US1913645A

US1913645A - Acoustical diaphragm

Info

Publication number: US1913645A
Application number: US633818A
Authority: US
Inventors: Stenger Willebald Conrad
Original assignee: Individual
Current assignee: Individual
Priority date: 1932-09-19
Filing date: 1932-09-19
Publication date: 1933-06-13
Anticipated expiration: 1950-06-13

Description

June 13, 1933. w. c. s'rENGl-:R 1,913,645

ACQUSTICAL DIAPHRAGM Filed Sept. 19, 1932 4 Sheets-Sheet l June 13, 1933. w. c. sTL-:NGER

ACOUSTICAL DIAPHRAGM Filed Sept. 19, 1932 4 Sheets-Sheet 2,

l l i l l l June 13, `l1933. w. c. STENGER' 1,913,545

ACOUSTICAL DIAPHRAGM Filed Sept. 19, 1932 lLSheets--Sheelz 3 June 13, 1933. w. c. sTENGx-:R 1313.645

ACOUSTICAL DIAPHRAGM Filed Sept. 19, 1952 4 Shees-Sheet 4 lIn-l s Rafic of the Radius of the Arch fo the Rads of the rc n .zo .as .as HlTfude of' the Arc Qn Percentage of the `'qrea lo? Base Patented June 13, 1933 WILLEBALD CONRAD STENGER, OF CHICAGO, ILLINOIS l ACOUSTICAL DIAPHRAGM Application. filed September 19, 1932.

This invention relates to the sounding elements in musical instruments, such as sound reproducing diaphragms of radio receivers, telephone receivers, or the thin sounding boards of playing instruments and the diaphragms of transmitters.

The objects of the invention are mainly to obtain more brilliance of tone, distinctness and faithful reproduction of transmitted sounds, although coming from instruments of widely different character, and to render diaphragms less persistent in vibrating at some unimpressed rate and producing undesirable overtones. A further purpose of the invention is to provide a sounding element of this class capable of vibrating as a whole but having a plurality of separate vibrating surfaces of different characteristics, and with arbitrarily arranged nodal lines separating 0 such surfaces whereby each of the surfaces becomes responsive to vibratory motions of distinctive character.

Other purposes of the invent-ion are to utilizel beneficial discoveries with reference to the Vform of diaphragms resulting from eX- perimental work to find the most favorable arching of the sounding surfaces of the diaphragm, and point of application of vibratory movements transmitted to the diahragm. With such purposes in view a new ormulae is provided for the construction of diaphragms.

The objects are accomplished by constructions as illustrated in the drawings, wherein:

Figure 1 is a plan of a diaphragm to illustrate that the center of application of energy for vibrating the diaphragm is definitely oil'- set from the geometric center thereof.

Figs. 2, 3 and 4 are edge views of the diam phragm illustrated by Fig. 1, showing that it may be either flat or more or less arcuate, for the purpose of adding rigidity to the diaphragm with reference to its weight.

Fig. 5 is a plan view of a conical diam phragm constructed according to this invention and showing a connection for receiving or transmitting motion to the diaphragm, which connection marks the acoustical center offset from the geometrical center of the diaphragm.

Serial No. 633,818.

Fig. 6 is a side view of the diaphragm shown in Fig. 5, illustrating by full lines with reference to broken lines, the change effected by 0H-centering the connection.

Fig. 7 is a fragmentary section taken on 55 the line 7-7 of Fig. 5.

Fig. 8 is a plan view of a multi-wall or pyramidal form of diaphragm, providing a plurality of vibrating surfaces, and including improvements illustrated by the preceding figures.

Fig. 9 is an end view of the diaphragm shown in Fig. 8.

Fig. 10 is an edge view of the wide side of the diaphragm.

Fig. 11 is an enlarged sectional detail taken on the line 11--11 of Fig. 8.

Fig. 12 is a plan view of a pyramidal form of the diaphragm, including the peripheral supporting therefor, and corner reinforcements.

Fig. 13 is a sectional view taken on the line 13--13 of Fig. 12, illustrating both the peripheral and central supports of the diaphragm.

Fig. 14 is a sectional detail taken on the line 14-14 of Fig. 13.

Fig. 15 is a sectional detail taken on the line 15-15 of Fig. 12.

n Fig. 16 is a fragmentary face view showlng one cornerof the diaphragm illustrated by Figs. 12 and 13.

Fig. 17 is a sectional view taken on the line 17-17 of Fig. 16. 85

Fig. 18 is a sectional view similar to that shown by Fig. 17, but shows a more thin and flexible peripheral support.

Fig. 19 is an enlarged sectional detail to show one manner of supporting the diaphragm near its center.

Fig. 20 illustrates in section another preferred mounting ofthe central part ofthe diaphragm.

Fig. 21 is a plan view of the supporting element for the center of the diaphragm.

Fig. 22 is a sectional detail taken on the line 22-22 of Fig. 9.

Fig. 23 shows in plan a center supporting ele: #ent for the diaphragm such as illustrated in Fig. 19, and indicates by dotted lines Where the folds are made in this element.

