EP1630785B1 - Soundboard with fibre reinforced composite material for stringed instruments - Google Patents

Description

The invention relates to a resonant panel in fiber composite construction for acoustic musical instruments, consisting of at least three, each extending over a substantial part of the entire surface of the resonant plate layers, of which the two outer layers each embedded a layer of embedded in a carrier material and in the respective Layer containing parallel longitudinal fibers and the middle layer has a lower density than the two outer layers.

In recent times, attempts have been made to produce the resonance plates of acoustic musical instruments in fiber composite construction. Structures in fiber composite construction generally consist of long fibers which are oriented in certain directions, and a carrier material, which is generally a thermosetting or thermoplastic plastic, in particular an epoxy resin system.

The previous efforts to produce resonant panels in fiber composite construction consistently aim to copy the acoustic properties of the wood to be replaced as possible. That's how it shows US 4,353,862 A a guitars resonance plate, in which a fiberglass impregnated with polyester resin is applied to a layer of wood. In this case, the weft threads of the glass fiber fabric run approximately parallel and the warp threads of the glass fiber fabric approximately transversely to the grain of the wood layer.

The EP 0 433 430 A relates to the resonating plate of a stringed instrument in which a number of layers are superimposed, each consisting of long fibers embedded in a carrier material. In this case, the long fibers run parallel to one another in each layer, while the fiber directions of the individual layers deviate from one another. The top and bottom cover layers of this resonator plate are made of wood to reduce the overall density of the resonator plate and achieve the desired damping characteristics.

By the US Pat. No. 3,880,040 Furthermore, a (corresponding to the preamble of claim 1) resonance plate of a guitar is known which has outer layers preferably extending parallel to the longitudinal direction long fibers and inner layers of wood.

The US 4,348,933 further shows a three-layered resonant plate of a keyboard instrument, wherein the two outer layers embedded in a support material, parallel to each other long fibers and the middle layer consists of wood whose fibers at an angle between 30 and 90 ° to stiffening ribs and under a Angle between 30 and 90 ° relative to the fibers of the two outer layers.

Subject of the EP 1 182 642 A Further, it is a three-layer resonant plate in which the middle layer forms a lower density core plate, while the two outer layers have a fiber coating of long fibers embedded in a substrate. Here, the fiber coating is single-layered and at the same time designed to be multidirectional.

Finally, out of the DE 21 15 119 B a resonance plate known whose core consists of foamed plastic and is covered on both sides by wooden reinforcing parts. The grain directions of these wooden reinforcing parts extend in the longitudinal or transverse direction of the resonance plate, so intersect at right angles.

The invention has for its object to develop a resonant plate of the type mentioned in that they on the one hand compared to excellent, manufactured in traditional construction solid wood resonance panels significantly improved acoustic quality, especially while maintaining the usual and desirable timbre of a solid wood Resonant plate has a much higher sound power, but that on the other hand in the Compared to known resonance panels in fiber composite construction characterized by a simplified manufacturing.

This object is achieved in a resonant plate of the type mentioned in that the long fibers of the two outer layers - based on an imaginary vertical longitudinal center plane of the resonance plate - under differing direction and / or amount of acute angles between 2 and 25 degrees, preferably between 3 and 8 degrees, are lost.
In particular, the invention is based on the following considerations and experiments:

The cause of the sound radiation of the instrument are the natural vibrations. Their frequencies and forms of vibration decisively determine the timbre of the instrument. The formation of the natural vibrations depends essentially on the anisotropy of the material of the resonant plate, i. from the directional dependence of its physical properties. Thus, the anisotropy of the sound velocity of the longitudinal waves, i. the ratio of the speed of sound in the longitudinal direction to the speed of sound in the transverse direction of the fiber path, in spruce wood at about 4: 1. In order to achieve the same timbre on a resonance panel in fiber composite construction as in a good wood resonance panel, it is therefore important to achieve the said anisotropy.

Attempts have now been made to produce the required anisotropy by crosswise positioning a plurality of unidirectional fiber scrims at certain angles on both sides of the core plate. The angles which the fiber longitudinal directions of the different fiber layers assume relative to one another determine the ratio of longitudinal to transverse stiffness.

However, these conventional approaches fail to recognize an acoustically significant property of resonant plates. Decisive for the sound radiation of the instrument are the vibration levels of the natural vibrations. They are dependent on the oscillating mass of the resonance plate, which must be as small as possible, if an effective sound radiation is to be achieved. Since now in fiber composite sandwich constructions by far the greater part of the total mass is not supplied by the core plate, but by the fiber coating, the total mass depends mainly on the number of necessary fiber coatings. It can be shown that even with the use of only two unidirectional fiber coatings per core plate side no acoustic advantages over the conventional spruce resonance plate can be achieved.

