US1843367A - Diaphragm - Google Patents

Description

Feb. 2, 1932. H. LANGLEY DIAPHRAGM Filed Feb. 4, 1929 @bijl I INVENTOR. mw( ATTORNEY.

Patented Feb. 2, 1932 UNITED STATES PATENT ori-*Ica RALPH H. LA NGLEY, OF CINCINNATI, OHIO, ASSIGNOR T THE OROSLEY RADIO COR- PORATION, OF CINCINNATI, OHIO, A CORPORATION 0F OHIO DIAPHRAGM Application led February 4, 1929. Serial No. 337,472.

My invention relates to diaphragms for reproducing the entire audible range of sounds, which diaphragms are employed without horns, so as to act as sounding boards. More f a particularly it relates to diaphragms which are made of a light vibrant material to which stiffness is imparted by means of shaping them into rounded or conical shapes.

Conical diaphragms of the sounding board type do not move to and fro as a unit when creating sound, except at very low frequencies, and for pure sounds at these frequencies. In the typical soundv box diaphragm used with a horny it is the endeavor to obt-ain as rigid and unitarily movable a structure as possible within audible frequencies, but this is not practical with larger diaphragms which function like sounding boards.

At low frequencies the larger diaphragms move in a unitary manner or with large areas of flexure, and to 4create an intense sound at low frequency a large amplitude of movement must be imparted. This is because the intensity of sound is proportional to the product of the square of the frequency and the square of the amplitude, so t-hat at lo7 frequency a large amplitude is necessary if intensity is desired. y

My diaphragm is particularly calculated to permit of large amplitude of movement, and is adapted particularly for the moving coil type of impell-er or receiver. In the magnetic type of receiver in which an armature moves :1.5 to and fro between magnetic poles defining La smallvair gap, it has not been practical to provide for large amplitude of movement of the armature, and hence the diaphragms of magnetic 'type loud speakers have not had to have a structure and mounting which permitted of large amplitude of movement. In the moving coil type of loud speaker, however, the impelleris a coil or coils of wire which are secured to the diaphragm and move in and out of a larger coil concentric therewith, so that since the small coil moves at right angles tothe magneticV field of the larger coil, there is no limited movement, such as in magnetic loud speakers.

It is familiar practice in the art to provide a conical diaphragm for a loud speaker which is mounted by means of a peripheral flange formed on the cone, either of the same material as the cone or of kid skin or rubber.

In such structures the following three conditions exist l. There. is at least a partial reflection of the vibrations at the base of the cone wher it joins the flat peripheral portion.

2. There is a substantially perfect reflection at the point where the plane peripheral portion is gripped under the heavy ring.

8. The plane peripheral portion being of definite dimensions has one or more definite natural periods of resonance which cont-ribute their effect to the performance of the complete diaphragm and produce points of greater response in the frequency characteristic.

The object o f my invention is to provide an edge support for the vibrating conical diaphragm which will be substantially free from inherent natural periods and yet which will be sufficiently flexible to permit the necessary large amplitude vibrations of the cone at the low frequencies. A further object of the invention is to provide a structure in which the natural modes of flexural vibration of the conical portion itself will be more nearly uniform at all frequencies and in which the transition from one mode of flexural vibration to another will be more gradual than is the case in structures employing a plane peripheral portion. 4This improvement makes the frequency response curve much more nearly uniform throughout the range of sound frequencies.

The exact nature of my-invention will be more clearly understood by reference to the attached drawing, but it is to be understood that the drawing represents only one form of the invention and that many other forms embodying the essential principles of the invention are possible.

The figure is a transverse section of a conical structure in accordance with my invention, the section being taken parallel to the direction of motion of the cone. It will be seen that the cone l consists of a small cylindrical portion 2 on which the moving coil 3 is wound. `The conical portion 4 springs from this cylindrical portion 2 and merges into a curved edge 5 which is turned back so that at its periphery 6 it forms one element of a cylinder whose axis is parallel to the direction of motion of the cone. .At this edge 6 there is secured to the diaphragm a narrow band of felt 7 which restslightly in a small depression 8 in the. supporting rin 9.

Vhen a diaphragm thus constructed is vibrated at low frequencies by means of forces acting through the coil 3 at its apex the conical portion moves in and out bodily and rolls the curved portion 5 as indicated by the dotted lines in thefgure. The extent of this rolling action and the point on the curved edge at which there ceases to be any motion-at all is determined by the frequency at which the diaphragm is excited and the amplitude through which it tends to move. As the frequency is increased and the amplitude decreases, asmaller and smaller portion of the curved/edge comes into play. It will be at once appreciated that at any frequency which may be impressed on the diaphragm, there will be some correct mode of vibration for the rolled edge Which will permit the conical portion to attain its proper maximum amplitude either by bodily motion as at the lower frequencies or/by flexural vibrations at the higher frequencies.

