US2229440A - Piano soundboard - Google Patents

Description

1941- R. w. CARLISLE PIANO SOUNDBOARD Filed Jan. 2, 1937 Patented Jan. 21, 1941 UNITED STATES PATENT OFFlQE PIANO SOUNDBOARD Application January 2, 1937, Serial No. 118,862

6 Claims.

This invention relates to musical instruments and soundboards as used therein, and more particularly in pianos, harps, violins and other instruments, in which a more or less flat, stiff soundboard is commonly used.

It is one object of this invention to greatly increase the acoustic efliciency of any given size of soundboard, especially with respect to low frequencies.

It is another object of this invention to provide means for constructing a musical instrument of any given class with a soundboard cnsiderably reduced in size without reducing its acoustic output.

It is another object of this invention to improve the purity of wave form of certain notes by preventing deleterious absorption of energy from the edge of a diaphragm into a frame or case structure.

It is another object of this invention to construct a musical instrument of the heavier class such as the piano with a cost greatly reduced by reason of the economies effected through the lightening of the case structure which is possible when using my invention.

The manner in which this invention attains these objects is illustrated with specific application to a piano in the accompanying drawing, in which Fig. 1 is a plan view of a part of a piano soundboard Fig. 2 is a section through the line 22 of Fig. l and the line 22 of Figure 6 Fig. 3 is part of a cross section through the line 33 of Fig. 1, and also a section through the line 3-3 of Fig. 2; and

Fig. 4 is an enlargement of the section through 4-4 of Fi 2.

Figure 5 is an end section view of the treble part of my soundboard through the line 55 of Figure 6, and

Figure 6 is a schematic plan view of a piano soundboard constructed according to my invention.

In the drawing referring first to Figs. 1 and 2, the strings I are shown disposed in spaced relationship to a soundboard 3. Each string is affixed at each end thereof to a relatively rigid metal string plate 5. A part of this string plate 5 is extended around'the edge of the soundboard 3 to form a frame 5' for the edge of said soundboard as shown in Fig. 2. Between the underside of said soundboard 3 and the upper surface of said frame 5' is interposed a resilient cushion required to encompass the strings, it follows that 10 the bridge 9 must necessarily be located close to one edge of the frame 5. The soundboard 3 is customarily reinforced with ribs as shown at 1 and 7'. At extreme low frequency it is desirable to secure the greatest possible amplitude of vibration over the largest possible area. In this manner the maximum sound radiation may be attained, since radiation from a surface is proportional to the product of the surface area and the velocity of vibration. The soundboard is vibrated by the strings I which vibrate against the bridge 9, the vibrations being carried to the soundboard 3 and causing the soundboard to vibrate. If a soundboard is not made flexible around its periphery only a small amplitude of vibration will occur; if it be made flexible around the entire periphery, or if it be suspended on a resilient cushion around the entire periphery, a large amplitude of vibration will occur in the immediate vicinity of the bridge but will not spread therefrom over the entire diaphragm at low frequencies because the diaphragm will tend to rock about its center and only the edge will move. If, however, in accordance with my invention as shown in Figure 6 that part of the edge 30-3l to which the bridge 9 is adjacent to be pivotally supported on the surface H], the ribs will act as levers to transmit the motion of the bridge 9 to the central portion of the soundboard 3, provided that the far side 3|, 32, 33, 34 is resiliently supported as shown in Figure 2 at 6. It is advantageous to make the pivoted side heavier, and the far side lighter, in order to improve this pivoting action.

As is customary in the art, a fibrous soundboard may be used having the grain thereof running substantially perpendicular to the bass strings, as shown in Fig. 1.

One manner in which pivotal support may be accomplished as shown in Figures 2 and 3 in which strips of wood I0 and I3, rounded at the top as shown in Fig. 2, are placed under the ribs 1 and 1, respectively, on the frame 5'. Strips II and II may be placed between said ribs and fitted between the frame 5' and the bottom surface of the soundboard 3, and having the surface juxtaposed to said soundboard rounded in the same manner as that of the strip it.

