Silent stringed musical instrument with piezo-electric pickup

Abstract: A silent violin has a body structure (1/2/3/4a-4d), strings (5a-5d) stretched over the body, a bridge (6) held in contact with the strings and having two leg portions (6a/6b) supported by the body structure and a piezoelectric converting unit (7a) inserted between the bridge and the body, although the piezoelectric converting unit is located under the two leg portions, the piezoelectric converting unit converts vibrations propagated from the strings through one of the two leg portions to an electric signal (S2), and an electric system faithfully produces electric sounds to be expected from the electric signal without any interference between the vibrations propagated through the two leg portions.

Description: This invention relates to a stringed musical instrument and, more particularly, to a silent stringed musical instrument equipped with pickup for converting vibrations of strings to an electric signal. DESCRIPTION OF THE RELATED ART A typical example of the electric stringed musical instrument is an electric guitar. A neck projects from a solid body, and strings are stretched over the solid body. An electromagnetic pickup is provided under the strings, and the electromagnetic pickup converts the vibrations of the associated string to an electric signal. The electric signal is supplied to a filter/amplifier circuit, and a speaker produces an electric guitar sound from the electric signal. On the other hand, an acoustic guitar has a sound chamber under the strings, and the sound chamber resonates with the vibrations of the strings. For this reason, the acoustic guitar sounds are radiated from the sound chamber, and give unique impression different from the electric guitar sounds to listener. Similarly, a bowed stringed musical instrument such as violin produces an acoustic violin sound through resonance of the sound chamber with the vibrations of each string, and the acoustic violin sound is loud. However, the acoustic violin disturbs the neighbor. For this reason, a silent violin has been developed. The silent violin has a pickup under the strings. When a player bows the silent violin, the pickup produces an electric signal from the vibrations of the strings, and the electric signal is amplified and filtered. If a player hears the electric sounds from a headphone, he can practice the violin without disturbance to the neighbor. Another silent violin is associated with an electronic sound generating system. A pickup also converts the vibrations of the strings to an analog signal, and a processor extracts pieces of music information from the analog signal. The pieces of music information are formatted into a music data code representative of pitches/velocity of a sound to be produced. The music data codes are supplied to a tone generator, and the tone generator produces an audio signal from the music data codes. The tone generator imparts. an envelope of acoustic violin sound or other acoustic musical instrument to the audio signal, and a sound system produces electronic sounds from the audio signal. Thus, either electric or electronic stringed musical instrument requires a pickup for producing an electric signal. As described hereinbefore, the acoustic stringed musical instruments such as an acoustic guitar and an acoustic violin produce acoustic guitar sounds and acoustic violin sounds from the resonant chambers defined in the bodies. A bridge is inserted between the body and the strings, and the vibrations are propagated from the strings through the bridge to the resonant chamber of the body. If the pickup directly detects the vibrations of the string, the electric/electronic sounds produced from the analog signal are different from the sounds to be expected, because the bridge serves as a kind of filter. For this reason, the silent violin already proposed is equipped with a pickup embedded in a bracket corresponding to the soundboard of an acoustic violin, and the bracket is located under the strings. The bridge of an acoustic violin usually has two leg portions, and the two leg portions are held in contact with the soundboard. The bridge of the silent violin has a similar configuration, and the two legs are held in contact with the bracket. The vibrations are propagated from a string through the two legs to the pickup. However, the electric/electronic sounds are sometimes weakened without damping the vibrations of the strings. Thus, the prior art silent stringed musical instrument has a problem in the stability. WO 91 15844 A discloses an electronic upright bass which produces sound closely approximating the sound produced by an acoustic upright bass. The bass includes a body defining compartments and slots placing the compartments in communication with the exterior of the body. The