PATENT DOCUMENT

Publication Number: US-10250972-B2
Application Number: US-201715468030-A
Country: US
Kind Code: B2

Title: Phase plug having non-round face profile

Abstract:
A phase plug having an input face circumscribed by a round profile and an output face circumscribed by a non-round profile, is described. The phase plug may include several arms radiating from a central axis and separated by radial channels extending axially from the input face to the output face. Planes containing the round profile and the non-round profile may be nonparallel, and sound ports at the output face may be asymmetrically disposed about a midline of the output face. Other embodiments are also described and claimed.

Claims:
What is claimed is: 
     
       1. A phase plug, comprising:
 a plug body having an input face separated from an output face along a central axis, wherein a round profile extends around the central axis on a proximal transverse plane and circumscribes the input face, wherein a non-round profile extends around the central axis on a distal transverse plane and circumscribes the output face, wherein the plug body includes a plurality of arms radiating from the central axis at the output face, wherein the plurality of arms have respective sidewalls forming a sound channel between the sidewalls, and wherein the sound channel radiates from the central axis and extends axially from the proximal transverse plane to the distal transverse plane between the plurality of arms. 
 
     
     
       2. The phase plug of  claim 1 , wherein the round profile is circular, and wherein the non-round profile is rectangular. 
     
     
       3. The phase plug of  claim 1 , wherein the plug body includes a central hub extending along the central axis, wherein each of the plurality of arms includes a pair of sidewalls extending radially outward from the central hub to an outer surface facing away from the central hub, and wherein each of the plurality of arms includes a distal surface defining a portion of the output face and extending between the pair of sidewalls. 
     
     
       4. The phase plug of  claim 3 , wherein each of the plurality of arms includes a cavity between the pair of sidewalls, and wherein at least one of the pair of sidewalls is between the cavity and the sound channel. 
     
     
       5. The phase plug of  claim 4 , wherein each of the plurality of arms includes a proximal surface defining a portion of the input face, wherein the cavity extends through the proximal surface, and wherein the pair of sidewalls, the central hub, the distal surface, and the outer surface surround the cavity. 
     
     
       6. The phase plug of  claim 4 , wherein each of the plurality of arms includes a proximal surface defining a portion of the input face, wherein the cavity extends through the outer surface, and wherein the pair of sidewalls, the central hub, the distal surface, and the proximal surface surround the cavity. 
     
     
       7. The phase plug of  claim 3 , wherein the output face is flat. 
     
     
       8. The phase plug of  claim 7 , wherein each of the plurality of arms includes a transitional edge between one of the pair of sidewalls and the output face. 
     
     
       9. The phase plug of  claim 7 , wherein the output face is not parallel to the input face. 
     
     
       10. The phase plug of  claim 3 , wherein the distal surfaces of the plurality of arms have distal surface areas at the distal transverse plane, and wherein the distal surface areas are asymmetrically sized. 
     
     
       11. The phase plug of  claim 10 , wherein a midline extends within the distal transverse plane and through the central axis, and wherein the distal surface areas on a first side of the midline are larger than the distal surface areas on a second side of the midline. 
     
     
       12. A phase plug, comprising:
 a plug body having an input face and an output face separated along a central axis, wherein a non-round profile circumscribes the output face, wherein the plug body includes a plurality of arms radiating from the central axis at the output face, wherein the plurality of arms have respective sidewalls forming a sound channel between the sidewalls, wherein each of the plurality of arms includes an outer surface extending axially from a rear edge on the input face to a front edge on the output face, wherein the rear edge is a smooth curve, and wherein the front edge includes an angle. 
 
     
     
       13. The phase plug of  claim 12 , wherein the plug body includes a circular profile extending around the central axis and circumscribing the input face, wherein the plug body includes a rectangular profile extending around the central axis and circumscribing the output face, wherein the circular profile includes the smooth curve, and wherein the rectangular profile includes the angle. 
     
     
       14. The phase plug of  claim 12 , wherein the plug body includes a central hub, wherein each of the plurality of arms includes a pair of sidewalls extending radially from the central hub to the outer surface, and wherein each of the plurality of arms includes a distal surface defining a portion of the output face and extending between the pair of sidewalls. 
     
     
       15. The phase plug of  claim 14 , wherein the plug body includes a circular profile extending around the central axis and circumscribing the input face within a proximal transverse plane, and wherein the output face is not parallel to the proximal transverse plane. 
     
     
       16. The phase plug of  claim 14 , wherein each of the plurality of arms includes a transitional edge between one of the pair of sidewalls and the output face. 
     
     
       17. A loudspeaker, comprising:
 a driver having a diaphragm; 
 a horn coupled to the driver, the horn having a mouth, and a throat on a throat plane; and 
 a phase plug between the diaphragm and the throat, the phase plug including a plug body having an input face facing the diaphragm and an output face facing the throat, wherein the output face is separated from the input face along a central axis, wherein the plug body includes a round profile extending around the central axis and circumscribing the input face, wherein the plug body includes a non-round profile extending around the central axis and circumscribing the output face, wherein the plug body includes a plurality of arms radiating from the central axis at the output face, wherein the plurality of arms have respective sidewalls forming a sound channel between the sidewalls, and wherein the sound channel extends axially from the diaphragm to the throat between the plurality of arms. 
 
