Music – Instruments – Rigid vibrators
Reexamination Certificate
2000-01-05
2001-05-29
Hsieh, Shih-Yung (Department: 2837)
Music
Instruments
Rigid vibrators
C084S189000, C084S190000, C084S192000
Reexamination Certificate
active
06239339
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a sound body for a stringed instrument, having an upper backframe designed as a frame, to which a soundboard is adhesively bonded, on which there are provided at least one bridge extending approximately diagonally and a cast frame with a set of strings, and having a lower backframe which is arranged under the upper backframe and is connected thereto.
Sound bodies of the type described above are an essential element of upright pianos, grand pianos and other stringed instruments. The tuning of the instrument is predefined by the sound body. It is desirable for an instrument or sound body which has been tuned once to keep the tuning constant. The tuning of the sound body remains constant when the exact position of the elements of the sound body and, above all, the tension of the strings remain unchanged. The wooden components of the sound body, in particular of the soundboard, are, however, subject to dimensional fluctuations in the event of fluctuations in the climatic conditions in the room, through which the tuning of the sound body and of the instrument is then changed. Even small changes in the relative atmospheric humidity at the transition from the heating period to the summertime conditions in the room or from the transition between an air-conditioned practice room and a concert hall which is hardly heated at all have the effect of swelling or shrinkage of the wood and therefore a change to the set tuning.
The sound body described at the beginning can be taken from German Patent 375 023. Here, the upper backframe is formed by a frame made of grooved strips, which are led around the entire circumference of the soundboard, improve the effect of the sound and at the same time are intended to ensure protection against stressing. In this case, the narrow upper edge of the grooved strips forms the supporting surface for the soundboard to be glued on. The lower backframe consists of a hollow frame, which has a somewhat larger external contour than the upper backframe and is stiffened by two transverse spars spaced apart from each other.
In the event of fluctuations in the climatic conditions, it is primarily the dimensions of the soundboard which change, but also the dimensions of the upper backframe. Neither the soundboard nor the supporting element of the sound body, the upper backframe, therefore satisfy the preconditions of dimensional stability under climatic fluctuations. In attempts to improve the dimensional stability of sound bodies, it has been shown that an attempt to hamper or prevent the dimensional changes to the soundboard often leads to damage, especially to plastic deformations or cracks in the soundboard.
SUMMARY OF THE INVENTION
The object of the invention is to provide a sound body which ensures that the tuning, once predefined, only changes to a slight extent in the event of fluctuations in the climatic conditions in the room.
Starting from the sound body described at the beginning the present object is achieved, according to the invention, in that the upper backframe is connected to the lower backframe only in its diagonally opposite connection regions facing the ends of said bridge, but has a clear spacing from the lower backframe in the remaining edge regions.
It is expedient if the thickness of the upper backframe decreases from a maximum value in the connection regions toward the remaining edge regions. The upper backframe therefore “floats” over the lower backframe in the remaining edge regions. This connection of the two backframes only in some sections largely prevents fluctuations in the tuning of the sound body or of the instrument caused by climatic fluctuations. In order to implement the connection of the upper backframe to the lower backframe in some sections, the thickness of the upper backframe, which is normally about 6 to 8 cm, can be reduced in those regions where the two backframes are not connected to each other. This reduction in the cross section is readily possible, since the upper backframe no longer has to contribute to the overall stability of the sound body.
Surprisingly, it has been established that the dimensional changes occurring as a result of the swelling and shrinkage of the soundboard can be tolerated to a considerable extent provided the two backframes are fixed in a defined position in relation to each other only in said connection regions, in which the bridge or its imaginary extension ends.
According to the invention, this fixed alignment to one another is primarily ensured by a torsionally rigid and dimensionally stable lower backframe, which represents a dimensionally stable reference element of the sound body and therefore preferably consists of metal. The upper backframe, on the other hand, can still preferably be produced from wood, since the necessary stability of the sound body is largely ensured by the lower backframe.
The upper and lower backframes can intrinsically be connected to each other in any desired way, but adhesively bonding the two backframes as a flat, thrust-resistant connection has proven to be particularly advantageous by comparison with point-by-point connections, for example by comparison with screwing. Furthermore, adhesive bonding offers the advantage that damage to the soundboard by drilled holes is avoided.
The soundboard preferably comprises strips which are glued to one another and whose fiber longitudinal direction is located approximately parallel to said bridge. In this case, the strips are preferably formed by wooden slats with a width of about 8 to 12 cm.
The aforementioned at least one bridge is an elongate main bridge, normally curved approximately in an S shape, which, in the case of previously known embodiments, generally extends diagonally over part of the soundboard and is adhesively bonded thereto. According to the invention, provision can additionally be made for said bridge to be fixed to the soundboard by means of a bridge tongue in each of the two said connection regions, the bridge tongues preferably being chamfered end sections formed in one piece with said bridge. The tone of the sound body is not impaired by the extension of the bridge as far as the connection region [lacuna] the aforementioned edge region of the soundboard.
The lower backframe is preferably formed by a frame whose external dimensions correspond approximately to those of the upper backframe. In order to be able to absorb high forces with the minimum use of material, the lower backframe preferably has at least one first strut, which is located approximately parallel to the strings fastened to the cast frame. Since the dimensional changes of the soundboard are usually the greatest in this direction, the effect of this first strut, which is able to absorb considerable tensile forces, is a particularly effective saving on material. A number of first struts arranged alongside one another increase this effect. If these first struts are inserted into the frame of the lower backframe and are designed such that their length can be varied with respect to this frame, the setting of a prestress of the lower backframe, which can be transmitted to the upper backframe and to the soundboard, is possible.
A comparable effect is achieved when the lower backframe has at least one second strut, which is located approximately parallel to said bridge. Here too, the effect is increased by the arrangement of a number of parallel second struts. If this second strut is inserted into the frame of the lower backframe and is designed such that its length can be varied with respect to this frame, a prestress can thereby be imparted to the aforementioned bridge. This means that the tone of the sound body can be varied or set in a simple way. For the purpose of setting the length, the struts, which are led through drilled holes in the frame or eyelets on the frame, are provided with threaded sections. By means of lock nuts, the desired length on the lower backframe can then be set continuously.
It is advantageous if the lower backframe has a flat, preferably ground upper
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