Abstract:
A phasing plug for use in a compression driver is configured with a central sound absorbing region that absorbs phase-distorted sound waves produced by an adjacent region of a vibrating diaphragm. The phasing plug is constructed from a plurality of generally hollow frusto-conical rings and a central conical element. The central conical element serves as a sound absorption region for absorbing phase-distorted sound waves. The phasing plug has a plurality of annular inlet apertures that permit sound waves to enter the phasing plug and traverse to an outlet region of the phasing plug. The outlet region is further enhanced by a plurality of wave guide rings that focus the exiting sound waves in a unified direction resulting in the dynamic reproduction and delivery of coherent high-frequency sound waves over a greater distance.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to electro-acoustic loudspeakers typically known as compression drivers and, more particularly, to an improved phasing plug for use in such compression drivers. 
       BACKGROUND OF THE INVENTION 
       [0002]    Compression drivers transform electrical signals into sound by actuating an internal semi-spherical diaphragm which in turn compresses air that is located between the diaphragm and a phasing plug to produce sound waves. A compression driver is designed to increase the efficiency of a loud speaker by compressing the acoustical energy and transferring it through a channel to the throat of a horn. The compression driver is equipped with a semi-spherical diaphragm which vibrates in response to electrical signals. The electrical signals are applied to a voice coil that is attached to the edge of the diaphragm. The voice coil is arranged such that the coil is concentric with the diaphragm and is immersed in a magnetic field. 
         [0003]    Most compression drivers have a phasing plug that is positioned adjacent to the diaphragm and has a corresponding semi-spherical input surface. The phasing plug is spaced away from the diaphragm so that there is no interference between the phasing plug and the diaphragm. The phasing plug forms the acoustical channel or pathway from the diaphragm to the throat of the horn. The purposes of the phasing plug are to compress the sound waves and to equalize the acoustic path lengths to thereby minimize high frequency distortions caused by phase cancellations, phase shifts and phase differentials. 
         [0004]    The phasing plug typically has a first surface that faces the diaphragm and a second surface facing the throat of a horn. Formed within the phasing plug are typically several acoustical pathways or apertures. In the past, numerous attempts have been made to optimize the phasing plug&#39;s acoustical pathways, such as by providing annular rings forming circumferential slits, by providing wedge-type sections forming radial slits, or by providing hole arrays, that transfer the sound energy from the diaphragm to the throat. These prior attempts have not produced satisfactory results in transforming the sound waves generated by the diaphragm without high frequency interference or distortion. 
         [0005]    Compression drivers comprising a traditional diaphragm coupled with known phasing plugs thus suffer from phase distortions that distort high frequency sound waves. The high fidelity sounds are suppressed and high quality reproduction of voice and music are not adequately obtained because phase distortions are produced by the sound waves emanating from the various portions of the diaphragm. The sound waves usually traverse paths of unequal length in passing to the throat of the horn so that the sound waves propagated from the diaphragm do not reach the throat in phase coherent form. 
         [0006]    As a result, currently available compression drivers usually require substantial electronic equalization by way of sound conditioning equipment. This electronic sound conditioning frequently causes the compression driver to be actuated at high power levels. This often results in overheating of the voice coil, which in turn reduces the operational life span of the compression driver. 
         [0007]    Therefore, one objective of the present invention is to provide a new and improved phasing plug which can provide increased sound clarity with minimal acoustic distortion. 
         [0008]    A further objective of the present invention is the provision of a new and improved phasing plug that has an enhanced frequency range and increased dynamic performance. 
         [0009]    Yet another object of the present invention is to provide a new and improved phasing plug that reduces the requirement for excessive active equalization and increases the operational life span of the compression driver. 
         [0010]    Therefore, there remains an unmet need for an enhanced phasing plug that reproduces accurate high frequency sound waves without a need for excessive electronic equalization of the electrical actuation signals of the compression driver. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention comprises a compression driver phasing plug. In a preferred configuration, the phasing plug reduces harmonic distortions caused by phase coherency anomalies. 
         [0012]    In a preferred embodiment, a phasing plug is provided for use in an acoustical compression driver. The phasing plug comprises a central wave guide member, at least intermediate wave guide member and a bottom wave guide member. The central wave guide member further includes a sound wave absorbing insert that forms a central sound wave absorbing region. The spaces between the wave guide members form a plurality of sound wave pathways and thus in combination create a sound wave inlet region. Preferably, the sound wave absorption region and sound wave inlet region are adjacent and correspond to a phase distortion zone and a phase coherent energy zone of the compression driver&#39;s diaphragm. 
