Patent Publication Number: US-2023136545-A1

Title: Directional acoustic device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Patent Application No. 63/274,505, entitled, “Directional Acoustic Device”, filed on Nov. 1, 2021, the disclosure of which is hereby incorporated herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present description relates generally to acoustic devices, including, for example, a directional acoustic device. 
     BACKGROUND 
     Acoustic devices can include speakers that generate sound and microphones that detect sound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain features of the subject technology are set forth in the appended claims. However, for purpose of explanation, several embodiments of the subject technology are set forth in the following figures. 
         FIGS.  1  and  2    illustrate aspects of an example apparatus in accordance with one or more implementations. 
         FIG.  3    illustrates a schematic perspective view of an example directional acoustic device in accordance with implementations of the subject technology. 
         FIG.  4    illustrates a schematic perspective view of an example directional component of a directional acoustic device in accordance with implementations of the subject technology. 
         FIG.  5    illustrates a schematic side view of another example directional acoustic device in accordance with implementations of the subject technology. 
         FIG.  6    illustrates a schematic top view of an example of directional audio output by the example directional acoustic device of  FIG.  5   , implemented in the apparatus of  FIG.  1   , in accordance with implementations of the subject technology. 
         FIG.  7    illustrates an example three-dimensional acoustic power distribution of directional audio output of the example directional acoustic device of  FIG.  5    in accordance with implementations of the subject technology. 
         FIG.  8    illustrates an example distribution of acoustic power as a function of frequency and azimuth of directional audio output by the example directional acoustic device of  FIG.  5    in accordance with implementations of the subject technology. 
         FIG.  9    illustrates a schematic top view of another example directional acoustic device in accordance with implementations of the subject technology. 
         FIG.  10    illustrates a schematic top view of another example directional acoustic device in accordance with implementations of the subject technology. 
         FIGS.  11  and  12    illustrate two example out-of-phase operational modes of the example directional acoustic device of  FIG.  10    in accordance with implementations of the subject technology. 
         FIG.  13    illustrates a flow chart of example operations that may be performed for directional audio output in accordance with implementations of the subject technology. 
         FIG.  14    illustrates another flow chart of example operations that may be performed for directional audio output in accordance with implementations of the subject technology. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology can be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, the subject technology is not limited to the specific details set forth herein and can be practiced using one or more other implementations. In one or more implementations, structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology. 
     Implementations of the subject technology described herein provide a directional acoustic device that can be implemented in various environments and/or apparatuses, such as apparatuses that include an enclosed environment. In one or more implementations, the directional acoustic device may be a directional speaker. A directional speaker, as described herein, may be a speaker that has an acoustic port through which sound (e.g., generated by a moving diaphragm or other sound-generating component) is projected, a back volume, and an elongated channel fluidly coupled to the back volume and configured to output sound from the back volume. Because the sound from the back volume will have a polarity (e.g., a negative polarity) that is opposite to a polarity (e.g., a positive polarity) output from the acoustic port, the sound from the back volume may cancel a portion of the sound from the acoustic port, in a direction defined by the arrangement of the elongated channel. In one or more implementations, a directional speaker may have more than one elongated channel fluidly coupled to the rear volume of the speaker. 
     An illustrative apparatus including a directional acoustic device is shown in  FIG.  1   . In the example of  FIG.  1   , an apparatus  100  includes an enclosure  108  and a support structure  104 . The enclosure may (e.g., at least partially) define an enclosed environment  131 . In the example of  FIG.  1   , the enclosure  108  includes top housing structures  138  mounted to and extending from opposing sides of the support structure  104 , and a sidewall housing structure  140  extending from each top housing structure  138 . 
     In this example, the enclosure  108  is depicted as a rectangular enclosure in which the sidewall housing structures  140  are attached at an angle to a corresponding top housing structure  138 . However, it is also appreciated that this arrangement is merely illustrative, and other arrangements are contemplated. For example, in one or more implementations, the top housing structure  138  and the sidewall housing structure  140  on one side of the support structure  104  may be formed from a single (e.g., monolithic) structure having a bend or a curve between a top portion (e.g., corresponding to a top housing structure  138 ) and a side portion (e.g., corresponding to a sidewall housing structure  140 ). For example, in one or more implementations, the top housing structure  138  and the sidewall housing structure  140  on each side of the support structure  104  may be formed from a curved glass structure. In this and/or other implementations, the sidewall housing structure  140  and/or other portions of the enclosure  108  may be or include a reflective surface (e.g., an acoustically reflective surface). 
     As illustrated in  FIG.  1   , the apparatus  100  may include various components such as one or more safety components  116 , one or more speakers  118 , and/or one or more other components  132 . In the example of  FIG.  1   , the safety component  116 , the speaker  118 , and the other component  132  are mounted in a structural space  130  at least partially within the support structure  104 . The other component  132  may include, as examples, one or more cameras, and/or one or more sensors. However, it is also contemplated that one or more safety components  116 , one or more speakers  118 , and/or one or more other components  132  may also, and/or alternatively, be mounted to the enclosure  108 , and/or to and/or within one or more other structures of the apparatus  100 . As shown in  FIG.  1   , the support structure  104  may include a first side  134 , an opposing second side  135 , and a bottom surface  136  that faces an interior of the enclosed environment  131  defined by the enclosure  108 . 
     In various implementations, the apparatus  100  may be implemented as a stationary apparatus (e.g., a conference room or other room within a building) or a moveable apparatus (e.g., a vehicle such as an autonomous or semiautonomous vehicle, a train car, an airplane, a boat, a ship, a helicopter, etc.) that can be temporarily occupied by one or more human occupants. In one or more implementations, (although not shown in  FIG.  1   ), the apparatus  100  may include one or more seats for one or more occupants. In one or more implementations, one or more of the seats may be mounted facing in the same direction as one or more other seats, and/or in a different (e.g., opposite) direction of one or more other seats. 
     In one or more use cases, it may be desirable to provide audio content to one or more occupants within the enclosed environment  131 . The audio content may include general audio content intended for all of the occupants and/or personalized audio content for one or a subset of the occupants. For example, in implementations in which the apparatus  100  is a moveable apparatus, it may be desirable to notify a particular occupant that their stop is upcoming or that the apparatus  100  has arrived at their stop, without conveying that notification to other occupants within the enclosed space. In these and/or other use cases, it may be desirable to be able to direct the audio content, or a portion of the audio content, to one or more particular locations within the enclosed environment  131  and/or to suppress the audio content and/or a portion of the audio content at one or more other particular locations within the enclosed environment  131 . In one or more implementations, the speaker  118  may be implemented as a directional speaker (which may also be referred to herein as a rear shotgun speaker), as discussed in further detail hereinafter in connection with  FIGS.  3 - 14   . 
