US3272281A - Transducer - Google Patents

Description

H. M. RUTTER Sept. 13, 1966 TRANSDUCER 2 Sheets-Sheet 1 Filed Dec.

'FIGJ INVENTOR HARVEY M. RU TTER ATTORNY Sept. 13, 1966 Filed Dec. 4 1964 H. M. RUTTER TRANSDUCER 2 Sheets-Sheet 2 INVENTOR HARVEY M. RUTTER BY r I 7 (I I ATTORNEY United States Patent 3,272,231 TRANSDUCER Harvey M. Rutter, 32 Gruhb Road, Malvern, Pa. Filed Dec. 4, 1964, Ser. No. 415,389 19 Claims. (Cl. 181-31) In the reproduction of music, it is found that there is a wide variation in the style and quality of'manufacture of commercially available recordings, and also in the degree of fidelity with which the original music was recorded. It is a premise of the following discussion that presently accepted music reproduction is not faithful to the recording itself, and therefore cannot be a reproduction of the original music, whether or not it was faithfully recorded. A number of electrical and mechanical components and processes are necessary to the art of recording and reproducing music, including what is generally known in the art as the loudspeaker, which finally radiates the audible sound. Obviously, if the loudspeaker does not perform ideally, there is no means for critically evaluating the other components and processes involved, for we must depend upon the radiated sounds as we hear it.

There is at present a great variety of devices generally known as loudspeakers. However, there is general disagreement among those skilled in the art, as to which of these produces the desired sound. Different loudspeakers of comparable quality produce very different musical sound when connected to the same signal source, and, since the object of the loudspeaker is to reproduce sonically the electrical input signals, which should have only one result, there is an implication that at least part of the accepted theory of loudspeaker design is invalid.

This invention provides means for the expansion and exploitation of a controlled combination of certain natural vibration phenomena. These phenomena are present at random in conventional loudspeakers, but they are not an integral part of, and indeed could not be incorporated into, accepted loudspeaker theory and practice.

It is an object of this invention to provide a sound reproduction system having a unique sound reproducing element and a unique mounting for said element, the element and its mounting coacting, when the element is excited by the application of energy impulses, to project into the atmosphere audible sound waves corresponding with exactitude, to the frequency and other attributes of the impulses by which it is excited.

Almost any rigid and elastic body, of whatever proportions or material will radiate audible sound to the atmosphere when excited by energy impulses in sonic frequencies. There appear to be three distinct modes in which this propagation and radiation of sound occurs. For the purpose of this discussion, the first of these is called molecular vibration and is believed to be a phenomenon of molecular strain without deformation or displacement of the body itself. When this occurs, there is an apparent wave propagation and audible sound is radiated, but there is otherwise no perceptible disturbance of the surface of the sound radiating body. The second mode will be referred to as surface deformation in which case the surface may have any number of separately but sympathetically vibrating areas separated by distinct nodes, in a manner similar to the harmonic vibration of a taut string. The third mode will be termed monolithic or massive vibration of the body as a Whole, and this occurs either by deflection or displacement.

Depending on the material, the proportions and the mounting of the radiating body, any of the three modes or any combination of two or more modes may occur. However, they may occur at random; one may interfere with the other; they will be reflections and standing waves,

3,272,281 Patented Sept. 13, 1966 and the amplitudes of the separate frequencies may be relatively altered. Also, any radiating body tends to respond resonantly to certain frequencies, resulting in unauthorized and exaggerated sounds. Thus the total radiated sound will not correspond to the exciting impulses.

With such random and uncontrolled behavior in mind, it is a major object of this invention to design a radiating body, and a mounting therefor, which will be free of the undesirable vibrations, while accommodating the said three modes in proper relation to the excitation, and thereby provide accurate reproduction throughout the audible range of the widest variety of tones and frequencies or combinations thereof.