         [0013]    In another embodiment the invention provides a phasing plug for use in a compression driver comprising a sound wave inlet region having a plurality of inlet apertures and an outlet throat region having a plurality of annular outlet apertures. The phasing plug has a central wave guide member having a first end and a second end, in which the first end has an integral recess formed therein. A sound absorbing material is inserted into the integral recess of the central wave guide member. The phasing plug further comprises at least one intermediate wave guide member and a bottom wave guide member. The central wave guide member, intermediate wave guide member and bottom wave guide member are disposed one within the other and co-axially aligned with the central wave guide member in a spaced apart relationship that forms a plurality of sound wave pathways there between. The sound wave pathways extend from the sound wave inlet region to the outlet throat region of the phasing plug. 
         [0014]    In another variation of the invention comprises a compression driver system having a phasing plug disposed between a throat of a bottom plate and a diaphragm of the compression driver. The phasing plug has a central wave guide member that includes a sound absorbing insert received into an integral recess formed on a first end of the central wave guide member. The phasing plug further comprises at least one intermediate wave guide member and a bottom wave guide member, by which each member is sized for co-axially insertion one within the other in a spaced apart relationship. The phasing plug has a sound wave pathways formed between the central wave guide member and the intermediate wave guide member. Correspondingly, the intermediate wave guide member and the bottom wave guide member form another sound wave pathway between them. The sound pathways extend from a sound wave inlet region adjacent to the diaphragm to an outlet throat region adjacent to the throat. 
         [0015]    Similarly, another variation comprises a compression driver system including a phasing plug disposed between a throat of a bottom plate and a diaphragm of the compression driver. This variation includes a phasing plug having a sound wave inlet region formed upon the outer circumferential surface area of the phasing plug and a sound wave absorption region formed upon the remaining central surface area of the phasing plug, A plurality of sound wave pathways are formed within the sound wave inlet region. The sound wave pathways extend from the sound wave inlet region adjacent to the diaphragm to an outlet throat region adjacent to the throat. In this variation the diaphragm has a phase coherent energy zone that is located adjacent the sound wave inlet region and a phase distortion zone located adjacent the sound wave absorption region. As a result the sound waves generated by the phase coherent energy zone enter the sound wave inlet region and sound waves generated by the phase distortion zone are absorbed by the sound wave absorption region. 
         [0016]    In other embodiments of the invention, several elements or components may be modified or have alternate constructions. In one alternate embodiment, the sound absorbing insert may further comprise a plurality of sound absorption grooves formed there upon or be fabricated from materials such as rubber, cork or high-density foam. Additionally, the phasing plug may include a wave guide array integrally formed with the outlet region. It is also contemplated that the sound wave pathways volumetrically expand from the inlet apertures to the annular outlet apertures of the phasing plug and this volumetric expansion may be exponential. In a preferred construction, the phasing plug has a central wave guide member, a intermediate wave guide members and a bottom wave guide member that are fabricated from a phenolic material. The bottom wave guide member may further comprise a wave guide surface circumferentially formed upon the outer diameter of a first end of the bottom wave guide member. 
         [0017]    In another variation, the phasing plug includes a sound absorbing insert and a first end of said central wave guide member that form a sound wave absorption region that occupies approximately the center ⅓ surface area of the phasing plug. Correspondingly, the sound wave inlet region occupies the remaining outer ⅔ circumferential ring area of the phasing plug. 
         [0018]    The phasing plug of the present invention provides numerous advantages over current phasing plugs and has particular advantages when used with a compression driver. The sound wave absorbing portion or region of the phasing plug absorbs phase distorted sound waves and at the same time, the phasing plug transmits coherent sound waves, such as coherent low and midrange sound waves and sound waves generated at the outer edges or exterior portions of the diaphragm. As a result the phasing plug transmits sound with increased clarity over the high-frequency range, while at the same time, maintaining audible definition over the high to midrange sound wave spectrum. 
         [0019]    The improved phasing plug reduces the need for electronic signal processing or equalization of the input signals to the compression driver and thus avoids over-heating of the voice coil resulting in energy conservation and increased compression driver. Since the use of the improved phasing plug requires less signal processing, the compression driver is less likely to be over-powered by associated signal conditioners. The phasing plug of the present invention reduces over-heating and conserves energy used by the compression driver because the sound wave transmission is inherently free from typical phase distortions and excessive electronic equalization is unnecessary. 