     In various implementations, the apparatus  100  may include one or more other structure, mechanical, electronical, and/or computing components that are not shown in  FIG.  1   . For example,  FIG.  2    illustrates a schematic diagram of the apparatus  100  in accordance with one or more implementations. 
     As shown in  FIG.  2   , the apparatus  100  may include structural and/or mechanical components  101  and electronic components  102 . In this example, the structural and/or mechanical components  101  include the enclosure  108 , the support structure  104 , and the safety component  116  of  FIG.  6   . In this example, the structural and/or mechanical components  101  also include a platform  142 , propulsion components  106 , and support features  117 . In this example, the enclosure  108  includes a reflective surface  112  and an access feature  114 . 
     As examples, the safety components  116  may include one or more seatbelts, one or more airbags, a roll cage, one or more fire-suppression components, one or more reinforcement structures, or the like. As examples, the platform  142  may include a floor, a portion of the ground, or a chassis of a vehicle. As examples, the propulsion components may include one or more drive system components such as an engine, a motor, and/or one or more coupled wheels, gearboxes, transmissions, or the like. The propulsion components may also include one or more power sources such as fuel tank and/or a battery. As examples, the support feature  117  may be support features for occupants within the enclosed environment  131  of  FIG.  1   , such as one or more seats, benches, and/or one or more other features for supporting and/or interfacing with one or more occupants. As examples, the reflective surface  112  may be a portion of a top housing structure  138  or a sidewall housing structure  140  of  FIG.  1   , such as a glass structure (e.g., a curved glass structure). As examples, the access feature  114  may be a door or other feature for selectively allowing occupants to enter and/or exit the enclosed environment  131  of  FIG.  1   . 
     As illustrated in  FIG.  2   , the electronic components  102  may include various components, such as a processor  190 , RF circuitry  103  (e.g., WiFi, Bluetooth, near field communications (NFC) or other RF communications circuitry), memory  107 , a camera  111  (e.g., an optical wavelength camera and/or an infrared camera, which may be implemented in the other components  132  of  FIG.  1   ), sensors  113  (e.g., an inertial sensor, such as one or more accelerometers, one or more gyroscopes, and/or one or more magnetometers, radar sensors, ranging sensor such as LIDAR sensors, depth sensors, temperature sensors, humidity sensors, etc. which may also be implemented in the other components  132  of  FIG.  1   ), a microphone  119 , a speaker  118 , a display  110 , and a touch-sensitive surface  122 . These components optionally communicate over a communication bus  150 . Although a single processor  190 , RF circuitry  103 , memory  107 , camera  111 , sensor  113 , microphone  119 , speaker  118 , display  110 , and touch-sensitive surface  122  are shown in  FIG.  2   , it is appreciated that the electronic components  102  may include one, two, three, or generally any number of processors  190 , RF circuitry  103 , memories  107 , cameras  111 , sensors  113 , microphones  119 , speakers  118 , displays  110 , and/or touch-sensitive surfaces  122 . 
     In the example of  FIG.  2   , apparatus  100  includes a processor  190  and memory  107 . Processor  190  may include one or more general processors, one or more graphics processors, and/or one or more digital signal processors. In some examples, memory  107  may include one or more non-transitory computer-readable storage mediums (e.g., flash memory, random access memory, volatile memory, non-volatile memory, etc.) that store computer-readable instructions configured to be executed by processor  190  to perform the techniques described below (e.g., including operating the speaker  118 ). 
     RF circuitry  103  optionally includes circuitry for communicating with electronic devices, networks, such as the Internet, intranets, and/or a wireless network, such as cellular networks and wireless local area networks (LANs). RF circuitry  103  optionally includes circuitry for communicating using near-field communication and/or short-range communication, such as Bluetooth®. 
     Display  110  may incorporate LEDs, OLEDs, a digital light projector, a laser scanning light source, liquid crystal on silicon, or any combination of these technologies. Examples of display  110  include head up displays, automotive windshields with the ability to display graphics, windows with the ability to display graphics, lenses with the ability to display graphics, tablets, smartphones, and desktop or laptop computers. In one or more implementations, display  110  may be operable in combination with the speaker  118  and/or with a separate display (e.g., a display of a smartphone, a tablet device, a laptop computer, a smart watch, or other device) of a separate device within the enclosed environment  131 . 
     Touch-sensitive surface  122  may be configured for receiving user inputs, such as tap inputs and swipe inputs. In some examples, display  110  and touch-sensitive surface  122  form a touch-sensitive display. 
     Camera  111  optionally includes one or more visible light image sensors, such as charged coupled device (CCD) sensors, and/or complementary metal—oxide—semiconductor (CMOS) sensors operable to obtain images within the enclosed environment  131  and/or of an environment external to the enclosure  108 . Camera  111  may also optionally include one or more infrared (IR) sensor(s), such as a passive IR sensor or an active IR sensor, for detecting infrared light from within the enclosed environment  131  and/or of an environment external to the enclosure  108 . For example, an active IR sensor includes an IR emitter, for emitting infrared light. Camera  111  also optionally includes one or more event camera(s) configured to capture movement of objects such as occupants within the enclosed environment  131  and/or objects such as vehicles, roadside objects and/or pedestrians outside the enclosure  108 . Camera  111  also optionally includes one or more depth sensor(s) configured to detect the distance of physical elements from the enclosure  108  and/or from other objects within the enclosed environment  131 . In some examples, camera  111  includes CCD sensors, event cameras, and depth sensors that are operable in combination to detect the physical setting around apparatus  100 . 
     In some examples, sensors  113  may include radar sensor(s) configured to emit radar signals, and to receive and detect reflections of the emitted radar signals from one or more objects in the environment around the enclosure  108 . In some examples, one or more microphones such as microphone  119  may be provided to detect sound from an occupant within the enclosed environment  131  and/or from one or more audio sources external to the enclosure  108 . In some examples, microphone  119  includes an array of microphones that optionally operate in tandem, such as to identify ambient noise or to locate the source of sound in space. 
     Sensors  113  may also include positioning sensors for detecting a location of the apparatus  100 , and/or inertial sensors for detecting an orientation and/or movement of apparatus  100 . For example, processor  190  of the apparatus  100  may use inertial sensors and/or positioning sensors (e.g., satellite-based positioning components) to track changes in the position and/or orientation of apparatus  100 , such as with respect to physical elements in the physical environment around the apparatus  100 . Inertial sensor(s) of sensors  113  may include one or more gyroscopes, one or more magnetometers, and/or one or more accelerometers. 
