US2051633A - Soundboard for pianos and other instruments or devices using soundboards - Google Patents

Description

1935- P/H. BILHUBER 2,051,633

SOUNDBOARD FOR PIANOS AND OTHER INSTRUMENTS OR DEVICES US ING SOUNDBOARDS Filed March 50,1 1955 2 Sheets-Sheet 1 INVENTOR.

BY b r 4W TTORNEY.

Aug. l8, 1936. P. H. BILHUBER 2,051,633

SOUNDBOARD FOR PIANOS 'AND OTHER INSTRUMENTS OR DEVICES USING SOUNDBOARDS Filed March 30, 19:s5 2- Sheets-Sheet 2 *;Ow kyz Patented Aug. 18, 1936 UNITED STATES PATENT OFFIQE BOARDS Paul H. Bilhuber, Douglaston, Long Island, N. Y., assignor to Steinway & Sons, New York, N. Y., a corporation of New York Application March 30, 1935, Serial No. 13,836

1 Claim.

The present invention relates to soundboards for pianos and other instruments or devices using soundboards.

It is an object of this invention to provide a uniform and scientifically correct soundboard adaptable for mounting in a piano casein a mansection of the latter by tapering the soundboard in all directions from the thickest portion to the thinnest portion thereof at the point of contact of the soundboard with the piano case.

Another object of the invention is to provide a soundboard having at least one side convexed or curved in all directions on parabolic curves, or substantially so, so as to graduate the thickness of the soundboard in all directions, and thereby compensate uniformly all around the soundboard for the stiifening induced by anchoring the soundboard at its edges.

Finally, the invention comprises the disposition of parts wherein the greatest mass or depth of the soundboard, the geographical center of the soundboard, and the bridge are substantially coincident.

With the foregoing and other objects in view, the invention will be more fully described hereinafter, and will be more particularly pointed out in the claim appended hereto.

In the drawings, wherein like symbols refer to like or corresponding parts throughout the several views- Figure l is a plan view of my improved soundboard for a grand piano viewed from the convex side thereof, the respective dotted line figures showing generally points of the same depth, the depth decreasing with the increase in size of the dot-dash line figures, and also showing in dot-dash line, the cross sectional line 3-3;

Figure 2 is a plan view of one form of the blank for the improved soundboard, the dot-dash line showing the final shape of the board for application to a piano, and showing means for obtaining ;the so-called geographical centre;

Figure 3 is a vertical section taken on line 33 of the soundboard, shown in Figure 1, which is constructed according to the present invention.

and showing the symmetrical tapering in thickness of the board from its deepest point to its marginal edge;

Figure 4 is an edge View of the soundboard blank in its original fiat or plane condition; and

Figure 5 is a sectional view taken through the soundboard fitted to its form or mold, to impart to it a substantially concavo-convex formation to the soundboard and showing the form or mold of slightly larger area than that of the soundboard to support the upwarcfly curved marginal edges of the board above the face of the form, the dotdash line showing the line of cut to remove the material of the soundboard above the line of cut.

Referring now to the drawings, and first to Figure 1, the soundboard I5 is shown in plan view looking towards the convex side. This convex side is shown in the lower part of Figure 3, the upper part thereof being fiat or in a plane.

' The greatest depth of the soundboard is indicated generally by the character 9 and the dotdash line figures indicate uniform depth lines. These figures are obtained from imaginary parallel planes passing through the soundboard, these planes being parallel with the uncurved side of the soundboard. These planes pass through the intersection points of vertical lines Illa, Ila, I2a, I3a, and Ma and the curved surface of the soundboard shown in Figure 3. So the figure Illa has the greatest depth of the figures indicated, the figure II represents less depth, the figure I2 still less depth and the figure I3 the least depth, except that the rim portion I4 has still less depth, and the least depth. The figures are arbitrarily chosen to clarify the description. Any other chosen depth figures will show the same relationship, namely, the gradual decrease in depth from the greatest depth point 9 to the thinnest portion of the board at the rim. The relationship of the bridge 29 to the lines of varying depth is shown in Fig. 2. The respective positions are relative only, as they are not intended to be mathematically accurate in drawings of this nature.