         [0020]    Additionally, the phasing plug also provides a focused sound wave projection by use of the wave guide rings at the termination point of each sound wave pathway. The wave guides facilitate the directional aiming of the sound waves. This directional aiming causes the sound waves to exit the throat region of the phasing plug on concentric and distinct pathways resulting in high-frequency (19 khz) waves that propagate in unison and are projected over greater distances. 
         [0021]    Further objects, features, and advantages of the present invention over the prior art will become apparent from the detailed description of the preferred embodiments which follows, when considered with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an exploded isometric view of a compression driver including an improved phasing plug in accordance with a first embodiment of the invention; 
           [0023]      FIG. 2  is an isometric view of a phasing plug in accordance with a first embodiment of the invention as viewed from above; 
           [0024]      FIG. 3  is an isometric view of a phasing plug in accordance with a first embodiment of the invention as viewed from below; 
           [0025]      FIG. 4  is an exploded isometric view of a phasing plug in accordance with a first embodiment of the invention; 
           [0026]      FIG. 5  is an exploded isometric sectional view of a phasing plug in accordance with a first embodiment of the invention taken along line  5 - 5  illustrated in  FIG. 4 ; 
           [0027]      FIG. 6  is a sectional view of a collapsed compression driver assembly of  FIG. 1 , taken along line  6 - 6 ; 
           [0028]      FIG. 7  is an enlarged sectional view of a portion of the compression driver illustrated in  FIG. 6 ; 
           [0029]      FIG. 8  is a isometric view of a phasing plug in accordance with a second embodiment of the invention as viewed from above; 
           [0030]      FIG. 9  is a isometric view of a phasing plug in accordance with a second embodiment of the invention as viewed from below; 
           [0031]      FIG. 10  is an exploded isometric view of a phasing plug in accordance with a second embodiment of the invention; 
           [0032]      FIG. 11  is an exploded isometric sectional view of a phasing plug in accordance with a second embodiment of the invention taken along line  11 - 11  illustrated in  FIG. 10 ; 
           [0033]      FIG. 12  is a sectional view of a collapsed compression driver assembly of  FIG. 1 , taken along line  6 - 6  in accordance with a second embodiment of the invention; 
           [0034]      FIG. 13   a  is an impedance vs. frequency graph illustrating the performance of a traditional phasing plug; 
           [0035]      FIG. 13   b  is an impedance vs. frequency graph illustrating the performance of a phasing plug in accordance with the present invention; and 
           [0036]      FIG. 13   c  is an impedance vs. frequency graph comparing the performance of the present invention with a traditional phasing plug. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention. 
         [0038]      FIGS. 1  illustrates one embodiment of a compression driver in exploded assembly form. The compression driver comprises a cap  102  that provides both supportive structure and protection for the internal components of the driver. A semi-spherical diaphragm  104  with an integral voice coil (not shown) covers a phasing plug  106 . The diaphragm  104  is secured to a top plate  108 . The same top plate  108  also captures a permanent magnet  110  between it and a bottom plate  112 . The phasing plug  106  is positioned between the bottom plate  112  and the diaphragm  104  and provides an acoustical conduit or pathway for sound waves to travel between the diaphragm  104  and a throat  114  integrally formed within the bottom plate  112 . Preferably, the bottom plate  112  defines a phasing plug receiving cavity  116  configured to receive a portion of the phasing plug  106 . 
         [0039]    It will be appreciated that the phasing plug of the invention could be utilized in other driver configurations, including drivers where the components thereof have configurations other than that as illustrated. The particular sizes of the phasing plug and associated driver elements may vary, and the driver may itself be utilized in a plurality of applications. 
         [0040]    The phasing plug  106  comprises a body which generally has a first or top side or surface and a bottom or second side or surface. These sides or surfaces are defined by one or more portions of the body. As detailed below, the body is preferably constructed from a plurality of assembled elements. 
         [0041]      FIG. 2  is an isometric view of a phasing plug  106  in accordance with a first embodiment of the invention, as viewed the top. The top side or surface  201  of the phasing plug  106  has a sound wave inlet region  202 . A plurality of inlet apertures  204  are defined in the inlet region  202 . The inlet apertures  204  preferably comprise circumferential slits formed or defined between individual frustro-conical elements or members (discussed in greater detail below) of the phasing plug  106 . As also shown in  FIG. 2 , the phasing plug  106  includes a central unwanted sound wave absorption region  206 . The sound wave inlet region  202  and sound wave absorption region  206  together form a generally semi-spherical inlet region  207 . In one specific version of the invention, the absorption region  206  comprises about ⅓ of the surface area of the inlet region of the phasing plug  106 . 