     As discussed herein, speaker  118  may be implemented as a directional speaker, in one or more implementations.  FIG.  3    illustrates a perspective view of an example directional speaker, in accordance with one or more implementations. As shown in  FIG.  3   , in one or more implementations, an acoustic device, such as speaker  118 , may include a diaphragm  308  mounted in a housing  300 . In the example of  FIG.  3   , speaker  118  includes a front volume  304  on a first side of the diaphragm  308  and a back volume  306  on an opposing second side of the diaphragm  308  and at least partially defined by the housing  300 . For example, the diaphragm may be mounted to an interior structure  302  of the speaker  118 , and the interior structure and the diaphragm  308  may sealingly separate the front volume  304  from the back volume  306 . The interior structure may be an interior wall, and/or may include a surround that extends around a peripheral edge of the diaphragm and/or a portion of a mounting structure (e.g., a basket) for the diaphragm and/or surround. 
     As shown, speaker components  309  may be disposed within the back volume  306 . As examples, the speaker components  309  may include a magnet, a voice coil, and/or structural components of the speaker  118 . In one or more implementations, a voice coil of the speaker  118  may be communicatively coupled to the processor  190  of  FIG.  2   . The processor  190  may generate control signals that cause a current through the voice coil that, in turn, causes movement of the diaphragm  308  that generates sound or audio output from the speaker  118 . 
     As shown in  FIG.  3   , the speaker  118  may include an acoustic port  305  fluidly coupling the front volume  304  to an external environment of the speaker  118 . Sound generated by motion of diaphragm  308  may be projected from the speaker  118  via the acoustic port  305 . In the example of  FIG.  3   , the front volume  304  is defined by in part by the diaphragm  308  and the interior structure  302  and in part by a portion of the housing  300  that extends forward from the diaphragm  308 . However, in other implementations, the housing  300  may extend around the back volume  306  and only up to the interior structure  302  and/or the diaphragm  308  such that the front volume  304  is a volume defined by a curved surface of the diaphragm and such that acoustic port  305  is defined by the peripheral edge of the diaphragm  308  itself. 
     As shown in  FIG.  3   , an acoustic device such as the speaker  118  may include a channel housing  310  extending from the housing  300 . The channel housing  310  may be a separate housing that is attached to the housing  300  or may be an integral extension of the housing  300 , in various implementations. The channel housing  310  (e.g., an interior surface of the channel housing  310 ) defines an elongated channel  315  within the channel housing  310  with a first end  311  that is fluidly coupled to the back volume  306  and a second end  312  that is fluidly coupled to the external environment of the speaker  118 . As shown, the channel housing  310  includes a slot  314  that fluidly couples the elongated channel  315  with the external environment, at a location between the first end  311  and the second end  312 . Although a single slot  314  is visible in the example of  FIG.  3   , the channel housing  310  may include multiple slots  314  (e.g., two slots  314  symmetrically disposed on opposing sides of the channel housing, three slots  314 , or more than three slots  314 ). 
     In the example of  FIG.  3   , the slot  314  extends along the length of the channel housing  310  in parallel with a longitudinal axis of the channel housing  310  and the elongated channel  315  defined therein.  FIG.  4    illustrates another example of the channel housing  310  in which multiple slots  400  are instead provided in the channel housing  310 . In the example of  FIG.  4   , the slots  400  are oriented transversely to the longitudinal axis of the channel housing  310  and are spaced apart along the length of the channel housing  310  in a direction that is parallel with the longitudinal axis of the channel housing  310  and the elongated channel  315  defined therein. In various implementations, the channel housing  310  may include one or more longitudinal slots such as the slot  314  of  FIG.  3    and/or one or more transverse slots such as the slots  400  of  FIG.  4   . 
     In the examples of  FIGS.  3  and  4   , the slot  314  has a uniform slot width along the elongated channel  315 , and the slots  400  are uniformly shaped and uniformly spaced along the elongated channel. For example, a uniform slot width may be implemented to form as narrow a projected beam as possible at all frequencies. In these uniform slot-width implementations, the projected beam becomes monotonically narrower as frequency increases. However, it is also appreciated that a longitudinal slot such as the slot  314  may have a slot width that changes along the length of the elongated channel  315 , and/or the slots  400  may have transverse slot lengths and/or longitudinal slot widths that change (e.g., from one slot  400  to a next slot  400 ) along the length of the elongated channel  315 . For example, an expanding slot width (e.g., expanding along the length of the elongated channel  315 ) can be implemented to generate a projected beam that settles at a particular beam width, such that the directivity of the projected beam is more constant with frequency. 
     For example, in one or more implementations, one or more longitudinal slots, such as the slot  314  of  FIG.  3   , may be implemented as an expanding slot having a slot width that is relatively narrow at a proximal slot end nearer to the housing  300  and expands in a direction parallel to the longitudinal axis of the channel housing  310  (e.g., and the elongated channel  315  defined therein) toward a distal slot end further from the housing  300 . In one or more implementations, the slot width can increase uniformly along the length of the channel housing  310  (e.g., at a constant expansion angle of between thirty degrees and sixty degrees, or at another constant expansion angle). In one or more other implementations, the slot width can have non-variations along the length of the channel housing  310 . It is appreciated that the exact expansion profile of a slot can be tailored for a particular implementation, to create a desired directivity of the negative polarity sound projected from the elongated channel  315 . 
     In one or more implementations, the slot  314 , and/or one or more transverse slots such as the slots  400 , may be covered by an acoustic mesh. In one or implementations, an acoustic mesh that covers the slot  314  and/or one or more transverse slots such as the slots  400  may have an acoustic resistance value that changes along the length of the elongated channel  315  (e.g., along a direction parallel to the longitudinal axis of the channel housing  310 ). For example, providing an acoustic mesh with an acoustic resistance value that changes along the length of the elongated channel  315  may help improve the directionality of the channel (e.g., as a function of frequency). 
     Because the front volume  304  and the back volume  306  are disposed on opposing sides of the diaphragm  308 , pressure changes generated, by the motion of the diaphragm  308 , in the front volume  304  have a polarity that is opposite to pressure changes on in the back volume  306 . That is, when the diaphragm  308  moves forward and compresses the air in front of the diaphragm (e.g., in the front volume  304 ), the diaphragm  308  simultaneously expands the volume of the back volume  306 , decompressing the air in the back volume. For this reason, sound generated with a positive polarity in the front volume  304  (e.g., and projected through the acoustic port  305 ) is also generated with a negative polarity in the back volume  306 . 