One manner of proceeding to provide the mold for shaping the soundboard is indicated in Fig. 2. The general outline of the initial blank board is shown by the character I6 in Figure 2. This shape is in a sense arbitrary, as most suitable to practical working conditions. It conforms closely to the ultimate outline of the soundboard itself, which is shown in dot-dash line and is indicated by the character I5. Thereupon lines are drawn on this initial blank I6 and from these lines, the geographical center of the board is determined in respect to its general position. One manner of ascertaining the geographical center of the board, is to divide the angle at the corner 30 and draw a bisecting line 3i and then divide vertical line 32 equally and draw a horizontal line 33 through the median point 36. Where these lines 3i and 33 intersect is the center. This point is indicated by 9 and in the preferred form corresponds to the greatest depth of the board. Having determined this depth point 9 of the board, in respect to the boundary line of the board, it is used as a point through which vertical planes pass radially in all directions. Each vertical section of the board is intended to show one plane side and one curved side, the curved side being determined by two parabolic curves with their deepest parts at the point 9 in Figure 2, or at the point 9 in Figure 3. The curved figure in Fig. 3 results from the section 33 of Figure 1. Here a curved radial plane was utilized to clarify the drawing and description. Each cross-sectional plane would necessarily show a different curvature. Having thus planned the desired curvature of the convex side of the board, a basis for the curvature of the mold hereafter to be described is obtained. These curved lines are preferably of parabolic shape, with their deepest portion coincident with the geographic center referred to. Thus whatever Vertical radial section be taken, the deepest point of the curved cross section will be at the geographic center or at any point decided to have the greatest depth, and the lines of curvature will be preferably of parabolic shape. Such a section is shown in Fig. 3, where the depth of the center 9 is slightly exaggerated to enable the two parabolic curves to be clearly shown. A horizontal plane passing through the intersection of the line 23 with the curve, would result in a point contact.

A mold i8 is shown in section in Figure 5, and the curved line 11 forms the concave portion of the mold, made in accordance with the hereinabove set forth description. The mold has rim portions If), to hold the soundboard against movement when placed therein. A soundboard blank 20 is shown in Fig. i, and is constructed of wood and the upper and lower faces thereof are disposed in parallel relation to each other.

The contour of the board shown in Figure 4 corresponds to that of Figure 1, or the dot-dash line contour of Figure 2.

This initial soundboard 2!! with both sides fiat is placed over a form or mold 63 which is of slightly larger area than the soundboard 20 and which is provided with a cavity or depression of concave configuration and formed preferably on parabolic curves as shown at l'i, the curved surface constituting the bottom wall of the cavity. This curved surface corresponds to the intended design. This cavity, designated generally as IT, has a major depth at its central portion equal substantially to the thickness of the initial soundboard 5 at its central axial portion. The contour of the mold corresponds to the contour of the curved surface of Figure 3 by way of illustration.

As the soundboard 2e and the form l8 are of relatively large longitudinal and transverse area, the middle or axial portion of the soundboard will sag or bend into the cavity ll and will conform snugly thereto so that placing of the soundboard over the mold imparts a corresponding curvature to the soundboard, as shown in Figure 5. Of course, any suitable means may be utilized in addition to the weight itself, if desired, for insuring the molding or fitting of the lower side of the soundboard 2D to the parabolic curvature of the bottom wall of the cavity ll, in order to give the soundboard its conforming shape.

After the soundboard 29 has been fitted to the desired curvature, the upper surface marginal portion of the soundboard is planed or otherwise removed so as to eliminate the upper outer marginal portion of the soundboard along the line 21 which is preferably in a plane passing through the rim of the mold. The upper surface of the soundboard shown in Fig. 5 is thereby finished into a plane surface. In Fig. 5, the line 2! is shown as slightly below the depth point of the upper curved surface. The cut could be along the line 2| as shown, or the line 2! can be taken as tangential to the upper curved surface. Such a tangential line would not show as clearly in the drawings. The result of these operations on the soundboard is to produce the article shown in Fig. 3, wherein the soundboard has a cross sectional configuration, in all directions about its deepest portion, which is plane-convex with the lowerconvex surface of the soundboard tapering off to the rim.

from its greatest depth point.

