US1722805A

US1722805A - Sound radiator

Info

Publication number: US1722805A
Application number: US126160A
Authority: US
Inventors: Clarence E Lane
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1926-07-31
Filing date: 1926-07-31
Publication date: 1929-07-30
Anticipated expiration: 1946-07-30

Description

.Jply 30, 192.9. c. E. LANE SOUND RADIATOR Filed July 31, 1926 phragms and I ing medium, or vice versa.

' reduced by attach July 30, 1929.

M63 1. LAN], OI ION'ICLAIB, NEW

nmsnr, assicxon To 1mm. marries:

monaroms,.moonronam, OF NEW YORK, N. Y., A CORPORATION 01' NEW YORK.

BOUND RADIATOR mum. fled my 81, 1926. mm Io. 120,160.

This invention relates to acoustic diaparticularly to large. diaphragms radiating directly into the air. An object "of the invention is to decrease a distortion from the introduction or generation of harmonies or other undesired frequencies by a vibrating diaphragm when operating to translate electrical or mechan-j ical energy into sound waves in a surround- A further object is to increase the mechanical ruggedness of large acoustic diaphragms without deleteriously affecting their acoustic roperties.

e invention is applicable to sound emitters of the'so-called hornless type of loud speakers which em loy a large vibratin surface to radiate directly into the air an particularly to sound emitters of the conical We; a ifliculty has been experienced in this t pe of sound emitter and similar structures. ue, it appears, to unsymmetrical vibration of the diaphragm which could'result from slight departures from symmetry in the structure. The introduction of vibrations of frequencies notresent in the actuating source considerab y impairs the faithfulness of reproduction of speech or music and is particularly objectionable where the sound radiator is employed in-quantative sound I studies to reproduce single frequency tones,"

or narrow bands of frequencies from which the harmonics or fr uencies without the 5 band havevbeen reduce below audibility by means of band pass filters of the well-known mechanical or electrical types.

Accordin to the resent invention this distortion 0 a conica diaphragm is eatly circular rein orc' members or ribs tot e diaphragm, spa

a art and concentric with the a it, so as to divide the diaphra into rtions of relatively small! area. e rein orcing members also serve to' increase the mechanical ruggedness of the structure and at the same time facilitate the design of the sound radiator by making its uency-response characteristic more rea y predictable. Bracing means may be'provid'ed, articularly.on,

ver large diaphragins, to end additions.

' sti ness and to prevent the reinforcing diaphragm does-not vibrate "in circular symmetrical portions about the driven por-' hers from vibrating independently of the diaphragm.

-While the theory as to the cause of this distortion of the radiated sound is not defi-Z nitely established, and while the invention is independent of the theory the cause of this distortion is believed to be unsymmetrical vibration. Experiments show ,that the lar tion but in sectors or patches which are more or less iinsymmetrically distributed and which vary in size and location with diiferenoe in the characteristics, the ainplitude ofthe harmonics introduced by the patch vibrations will be greater than'the amplitude of the harmonics introduced by vibration of the diaphragm as a whole, thus giving a greater distortion.

In the case of one form of conical shaped diaphragm now much used in so-called loud speakers, the vibrations of which have been investigated, and which is typical of this class 0 diaphragms, fundamental resonance occurs at a frequency of about 100 cycles and vibration ;-:-results in "the generation of harmonics of this frequenc to some extent. The patchesQhowever, wou d be resonant at "higher frequencies, probably covering a p t to frequency. Experiments'also show that PATENTiOFFlCE." 1

range of about 200 to 500 cycles, and I parently therefore, distortion due to t 0,

patch vi ration would introduce harmonics of these frequencies. The harmonics gen-' erated by the vibration of the patches would,

therefore, as compared with the harmonics due to thevibration of the diaphragm when moving as a whole, be of greater amplitude,

due to the marked departure from linearity in the relation between the driving force and displacement inthe patches, as pointed out above, and also of higher frequency, Since -ing igher natural frequencies.

the ear is most sensitive at about 1000 cycles and does not vary appreciably in sensitivity over an approximate frequency range of 500 to 3000 cycles, it follows that the harmonics introduced by the patches would cause a greater response in the car than the barmonies introduced by the diaphragm moving as a unit, not only because of their relatively large amplitude but also because their frequency range would correspond to the frequencles at which the ear is most sensitive. Upon the basis of this theory the distortion in the diaphragm could be reduced by reventing the patch vibration or by divi ing the atches into several smaller patches hav- Because of their higher frequency, these patches would vibrate at smaller amplitudes, thus operating over small, practically linear portions of their characteristic curves, and would produce a relatively small amount of distortion. The frequency of a large portion of these harmonics would, furthermore, be appreciably above 3000 cycles and therefore in a range at which the ear is relatively less sensitive.

The invention may be more readily understood by referring to the drawing, in which Figs. 1 and 2 are front and side views, respectively, partly in section, of a. sound radiator employing a cone shaped diaphragm provided with reinforcing members in accordance with this invention; Fig. 3 is a modification of the structure shown in Fig. 1, and Fig. 4 is a sectional View of a relatively large conical diaphragm provided with a means for bracing the reinforcing members.

In the drawing, the standard 5 carries at its upper portion a bracket to which the actuating means 17 is attached. The diaphragm 7 of light flexible sheet material such as pa ,er parchment, thin metal or the like, speci cally shown as conical in form, is joined at its periphery to an edge of a second member 8 of sheet material, shown in this case as a truncated cone. The other edge of the frusto-conical surface is secured by screws or other means to ring 9 which is part of the standard 5. Rod 10 suitably attached to the surface 7 at its apex connects the surface to the actuating means 17. This actuating means may be of any desired form, for example, any well known type telephone receiver. A suitable form of electromagnetic driving means is described in Patent No. 1,365,8i 8 of Jan:..ary18, 1921 to H. C. Egerton. In Fig. 2 the reinforcing means 0 are shown in the form of hollow truncated cones, preferably of light flexible material, which are suitably attached to the diaphragms 7 and 8.