     In one or more implementations, the channel housing  310  and the elongated channel  315  defined therein direct a portion of the negative polarity sound generated in the back volume  306  to a location that is defined by the orientation of the elongated channel  315 . In the examples of  FIGS.  3  and  4   , the slot  314  and/or the slots  400  allow portions of the negative polarity sound to leak out of (e.g., exit) the elongated channel to the external environment at various locations along the length of the elongated channel. Because the negative polarity sound that exits the slot(s) leaks out of the elongated channel to at various distances from the source of the sound, the negative polarity sound exits with varied phases that substantially cancel out the negative polarity sound in a direction perpendicular to the longitudinal axis of the elongated channel  315 . In this way, the elongated channel  315  directs the negative polarity sound through the second end  312  in a direction of the longitudinal axis of the elongated channel. Moreover, because the sound directed in the direction of the longitudinal axis is negative in polarity with respect to the positive polarity sound projected from the acoustic port  305 , a portion of the positive polarity sound projected from the acoustic port  305  that propagates into the region of the external environment in which the negative polarity sound is directed (by the elongated channel  315 ) will be at least partially cancelled in that region. Thus, the speaker  118  of  FIG.  3    can generate audible sound in some parts of the environment and a zone of quiet in another part of the environment. 
     Thus, in the example of  FIG.  3   , the speaker  118  is configured to project positive polarity sound, generated by a motion of the diaphragm  308 , through the acoustic port  305 , and to project negative polarity sound, generated by the motion of the diaphragm  308 , through the elongated channel  315 . In this example, the positive polarity sound, when projected through the acoustic port  305 , generates audible sound in a first region of the external environment of the speaker  118 , and the negative polarity sound, when projected through the elongated channel  315 , cancels at least a portion of the positive polarity sound in a second region of the external environment. 
     In the example of  FIG.  3   , the acoustic port  305  is aligned in a first direction and the elongated channel  315  is aligned in a second direction substantially perpendicular to the first direction. However, this is merely illustrative. In other implementations, the channel housing  310  and/or the elongated channel  315  defined therein can be oriented in any direction (relative to the first direction in which the acoustic port  305  is aligned) in which it is desired to cancel or suppress some or all of the sound emitted from the acoustic port  305 . 
     In the examples of  FIGS.  3  and  4   , the channel housing  310  is a cylindrical housing having a cylindrical interior cavity that defines a cylindrical elongated channel. However, in other implementations, the shape of the channel housing and/or the elongated channel defined therein can be rectilinear or can be implemented in any other arrangement with an elongated dimension and various cross-sectional shapes. In one or more implementations, the channel housing  310  and/or the elongated channel  315  defined therein can have a length that is similar to or substantially larger than a diameter of the diaphragm  308 . For example, diaphragm  308  may have a diameter of less than one inch, or between one inch and ten inches (as examples), and the channel housing  310  and/or the elongated channel  315  may have a longitudinal length of greater than ten inches or greater than twelve inches (as examples) from the housing  300  (e.g., from the first end  311  to the second end  312 ). 
     In the example of  FIG.  3   , the speaker  118  has a single channel housing  310  and a single corresponding elongated channel  315  coupled to the back volume  306 . However, in other implementations, a directional acoustic device such as the speaker  118  may have more than one channel housing defining more than one corresponding elongated channel coupled to the back volume  306 . 
     For example,  FIG.  5    illustrates an example in which the channel housing  310  is a first channel housing and the elongated channel  315  is a first elongated channel, and the speaker  118  includes a second channel housing (e.g., channel housing  501 ) extending from the housing  300  and defining a second elongated channel (e.g., elongated channel  515 ). In this example, the elongated channel  515  includes a first end  511  that is fluidly coupled to the back volume  306  and a second end  513  that is fluidly coupled to the external environment of the speaker  118 . As with the channel housing  310 , the channel housing  501  may include one or more slots (e.g., longitudinal slots such as slot  314  of  FIG.  3    and/or transverse slots such as slots  400  of  FIG.  4   ) that fluidly couple the elongated channel  515  with the external environment at one or more locations between the first end  511  and the second end  513 . For example, the channel housing  501  may include one or more slots that extend along the length of the channel housing  501  in parallel with a longitudinal axis of the channel housing  501  and the elongated channel  515  defined therein (e.g., as in the example of the slots  314  of the channel housing  310  of  FIG.  3   ), and/or one or more slots that are oriented transversely to the longitudinal axis of the channel housing  501  and are spaced apart along the length of the channel housing  501  in a direction that is parallel with the longitudinal axis of the channel housing  501  and the elongated channel  515  defined therein (e.g., as in the example of the slots  400  of the channel housing  310  of  FIG.  4   ). 
     In the example of  FIG.  5   , the elongated channel  315  and the elongated channel  515  extend along a common longitudinal axis  517  from opposing sidewalls  521  and  523  of the housing  300 . However, in other implementations, the elongated channel  315  and the elongated channel  515  may extend from the opposing sidewalls  521  and  523  of the housing  300  along laterally separated parallel longitudinal axes, or along longitudinal axes that are not parallel, to direct negative polarity sound from the back volume  306  to any of various desired locations and/or directions in the external environment for which cancellation or suppression of sound emitted from the acoustic port  305  is desired. 
     In the example of  FIG.  5   , a positive polarity sound  506  may be projected substantially omnidirectionally (e.g., over a hemisphere, in this example) from the acoustic port  305 , as indicated by arrows  500 . As shown, the positive polarity sound  506  propagates from the acoustic port  305  to regions  508 ,  510 ,  514 , and  518  in the external environment of the speaker  118 . However,  FIG.  5    also illustrates how negative polarity sound  512  is projected, in a direction  502 , from the elongated channel  515  defined by channel housing  501  to the region  514 , and negative polarity sound  516  is projected, in a direction  504 , from the elongated channel  315  defined by channel housing  310  to the region  518 . The negative polarity sound  512  may thus cancel at least a portion of the positive polarity sound  506  that is present in the region  514 , and the negative polarity sound  516  may thus cancel at least a portion of the positive polarity sound  506  that is present in the region  518 . In this way, the speaker  118  may generate audible sound at various locations and suppress or cancel the audible sound to generate one or more areas of relative quiet in the external environment of the speaker  118 . 
       FIG.  6    illustrates an example in which the speaker  118  of  FIG.  5    is implemented in an enclosed environment, in accordance with one or more implementations. In the example of  FIG.  6   , a top view of elements of the apparatus  100  of  FIG.  1    are shown, including the speaker  118  mounted at or near the top of the enclosed environment  131  defined by the enclosure  108 . For example, the speaker  118  may mounted to and/or partially within the support structure  104  of  FIG.  1    in one or more implementations. 
