively coupled to the second port. The optical sensor can include an emitter that emits radiation of a first wavelength and of a second wavelength, different than the first wavelength, through the second port and a detector operable to detect radiation of the first and second wavelength after the radiation is reflected off the user&#39;s ear where the first and second wavelengths have different frequency dependences on human skin. The processor can be operatively coupled to receive output from the detector, and can be configured to calculate a ratio of detected radiation of the first wavelength to detected radiation of the second wavelength and generate an in-ear detect signal based on the calculated ratio being within a predetermined range. The device can further include an accelerometer and the processor can generate the in-ear detect signal based on a combination of a signal output by the accelerometer and the calculated ratio of detected radiation of the first wavelength to detected radiation of the second wavelength. The speaker housing portion can include a front volume acoustically separated from a back volume where the front volume is disposed between the audio driver and the first acoustic port and the back volume being disposed behind the audio driver. The battery can be disposed within the back volume and can have an exterior surface along with first and second electrical interconnects extending away from the exterior surface that enable the battery to be operatively coupled to the one or more electronic components within the device housing. The battery can have a hydrophobic coating deposited over an entire exterior surface of the battery except for the first and second electrical interconnects. The hydrophobic coating can be a type N parylene. The hydrophobic coating can be between 15-30 microns thick. The battery can further include a second hydrophobic coating sprayed over the first coating in a portion of the battery facing the back volume. The second hydrophobic coating can be a fluorochemical acrylic polymer. The audio driver can cooperate with an inner surface of the speaker housing to define a front volume within the speaker housing portion for the audio driver that is sealed to an ambient environment except for a free flowing air path to the ambient environment through the first acoustic port. The earphone or acoustic device can further include a microphone disposed within the front volume of the device housing. The processor can be operatively coupled to receive output from the microphone and can be configured to change an audio profile of the audio driver based on output from the microphone. The speaker housing can be sized and shaped to fit within a user&#39;s ear without any portion of the earphone being inserted into the user&#39;s ear canal. The microphone can be tuned to listen to low frequencies in the front volume that are indicative of a quality of fit of the earphone in a user&#39;s ear, and the processor can be configured to adjust the audio settings of the audio driver based on the output from the microphone. The processor can be configured to boost low frequency sound generated by the audio driver if the processor determines that the speaker housing forms a poor seal in a user&#39;s ear. 
     To better understand the nature and advantages of the present invention, reference should be made to the following description and the accompanying figures. It is to be understood, however, that each of the figures is provided for the purpose of illustration only and is not intended as a definition of the limits of the scope of the present invention. Also, as a general rule, and unless it is evident to the contrary from the description, where elements in different figures use identical reference numbers, the elements are generally either identical or at least similar in function or purpose. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  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; 
         FIG. 2  is a simplified block diagram of various components of a portable wireless listening system according to some embodiments; 
         FIGS. 3A-3C  are simplified views of a portable wireless earbud according to some embodiments; 
         FIG. 3D  is a simplified partial cross-sectional view of a speaker housing that illustrates the placement of select components within the earbud depicted in  FIGS. 3A-3C  according to some embodiments; 
         FIG. 3E  is a simplified perspective view of a battery having a hydrophobic coating formed thereon according to some embodiments; 
         FIG. 3F  is a simplified perspective view of an optical sensor according to some embodiments; 
         FIG. 3G  is a simplified cross-sectional view of the optical sensor shown in  FIG. 3F ; 
         FIGS. 3H and 3I  are simplified cross-sectional views of the optical sensor shown in  FIGS. 3E and 3F  illustrating the fields of view of the light emitters and photodetector in the sensor according to some embodiments; 
         FIG. 4A  is a simplified side view of the earbud depicted in  FIGS. 3A-3C ; 
         FIG. 4B  is a simplified cross-sectional view of the earbud depicted in  FIG. 4A  taken through a portion of the earbud stem; 
         FIG. 4C  is a simplified exploded view of various components positioned within the stem portion of an earbud according to some embodiments; 
         FIG. 5A  is a simplified partial view of the earbud depicted in  FIGS. 3A-3C  (without the stem) looking towards an acoustic port; 
         FIG. 5B  is a simplified cross-sectional view of the earbud shown in  FIG. 5A  taken through the acoustic port; 
         FIG. 5C  is a simplified illustration of a speaker housing portion of an earbud that includes a multilayer mesh having a convex profile according to some embodiments; 
         FIG. 5D  is a simplified exploded view of the multilayer mesh shown in  FIG. 5C  according to some embodiments; 
         FIG. 5E  depicts two separate cross-sections of the multilayer mesh shown in  FIGS. 5C and 5D  taken through lines A-A and lines B-B shown in  FIG. 5C , respectively; 
         FIGS. 6A-6C  are simplified plan views of a charging case that can store a pair of earbuds, such as the earbuds depicted in  FIGS. 3A-3C , according to some embodiments; 
         FIG. 7A  is a simplified exploded view of various components that make up a lid enclosure sub-assembly that can be assembled together to form a lid of the charging case depicted in  FIGS. 6A-6C  according to some embodiments; 
         FIG. 7B  illustrates a bistable hinge according to some embodiments that can be incorporated into a charging case, such as the charging case depicted in  FIGS. 6A-6C ; 
         FIG. 7C  is a simplified perspective view of a bi-stable hinge according to additional embodiments that can be incorporated into a charging case, such as the charging case depicted in  FIGS. 6A-6C ; 
         FIG. 8  is a simplified exploded view of various components that make up an insert sub-assembly that can be assembled together to form an interior portion of the charging case depicted in  FIGS. 6A-6C ; 
         FIG. 9  is a simplified exploded view of various components that make up a skeleton sub-assembly that can form an interior portion of the charging case depicted in  FIGS. 6A-6C ; 
         FIG. 10A  is a simplified exploded view of various components that make up a coil sub-assembly that can be attached to the skeleton sub-assembly shown in  FIG. 9  according to some embodiments; 
         FIG. 10B  is a simplified illustration of a wireless power charging device that can wirelessly provide power to the charging case depicted in  FIGS. 6A-6C  according to some embodiments; 
         FIG. 10C  is a simplified perspective view of a charging case according to some embodiments positioned on a wireless charger during a charging operation; 
         FIG. 10D  is a simplified top view illustration of a wireless charger showing the position of magnets disposed within a charging case according to some embodiments with respect to a magnetic array of the wireless charger; 
         FIG. 10E  is a simplified cross-sectional view in the region C-C shown in  FIG. 10C ; 
         FIG. 11  is a simplified exploded view of various components that make up a bottom enclosure sub-assembly of the charging case depicted in  FIGS. 6A-6C  according to some embodiments; and 
         FIG. 12  is a simplified exploded view of the subassemblies  700 ,  800 ,  900 ,  1000  and  1100  arranged together according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the disclosure pertain to a portable wireless listening that can deliver high-end acoustic performance to a user along with a pleasant and intuitive user experience. Other embodiments pertain to a case for charging and storing one or more portable wireless listening devices. Still other embodiments pertain to a system that includes both a pair of portable wireless listening devices and a charging case for the devices. 
     As used herein, the term “portable listening device” includes any portable device configured to be worn by a user and placed such that a speaker of the portable listening device is adjacent to or in a user&#39;s ear. A “portable wireless listening device” is a portable listening device that is able to receive and/or send streams of audio data from or to a second device without a wire connecting the portable wireless listening device to the second device using, for example, a wireless communication protocol. 
     Headphones are one type of portable listening device, headsets (a combination of a headphone and an attached microphone) are another and hearing aids (in-ear devices that are designed to augment sounds from the surrounding environment to improve a user&#39;s hearing) are still an additional type of portable listening device. 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 earcups connected to each other by a headband, and earphones (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 “earphones”, which can also be referred to as ear-fitting headphones, includes both small headphones, sometimes referred to as “earbuds”, 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 canal phones, that are inserted in the ear canal itself. Thus, earphones can be another type of portable listening device that are configured to be positioned substantially within a user&#39;s ear. 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. 
     Example Wireless Listening System 
       FIG. 1  is an example of a wireless listening system  100  according to some embodiments. System  100  can include a host device  110 , a pair of portable wireless listening devices  130  and a charging case  150 . Host device  110  is depicted in  FIG. 1  as a smart phone but can be any electronic device that can transmit audio data to portable listening device  130 . Other, non-limiting examples of suitable host devices  110  include a laptop computer, a desktop computer, a tablet computer, a smart watch, an audio system, a video player, and the like. 
