The present invention generally relates to acoustic devices, and more particularly, to an anti-diffraction and phase correction structure for a planar magnetic transducer.
Planar magnetic transducers use a flat, lightweight diaphragm suspended in a magnetic field rather than a cone attached to a voice coil. The diaphragm in a planar magnetic transducer includes a conductive circuit pattern that, when energized, creates forces that move the diaphragm in the magnetic field to produce sound.
The structures encountered by a sound wave traveling from the diaphragm are obstacles that may negatively interfere with the sound wave. It is desirable for a sound wave as emitted from a diaphragm to encounter as little interference as possible as it travels from the diaphragm.
Preferred embodiments of the invention include a planar magnetic transducer that minimizes diffraction of the main sound wave, minimizes the effects of reflected sound waves and minimizes the phase distortion.
A preferred embodiment of the invention includes a planar magnetic transducer having one or more anti-diffraction structures positioned adjacent to one or more magnets for eliminating diffraction of a sound wave around the magnets, the sound wave emitted from a diaphragm and passing by the magnets.
A preferred embodiment of the invention includes a planar magnetic transducer having one or more diffusion structures positioned adjacent to one or more magnets for minimizing reflections of the sound wave.
A preferred embodiment of the invention includes a planar magnetic device having one or more wave guides positioned adjacent to one or more magnets for creating a uniform wavefront.
Preferred embodiments of the present invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
Planar magnetic transducers comprise a flat, lightweight diaphragm suspended in a magnetic field. A structure of magnets coupled to stator plates are arranged at a distance from the diaphragm to effect the magnetic field. The diaphragm in a planar magnetic transducer includes a conductive circuit pattern that, when energized, creates forces that move the diaphragm in the magnetic field to produce sound.
A sound wave emitted from a diaphragm and traveling through air in a planar transducer will encounter the magnetic structure and stator plate as obstructions in its path of travel. The obstructions may cause the user to hear distortions in the sound, depending on the particular wavelength of the sound wave. If the wavelength of the sound wave is longer then the width of the obstruction, then the wave generally passes through without distortion.
If the wavelength is of comparable size to the obstruction, diffraction patterns are formed, causing distortions to the sound wave. When the diffracted waves and the main sound wave arrive at the listener's ears at the same time, distortion of the sound occurs and the stereo imaging is affected. When sound waves go around the obstacle they arrive at the listener's ear at slightly different times compared to the main sound wave, causing phase distortion.
If the wavelength is smaller than the obstruction, then in addition to diffraction patterns, the sound wave is reflected. The reflected sound waves interact with new sound waves emitting from the diaphragm to create constructive and destructive interference patterns at certain frequencies, causing further distortion. Further, the space between the obstructions can create resonant chambers which influence frequency response.
Preferred embodiments of the invention include a planar magnetic transducer that minimizes diffraction of the main sound wave, minimizes the effects of reflected sound waves and minimizes the phase distortion. A preferred embodiment of the invention includes an anti diffraction structure that can be considered as a particular version of a wave guide planar magnetic transducer having one of more wave guides positioned adjacent to one or more magnets.
One of the primary objectives of preferred embodiments is to create a uniform wavefront that results in much smoother frequency response, better imaging, smoother phase response, better high frequency extension and higher efficiency. Anti-diffraction plate 12 eliminates the resonant chambers in front of the diaphragms and creates an acoustic chamber with higher pressure. Higher pressure creates a better acoustical impedance match between diaphragm and air increasing the efficiency of the transducer and creates better high frequency extension. Anti-diffraction plate 12 can be used with standard long bar magnets to achieve the reduction in diffraction in a cost-effective way.
Referring to
Further, while anti-diffraction plate 12 is shown in a particular configuration and as a circular shape, and while array 10 is shown with three magnets of a particular shape, size or configuration, it is understood that variations on the structures, including different quantity, shape, and dimensions of array 10 and anti-diffraction plate 12, are within the scope of the embodiments of the invention.
Anti-diffraction plate 12 may be constructed from any suitably rigid material that will not interfere with the magnetic forces of the magnets, including plastic, metal, or composite materials. In a preferred embodiment, anti-diffraction plate 12 is made of a rigid plastic material mounted adjacent to magnet array 10. Long bar magnets are spaced in parallel, in alignment with the anti-diffraction structures 16 of plate 12. The shape of each anti-diffraction structure comprises a flat bottom surface, and a curved top surface.
In contrast, view 402 shows a main audio wavefront 32 traveling from diaphragm 14 of the planar magnetic device. As wavefront 32 passes the combined structures of the anti-diffraction structures 16 positioned adjacent to the magnets, diffraction patterns are eliminated or minimized due to the surface shape of the anti-diffraction structures 16. The anti-diffraction structures 16 accordingly smooth out the “corner” shape of the of the magnets as seen in cross section, eliminating or reducing diffraction waves. The anti-diffraction structures 16 cause a smoother frequency response and a more precise imaging of the sound wave.
In addition to distortion of the sound waves from the diaphragm caused by diffraction as described above, sound waves of a particular wavelength may be reflected off the surface of the magnet facing the diaphragm, interfering with oncoming sound waves generating from the moving diaphragm.
Other features, aspects and objects of the invention can be obtained from a review of the figures and the claims. It is to be understood that other embodiments of the invention can be developed and fall within the spirit and scope of the invention and claims.
The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Various additions, deletions and modifications are contemplated as being within its scope. The scope of the invention is, therefore, indicated by the appended claims rather than the foregoing description. Further, all changes which may fall within the meaning and range of equivalency of the claims and elements and features thereof are to be embraced within their scope.
This application claims the benefit of U.S. Provisional Patent Application No. 61/892,417, filed Oct. 17, 2013, the entirety of which is incorporated by reference as if fully set forth herein.
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International Search Report and Written Opinion dated Feb. 4, 2015 for PCT/US2014/061246, 7 pgs. |
Number | Date | Country | |
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20150110326 A1 | Apr 2015 | US |
Number | Date | Country | |
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61892417 | Oct 2013 | US |