     As shown in  FIG.  6   , the apparatus  100  may include an enclosure  108  having one or more acoustically reflective portions such as reflective surfaces  112  and defining an enclosed environment  131 . For example, the acoustically reflective portions may be formed by planar or curved glass structures. In one or more implementations, the reflective surfaces  112  of the enclosure  108  may be implemented as windows or portions of a door of a room (e.g., a conference room in a building) or of a moveable platform (e.g., vehicle, such as an autonomous or semiautonomous vehicle). 
     In the example of  FIG.  6   , the apparatus  100  includes a seat  600  within the enclosed environment  131  for an occupant, and a speaker  118  (e.g., a directional speaker) configured to direct audio output toward the seat  600  and to cancel at least a portion of the audio output in a region (e.g., region  514 ) that is within the enclosed environment  131  and adjacent the acoustically reflective portion of the enclosure. The audio output from the speaker may be a positive polarity audio output (e.g., positive polarity sound  506 ) projected from an acoustic port (e.g., acoustic port  305 ) of the speaker  118 . As shown, in this implementation, the speaker  118  includes an elongated channel  515  fluidly coupled to a back volume  306  of the speaker  118 , and the speaker  118  is configured to cancel at least the portion of the audio output in the region  514  within the enclosure  108  and adjacent one of the acoustically reflective portions (e.g., reflective surface  112 ) of the enclosure  108 , by projecting a negative polarity audio output (e.g., negative polarity sound  512 ) from the back volume  306  through the elongated channel  515 . 
     In one or more implementations, the apparatus  100  may be implemented as a moveable platform such as a vehicle (e.g., an autonomous vehicle that navigates roadways using sensors and/or cameras and substantially without control by a human operator, a semiautonomous that includes human operator controls and that navigates roadways using sensors and/or cameras with the supervision of a human operator, or a vehicle with the capability of switching between a fully autonomous driving mode, a semiautonomous driving mode, and/or a human controlled mode). In various versions of such an implementation, any or all of the seats of the apparatus may be oriented toward the interior of the vehicle or facing out the sides of the vehicle (e.g., the left and/or right sides and/or the front and/or rear sides of the vehicle), facing toward the front of the vehicle, facing toward the rear of the vehicle, and/or rotatable between various orientations. 
     In the example of  FIG.  6   , the seat  600  is a first seat facing in a first direction (e.g., a forward direction of a vehicle) and the elongated channel  515  is a first elongated channel. In this example, the apparatus  100  (e.g., the autonomous or semiautonomous vehicle) includes a second seat (e.g., seat  604 ) in the enclosed environment  131  facing in a second direction opposite the first direction. For example, the seat  600  may include a seatback  602  that has seatback surface configured to interface with an occupant seated in the seat  600 , and the seatback  602  may define the direction in which the seat  600  faces. For example, the seat  604  may include a seatback  606  that has seatback surface configured to interface with an occupant seated in the seat  604 , and the seatback  606  may define the direction in which the seat  604  faces. In the example of  FIG.  6   , seat  604  faces the seat  600 , and may also be facing a rear of the apparatus  100 . However, this is merely illustrative and, in other implementations, the seat  604  may face in the same direction as the seat  600  (e.g., toward the front of a vehicle). In one or more implementations, the seat  604  may be rotatable from an orientation that faces in the same direction as the seat  600  (e.g., toward the front of a vehicle, such as in a human operator mode or a semi-autonomous mode) to an orientation that faces toward the seat  600  (e.g., in the opposite direction of the seat  600 , such as in an autonomous driving mode) or to another orientation such as facing out the left or right side of the vehicle (e.g., in the autonomous driving mode). 
     In one or more implementations, the acoustically reflective portion of the enclosure  108  may be formed from a first curved glass structure mounted to and extending from a first side of a central support structure (e.g., support structure  104  of  FIG.  1   ) that runs from a front end of the autonomous or semiautonomous vehicle to a rear end of the autonomous or semiautonomous vehicle. In the example of  FIG.  6   , the apparatus  100  (e.g., the autonomous or semiautonomous vehicle) includes a second acoustically reflective portion (e.g., a second reflective surface  112 , such as a surface of a second curved glass structure mounted to and extending from a second side of the central support structure). As shown the second acoustically reflective portion may be disposed adjacent the region  518  and opposite the first acoustically reflective portion that is adjacent the region  514 . 
     In the example of  FIG.  6   , the speaker  118  includes an elongated channel  315  (e.g., a second elongated channel in this example) fluidly coupled to the back volume  306  of the speaker  118 , and the speaker  118  is further configured to project the positive polarity audio output (e.g., the positive polarity sound  506 ) from the acoustic port  305  toward the seat  604  and to cancel at least a portion of the audio output in a region  518  within the enclosure  108  and adjacent the second curved glass structure by projecting the negative polarity audio output (e.g., negative polarity sound  516 ) from the back volume  306  through the elongated channel  315 . 
     In the example of  FIG.  6   , the speaker  118  may be implemented using the structures shown in  FIG.  3    and/or  FIG.  5   , including a housing  300 , an acoustic port  305  in the housing  300  and facing in a first direction, and a pair of directional audio features (e.g., a pair of elongated channels such as the elongated channel  315  and the elongated channel  515 ) that extend in respective second and third directions from the housing, the second and third directions substantially opposite to each other and substantially perpendicular to the first direction. In this example, an audio output (e.g., the negative polarity sound  512 ) from a first of the pair of directional features (e.g., the elongated channel  515 ) cancels at least the portion of the audio output (e.g., a portion of the positive polarity sound  506 ) in the region  514  within the enclosed environment  131  and adjacent the acoustically reflective portion (e.g., the reflective surface  112  adjacent the region  514 ) of the enclosure  108 , and an audio output (e.g., the negative polarity sound  516 ) from a second of the pair of directional features (e.g., the elongated channel  315 ) cancels at least another portion of the audio output in another region (e.g., region  518 ) within the enclosed space and adjacent another acoustically reflective portion (e.g., the reflective surface  112  adjacent the region  518 ) of the enclosure. As in the examples of  FIGS.  3  and  4   , each of the pair of directional features (e.g., the elongated channel  515  and the elongated channel  315  formed, respectively, by the channel housing  501  and the channel housing  310 ) includes one or more slots (e.g., one or more slots  314  and/or one or more slots  400 ) that allow a portion of a negative polarity audio output from a back volume  306  of the speaker  118  to exit the respective directional feature into the enclosed environment  131 . 