         [0042]      FIG. 3  is an isometric view of the phasing plug  106  in accordance with a first embodiment of the invention, as viewed from the bottom. As illustrated, the phasing plug  106  has a bottom side or surface  302 . This side or surface  302  includes an outlet throat region  304 . The throat region  304  preferably includes a wave guide array formed from a plurality of annular rings  306  that extend axially from a plurality of annular outlet apertures  305 . The annular rings  306  combine to form a wave guide element associated with the throat region  304 . 
         [0043]    As detailed above, the phasing plug  106  may preferably be configured to be mounted to a lower plate  112  of a compression driver  100  (see  FIG. 1 ). For this purpose, the phasing plug  106  may include one or more mounting bosses  208 . These mounting bosses  208  extend outwardly from the bottom side or surface  302 . In one embodiment, the bosses  208  are integrally formed with a portion of the body of the phasing plug  106  and define generally planar mounting surfaces. These surfaces are preferably configured to mount to the bottom plate  112 . It is contemplated that the receiving cavity  116  may have mating recesses formed thereon for receiving and retaining the mounting bosses  208  of the phasing plug  106 . 
         [0044]    In one embodiment, the phasing plug  106  (or various portions or elements thereof) is fabricated using injection molding methods from a phenolic high-temperature bake-a-lite material or a high-density polymer plastic. It is contemplated that other materials may be used such as high impact polymers, resins, polycarbonates, metal alloys, and ceramics. Additionally, other suitable methods of manufacture may be implemented such as machining, casting, and thermo-forming. 
         [0045]    One embodiment of the phasing plug  106  will be described in more detail with reference to  FIG. 4 . In one embodiment, the phasing plug  106  comprises a plurality of members or elements which are connected or associated with one another. As illustrated, the phasing plug  106  comprises a first, top or central wave guide member  400 , a bottom or exterior wave guide member  406 , and one or more (and preferably two), intermediate wave guide members  402 ,  404 . As illustrated, the central wave guide member  400  is disposed at least partially within a first of the intermediate wave guide members  402 , which first intermediate wave guide member  402  is disposed at least partially within the second intermediate wave guide member  404 , which second intermediate wave guide member  404  is disposed at least partially within the bottom wave guide member  406 , all of those members  400 ,  402 ,  404 ,  406  preferably being substantially co-axially aligned with one another. 
         [0046]    The wave guide members  400 , 402 ,  404  and  406  are preferably arranged in a spaced relationship to one another. In one embodiment, mounting bosses or feet  208  extend from a bottom or outer surface of the central wave guide member  400  and each of the intermediate wave guide members  402 , 404  (as indicated above, such bosses or feet  208  also extend from the bottom wave guide member  406 , which defines the bottom exterior of the phasing plug  106 , as illustrated in  FIG. 2 ). Top or inner surfaces of the intermediate and bottom wave guide members  402 ,  404  and  406  may define corresponding mounting recesses  408  for receiving the mounting bosses  208  of the central wave guide member  400  or intermediate wave guide member  402 ,  404 , thereabove. 
         [0047]    When assembled, the phasing plug  106  comprising the wave guide members  400 ,  402 ,  404  and  406  has a semi-spherical inlet region  207  (See  FIG. 2 ) that preferably accurately corresponds to the shape and structure of the compression driver diaphragm  104  and an outlet throat region  304  (See  FIG. 3 ). 
         [0048]    The various elements or members of the phasing plug  106  will be described in greater detail with reference to  FIG. 5 . In one embodiment, each of the members comprising the phasing plug  106  has several surfaces. 
         [0049]    The central wave guide member  400  comprises a body which preferably has the form of an open cone having a top or first end  501  and a bottom or second end  502 . The body has an inner surface  505  and an outer surface  504 . The first end  501  of the central conical member  400  defines an opening or recess  503 . The second end  502  is preferably closed. Being cone-shaped, the first end  501  has a greater size (diameter and circumference) than the second end  502 . In a preferred embodiment, the second end  502  of the central wave guide member  400  defines an outlet wave guide protrusion  506  that axially extends from the conical termination point of the second end  502 . 
