Abstract:
A dipole radiating dynamic speaker design comprises a diaphragm ( 32 ) providing a surface for radiating acoustic output, a voice coil assembly ( 36 ) for driving the diaphragm, and a magnet system for providing magnetic flux across the voice coil assembly. The speaker incorporates a vented pole flux conductor ( 42 ) and a vent adjacent to the diaphragm permitting the rearward acoustic output to propagate away from the diaphragm producing acoustic output as a dipole radiator. 
     A method of utilizing the dipole radiating dynamic speaker design for tweeter and mid-range speaker applications used in home, automotive, and professional audio systems is disclosed. In addition a novel enclosure design is disclosed that utilizes a front panel perimeter vent providing improvement of audio reproduction quality for mid-range speaker applications.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a dynamic speaker design utilizing a diaphragm, voice coil assembly, and magnet system producing acoustic output as a dipole radiator. The invention also relates to a method of utilizing the dipole radiating dynamic speaker design for tweeter and mid-range speaker applications used in home, automotive, and professional audio systems. 
   Dynamic speakers utilizing a diaphragm, voice coil assembly, and magnet system providing acoustic output as monopole radiators have been manufactured for many years and are still widely used in commercial, professional, and home applications. The dynamic speaker has endured as the most popular speaker design due to its low cost, compact design, ease of use, and reliability. However, the dynamic monopole speaker audio reproduction quality is considered inferior to other more expensive speaker design technologies such as electrostatic, planar magnetic, and ribbon type. 
   A dynamic speaker system generally utilizes multiple dynamic speakers that provide acoustic output for specific frequency ranges. Dynamic speakers that provide mid-frequency and high-frequency acoustic output are generally known as mid-range and tweeter units, respectively. This patent addresses the design deficiencies with prior art mid-range and tweeter dynamic speakers. 
   A brief explanation of acoustic wave propagation is necessary to effectively describe the prior art dynamic speaker design deficiencies. A speaker generates acoustic wave output by converting an electrical signal into mechanical diaphragm motion. In operation, the diaphragm vibrates proportional to the electrical signal passing through the voice coil producing forward and rearward propagating acoustic wave output. The diaphragm movement produces half of the acoustic output energy in the forward direction and half in the rearward direction. This fundamental wave propagation principal is common to all speakers producing acoustic output in response to diaphragm motion. 
   In general, speakers that provide low frequency output utilize an enclosure to prevent acoustic cancelation caused by the interaction of the forward and rearward wave propagation. Typically, midrange and tweeter dynamic speakers are mounted in a common enclosure with other low frequency producing dynamic speakers. The low frequency dynamic speaker produce acoustic output of sufficient magnitude within the enclosure that damage to the mid-range and tweeter diaphragms would result if acoustic isolation were not provided. As a result, the prior art of mid-range and tweeter dynamic speaker design incorporate a means of blocking the acoustic output from other speakers in order to isolate and protect the diaphragm. These mid-range and tweeter dynamic speakers produce acoustic output in only one direction as monopole radiators. 
   The main flaw in the prior art dynamic speaker design is the incorporation of the acoustic wave blocking means. The acoustic wave blocking means also acts to block the rearward propagating acoustic output from the tweeter or mid-range speaker. As a result, the trapped rearward propagating acoustic output is reflected within a space internal to the speaker causing acoustic wave distortion known as constructive and destructive interference. This distorted acoustic output is dissipated primarily on the diaphragm due the reflective characteristic of the materials utilized in the dynamic speaker construction. Subsequently, the forward propagating acoustic output is corrupted due to the dissipation of the distorted acoustic output from the rearward propagating acoustic output. In effect, half of the dynamic monopole speaker acoustic output energy is distorted and dissipated on the diaphragm causing significant degradation of the forward propagating acoustic output accuracy. As a result the dynamic monopole speaker design produces inferior imaging resolution and audio reproduction accuracy compared to other speaker design technologies. 
   The prior art of dynamic speaker design does not effectively address the audio reproduction quality degradation caused by the containment of the rearward propagating acoustic output. 