Loudspeakers, for the most part, are designed to operate by vibrational displacement of the radiating element as a whole, or what has been referred to above as massive vibration, whereas this invention provides means for utilizing all three natural vibration modes as described above, in a single radiating element. In loudspeaker design, much effort is devoted to providing rigidity of the radiating element, so that it will move as a whole without either internal or surface vibrations, whereas in this invention, the radiating element is intended to be stressed, deformed and deflected.

The above and other objects will be made clear in the following detailed description, taken in connection with the annexed drawings in which:

FIGURE 1 is a perspective view partially in section, of the improved sound reproducing element and its mount- FIGURE 2 is a transverse cross-section of the base of said element and its mounting; and

FIGURE 3 is a partial schematic cross-section through an electromagnetic device for applying mechanical impulses to the sound radiating body.

Briefly, the present invention may be described as a rigid but resilient plate mounted as a cantilever and excited at its free end. At its base the plate is subject to restraint and damping by an amorphous, semi-fluid mass interposed between portions of the base and its mounting. The plate is preferably made of low density brittle material having a low modulus of elasticity. Excitation is by mechanical connection of the free end to a conventional loudspeaker voice coil. It cannot be too strongly emphasized that the manner and means of excitation are immaterial so long as excitation occurs at or near the free end. It matters not at all whether the source is connected by electromagnetic, elastrostatic, mechanical or other means. A presently preferred excitation means is shown in FIGURE 3 and this means offers certain overall design advantages in connection with the music radiator hereinafter discussed. FIGURE 3 must be taken, however, as illustrative rather than definitive or limiting.

As noted, the fundamental concept is of a cantilever excited at its free end and restrained rather than fixed at its base. The term cantilever ordinarily calls to mind a horizontally protruding beam having one end firmly fixed in a vertical wall and the opposite end perfectly free. The term cantilever is used in this case, however, as a matter of convenience, in the absence of a word more aptly describing the particular structure of this invention. True, the sound radiating body has its major dimensions vertical rather than horizontal and its base end is restricted rather than fixed. Nevertheless, regardless of its angle to the vertical, and regardless of its restraint as against fixation the stress-strain distribution under sonic frequency excitation adjacent the free end so far approximates that of the conventional cantilever that use of the term is deemed justified. The form and proportions shown are what thus far have been found to be optimum and for full compliance with the statute, the unusual step has been taken of dimensioning the drawings. These dimensions, though optimum in the light of present knowledge, are not critical and form a concrete example rather than a limitation. Although, in any given case, the form, proportions and dimensions are critical relative to each other, the overall size of the device may be varied within wide limits.

Referring now to the drawings there is shown a sound radiating element having plane radiating surfaces 12. These are symmetrical about a' central, vertical plane C-L (FIGURE 2). The free edge 14 has secured thereto a stiffening strip 16 of wood or similar material to which, in turn, is secured a metal clip 18 to which a voice coil 60 (shown in FIGURE 3) is mechanically connected by a strap 52. The strip 16 and the clip 18 are designed to excite, equally, the entire extent of the free end 14 of the radiating element 10.

The radiating element 10 may be defined as a body having uniform length, uniform width and varying thickness. The thickness is greatest at the restrained end, and the element is tapered in such a manner that the stress, produced by a static load at the free end, is least at the restrained end and progressively increases toward the free end. This tends to make the propagation of induced vibrations unidirectional, which is a requirement for proper operation, because the vibrations tend to propagate from a region of high stress to a region of lower stress. The taper further allows increased deflection of the element for radiation of low frequency vibrations. The element is tapered in thickness rather than in width so that the full width is available, at the region of maximum deflection, for maximum coupling to the surrounding air when radiating low frequency vibrations, and this requirement would not be met if the radiating face had, for example, a triangular shape.

At the restrained end 20 of the element 10 there is formed an integral central tongue 22, a part of which occupies a slot in the base member 24 which forms part of the ultimate frame of the device. Framing for loudspeakers of all types is largely conventional, forms no part of this invention, and is not disclosed herein.