     As depicted graphically in  FIG. 1 , host device  110  can be wirelessly communicatively coupled with portable wireless listening devices  130  and charging case  150  through wireless communication links  160  and  162 . Similarly, portable wireless listening devices  130  can be communicatively coupled to charging case  150  via wireless communication link  164 . Each of the wireless communication links  160 ,  162  and  164  can be a known and established wireless communication protocol, such as a Bluetooth protocol, a WiFi protocol, or any other acceptable protocol that enables electronic devices to wirelessly communicate with each other. Thus, host device  110  can exchange data directly with portable wireless listening devices  130 , such as audio data, that can be transmitted over wireless link  160  to wireless listening devices  130  for play back to a user, and audio data that can be received by host device  110  as recorded/inputted from microphones in the portable wireless listening devices  130 . Host device  110  can also be wirelessly communicatively coupled with charging case  150  via wireless link  162  so that the host device  110  can exchange data with the charging case, such as data indicating the battery charge level data for case  150 , data indicating the battery charge level for portable wireless listening devices  130 , data indicating the pairing status of portable wireless listening devices  130 . 
     Portable wireless listening devices  130  can be stored within case  150 , which can protect the devices  130  from being lost and/or damaged when they are not in use and can also provide power to recharge the batteries of portable wireless listening devices  230  as discussed below. In some embodiments portable wireless listening devices  130  can also be wirelessly communicatively coupled with charging case  150  via wireless link  164  so that, when the devices are worn by a user, audio data from case  150  can be transmitted to portable wireless listening devices  130 . As an example, charging case  150  can be coupled to an audio source different than host device  110  via a physical connection, e.g., an auxiliary cable connection. The audio data from the audio source can be received by charging case  150 , which can then wirelessly transmit the data to wireless listening devices  130 . That way, a user can hear audio stored on or generated by an audio source by way of wireless listening devices  130  even though the audio source does not have wireless audio output capabilities. 
     According to some embodiments, each individual portable wireless listening device  130  can include a housing  132  formed of a body  134  and a stem  136  extending from body  134 . Housing  132  can be formed of a monolithic outer structure. Body  134  can include an internally facing microphone  138  and an externally facing microphone  140  for purposes discussed herein. Externally facing microphone  140  can be positioned within an opening defined by portions of body  134  and stem  136 . By extending into both body  134  and stem  136 , microphone  140  can be large enough to receive sounds from a broader area around the user. In some embodiments, housing  132  can define an acoustic port  142  that can direct sound from an internal audio driver out of housing  132  and into a user&#39;s ear canal. In other embodiments, portable wireless listening devices  130  can include a deformable eartip that can be inserted into a user&#39;s ear canal enabling the wireless listening devices to be configured as in-ear hearing devices. 
     In the depicted embodiment, stem  136  has a substantially cylindrical construction along with a planar region  144  that does not follow the curvature of the cylindrical construction. Planar region  144  can indicate an area where the wireless listening device is capable of receiving user input. For instance, in some embodiments user input can be inputted by squeezing stem  136  at planar region  144 . In some embodiments, planar region  144  can include a touch sensitive surface in addition to or instead of pressure sensing capabilities, that allow a user to input touch commands, such as contact gestures. Stem  136  can also include electrical contacts  146 ,  148  for making contact with corresponding electrical contacts in charging case  150 , as will be discussed further herein. 
     As will be appreciated herein, portable wireless listening devices  130  can include several features can enable the devices to be comfortably worn by a user for extended periods of time and even all day. Housing  132  can be shaped and sized to fit securely between the tragus and anti-tragus of a user&#39;s ear so that the portable listening device is not prone to falling out of the ear even when a user is exercising or otherwise actively moving. Its functionality can also enable wireless listening devices  130  to provide an audio interface to host device  110  so that the user may not need to utilize a graphical interface of host device  110 . In other words, wireless listening devices  130  can be sufficiently sophisticated that they can enable the user to perform day-to-day operations from host device  110  solely through interactions with wireless listening devices  130 . This can create further independence from host device  110  by not requiring the user to physically interact with, and/or look at the display screen of, host device  110 , especially when the functionality of wireless listening devices  130  is combined with the voice control capabilities of host device  110 . Thus, wireless listening devices  130  can enable a true hands free experience for the user. 
       FIG. 2  is a simplified block diagram of various components of a wireless listening system  200  according to some embodiments that includes a host device  210 , a pair of portable wireless listening devices (PWLDs)  230  (e.g., a right PWLD  230  and a left PWLD  230 ) and a charging case  250 . System  200  can be representative of system  100  shown in  FIG. 1  and host device  210 , portable wireless listening devices  230  and charging case  250  can be representative of host device  110 , portable wireless listening devices  130  and charging case  150 , respectively. Each portable wireless listening device  230  can receive and generate sound to provide an enhanced user interface for host device  210 . For convenience, the discussion below refers to a single portable wireless listening device  230 , but it is to be understood that, in some embodiments, a pair of portable listening devices can cooperate together for use in a user&#39;s left and right ears, respectively, and each portable wireless listening device in the pair can include the same or similar components. 
     Portable wireless listening device  230  can include a computing system  231  that executes computer-readable instructions stored in a memory bank (not shown) for performing a plurality of functions for portable wireless listening device  230 . Computing system  231  can be one or more suitable computing devices, such as microprocessors, computer processing units (CPUs), digital signal processing units (DSPs), field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs) and the like. 
     Computing system  231  can be operatively coupled to a user interface system  232 , communication system  234 , and a sensor system  236  for enabling portable wireless listening device  230  to perform one or more functions. For instance, user interface system  232  can include a driver (e.g., speaker) for outputting sound to a user, one or more microphones for inputting sound from the environment or the user, one or more LEDs for providing visual notifications to a user, a pressure sensor or a touch sensor (e.g., a resisitive or capacitive touch sensor) for receiving user input, and/or any other suitable input or output device. Communication system  234  can include wireless and wired communication components for enabling portable wireless listening device  230  to send and receive data/commands from host device  210 . For example, in some embodiments communication system  234  can include circuitry that enables portable wireless listening device  230  to communicate with host device  210  over wireless link  260  via a Bluetooth or other wireless communication protocol. In some embodiments communication system  234  can also enable portable wireless listening device  230  to wirelessly communicate with charging case  250  via wireless link  264 . Sensor system  236  can include proximity sensors (e.g., optical sensors, capacitive sensors, radar, etc.), accelerometers, microphones, and any other type of sensor that can measure a parameter of an external entity and/or environment. 
     Portable wireless listening device  230  can also include a battery  238 , which can be any suitable energy storage device, such as a lithium ion battery, capable of storing energy and discharging stored energy to operate portable wireless listening device  230 . The discharged energy can be used to power the electrical components of portable wireless listening device  230 . In some embodiments, battery  238  can be a rechargeable battery that enables the battery to be repeatedly charged as needed to replenish its stored energy. For instance, battery  238  can be coupled to battery charging circuitry (not shown) that is operatively coupled to receive power from charging case interface  239 . Case interface  239  can, in turn, electrically couple with earbud interface  252  of charging case  250 . In some embodiments, power can be received by portable wireless listening device  230  from charging case  250  via electrical contacts within case interface  239 . In some embodiments, power can be wirelessly received by portable wireless listening device  230  via a wireless power receiving coil within case interface  239 . 
     Charging case  250  can include a battery  258  that can store and discharge energy to power circuitry within charging case  250  and to recharge the battery  238  of portable wireless power listening device  230 . As mentioned above, in some embodiments circuitry within earbud interface  252  can transfer power to portable wireless listening device  230  through a wired electrical connection between contacts in charging case  250  that are electrically coupled to contacts in portable wireless listening device  250  to charge battery  238 . While case  250  can be a device that provides power to charge battery  238  through a wired interface with device  230  in some embodiments, in other embodiments case  250  can provide power to charge battery  238  through a wireless power transfer mechanism instead of or in addition to a wired connection. For example, earbud interface can include a wireless power transmitter coil that can couple with a wireless power receiving coil within portable wireless listening device  230 . 