     In the examples of  FIGS.  5  and  6   , the speaker  118  includes two directional audio features (e.g., the elongated channel  515  and the elongated channel  315  formed, respectively, by the channel housing  501  and the channel housing  310 ) that extend in opposite directions from the housing  300 .  FIG.  7    illustrates a three-dimensional representation of the audio power of the speaker  118  in an implementation in which positive polarity sound is emitted omnidirectionally from the speaker  118 , and the speaker  118  includes two directional audio features (e.g., the elongated channel  515  and the elongated channel  315  formed, respectively, by the channel housing  501  and the channel housing  310 ) that extend in opposite directions from the housing  300 . As shown in  FIG.  7   , the emission of the audible sound is projected into the regions  508  and  510  (e.g., in the positive and negative “x” directions in the figure), and cut off from projecting into the regions  514  and  518  (e.g., in the positive and negative “y” directions in the figure).  FIG.  8    illustrates a two-dimensional representation of audio power as a function of azimuth and frequency, showing that the speaker  118  of  FIGS.  5  and  6    can generate a “notch cardioid” emission pattern having emission bands  800  that are substantially narrower than a conventional cardioid pattern. 
     Although the examples of  FIGS.  5  and  6    illustrate a speaker  118  that includes two directional audio features (e.g., the elongated channel  515  and the elongated channel  315  formed, respectively, by the channel housing  501  and the channel housing  310 ) for cancelling sound from the speaker in two corresponding directions, the speaker  118  may include one or more additional directional features that extend in one or more other directions for which cancellation or suppression of the emitted sound of the speaker is desired. 
     For example,  FIG.  9    illustrates an implementation in which the speaker  118  includes a third channel housing  910  extending from the housing  300  and defining a third elongated channel  915  with a first end  911  that is fluidly coupled to the back volume  306  and a second end  913  that is fluidly coupled to the external environment of the speaker  118 . As shown, the third channel housing  910  may include a slot  914  that fluidly couples the third elongated channel  915  with the external environment at a location between the first end  911  and the second end  913 . In this example, the third elongated channel  915  extends along a longitudinal axis that is substantially perpendicular to the common longitudinal axis (e.g., the common longitudinal axis  517  shown in  FIG.  5   ) of the elongated channel  515  and the elongated channel  315 . 
     In the example of  FIG.  9   , negative polarity sound  900  emitted from the back volume  306  via the third elongated channel  915  cancels a portion of the positive polarity sound  506  in the region  508 . In one or more implementations, the speaker  118  in the configuration of  FIG.  9    may be mounted differently in an apparatus  100  than the speaker  118  in the configuration of  FIGS.  5  and  6   . For example, in the configuration of  FIGS.  5  and  6   , the speaker  118  may be mounted with the acoustic port  305  facing downward (e.g., toward a floor of the apparatus) or upward (e.g., toward a ceiling of the apparatus), such as to primarily project audible sound in forward and rearward directions within the apparatus  100 , while cancelling or suppressing sound in left and right directions. 
     In the configuration of  FIG.  9   , the speaker  118  (e.g., including three directional components) may be mounted within the apparatus  100  such that the acoustic port  305  faces a seat (e.g., seat  600  or seat  604 ) within the apparatus, and cancels the audio output in the direction of one or more other seats and/or one or more non-occupant locations within the apparatus. This configuration can be useful, for example, for directing personalized audio content (e.g., personalized notifications) to a particular occupant within the enclosure  108 . For example, the speaker  118  in the configuration of  FIG.  9    may be used to notify an occupant in a particular seat within an autonomous or semiautonomous vehicle that the autonomous or semiautonomous vehicle has reached the destination of that occupant, to play audio corresponding to video being viewed by that occupant (e.g., on a personalized video screen for that occupant or personal device of that occupant), and/or to provide any other personized audio content to a particular occupant at a particular location toward which the acoustic port  305  faces. 
     In the examples of  FIGS.  3 - 9   , the directional audio cancelling features of the speaker  118  are provided whenever the speaker  118  is operating (e.g., passively due to the venting of back volume pressure through the elongated channels). In some use cases, it may also be desirable to be able to selectively use the directional audio cancelling features of a directional speaker. 
       FIG.  10    illustrates an example in which the directional audio cancelling features of a directional speaker, such as speaker  118 , can be selectively activated and deactivated. In the example of  FIG.  10   , speaker  118  is provided with multiple sound-generating elements that can be operated in-phase or out-of-phase. In the example of  FIG.  10   , a single channel housing  310  and corresponding elongated channel  315  and slot  314  are shown, for simplicity of the discussion of the multiple sound-generating elements. However, it is appreciated that the speaker  118  of  FIG.  10    can be provided with two elongated channels as in the examples of  FIGS.  5  and  6   , three elongated channels as in the example of  FIG.  9   , or any suitable number of elongated channels coupled to the back volume  306 . 
     In the example of  FIG.  10   , speaker  118  includes, in addition to the acoustic port  305  and the diaphragm  308  described in, for example,  FIG.  3   , an additional acoustic port  1005  in the housing  300 . As shown, the acoustic port  305  and the additional acoustic port  1005  may face in directions that are substantially opposite and substantially perpendicular to the direction along which the channel housing  310  extends in one or more implementations. For example, in an implementation in which the speaker  118  includes two elongated channels from the back volume  306  (e.g., acoustic ducts defined by the channel housing  310  and the channel housing  501 , as in the examples of  FIGS.  5  and  6   ), the acoustic port  305  may face in a first direction, elongated channels  315  and  515  defined respectively by the channel housing  310  and the channel housing  501  may face in second and third directions substantially perpendicular to the first direction, and the additional acoustic port  1005  may face in a fourth direction substantially opposite the first direction and substantially perpendicular to the second and third directions. In one or more other implementations (e.g., an implementation in which the speaker  118  includes a single elongated channel  315  as in the example of  FIG.  10   ), the acoustic port  305  and the acoustic port  1005  may face in different directions that are not anti-parallel (e.g., substantially perpendicular directions or other relative different directions). 