     
     
       18. The loudspeaker of  claim 17 , wherein the plug body includes a central hub, wherein each of the plurality of arms extends radially from the central hub, wherein the round profile is circular, and wherein the non-round profile is rectangular. 
     
     
       19. The loudspeaker of  claim 17 , wherein the output face is proximal to the throat, wherein the output face is parallel to the throat plane, and wherein the output face is not parallel to a proximal transverse plane containing the round profile. 
     
     
       20. The loudspeaker of  claim 17 , wherein the loudspeaker includes a back volume behind the diaphragm, wherein each of the plurality of arms includes a pair of sidewalls extending radially from the central axis and a cavity between the pair of sidewalls, and wherein the cavity is a portion of the back volume.

Description:
BACKGROUND 
     Field 
     Embodiments related to loudspeakers, are disclosed. More particularly, embodiments related to loudspeakers having phase plugs, are disclosed. 
     Background Information 
     Loudspeakers, e.g., horn loudspeaker, can include a speaker diaphragm to radiate sound into a throat of an acoustic horn. The acoustic horn transmits the sound along an enlarging horn volume from the throat to a mouth, and radiates the sound efficiently from the mouth into a surrounding environment. A phase plug is used to direct sound waves from the diaphragm to the throat. A device that contains a phase plug between a diaphragm and an exit of the device is commonly known as a compression driver. In the context of compression drivers, a phase plug may be placed between the speaker diaphragm and the throat. Slots in the phase plug direct sound from an input side, i.e., at the radiating surface of the diaphragm. The slots are shaped to recombine the radiated sound in phase at an output side, i.e., at the throat. Circumferential-type phase plugs have annular slots that extend circumferentially around a central axis. The radiating diaphragm and the receiving throat are typically circular. Accordingly, the phase plug typically has an input side and an output side that both include circular profiles to match the adjacent diaphragm and throat geometries. 
     SUMMARY 
     Phase plugs having circular profiles at both an input side and an output side function when used in loudspeakers having conventional acoustic horns. More particularly, when the acoustic horn has a circular cross-sectional area at a throat that transitions gradually from the throat to a circular or non-circular cross-sectional area at a mouth, then a circular output side of a phase plug may match the acoustic horn. If the acoustic horn had a specialized geometry, however, a typical phase plug may not adequately match the acoustic horn. For example, if an acoustic horn has a sharp bend between a throat and a mouth, the throat could have a non-circular cross-sectional area, and a circular-output phase plug may not match the acoustic horn. 
     In an embodiment, a loudspeaker includes a phase plug between a diaphragm of a speaker driver and a throat of an acoustic horn. The phase plug conforms to the geometry of the diaphragm and the throat, and thus, an input face of the phase plug adjacent to the diaphragm may have a geometry different than an output face of the phase plug adjacent to the throat. More particularly, the input face may have a round profile extending around a central axis, and the output face may have a non-round profile extending around the central axis. The round profile may match a shape of the diaphragm, and the non-round profile may match a shape of the throat. For example, the round profile may be circular to match a circular diaphragm, and the non-round profile may be rectangular to match a rectangular throat. The phase plug may have several arms separated from each other by intervening radial channels. That is, the radial channels may extend axially from the input face to the output face between adjacent arms to carry sound from the diaphragm to the horn throat. 
     The arms of the phase plug may extend radially from a central hub disposed along the central axis, and each arm may have a radially-facing outer surface. In an embodiment, at least one of the outer surfaces includes a portion of the input face and the output face, and the outer surface transitions in an axial direction from a smooth curve at the round profile of the input face to an angle at the non-round profile of the output face. Similarly, the outer surface may transition in the axial direction from a smooth contour surface to an angled contour surface having a ridge. 
     In an embodiment, the input face and the output face are oriented to conform to an angle of the diaphragm and the throat relative to the central axis. For example, the central axis may be orthogonal to a radiating surface of the diaphragm and oblique to a throat plane. A distal plane containing the non-round profile circumscribing the output face may be tilted to be parallel to the throat plane, and a proximal plane containing the round profile circumscribing the input face may be parallel to the radiating surface. Thus, the distal plane containing the profile of the output face may not be parallel to the proximal plane containing the profile of the input face. The asymmetry in the phase plug geometry may allow the phase plug to conform to adjacent loudspeaker components. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a loudspeaker, in accordance with an embodiment. 
         FIG. 2  is a perspective view of a phase plug, in accordance with an embodiment. 
         FIG. 3  is a schematic view of envelope profiles of a phase plug, in accordance with an embodiment. 
         FIG. 4  is a side view of an envelope of a phase plug, in accordance with an embodiment. 
         FIG. 5  is a perspective view of a phase plug, in accordance with an embodiment. 
         FIG. 6  is a front view of an output face of a phase plug, in accordance with an embodiment. 