compartments and slots permit the bass to operate like the top table and portals of an acoustic upright bass. Piezoelectric transducers are located beneath the feet of the bridge and, thus, convert the authentic vibration of the body to electrical signals for reproduction through an amplifier and speakers. Magnetic pickups mounted beneath the strings of the instrument provide the component of the sound corresponding to the pure clean vibration of the strings. Moreover, attention is drawn to US-A-4 147 084, WO 92 17879 A, US-A-5 463 185, and US-A-4 632 002. SUMMARY OF THE INVENTION It is therefore an important object of the present invention to provide a silent stringed musical instrument, which faithfully produces electric/electronic sounds. The present inventor contemplated the problem inherent in the prior art silent stringed musical instrument, and noticed that the vibrations of one leg sometimes became anti-phase to the other leg at a certain frequency. The vibrations of one leg canceled the vibrations of the other leg, and the unintentional change of loudness was due to the cancellation. The present inventor held the pickup to one of the two legs. One of the legs was directly held in contact with the bracket, and the other leg was held in contact with the bracket through the pickup. In this instance, the pickup changed the frequency characteristics of the bridge, and a problem was encountered in the fidelity of the electric/electronic sound. To accomplish the object, the present invention proposes to convert vibrations of strings to an electric signal through a pickup inserted between two legs of a bridge and a body structure but detecting the vibrations propagated through one of the two legs. In accordance with one aspect of the present invention, there is provided a silent stringed musical instrument comprising a body structure including a body having an upper surface and a bridge having a supporting bridge portion and two leg portions projecting from the supporting bridge portion to the upper surface, at least one string stretched over the upper surface of the body and held in contact with the supporting bridge portion so as to propagate vibrations thereto, and a vibration-to-electric signal converter located between the two leg portions and the body and converting the vibrations propagated through one of the two leg portions to an electric signal, and does not convert vibrations propagated through the other one of said two by portions to an electric signal. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the silent stringed musical instrument will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which: Fig 1 is a plan view showing a silent violin according to the present invention, Fig 2 is a cross sectional view showing a pickup incorporated in the silent violin according to the present invention, Fig. 3 is a cross sectional view from a different angle showing the pickup embedded in a bracket, Fig. 4 is a partially cut-away front view showing the connection between a piezoelectric converting unit and a coaxial cable incorporated in the silent violin; Fig. 5 is a cross sectional view showing a substrate incorporated in the piezoelectric converting unit; Fig. 6 is a bottom view showing the layout of the lower surface of the substrate; Fig 7 is a plan view showing a piezoelectric element incorporated in the piezoelectric converting unit, Fig. 8 is a cross sectional view showing the piezoelectric element, Fig. 9 is a plan view showing a ground electrode incorporated in the piezoelectric converting unit, and Fig. 10 is a development view showing a shield layer for the piezoelectric converting unit DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to figure 1 of the drawings, a silent violin embodying the present invention comprises a body 1, a fingerboard 2 projecting from the body 1 and a string holder 3 attached to the body 1. The body 1 is solid, and no resonant chamber is formed in the body 1. The body I may be formed of wooden pieces or synthetic resin pieces. A suitable damping member may be inserted in the body 1 so as to damp the vibrations propagated to the body. The body 1 has a configuration like a half of the sound chamber of an acoustic violin, and the other half of the sound chamber is replaced with a chin rest 1a. While a violinist is playing a tune, he puts his chin on the chin rest 1a, and bows the silent violin. The fingerboard 2 has a peg box 2a, and the peg box 2a defines an inner space. The silent violin further comprises four peg screws 4a, 4b, 4c and 4d and four strings 5a, 5b, 5c and 5d. The peg screws 4a to 4d are screwed into the peg box 2a, and project the leading end portions thereof into the inner space. The four strings 5a to 5d are respectively wound on the peg screws 4a to 4d, and are anchored at the other ends thereof