   The following drawings illustrate prior art mid-range and tweeter dynamic monopole speaker design. Those skilled in the art of dynamic speaker design, operation, and manufacture will be familiar with the construction and operation. The following drawings illustrate prior art dynamic speaker design deficiencies described above. 
     FIG. 1  illustrates a typical prior art dynamic monopole speaker design. Dynamic mid-range and tweeter speakers generally contain the following main components: a diaphragm  10 , a voice coil assembly  12  containing the voice coil and former, front and rear flux conductor plates  14  and  16 , a solid pole flux conductor  18 , a permanent magnet  20 , and a mounting frame  22 . The flux conducting components are composed of a ferro-magnetic material, for example, steel. This dynamic speaker construction utilizes a solid pole flux conductor  18  secured to the rear flux conductor plate  16 . This construction provides an economical speaker assembly that has been manufactured for many years. However, this construction suffers from the fundamental design flaw that degrades the audio reproduction quality. The solid pole flux conductor  18  acts to block the rearward propagating acoustic output emanating from the vibrating diaphragm  10 . The area contained between the diaphragm  10  and the solid pole flux conductor  18  forms a closed chamber that traps the rearward propagating acoustic output. As a result, the rearward propagating acoustic output forms constructive and destructive waveform interference that is reflected and dissipated on the diaphragm  10 . This distorted acoustic output negatively impacts the forward propagating acoustic output resulting in audio reproduction quality degradation. 
     FIG. 2  illustrates an improved prior art dynamic monopole speaker construction. This dynamic speaker is designed with the same components as described in  FIG. 1  with the exception of the following components. The improved design utilizes a vented pole flux conductor  24  containing a cylindrical hole providing a passage to a rear chamber C 1  formed by a sealed rear housing  26 . The rear chamber C 1  contains acoustic damping material  28  which acts to dampen the rearward propagating output by dissipating a portion of the rearward propagating acoustic output over time. However, this construction entraps half of the acoustic output energy within the limited volume of chamber C 1  and does not adequately address the adverse effects caused by the fundamental design flaw. The stored acoustic output contained in the rear chamber is reflected and dissipated on the diaphragm  10  which negatively impacts the forward propagating acoustic output resulting in audio reproduction quality degradation. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is the primary object of this invention to improve the audio reproduction quality of dynamic speakers used in home, automotive, and professional applications. It is another principal object of the present invention to provide a dynamic speaker design utilizing a diaphragm, voice coil assembly, and magnet system that produces acoustic output as a dipole radiator. It is a further object of the present invention to provide a method of utilizing the dipole radiating dynamic speaker design for tweeter and mid-range speaker applications used in home, automotive, and professional audio systems. 
   The present invention provides a significant advance in the art by providing a dynamic speaker that produces acoustic output as a dipole radiator. In contrast to prior art dynamic speaker design, the dipole radiator produces acoustic output of equal magnitude in the forward and rearward directions permitting the diaphragm to move only in response to the electrical input signal. In accordance with the present invention a venting means is provided to permit the rearward acoustic output to propagate away from the diaphragm, thus minimizing or eliminating the adverse effects that cause audio reproduction quality degradation. The dipole radiating dynamic speaker design disclosed herein utilizes vents that provide minimal obstruction to the rearward acoustic output propagation and thus in effect produces acoustic output as a dipole radiator. 
   The invention further provides a point source acoustic dipole output that produces superior imaging resolution, and improved audio reproduction accuracy compared to the prior art speaker design. The invention further provides an inexpensive means to manufacture a dipole radiating speaker with conventional dynamic speaker manufacturing techniques, equipment, and components. Previously dipole radiating speakers were only available in other more expensive speaker design technologies such as electrostatic, planar magnetic, and ribbon type. 
   The invention further provides a method of utilizing the dipole radiating dynamic speaker without the need for an enclosure by mounting the speaker on a panel device that permits the rearward acoustic output to propagate away from the diaphragm. The invention further provides a method of utilizing the dipole radiating dynamic speaker for mid-range applications with a front panel perimeter vented enclosure design that permits a portion of the acoustic output to directly exit the enclosure providing improved audio reproduction quality compared to prior art enclosure designs. 