         FIG. 7  is a rear view of an input face of a phase plug, in accordance with an embodiment. 
         FIG. 8  is a schematic view of interconnected radial channel areas of a phase plug, in accordance with an embodiment. 
         FIG. 9  is a front view of a portion of an arm of a phase plug, in accordance with an embodiment. 
         FIGS. 10A-10B  are cross-sectional views, taken about line A-A of  FIG. 9 , of an arm of a phase plug having a cavity, in accordance with an embodiment. 
         FIGS. 11A-11B  are cross-sectional views, taken about line B-B of  FIG. 9 , of an arm of a phase plug having a cavity, in accordance with an embodiment. 
         FIG. 12  is a detail view, taken from Detail A of  FIG. 10B , of a transitional edge of an arm of a phase plug, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe a phase plug having an input face circumscribed by a round profile and an output face circumscribed by a non-round profile. The phase plug may be a component of a loudspeaker used in a consumer electronics device, such as a desktop computer, a laptop computer, a tablet computer, a mobile device, a wearable computer, or a loudspeaker system. The phase plug may, however, be incorporated into other devices and apparatuses, such as a medical device or a motor vehicle, to name only a few possible applications. 
     In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment,” or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment,” or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description may denote a relative position or direction. For example, “in front of” may indicate a first direction away from a reference point. Similarly, “behind” may indicate a location in a second direction orthogonal to the first direction. Such terms are provided to establish relative frames of reference, however, and are not intended to limit the use or orientation of a phase plug to a specific configuration described in the various embodiments below. 
     In an aspect, a phase plug includes a first face, e.g., an input face, circumscribed by a round profile, and a second face, e.g., an output face, circumscribed by a non-round profile. The phase plug may have an envelope defined by radiating arms and radially oriented slots. A lateral surface of the envelope can transition from the input face to the output face. More particularly, outer surfaces of the arms can transition from a smooth curve at the input face to an angled edge at the output face. Accordingly, the phase plug can transition between a round input face to a rectangular output face. The input face can conform to a loudspeaker diaphragm and the output face can conform to a throat of a loudspeaker horn. 
     Referring to  FIG. 1 , a cross-sectional view of a loudspeaker is shown in accordance with an embodiment. A loudspeaker  100  may include a driver  102  to radiate sound toward a phase plug  104 . Loudspeaker  100  may be a horn loudspeaker having a compression driver coupled to an acoustic horn  106 . Driver  102  can include a diaphragm  108  coupled to a speaker motor, e.g., a voicecoil and magnet assembly. The motor can drive diaphragm  108  back-and-forth along a central axis  110  to radiate sound toward horn  106  through phase plug  104 . Phase plug  104  may include an input face  112  adjacent to (and/or facing) diaphragm  108 , and an output face  114  adjacent to (and/or facing) a throat  116  of horn  106 . Output face  114  may be separated from input face  112  along central axis  110 , and thus, sound radiated by diaphragm  108  may enter input face  112  and travel through phase plug  104  along central axis  110  to exit from output face  114  toward throat  116 . 
     Horn  106  may extend along a horn axis  120  between throat  116  and a mouth  122 . Throat  116  can be disposed on a throat plane  118  oriented transverse to central axis  110 . More particularly, throat  116  can include a cross-sectional area on throat plane  118 , and the cross-sectional area may have an area profile extending around central axis  110 . The cross-sectional area of horn  106  may change along horn axis  120 . For example, the cross-sectional area at throat  116  may be noncircular, and the cross-sectional area of horn  106  at mouth  122  may be circular. The transition between throat  116  and mouth  122  may occur over one or more bends in horn  106 . For example, horn axis  120  may have a bend  124  near throat  116  such that a portion of horn axis  120  proximal to bend  124  is more closely aligned with central axis  110  than a distal portion of horn axis  120  distal to bend  124 . To transmit high-frequency sound waves through bend  124 , it may be advantageous to have an asymmetric cross-sectional profile at throat  116 . That is, high-frequency sound waves may transmit better through bend  124  when a width of a throat area differs from a length of the throat area. Accordingly, the cross-sectional area of throat  116  may be noncircular. In an embodiment, throat  116  has a rectangular cross-sectional area. 
     Phase plug  104  may be disposed between driver  102  and horn  106 . In an embodiment, output face  114  is adjacent to throat  116 . For example, output face  114  maybe coplanar with throat plane  118 . Alternatively, output face  114  may be proximal to throat  116 , i.e., output face  114  may be spaced apart from throat  116  between input face  112  and throat plane  118 . Output face  114  may be parallel to throat plane  118 . As described below, output face  114  may or may not be parallel to input face  112 . That is, planes containing the profiles of input face  112  and output face  114  may be parallel or non-parallel to each other. Accordingly, phase plug  104  may conform to diaphragm  108  at a proximal end and may conform to throat  116  at a distal end. 
