US1853721A

US1853721A - Sound reproducer

Info

Publication number: US1853721A
Application number: US677613A
Authority: US
Inventors: Kenneth D Bryson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1923-11-30
Filing date: 1923-11-30
Publication date: 1932-04-12
Anticipated expiration: 1949-04-12

Description

April '12, 1932,

K. D. BRYSON SOUND RIP-PRODUCER Filed Nov. 1923 Patented Apr. 12, 1932 i UNITED SFTATES PATENT OFFICE A KENNETH BRYSON, OF'CLEVELAND HEIGHTS, OHIO, ASSIGNOR TO RADIO CORPORA- TION OF AMERICA, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE SOUND REPRODUCER I "hence I am able to produce a wider range of frequencies than has heretofore been possible with sound radiating elements'of like size. In most devices heretofore employed, diaphragms with fixed edges have been used in connection with horns. Such diaphragms and horns respond better to some frequencies than to others, and usually introduce unpleasing characteristics due tothe fact that the.

. frequencies of good response do not generally form a harmonic system.

In order to avoid such objections as mentioned and to produce a device which may respond' more uniformly to .a relatively large range of frequencies, I employ a sound radiating element which is a light, relatively rigid structure so mounted that everypart of the sound radiatin element is free to vibrate substantially wit out external restraint other than that of the air or other fluid me dium to which sound waves are imparted. Thus it is possible for every part of the sound radiating element to move backward and forgward with the same amplitude. With excessive weight in the peripheral zone the inertia of the periphery is increased to such an extent that the wall of the sound radiating element has a tendency to buckle and consequently a transverse wave in the sound radiating element is set up.

. To obtain the degree of rigidity and lightness required for good operation, I prefer to employa sound radiating element having one or more curved surfaces. Better results are usually obtained if. that part of the active surface near the periphery is made more rigid by giving greater thickness to the peripheral zone or by increasing the curvature of the peripheral zone, or by any other suitable means which does not prevent the sound radiating element from vibrating substantially as a whole. Without such stiflz'en'ing or other suitable means to prevent independent vibrations of the periphery, there is a tendency for the periphery to start independent vibrations under some conditions, and it is thus important for the sound radiating element to have such stiffening-but substantially nonsupporting means surrounding a portion of the periphery to prevent such independent pe ripheral vibrations.

The member which actuates the device by transmitting vibrations to it should be attached to the active surface at or near its central portion. A convenient means for mounting the device so as to eliminate external restraint to its motion is to have such actuating member form the sole support for the radiating element.

These and other objects will be apparent from the following description and annexed drawings, in which Figure 1 is a diagrammatic view partly in section of one form of sound radiating element and the means to actuate it.

Fig. 2 is a diagrammatic view of another form of cone.

Fig. 3 is a diagrammatic view showing my device with a bafiie surrounding the same.

Fig. 4 is a modified form of the device in which the position of the magnetophone is reversed.

Fig. 5 is a diagrammatic view of another form of baffle in connection with my device.

Fig. 6 is a diagrammatic. view showing a different form of sound radiating element.

. In the practical construction of my device I have found that the simplest form which gives good results is a cone of relatively'thin,

' stifi' material capable of being actuated and for example the screw 5. The supporting member 2 may be actuated by any suitable device, such as a magnetophone, indicated diagrammatically-at M, and which gives it a longitudinal vibration.

The material forming the sound radiating element preferably should be a relatively thin, hard or stiif material, such for example as bakelite, hard rubber, wood, chemically treated or impregnated paper or the like, and the material, together with its thickness and hardness, may be varied according to the results desired. I have found, for example, that with the use of thin paper a volume substantially the same as that of a diaphragm and horn of usual construction can be obtained and that the reproduction is accurate andthe quality of tone produced is excellent. I have found experimentally that if a sound radiating element such as a disk having a plane surface is used for the sound radiating element, the volume of sound emitted is poor, probably because most of the energy is used in bending or setting up transverse waves in the material. On the other hand, a hollow, conical element tends to resonate if the angle at the vertex of the cone is too small. In order, therefore, to prevent these undesirable results, I use an element of thin, stiff material having a curved or concave surface, so designed as to give the required mechanical stiffness, and which will not resonate and yet which will give good volume. Such an element may be substantially conical and, depending on the zone material, may have an angle at its vertex of about 135.", as shown in Fig. 1, or the side of the cone may be additionally curved in a longitudinal direction so that it flares outwardly and is thus curved both transversely and longitudinally of the cone, thus forming a shape which may, in part, approach that of a spheroid or even a sphere. Such a double curved shape is diagrammatically indicated in Fig. 6 at 1e.

