US 3328537 A
Description (OCR text may contain errors)
June 27, 1967 w. HECHT HIGH FRQUENCY SOUND TRANSLATING DEVICE Filed Jan. @1964 SEE.
INVENTOR HECHT Mam W United States Patent 3,328,537 HIGH FREQUENEY SOUND TRANSLATING DEVICE William Hecht, 11 Normandy Terrace, West Orange, NJ. 07057 Filed Jan. 9, 1964, Ser. No. 336,682 7 (Zlaims. (6i. 179115.5)
This invention relates generally to high frequency sound translating devices, and particularly to diaphragm constructions for such devices.
It is an object of this invention to provide a high frequency sound translating device which is non-resonant at all frequencies within its normal range of frequency operation.
It is also an object of this invention to provide a composite diaphragm which has a self-sustaining, foraminous support component which is non-resonant, and an attached diaphragm component which is likewise nonresonant.
It is another object of this invention to provide a composite diaphragm which will consist of non-resonant components, one of which provides a non-rigid, self-sustaining support, and the other of which is capable of moving air.
Yet another object of my invention is to provide a diaphragm for a high frequency sound translating device which has a high degree of compliance.
A still further object of my invention is to provide a spacer for the voice coil and diaphragm assembly of a high frequency sound translating device.
These objects and advantages as well as other objects and advantages may be attained by the device shown by way of illustration of the inventive concept in the drawings in which: I 7
FIGURE 1 is a vertical sectional view of the entire assembly of the high frequency sound translating device;
FIGURE 2 is a top plan view of the rubber spacer;
FIGURE 3 is a partly exploded, elevational view of the diaphragm and voice coil assembly; and
FIGURE 4 is a perspective view of the high frequency sound translating device with the voice coil and diaphragm removed.
Sound translating devices usually employ a rigid, impenetrable diaphragm to move air in response to electrical impulses. High frequency transducers now in general use may employ a thin, shell-like, rigid, convex dome as the diaphragm. Rigid diaphragms will inevitably resonate and will color the signal or tone produced by the electrical impulse, so that they will not accurately re-create the original sound corresponding to the electrical impulse. On the other hand, a soft, convex diaphragm is too readily deformable, by the resistance and inertia of the air column which it must move, to produce any appreciable sound. While the soft diaphragm will not resonate, it also will not produce any significant sound. The utility of the vast area of diaphragrns having intermediate qualities between softness and rigidity has remained largely unexplored until the present discovery. It has been found that it is possible to produce a composite diaphragm for the reproduction of high frequency sound which is sufficiently dense and rigid to produce significant volumes of sound, yet is sufliciently non-resonant within the frequency range of its operation that it will not color the signal that it translates from electrical impulse to sound vibrations. This is accomplished by providing a non-resonant composite diaphragm which is sufiiciently rigid to move air, and yet be non-resonant in its frequency range of operation.
A woven fabric, preferably cotton sheeting, having about 64 threads per inch of warp and 64 threads per inch 3,328,537 Patented June 27, 1967 of woof, is suitable for preparing a support for the diaphragm. The material is not initially self-sustaining, but is limp and foraminous. It is coated with a thin layer of epoxy resin. Many other suitable resins are Well known to the industry. The material is then placed within the complementary parts of a die having cavities to form a dome approximately two inches in diameter and approximately three-quarters of an inch high. Heat is applied for a sufficient period to set the resin, and the dome is removed from the die.
The resin is used only to give the fabric a self-sustaining character. The resin is not applied thickly enough to close the interstices of the fabric. After the support is set by the resin, a thin film of fluidized rubber or similar rubber-like material is then sprayed or brushed on the dome to close the interstices. This is allowed to dry to a thin film. This thin film of rubber on the support defines a radiating area in the diaphragm that moves the air. It
The domed composite diaphragm produced will be selfsustaining, will yield slightly to pressure in excess of 1% ounces, but will exert increasing resistance after being depressed approximately of an inch. Greater pressure must be exerted in order to produce additional deformation. Although its rigidity is slight, it is sufficient to restore it to its original convexity. The preferred degree of rigidity attained through use of the resin can be easily determined by experimentation. Too thick a coat of resin, will produce a hard unyielding dome support for the diaphragm which will resonate and give a colored response. On the other hand, too little resin will provide a support for the diaphragm which is not sufliciently self-sustaining to return to its original convex shape when deformed lightly by manual manipulation. The interstices of the fabric is closed by the rubber film so that the dome is impenetrable by air and can move an air column.
The diaphragm to be utilized is thus a composite structure, respecting which composite structure, the resin impregnated fabric dome is the supporting component of the composite diaphragm. The support is free of resonance characteristics and yet highly responsive to migrations of the voice coil to which it is attached.
The second component of the diaphragm is the thin rubber film which is non-resonant and flexible when applied to the support. Rubber, or any rubber-like material is suitable as the second component or lining of the composite diaphragm. By itself, this material is non-resonant, but so flexible as to be incapable to move a column of air and accurately to follow the excursions of a voice coil because it is too readily deformable, and totally lacks any rigidity. When applied to the slightly rigid support, which is non-resonant, it forms a diaphragm of suflicient rigidity to move air at the predetermined high frequency range. The support and film-lining do not together have a resonance period of any measurable degree sufiicient to color the transducers response in the frequency range of operation.