     Charging case  250  can also include a case computing system  255  and a case communication system  251 . Case computing system  255  can be one or more processors, ASICs, FPGAs, microprocessors, and the like for operating case  250 . Case computing system  255  can be coupled to earbud interface  252  and can control the charging function of case  250  to recharge batteries  238  of the portable wireless listening devices  230 , and case computing system  255  can also be coupled to case communication system  251  for operating the interactive functionalities of case  250  with other devices, including portable wireless listening device  230 . In some embodiments, case communication system  251  includes a Bluetooth component, or any other suitable wireless communication component, that wirelessly sends and receives data with communication system  234  of portable wireless listening device  230 . Towards this end, each of charging case  250  and portable wireless listening device  230  can include an antenna formed of a conductive body to send and receive such signals. Case  250  can also include a user interface  256  that can be is operatively coupled to case computing system  255  to alert a user of various notifications. For example, the user interface can include a speaker that can emit audible noise capable of being heard by a user and/or one or more LEDs or similar lights that can emit a light that can be seen by a user (e.g., to indicate whether the portable listening devices  230  are being charged by case  250  or to indicate whether case battery  258  is low on energy or being charged). 
     Host device  210 , to which portable wireless listening device  230  is an accessory, can be a portable electronic device, such as a smart phone, tablet, or laptop computer. Host device  210  can include a host computing system  212  coupled to a battery  214  and a host memory bank  134  containing lines of code executable by host computing system  212  for operating host device  210 . Host device  210  can also include a host sensor system  215 , e.g., accelerometer, gyroscope, light sensor, and the like, for allowing host device  210  to sense the environment, and a host user interface system  216 , e.g., display, speaker, buttons, touch screen, and the like, for outputting information to and receiving input from a user. Additionally, host device  210  can also include a host communication system  218  for allowing host device  210  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  218  can also communicate with communication system  234  in portable wireless listening device  230  via a wireless communication link  262  so that host device  210  can send audio data to portable wireless listening device  230  to output sound, and receive data from portable wireless listening device  230  to receive user inputs. The communication link  262  can be any suitable wireless communication line such as Bluetooth connection. By enabling communication between host device  210  and portable wireless listening device  230 , wireless listening device  230  can enhance the user interface of host device  210 . 
     Earbuds 
     Portable wireless devices according to some embodiments can include a number of different features that provide a user with improved audio quality and a superior user experience as compared to many previously known portable wireless devices. To illustrate and explain some such features, reference is made to  FIGS. 3A-3C , which are simplified views of a wireless earbud  300  according to some embodiments. Specifically,  FIG. 3A  is a simplified plan view of a first side of earbud  300 ,  FIG. 3B  is a simplified plan view of a second side, opposite the first side of earbud  300 , and  FIG. 3C  is a simplified top view of earbud  300 . 
     Earbud Housing 
     Earbud  300  includes a housing  302  that can be made from, for example, a hard radio frequency (RF) transparent plastic such as acrylonitrile butadiene styrene (ABS) or polycarbonate. In some embodiments, housing  302  can be made from one or more components that can be bonded together (e.g,. with tongue and groove joints and an appropriate adhesive) to form a monolithic housing structure with a substantially seamless appearance. Housing  302  forms a shell that defines an internal cavity in which the various components of earbud  300  are housed. As depicted housing  302  can include two primary sections: a speaker housing  310  and a stem  312  that protrudes away from the speaker housing at an angle. As discussed below, the cavity portion within speaker housing  310  can hold an audio driver and battery while the cavity portion within stem  312  can hold a primary circuit board and other electronics. In some embodiments, stem  312  can also include electrical contacts  322 ,  324  at the distal tip of the stem. Electrical contacts  322 ,  324  provide a physical interface that can be electrically coupled with corresponding electrical contacts in a corresponding charging case (e.g., charging case  150 ). It is to be understood that embodiments are not limited to the particular shape and format of the housing  302  depicted in  FIGS. 3A-3C . For example, in some embodiments the housing does not include a stem or similar structure and in some embodiment an anchor or other structure can be attached to or extend away from the housing to further secure the earbud to a feature of the user&#39;s ear. 
     Earbud  300  can be configured to have an open, unsealed acoustic architecture that is sometimes referred to as a “leaky acoustic architecture”. That is, in some embodiments earbud  300  does not include a deformable eartip that is included on canal phones and that is configured to be inserted into a user&#39;s ear canal to form an airtight seal between the eartip and the user&#39;s ear. Instead, speaker housing  310  can be sized and shaped to fit within a user&#39;s ear without being inserted into the ear canal and all acoustic air volumes within earbud  300  have a free flowing air path to the ambient. 
     Speaker housing  310  is the primary support mechanism for earbud  300  when the earbud is positioned within a user&#39;s ear and speaker housing  310  can be shaped to rest between a user&#39;s tragus and anti-tragus without putting unwanted pressure on the crus helix, which could lead to a source of discomfort when the earbud is engaged in a user&#39;s ear for a long period of time. Towards this end, speaker housing  310  is contoured to allow the speaker housing portion to sit deep within the space between the tragus and anti-tragus of a user&#39;s ear to form a pseudo seal (sometimes referred to as a passive seal) between the housing and user&#39;s ear even though earbud  300  is not a canal phone and does not include a deformable eartip that is inserted into the user&#39;s ear canal. The pseudo seal allows earbud  300  to have improved audio quality compared to other leaky architecture earbuds without creating potential pressure build-up within a user&#39;s ear that can be created by earbuds with deformable eartips and that some user&#39;s find uncomfortable. 
     Speaker housing  310  is further contoured such that certain surfaces of the housing are not in contact with any portion of an average user&#39;s ear. These non-contact portions provide locations for various features of earbud  300  including a primary acoustic port  314 , a base port  316  and a control leak  318 . Acoustic port  314  provides an acoustic pathway for sound generated by a driver (not shown in  FIGS. 3A-3C ) within speaker housing  310  to reach a user&#39;s ear canal. When earbud  300  is inserted in a user&#39;s ear, acoustic port  314  is positioned at a location that is generally not in physical contact with the user&#39;s ear and adjacent to but spaced slightly apart from the user&#39;s ear canal. In some embodiments acoustic port  314  can be covered by an acoustic membrane and mesh as described below. 
     Base port  316  can be an opening in speaker housing  310  that provides an acoustic pathway from the driver that 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, bass port  316  can provide an opening for the air to easily move out to, and be drawn in from, the atmosphere, thereby allowing earbud  300  to provide higher quality bass notes. Tuned bass port  316  can be configured to achieve a certain rate of airflow when the driver is operating. This rate of air flow can be altered by the shape and size of tuned bass port  316 , which can be tuned in various ways according to design. As depicted in  FIG. 3B , base port  316  can be positioned at a location that is generally not in physical contact with a user&#39;s ear when earbud  300  is worn. 
     Earbud  300  can also include a control leak  318  positioned at a location that is generally not in physical contact with a user&#39;s ear. Control leak  318  can be an opening within speaker housing  310  that allows air to flow out of housing  302 . However, the result achieved by releasing the air out of housing  302  through the control leak  318  can be different from the result achieved by bass port  316 . For instance, instead of improving bass sound quality, control leak  318  can provide an atmospheric pass-through between an outside environment and acoustic port  314  when earbud  300  is worn by a user so that speaker housing  310  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. Like bass port  316 , control leak  318  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  318 , which can be tuned in various ways according to design. Towards this end, control leak  318  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. It is to be appreciated that the specific positions of bass port  316  and control leak  318  can be chosen to minimize occlusion and acoustic coupling with other internal components. Also, in some embodiments control leak  318  and/or bass port  316  can be covered by an appropriate mesh to prevent moisture and contaminants from entering the internal cavity of speaker housing  310 . 
     Earbud  300  can also include an optical sensor  320  that can be used to determine when the eartip has been inserted into an ear canal. Optical sensor  320  can be strategically positioned at a location along housing  302  that is likely to be in contact with or directly facing an inner surface of the average user&#39;s ears when the earbuds are worn by the user. In this manner, optical sensor  320  can be used, sometimes in conjunction with other sensors, to determine whether earbud  300  is worn by a user and positioned within the user&#39;s ear as discussed in more detail below. In some embodiments optical sensor  320  can be positioned behind an optically transparent window  328  that is positioned along speaker housing  310 . 
     Battery 
       FIG. 3D  is a partial cross-section of speaker housing  310  that illustrates the placement of select components within earbud  300 . Specifically shown in  FIG. 3D  are audio driver  330  and battery  340  along with internal walls  350  and  356  that divide the interior portion of speaker housing  310  forming a front volume  352  and a back volume  354  for audio driver  330 . Wall  356  further separates the back volume  354  from a non-acoustic volume  358  that extends from behind battery  340  within speaker housing  310  into the stem  312 . 