to the string holder 3. Thus, the strings 5a to 5d are stretched between the peg screws 4a to 4d and the string holder 3. The silent violin further comprises a bridge 6 attached to the body 1 under the strings 5a to 5d, an electric system 7 for producing an audio signal S1 from the vibrations of the string 5a/5b/5c/5d and a sound system 8 for producing electric sounds from the audio signal S1. The electric system 7 includes a pickup 7a described hereinlater in detail and a filter/amplifier circuit 7b. The bridge 6 is held in contact with the strings 5a to 5d, and propagates vibrations of the strings 5a to 5d to the pickup 7a. The pickup 7a converts the vibrations of the strings 5a to 5d to an analog signal S2, and the analog signal S2 is supplied from the pickup 7a to the filter/amplifier circuit 7b. The filter/amplifier circuit 7b filters and amplifies the audio signal S1, and supplies the audio signal S1 to the sound system 8. The sound system 8 produces the electric sounds. The sound system 8 may have a headphone Figs 2 and 3 illustrates the bridge 6 incorporated in the silent violin The bridge 6 is provided between the body 1 and the strings 5a to 5d, and a pickup 7a is inserted between the leg portions 6a and 6b of the bridge 6. The bridge 6 is implemented by a thin wooden plate, and has supporting bridge portion 6c and the leg portions 6a/6b. The strings 5a to 5d are received in grooves of the supporting bridge portion 6c, and the bridge 6 imparts tension to the strings 5a to 5d. The leg portions 6a/6b project from the both side portions of the supporting bridge portion 6c, and the leg portions 6c and the pickup 7a are fixed to the body 1. In this instance, a piezoelectric converting unit serves as the pickup 7a. While the strings 5a to 5d are vibrating, the vibrations are firstly propagated to the supporting bridge portion 6c, and pass the leg portions 6a/6b. The vibrations reach the pickup 7a, and the pickup 7a converts the vibrations to the electric signal S2. A through-hole 1a is formed in the body 1, and a lower surface of the pickup 7a is exposed to the through-hole 1a A coaxial cable 7c is inserted into the through-hole 1a, and is connected to the piezoelectric converting unit 7a as shown in figure 4. The piezoelectric converting unit 7a includes a substrate 7d, a piezoelectric element 7e bonded to the lower surface of the substrate 7d and a ground electrode 7f bonded to the lower surface of the piezoelectric element 7e. The substrate 7d, the piezoelectric element 7e and the ground electrode 7f are equal in length and width to one another, and are shaped into a rectangular configuration as shown in figures 5 to 9. The substrate 7d is formed of insulating material such as, for example, glass epoxy resin, and is uniform in thickness. A circular aperture 7g is formed in the substrate 7d, and is located on a virtual center line perpendicular to the longitudinal direction of the substrate 7d. The circular aperture 7g penetrates through the substrate 7d in a direction of thickness, and is exposed to the upper surface and the lower surface of the substrate 7d. Conductive strips 7h and 7j are formed on the lower surface of the substrate 7d, and are, by way of example, formed of copper or nickel silver. The conductive strips 7h and 7j are uniform in thickness, and the inner surface defining the circular aperture 7g is covered with the conductive strip 7h. Partition region 7k spaces the conductive strips 7h/7j from each other, and, accordingly, the conductive strips 7h and 7j are electrically isolated from each other. The partition region 7k extends in the direction of width of the substrate, and is slightly spaced from the aperture 7g. The conductive strips 7h/7j may be patterned from a conductive strip by using an etching technique. The piezoelectric element 7e is, by way of example, formed of polyvinylidene fluoride, and is uniform in thickness. A circular aperture 7m is formed in the piezoelectric element 7e, and is also deviated from the virtual center line perpendicular to the longitudinal direction of the piezoelectric element 7d. Conductive strips 7n/7o of copper or nickel silver are formed on the upper surface of the piezoelectric element 7d, and are uniform in thickness. A partition region 7p separates the conductive strips 7n/7o from each other, and, accordingly, the conductive strips 7n/7o are electrically isolated from each other. The partition region 7k is also deviated from the virtual center line. The conductive strips 7n/7o are patterned from a conductive layer by using an etching. The lower surface of the piezoelectric element 7e is covered with a conductive layer 7q of copper or nickel silver, and the conductive layer 7q is uniform in thickness. The inner surface defining the circular aperture 7m is not covered with any conductive material. The