Referring now to the drawings in detail, a magnet 11 with a generally circular pole piece 9 is provided and a corresponding complementary pole plate 12 having a central aperture 13 in general opposition to the circular pole piece 9. A magnet keeper 10 spans the distance between the pole plate 12 and the magnet 11. The air gap 13 between the pole piece 9 and the pole plate 12 is .040 of an inch. A composite diaphragm 14 is prepared in accordance with the foregoing procedure. The edge of the composite diaphragm 14 has a short flange 8 to which is cemented the upper portion of a voice coil 15. The voice coil has twolayers of turns of Wire and the outer layer is slightly shorter by a few turns than the inner one to provide an attachment seat for the flange 8. (See FIGURE 3.) The adjacent turns of Wire of the voice coil 15 are adhered to each other to form a strong, rigid, tubular coil. This voice coil 15, is dimensioned to surround the circular pole piece 9 of the magnet 11. The external diameter of the pole piece 9 may be 2.000 inches. The internal diameter of the voice coil 15 may be 2.035 inches and its external diameter 2.045 inches. The spider 16, or spacing member is made of rubber, or rubber-like material, which is highly compressible. The main body of the spider 16 is about an inch in diameter, .019 to .020 inch thick and has 16 radial, integrally formed legs 17, each of an inch wide and /8 of an inch long. The spider 16 lies on top of the pole piece 9 with the legs 17 extending down along the magnet 11. When the pole piece 9 is embraced by the voice coil 15, the legs 17 of the spider 16 will be engaged generally between the internal surface of the voice coil 15 and the pole piece 9, extending along the sidewall 18 of the magnet 11. The internal diameter of the aperture of the pole plate 12 is 2.080 inches, providing adequate, but close clearance for the voice coil 15. The voice coil may be made of #35 wire, rendered self-sustaining by the application of lacquer or similar material in the conventional manner. The spider 16 is seized only lightly by the voice coil 15, and is sufficiently compliant to permit excursions of the voice coil 15 in response to the magnetic driving forces. The leads 19 from the voice coil are preferably extended through the diaphragm 14, A mounting plate 20 is attached to the pole plate 12.
The slightly rigid, resilient, fabric, composite diaphragm 14 with the soft film diaphragm overlying the fabric interstices is free of measurable resonance within the range of its normal operation, 2,000 to 18,000 c.p.s. and the spacing spider permits a high degree of compliance, resulting in an uncolored response through complete absence of resonance of the diaphragm.
The foregoing description is merely intended to illustrate an embodiment of the invention. The component parts have been shown and described. They each may have substitutes which may perform a substantially similar function; such substitutes may be known as proper substitutes for the said components and may have actually been known or invented before the present invention; these substitutes are contemplated as being within the scope of the appended claims, although they are not specifically catalogued herein.
What is claimed:
1. A high frequency sound transmitting device comprising:
'(a) a pair of complementary pole pieces of a magnet defining a generally circular air gap between them,
(b) a voice coil operably positioned in the gap,
(c) a fabric dome defining a diaphragm attached to the voice coil and positioned beyond the air gap,
(d) a coating on the diaphragm imparting a slightly rigid, resilient, yieldable, self-sustaining character and leaving the fabric interstices open,
(e) a soft film adhering to the diaphragm, defining a radiating area and rendering it impenetrable to air, and closing the fabric interstices,
(f) a means for supporting the diaphragm and voicecoil assembly.
2. A high frequency sound translating device comprising:
(a) a device according to claim 1, in which the coating is a thermo-setting resin.
3. A high frequency sound translating device compris ing:
(a) a device according to claim 1 having no substantial resonance in the range of 2,000 to 18,000 c.p.s.
4. A high frequency sound translating device compris- (a) a device according to claim 1, in which the film is rubber.
5. A high frequency sound translating device comprising:
(a) a composite diaphragm including a support formed of a soft drapable fabric dome,
(b) an impregnation of the fabric of the dome to render it self-sustaining, slightly resilient, and readily deformable, and
(c) a soft film on the fabric to render it impenetrable to air,
((1) a means to support the diaphragm.
6. A high frequency sound translating device comprising:
(a) a pair of complementary pole pieces of a magnet defining a generally circular air gap between them,
(b) a voice coil operably positioned in the gap,
(c) a fabric dome attached to the voice coil and positioned beyond the air gap,
(d) a coating on the fabric insufficient to fill the interstices and imparting a slightly rigid, resilient, selfsustaining character and subject to deformation upon the application of approximately 1% ounces of pressure, and defining a diaphragm support,
(e) a soft continuous film adhering to the fabric diaphragm, defining a radiating area and rendering it impervious to air, and defining a diaphragm-component of a composite diaphragm,
(f) a means for supporting the diaphragm and voicecoil assembly.
7. A high frequency sound translating device comprising (a) a voice coil,
(b) a fabric dome attached to the voice coil and defining a diaphragm,
(c) a coating on the fabric diaphragm imparting a slightly rigid, resilient, yieldable, self-sustaining character, and leaving the fabric interstices open,
((1) a soft film adhering to the fabric diaphragm defining a rediating area and rendering it impenetrable to air, and closing the fabric interstices.
References Cited UNITED STATES PATENTS 1,926,187 9/1933 Young 179115.5 2,303,989 12/1942 Cunningham 179-1 15.5 2,502,853 5/1950 Keddie 179115.5 2,812,825 11/1957 Matthews 179-1 15.5 2,818,130 12/1957 Whiteley 181-32 FOREIGN PATENTS 106,394 5/ 1927 Austria. 713,126 8/1931 France.
KATHLEEN H. CLAFFY, Primary Examiner.
F. N. CARTEN, A. MQGILL, Assistant Examiners.