     The embodiment depicted in  FIG. 3D , does not include a wall that separates battery  340  from audio driver  330 . Eliminating the wall allows battery  340  to be increased in size (and thus store more energy, which in turn enables earbud  300  to be powered for longer use times) but places battery  340  in the back volume  354  of driver  330  potentially exposing the battery to moisture ingress from the ambient (e.g., port  316  couples back volume  354  to the ambient). To protect the battery from potential corrosion, embodiments can coat battery  340  with a hydrophobic coating, such as parylene coating.  FIG. 3E  is a simplified perspective view of battery  340  having hydrophobic coating  342  formed thereon. In some particular embodiments, a type N parylene coating between 15-30 microns thick is deposited over the entire surface of battery  340  with the exception of the two battery contacts  344 ,  346 , which can be masked during the coating process. In some embodiments, a second hydrophobic coating can be formed over the first coating on all or a portion of battery  340 . The second coating can provide additional protection against moisture ingress to the battery and help prevent defects or holes that might be incurred in the first coating during an assembly stage. The second coating can be, for example, a polyurethane, a fluorochemical acrylic polymer or similar material, that can be spray coated over hydrophobic coating  342 . In some embodiments the second coating can be between 12-30 microns thick and/or can be coated over only a portion of battery  340 , such as portion  345  (designated in  FIG. 3D  by dotted lines) that faces back volume  340  and is in a region where the battery may be handled during assembly of earbud  300 . 
     User-Specific Audio Settings 
     As mentioned above, speaker housing  310  of earbud  300  can be sized, shaped and contoured such, when earbud  300  is worn, the speaker housing  310  rests between the tragus and anti-tragus of a user&#39;s ear forming a passive seal with inner surfaces of the user&#39;s ear that surrounds the user&#39;s ear canal. When a relatively strong passive seal is formed, earbud  300  can be said to have a high quality fit as the passive seal can block noise from the outside environment providing an improved listening experience. Because user&#39;s ears can vary widely, however, the strength of the passive seal or whether or not a passive seal is formed, can vary between users. Depending on the strength of or the presence of a passive seal, certain frequencies of the audio signal can be adjusted to obtain a higher quality signal. 
     In some embodiments, earbud  300  includes an internal microphone  332  within the front volume of speaker housing  310 . Microphone  332  can be tuned to listen to low frequencies in the front volume and electronics within earbud  300  (e.g., a processor) can detect a quality of the fit of the earbud within a user&#39;s ear and adjust the audio settings based on the fit quality. For example, if speaker housing  310  does not form a passive seal in a user&#39;s ear, the low frequency sound generated by driver  330  can be boosted to make up for the leaky fit of the earbud. If, on the other hand, speaker housing  310  forms a strong passive seal in a user&#39;s ear, the low frequency sound may not need to be boosted at all. In one particular implementation, earbud  300  can adjust audio settings (e.g., adjust the low frequencies of sound generated by driver  330 ) according to anyone of six different profiles depending on how strong or how leaky the fit is between speaker housing  310  and an individual user&#39;s ear. As an example, each of the six different profiles can have a different setting for bass and/or mid-range frequencies depending on the amount of bass picked up by microphone  332 . In embodiments where earbud  300  is one of a left or a right earbud, each of the left and right earbuds can detect the strength of that earbud in the user&#39;s respective ear and adjust the frequency response of the earbud independent of the other earbud. As would be understood by a person of skill in the art, embodiments are not limited to any particular number of audio profiles and some embodiments can include fewer than six different profiles while other embodiments can include more than six profiles. 
     In-Ear Detect 
     As mentioned above, earbud  300  can include an optical sensor  320  that can be used to determine if the earbud is in a user&#39;s ear. Optical sensor  320  is positioned along a surface of earbud  300  that, when the earbud is worn by a user, faces the user&#39;s ear. Optical sensor  320  can include one or more emitters and one or more detectors. In some embodiments, the emitter can be a laser diode or a light emitting diode (LED) and the detector can be a photo diode. 
     Optical sensor  320  can emit radiation (e.g., infrared light) that, when it contacts a surface is reflected back to and detected by sensor  120 . When earbud  300  is worn, the emitted radiation is reflected off the inner portion of a user&#39;s ear and detected by the detector within sensor  120 . When it is determined that earbud  300  is positioned within a user&#39;s ear, audio can played through the earbud for the user&#39;s enjoyment. If, on the other hand, optical sensor  320  determines that the earbud is not in a user&#39;s ear, audio playback can be halted or otherwise stopped. To avoid false positives, optical sensor  320  can distinguish between scenarios in which the optical sensor is positioned adjacent to skin (i.e., the skin of user&#39;s ear) and scenarios in which the optical sensor is located next to a different material (e.g., a table top, fabric in a user&#39;s pocket, etc.) as described below. 
     The spectral response of human skin is characterized by peaks and valleys. For example, the reflectivity of human skin is relatively high (e.g., about 50-60%) at a wavelength of 1065 nm and is relatively low (e.g., about 5-10%) at a wavelength of 1465 nm. As a result, the presence of skin can be monitored by a sensor that emits light at 1065 nm and 1465 and that measures the amount of light reflected from a target object at these wavelengths. In some embodiments, optical sensor  120  includes two separate emitters that emit two different wavelengths of radiation that have different frequency responses to human skin. Thus, when reflected light emitted by sensor  120  is detected by the sensor, the ratio of the two wavelengths can be used to determine whether the surface that the radiation was reflected from was human skin or some other materials, such as a wood or metal table top. For example, when the ratio between the two wavelengths is within a certain range, sensor  320  can determine that the detected radiation was reflected off of human skin, which can in turn be used either alone or in conjunction with data from other sensors within earbud  300  (e.g., an accelerometer) to determine that earbud  300  is positioned in a user&#39;s ear. 
     As an illustrative non-limiting embodiment, reference is made to  FIGS. 3F and 3G  which depict an embodiment of optical sensor  320 . As shown in  FIG. 3F , optical sensor  320  includes a circuit board  360  (e.g., a printed circuit board) along with two light emitters  362  and a detector  364 , all of which are mounted to circuit board  360 . Light emitters  362  can be light emitting diodes and detector  364  can be a common photodiode, an avalanche photodiode (APD) or a collection of single photon avalanche diodes (SPADs). In other embodiments light emitters  362  can be lasers (e.g., vertical cavity surface emitting lasers referred to as “VC SELs”) or other appropriate light emitting devices and detector  364  can be a phototransistor. 
     Circuit board  360  can be mounted in a sensor package  365  as shown in  FIG. 3G . In some embodiments sensor package  365  includes various external and internal walls  367  that create two separate cavities spaced apart from, and optically isolated from, each other. Light emitters  362  can be positioned within a first cavity  365 ( 1 ) while detector  364  can be positioned with a second cavity  365 ( 2 ). An optical window  370  that is transparent to the wavelength of radiation emitted from light emitters  362  can be mounted (e.g., attached by a pressure-sensitive adhesive or other suitable mounting approach) to a top surface of sensor package  365  and package  365  can include first and second pass through regions  366 ,  368 , spaced apart from and directly above the light emitters  362  and detector  364 , respectively. Pass through regions  366 ,  368  can be, for example, openings formed through an exterior wall  367  of package  365 . In some embodiments, first pass through region  366  can include two separate openings such that one of the two openings is spaced apart from and directly above each of the two light emitters  362 . 
     As shown in  FIG. 3F , sensor package  365  can also include first and second filters  372 ,  374 . Filter  372  can be positioned in the optical path between light emitters  362  and first pass through region  366  while filter  374  can be positioned in the optical path between photodetector  366  and second pass through region  368 . Each of the filters  372 ,  374  can be configured to allow a predetermined set of radiation wavelengths to pass through the filter while blocking radiation outside the predetermined set. The filters  372 ,  374  can also beneficially be used as mechanical barriers to isolate against contamination (liquid, dust, other ingress). 
     In some embodiments, each of filters  372 ,  374  can be band-pass filters. Since the two light emitters  362  emit radiation at different wavelengths, in some embodiments filter  372  can include first and second areas that pass different bands of radiation a corresponding to the emitted wavelength from light emitters  362 . For example, in a configuration in which the two light emitters  362  emit radiation at  1065  nm and  1465  nm, respectively, filter  372  can include a band-pass filter in a first area that allows a first relatively narrow band of radiation centered at  1065  nm to pass while blocking radiation outside the first band and a band-pass filter in a second area that allows a second relatively narrow band of radiation centered at  1465  nm to pass while blocking radiation outside the second band. 