     In the example of  FIG.  10   , the speaker  118  may include the diaphragm  308  (e.g., a first diaphragm that separates the acoustic port  305  from the back volume  306  of the speaker  118 ), and a second diaphragm  1008  that separates the additional acoustic port  1005  from the back volume  306  of the speaker  118 . In this configuration, because the diaphragm  308  and the second diaphragm  1008  (e.g., interior surfaces of the diaphragm  308  and the second diaphragm  1008 ) interface with the same back volume  306 , operating the diaphragm  308  and the second diaphragm  1008  in phase (e.g., to both output positive polarity sounds) causes pressure changes within the back volume  306  that cause negative polarity sound  1100  to be directed through the elongated channel  315  defined by the channel housing  310  (e.g., and/or through any other elongated channels coupled to the back volume), which cancels a portion of the positive polarity sound in the direction of the elongated channel  315  (e.g., as shown in  FIG.  11   ). In this use case, the directional audio cancelling features of the speaker  118  are activated. 
     In another use case illustrated in  FIG.  12   , operating the diaphragm  308  and the second diaphragm  1008  out of phase (e.g., to output positive polarity sound from the acoustic port  1005  and negative polarity sound from the acoustic port  305 ) causes the pressure within the back volume  306  to remain substantially constant, in which case no sound (e.g., a zero output  1200 ) is projected through the elongated channel  315  defined by the channel housing  310  (e.g., and/or through any other elongated channels coupled to the back volume). In this use case, the directional audio cancelling features of the speaker  118  are deactivated. Thus, by modifying the in-phase/out-of-phase operation of the two speaker diaphragms, the directional audio suppression features of the speaker  118  can be turned on and off, in one or more implementations. 
       FIG.  13    illustrates a flow diagram of an example process  1300  for operating a directional acoustic device in accordance with implementations of the subject technology. For explanatory purposes, the process  1300  is primarily described herein with reference to the apparatus  100  and the speaker  118  of  FIGS.  1 - 12   . However, the process  1300  is not limited to the apparatus  100  and the speaker  118 , and one or more blocks (or operations) of the process  1300  may be performed by one or more other components of other suitable devices or systems. Further for explanatory purposes, some of the blocks of the process  1300  are described herein as occurring in serial, or linearly. However, multiple blocks of the process  1300  may occur in parallel. In addition, the blocks of the process  1300  need not be performed in the order shown and/or one or more blocks of the process  1300  need not be performed and/or can be replaced by other operations. 
     As illustrated in  FIG.  13   , at block  1302 , a sound may be generated, with a speaker (e.g., speaker  118 ), at an occupant location (e.g., a location in the region  508  or a location within the region  510 ) of an enclosed space (e.g., enclosed environment  131 ). For example, the occupant location may be a location of a seat (e.g., an implementation of a support feature  117 , such as a seat  600  or a seat  604 ) within the enclosed space. Generating the sound may include actuating a sound generating element of the speaker, such as a diaphragm  308  of the speaker  118 . The sound may be a positive polarity sound (e.g., positive polarity sound  506 ) generated by the actuation of the diaphragm. 
     At block  1304 , the sound may be suppressed, with an acoustic duct structure (e.g., an elongated channel, such as elongated channel  315 ,  515 , and/or  915 , that is fluidly coupled to a back volume  306  of the speaker and defined by a channel housing, such as channel housing  310 ,  501 , and/or  910 ) of the speaker and concurrently with the generating of the sound at the occupant location, at a non-occupant location (e.g., a location within the region  514 , the region  518 , or the region  508 ) of the enclosed space. For example, the non-occupant location may be a location adjacent an acoustically reflective surface (e.g., reflective surface  112 , such as a top housing structure  138  and/or a sidewall housing structure  140 ) of an enclosure (e.g., enclosure  108 ) defining the enclosed space. 
     For example, suppressing the sound at the non-occupant location may include projecting, through the acoustic duct structure from a back volume of the speaker, a negative polarity version of the sound (e.g., negative polarity sound  512 , negative polarity sound  516 , or negative polarity sound  900 ) that cancels the portion of the positive polarity sound that is present at the non-occupant location. In one or more implementations, the sound may also be suppressed at one or more additional non-occupant locations, such as by projecting the negative polarity version of the sound through one or more additional acoustic duct structures that are fluidly coupled to the back volume of the speaker that is generating the positive polarity sound. 
     In one or more implementations generating the sound at the occupant location may include operating first and second speaker membranes in phase (e.g., as described herein in connection with  FIGS.  10  and  11   ). In these implementations, the process  1300  may also include ceasing suppressing the sound at the non-occupant location of the enclosed space by operating the first and second speaker membranes out of phase (e.g., as described herein in connection with  FIG.  12   ). 
       FIG.  14    illustrates a flow diagram of an example process  1400  that may be performed as part of, or separately from, the process  1300  of  FIG.  13   , in accordance with implementations of the subject technology. For explanatory purposes, the process  1400  is primarily described herein with reference to the apparatus  100  and the speaker  118  of  FIGS.  1 - 12   . However, the process  1400  is not limited to the apparatus  100  and the speaker  118  of  FIGS.  1 - 12   , and one or more blocks (or operations) of the process  1400  may be performed by one or more other components of other suitable devices or systems. Further for explanatory purposes, some of the blocks of the process  1400  are described herein as occurring in serial, or linearly. However, multiple blocks of the process  1400  may occur in parallel. In addition, the blocks of the process  1400  need not be performed in the order shown and/or one or more blocks of the process  1400  need not be performed and/or can be replaced by other operations. 
     As illustrated in  FIG.  14   , a sound may be generated, with a speaker (e.g., speaker  118 ), at an occupant location (e.g., a location within the region  508  or a location within the region  510 ) of an enclosed space (e.g., the enclosed environment  131  defined by the enclosure  108 ) by, at block  1402 , operating a sound-generating component (e.g., diaphragm  308 ) of the speaker to generate positive polarity sound (e.g., positive polarity sound  506 ) on a first side of the sound-generating component and negative polarity sound (e.g., negative polarity sound  512 ,  516 , and/or  900 ) on a second side of the sound-generating component, and, at block  1404 , projecting the positive polarity sound from an acoustic port (e.g., acoustic port  305 ) of the speaker toward the occupant location of the enclosed space. 
     As illustrated in  FIG.  14   , the sound may be suppressed, with an acoustic duct structure (e.g., elongated channel  315  defined by channel housing  310 , elongated channel  515  defined by channel housing  501 , and/or elongated channel  915  defined by channel housing  910 ) of the speaker and concurrently with the generating of the sound at the occupant location, at a non-occupant location (e.g., a location within the region  514  and/or a location within the region  518 ) of the enclosed space by, at block  1406 , projecting the negative polarity sound from the acoustic duct structure toward the non-occupant location of the enclosed space. In one or more implementations, the process  1300  and/or the process  1400  may also include suppressing the sound, with an additional acoustic duct structure of the speaker and concurrently with the generating of the sound at the occupant location and the suppressing of the sound at the non-occupant location, at an additional non-occupant location of the enclosed space (e.g., as described herein in connection with, for example,  FIGS.  5 ,  6   , and/or  9 ). 
