US 2565069 A
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Allg- 1951 B. A. ENGHOLM 2,565,069
LOUD-SPEAKER OF THE DOUBLE DIAPHRAGM TYPE Filed March so, 1946 2 Sheets-Sheet 1 INVENTOR BERNARD A. ENGHOLM, DECEASED, BEATRICE H. ENGHOLM, EXECUTRIX,
21, 1951 B. A. ENGHOLM LOUD-SPEAKER OF THE DOUBLE DIAPHRAGM TYPE 2 Sheets-Sheet 2 Filed March 50, 1946 628$ 55 R380 uzm 33E 2 82 s OCH 8 INVENTOR BERNARD A. E-NGHOLM, DECEASED, BEATRICE H. ENGHOL RELATIV E RESPONSE IN DB.
Patented Aug. 21, 1951 LOUD-SPEAKER OF THE DOUBLE DIAPHRAGM TYPE Bernard A. Engholm, deceased, late of Shaker Heights, Ohio, by Beatrice H. Engholrn, executrix, Cleveland, Ohio, ,assignor to The Rola Company, Inc., Cleveland, Ohio, a corporation of Ohio Application March 30, 1946, Serial No. 658,417
This invention relates to loud speakers, particularly those used in radio receiving sets, public address systems and the like.
One of the difficulties experienced in radio reception is the reproduction of notes in the high frequency portion of the audible range. Experience has shown that a loud speaker diaphragm must possess sufiicient mass to withstand handling in assembly and transportation, but that the response of the diaphragm diminishes progressively as the mass increases. Thus, a diaphragm which normally would be satisfactory for mechanical reasons, would be limited in response to about five thousand cycles, but the audible range is considerably above that limit. However, if the mass were reduced to approach the degree of desirable response the diaphragm would be too fragile to be useful.
An object of the present invention is to make a diaphragm construction which will increase the frequency range of present known loud speaker diaphragms by several thousand cycles, without reducing the mechanical strength of the structure. The invention contemplates additionally a construction that will effect such change in the higher frequency range without in any way diminishing the present range of responsiveness in the lower frequency range, and without requiring changes in the present construction of a speaker. In the drawings, Fig. 1 illustrates a side elevation, partly in section, of a loud speaker embodying the present invention; Fig. 2 is a front view of the speaker; Fig. 3 is a section on a large scale through the region of connection between the voice coil form and the diaphragm, and Fig. 4 is a diagram illustrating the response curves of the diaphragms of loud speakers with and without the invention of the present application.
The present invention is shown in connection with a loud speaker having the customary magnetic structure I0, housing I l, voice coil form l2, diaphragm l5, inner support 55 for the diaphragm and voice coil form, and an outer support I! for the diaphragm. The diaphragm I5 is usually frusto-conical in form, with a cylindrical neck that is adapted to extend into the cylindrical voice coil form and to be cemented thereto. The foregoing assembly is typical of loud speaker units which have heretofore been in general use.
The present invention contemplates an increase in the responsiveness of the loud speaker, particularly in the high frequency audible range, and the preferred form for accomplishing such result embodies a second diaphragm 25, preferably shown as frusto-conical in shape, but of smaller size than the diaphragm IS. The smaller diaphragm is disposed within the larger and is supported with reference thereto in such manner that the walls of the two diaphragms are separated, whereby they are free to vibrate independently of each other. The smaller diaphragm has a substantially cylindrical neck portion 26 which is adapted to extend into the neck of the diaphragm i5 and to be cemented thereto. Thus, movement of the voice coil form in response to current undulations produces a vibratory reponse in both diaphragms.
The smaller diaphragm has less mass than the larger and is preferably supported solely by the neck portion thereof within the larger diaphragm. Preferably the axial length of the diaphragm 25 is shorter than the axial length of the diaphragm l5 whereby the smaller is disposed within the confines of the larger.
Each diaphragm may be molded of fibrous material in the same manner as heretofore has been the practice for making a single diaphragm. As heretofore stated, however, the mass will differ, and it has been found that satisfactory results will be obtained if the large diaphragm of what is commonly known as a 10 speaker has a Weight of 5.8 grams, and if the smaller diaphragm has a weight of 1.4 grams. The weight ratio is thus substantially 4 to 1. The diaphragms are shown as being slightly curved in cross-section, but if desired they may be straight. It has also been found, where the large base diameter of the diaphragm I5 is 10'', that satisfactory results will be obtained if the large base diameter of the diaphragm 25 is 3 inches.
Figure 4 shows response curves for two loud speakers, one having the large diaphragm alone and the other having the double diaphragm of the present invention. The response curve of the former is indicated at B and that of the latter at A. In the diagram, the relative response in decibels is plotted against the frequency in cycles per second, and the curve A shows that the loud speaker having a single diaphragm has a definite downward trend (representing the practical limit of satisfactory response) at 5,000 cycles per second, while the loud speaker equipped with the double diaphragm does not out off until about 8,000 cycles per second. There is thus a gain in response of about 3,000 cycles per second.
An advantage of the present invention is the fact that improved operating characteristics of a loud speaker may be obtained without requiring changes to be made in the present construction. Moreover, the smaller diaphragm may be inserted within the larger and rigidly fastened thereto adjacent the region of connection to the voice coil form, as a result of which a marked increase in the responsive range is obtained without materially adding to the costof the speaker construction.
What is claimed is:
1. A loud speaker of a double diaphragmtype comprising three hollow members secured 'together, namely, a cylindrical voice coil form, a flaring outer diaphragm of conical form having a cylindrical neck extending within the Voice coil form and attached thereto, an inner diaphragm of conical form flaring at a less angle than the outer diaphragm and having a cylindrical neck extending within the cylindrical neck of the outer diaphragm, and attached thereto, and a voice coil wound on the exterior of the voice-coil-form and surrounding also both of said necks.
2. In a loud speaker of the double diaphragm type, a hollow voice coil form havingavoice coil on' the exterior thereof, an outer flaring diaphragm of conical form having a hollow neck extending within the voice coil form and secured thereto, an inner flaring diaphragm of conical form having a hollow neck extending within and secured to both the voice call form and the outer diaphragm.
BEATRICE H. ENGHOLM, Executria: of the Estate of Bernard A. Engholm,
REFERENCES CITED The following references are of record in the ..file,of this patent:
UNITED STATES PATENTS Number Name Date 1,693,223 :Danziger et al Sept. 27, 1928 1,848,433 Pridham Mar. 8, 1932 I 1 ,897,294 Bernard Feb. 14, 1933 1,953,542 Pridham Apr. 3, 1934 1,991,221 Kingsford Feb. 12, 1935 2,007,747 Ringel July 9, 1935 2,084,945 Cornwell June 22, 1937 2,231,479 Perry Feb. 11, 1941 2,371,951 Cook Mar. 20, 1945 FOREIGN PATENTS Number Country Date 107,236 Australia Apr. 20, 1939 413,758 Great Britain July 26, 1934 451,754 Great Britain Aug. 11, 1936