         [0050]    In a preferred embodiment, a sound absorbing insert  500 A is received into the recess  503  at the first end  501  of the central wave guide member  400 . The sound absorbing insert  500 A comprises a body having a convex arcuate shaped top exterior surface that substantially corresponds to a concave shape of an adjacent portion of the diaphragm  104  (see  FIG. 1 ). The insert  500 A is preferably fabricated from a material well suited to absorb sound waves examples of such material are rubber, cork, high-density foam or other similar materials. The insert  500 A is attached to the central wave guide member  400  within the recess  503 , such as by using suitable adhesives such as an epoxy. However, it is contemplated that other methods may be used to connect or otherwise associate the insert  500 A to or within the central wave guide member  400 , such as mechanical fasteners, press-fit coupling or both. Additionally, a combination of adhesives and other methods/elements may be combined to connect the insert  500 A to the central wave guide member  400 . 
         [0051]    In one embodiment, the first intermediate wave guide member  402  is generally frusto-conical in shape and has a first end  507 , a second end  508 , an inlet surface  509  at the first end  507 , an interior surface  510  and an exterior surface  512 . In the embodiment in which the first intermediate wave guide member  402  is generally frusto-conical, the member is larger in size (diameter and circumference, in this case) at the first end  507  than at the second end  508 . Further, the first and second ends  507 ,  508  of the member  402  are open, thus defining a first open end and an outlet aperture  514 . In one embodiment, an annular wave guide ring  516  extends axially from the outlet aperture  514 . 
         [0052]    In one embodiment, the first intermediate wave guide member  402  has a thickness comprising the distance between the inner surface  510  and outer surface  512 . In one embodiment, the first end  507  is larger in diameter and is concentric with the second end  508 , and forms an axially symmetrical frusto-conical member having a generally a tapering wall thickness from the first end  507  to the second end  508 . 
         [0053]    The inlet surface  509  preferably comprises a convex arcuate shaped inlet surface that substantially corresponds to the concave shape of an adjacent portion of the diaphragm  104 . Preferably, the interior dimensions of the first intermediate wave guide member  400  are slightly larger than the exterior or outer dimensions of the central wave guide member  400  so as to accommodate a portion of the central wave guide member  400  therein. 
         [0054]    The interior surface  510  of the first intermediate wave guide member  402  preferably comprises a substantially smooth surface. Formed into the inner surface  510  are one or more mounting recesses  408  configured to receive the one or more corresponding mounting bosses  208  of the central wave guide member  400 . As described in more detail below, the interior surface  510  of the first intermediate wave guide member  402  and the exterior surface  504  of the central wave guide member  400  are positioned in a spaced apart relation that forms a sound wave pathway there between. 
         [0055]    The exterior surface  512  of first intermediate wave guide member  402  similarly also preferably comprises a substantially smooth surface. Located at the exterior surface  512  are the above-described mounting bosses or feet  208  configured for insertion into corresponding mounting recesses  408  of the second intermediate wave guide member  404 . 
         [0056]    In similar arrangement to the first intermediate wave guide member  402  described above, the second intermediate wave guide member  404  is preferably also a frusto-conical shaped member having a first end  517 , a second end  518 , an inlet surface  519  at the first end  517 , an interior surface  520 , an exterior surface  522  and an outlet aperture  524  at the second end  518 . Axially extending from the outlet aperture  524  is an annular wave guide ring  526 . The second intermediate wave guide member  404  is preferably sized slightly larger than the first intermediate wave guide member  402  to receive at least a portion of the first intermediate wave guide member  402  therein. 
         [0057]    The bottom or base wave guide member  406  is similarly preferably a frusto-conical shaped member having a first end  527 , a second end  528 , an inlet surface  529  at the first end  527 , an interior surface  530 , an exterior surface  532  and an outlet aperture  534  at the second end  528 . Axially extending from the outlet aperture  534  is an annular wave guide ring  536 . In one embodiment, the bottom wave guide member  406  is configured with a circumferential wave guide surface  538  that is formed at the exterior of the first end  527 . In general, wave guide surface  538  is an extension area having an outermost surface which is generally parallel to the central axis of member  406 . The bottom wave guide member  406  is preferably sized slightly larger than the second intermediate wave guide member  404  to receive at least a portion of that member therein. 