Because the tongue 22 is longer than the depth of the slot in the base member 24, there is a gap between the end 20 of the radiating element 10 and the base member 24. The tongue 22 fixes the lateral position of the radiating element 10' in relation to the base member 24, and it has only sufficient stiffness to define the central position of the radiating element 10 as the plane C-L (FIGURE 2). Since, in normal vibration there is no significant stress in the region of the tongue, it plays no active part in the operation of the device, except to tend to retain the radiating element in this central position.

Blocks 26 of sponge rubber or other low strength, resilient material are placed in the space between the end 20 of the element 10 and the surface of the base member 24 adjacent each side of the tongue 22. Since the amplitude of the movement of the end 20 relative to the base member 24 is so small as to be negligible in the area of the blocks 26, these blocks function only to prevent inward migration of the semi-fluid damping compound next to be described. In length the blocks 26 are coextensive with the width of the element 10.

The semi-fluid material above referred to is of high viscosity and is extremely adhesive. By way of specific example, a preferred material is 97% polybutenes and 3% hydrogenated castor oil. As a genus, the term butene includes all of the isomers of butylene, hence the term polybutene as used herein is intended to cover any and all polymers of any and all of the isomers of butylene. Any substance having similar flow characteristics and similar physical and chemical stability may be used, or there may be substituted any flexible solid material provided it has the required damping characteristics.

This material is used at 28 to fill the spaces between the blocks 26 and the outer faces 30 and 32 of the element 10 and the base member 24 respectively and is held in place by woven fabric tapes 34. The viscous coupling of the radiating element 10 to the base member 24 is fundamental to the operation of the device. A similar but solidly mounted radiating element would tend to respond only to certain frequencies in a resonant manner, after the manner of a taut string in harmonic vibration. By the base mounting herein described, these resonant harmonic vibrations are damped to the required level and it is then found that, with this construction, the radiating element responds similarly to all frequencies, as if it did not actually have a fixed length. One important function of the viscous material is to prevent reflection of vibration-s from the base of the radiating element, and this damping effect makes the radiating element substantially non resonant. Another important function is to provide resistance so that force applied at the free end causes deflection by bending of the element rather than by simple displacement.

The element It) is formed of foamed or expanded polystyrene which seems the best material currently available. New materials, however, make their appearance almost every week and it not only is possible but probable that better materials will become available. It is not intended therefore, to limit this invention to foamed polystyrene.

Referring now to FIGURE 3, which is illustrative and not definitive of the power portion of the apparatus, the strap 52, which, in FIGURE 1 is shown as having one end attached to the free end 14 of the element 10, is shown in FIGURE 3 as having its opposite end attached to a nonmagnetic rod 54. The opposite end of the rod 54 has a head 56 which supports a shell 58 on which a voice coil 60 is wound. Each end of the rod 54 is secured to a diaphragm 62. Each of the diaphragms 62 is marginally secured to a magnet 64 of which a portion 66 surrounds the voice coil 60 and another portion 68 penetrates the voice coil 60 and surrounds the rod 54. The magnet 64 is mounted on a suitable support 70 through which freely pass lead wires 72 for delivering electrical impulses to the voice coil 60.

The strap 52 is of spring steel and its function is similar to that of a cross-head and connecting rod. The vibrations of the rod 54 are axial and linear; the motion of the free end 14 of element 10 is essentially arcuate, and both motions are accommodated by the strap 52.

Disclosure has been made of a form of this invention which seems optimum in the light of the current knowledge and experiment. As the drawings make clear the element 10 is trapezoidal in transverse cross-section and has plane sound radiating surfaces symmetrical on opposite sides of a central plane. That is, the element 10 has substantially uniform length and substantially uniform width, but has varying thickness. The average thickness, however, is substantial as compared to either length or width so that the element 10, though sufficiently resilient to reproduce energy impulses in the form of mechanical vibrations in compound and multiple sonic frequencies, is, nevertheless, a substantially rigid body. Quite possibly it may be found that some proportions may be altered or that the element may be made asymmetrical or that the radiating surfaces 12 may be given some curvature instead of being made plane as disclosed. The invention is not, therefore, to be limited to the details of the disclosure, but only as set forth in the subjoined claims.