The execution according to the EP 1182642 A solves the above-mentioned problem in that the fiber coating provided on one or both sides of the core plate is single-layered and at the same time multidirectional. Due to the single-layer design of the fiber coating, the desired low mass of the resonance plate is achieved and the multidirectional fiber coating the individual areas of the resonance plate receive the desired ratio of longitudinal to transverse stiffness.

The solution according to the present invention now goes a substantial step beyond the above-described prior proposal. It is based on the knowledge that - contrary to the previous opinion of the experts - it is quite possible to achieve the required anisotropy of the sound velocity of the longitudinal waves using a single long fiber layer (with long fibers arranged parallel within the layer) on both sides of a core plate. if in this case the fibers of the two layers extend at acute angles (with reference to an imaginary vertical longitudinal center plane of the resonance plate). The single layer of the two layers allows the necessary for achieving the desired high sound radiation low mass of the resonance plate.

Advantageous embodiments of the invention are the subject of the dependent claims and will be explained in connection with the description of some illustrated in FIGS. 1 to 7b of the drawings embodiments.

1 shows a first embodiment of a resonator plate according to the invention in a schematic, exploded view of its three layers 1, 2 and 3. The middle layer 1, which forms a core plate, has a lower density than the two outer layers 2 and 3. It may consist of wood or hard foam and contain long fibers which extend parallel to an imaginary vertical longitudinal center plane 4 of the resonance plate.

The two outer layers 2 and 3 each contain a layer of long fibers embedded in a support material (e.g., epoxy resin) which are parallel to each other within the respective layer. With the imaginary vertical longitudinal center plane 4 of the resonance plate, the long fibers of the layers 2 and 3 form opposite angles 5 and 6 in opposite directions: the long fibers of the upper layer 2 are counterclockwise and the long fibers of the lower layer 3 are offset clockwise from the vertical longitudinal center plane 4 ,

If one thinks of a horizontal longitudinal center plane of the resonance plate (thus with symmetrical construction of the resonance plate approximately the horizontal center plane of the middle layer 1), then the two outer layers 2 and 3 lie above or below this imaginary horizontal longitudinal center plane, whereby their long fibers - related to the imaginary vertical longitudinal center plane 4 of the resonance plate - run at different angles 5 and 6, respectively.

In the embodiment of FIG. 2, too, the long fibers of the two outer layers 2 and 3 embedded in a carrier material run in opposing and different-sized angles 5 and 6 (relative to the vertical longitudinal center plane 4 of the resonance plate). Unlike in the embodiment of FIG. 1, in the resonant plate of FIG. 2, the long fibers of the middle layer 1 are not parallel to the vertical longitudinal center plane 4, but are rotated by an angle 7 in the clockwise direction with respect to this plane.

In the variant shown in Fig. 3, the long fibers of the two outer layers 2 and 3 extend at angles 5 and 6, both rotated counterclockwise relative to the vertical longitudinal center plane 4 and are only slightly different in size, while the long fibers of the middle layer 1 are offset by an angle 7 in a clockwise direction relative to the plane 4. If one imagines a horizontal longitudinal median plane laid through the resonance plate (which with symmetrical structure of the three layers with the horizontal center plane of the middle layer coincides), so run the long fibers of the upper layer 2 at a different angle 5 than the long fibers in the lying below the imaginary horizontal longitudinal center plane region of the middle layer 1 (angle 7). A corresponding consideration applies to the course of the long fibers in the lower layer 3 (angle 6) and the long fibers in the lying over the imaginary horizontal longitudinal center plane region of the middle layer 1 (angle 7).

The embodiment of FIG. 4, in comparison to the variant of FIG. 1 has two peculiarities: The portion of the resonator plate, which is intended to support a vise and is therefore subject to increased pressure, is by an additional layer 9 of in a Reinforced backing material embedded fibers. Suitably, the layers 9 are mounted on the underside of the upper layer 2 and on the (the vise facing) underside of the lower layer 3. The fiber direction of the layers 9 is in each case opposite to the fiber direction of the layers 2 and 3.

The second special feature of the embodiment according to FIG. 4 is that subareas 10 above and below the middle layer 1 forming the core plate have no fiber coating. However, the layers 2 and 3 consisting of long fibers and carrier material extend over a substantial part of the entire surface of the resonance plate.

In the embodiment of the invention shown in FIG. 5, the middle layer 1 is formed as a non-long fiber reinforced core plate. The long fibers in the two outer layers 2 and 3 run here (as in the variant of FIG. 1) in opposite directions to the vertical longitudinal center plane 4 twisted, different sized angles 5 and 6 respectively.

Finally, FIG. 6 shows an embodiment in which the long fibers of the two outer layers 2 and 3 embedded in a carrier material are in the same direction but at different angles 5 and 6, respectively, with respect to the vertical one Longitudinal center plane 4 of the resonance plate are offset. The middle layer 1 contains long fibers that run parallel to the longitudinal center plane 4. Instead, however, for example, a middle layer 1 can be used without long fibers.