   The dipole radiating dynamic speaker broadly comprises a diaphragm providing a surface for radiating acoustic output, a voice coil assembly for driving the diaphragm, and a magnet system for providing magnetic flux across the voice coil assembly. The speaker incorporates a vented pole flux conductor and a vent adjacent to the diaphragm to permit the rearward acoustic output to propagate away from the diaphragm providing acoustic output as a dipole radiator. 
   The dipole radiating dynamic speaker functions under the same electro-dynamic principles as conventional dynamic speakers. In operation, the diaphragm vibrates proportional to the electrical signal passing through the voice coil producing forward and rearward propagating acoustic output. The dipole radiating dynamic speaker construction utilizes a vented pole flux conductor that provides a passage for the rearward acoustic output that is generated by the diaphragm contained within the perimeter of the voice coil assembly. The vent located between the frame and the front flux conductor plate provides a passage of minimal obstruction for the rearward acoustic output that is generated by the diaphragm adjacent to the voice coil assembly.  FIG. 7  illustrates the acoustic output passages provided by a typical dipole radiating dynamic speaker. It is readily apparent that the rearward propagating acoustic output travels away from the diaphragm thus minimizing or eliminating the adverse effects that cause sound quality degradation. By permitting the rearward propagating acoustic output to exit the rear of the speaker with minimal obstruction the diaphragm moves only in proportion to the electrical input signal and is not negatively impacted by trapped acoustic output. The speaker may additionally contain acoustic damping material to cover reflective surfaces to reduce acoustic reflections internal to the speaker. 
   Further objects and advantages of the present invention will become apparent as the following embodiments of the present invention are discussed in connection with the drawings. However, it is to be noted that the drawings provide fundamental concept illustration only and do not limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  illustrates a side elevation cross sectional view of a typical prior art dynamic monopole speaker design. 
       FIG. 2  illustrates a side elevation cross sectional view of an improved prior art dynamic monopole speaker design. 
       FIG. 3  illustrates a side elevation cross sectional view for a preferred embodiment of a dipole radiating dynamic speaker design. 
       FIG. 4  illustrates a side elevation cross sectional view of a dipole radiating dynamic speaker design utilizing a solid pole flux conductor. 
       FIG. 5  illustrates a side elevation cross sectional view of a dipole radiating dynamic speaker design utilizing vented front and rear flux conductor plates. 
       FIG. 6  illustrates a side elevation cross sectional view of a dipole radiating dynamic speaker design utilizing a conventional dome diaphragm. 
       FIG. 7  illustrates a side cross sectional view of the acoustic output path for the dipole radiating dynamic speaker. 
       FIG. 8  illustrates a cross sectional view of a speaker mounting means utilizing dipole radiating dynamic speakers. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 3 , in accordance with the present invention the dipole radiating dynamic speaker broadly comprises a frame  30 , diaphragm  32 , suspension  34 , voice coil assembly  36 , front flux conductor plate  38 , rear flux conductor plate  40 , vented pole flux conductor  42 , permanent magnet  44 , and acoustic damping material  46 . 
   The frame  30  contains a centrally located aperture for the purpose of supporting the diaphragm  32 . In accordance with the present invention, the frame  30  comprises a plurality of integral standoff posts located on the rear surface that provide a vent between the frame  30  and the front flux conductor plate  38 . This vent provides a passage of minimal obstruction for the rearward acoustic output to propagate away from the diaphragm  32 . 
   The diaphragm  32  is preferably an inverted dome shape and composed of a suitably light weight rigid material. The diaphragm  32  perimeter is preferably attached with an adhesive to a suspension  34  that suspends the diaphragm within the speaker assembly. In accordance with the present invention, the diaphragm  32  may incorporate an integral suspension formed as a single device, thus eliminating the requirement for the suspension  34  component. 