     Driver  102  of loudspeaker  100  may include a back volume  126  behind diaphragm  108 . As described below, back volume  126  may be in fluid communication with phase plug  104 . That is, phase plug  104  may include one or more cavities, and the cavities may form portions of back volume  126 . That is, the cavities may be in fluid communication with back volume  126 . Accordingly, phase plug  104  as described below can increase back volume  126  as compared to existing phase plugs. An increased back volume size can improve loudspeaker low frequency efficiency. 
     In an embodiment, phase plug  104  is mounted within a housing  150 . Housing  150  may be a shell that mates with an outer envelope surface of phase plug  104 . Sound is directed though housing  150  from diaphragm  108  to throat  116 , and more particularly, sound is directed through channels formed between housing  150  and phase plug  104 , as is known in the art. Housing may be a membrane wrapped over an outer envelope surface of phase plug  104 , or may be an integral part, e.g., a molded part, that mates with phase plug  104  by receiving phase plug within an inner volume. The inner volume may be defined by an inner surface of a wall of housing  150 . For example, housing  150  may have a wall of a predetermined thickness between the inner surface and an outer surface. Accordingly, the inner volume may have a geometry matching an outer geometry of phase plug  104 . That is, the inner volume of housing  150  may have an entrance profile that is round and an exit profile that is non-round. The inner volume may be a lofted volume transitioning between a curve of the entrance profile to an angle of the exit profile, and thus, may conform to the envelope of phase plug  104  described below. Housing  150  forces sound waves to go through channels defined between arms of phase plug  104  from the entrance of the inner volume to the exit of the inner volume. That is, housing  150  may separate the sound-propagating channels of phase plug  104  from back volume  126 . In an embodiment, housing  150  may provide a partition between sound-propagating channels of phase plug  104  while allowing fluid communication between back volume  126  and non-sound-propagating cavities of phase plug  104 , as described below with respect to  FIG. 10A . 
     Referring to  FIG. 2 , a perspective view of a phase plug is shown in accordance with an embodiment. Phase plug  104  may have a plug body  202 . In an embodiment, plug body  202  is a monolith. That is, the plug body  202  can be formed as a single piece having the features described below. By way of example, plug body  202  can be a singular part formed by a molding process. 
     Plug body  202  may have several arms  204  extending between input face  112  and output face  114 . For example, each arm  204  may extend radially outward from a central hub  206  of plug body  202 . Central hub  206  may be a central shaft-like portion oriented and extending along central axis  110 . By way of example, central hub  206  may have a rectangular cross-sectional area. Each arm  204  may be attached to central hub  206  at an innermost region  207 . Each arm  204  may radiate, i.e., extend radially, from central axis  110 . More particularly, arms  204  can have cross-sections spreading in a transverse direction from central hub  206 . The arms  204  may project toward an outer surface  208  radially outward from the innermost region. Outer surface  208  of each arm  204  may extend axially from input face  112  at a proximal end of phase plug  104  to output face  114  at a distal end of phase plug  104 . Outer surface  208  may be concave and curve around central axis  110  and central hub  206 . 
     In an embodiment, phase plug  104  has an envelope bounded at a proximal end by input face  112  and at a distal end by output face  114 . The envelope has a lateral surface bounded by outer surface  208 . That is, the lateral surface of the envelope is tangent to each of the outer surfaces  208  of arms  204 . For example, if phase plug  104  were to have a round input face  112  parallel to a round output face  114 , the envelope would be a frustum. In an embodiment, the lateral surface of the envelope of phase plug  104  includes an angled surface contour that transitions into a smooth surface contour. For example, outer surface  208  may extend axially from a rear edge  210  on input face  112  to a front edge  212  on output face  114 . Rear edge  210  may be a smooth curve, and front edge  212  may include an angle  214 . Angle  214  may be a corner where output face  114  meets the adjacent surfaces of outer surface  208 . 
     As outer surface  208  of arm  204  transitions from angle  214  at front edge  212  of output face  114  to the smooth curve at rear edge  210  of input face  112 , a ridge  216  on outer surface  208  may gradually transition into a smooth surface contour. That is, at a point in the transition between input face  112  and output face  114 , ridge  216  having a peak or a vertex may arise. Ridge  216  may have an angled surface contour that includes angle  214  that decreases in a rearward direction. For example, the angled vertex of ridge  216  may decrease from a right angle (or an angle in a range of 80-100 degrees) at front edge  212  to a larger angle, e.g., an obtuse angle, at a more proximal location. Ridge  216  may disappear and outer surface  208  may have a smooth surface contour at a ridge terminus  217 . Ridge terminus  217  is on outer surface  208  axially between input face  112  and output face  114 . 