The active area of the sound radiating surface used is generally large enough to reproduce sounds efiectively without employing a horn, but for some purposes it is desirable to use a smaller surface, in which case the member may be mounted in an opening in a sound barrier with a small clearance between the periphery of the member and that of the opening so as to substantially prevent interference between sound waves radiated from the back and front of the member. The barrier may be a box enclosing the source, or simply a bafiie of any desired shape. 7

In Fig. 2 is shown a similar cone 1a of gradually increasing thickness.

The form of my invention shown in Fig. 3 constitutes a cone 1b with the outer edge turned back as shown at 6 and with the baffle member, such as an annular ring 7 disposed adjacent the periphery of the cone. This ring may be of any desired width to substantially prevent interference between sound waves radiated from the back and the front of the members.

Fig. 4 shows a cone 10 similar to Fig. 3 with the position of the magnetophone reversed. I

In Fig. 5 the battle is indicated as a box 8 enclosing the cone 1d, the actuating magnetophone M being disposed within the box.

It is obvious of course that I may make a hollow sound radiating element of any desired shape, that is, the sound radiating element may vary widely in its shape for various kinds of. reproduction and when two surfaces are used, they may be opposed so that a denble conical, or substantially a spherical or spheroidal shape is obtained. It will be seen that it is more advantageous and efiicient to design the cone so that a sound wave will be developed from the open base of the cone in substantially a plane, because the greatestpressures are developed from a given vamplitude and energy input.

With any of these constructions it will be seen, however, that I have preserved the same fundamental characteristics that the active sound radiating element comprises a curved surface, every portion of which may be moved bazkward and forward with the same amplitu e.

While applicants preferred shape of a sound radiating element is a cone, it is to be understood that the thin, stiff material forming the sound radiating element may be of any desired shape which will give it sufiicient rigidity. Preferably the sound radiating element is a sheet of thin stifi' material shaped to form a hollow body presenting a concave or other curved or complex surface.

Applicant therefore desires for the sake of brevity, to use the generic term depressed or depressed sheet which is to be understood as including cones or any of the shapes referred to above, it being obvious that there are many forms which the sound radiating element may take and still be sufiiciently rigid to serve as operative elements.

The vibration transmitting member is preferably secured to the sound radiating element substantially at that part of the depressed portion-farthest away from the plane of the periphery. Thus. when the element is conical or substantially symmetrical in shape it is secured substantially at the center of the sound radiating element, and by this term applicant intends to define the location of the vibration transmitting member as located either on the geometric center or in the neighborhood of the'eenter of the sound radiating element.

It will thus be seen that with my device I have provided a sound radiating elementwhicii will respond accurately to the vibrameans, so that an efiicient and accurate transmission 1n sound waves can be made of varlous vibrations received from the actuating means.

Furthermore, it is to be understood that the particular forms of apparatus shown and described, and the particular procedure set forth, are presented for purposes of explanation and illustration and that various modifications of said apparatus and procedure can be made without departing from my invention as defined in the appended claims.

What I claim is:

1. In a device of the character described, asound radiating element comprising a substantially conical body of thin, stiff material, the angle at the vertexlying between the limits marked by resonance of the enclosed air on the one hand, and bending of the cone material on the other, and a vibration transmitting member secured to said body substantially at its central portion, and forming the sole support therefor, whereby positive motion is givento the sound radiating element which is free to vibrate substantially as a whole. 1

2. A loud speaking device for the propagation of sound waves of relatively high intensity, including a sound radiating element comprising a substantially'conical body of thin, stifi' material, and a vibration transmitting member secured to said body substantially at its central portion and forming the sole support therefor, said conical body having a greater thickness near the periphery than at its central portion.

