US2873812A - High frequency loudspeaker structure - Google Patents

Description

Feb. 17, 1959 R. c. AVEDON 2,873,812

HIGH FREQUENCY LOUDSPEAKER STRUCTURE Filed Sept. 5, 1957 5 Sheets-Sheet 1 Feb. 17, 1959 R. c. AvEDoN 2,873,812

HIGH FREQUENCY LOUDSPEAKER STRUCTURE Filed Sept. 5, 1957 5 Sheets-Sheet 2 d V' "w WWU! r A. A 0

FEQUENCY IN CYCLES PEFSECOND Feb. 17, 1959 R. c. Avn-:DON 2,873,812

HIGH FREQUENCY LOUDSPEAKER STRUCTURE Filed Sept. 5, 1957 3 Sheets-Sheet 5 United States Patent O.F

HIGH FREQUENCY LOUDSPEAKER STRUCTURE Robert C. Avedon, Northbrook, Ill., assignor to Electro- Voice, Incorporated, Buchanan, Mich., a corporation of Indiana Application September 5, 1957, Serial No. 682,234

Claims. (Cl. 181-31) The present invention relates to high frequency loudspeakers commonly termed tweeters, and more particularly to the horn throat structure of such loudspeakers.

In high fidelity reproducing systems, it is common to use a plurality of reproducers, each being specifically designed for reproduction of a particular frequency band. These reproducers are combined in the system with a suitable electrical network which allows each reproducer to receive only signal energy of its own specific bandwidth. Such a system allows for special design of each reproducer which results in extended and more uniform frequency response. It has been found, however, that the dynamic tweeters commonly employed in such systems show a marked drop in response in the vicinity of 13,000 cycles and above. This has lead to some investigation and theorizing on the operation of the present type high frequency loudspeakers, which has resulted in a construction which gives a good response through 20,000 cycles and response as high as 40,000 cycles.

In accordance with the present invention, an assumption was made that the prior art high frequency dynamic loudspeakers at some frequency above 12,000 cycles encounter an action of the diaphragm which no longer is a piston action as has been assumed for many years. If this were the case, interference of the air mass adjacent the diaphragm might ybring about a particle motion in the air chamber which would result in cancellation or no resultant particle motion at the horn throat even though the diaphragm tended to respond to higher frequencies. Apparently the response of the diaphragm is no longer that of a piston, and hence, if a particular conguration of multiple paths from the diaphragm were provided, there might not be cancellation of the sound energy.

It, therefore, is an object of the present invention to provide an improved high frequency loudspeaker structure which will extend the range of frequencies reproduced in a dynamic unit.

, It is a further object of the present invention to provide an improved high frequency loudspeaker of dynamic type which will produce a good response exceeding 20,000 cycles and have a response extending to 40,000 cycles.

Another object of the invention is to provide an improved loudspeaker structure which has a new and different throat structure adjacent the diaphragm to improve the response characteristic.

Other and further objects of the invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a cross-sectional view of a horn and cover for a dynamic high frequency loudspeaker;

Figure 2 is a diagrammatic cross-sectional view of a horn, a cover for the dynamic unit, and the dynamic dia- Phragm;

Figure 3 is a diagrammatic top view of the horn, cover and diaphragm shown in Figure 2;

Figure 4 is a response curve of an ultra high frequency 2,873,812 Patented Feb. 17, 1959 ICCy loudspeaker unit embodying the teachings of the present invention;

Figure 5 is a response curve of two assembled systems showing the improvement obtained 'by the use of the very high frequency loudspeaker embodying the present invention;

Figure 6 is a schematic showing of the conventional diaphragm and horn for the purpose of explaining the probable operation of the present invention; and

Figure 7 is a schematic showing of the improved horn of the present invention with the dynamic diaphragm.

Figure 1 shows a crosssectional view of an actual embodiment of the present invention comprising a horn 11 having a plurality of supporting ribs 12 connected to a phasing member 13 comprising a section of a sphere. The horn 11 is connected to a cover 14 adapted to be secured to the housing which contains the magnetic circuit, the diaphragm and the voice coil. Suitably supported by a plurality of ribs is a structure l5 having a concave surface 16 located closely adjacent to the domed surface of a dynamic diaphragm. The structure 15 com` prises a cylinder having a ilat top surface 17 provided with an axial aperture 18. The flat top surface 17 is parallel to the bottom flat surface of the central phasing member 13.