     Similarly, in some embodiments filter  374  can be configured to form a dual-band band-pass filter that includes first and second passbands at the same first and second wavelengths emitted by light emitters  362 . Thus, filter  374  can be configured to only allow light emitted from the light emitters  362  and reflected back through window  370  into opening  368  to reach detector  364  while blocking light (including ambient light) at other wavelengths. To distinguish between measurements associated with the two different light emitters  362 , in some embodiments the two light emitters  362  can emit radiation at different times (e.g., using time-division multiplexing). As an example, the two light emitters  362  can emit light in an alternating pattern. The measurements of detector  364  can then be synchronized to the emitted light pattern so that separate measurements for the first and second wavelengths can be made. 
     In one specific implementation, optical sensor includes two light emitters  362  in which one of the light emitters that emits light at a wavelength of 1065 nm and a second of the light emitters emits light at a wavelength of 1465 nm. The ratio R of reflected light at 1065 nm to reflected light at 1465 nm can be monitored and compared to a threshold level X (e.g., 2.0 or other suitable value). When the ratio R is less than X, it can be concluded that optical sensor  320  is not adjacent to human skin. When the ratio R is greater than X, it can be concluded that sensor  320  is adjacent to human skin. 
     As shown in  FIGS. 3G and 3H , light emitters  362  can be aligned to emit radiation through filter  372 , through pass through  366  and through window  370 , while detector  364  can be aligned to detect radiation that passes through window  370 , into pass through  368  and through filter  374 . Radiation emitted from light emitters  362  can be in the form of a light cone in which the radiation spreads out from each of light emitters  362  as it travels further from each emitter. Thus, the two light emitters  362  can emit light cones  376 ,  377 , respectively. Similarly, the field of view (FOV) of detector  364  can be viewed as a cone  378  where the field gets larger with distance from the photodetector. In some embodiments light emitters  362  are aligned and configured to emit light cones  376 ,  377  that overlap in an area  380  ( FIG. 3G ). The light emitters and optical paths of sensor  320  are configured such that overlapping area  380  is present the distances at which skin of a user&#39;s ear is reasonably going to be positioned when the earbud that includes optical sensor  320  is worn. The FOV of detector  364  is configured such that it overlaps with the light cones  376  and  378  of the light emitters  362  in an area  382  at a distance at which skin of a user&#39;s ear is reasonably going to be positioned when the earbud that includes optical sensor  320  is worn but is non-overlapping in an area  384  creating a FOV gap immediately adjacent to an outer surface of window  370  ( FIG. 3H ). In this manner, photodetector  362  is configured and aligned to detect radiation that is emitted from light detectors  362 , reflected off a user&#39;s ear back to detector  364 . 
     Force Sensor 
     A force sensor can be positioned along stem  312  to allow a user to control various aspects of earbuds  300 . In some embodiments, the force sensor (not visible in any of  FIGS. 3A-3C ) can be disposed within stem  312  adjacent to a planar region  326  on the stem. A user can provide input through the force sensor by squeezing stem  312  at the planar region  326 . Planar region  326  provides convenient tactile feedback to a user in locating the user input region provided by the force sensor. A person of skill in the art will appreciate that planar region can be replaced by or enhanced by one or more other features that provide additional and/or improved tactile feedback including, as examples, bumps, grooves, recesses, etc. 
     Further details of the force sensor are explained with reference to  FIGS. 4A to 4C  where  FIG. 4A  is a side view of earbud  300 ,  FIG. 4B  is a simplified cross-sectional view of earbud  300  taken through a portion of stem  312 , and  FIG. 4C  is an exploded view of some of the components that fit within stem  312 . Planar region  326  of stem  312  is clearly visible in  FIG. 4A , and as discussed above, the planar region provides a visual and tactile indication to a user that defines a pressure-sensitive zone where earbud  300  accepts user input by squeezing stem  312 . 
     Stem  312  defines an interior cavity  400  extending along a length of the stem in which components of earbud  300  are positioned. As shown in  FIG. 4B , a force sensor  410 , an antenna  420 , and a system in a package (SIP)  430  can be positioned within cavity  400 . Antenna  420  can extend along a majority of a length of stem  312  and SIP  430  can be positioned in an opposing relationship with the antenna. Force sensor  410  can include a full loop flex  412  that has a first side directly biased against an interior surface of stem  312  and a second side facing SIP  430 . A conductive coating  414  or other conductive element contained within or laminated to flex  412 , which serves as a first of two electrodes of the force sensor, can be formed at the second side (e.g., the copper layers already within the flex can act as an electrode). An outer portion  432  SIP  430  can be coated with a thin metal layer to serve as the second of the pair of electrodes for force sensor  410 . Flex loop  412  wraps around SIP  430  and is separated from a sidewall of the SIP by a foam insert  440 . When a user squeezes stem  312  in the planar region  326 , the flex  410  is pushed toward SIP  430  and the gap between the two electrodes  414 ,  432  is reduced creating a change in capacitance that can be detected generating a user-input signal that can be acted upon by electronics within earbud  300  to carry out a predetermined function. For example, in some embodiments squeezing stem  312  can initiate a voice-activated, virtual assistant, such as Siri that is built into various Apple products, and/or activate play, pause, skip and/or back functions to control an audio stream played over earbud  300 . 
     In some embodiments, touch pixels can be formed on the side of flex  412  that faces the interior wall of stem  312  enabling the planar region  326  to be used as both a touch surface and a force sensitive region. For example, the touch pixels can be built into copper layers formed in flex  412 . 
     As shown in  FIG. 4C , in some embodiments SIP  430  can fit entirely within the cavity defined by stem  312 . SIP  430  can include a contact region  452  and circuitry (not visible in  FIG. 4C ), including one or more integrated circuits, that control much of the operation of earbud  300  and are overmolded. For example, in some embodiments SIP  430  can include a main processor that controls the operation of earbud  300 , charging circuitry, an accelerometer, a wireless communication controller, support components for antenna  420 , uplink and downlink communication circuitry and user-interface circuitry, among others. Moving the SIP and its associated circuitry to the stem portion  312  of earbud  300  enables speaker housing  310  to be smaller than it otherwise would be (while including an appropriate sized battery) thus enabling the speaker housing to fit more comfortably in a user&#39;s ear for an improved user experience. 
     Also shown in  FIG. 4C  is cap  450  that is part of overall housing  302  and can be affixed to an end of stem  312  forming a water tight seal with the stem. A bottom microphone  454  can be attached to an interior surface of cap  450  and the cap include an acoustic port (not shown) that allows the microphone to capture sounds from the environment. Cap  450  can also include two seats along its external surface on opposite sides of the cap for the two contacts  322 .  324 . Seats are recessed a sufficient amount such that the contacts  322 ,  324  can be secured to the seats and positioned flush with an outer surface of cap  450  creating a smooth, seamless structure that has an improved appearance and reliability. An electrical connection to circuitry within stem  312  can be made to each of contacts  322 ,  324  through an appropriate cutout or opening cap  312  that can be covered by the contacts. 
     Acoustic Port Mesh 
     Earbud  300  can include a mesh that covers acoustic opening  314  to prevent dust and debris from entering housing  302 . In some embodiments the mesh can be formed as a multi-layered structure including a cosmetic mesh and an acoustic mesh where the cosmetic mesh forms an outer surface of earbud  300  and is formed of an interlaced network of stiff wire, while the acoustic mesh is positioned within acoustic port  314  beneath the cosmetic mesh and is formed of a porous fabric. As a specific non-limiting example, the cosmetic mesh can be formed of interlaced stainless steel and the acoustic mesh can be formed of polyester. 
     Because earphones are worn directly in a user&#39;s ear, earphones are susceptible to a build-up or collection of wax that can collect within the acoustic port between a speaker driver and a user&#39;s ear canal. Such wax build-up can muffle or otherwise adversely impact the sound quality of an earphone. In some embodiments, earbud  300  can include a wax gutter that sits adjacent to but outside the acoustic zone of the earbuds and collects ear wax so that the ear wax does not interfere with the sound quality of the earbuds. 