In embodiments according to FIGS. 1, 4 and 5, in which the long fibers of the two outer layers extend at opposite angles, these angles can be between 2 and 25 degrees, preferably between 3 and 8 degrees.

In an embodiment according to FIG. 3, in which the long fibers of the two outer layers are offset in one direction and the long fibers of the middle layer are offset in the other direction with respect to the vertical longitudinal center plane, the equidirectional angle of the two outer layers can be between 2 and 25 degrees , preferably between 3 and 8 degrees, and the opposing angles of the middle layer are 1.2 to 2.5 times the value of the former angle.

Finally, a further expedient embodiment of the invention will be explained with reference to FIGS. 7a, 7b. It relates to a measure that relates primarily to the stability of the resonator plate, but also has an influence on the anisotropy of the speed of sound of the longitudinal waves and is therefore taken into account appropriately in choosing the angle of the long fibers.

7a, 7b, the resonant plate consists of a core plate 11 and two outer layers 12, 13. These two outer layers, as explained with reference to FIGS. 1 to 6, each contain a layer of in a carrier material embedded long fibers, wherein in each layer, the long fibers each extend parallel to each other, while the long fibers of the two layers have different angles.

The core plate 11 is formed in this embodiment so that it has a vertical longitudinal center plane 25 enclosing middle zone of increased longitudinal compressive strength. This zone is shown at the Embodiment formed by a strip 22 high longitudinal compressive strength, which preferably consists of spruce wood. The side of this central zone of the core plate 11 is followed by two outer strips 23, which consist of a material of low density (and correspondingly low compressive strength), preferably made of balsa wood or hard foam.

This construction of the core plate ensures that in particular the two end regions 14, 15 of the central zone of the resonance plate, which must absorb the high compressive forces F, -F generated by the string tension of the instrument, have the necessary longitudinal compressive strength and not under the effect of these forces can buckle.

The high compressive strength strip 22 suitably occupies a width of 10 to 25%, preferably 14 to 20%, of the overall width of the contour of the resonance plate. Depending on the selected dimensions and strength properties of the strips 22, 23 results in a different contribution of the core plate 11 to the anisotropy of the resonance plate. This contribution should be considered when choosing the angles of the long fibers of the outer layers 12, 13 to set the desired anisotropy.

Claims (10)

1. Soundboard of composite fibre material construction for acoustic musical instruments, which contains three sheets (1, 2, 3) which each extend over a substantial part of the entire surface of the soundboard, of which the two outer sheets (2, 3) each contain a layer of long fibres embedded in a carrier material and the middle sheet (1) has a lower density than the two outer sheets (2, 3), characterised in that the long fibres of the two outer sheets (2, 3) - relative to a perpendicular longitudinal central plane (4) of the soundboard - extend at acute angles (5, 6) between 2 and 25°, preferably between 3 and 8°, which deviate from one another in terms of direction and/or magnitude.
2. Soundboard as claimed in Claim 1, in which the long fibres of the two outer sheets (2, 3) extend at opposing acute angles (5, 6) - relative to the perpendicular longitudinal central plane (4) of the soundboard.
3. Soundboard as claimed in Claim 1, in which the long fibres of the two outer sheets (2, 3) extend in the same direction but at different angles (5, 6) - relative to the perpendicular longitudinal central plane (4) of the soundboard.
4. Soundboard as claimed in Claim 1, in which the middle sheet (1) is constructed as a core plate which is not reinforced by long fibres.
5. Soundboard as claimed in Claim 1, in which the middle sheet (1) also contains a layer of long fibres embedded in a carrier material.
6. Soundboard as claimed in Claims 2 and 5, in which the long fibres of the middle sheet (1) extend at angle which lies between the opposing acute angles (5, 6) of the two outer sheets (2, 3), preferably parallel to the vertical longitudinal central plane (4) of the soundboard.
7. Soundboard as claimed in Claims 2 and 5, in which the long fibres of the two outer sheets (2, 3) extend at opposing acute angles (5, 6) of different sizes - relative to the perpendicular longitudinal central plane of the soundboard - and the long fibres of the middle sheet (1) extend at an angle (7) which is in the same direction as the smaller (6) of the two opposing angles (5, 6).
8. Soundboard as claimed in Claims 3 and 5, in which the long fibres of the two outer sheets (2, 3) extend at angles (5, 6) in the same direction - relative to an imaginary vertical longitudinal central plane (4) of the soundboard - and the long fibres of the middle sheet (19) extend at an opposing angle (7).
9. Soundboard as claimed in Claim 1, in which individual part-regions of the soundboard, preferably a part-region of the soundboard which is intended for support of a soundpost, are reinforced by an additional layer (9) of fibres embedded in a carrier material.
10. Soundboard as claimed in Claim 1, in which a part of the soundboard which includes the two end regions (14, 15) of a central zone of the soundboard (11) has a longitudinal compression strength which is greater than the longitudinal compression strength of the remaining part of the soundboard, in particular of the two outer zones of the soundboard laterally adjoining the central zone.

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