A resilient cushion may be used as shown at 6 in Fig. 2 around any part of the periphery of the soundboard 3 or all of said periphery, preferably excepting the region 3" adjacent to the low frequency bridge 9 in Figures 1 and 6, as located between and 3! as shown in Figure 6. In one embodiment this resilient support of the soundboard 3 upon the frame 5' is secured by the use of one or more layers of a resilient, continuously undulating strip I2. To avoid audible vibrations therein strips of fabric l3 and I4 as shown in Fig. 4 may be placed immediately above and below it respectively. Loose felt or cotton wadding [5 may also be interposed in the interstices above and below the spring [2 to prevent leakage of air around the edge of the soundboard, which would cause a certain loss in low frequency radiation. It is also possible to damp vibrations of the edge of the diaphragm by inserting more of such damping material. This is particularly useful around the treble end of the soundboard 34, 3E, 36 of Figure 6; the tone quality of the radiated sound depends to a considerable extent upon providing exactly the right width of soundboard and properly damping the edges thereof.

Furthermore, the excessive damping which has previously been placed upon treble ends of soundboards due to their rigid attachment to the case 2 3 is obviated by the resilient connection means herein provided. This permits the radiation of purer and more sustained tones. It also permits economies in case construction since variations in said case will not affect the performones.

In order that the soundboard to may be very narrow at the treble end of the soundboard, the

frame 5' may be extended inwardly as shown at 25 and 2b in Fig. 5 so that the strings may have over a length greater than the width of the soundboard.

As shown in Fig. 5 the soundboard 3d at the treble end of the instrument should be made of relatively thinner and harder material than the remainder of the soundboard. Furthermore, the bridge connecting the treble strings to this small, hard and stiff portion of the soundboard should be extremely light and stiff, as indicated by the narrow bridge to in Fig. 5. The degree of resiliency and damping of the mounting of the edges of the soundboard 13a to said extensions .25 and 243 may by use of the means illustrated in Figs. 3 and 4 be predetermined to secure any desired degree of sustenance of high frequency tone.

Any elongated member of a resilient nature may be utilized around the periphery of the soundboard such as rubber tubing or other flexible tubing. This may be varied in flexibility and in damping qualities as desired around the periphery of the soundboard.

The soundboard shown in the drawing is customarily crowned and flexed, as Well known in the piano art.

Although pianos are customarily constructed with flexed strings as resonators, they are sometimes constructed utilizing tuning forks, as well known in the art. The soundboard constructed herein described is equally applicable to use with resonators other than string-s.

In one embodiment of my invention, a piano soundboard is mounted on a flexible suspension comprised of two layers of corrugated steel strip .009 inch thick and inch wide at all points around the periphery except that part adjacent to the bass bridge. The ratio of the deformation at the center of the soundboard to the force applied on the soundboard by the strings is .091 inch per pound, whereas without the flexible suspension the stiffness due to the flat soundboard alone Without the rib supports is .05G, showing nearly a 2 to 1 improvement in flexibility and a consequent improvement in low frequency efficiency. This feature of added flexibility becomes increasingly important as the size of an instrument is reduced.

1 claim:

1. In .a piano, a soundboard pivotally supportalong the edge adjacent to the bridge and flexibly supported along other edges, means for re-inforcing said soundboard, said means bein stiffer along said pivotally supported edge than along the flexibly supported edges.

2. In a piano, a soundboard pivotally supported along the edge adjacent to the bridge and flexibly supported along other edges, the side of said soundboard opposite to said pivoted edge being lighter in weight than the pivotally supported side.

3. In a piano, a fibrous soundboard having the grain thereof running perpendicular to the strings, a bridge on said soundboard near one edge thereof, reinforcing ribs on the soundboard perpendicular to said grain and means for pivotally supporting said soundboard along the edge adjacent to said bridge, and means for flexibly supporting said soundboard at the ends of the aforementioned grain.

4. In a musical instrument, a flexed soundboard supported around its edge by means comprised of a metal spring strip having an undulating shape and a compressible damping material disposed around the spring strip, said damping material controlling vibrations of the edge of the soundboard.

5. In a piano a frame having a rigid fulcrum thereon, a soundboard pivoted on said fulcrum and resilient means on the frame for supporting the opposite end of the soundboard yieldably to accommodate pivotal mounting about the fulcrum and a bridge mounted on the soundboard adjacent said rigid fulcrum.

6. A soundboard having a bass and treble por tion, rigid supporting members under each edge of the treble portion, resilient means interposed intermediate said supporting member and said treble portion, means pivotally supporting said soundboard at a point remote from said treble portion, and means positioned intermediate said resilient means and said treble portion of said soundboard for modifying the resilience and damping effiect of said resilient means.

RICHARD W'ALLACE CARLISLE.

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