     An embodiment of earbuds  300  that includes a wax gutter is shown in  FIGS. 5A and 5B  where  FIG. 5A  is a simplified partial view of an earbud  300  (without stem  312 ) looking towards acoustic port  314  and  FIG. 5B  is a simplified cross-sectional view of earbud  300  taken through acoustic port  314 . In some embodiments acoustic port  314  can be formed as a cutout through a wall  311  of speaker housing  310 . As shown in  FIG. 5B , wall  311  has a thickness of Y and can include first and second edges  311   a,    311   b  separated by a shelf  311   c.  Edges  311   a,    311   b  can extend around an entire perimeter of acoustic port  314  and the acoustic port can include an opening  501  at the exterior surface of speaker housing  310  that is defined by edge  311   a.    
     As shown in  FIGS. 5A and 5B , earbud  300  can include a multilayer mesh  500  disposed within primary acoustic port  314  and extending over a cross-section of the acoustic port. Mesh  500  can include an outer cosmetic mesh  504  and a separate acoustic mesh  506 . Mesh  500  can be coupled to speaker housing  310  by an annular support  508  and can be positioned to span across the entirety of acoustic port  314 . Earbud  300  can include an acoustic dead zone  510  that surrounds an outer periphery of acoustic port  314 . Dead zone  510  includes wax gutter  502 , which is gap or space formed between an inner edge of speaker housing  310  and mesh  500 , along with the area occupied by support  508 . During use of earbuds  300 , ear wax can collect in wax gutter  502 . Then, as additional ear builds-up on earbud  300 , the wax can start to spread away from gutter  502  into acoustic dead zone  510 . The combination of was gutter  502  and acoustic dead zone  510  allows an amount of ear wax to collect on earbud  300  without adversely impacting the sound quality of the earbud. 
     To further reduce ear wax build-up, in some embodiments mesh  500  is recessed within acoustic port  314  such that mesh  500  is spaced a distance X from the opening  501  at the exterior surface of speaker housing  310  in order to space the mesh further away from a user&#39;s ear. In some embodiments, X can be between 0.3 and 2.0 mm and in some embodiments X can be between 0.5 and 1.0 mm. 
     In the embodiment depicted in  FIG. 5B , mesh  500  is shown as having a concave profile in which the center of mesh  500  is recessed further within acoustic port  314  than the outer edges of mesh  500 . In some embodiments, however, mesh  500  can have a convex shape in which the center of mesh  500  is still recessed within acoustic port  314  but is recessed than the outer edges of mesh  500 . The convex shape can help keep earwax build-up within the acoustic deadzone  510  and away from interfering with audio waves  512  directed acoustic port  314 . 
       FIG. 5C  is a simplified illustration of speaker housing  310  that includes a multilayer mesh  550  that has a convex profile according to some embodiments. For ease of illustration, speaker housing  310  is depicted in  FIG. 5C  without stem  312 . As shown in  FIG. 5C , wax gutter  502  surrounds multilayer mesh  550  and the multilayer mesh has two side-by-side openings  552 ,  554  rather than a single opening. 
       FIG. 5D  is a simplified exploded view of multilayer mesh  550  that can be disposed over acoustic port  314  according to some embodiments. Similar to mesh  500 , multilayer mesh  550  can include an outer cosmetic mesh  560  and a separate acoustic mesh  564 . A stiffener  568  made out of a rigid material can provide additional structure to the mesh and can define the side-by-side openings  552 ,  554  that allow sound to exit the earbuds from acoustic port  314 . Acoustic mesh  564  can be adhered to stiffener  568  by an adhesive  566 . Similarly, cosmetic mesh  560  can be adhered to acoustic mesh  564  by an adhesive  562 . In some embodiments, one or both of adhesives  562 ,  566  can be a thin flexible pressure sensitive adhesive (PSA) layer. 
       FIG. 5E  depicts two separate cross-sections of multilayer mesh  550  taken through lines A-A and lines B-B shown in  FIG. 5C , respectively. As shown in  FIG. 5E , mesh  550  can have a convex shape such that the edges of the mesh are spaced further away from the exterior surface of speaker housing  310  than the central portion of the mesh. The central portion of mesh  550  can still be recessed from the exterior surface of speaker housing  310  by a distance X, which in some embodiments can be between 0.3 and 1.5 mm and in some embodiments X can be between 0.5 and 1.0 mm. 
     Charging Case 
     Some embodiments of the disclosure pertain to a charging case that can store and charge a portable wireless listening device or a pair of portable wireless listening devices, such as a pair of earbuds  300 . The charging 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. 6A-6C  are simplified plan views of a charging case  600  that can store a pair of earbuds, such as earbuds  300 , according to some embodiments of the present disclosure. As shown in each of  FIGS. 6A-6C , case  600  can include a lid  602  and a body  604  that forms an internal cavity for housing a pair of wireless listening devices  300   a,    300   b  that can be worn in a user&#39;s left and right ears, respectively.  FIGS. 6A and 6B  are front plan views of charging case  600  and  FIG. 6C  is a rear plan view of the charging case. Charging case  600  is depicted in  FIG. 6A  with lid  602  in an open position while  FIGS. 6B and 6C  depict the charging case with the lid in a closed position. Lid  602  can be attached to body  604  by a hinge  610  (shown in  FIG. 6C ) that enables the lid to be moved between an open position (in which the earbuds  300   a,    300   b  can be inserted into or removed from case  600 ) and a closed position (in which the lid  602  covers the earbuds  300   a,    300   b  thereby completely enclosing the earbuds within the charging case  600 ). 
     In some embodiments, charging case  600  can include an internal frame (not visible in any of  FIGS. 6A-6C ) including portions designed to provide contours and surface features against which wireless listening devices  300   a,    300   b  can rest in strategic positions discussed herein to minimize the size of case  600 . Details of an exemplary internal frame according to some embodiments are discussed below. 
     To minimize the overall size of charging case  600 , earbuds  300   a,    300   b  can be positioned at strategic angles when placed in case  600 . In some embodiments, each stem of the earbuds  300   a,    300   b  is positioned at an angle with respect to two axis: an x-axis and a y-axis, instead of being positioned substantially vertically within the charging case. For purposes of description, the x-axis runs between earbuds  300   a,    300   b,  the y-axis runs between the front and the back of charging case  600 , and the z-axis runs between the bottom of body  604  and the top of lid  602 . 
     Case  600  can be configured to charge wireless listening devices  300   a,    300   b  when they are housed in case  600 . Towards this end, in some embodiments case  600  can include two pairs of electrical contacts (not visible in  FIGS. 6A-6C ) for making electrical contact with respective contacts on the stems of each earbud so that charge can flow from an internal battery (not shown) of case  600  to internal batteries of the earbuds  300   a,    300   b.  The charging case internal battery can be charged by an external power supply that is electrically coupled to case  600  via a connector  606 . Connector  606  can be any appropriate physical connector interface, such as a lightning connector port developed by Apple, a USB-C port, a mini USB port or the like. In some embodiments charging case  600  also includes a wireless power receiving coil (not shown) to wirelessly receive power that can be used to charge the internal battery as discussed in more detail below. 
     In some embodiments charging case  600  is highly resistant to moisture ingression and can be designed to meet IPX4 water resistance standards. Towards this end, electrical components within case  600  (e.g., the charging case battery, the circuit board on which the processor and other electronic circuitry that controls the operation of the charging case, etc.) can be sealed within an internal system volume that is sealed with external system seals. Additionally, each electrical component can be sealed individually with a conformal coating or adhesive. Some embodiments can further include a barometric vent within the connector  606  module that is permeable to air but not liquids. The barometric vent allows charging case  600  to be tested, in the manufacturing line, immediately after manufacture of the case is completed to determine if the charging case is fully sealed in accordance with the manufacturer expectations, for example, in accordance with the IPX4 requirements. 
     Case  600  can also include a visual indicator  608  configured to emit different colors of light. Visual indicator  608  can change colors depending on the charge status of the case. As an example, indicator  608  can emit green light when the case is charged, emit orange light when the charging case battery is charging and/or when the charging case battery has less than a full charge, and red light when the charging case battery is depleted. When viewed from outside of case  600 , visual indicator  608  can have a circular shape, or any other suitable shape, such as square-like, rectangular, oval, and the like. Case  600  can also include a user-interface  612 , such as a button, that when activated and when the earbuds are stored within case  600  with lid  602  open, initiates a pairing routine that allows the earbuds to be paired with a host device. 