     Phase plug  104  may include one or more radial channels  218  extending axially from input face  112  to output face  114 . For example, phase plug  104  may have at least three radial channels  218  between at least three arms  204 . Each radial channel  218  may radiate from central axis  110 . For example, radial channel  218  may be a radial slit having a channel depth extending transverse to the lateral surface of the envelope of phase plug  104  to an exposed surface of central hub  206 . Radial channel  218  may have a channel width that separates one arm  204  from an adjacent arm  204  in a peripheral direction, i.e., a direction around central axis  110 . Radial channel  218  may have a channel length that extends through phase plug  104  in an axial direction from diaphragm  108  to throat  116  ( FIG. 1 ). Accordingly, radial channel  218  may guide sound waves from diaphragm  108  to throat  116 . Radial channels  218  may be peripherally spaced, rather than circumferentially spaced as in a circumferential-type phase plug  104 . Thus, radial channels  218  can be formed in phase plug  104  during a single molding process. Although not restricting, it will be appreciated that radial slots can be easier to form and can be fabricated with higher tolerances than circumferential slots of circumferential-type phase plugs because circumferential-type phase plugs are typically assembled from multiple pieces and have attendant tolerance stack ups. 
     Referring to  FIG. 3 , a schematic view of envelope profiles of a phase plug is shown in accordance with an embodiment. The schematic view of  FIG. 3  views the envelope profiles along central axis  110 . The envelope profiles represent edges of a front-facing boundary and a rear-facing boundary of the envelope of phase plug  104 . For example, the front-facing boundary of the envelope may extend across output face  114 , and the rear-facing boundary of the envelope may extend across input face  112 . In an embodiment, the envelope of plug body  202  includes a round profile  302  extending around central axis  110 . Round profile  302  may circumscribe input face  112 . That is, round profile  302  may include and be tangent to rear edges  210  of the arms  204  of phase plug  104 . By way of example, round profile  302  may be circular, elliptical, or any other curve in a plane extending along input face  112 . 
     In an embodiment, the envelope of plug body  202  includes a non-round profile  304  extending around central axis  110 . Non-round profile  304  may circumscribe output face  114 . That is, non-round may include and be tangent to front edges  212  of the arms  204  of phase plug  104 . By way of example, non-round profile  304  may be rectangular, square, or be any other polygon in a plane extending along output face  114 . Non-round profile  304  may include angle  214 . 
     A maximum radius of round profile  302  may be greater than a maximum width (or half the maximum width) of non-round profile  304 . Similarly, an area circumscribed by non-round profile  304  may be less than an area circumscribed by round profile  302 . Phase plug  104  can therefore converge from a larger area at diaphragm  108  to a smaller area at throat  116 . Sound emitted by diaphragm  108  can likewise converge through radial channels  218  between input face  112  and output face  114  before entering throat  116  and expanding along horn axis  120  toward the mouth  122 . 
     In an embodiment, non-round profile  304  may have an area larger than an area circumscribed by round profile  302 . For example, phase plug  104  may have slots that converge to exit plug output face  114  over a longer than typical length. In such case, the area of non-round profile  304  may be larger than the area of round profile  302 . 
     Referring to  FIG. 4 , a side view of an envelope of a phase plug is shown in accordance with an embodiment. Input face  112  may be on, or may intersect, a proximal transverse plane  402  oriented transverse to central axis  110 . For example, round profile  302  may extend around central axis  110  on or within proximal transverse plane  402  and may circumscribe input face  112 . Similarly, output face  114  may be on, or may intersect, a distal transverse plane  404  separated from proximal transverse plane  402  along central axis  110 . For example, non-round profile  304  may extend around central axis  110  on or within distal transverse plane  404  and may circumscribe output face  114 . Accordingly, input face  112  may be separated from output face  114  along central axis  110 , and output face  114  may not be parallel to proximal transverse plane  402  containing the profile of input face  112 . Radial channels  218  can therefore extend axially from proximal transverse plane  402  to distal transverse plane  404 , or from input face  112  to output face  114 , between arms  204  within the envelope of phase plug  104  ( FIG. 2 ). 
     Distal transverse plane  404  containing the non-round profile of output face  114  and proximal transverse plane  402  containing the round profile of input face  112  may or may not be parallel to one another. When the transverse planes are parallel to each other, central axis  110  may be orthogonal to both planes. Alternatively, when the transverse planes are not parallel to each other, one or both of the planes may be oblique to central axis  110 . Accordingly, input face  112  and output face  114  may or may not be parallel to each other. For example, central axis  110  may be orthogonal to input face  112 , and central axis  110  may be oblique to output face  114 . Therefore, in an embodiment output face  114  is not parallel to input face  112 . In an embodiment, an angle of tilt between proximal transverse plane  402  and distal transverse plane  404 , or between output face  114  and input face  112 , is in a range of 2-10 degrees, e.g., 5 degrees. 