It will be observed that the molding or curving of the soundboard, as shown in Fig. 5, results in a certain degree of tension between the fibers, and as the fibers remain in this condition in the finished article, the soundboard is more susceptible to vibration and thus is increased as to its reso-.

nance characteristics. It will also be noted that the tapering in thickness of the soundboard 20, as finished, and shown in one embodiment in Fig. 3, is gradual and symmetrical from and in all directions about the greatest depth point to the extreme outer marginal portions of the soundboard. With this construction, when the soundboard is glued or anchored in a piano case, or the like, there is provided an inherent flexibility and elasticity to the soundboard which is proportioned so that the body of the soundboard decreases in depth from its center 9 and in all directions.

When a soundboard 20 as heretofore used is mounted in a piano or the like, it is glued or otherwise suitably anchored or secured at its marginal edges and consequently vibration is impeded at the edges and the full effect of the soundboard is lost, and the dampening of the vibrations in the soundboard is not compensated for. This invention provides means for such compensation,

Each radial section of the soundboard of Figures 1, 2, 3, and 5 will show a different curvature, but all the curvatures will be of like character, in that they have a deepest point and a tapering contour therefrom. The action of the soundboard,

with a convex surface struck on the parabola, or

substantially so, better meets the scientific construction of the soundboard for diaphragmatic vibratory action and for actuation of the sound waves set up by the action of the soundboard along the entire surface or area of the soundboard.

In mounting the soundboard iii in the piano casing, it is preferable to dispose the same with the convex or parabolic surface uppermost, and of course the soundboard structure may be given various other configurations than parabolic within the scope of the claims and the spirit of :the invention.

The improved soundboard vibrates as a whole, in the same manner as a single diaphragm, and the invention solves this problem.

The diaphragmatic vibration is assisted by the relatively thick center and tapering edges. The mass tends to be concentrated at the center and the flexibility distributed towards the edges, with the portion adjacent to the rim or edges being more capable of easy movement.

Finally in the preferred embodiment, the greatest depth point, the geographical center 9 of the soundboard and the bridge 29 are all coincident or very nearly so, the vibrations of the bridge resulting from the striking of the strings translating themselves at the geographical center to the deepest part of the soundboard, and then distributing themselves along the radii of the soundboard to its rim in true diaphragm fashion. The improved soundboard avoids that effect produced by segmental or partial vibration, as in soundboards heretofore proposed. In these, a certain section vibrated at the same time with another section, and at certain times these sections were out of balance with one another. The improved board acts diaphragmatically over the maximum vibratory area.

As will be clear to one skilled in the art, soundboards, after having been prepared as described, are then fitted with ribs and bridges in the conventional manner.

The tendency of the improved soundboard to vibrate as a Whole is increased, without breaking up into higher modes of vibration.

My invention has been illustrated and described,

but it is understood that changes may be made in the form of details and in the construction and arrangement of parts without departing from the spirit and scope of the invention or the scope of the appended claim.

I claim:

A soundboard for pianos and other instruments or devices using Soundboards, comprising a body portion having a curved contour the fibers thereoi being under tension, the greatest thickness of the body portion being at the geographical center of the soundboard, said body portion decreasing in thickness progressively from its geographical center in all directions to the parts of least thickness at the rim portion of the soundboard in substantially uniform progression and such tension of the fibers extending from the geographical center to the rim portion of the board, planes parallel with each other and with the plane surface of the body portion forming sections having a contour symmetrical to the outer contour of the soundboard, the body portion at each part of said sections having the same thickness, whereby the mass is concentrated at the central portion and the amplitudes of the vibrations decrease towards the rim portion, said soundboard acting as a whole, when subjected to vibration, in the same manner as a diaphragm.

PAUL H. BILHUBER.

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