   The suspension  34  is composed a suitably thin flexible material and permits the diaphragm  32  to move in response to electrical current flowing through the voice coil. The suspension  34  is attached to the front surface of the frame  30  at the inner circumferential edge of the aperture. Alternatively, the suspension  34  may be attached to the rear surface of the frame  30  at the inner circumferential edge of the aperture to increase the vent height dimension between the frame  30  and the front flux conductor plate  38 . This construction provides a larger pathway area for the rearward acoustic output to propagate. 
   The voice coil assembly  36  is of conventional design and consists of a wire coil wound on the perimeter of a non magnetic cylindrical former. The voice coil wires are terminated to conventional electrically conductive terminals (not shown) by conventional manufacturing means. The diaphragm  36  is secured to the front circular edge of the cylindrical shaped voice coil assembly  36  with an adhesive. The voice coil assembly  36  diameter is generally proportioned to a size less than the diameter of the diaphragm  32 . The voice coil assembly  36  is situated in a circular air gap formed between the front flux conductor plate  38  and the vented pole flux conductor  42 . The frame  30  is positioned relative to the front flux conductor plate  38  enabling the voice coil assembly  36  to be aligned centrally within the air gap. 
   The vented pole flux conductor  42  is centrally located and conducts the magnetic flux from the rear flux conductor plate  40  to the air gap. Preferably, the vented pole flux conductor  42  contains an axially located hole that provides a passage of minimal obstruction for the rearward acoustic output to propagate away from the diaphragm  32 . The vented pole flux conductor  42  is secured to the rear flux conductor plate  40  via conventional mechanical means and/or adhesive. Alternatively, the vented pole flux conductor  42  and the rear flux conductor plate  40  may be constructed as a single device. The vented pole flux conductor  42  may be of any shape that fits the mechanical constraints of the speaker assembly and is not limited to a cylindrical form, nor a specific ratio of hole size to outside diameter. The flux conducting components are composed of a ferro-magnetic material, for example, steel. 
   A permanent magnet  44  is secured with adhesive between the front flux conductor plate  38  and the rear flux conductor plate  40  forming a magnet assembly that provides the source of magnetic flux. Alternatively, an electromagnet may be utilized in place of the permanent magnet  44 . The speaker may also utilize acoustic damping material  46  secured to the front flux conductor plate  38  to provide acoustic wave absorption of the rearward propagating acoustic output. Additionally, acoustic damping material may be located between the vented pole flux conductor  42  and the diaphragm  32  for reducing acoustic reflections. 
     FIG. 4  illustrates an alternate embodiment of the dipole radiating dynamic speaker. The design is of similar construction as the apparatus described in  FIG. 3  with the exception that the vented pole flux conductor  42  is replaced with the solid pole flux conductor  48  and acoustic damping material  50 . 
   This design incorporates a solid pole flux conductor  48  providing increased flux conducting capacity over the design of FIG.  3 . thus increasing the acoustic output efficiency. The solid pole flux conductor  48  is secured to the rear flux conductor plate  40  via conventional mechanical means and/or adhesive. The acoustic damping material  50  is secured to the solid pole flux conductor  48  to provide acoustic damping of the rearward propagating acoustic output. The voice coil assembly  36  may be of a conventional design or alternatively, the former may be acoustically porous to permit the rearward acoustic output to propagate away from the diaphragm  32 . The former may contain holes, slots, or other form to permit acoustic propagation. 
     FIG. 5  illustrates an alternate embodiment of the dipole radiating dynamic speaker. The design is of similar construction as the apparatus described in  FIG. 3  with the exception that the front and rear flux conductor plates  38 ,  40 , voice coil assembly  36 , vented pole flux conductor  42 , and the frame  30  are replaced with the vented front and rear flux conductor plates  52 ,  54 , voice coil assembly  56 , vented pole flux conductor  58  and frame  60 . 