     In an embodiment, one or more of input face  112  or output face  114  may be flat. For example, output face  114  may lie within distal transverse plane  404 , and thus, output face  114  may be flat. Similarly, input face  112  may lie within proximal transverse plane  402 , and thus, input face  112  may be flat. Alternatively, one or more of input face  112  or output face  114  may be curved. For example, output face  114  may be a curved output face  406  and/or input face  112  may be a curved input face  408 , as represented by the dashed lines in  FIG. 4 . Accordingly, the envelope of phase plug  104  may have a curved distal or proximal surface. Central axis  110  may be orthogonal to the curved distal or proximal surface, and may pass through the curved distal or proximal surface near an apex of a bulge of output face  114  or input face  112 . Although curved output faces  406 ,  408  are shown as having a convex contour, it will be appreciated that curved output faces  406 ,  408  may be concave. Curved output faces  406 ,  408  may not be contained within distal transverse plane  404  or proximal transverse plane  402 , however, front edge  212  at which the distal surface of the envelope meets a lateral surface of the envelope may extend around central axis  110  within distal transverse plane  404 . Similarly, rear edge  210  at which a proximal surface of the envelope meets the lateral surface of the envelope may extend around central axis  110  within proximal transverse plane  402 . Accordingly, phase plug  104  may be formed to have any envelope, including envelope surfaces and profiles, to allow phase plug  104  to conform to surface areas and profiles of diaphragm  108  or horn  106  of loudspeaker  100 . That is, input face  112  and output face  114  of phase plug  104  may each have respective round or non-round profiles and/or curved or flat surfaces to conform to corresponding shapes and contours of an adjacent loudspeaker component. For example, curved input face  408  may be a surface of revolution, e.g., a complex convex surface, about central axis  110  that follows a shape of diaphragm  108 . The conformance between input face  112  or  408  and diaphragm  108  (which may in turn be flat or curved) can minimize, or control to a specific value, a volume of air between phase plug  104  and diaphragm  108 . An example of an alternative phase plug geometry is described below. 
     Referring to  FIG. 5 , a perspective view of a phase plug is shown in accordance with an embodiment. Phase plug  104  as shown in  FIG. 5  may represent a variation of a phase plug  104  as described above with respect to  FIGS. 1-4 , and thus, shall be described using similar terminology. In an embodiment, phase plug  104  has an envelope having a polygonal or a quasi-polygonal profile  502  extending around a distal boundary of the envelope, and a circular profile  504  extending around a proximal boundary of the envelope. Here, a polygonal profile is distinguished from quasi-polygonal profile  502  in that a polygonal profile may have a shape defined by several straight line segments joined in a closed figure at several angles. By contrast, quasi-polygonal profile  502  may have a shape defined by several straight or curvilinear line segments joined in a closed figure at several angles. Quasi-polygonal profile  502  may not actually be polygonal (or rectangular) because an end of phase plug  104  may be truncated before reaching a rectangular profile, causing the edges to be curved as shown in  FIG. 5 . It will be appreciated, however, that in an embodiment profile  502  may be polygonal (e.g., rectangular as shown in  FIG. 2 ). Circular profile  504  may include smooth curves on rear edges  210  of arms  204 , and quasi-polygonal profile  502  may include four angles  214  on front edges  212  of arms  204 . 
     As described above, arms  204  (of which there are six in this case) can be attached to central hub  206  and can radiate outward toward respective outer surfaces  208 . More particularly, each arm  204  may include a pair of sidewalls  506  extending radially from central hub  206  to outer surface  208 . Sidewalls  506  can face inward toward an adjacent radial channel  218 . That is, radial channel  218  can extend axially between arms  204  to separate the arms  204  in a peripheral direction, and thus, sidewalls  506  of adjacent arms  204  may face radial channel  218  in the peripheral direction. By contrast, outer surface  208  may face away from central hub  206  in a radial direction orthogonal to both the axial direction and the peripheral direction. 
     Referring to  FIG. 6 , a front view of an output face of a phase plug is shown in accordance with an embodiment. Each arm  204  may include a distal surface  602 . Distal surface  602  can define a portion of output face  114 . That is, distal surface  602  may be a portion of output face  114  extending along a front surface of arm  204 . The front surface of arm  204  may be the portion of output face  114  radially outward of central hub  206  and extending along distal transverse plane  404  between sidewalls  506  and outer surface  208  of arm  204 . 
     Each radial channel  218  of phase plug  104  may have a forward-facing cross-sectional area. The cross-sectional area may be referred to as a distal port  604 . The distal ports  604  may be arranged about a midline  608 . Midline  608  may extend within distal transverse plane  404  and through central axis  110 . In an embodiment, phase plug  104  has at least two distal ports  604  having respective shapes and sizes. By way of example, distal port  604   a  on a first side  606  of a midline  608  may have a first shape and size, and distal port  604   b  on a second side  610  of midline  608  may have a second shape and size. Distal port  604   a  and distal port  604   b  may be mirrored about midline  608 , but may be sized differently. For example, distal port  604   a  on first side  606  of midline  608  may be larger than distal port  604   b  on second side  610  of midline  608 . 
     A difference in size between distal ports  604  mirrored about midline  608  may result from distal transverse plane  404  non-parallel relative to proximal transverse plane  402 . More particularly, tilting distal transverse plane  404  relative to central axis  110  can cause distal ports  604  on each side of midline  608  to have relatively different shapes and sizes. This difference in shape and size may cause an asymmetry in distal surfaces  602  of arms  204 . 