Fig. 3 shows the invention applied to a sound radiator in which the conical diaphragm-s are truncated obliquely with respect to the axis, thus making the periphery elliptical. The reinforcing

members

11, 12, etc., are positioned symmetrically with respect to the peripheral portion of the diaphragm 13 about the driving point 14.

In very large sound radiators, it may be necessary to provide bracing means to prevent the reinforclng members from vibrating independently of the diaphragm. As shown in Fig. 4, braces 16 which may be of wood or other light material are provided for this purpose and are attached at one end to the edge of the reinforcin members 15 which project from the diap ragm and at the. other end to the diaphragm. These braces also lend additional stiffness to the structure as a whole.

It is to be understood that the invention in certain aspects, as is evidenced by the claims, is not limited to diaphragms of conical shape or large size or those actin directly into t e air.. While it seems pre erable to employ reinforcing members which are similar in shape to the periphery of the diaphragm and positioned symmetrically about the driving point, the scope of the. invention includes reinforcing members of other shapes and having various positions on the diaphragm.

What is claimed is:

1. A large acoustic diaphragm for radiating directly into the air, in combination with means attached to said diaphragm at a dis:

tance from the periphery for driving it, and-means for stiffenin said diaphragm, said means dividing said diaphragm into concentric symmetrical areas about its driven portion.

2. A diaphragm in accordance with claim l in which the stiffening is produced by reenforcing ribs attached to the diaphragm.

3. An acoustic conical dia hragm having a plurality of hoop-like sti ening ribs, one edge of each of which is secured to said dia* phragm.

4. An acoustic diaphragm for radiating directly into the air and means for stiffening said diaphragm comprising a relatively rigid bracing member attached to and extending away from said diaphragm and means rigidly connecting a portion of the bracing means remote from said diaphragm with a plurality of points on said diaphragm to form a rigid trussed structure therewith.

5. An acoustic diaphragm of thin sheet material and stiffening means for said diaphragm comprising a pluralit of relatively rigid stifiening members attac ed to and extending away from said diaphragm, and means extending from a plurality offpoints in said diaphragm to eac of said sti ening members to form a trussed structure witn said diaphragm.

6. A large acoustic diaphragm for radi ating directly into the airand shaped to correspond to the curved surface of a cone and circular stiffening ribs attached to said diaphragm, spaced apart and concentric with the apex.

7. An acoustic diaphragm having a natural frequency of less than 200 cycles, and means attached to said diaphragm to reduce the amplitude of the harmonics generated by said diaphragm.

8. An acoustic diaphragm having a natural frequency of less than 200 cycles, and means attached to said diaphragm to change the frequenc of the harmonics generated by said diap ragm to frequencies at which the car is relatively less sensitive.

9. A direct acting acoustic diaphragm, and means attached to said diaphragm to decrease the amplitude of the harmonlcs introduced by the unsymmetrical vibrating portions of said diaphragm.

10. A direct acting acoustic diaphragm, and means attached to said diaphragm to divide the unsymmetrical vibrating portions of said diaphragm into vibrating portions having higher natural frequencies.

11. A sound radiator comprising a diaphragm having a conical and a frusto-conical portion joined at their peripheries, means for directly driving a portion of said diaphragm, and reinforcing means comprising a plurality of annular members positioned symmetrically with respect to the driven portion of said. diaphra m. A

12. A sound radiator comprising a diaphragm having a conical portion and a frusto-conical portion joined at their periphcries, means for drivin said diaphragm at the apex of said conica portion, means for supporting said diaphragm at the edge opposite the base of said frustro-conical portion, and reinforcing means comprising a plurality of hollow truncated cones having their bases secured to a surface of said diaphragm and positioned symmetrically about its driven portion. 7

13. An acoustic diaphragm reinforced by a pluralit of stifiening members, one edge of'each 0 said stiffening members being secured to the diaphragm, bracing means attached at one end to one of said stiffening members and at the other end to the diaphragm.

14. The combination with a conical diaphragm of at least one baflle located at the concave side of the cone and positioned be tween the apex and the base of the cone to sub-divide the resonance chamber formed by the concavity of the cone.

15. The combination with a conical diaphragm of a cone frustum secured to the inner wall of the cone between the apex and the base of the cone to sub-divide the resonance chamber formed by the concavity of the cone.

16. The combination with a conical dia-- phragm of at least one baflle located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formed b the concavity of the cone, said baflle exten ing inwardly toward the axis of the cone and being provided with at least one opening.

17. The combination with a conical diaphragm of at least two bafiles located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formed by the concavity of the cone, each of said bafiles extending inwardly toward the axis of the cone and being provided with at least one opening.

18. The combination with a conical diaphragm of at least one bafile located at the concave side of the cone and positioned between the a ex and the base of the cone to sub-divide t e resonance chamber formed b the concavity of the cone, said baffle exten ing inwardly toward the axis of the cone and being provided with a central opening.

19. The combination with a conical diaphragm of at least one bafile located at the concave side of the cone and positioned between the apex and the base of the cone to sub-divide the resonance chamber formed b the concavity of the cone, said baflie exten ing inwardly toward the axis of the cone and being provided with a central opening reinforced at its edge.

In witness whereof, I hereunto subscribe my name this 30th day of July A. D., 1926.

CLARENCE E. LANE.