Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1998-07-23
2001-02-06
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S399000, C381S408000
Reexamination Certificate
active
06185310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is generally directed to transducers which incorporate a vibrating diaphragm, and more specifically, to planar magnetic acoustic transducers which include permanent bar magnets mounted in spaced rows on opposite sides of the diaphragm on which an electrical conductor circuit has been applied. The invention includes pole elements formed in opposing frame sections between which the diaphragm is mounted so that the pole elements are spaced intermediate each of the rows of magnets on opposite sides of the diaphragm. The spacing and size of the rows of magnets and pole elements is such as to ensure that substantially the entire active area of the diaphragm is driven except at points intermediate the opposing pole elements to thereby provide for a smoother frequency response for the transducer when in use.
2. History of the Invention
In microphone transducers, acoustic pressure variations act on a diaphragm surface causing the diaphragm to vibrate. The resultant vibrations of conductors associated with the diaphragm, while retained within a magnetic field of the transducer, create a voltage signal of similar time variance and intensity characteristics as the acoustic signal used to supply the conductors of the diaphragm. In a loudspeaker transducer, an audio signal current flows through conductors of a diaphragm. Current flowing through the conductors reacts with the magnetic field of magnets mounted in proximity to the diaphragm, thereby causing magnetic forces to act on the conductors that create sound pressure waves along the diaphragm surface which are proportional and synchronous to audio signals applied to the conductors.
Diaphragms of planar magnetic loudspeakers are normally held loose or under tension in a plane parallel to the pole faces of one or more permanent magnets so as to be in the static magnetic field of the magnets. An active surface area of the diaphragm, which is an area of the diaphragm which is not constrained from motion by a rigid supporting frame to which the diaphragm is attached, is vibrated when electrical signals are provided to the conductor circuits attached to the diaphragm. Conductors are attached to the diaphragm in runs which, in many transducers, are generally parallel with the edges or pole faces of the permanent magnets. The path of the conductors on the diaphragm is chosen so that current flowing therethrough produces net magnetic forces of uniform direction for all of the conductor segments or runs along the active surface of the diaphragm by causing the general direction of diaphragm motion to always be perpendicular to the diaphragm surface.
The diaphragm active surface area is chosen for particular acoustic response characteristics, such as frequency response or dispersion. The spacing of conductors and the adjacent magnets are chosen so that the diaphragm is uniformly driven across its entire active surface area for low distortion or maximum band width. As an alternative, the conductor spacing may be chosen for optimum efficiency for a particular frequency band width or for various other reasons. The electrical circuit formed by conductor runs or segments on the diaphragm is designed concurrent with the arrangement of permanent magnets so that sufficient magnetic field strength and proper magnetic field orientation is provided to all active conductor segments or runs to achieve adequate transducer efficiency. This “useful” magnetic field is provided substantially parallel to the diaphragm.
Conductor runs on the diaphragm may take a variety of configurations, including round or rectangular. The conductors may be bonded to a diaphragm or chemically etched from foil laminates. The conductor dimensions, compositions and circuit arrangements are often chosen to meet a desired circuit impedance requirement for maximum efficiency within practical limitations. At the present time, aluminum conductors are preferably utilized for conductors due to lower mass and lower overall mass-resistivity product produced over other conductor metals. Lower mass has an inherent advantage for fast transient response and lower mass-resistivity product equates to higher efficiency.
The magnet materials are chosen for cost, ease of fabrication and magnetic parameters. Optimal magnet spacing, geometry and dimensional criteria may vary the magnetic material utilized in a particular application. An air gap dimensions, the spacing between a diaphragm of magnetic transducers and the magnets thereof, should be minimized for maximum efficiency but must be chosen to allow for adequate diaphragm motion at low frequencies. The optimum spacing between adjacent magnets of each assembly is also influenced directly by the air gap dimension.
The advantages of planar magnetic loudspeakers over other electromagnetic arrangements is that planar magnetic loudspeakers have lower distortion and more accurate phase response when compared to cone radiator type loudspeakers. U.S. Pat. No. 3,939,312 to McKay discloses a push-pull type planar magnetic transducer arrangement wherein magnets are positioned to direct a magnetic flux across the diaphragm at a slant angle with conductor runs applied to the diaphragm. In U.S. Pat. No. 4,471,173 to Winey, another push-pull magnetic arrangement is shown wherein magnets are positioned in alternating sets of rows so that magnetic fluxes are supposed to be directed tangential to the diaphragm from the north pole face of one magnet to the south pole face of an adjacent magnet and so forth across the width of the transducer with the magnets in opposing assemblies of magnets on opposite sides of a diaphragm providing repellant magnetic forces to bound the path of the magnetic flux field.
In U.S. Pat. No. 4,337,379 to Nakaya, arrays of square magnets alternating in polarity are disclosed which are retained in two similar assemblies of equivalent magnetic pole structures with a diaphragm contoured with conductor patterns arranged to minimize resonance mode inherent in some planar transducer designs.
Each of these magnetic transducer designs and other prior art structures create a long, and therefore low, permanence path for the magnetic flux from the pole faces of the magnets proximate to the conductors carried by the sound producing diaphragms. Gauss' law dictates that the flux of each permanent magnet must form a closed loop through both poles of each magnet and take the highest permanence path from pole face to pole face. Therefore, the longer the flux path, the less efficient the transducer.
SUMMARY OF THE INVENTION
This invention is directed to planar magnetic acoustical transducers having optimized operating efficiencies and, more specifically, to such transducers which are utilized as speakers for generation of sound. The transducers include housings defined by opposing metallic frame sections between which is mounted a flexible sound generating diaphragm on which electrical conductor runs are applied for receiving electrical signals from an outside source. The opposing frame sections each have an inner surface which supports a plurality of rows of permanent bar magnets and which rows are secured thereto in generally equally spaced relationship with respect to one another. Spaced between the rows of magnets and from each of the rows of magnets are a plurality of pole elements which are integrally formed in the frame sections so as to extend toward the diaphragm within the housing. In the preferred embodiment, the pole elements include outer surfaces which are substantially co-planar with respect to pole faces of the magnets which are spaced closely to and on opposite sides of the diaphragm. Slots are provided through each frame section between each pole element and an adjacent row of magnets allowing sound waves to pass therethrough. Also, in the preferred embodiment, each of the magnets has a height to width ratio which is less than unity and like pole faces of the magnets are aligned with one another on opposite sides of the diaphragm.
The width of the active surface area o
Delorme Marc
Kermani Mohammad
Montour Michael
Phillips Scott
Thigpen F. Bruce
Dowell & Dowell , P.C.
Eminent Technology Incorporated
Le Huyen
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