     In an embodiment, distal surfaces  602  of arms  204  at the distal end of phase plug  104  have respective distal surface areas at distal transverse plane  404 . Distal surface areas of arms  204  may correspond to the distal ports  604 . For example, when distal ports  604  are symmetrically disposed about midline  608 , i.e., when distal port  604   a  on first side  606  has a same cross-sectional area as distal port  604   b  on second side  610 , distal surface area  602   a  may equal distal surface area  602   b . By extension, when distal ports  604  are asymmetrically sized about midline  608 , distal surface areas mirrored about midline  608  may be asymmetrically sized. For example, distal surface area  602   a  on first side  606  of midline  608  may be different than, e.g., larger than, distal surface area  602   b  on second side  610  of midline  608 . 
     Asymmetries in distal port  604  and/or distal surface areas  602  may be uniaxial. When distal transverse plane  404  is tilted relative to proximal transverse plane  402 , and midline  608  remains parallel relative to proximal transverse plane  402 , asymmetries may occur in a vertical direction, i.e., on first side  606  and second side  610 , but ports and surface areas in a horizontal direction may remain symmetric. Accordingly, two or more distal ports  604  or distal surfaces  602  on a same side of midline  608  may be symmetrically sized and mirrored relative to each other about a vertical midline orthogonal to midline  608 . By contrast, the symmetric pair of ports on the first side  606  of midline  608  may be asymmetric relative to a corresponding symmetric pair of ports on an opposite side of midline  608 . 
     The front view of phase plug  104  illustrates sidewalls  506  extending from central hub  206  in a radially outward direction. The radially outward direction, however, may not be linear. For example, sidewalls  506  may extend radially outward and flare such that a width of distal surface area is greater near a radial extremity of arm  204  than the width of distal surface area nearer to central hub  206 . 
     Referring to  FIG. 7 , a rear view of an input face of a phase plug is shown in accordance with an embodiment. Each arm  204  may include a proximal surface  702 . Proximal surface  702  can define a portion of input face  112 . That is, proximal surface  702  may be a portion of input face  112  extending along a rear surface of arm  204 . The rear surface of arm  204  may be the portion of input face  112  radially outward of central hub  206  and extending along distal transverse plane  404  between sidewalls  506  and outer surface  208  of arm  204 . 
     Each radial channel  218  of phase plug  104  may have a rear-facing cross-sectional area. The cross-sectional area may be referred to as a proximal port  704 . In an embodiment, the proximal ports  704  of phase plug  104  are symmetrically arranged about central axis  110 . For example, when input face  112  includes is orthogonal to central axis  110  and includes circular profile  504 , proximal ports  704  may have a same shape and size and may be symmetrically distributed in a peripheral direction around central axis  110 . Alternatively, when central axis  110  is oblique to input face  112 , proximal ports  704  may be asymmetrically disposed about a midline, similar to the asymmetries described above with respect to distal ports  604  relative to midline  608 . Proximal surfaces  702  of arms  204  may have surface areas that are symmetric or asymmetric corresponding to proximal ports  704 , and similar to the embodiments of distal surfaces  602  described above. 
     Referring to  FIG. 8 , a schematic view of interconnected radial channel areas of a phase plug is shown in accordance with an embodiment. A cross-sectional area of a single radial channel  218  may vary in an axial direction. For example, a port area of proximal port  704  can be different than a port area of distal port  604 . In an embodiment, an area of distal port  604  is greater than an area of proximal port  704 . Differences between the port areas of proximal port  704  and distal port  604  may change the acoustic impedance versus frequency seen by the transducer diaphragm  108 , and may manage local air particle velocities. In a phase plug used over a wide frequency bandwidth, maintaining low particle velocities in all section of the phase plug is typically necessary to achieve desired acoustic output levels. 
     Referring to  FIG. 9 , a front view of a portion of an arm of a phase plug is shown in accordance with an embodiment. An exterior of arm  204  can include smooth surfaces, e.g., along sidewalls  506  between proximal port  704  and distal port  604 . The exterior can also include angular surfaces, e.g., along an edge where sidewall  506  meets outer surface  208  or at ridge  216 . As described above, the smooth surface contours and angular surface contours can result from an axial transition between round profile  302  and non-round profile  304  of phase plug  104 . In an embodiment, arm  204  has a solid cross-section throughout. That is, the volume of arm  204  defined between sidewalls  506 , outer surface  208 , distal surface  602 , and proximal surface  702 , may be solid. Alternatively, as described below, one or more arms  204  of phase plug  104  may have a cored-out section. 
     Referring to  FIG. 10A , a cross-sectional view, taken about line A-A of  FIG. 9 , of an arm of a phase plug having a cavity is shown in accordance with an embodiment. Each arm  204  of phase plug  104  may include a cavity  1002 . Cavity  1002  can be on an opposite side of sidewall  506  from an adjacent radial channel  218 . More particularly, cavity  1002  may be between a pair of sidewalls  506 , and sidewalls  506  may isolate cavity  1002  from radial channels  218  on either side of arm  204 . Thus, at least one of the pair of sidewalls  506  may be between cavity  1002  and radial channel  218 . 