In its preferred form my diaphragm is formed by revolving about an axis, a straight line which intersects the axis and which terminates at a finite distance from the axis in a tangent curve whose radigs is not less than 1/5 of the length of the straight line fr om its intersection with the axis to the point of tangency with the curve. This particular structure is calculated to give the best results utilizing a crisp, light weight, moldable mate rial such as a filled fabric or' other plasticizable sheet.

It will also be evident that in this structure there is no definite point or line at which complete or even partial reiiection takes place, the vibrational motion of the conical portion being gradually of lesser and lesser amplitude as points further out on the curved edge are reached. f

It is, of course, to be understood that the above discussion applies rigorously only du r'- ing the first few cycles of any impressed vibration and that the complete diaphragm assumes a definite Vibration pattern very rapidly after the vibrations are first impressed. After this pattern has been established, there is no longer any question of reflections as such, but the presence of any definite reflection points would.` have an eect in establishing the vibration pattern of the diaphragm and would tend to make the diaphragm more responsive to'certain frequencies than others.

4The absence of such definite reflection points in diaphragms constructed in accordance with of the curved edge, it is terminated by secur# ing it to a felt cushion which leaves the edge of the diaphragm itself still free to vibrate at small amplitudes and almost completely destroys any reflection of the edge due to the absorbing character of the felt.

As in all other vibrating cones of reasonably small dimensions, it is necessary to provide a flat surface around the vibrating cone of dimensions suicient to prevent sound Waves departing from the rear surface from interfering with sound Waves departin from the front surface of the cone. The imensions of this surface must be chosen withy respect to the allowable dimensions of the complete device and the lowest frequencies which it is desired to reproduce. The felt edge in my diaphragm is therefore arranged to makecontact with the rim to which this flat surrounding surface can be fastened.

One of the features of the particular shape is that the cylindrical back-turned portion is quite rigid to any vibrations which are applied to it in a direction axial to it, so that under the conditions of use illustrated there is a minimum of sound generation in the said cylindrical portion. The secondary result of this feature is that the curve of the structure acts to gradually damp off the'flexural vibrations illustrated to the diaphragm. Another result is t-hat the support as applied to the back edge of the cylindrical portion isl chiefly called upon to serve as a guide, a seal,

and an insulator, and not as a retaining element in any sense.

By dropping the felt into a slight channellikef depression in the housing, I avoid excessive frictional movement of the felt along the housing and force the curved element of the diaphragm to absorb slightly more of the high amplitude movements imparted to the conical part than it would otherwise. In general use the diaphragm is not called upon to move through large enough distance to require this feature of my construction. Un-

dei' normal conditions the device will function with nothing at all as an absorber, seal or retainer at the back edge of the cylindrical portion.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

l. In a Vibrating device, va diaphragm sounding board having a central conical portion and a curved annular peripheral l,por-

tion Whose section is tangent to each element of the conical portion, and whose radius is of the order of 1/5 of the straight side of the conical portion.

2. In a diaphragm for the reproduction of sound as a sounding board, a central conical portion and a curved peripheral portion so formed that the section of the diaphragm parallel to its axis consists of a straight line representing the element of the cone and a portion of a circle tangent to the straight line, the said portion of a circle having a radius not less than 15 of the length of the said straight line.

3. For a diaphragm of sound as a .sounding board, a surface of rotation obtained by revolving about an axis a straight line which intersects the axis and which terminates at a finite distance from the axis in a tangent curve whose radius of -curvature is not less than 1/5 of the distance along the straight line from its intersection With the axis of rotation to the point of tangency with the curve.

4. In a diaphragm serving as a sounding board, the combination of a conical portion having at its apex a cylindrical portion to which a coil of Wire is attached to serve as a moving coil, and at its periphery a returnbent curved portion having a radius of, curvature substantially 1/5 the side length of said conical portion terminating in a cylindrical portion, for the purpose described.

5. In a diaphragm serving as a sounding board the combination of a conical portion terminating at its periphery in a curved portion Which is return-bent about a radius of curvature of the order of 1/5 the straight side of said conical portion to'form' a cylindrical portion, whereby the maximum response to flexural vibrations imparted to the diaphragm is adjacentthe edgev of the cone and the minimum response thereto is at the said cylindrical portion, and sound deadening means about said cylindrical portion.

6. In a diaphragm serving as a sounding board the combination of a conical portion terminating at its periphery in a curved portion which is return-bent about a radius of curvature of the, order 0f 1/5 the straight side of said conical portion to form a cylindrical portion, whereby ,the maximum response to flexural vibrations imparted to the diaphragm is adj acent'the edge of the cone and the minimumresponse thereto is at the said cylindrical portion, and means surrounding the diaphragm for baffling the sound emanating therefrom, and a member which acts as an absorber to sound constituting a seal i kbetween the diaphragml and the baiiiing means.

RALPH H. LANGLEY.

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