         [0058]    Additional details of the phasing plug  106  will now be described with reference to  FIG. 6 , which is a sectional view of an assembled compression driver  100  encapsulating a phasing plug  106  of the present invention. The compression driver  100  in operative form has a diaphragm  104  with a phase coherent energy zone  602  and a phase distortion zone  606 . The phase coherent energy zone  602  is preferably positioned or located adjacent to the sound wave inlet region  202  of the phasing plug  106  (see  FIG. 2 ). The phase distortion zone  606  is preferably positioned or located adjacent to the sound wave absorption region  206  of the phasing plug  106  (see  FIG. 2 ). In operation, the phase coherent energy zone  602  generates phase coherent sound waves that are directed toward and received into the plurality of inlet apertures  204  of the sound wave inlet region  202  of the phasing plug  106 . Correspondingly, the phase distortion zone  606  generates phase shifted or distorted sound waves that are directed toward and acoustically absorbed by the sound wave absorption region  206  of the phasing plug  106 . 
         [0059]    As best illustrated in  FIG. 6 , the central wave guide member  400  and the intermediate and bottom wave guide members  402 ,  404  and  406 , in combination with the receiving cavity  116  of the bottom plate  112 , provide or define a plurality of coaxial annular sound wave pathways  608 ,  610 ,  612  and  614 . The sound wave pathways  608 ,  610 ,  612  and  614  extend from the inlet apertures  204  and converge toward the throat  114  of the bottom plate  112 . 
         [0060]    A first sound wave pathway  608  is an acoustical volumetric region formed between a surface of the bottom plate  112  which defines the receiving cavity  116  and the exterior surface  532  of the bottom wave guide member  406 . This first sound wave pathway  608  begins at the inlet aperture  204  and volumetrically increases (preferably exponentially) toward the throat  114  of the bottom plate  112 . In one embodiment shown in a combination of  FIGS. 6 and 7 , the inlet aperture  204  of this first sound wave pathway  608  includes the wave guide surface  538  that facilitates entry of sound waves generated by the vibrating diaphragm  104  into the first sound wave pathway  608 . In operation, the wave guide surface  538  and inlet aperture  204  of the first sound wave pathway  608  combine to form an acoustical summing zone  700  that channels very high frequency sound waves generated by the diaphragm  104  into the phasing plug  106  and also provides a means for heat dissipation or cooling for the adjacently located diaphragm  104  and voice coil by circulating air around the summing zone. 
         [0061]    Referring back to  FIG. 6 , a second sound wave pathway  610  is an acoustical volumetric region formed between the interior surface  530  of the bottom wave guide member  406  and the exterior surface  522  of the second intermediate wave guide member  404 . Similar to the first wave guide pathway  608 , the second wave guide pathway  610  begins at its corresponding inlet aperture  204  and volumetrically increases exponentially toward the throat  114  of the bottom plate  112 . Likewise, third and fourth sound pathways  612  and  614  comprise acoustical volumetric regions formed between the interior and exterior surfaces of the first and second intermediate wave guide members  402 ,  404  and the central and first intermediate wave guide members  400 ,  402 . In one embodiment the volume defined by the sound wave pathways  608 ,  610 ,  612  and  614  is acoustically tuned for a particular octave or frequency range. 
         [0062]    Each sound wave pathway  608 ,  610 ,  612  and  614  is volumetrically proportioned to provide equal acoustic pathways for the sound waves generated by the vibrating diaphragm  104 . Additionally, the individual volume of each sound wave pathway  608 ,  610 ,  612  and  614  preferably increases exponentially away from the diaphragm  104 . This proportionality provides a plurality of sound wave pathways  608 ,  610 ,  612  and  614  of substantially equal acoustical lengths so that sound waves emanating from the diaphragm  104  traverse paths of substantially the same length and arrive at the throat  114  in phase coherent form. As a result, the sound waves are reproduced with increased uniformity and fidelity across a wide range of frequencies. In one specific embodiment the reproducible frequency range is from 600 Hz to 25 kHz. It will be appreciated that the volume of the pathways  608 ,  610 ,  612 , and  614  may be controlled by the distance between members (by the spacing of the members and/or the taper of the surfaces thereof). 
         [0063]    The annular wave guide rings  516 ,  526  and  536  of the first and second intermediate and bottom wave guide members  402 ,  404  and  406  and the outlet wave guide protrusion  506  of the central wave guide member  400 , preferably terminate along a substantially common plane such as the bottom surface of bottom plate  112 . The annular wave guide rings and protrusion are concentrically aligned and extend parallel to the central axis of each wave guide member. The wave guide rings and protrusion function together to uniformly direct and focus the sound waves from each sound wave pathway into the throat of a horn (not shown) coupled with the compression driver  100 . 