3. A loud speaking device for the propagation of sound waves of relatively high intensity, including a sound radiating element comprising a depressed sheet of thin, stiff material, a vibrationtransmitting member secured to said element substantially at 1ts central portion and forming the sole support therefor, whereby said sound radiating element is free to vibrate substantially as a whole, said element being relatively slightly stiffer near its peripheral edge to prevent independent vibration in the peripheral zone thereof, and means surrounding at least a portion of the convex side of the sound ra diating element to substantially prevent interference between, the sound Waves emanating from the convex side and the concave side of said element. A

4. In a loud speaking device for the direct propagation of sound waves of relatively igh intensity, a sound radiating element, a vibration transmitting member secured to said element substantially at its central portion-,said element being mounted to vibrate substantially as a whole and to propagate sound waves from the entire active surface thereof direct to the atmosphere, and a sound barrier surrounding the periphery of said contact therewith to substantially prevent interference of the sound waves thus produced. 5. A loud speaking device for'the propagation of sound waves of relatively hlgn intensity, including a sound radiating element comprising a substantially conical body of thin, 'stifi material, and a vibration transmitting member secured to said body substantially at its central portion and forming the sole support therefor, whereby said sound radiating element is free to vibrate substantially as a whole, and means surrounding at least a portion-of the convex side of the sound radiating element to substantially prevent interference betweenf the sound waves produced.

6. A loud speaking device for the propa gation of sound waves of relatively high intensity, including a substantially conical sound radiating body, and a vibration transmitting member secured thereto substantially at its apex to support said body, said sound radiating body being formed of thin, stiff material, and havin substantially non-supporting means provided to prevent the periphery of said conical body from starting independent vibrations.

7. A device for the direct propagation of sound waves of relatively high intensity, including a sound radiating element comprising a depressed sheet of thin, stiff material, and a vibration transmitting member secured to said body substantially at that part of the depressed portion farthest away from the plane of the periphery, and forming a support therefor, whereby said sound radiating element is free to vibrate substantially as a whole, said sound radiating element having substantially non-supporting means surthe periphery of said sound radiating element and normally out of contact therewith to substantially prevent interference of the sound waves thus produced.

9. A-device for the direct propagation of sound waves of relatively high intensity, including a sound radiating element comprising a depressed sheet'of thin, stiff material, a vibrationtransmitting member secured to said element substantially at that part of thedepressed portion farthest away from the plane of the periphery, and forming a support therefor, and means surrounding one side of the sound radiating element to suppress substantially entirely the pressure Wave developed by said side of the sound radiating element, said means being closely adjacent to, but normally out of contact with the sound radiating element when the latter is not in motion, whereby without the necessity of increasing the size of the sound radiating element the radiation of low notes from the sound radiating element is substantially increased.

10. A device for the direct propagation of sound waves of relatively high intensity, a sound radiatin pressed sheeto thin, stiff material, a vibration transmitting member secured to said element substantially at that part of the depressed portion farthest away from the plane of the periphery, and forming a support therefor, and means surrounding one side of the sound radiating element to suppress substantially entirely the pressure wave developed by said side of the sound radiating element, said means being closely adjacent to, but normally out of contact with the sound radiating element, whereby withoutthenecessity of increasing the size of the sound radiatin element the radiation of low notes from t e sound radiating element is substantially increased.

11. In a device of the character described, a sound radiating element comprising a substantially conical body of thin, stiff material, I

the angle at the vertex of the cone being substantially more than 90, and a vibration transmitting member secured to said body substantially at its central portion and forming the sole support therefor, whereby positive motion is given to the sound radiating element which is free to vibrate substantially as a whole, and means for preventing independent vibrations in the peripheral zone of said sound radiatin element.

12. In a device 0 the character described, a sound radiating element comprising a substantially conical body of thin, stifi' material, the angle at the vertex lying between the limits markedby resonance of the enclosed air on the one hand, and bending of the cone material on the other, and a vibration transmitting member secured to said body substantially at its central portion, and forming.

the sole support therefor, whereby positive motion is given to the sound radiating element which is free to vibrate substantially as a whole, and means for preventing independent vibrations in the peripheral zone of said sound radiating element.

13. In a loudspeaking device for the direct propagation of sound waves of relatively high intensity, a sound radiating element, a

vibration transmitting member secured to said element substantially at its central portion, said element being mounted to vibrate substantially as a whole and to propagate sound waves from the entire. active surface thereof direct to the atmosphere, and a sound signature.

KENNETH D. BRYSON.

element comprising a de-