What is claimed is:

1. A device for converting energy impulses into audible sound comprising: a sound radiating element of substantially uniform length and width of varying thickness having one end substantially restrained and the opposite end substantially free and means for exciting the free end of said element in response to said energy impulses.

2. A device as set forth in claim 1 in which the sound radiating element has a generally tapered longitudinal cross-section having its greatest thickness adjacent its restrained end.

3. A device as set forth in claim 1 in which the sound radiating element has a trapezoidal longitudinal crosssection in planes parallel to its deflection.

4. A device as set forth in claim .2 in which said sound radiating element is made of substantally rigid cellular material.

5. A device as set forth in claim 2 in which the sound radiating element is symmetrical in cross-section about a central longitudinal plane perpendicular to its base.

6. A device for converting energy impulses into audible sound comprising a sound radiating element, mounted as a cantilever, substantially restrained at its base and substantially free at its opposite edge; a base member; said sound radiating element having, at its base, a tongue fixed to said base member, the thickness of said sound radiating element at its base execeeding that of said tongue and vibration damping means adjacent the free margins of said base between said base and said base member.

7. A device as set forth in claim 6 in Which said sound radiating element is formed of foamed polystyrene.

8. A device as set forth in claim 6 in which said damping means comprises, essentially, a .polybutene.

9. A device as set forth in claim 7 in which said damping means comprises, essentially, a polybutene.

10. A device as set forth in claim 8 including solid bodies of deformable, essentially elastic material between said tongue and said damping means.

11. A device as set forth in claim 9 including bodies of deformable, essentially elastic material between said tongue and said damping means.

12. A device for converting energy impulses into audible sound comprising: a sound radiating element mounted as a cantilever having one end substantially restrained and the opposite end substantially free, said element having a generally tapered longitudinal cross-section with its greatest thickness adjacent its restrained end, said element being formed of foamed polystyrene and means for loading the free end of said element in response to said energy impulses.

13. A device for converting energy impulses into audible sound comprising: a sound radiating element, said element having major, generally rectilinear surfaces and minor, generally trapezoidal surfaces and being substantially restrained at its base and substantially free at its 5 opposite edge; a base member; said base and said base member having mutually confronting surfaces generally normal to the major surfaces of said sound radiating element; means connecting the base of said sound radiating element to said base member, said means having a crosssectional area less than the area of the confronting surfaces of said base and said base member; vibration damp ing means interposed between said confronting surfaces; and means for exciting vibrations in the sonic range at said opposite edge.

14. A device as set forth in claim 13 in which said sound radiating element is formed of foamed polystyrene.

15. A device as set forth in claim 13 in which said damping means comprises, essentially, a polybutene.

16. A device as set forth in claim 14 in which said damping means comprises, essentially, a polybutene.

17. A device as set forth in claim 15 including solid bodies of deformable, essentially elastic material between said connecting means and said damping means.

18. A device as set forth in claim 16 including bodies of deformable, essentially elastic material between said connecting means and said damping means.

19. A device as set forth in claim 13 in which said damping means comprises at least one substantially solid flexible body cooperating with a viscous fluid.

References Cited by the Examiner UNITED STATES PATENTS RICHARD B. WILKINSON, Primary Examiner.

LEO SMILOW, Examiner.

S. J. TOMSKY, Assistant Examiner.

Claims (1)

1. A DEVICE FOR CONVERTING ENERGY IMPULSES INTO AUDIBLE SOUND COMPRISING: A SOUND RADIATING ELEMENT OF SUBSTANTIALLY UNIFORM LENGTH AND WIDTH OF VARYING THICKNESS HAVING ONE END SUBSTANTIALLY RESTRAINED AND THE OPPOSITE END SUBSTANTIALLY FREE AND MEANS FOR EXCITING THE FREE END OF SAID END ELEMENT IN RESPONSE TO SAID ENERGY IMPULSES.

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