         [0064]    A phase plug  106 A in accordance with another embodiment of the invention is illustrated in  FIGS. 8-12 . In these figures, like reference numerals have been utilized to designate like elements to the phase plug  106  illustrated in  FIGS. 1-7  and described above, except that the reference numerals utilized to designate this embodiment have been assigned the alphabetical extension “A” or “B”. For example, the conical member  400  of the first embodiment is essentially the same as the conical member  400 A of the second embodiment. This reference numeral designation scheme is utilized to avoid undue prolixity and avoid obscuring the invention and the alternate embodiment. The primary elements, as described above, have been designated in  FIGS. 8-12 , however not every surface or element is numbered for clarity. 
         [0065]    Reference is now made to  FIGS. 8 and 11  which clearly illustrates an alternate embodiment phase plug  106 A having sound absorption groves  800  formed within the sound wave absorption insert  500 B. The grooves  800  provide enhanced sound wave absorption because the sound waves are permitted to penetrate deeper in to the absorption insert  500 B and thus a greater volume of the insert  500 B is used for sound wave absorption. Furthermore, the grooves  800  provide additional surface area for sound waves entering the insert  500 B from various directions and angles. As best illustrated in  FIGS. 11 and 12 , the grooves  800  begin on the external surface  802  and extend partially into the insert  500 B towards the inner surface  804 . 
         [0066]    The sound absorbing insert  500 B is received into an integral recess  503 A defined by a central wave guide member  400 A. The sound absorbing insert  500 B preferably comprises a convex arcuate shaped surface  802  that substantially corresponds to an adjacent concave portion of an adjacent diaphragm  104  (see  FIG. 12 ). The insert  500 B is preferably fabricated from a material well suited to absorb sound waves examples of such material are rubber, cork, high-density foam or other similar materials. The insert  500 B is attached to the central wave guide member  503 A, such as in the manner described above relative to the insert  500 . 
         [0067]      FIGS. 13   a - 13   c  are a series of impedance vs. frequency graphs comparing the performance of the present invention with a traditional phasing plug. In  FIG. 13   a , a first frequency curve  900  is based on sound performance of a traditional phasing plug is illustrated. As can be seen in the graph of  FIG. 13   a , the first curve  900  has several anomalies  902  that reflect phase distortions in the sound performance of the traditional phasing plug. 
         [0068]    In comparison,  FIG. 13   b  illustrates a second frequency curve  910  that is based on sound performance data for the improved phasing plug of the present invention. In contrast, the second curve  910  is generally flat and absent of such phase distortions. 
         [0069]    As best illustrated in  FIG. 13   c , which combines the graphs of  FIGS. 13   a  and  13   b , the end regions (at high frequencies) of both curves are substantially different or divergent, as the first curve  900  representing the performance of the traditional phasing plug has a very steep drop-off and includes anomalies  902 . In comparison, second curve  910  which represents the performance of the improved phasing plug of the present invention, has an anomaly free ending region having a gradual and smooth drop-off  912 . 
         [0070]    It will be appreciated that the phasing plug of the invention and a driver including a phasing plug in accordance with the invention may have other configurations than just as described and illustrated. For example, in one embodiment, the phasing plug may include a greater or lesser number of intermediate wave guide members depending upon the overall size of the phasing plug required for the compression driver. Thus a larger phasing plug may include three or more intermediate wave guide members, or as few as one (or zero) intermediate wave guide members. 
         [0071]    The phasing plug (and the various portions or members thereof) may have other shapes than as illustrated. For example, the phasing plug could be oval rather than generally circular in shape. 
         [0072]    As indicated, in one embodiment, the phasing plug may be constructed from a plurality of separate members. In yet another embodiment, the phasing plug may have a unitary or single piece construction. In this embodiment, the wave guide members may be manufactured as a single unit, such as with injection molding or casting methods. 
         [0073]    In another variation, the phasing plug may be combined with one or more portions of the driver. For example, the central wave guide member, intermediate and bottom wave guide members might be fabricated as a single piece construction integrally formed with the driver bottom plate. Thus, the driver bottom plate and the phasing plug may be a single unitary element or portion of the compression driver. In an alternate variation of the unitary bottom plate/phasing plug element, the sound absorbing insert may be embedded during the fabrication of the bottom plate/phasing plug element or alternatively, the sound absorbing insert may be attached to the central wave guide recess in a separate subsequent process. The unitary bottom plate/phasing plug may be fabricated from various metals, alloys or polymers using several known manufacturing processes or methods such as injection molding, casting and machining to name a few. 