Reference now may `be had to Figure 2, which is a diagrammatic representation of the horn, a cover and the diaphragm of the type embodying the present invention, and which was illustrated in Figure l. The representation in Figure 2 by the elimination of certain mechanical details provides a better basis for the explanation of the structure and its relation to other parts of the loudspeaker unit. It will be noted in Figure 2 that there has been shown a dome shaped diaphragm 19 which is clamped between two washers 21 in a portion of the cover housing 14 engaging the magnetic circuit member 22. A central magnetic circuit member 23, which generally is of cylindrical shape, provides an air gap for receiving the voice coil 24 depending from the dome shaped structure 19 of the diaphragm. In a particular embodiment, such as that illustrated in Figure 2, the permanent magnet structure comprising the members 23 and 22 has a flux density so as to provide from 18,000 to 20,000 gauss in the air gap. The diaphragm 19 in this particular embodiment has a domed structure which is about one inch in diameter and is clamped approximately one-sixteenth inch from the voice coil to place the primary resonance ot the electromechanical system including the diaphragm at approximately 4,000 cycles. The voice coil 24 is sevensixty-fourths of an inch long formed so as to be selfsupporting out of round No. 38 aluminum wire.

It will be noted in Figures 2 and 3 that various dimensions have been indicated by letters. Typical measurements for these dimensioos are given in the following table:

Inches A .670 B .375 C .093 D .312 E .010 F .010 G .234 H .686 J .175 K .734 L .906 M 1.031

The response curve in Figure 5 shows the operation from three to forty kilocycles. Excellent response is obtained through twenty kilocycles, and, while the energy output from twenty to forty kilocycles is much lower, it nevertheless is believed to be useful in the operation Aof the improved very high frequency loudspeaker. When a device having the characteristics shown in Figure 4 is combined with other loudspeaker units in a system with a network and mounted in a suitable enclosure,it will be noticed that the curve B is much smoother and greatly extended over the curve A, which shows the same components with the exception that the prior type of tweeter was employed.

While the invention is not to be limited thereby, the structure arrived at was based upon certain assumptions which can best be understood by referring to Figures 6 and 7. Previous theories of operation vof dynamic diaphragms have assumed that the entire domed structure moved back and forth like a piston. Reproduction curves and direct visual observation of the exposed diaphragm without any loading structure, however, indicated that no high frequency energy was translated into sound at and above 12,000 or 13,000 cycles. This absence of sound energy was assumed tovbe due to a change in the operation of the dome shaped diaphragm structure from a piston to one where the peripheral portions might be moving forwardly while intermediate or central portions might be moving in the opposite direction, thus causing to exist a phase angle difference of 180 degrees between the velocities of these two portions of the diaphragm. Thus, in the representationin Figures 6 and 7 the arrows C show the peripheral portion of the diaphragm moving downwardly, while an intermediate or central portion is moving upwardly as indicated by the arrows D. This would tend to cause a motion of the air beneath the loadingplug in Figure 6 so that in effect there is little or no particle motion at the horn throat and hence no sound energy produced. In both Figures 6 and 7 the magnitudes of the arrows A and B show relatively the magnitudes of particle displacement. If this were the case, the operation in Figure 7 illustrates that air masses could be moved in different directions as shown through multiple paths of sufficiently differing lengths so as to result in zero phase angle difference of the velocities at points X where the multiple sound paths converge to enter the horn lwith the result that the higher frequencies, namely those above about 12,000 cycles, could be produced by the non-piston action of the diaphragm. Thus, in accordance with the present invention theconventionalloading plug has been replaced by a phasing structure or throat structure having a particular relation to the components so as to produce the improved overall response characteristic shown in Figure 4 and to greatly improve network operation illustrated in Figure 5.

While for the purpose of illustrating and describing the present invention a particular embodiment has been illustrated in the drawings, it is to be understood that the invention is not to be limited thereby since such variations are contemplated as may be commensurate with the spirit and scope of the invention set forth in the accompanying claims.

l claim as my invention:

l. In a high frequency loudspeaker having a diaphragm with a spherical convex outersurface, a horn for said diaphragm, and a multi-path throat structure for said horn adjacent said diaphragm comprising a cylindrical member having a at end and a concave end, said concave end having a surface parallel to the convex surface of said diaphragm, said cylindrical member having an axial hole, and a second member comprising a section of a sphere having a plane surface parallel to the flat end of said cylindrical member.

2. The loudspeaker of claim l wherein said cylindrical member has a diameter less than the horn throat diameter, and said second member has a diameter less than said cylindrical member.

3. In a high frequency loudspeaker having a diaphragm with a convex outer surface, a horn for said diaphragm, and a coaxial throat structure for said horn adjacent said diaphragm comprising a cylindrical member having a ilat end and a concave end, said concave end having a surface parallel to the convex surface of said diaphragm, said cylindrical member having an axial opening, and a second coaxial member having a plane surface parallel to the flat end of said cylindrical member and a coaxial convex surface intersecting said plane surface.

4. The loudspeaker of claim 3 wherein the radius of the diaphragm convex outer surface is substantially twice the radius of the convex surface of said second member.

5. The loudspeaker of claim 3 wherein the opening is not more than one-fifth of the diameter of said cylindrical member.

No references cited.

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