     In some embodiments charging case  600  can include multiple different sub-assemblies that, when assembled together, make up the entirety of the charging case.  FIGS. 7A-11  are simplified exploded views of various sub-assemblies that can be combined together, as illustrated in  FIG. 12 , according to some embodiments. 
     Lid Enclosure Sub-Assembly 
       FIG. 7A  is a simplified exploded view of various components that make up a lid enclosure sub-assembly  700  and that can be assembled together to form lid  602 . As shown in  FIG. 7A , some of the main components of sub-assembly  700  include a lid enclosure  710 , a lid insert  720  and a hinge  740  that is discussed in more detail in  FIG. 7B . Lid enclosure  710  defines an outer surface for the lid  602  of charging case  600 . Lid insert  720  fits within and can be bonded to lid enclosure  710  to define an inner surface of lid  602 . When stored in charging case  600 , earbuds  300   a,    300   b  can include a first portion (including the stems) that extends into an earbud receiving portion (e.g., a cavity) of the body  604  of the charging case and a second portion (including an upper portion of the speaker housing) that is positioned within an earbud receiving portion of the lid. A lower surface of lid insert  720  can be contoured to match a profile of the portion of the speaker housing of each earbud that extends into the lid  602 . 
     A lid retention magnet  712  and lid retention shunt  714  can be secured to lid insert  720 . Magnet  712  can be attracted to a magnetic component in body  604 . For example, a shunt  822  (shown in  FIG. 8 ) formed of a ferrous block of material, such as steel, can be positioned within body  604  immediately below a top surface of the charging case body and aligned with magnet  712  when lid  602  is in the closed position. Magnet  712  can be attracted to shunt  822  when the magnetic fields from magnet  712  interact with the ferrous properties of shunt  822 . According to some embodiments, shunt  822  can operate as a hybrid retention and sensor shunt that can help lid  602  stay closed by attracting magnet  712 , but also be used as a sensor component so that a sensor, such as a hall-effect sensor, positioned below shunt  822  can detect when lid  602  is opened or closed by the presence of a magnetic field through shunt  822 . 
     Two magnets  716  can be disposed within the space between lid enclosure  710  and lid insert  720  and positioned along a back surface of the charging case. Magnets  716  can assist in the alignment of the charging case to a wireless charging device as discussed in more detail below. A pair of DC shields  718  can be disposed between the magnets  716  and the earbud receiving portion of lid  602  defined by the lid insert  720 . The DC shields can serve to isolate electronic components within charging case  600  (including earbuds stored within the case) from magnetic fields generated by the  716 . A pair of foam inserts  722  can also be included in upper lid sub-assembly  700  and disposed between lid enclosure  710  and lid insert  720 . 
     In some embodiments, hinge  740  can be a bistable hinge that has two stable states: an open state and a closed state. Between the open and closed states, hinge  740  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 will either pull the lid open or pull the lid closed depending on which direction away from the neutral position the lid is moved. Thus, the lid can close without requiring a large number of magnets to generate a high magnetic attraction force to close the lid.  FIG. 7B  illustrates a bistable hinge  740  according to some embodiments. Specifically,  FIG. 7B  is a simplified perspective view of a hinge  740  that can be incorporated into lid  602  according to some embodiments. 
     Bistable hinge  740  can be formed as part of a lid  602  of a case. Bistable hinge  740  can include a first leaf  741  and a second leaf  743  that provide the frame for hinge  740 . First leaf  741  can be fitted between lid enclosure  710  and lid insert  720  to connect hinge  740  to the lid. Second leaf  743  can be secured to body  604 . Each of the two leafs  741 ,  743  includes a planar back surface  745  that forms part of the exterior surface of the charging case. 
     Hinge  740  includes first and second pivot points about which bistable hinge  740  can move to effectuate bistable opening and closing of lid  602 . As an example, bistable hinge  740  can include a first pivot point  742  along a first shaft  744  that forms a first axis about which bistable hinge  740  rotates and a second pivot point  746  along a second shaft  748  that forms a second axis about which bistable hinge  740  rotates. The relative position between first shaft  744  and second shaft  748  can be fixed so that first shaft  744  and second shaft  748  are positioned a distance away from one another. An axis intersecting the first and second pivot points  742  and  746  can define the neutral position where bistable hinge  740  does not pull in either direction to open or close lid  602 . 
     A first end of a piston rod  750  can be coupled to second shaft  748  so that piston rod  750  can pivot around second pivot point  746  as bistable hinge  740  transitions between open and closed positions, and a second end of piston rod  750  opposite from its first end can be attached to a stopper  752 . Stopper  752  can include a flange region  754  that is annular in construction and is positioned around a portion of piston rod  750  and perpendicular to an outer surface of piston rod  750 . A maximum open angle of lid  602  can be controlled with faces on first leaf  741  and second leaf  743  that hard stop on one another to prevent further motion of the hinge  740 . In one particular implementation, hinge  740  can be designed to span fully open angles for lid  602  from 110 to 120 degrees, centered around 115 degrees. 
     To generate the spring-loaded forces for the operation of bistable hinge  740 , a spring  756  can be implemented between a piston guide  758  and second pivot point  746 . Spring  756  can be a coil spring that is wound about a portion of piston rod  750  so that it can apply force against piston guide  758 . In certain instances, spring  756  is conical where it is wider in one end and narrower in the opposite end so that spring  756  can provide a force profile during transition between compressed and extended states. In some implementations, the conical spring can be designed to buckle when compressed to a certain extent where the buckling is controlled and yields a repeatable hinge torque profile. Spring  756  can generate force in a direction that is along an axis of piston rod  750  but directed away from piston guide  758 . The direction of this force, when compared to the axis formed by the first and second pivot points  742  and  746  can effectuate the bistable operation of hinge  740 . 
       FIG. 7C  is a simplified perspective view of a bistable leaf spring hinge  780  that can be incorporated into lid  602  instead of hinge  740  according to some embodiments. Hinge  780  includes a first pivot point  742  through which a shaft  744  extends as described above with respect to hinge  740 . Hinge  780  does not include a link rod or the conical wire spring that envelopes the link rod. Instead, hinge  780  includes a leaf spring  782  that is connected to leaf  741  by first and second rods  748 ,  788 . The design of leaf spring hinge  780  can provide a number of benefits including a lower part count, a lower cost due to the lower part count and fewer assembly steps, improved reliability and a smaller neutral angle range resulting in a better user experience. 
     Body Insert Sub-Assembly 
       FIG. 8  is a simplified exploded view of various components that make up an insert sub-assembly  800  and that can be assembled together to form an interior portion of body  604 . As shown in  FIG. 8 , sub-assembly  800  includes an earbud carrier  810  and a contact carrier  820 . Earbud carrier  810  can be formed of a monolithic structure designed to provide first and second bowl regions  812   a,    812   b  spaced apart from each other that are each configured to accept a portion of the earbuds  300   a,    300   b,  respectively. Each of the bowl regions  812   a,    812   b  can include a receiving surface contoured to accept and match the exterior profile of a lower portion of the speaker housing of each earbud. Each of the cavities  812   a,    812   b  opens, at a bottom portion of the cavity, to a respective tubular extension  814   a,    814   b.    
     Contact carrier  820  can include separate, first and second contact carriers  820   a,    820   b  that can be coupled and bonded to extensions  814   a  and  814   b,  respectively, of earbud carrier  810 . Each tubular extension is sized and shape to accept a portion of the stem of its respective earbud such that the tubular extension surrounds an upper portion of the stem. A lower portion of each stem, including the end of the stem upon which electrical contacts (not shown in  FIG. 8 ) are positioned, protrudes through its respective tubular extension into its corresponding contact carrier. Each of the contact carriers  820   a,    820   b  includes features that enable electrical contacts (not shown in  FIG. 8 ) within charging case  600  to be secured to the contact carrier while a portion of the contacts extends into interior space of the contact carrier enabling the charging case contacts to be electrically coupled with the earbud contacts. In some embodiments, the contacts can be sealed from the outside environment to protect them from moisture. For instance, sealing rings can be strategically positioned at interface regions that are entry points to the charging case. 
     In some embodiments, earbud carrier  810  can be configured to seal the internal components of charging case  600  from the outside environment through the top of the case body  604 . Thus, a sealing structure (not shown) formed of a pliable material suitable for sealing purposes can be disposed between the intersection of earbud carrier  810  and body  604 . For instance, the sealing structure can extend around the perimeter of an upper portion of earbud carrier  810  and an inner surface of body  604 . 