         [0074]    In another embodiment, the wave guide members may be joined by other structural methods and still achieve the spaced apart relationship. For example, in place of having bosses and mating recesses, this embodiment may utilize flanges and slots, pins and holes, or tung and groves between the wave guide members. 
         [0075]    As indicated above, in one embodiment, the sound wave inlet region of the phasing plug occupies or comprises about the outer ⅔ circumferential area of the phasing plug and corresponds to an adjacent phase coherent energy zone of the diaphragm, while the sound wave absorbing region occupies the center ⅓ circular surface area of the phasing plug and corresponds to an adjacent phase distortion zone of the diaphragm. In a preferred embodiment, the center or central ⅓ sound wave absorbing region is completely devoid of any sound wave inlets (i.e. the sound wave absorbing region extends radially outward from a center of the phasing plug a sufficient distance to comprise at least ⅓ of the total top area of the phasing plug (or about 0.8 of the radius of the phasing plug when the phasing plug is generally circular in shape), thus comprising a central circular area). In other embodiments, however, the size and shape of this region may vary. For example, the sound wave inlet region might comprise the outer ¾ and the sound wave absorbing region might comprise the center ¼ of the top surface area of the phasing plug. 
         [0076]    In one embodiment, the sound wave absorbing region is sized and located relative to the diaphragm of the driver with which it is to be associated. In one embodiment, the sound wave absorbing region is sized to correspond to the central ⅓ area of the driver. In the case where the diaphragm and phasing plug are generally circular in shape, this area would extend outwardly from the center about the 0.8 of the radius of the diaphragm/phasing plug. 
         [0077]    As indicated, the sound wave absorbing region is preferably a portion of the phasing plug which is designed to absorb, and thus not reflect or transmit, sound waves. The sound wave absorbing region may be defined by a plug which is located in a top or central wave guide member. In another embodiment, the sound wave absorbing region may comprise a portion of that top or central member (i.e. be formed integrally therewith). For example, the central wave guide member may be a unitary construction that is fabricated using a sound absorption material (e.g., cork, rubber or foam). In this example, the sound wave pathway surfaces may then be coated or laminated with a material that facilitates sound wave transmission. Conversely, the surfaces intended for sound wave absorption may remain un-coated and thus facilitate sound wave absorption upon those surfaces. The other wave guide members may be fabricated in a similar manner where the sound wave transmission surfaces are coated or laminated with materials that facilitate sound wave transmission. 
         [0078]    The phasing plug of the present invention has numerous advantages over current phasing plugs and has particular advantages when used with a compression driver. In particular, the phasing plug produces enhanced sound quality by transmitting sound waves in phase coherent form. The sound wave absorbing portion or region of the phasing plug absorbs phase distorted sound waves (typically low to midrange frequency sound waves) generated at a central or center portion of a compression driver diaphragm. At the same time, the phasing plug transmits coherent sound waves, such as coherent low and midrange sound waves and sound waves (typically midrange to high frequency sound waves) generated at the outer edges or exterior portions of the diaphragm. This has the advantage that the phasing plug transmits sound with increased clarity over the high-frequency range, while at the same time, maintaining audible definition over the high to midrange sound wave spectrum. 
         [0079]    The improved phasing plug also has the advantages that it reduces the need for electronic signal processing or equalization of the input signals to the compression driver, avoids over-heating of the voice coil and conserves energy. Since the use of the improved phasing plug requires less signal processing, the compression driver is less likely to be over-powered by associated signal conditioners. Over-powering or over-equalization is a frequent occurrence when using a traditional phasing plug with a compression driver, and such over-equalization has adverse impact upon the compression driver such as over-heating the voice coil and consuming excessive electrical power. The improved phasing plug of the present invention reduces over-heating and conserves energy used by the compression driver because the sound wave transmission is inherently free from typical phase distortions and excessive electronic equalization is unnecessary. 
         [0080]    The improved phasing plug also provides a focused sound wave projection region by use of the wave guide rings at the termination point of each sound wave pathway. The annular rings and central protrusion provide a plurality of concentric wave guides that facilitate the directional aiming of the sound waves. This directional aiming causes the sound waves to exit the throat region of the phasing plug on concentric and distinct pathways resulting in high-frequency (19 khz) waves that propagate in unison and are projected over greater distances. 
         [0081]    It will be understood that the above described arrangements of the apparatus and the method therefrom are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the invention as defined in the claims.