     In an embodiment, cavity  1002  extends laterally through outer surface  208  of arm  204 . More particularly, cavity  1002  may extend radially from central hub  206  outward into a space surrounding phase plug  104 , e.g., back volume  126 . Accordingly, cavity  1002  may be surrounded within arm  204  by the pair of sidewalls  506 , central hub  206 , distal surface  602 , and proximal surface  702 . As such, cavity  1002  may be a core-out of arm  204  opening toward a space laterally outward of phase plug  104 . By contrast, radial channels carrying sound through phase plug may be closed off from back volume  126  by a wall of housing  150 . In an embodiment, a hole in the wall of housing  150  surrounding the outer envelope of phase plug  104  may be aligned with an entrance to cavity  1002  to place cavity  1002  in fluid communication with back volume  126  through the hole (not shown). 
     Referring to  FIG. 10B , a cross-sectional view, taken about line A-A of  FIG. 9 , of an arm of a phase plug having a cavity is shown in accordance with an embodiment. Cavity  1002  may extend axially from distal surface  602  outward into a space surrounding phase plug  104 , e.g., back volume  126 . For example, cavity  1002  may extend through proximal surface  702 . Accordingly, cavity  1002  may be surrounded within arm  204  by the pair of sidewalls  506 , central hub  206 , distal surface  602 , and outer surface  208 . As such, cavity  1002  may be a core-out of arm  204  opening toward a space behind phase plug  104 . 
     Referring to  FIG. 11A , a cross-sectional view, taken about line B-B of  FIG. 9 , of an arm of a phase plug having a cavity is shown in accordance with an embodiment. Cavity  1002  extending laterally outward from arm  204  in a radial direction away from central hub  206  can form a space contained within arm  204  between output face  114  and input face  112 . Referring to  FIG. 11B , a cross-sectional view, taken about line B-B of  FIG. 9 , of an arm of a phase plug having an alternative embodiment of a cavity is shown in accordance with an embodiment. Cavity  1002  extending axially outward from arm  204  in an axial direction away from output face  114  can form a space contained within arm  204  between central hub  206  and outer surface  208 . 
     As described above, back volume  126  of driver  102  may be in acoustic communication with core-outs in arms  204  of phase plug  104 . For example, cavity  1002  may extend laterally outward or axially outward from phase plug  104  into back volume  126 . Accordingly, cavity  1002  may be a portion of back volume  126 . Cavity  1002  may be separated from radial channels  218  by sidewalls  506 , however, and thus, cavities may increase a total volume behind diaphragm  108  without causing cancellations with sound emitted in front of diaphragm  108 . Increasing the total volume of driver  102  behind diaphragm  108  can improve loudspeaker  100  performance. 
     Loudspeaker  100  performance can also be improved by minimizing cancellations between sound waves as sound moves through radial channel  218  in front of diaphragm  108 . The transition between proximal port  704  to distal port  604  may be configured to minimize such cancellations. More particularly, sound cancellations, such as in the high frequency range, may be minimized by controlling how sound waves travel through each channel, which affects how the sound waves recombine at an exit of the phase plug. In an embodiment, sound output may also be controlled by a design of a transitional edge  1004  between sidewall  506  and distal surface  602  ( FIG. 10B ). 
     Referring to  FIG. 12 , a detail view, taken from Detail A of  FIG. 10B , of a transitional edge of an arm of a phase plug is shown in accordance with an embodiment. Each arm  204  may include transitional edge  1004  between sidewall  506  and output face  114 . For example, arm  204  may include respective transitional edges  1004  between each sidewall  506  of the pair of sidewalls flanking cavity  1002 , and output face  114 . Transitional edge  1004  may be a fillet, a chamfer, or another contour transitioning between the surfaces of sidewall  506  and output face  114 . For example, transitional edge  1004  may be a convex surface having a radius  1202 . Transitional edge  1004  may be contrasted with an edge having the sharp corner  1204 , as represented by a dashed line in  FIG. 12 . In an embodiment, transitional edge  1004  allows air to diverge smoothly from radial channel  218  into a space in front of phase plug  104 . Such an edge can keep local air particle velocity lower at the exit of the phase plug where the sound waves enter the throat of horn  106 . The smooth divergence of air can slow a velocity of sound waves prior to the sound waves entering throat  116  of horn  106 . For example, analytical modeling of phase plug  104  having a flat output face  114  and a contoured transitional edge  1004  has shown that air velocity can be reduced significantly to allow a higher volume velocity through the same size phase plug slot for higher sound output levels. In general, keeping air velocity below approximately 15 m/s can keep air flow in a laminar range, which prevents turbulence. Turbulence causes undesirable noise generation, and thus, limits a maximum achievable sound output level, especially at lower frequencies where higher volume velocities are required to maintain a constant sound pressure level. Phase plug  104  can be used in loudspeaker drivers to reduce sound cancellations in a range of 300 Hz to 20 kHz. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20170323
Publication Date: 20190402
Grant Date: 20190402
Priority Date: 20170323
Inventors: Sheerin, John H.
HUWE, ETHAN L.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R1/347", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2201/34", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/347", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2201/34", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2201/34", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 63583149