Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having electrostatic element
Patent
1992-03-23
1994-02-01
Ng, Jin F.
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having electrostatic element
381203, 381193, H04R 2500
Patent
active
052838366
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to audio transducers and particularly to planar diaphragm loudspeakers.
BACKGROUND OF THE INVENTION
Planar diaphragm loudspeakers have been in use for over twenty years but have never achieved the same popularity as cone-type speakers, due primarily to their cost and to their size and different performance characteristics.
Numerous examples of such speakers may be found in the patent literature, for example, U.S. Pat. No. 3,674,946 Winey, U.S. Pat. No. 3,919,499 Winey, U.S. Pat. No. 3,829,623 Willis et al, U.S. Pat. No. 4,468,530 Torgeson and U.S. Pat. No. 4,471,172 Winey. The last mentioned patent illustrates the structure of a typical planar diaphragm speaker, which comprises a polyester film diaphragm, a current carrying conductor adhered to the diaphragm, spaced bar magnets for generating a magnetic field which intersects the conductor, with the conductor typically being positioned in alignment with the gaps between the bar magnets. When an exciting current passes through the conductor, the diaphragm will be vibrated by the reactive forces generated by the interfering magnetic fields surrounding the conductor and between the adjacent bar magnets.
Most existing planar diaphragm speakers in commercial production utilize polyester film, such as Mylar (registered trade mark) having a thickness of the order of 0.01 mm to 0.1 mm. The present applicant believes that the quality of sound produced by speakers constructed in this way is to a certain extent colored by the use of polyester film or similar materials. Furthermore, the use of such materials results in manufacturing difficulties, such as the ease with which the film may be properly tensioned and the care with which the film must be handled during manufacture.
SUMMARY OF INVENTION AND OBJECT
It is an object of the present invention to provide an improved planar diaphragm loudspeaker in which the above described disadvantages are at least ameliorated.
The invention therefore provides an audio transducer comprising a planar diaphragm, a conductor defining a voice coil or grid secured to said diaphragm, and means for creating magnetic fields which intersect said conductor, said diaphragm being supported in a tensioned overlying relationship with said magnetic field creating means, characterized in that said planar diaphragm comprises a lightweight woven cloth having a first region substantially coincident with said voice coil or grid treated to close the open mesh of the woven cloth, and a second region substantially surrounding said first region in which the mesh of said cloth is substantially open and baffle means overlying but spaced from said second region.
The use of a suitable treated woven cloth having a perimetral open mesh region results in a significant reduction in out of phase vibrations and distortion of the regions which are not under the direct influence of the voice coil or grid and the magnetic fields. Furthermore, the woven cloth is stronger and more flexible than polyester film and may be more easily and more effectively tensioned and handled during the manufacturing process than polyester film. Best results are achieved when the diaphragm is very taut and such tautness is more easily achieved when a suitable woven cloth is used.
One suitable woven cloth material comprises a polyester mesh of the type used in the screen printing industry. Silk screening mesh is particularly suitable because it is made up of monofilaments which are woven to extremely accurate tolerance so the woven cloth has a predictable weight thickness and strength characteristics. It is preferred that high quality cloth, such as ZBF, be used for best results.
If desired, a finer mesh may be selected for speaker elements required to produce higher frequency sound, and in this regard a screen mesh having about 100-120 threads per centimeter has been found to be suitable. Similarly, a coarser mesh, say having only 90 to 100 threads per centimeter may be used for speaker elements required to produce lower frequency sou
REFERENCES:
patent: 3919499 (1975-11-01), Winey
patent: 4384173 (1983-05-01), Briefer et al.
Ng Jin F.
Tran Sinh
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