   The vented pole flux conductor  58  is secured to the vented rear flux conductor plate  54  via mechanical means and/or adhesive. Alternately, a solid pole flux conductor may be used in place of the vented pole flux conductor  58 . The vented front and rear flux conductor plates  52  and  54  permit the rearward acoustic output to propagate away from the diaphragm. The vented front and rear flux conductor plates  52  and  54  may contain holes, slots, or other form to permit acoustic propagation. The flux conducting components are composed of a ferro-magnetic material, for example, steel. 
     FIG. 6  illustrates an alternate embodiment of the dipole radiating dynamic speaker. The voice coil assembly  12  is of conventional design and consists of a wire coil wound on a non-magnetic cylindrical former. The voice coil assembly  12  is situated in a circular air gap formed between the front flux conductor plate  14  and the vented pole flux conductor  24 . The voice coil wires are terminated to conventional electrically conductive terminals (not shown) by conventional manufacturing means. 
   The diaphragm  10  is secured to the front circular edge of the voice coil assembly  12  and to the frame  22  with an adhesive. The diaphragm  10  incorporates an integral suspension permitting the diaphragm  10  to move in response to electrical current flowing through the voice coil. The frame  22  is positioned relative to the front flux conductor plate  14  enabling the voice coil assembly  12  to be aligned centrally within the air gap. 
   The vented pole flux conductor  24  is secured to the rear flux conductor plate  16  via conventional mechanical means and/or adhesive. The vented pole flux conductor  24  may be of any shape that fits the mechanical constraints of the speaker assembly and is not limited to a cylindrical form. The vented pole flux conductor  24  conducts the magnetic flux from the rear flux conductor plate  16  to the air gap and provides a passage for the rearward acoustic output to propagate away from the diaphragm  10 . The flux conducting components are composed of a ferro-magnetic material, for example, steel. 
   A permanent magnet  20  is secured with adhesive between the front flux conductor plate  14  and the rear flux conductor plate  16  forming a magnet assembly that provides the source of magnetic flux. The speaker may also contain acoustic damping fiber secured to the vented pole flux conductor  24  to provide acoustic wave absorption for the rearward propagating acoustic output. 
     FIG. 8  illustrates a preferred method of utilizing the dipole radiating dynamic speaker design for tweeter and mid-range applications. The speaker system is broadly comprised of a dipole radiating tweeter  62 , dipole radiating mid-range speaker  64 , enclosure front panel  66 , enclosure body  68 , and acoustic damping fiber  70 . 
   The dipole radiating tweeter  62  and dipole radiating mid-range speaker  64  are mounted to the enclosure front panel  66  via conventional means. 
   The enclosure front panel  66  is preferably constructed of a suitably rigid material and form that extends beyond the enclosure body  68 . The enclosure body  68  is preferably constructed of a suitably rigid material, for example, medium density fiberboard. The dipole radiating tweeter  62  is located on the enclosure front panel  66  such that it is external to the enclosure body  68  permitting the rearward propagating acoustic output from the dipole radiating tweeter  62  to disperse in free space unobstructed. The dipole radiating mid-range speaker  64  is located on the enclosure front panel  66  such that the enclosure body  68  surrounds the rear of the dipole radiating mid-range speaker  64 . 
   A means is provided such that a vent V 1  is formed between the enclosure front panel  66  and the enclosure body  68  perimeter. The vent dimensions are selected to optimize the audio reproduction quality from the dipole radiating mid-range speaker  64 . The enclosure body  68  generally contains acoustic damping fiber  70  for reducing acoustic reflections within the enclosure body  68 . Additionally, a vent V 2  of conventional form may be utilized for tuning the enclosure low frequency acoustic output. 
   The following dimensions and specifications describe a typical dipole radiating dynamic speaker design as illustrated in  FIG. 3  for use in a tweeter application. 