Fig. 24 is a diagram showing the extent to which the side walls of the diaphragm are arched.

#Fig 25 is a graph for use in finding the correct center for arching the diaphragms.

The construction to which this invention relates has been developed from experiments with diaphragms of various forms, materials and mountings therefor, and in this experimental work it appeared that diaphragms arranged to receive vibratory motions through mechanical connections or a coil, which are located at the geometrical center, or which impressed the vibratory motions in some manner to the diaphragm at its true center, that an undesirable interference occurred in the responsive diaphragm to the impressed vibrations. Objectionable overtone effects and discordant intervals of musical sounds and of the voice seemed to be caused by the natural dominant tone of the diaphragm, or by effect or results of oscillatory movements between two or more intervals. It was found that by changes in the construction here described, the diaphragms would function with greater fidelity and clarity. These changes are mainly the fixing of an acoustical center which does not coincide with the geometrical center of the diaphragm, and a slight arching of the diaphragm.

An example of the diaphragm thus ccnstructed would be a paper sheet, pressed while wet and under heat into a pyramid having a rectangular base. The side walls slant at varying degrees. The four surfaces of the diaphragm are separated by nodal lines resulting from a crease in the paper, or other material of which the diaphragm may be formed, at the edges of the meeting surfaces. Each of the surfaces is arched, the function of which arch is to afford greater uniformity in strength and resistance, and to give more stability to the vibratory movement of the diaphragm. This rectangular and pyramidal form of diaphragm may be truncated and provided with a collar at the apex for carrying the movable coil of the dynamic type of speaker. The height of the pyramid is determined according to the tensile strength and relation to the specific gravity of the material used.

In the drawings, Figure l shows a diaphragm l, circular in outline, with its een ter at 2. According to this invention, should this diaphragm be used for example in a radio receiver, motion would be transmitted and delivered to the diaphragm at the point 3, marked the acoustical center. The distance which this center is offset from the center 2 is found by taking the square root of the area of the diaphragm and dividing it by 84. In the form shown by Fig. 5, the area of the base 4 of the cone, divided by 84 gives the extent of offset of the acoustical center 5.

Figures 3 and 4: illustrate arcuate diaphragme having less altitude than the one shown by Fig. 6, as these diaphragms may be made of more rigid material and thus require less altitude than the lighter` diaphragm illustrated by Fig. 6. In Fig. 6, the conical form of diaphragm is shown truncated for convenience in attaching the pin 6, which transmits vibratory movements to the diaphragm.

Experience has proved that in pyramidal forms of sounding bodies there is a very definite relation between the area of a sounding body, the height or altitude of the pyramid and the proper arch for the walls of the sounding body. The radius of arch is found by multiplying the radius of arc by a factor. The factor equals one plus sixteen times the altitude of the pyramid divided by the square root of the area of the base.

In the case of rectangular diaphragme the length of the base of the side wall is equivalent to and is used instead of the square root of the area of the base.

As an illustrative example assume that the area of the base is 625. The square root of the length of an equivalent side is twentyfive. Assume that the altitude is 12.5. Then the altitude is fifty percent of the length of the side of the base. Fifty percent of sixteen is eight. Eight plus one equals nine. Hence, nine is the factor or the ratio of the radius of the arch to the radius of the arc.

In a similar manner if a side has a base line of thirty-six and the altitude is nine, the percentage is twenty-tive. Twenty-five percent of sixteen is four; add one, equals five. Hence the factor five. The factor for all altitude ratios up to fifty percent is graphically shown in Fig. 25.

The concavity of the diaphragms, 3 and 4, is increased by such an arch or curvature imparted thereto from the center to the periphery. This curving or arching of the diaphragm is better illustrated by the one shown in Fig. l0, where the broken lines 7 indicate the straight sides of a cone or pyramid,`whereas, the full lines 8 indicate the extent of arching imparted to the diaphragm surfaces according to this specification. i

The arch consistent with the best results has a radius which may also be determined by the altitude of the cone or pyramid in percentage of the square root of the base of such cone or pyramid, multiplied by factor which may be found by reference to graph Q5. For example, if the altitude is l0 percent of the square root of the area of the base, the ratio of the radius of the arch, with reference to the radius of the arc passing through points 9, l0 and 1l, Fig. 10, would be two and six-tenths times. Fig. 24, the center for the arc is indicated at Referring to 12, or 12, and the center of the arch is indicated at 13 and 13', in the two examples illustrated by this figure.

The diaphragm illustrated by Figs. 8 t0 11 inclusive is rectangular in outline pressed to pyramidal form of unequal sides and calculated as to all its dimensions on the basis of the factor found by taking the square root of the area of its base. The altitude or distance between the base of the pyramid and its apex is dependent upon the nature of the material forming the diaphragm. Rigidity is added by increasing the altitude. The side walls 14 and 15 extend upwardly at the same angle.

The acoustic center 16 is the normal distance to one side of the geometrical center 17. The

side walls

18 and 19 do not slant at the same angle.

