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Publication numberUS2565069 A
Publication typeGrant
Publication dateAug 21, 1951
Filing dateMar 30, 1946
Priority dateMar 30, 1946
Publication numberUS 2565069 A, US 2565069A, US-A-2565069, US2565069 A, US2565069A
InventorsEngholm Beatrice H
Original AssigneeRola Company Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Loud-speaker of the double diaphragm type
US 2565069 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

Allg- 1951 B. A. ENGHOLM 2,565,069



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

2 Claims.

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

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1693223 *Jan 4, 1927Nov 27, 1928Danziger Harold LSound reproducer
US1848433 *Sep 9, 1929Mar 8, 1932Magnavox CoLoud speaker element
US1897294 *Jul 30, 1931Feb 14, 1933Radio Electr Soc FrLoud speaker and like apparatus
US1953542 *Aug 6, 1929Apr 3, 1934Magnavox CoSound reproducing device
US1991221 *May 17, 1930Feb 12, 1935Atwater Kent Mfg CoTelephonic apparatus
US2007747 *Mar 17, 1933Jul 9, 1935Rca CorpAcoustic apparatus
US2084945 *Dec 5, 1935Jun 22, 1937Cornwell Lionel BLoudspeaker
US2231479 *Aug 24, 1938Feb 11, 1941Rca CorpSignal translating apparatus
US2371951 *Jan 7, 1943Mar 20, 1945Gen ElectricDouble diaphragm loud-speaker
AU107236B * Title not available
GB413758A * Title not available
GB451754A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2845135 *Sep 26, 1955Jul 29, 1958Arthur BlumenfeldAuxiliary wave propagating and directing attachment for loudspeaker diaphragms
US2852089 *Jul 2, 1956Sep 16, 1958Arthur BlumenfeldCombined loudspeaker diaphragm and horn
US2897292 *Apr 19, 1956Jul 28, 1959Francois Joseph Gerard V BoschHigh fidelity loudspeaker
US3044570 *Apr 2, 1958Jul 17, 1962Watts Ltd Cecil ELoudspeakers
US3292730 *Jan 21, 1966Dec 20, 1966Mcgregor Electronics IncSpeaker cone unit
US4477699 *Mar 10, 1982Oct 16, 1984Pioneer Electronic CorporationMechanical two-way loudspeaker
U.S. Classification381/186, 381/182, 381/432
International ClassificationH04R9/00, H04R9/06
Cooperative ClassificationH04R9/063
European ClassificationH04R9/06A