   Diaphragm diameter=1.0 inch 
   Voice coil diameter=0.52 inches 
   Voice coil former height=0.30 inches 
   Voice coil layers=2 
   Voice coil height=0.08 inches 
   Voice coil wire=AWG 39 
   Voice coil resistance=4.0 ohms 
   Vented pole flux conductor outer diameter=0.50 inches 
   Vented pole flux conductor inside diameter=0.35 inches 
   Magnet system air gap=0.030 inches 
   Magnet system air gap height=0.10 inches 
   Magnet diameter=2.75 inches 
   Magnet height=0.63 inches 
   Frame vent height=0.35 inches 
   Diaphragm/voice coil assembly moving mass: 0.25 grams 
   Acoustic damping material thickness=0.063 inches 
   Acoustic output frequency range: 1000 Hertz to 15000 Hertz. 
   A preferred method for utilizing dipole radiating speakers in a system as illustrated in  FIG. 8  is described below. The speaker system shall be capable of reproducing the frequency range of 80 Hertz to 15,000 Hertz utilizing two speakers. A crossover device of conventional design is utilized to provide the intended frequency signal for the appropriate speaker. For frequency production below 80 Hertz, a separate speaker called a subwoofer may be utilized. The design and utilization of a subwoofer is well known to those skilled in the art and is not described herein. 
   The dipole radiating tweeter shall provide acoustic output for the frequency range of 1000 Hertz to 15,000 Hertz. In operation, the dipole radiating dynamic tweeter may be mounted to a panel without an enclosure such that the diameter of the panel is selected to support the frequency range intended for the speaker. Acoustic wave theory requires that the panel diameter be at least the lowest wavelength divided by two in order to produce acoustic output without attenuation. For example, the above speaker will provide acoustic output down to 1000 Hertz requiring the panel diameter to be at least this wavelength divided by two. This calculation [1100 ft/s÷1000 Hz÷2×12 in/ft] yields a panel diameter of at least 6.6 inches to support acoustic output down to 1000 Hertz. The dipole radiating tweeter should be mounted to the panel such that the acoustic output is permitted to propagate unobstructed away from the diaphragm. Acoustic damping material may be utilized on the front and rear panel surfaces to reduce acoustic reflections from the panel. This utilization of the dipole radiating dynamic tweeter is the preferred method as the acoustic output is permitted to travel away from the diaphragm unobstructed in both the forward and rearward directions thus minimizing the adverse effects that cause sound quality degradation. 
   A dipole radiating mid-range speaker shall be utilized to provide the frequency range from 80 Hertz to 1000 Hertz. It is possible to mount the dipole radiating mid-range speaker to a panel without an enclosure to reproduce this frequency range, however the panel diameter would be large and may require equalization of the lower frequencies in order to produce accurate acoustic output. Alternatively, this task is effectively accomplished through the utilization of an enclosure. There are various enclosure types that are utilized in current production such as bass reflex, acoustic suspension, and transmission line. It is not with in the scope of this patent to describe the advantages, disadvantages, and characteristics of each type. However, the use of a front panel perimeter vented enclosure design will provide significant improvement of the acoustic output quality compared to prior art enclosures. 
   Referring to  FIG. 8 , the dipole radiating tweeter  62  and dipole radiating mid-range speaker  64  are mounted to the enclosure front panel  66 . The vent V 1  dimension between the enclosure front panel  66  and the enclosure body  68  is adjusted to optimize the enclosure for the most accurate acoustic output from the dipole radiating mid-range speaker  64 . A typical gap dimension for vent V 1  for the purpose of experimentation is 0.25 inches. The advantage of this enclosure design is a portion of the mid-range acoustic output is permitted to directly exit the enclosure providing improved acoustic quality compared to prior art enclosure designs. The enclosure may additionally incorporate holes, slots, or ports for the purpose of tuning the enclosure low frequency acoustic output. 
   The front panel perimeter vented enclosure design may be applied to floor-standing or a small bookshelf designs and is also applicable to conventional dynamic mid-range and woofer speakers. In addition, alternative embodiments utilizing this enclosure design will be obvious to those skilled in the art and are not limited to the example described above. 
   While the above descriptions provide some specific design concepts, these should not be construed as limitations on the scope of the invention, but rather as examples of various embodiments. It should be apparent to those skilled in the art that various other revisions, omissions and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than solely by the examples given.