The diaphragm may be mounted at its periphery on a chassis 20, Fig. 11, through a flexible rectangular frame 21 attached to the inwardly bent base flange 22. Diaphragm surfacing coatings 23 and 24 are sometimes employed when necessary to render the material of the diaphragm impervious to moisture.

The diaphragm illustrated by Figs. 12 to 18 inclusive is similar in general form to that illustrated by Fig. 8 but with some variations, the center collar-shaped reinforcement 2G being cylindrical to support the movable' coil of a dynamic speaker, and the marginal bends 27 being doubled back on themselves to increase resilience in the marginal support of the diaphragm.

The marginal corners of the diaphragm are split in this instance and reinforced by a light leather strip 28. Centrally the diaphragm is supported on the chassis 29 through a resilient connection 30 such as illustrated by Fig. 21, which is a development of this supporting member with the lines upon which it is creased indicated at 31. The central support may be formed of paper. Fig. 23 illustrates a variation 32 of this supporting means for use in connection with electromagnetic speakers having armatures indirectly connected with the diaphragm.

The large

sectional views

19 and 20 indicate the movable coil 33 attached to collar 26. In one case the support 30 is secured to the face or delivery side of the diaphragm and to the pole of the magnet by screw 34. In Fig. 20

'- the resilient support 30 is secured to the rear face of the diaphragm and to the chassis 29.

Referring to Figs. 8 and 12 where the four sides of the diaphragms meet respectively on the

lines

35 and 36 the crease adds rigidity along such lines and around which the separate walls of the diaphragm may hinge in independent oscillatory movements.

Thus while the diaphragm is vibrating as a whole, independent vibrations occur in the separate walls thereof. Vhile this diaphragm may vibrate with the same amplitude throughout, waves on its separate surfaces are of less amplitude toward the center than near the periphery. This is due to its form, the more

rigid valleys

35 and 36 radiating from the center.

For best results with the pyramidal form of diaphragm with a rectangular base illustrated by Figs. 8 and 12 it is found that the dimensions of the base should be unequal, with substantially the following proportions based on the square root of the area of the base. The long dimension is four-thirds of the square root of the base. and the short dimension is three-fourths of the square root of the base. f

In using the invention these peculiar characteristics as to dimensions and form are followed whether the diaphragm is used for the direct reception and transmission of sound waves or the reproduction of sound when the waves are mechanically or electromagnetically imparted to the diaphragm or in a musical instrument such as the sounding board of a piano.

I claim:

1. In an acoustic instrument, a sounding element of pyramidal shape, an arch in said sounding element based on altiude, divided by the square root of the area of the base.

2. In an acoustic instrument, a p; amidal sounding element having a rectangu.V .r base, arches in the side walls of said element, the radii of said arches being a function of the altitude of the pyramid divided by the base of the side wall.

3. In a musical instrument a sound wall, an arch in said sound wall, a factor for the radius of said arch equal to one plus sixteen times the altitude divided by the Asquare root of the area of the base. f

4. A diaphragm for sound instruments in combination with means for imparting vibratory motions to the diaphragm and an operative connection betwee the diaphragm and said means which is attached to the diaphragm to one side of the geometrical center of the diaphragm the distance of approximately one eighty-fourth of the square root of the area of the diaphragm.

5. A diaphragm for sound instruments of conical form and means for vibrating the diaphragm mounted thereon in offset relation with the gecmerical center of the diaphragm an extent equal to substantially one eightyfourth of the square root of the area of the base of the cone formed by the diaphragm.

6. A sounding element having a pyrainidal shape, and means co nected with said element for imparting vibratory motions thereto, the connection between said means and the sounding element being offset from the geometrical center of the sounding element a disf.' ance approximating one eighty-fourth of the square o the area of the base of the pyramid formed by said element.

7. A diaphragm for sound instruments having a plurality of sides inclined toward a common apex, located substantially one eighty-fourth of the square root of the base oi' the diaphragm to one side of the geometrical center of the diaphragm.

8. A diaphragm for sound instruments supported at its periphery by a reversely folded peripheral extension of the diaphragm, and means for supporting the center of the diaphragm comprising a reversely folded resilient member.

9. A diaphragm for sound instruments supported at its periphery by a reversely folded peripheral extension of the diaphragm, means for supporting the center of the diaphragm comprising a reversely folded resilient member, and means attached to the diaphragm for imparting vibratory motions to the diaphragm, said means being disposed with its axis spaced to one side of the geometrical center of the diaphragm a distance equal to one eighty-fourth of the square root ot the area of the base ot the diaphragm.

l0. A diaphragm for acoustic instruments having an operative cent-ral connect-ion Which is located substantially one eightyi`ourth of the square root of the area of the diaphragm to one side ot the geometrical center of the diaphragm, said diaphragm being arched, the radius of which arch is based on altitude divided by the square root of the area of the diaphragm.

ll. An acoustical diaphragm of pyramidal torni having a rectangular base, the dimensions ot said base being unequal, the long side having a value Which is four-thirds of the square root of the base, and the shorter side having al length which is substantially three-fourths of the square root of lthe base.

Signed at Chicago in the county of Cook and State of Illinois this 25th day of August 1932.

VILLEBALD CONRAD STENGER.