     Body Enclosure Insert Sub-Assembly  800  can also include lid retention shunt  822  discussed above, earbud retention magnets  824  and earbud retention shunt  826 . 
     Skeleton Sub-Assembly 
       FIG. 9  is a simplified exploded view of various components that make up a skeleton sub-assembly  900  and that can be attached to bottom insert sub-assembly  800  within body  604 . Skeleton sub-assembly  900  includes an internal frame  910  that can be formed of a monolithic structure designed to provide contours and surface features against which various electronic components within charging case  600  can rest and/or attach. That is, internal frame  910  can provide a structural backbone for some of the internal components of charging case  600 , and in the embodiment depicted in  FIG. 9 , internal frame  910  provides mounting locations for a battery module  920  and a circuit board module  930  as well as a coil sub-assembly  1100  discussed with respect to  FIG. 11 . Additionally, earbud carrier  810  can be mounted to an upper surface of internal frame  900  such that extensions  814   a,    814   b  extend through openings  914   a,    914   b  of the internal frame  910 . 
     Battery module  920  includes a battery that provides power for the charging case and that can be used to recharge the batteries of one or both of earbuds  300   a,    300   b  when the earbuds are stored in charging case  600 . Circuit board module  930  can include a circuit board  932  upon which electronic components can be mounted. In some embodiments, circuit board  932  can be a rigid, multi-layer printed circuit board and electronic components and circuitry that provide the functionality, or a portion of the functionality, of one or more of case communication system  251 , earbud interface  252 , power receiving circuitry  253 , computing system  255 , and user interface  256  discussed with respect to  FIG. 2 . A flexible circuit board  934  can also be coupled circuit board  932  to provide an electrical connection to electrical contacts  936  of the charging case  600 , which can be mounted to contact carriers  820   a,    820   b  as discussed above. 
     Coil Sub-Assembly 
       FIG. 10A  is a simplified exploded view of various components that make up a coil sub-assembly  1000  that can be laminated to an inner surface of the bottom enclosure. In one particular embodiment, coil sub-assembly  1000  can be positioned between battery module  920  and a rear inner surface of bottom enclosure  1110  (see  FIG. 11 ). Coil sub-assembly  1000  can include a power receiving coil  1010 , a coil shield  1012 , a button housing  1014 , an nanocrystalline shield  1016 , a circuit board  1018  and a flex circuit  1020 . 
     Coil sub-assembly  1000  enables charging case  600  to be inductively charged by an appropriate charging device. For example,  FIG. 10B  is a simplified illustration of a wireless power charging device  1050  that includes a power transmitting coil  1052  positioned within a housing  1054 . Charging device  1050  also includes a cable  1056  that enables device  1050  to receive power from an external source. During wireless power transfer charging case  600  can be positioned on charging device  1050  as shown in  FIG. 10C  and transmitter coil  1052  can generate a time-varying magnetic flux, which can propagate through device housing  1054  and through the housing of charging case  600  where it can be received by receiving coil  1010 . The time-varying magnetic flux interacts with receiver coil  1010  to generate a corresponding current in receiver coil  1010 . The generated current can be used by charging case  600  (e.g., by electronic circuitry on circuit board  1018 ) to charge the battery within battery module  920 . 
     Magnetic fields generated during a charging operation can potentially interfere with or harm circuitry within charging case  600 . To prevent such fields from damaging or otherwise undesirably interfering with circuitry within charging case  600 , coil shield  1012  can be positioned directly adjacent to power receiving coil  1010  such that coil shield  1012  shadows coil  1010  and is between the coil and circuit board  1018 . 
     Button housing  1014  provides a structure for a user-input button  1114  (see  FIG. 11 ) that, in some embodiments, allows a user to initiate a process to wireless pair earbuds  300   a,    300   b  with a host device using a wireless communication protocol, such as Bluetooth. In some embodiments, a memory unit in the earbuds or the charging case stores information on previous pairings that enables the earbuds to be automatically paired with an authorized host device when the earbuds and authorized host device are within range of each other. In such embodiments, input button  1114  can be used to initiate pairing of earbuds with a new device with each a pairing was not previously made. 
     To improve charging efficiency, charging case  600  can include a permanent magnet array that aligns receiving coil  1010  with a transmitting coil of a compatible wireless charger, such as transmitting coil  1052 . In some embodiments, the magnet array can includes four separate magnets positioned near the corners of the back surface of charging case  600 . For example, in some embodiments the magnet array can include a first pair of magnets  716  disposed within lid enclosure  710  (see  FIG. 7A ) along the rear surface  620  ( FIG. 6C ) of charging case  600  and a second pair of magnets  1136  disposed within bottom enclosure  1110  (see  FIG. 11 ) along the rear surface  620 . DC shields  718  ( FIG. 7A ) and  1138  ( FIG. 11 ) can be positioned adjacent to each magnet to isolate electronic components within charging case  600  from magnetic fields generated by the magnets  716 ,  1136 . Due to the compact size of charging case  600 , in order provide appropriate spacing between the magnets so that the magnets can align with corresponding magnetic structures in the wireless charger (e.g., an array of magnets  1062  as shown in  FIG. 10D ), in some embodiments the magnets  716  are positioned in the lid  602  of the charging case while magnets  1136  are positioned in the body  604  of the charging case. 
     In some embodiments, magnets  716 ,  1136  are positioned at the outer edges of the charging case  600  such that the magnets are positioned along the curvature of lid  602  and body  604  as shown, for example, in  FIG. 10E . Also, as shown in  FIG. 10D , in some embodiments magnets  716 ,  1136  are positioned along a radius that is slightly less than the radius of magnet array  1062 . When the charging case  600  is positioned on wireless charging device  1050 , the magnets  716 ,  1136  align to magnetic array  1062  creating a magnetic field that has a pull direction downwards and towards the inner ring of magnetic array  1062  centering charging case  600  on wireless charging device  1050 . The placement of the magnets  716 ,  1136  along the curvature of the housing of charging case  600  creates a gap or space  1070  between the charging case magnets  716 , 1136  and the charging device magnets  1062 , which can help prevent magnetic particles from getting stuck in the attraction zone between the magnets. Bottom Enclosure Sub-Assembly 
       FIG. 11  is a simplified exploded view of various components that make up a bottom enclosure sub-assembly  1100  according to some embodiments. Sub-assembly  1100  includes a bottom enclosure  1110  that defines an outer surface of the body  604  of charging case  600 . Bottom enclosure is complementary to lid enclosure  710  and the two components can be coupled together in a clam shell arrangement by a hinge, such as hinge  740  or hinge  780 . Bottom enclosure  1110  can include one or more cutouts for various features of charging case  600 . As depicted in  FIG. 11 , a cutout  1112  is formed at a central location on the rear surface of enclosure  1110  and a button  1114  extends through cutout  1112  such that an outer surface of button  1114  is flush with an exterior surface of bottom enclosure  1110 . An o-ring  1116  can form a seal between button  1114  and enclosure  1110  to reduce or prevent the ingress of moisture through cutout  1112 . Button  612  shown in  FIG. 6C  can be representative of button  1114 . 
     Enclosure  1110  can also include a smaller cutout (not shown in  FIG. 11 ) on its surface opposite cutout  1112  that for a light guide  1118  that directs light from an emitter  1120 , such as an LED of VSCEL, to the exterior surface of charging case  600 , and a third cutout (also not shown in  FIG. 11 ) on a bottom surface of enclosure  1110 . The third cutout provides an opening for a receptacle connector  1130  that enables a physical connector to be plugged into charging case  600 . As described with respect to  FIG. 6 , in some embodiments the physical connector can be a Lightning Connector by Apple, Inc. but embodiments are not limited to any particular connector type and in other embodiments connector  1130  can be any other appropriate small form factor connector including a USB-C connector, a mini- or micro-USB connector or the like. 
     Also shown in  FIG. 11  are magnets  1136  and DC shields  1138  discussed above.  FIG. 12  is a simplified exploded view of the subassemblies  700 ,  800 ,  900 ,  1000  and  1100  arranged together according to some embodiments. As shown in  FIG. 12 , subassemblies  800 ,  900 ,  1000  and  100  form the body portion  604  of charging case  600 . Subassembly  700  generally forms the lid  602  of the charging case except for the leaf  743  portion of hinge  740  that is mounted to body  604  enabling the hinge to connect the lid  602  to body  604 . 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. Also, while different embodiments of the invention were disclosed above, the specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. Further, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings. 
     Finally, it is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users.