     Various processes defined herein consider the option of obtaining and utilizing a user&#39;s personal information. For example, such personal information may be utilized in order to provide personalized audio from a directional acoustic device. However, to the extent such personal information is collected, such information should be obtained with the user&#39;s informed consent. As described herein, the user should have knowledge of and control over the use of their personal information. 
     Personal information will be utilized by appropriate parties only for legitimate and reasonable purposes. Those parties utilizing such information will adhere to privacy policies and practices that are at least in accordance with appropriate laws and regulations. In addition, such policies are to be well-established, user-accessible, and recognized as in compliance with or above governmental/industry standards. Moreover, these parties will not distribute, sell, or otherwise share such information outside of any reasonable and legitimate purposes. 
     Users may, however, limit the degree to which such parties may access or otherwise obtain personal information. For instance, settings or other preferences may be adjusted such that users can decide whether their personal information can be accessed by various entities. Furthermore, while some features defined herein are described in the context of using personal information, various aspects of these features can be implemented without the need to use such information. As an example, if user preferences, account names, and/or location history are gathered, this information can be obscured or otherwise generalized such that the information does not identify the respective user. 
     In accordance with aspects of the subject disclosure, an acoustic device is provided that includes a diaphragm mounted in a housing; a front volume on a first side of the diaphragm; a back volume on an opposing second side of the diaphragm and at least partially defined by the housing; an acoustic port fluidly coupling the front volume to an external environment of the acoustic device; and a channel housing extending from the housing and defining an elongated channel with a first end that is fluidly coupled to the back volume and a second end that is fluidly coupled to the external environment, the channel housing having a slot that fluidly couples the elongated channel with the external environment at a location between the first end and the second end. 
     In accordance with aspects of the subject disclosure, an apparatus is provided that includes an enclosure having an acoustically reflective portion and defining an enclosed environment; a seat within the enclosed environment for an occupant; and a directional speaker configured to direct audio output toward the seat and to cancel at least a portion of the audio output in a region that is within the enclosed environment and adjacent the acoustically reflective portion of the enclosure. 
     In accordance with aspects of the subject disclosure, a method is provided that includes generating, with a speaker, sound at an occupant location of an enclosed environment; and suppressing the sound, with an acoustic duct structure of the speaker and concurrently with the generating of the sound at the occupant location, at a non-occupant location of the enclosed environment. 
     Implementations within the scope of the present disclosure can be partially or entirely realized using a tangible computer-readable storage medium (or multiple tangible computer-readable storage media of one or more types) encoding one or more instructions. The tangible computer-readable storage medium also can be non-transitory in nature. 
     The computer-readable storage medium can be any storage medium that can be read, written, or otherwise accessed by a general purpose or special purpose computing device, including any processing electronics and/or processing circuitry capable of executing instructions. For example, without limitation, the computer-readable medium can include any volatile semiconductor memory, such as RAM, DRAM, SRAM, T-RAM, Z-RAM, and TTRAM. The computer-readable medium also can include any non-volatile semiconductor memory, such as ROM, PROM, EPROM, EEPROM, NVRAM, flash, nvSRAM, FeRAM, FeTRAM, MRAM, PRAM, CBRAM, SONOS, RRAM, NRAM, racetrack memory, FJG, and Millipede memory. 
     Further, the computer-readable storage medium can include any non-semiconductor memory, such as optical disk storage, magnetic disk storage, magnetic tape, other magnetic storage devices, or any other medium capable of storing one or more instructions. In one or more implementations, the tangible computer-readable storage medium can be directly coupled to a computing device, while in other implementations, the tangible computer-readable storage medium can be indirectly coupled to a computing device, e.g., via one or more wired connections, one or more wireless connections, or any combination thereof. 
     Instructions can be directly executable or can be used to develop executable instructions. For example, instructions can be realized as executable or non-executable machine code or as instructions in a high-level language that can be compiled to produce executable or non-executable machine code. Further, instructions also can be realized as or can include data. Computer-executable instructions also can be organized in any format, including routines, subroutines, programs, data structures, objects, modules, applications, applets, functions, etc. As recognized by those of skill in the art, details including, but not limited to, the number, structure, sequence, and organization of instructions can vary significantly without varying the underlying logic, function, processing, and output. 
     While the above discussion primarily refers to microprocessor or multi-core processors that execute software, one or more implementations are performed by one or more integrated circuits, such as ASICs or FPGAs. In one or more implementations, such integrated circuits execute instructions that are stored on the circuit itself. 
     Those of skill in the art would appreciate that the various illustrative blocks, modules, elements, components, methods, and algorithms described herein may be implemented as electronic hardware, computer software, or combinations of both. To illustrate this interchangeability of hardware and software, various illustrative blocks, modules, elements, components, methods, and algorithms have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application. Various components and blocks may be arranged differently (e.g., arranged in a different order, or partitioned in a different way) all without departing from the scope of the subject technology. 
     It is understood that any specific order or hierarchy of blocks in the processes disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes may be rearranged, or that all illustrated blocks be performed. Any of the blocks may be performed simultaneously. In one or more implementations, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     As used in this specification and any claims of this application, the terms “base station”, “receiver”, “computer”, “server”, “processor”, and “memory” all refer to electronic or other technological devices. These terms exclude people or groups of people. For the purposes of the specification, the terms “display” or “displaying” means displaying on an electronic device. 
     As used herein, the phrase “at least one of” preceding a series of items, with the term “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (i.e., each item). The phrase “at least one of” does not require selection of at least one of each item listed; rather, the phrase allows a meaning that includes at least one of any one of the items, and/or at least one of any combination of the items, and/or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or at least one of each of A, B, and C. 
     The predicate words “configured to”, “operable to”, and “programmed to” do not imply any particular tangible or intangible modification of a subject, but, rather, are intended to be used interchangeably. In one or more implementations, a processor configured to monitor and control an operation or a component may also mean the processor being programmed to monitor and control the operation or the processor being operable to monitor and control the operation. Likewise, a processor configured to execute code can be construed as a processor programmed to execute code or operable to execute code. 
     Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some implementations, one or more implementations, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the subject technology or that such disclosure applies to all configurations of the subject technology. A disclosure relating to such phrase(s) may apply to all configurations, or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples. A phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment described herein as “exemplary” or as an “example” is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, to the extent that the term “include”, “have”, or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim. 
     All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for”. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. Unless specifically stated otherwise, the term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neutral gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the subject disclosure.