ground electrode 7f is formed of conductive material such as, for example, copper or nickel silver, and an elliptical aperture 7r is formed around the virtual center line perpendicular to the longitudinal direction of the ground electrode 7f. The substrate 7d, the piezoelectric element 7e and the ground electrode 7f are laminated on one another, and adhesive compound on a peripheral area 7s and the partition regions 7k/7p bonds the substrate 7d to the piezoelectric element 7e. For this reason, the conductive strips 7j/7h are held in contact with the conductive strips 7n/7o, and no adhesive compound is interposed between the conductive strips 7j/7h of the substrate 7d and the conductive strips 7n/7o of the piezoelectric element 7e. The adhesive compound is insulative, and the conductive strips 7j/7n are electrically isolated from the conductive strips 7h/7o. The piezoelectric element 7e is bonded to the ground electrode 7f by using conductive adhesive compound, and the conductive layer 7q is held on contact with the ground electrode 7f. If the insulating adhesive compound is used for the assemblage between the piezoelectric element 7e and the ground electrode 7f, the insulating adhesive compound may bond a part of the piezoelectric element 7e and a part of the ground electrode 7q without breakage of electric path therebetween. The circular aperture 7g is aligned with the circular aperture 7m, and the elliptical aperture 7r is overlapped with the circular apertures 7m/7g. The through-hole 1a is further aligned with the elliptical aperture 7r and the circular apertures 7m/7g. Turning back to figure 4, the coaxial cable 7c include conductive core line 7s coated with an inner PE insulating layer 7t and an outer conductive line 7u formed from a copper net and coated with an outer PVC insulating layer 7v. A leading end portion of the conductive core line 7s projects from the inner PE insulating layer 7t, and a leading end portion of the outer conductive line 7u is uncovered with the outer PVC insulating layer 7v. However, the inner PE insulating layer 7t electrically isolates the conductive core line 7s from the outer conductive line 7u. The conductive core line 7s is inserted into the circular aperture 7g, and is bonded to the substrate 7d by means of a solder piece 7w. The solder piece 7w is coated with epoxy resin 7x, and the epoxy resin 7x electrically isolates the solder piece 7w. The conductive core line 7s is held in contact with the conductive strip 7h covering the inner surface defining the circular aperture 7g, and is electrically connected to the conductive layer 7o through the conductive strip 7h. However, the conductive strips 7j/7n are electrically isolated from the conductive core line 7s. The inner PE insulating layer 7t is inserted into the circular aperture 7m, and the outer conductive line 7u is soldered to the ground electrode 7f. The outer conductive line 7u is held in contact with the conductive layer 7q in the elliptical aperture 7r. Thus, the outer conductive line 7u is electrically connected through the ground electrode 7f to the conductive layer 7q, and in never directly soldered to the conductive layer 7q. The reason why the outer conductive line 7u is indirectly connected to the conductive layer 7q is that the indirect connection prevents the piezoelectric material from destruction of the polarization during the soldering. The outer conductive line 7u is firstly soldered to the ground electrode 7f, and, thereafter, the ground electrode 7f is bonded to the piezoelectric element 7e. The laminated structure of the substrate 7d/ the piezoelectric element 7e/the ground electrode 7f, the outer conductive line 7u and the inner PE insulating layer 7t are coated with a shield tape 7y. The shield tape 7y is formed from an aluminum foil, and has a wide central portion 7ya, narrow end portions 7yb/7yc projecting from both sides of the wide central portion 7ya and tongue portions 7yd/7ye projecting from the narrow end portions 7yb/7yc, respectively. The shield tape 7y is bent along broken lines and dots-and-dash lines. A rectangular central area 7yf is brought into contact with the upper surface of the substrate 7d, and both rectangular side areas 7yg/7yh are bent toward the lower surface of the ground electrode 7f. The narrow end portions 7yb/7yc are also bent toward the lower surface of the ground electrode 7f, and either rectangular central area 7yg/7yh or the narrow end portion 7yb/7yc is directly held in contact with the lower surface of the ground electrode 7f. In this way, the rectangular side areas 7yg/7yh and the narrow end portions 7yb/7yc are laminated on the lower surface of the ground electrode 7f. The shield tape 7y further includes tongue portions 7yj/7yk projecting from the rectangular side areas 7yg/7yh, and the rectangular side areas 7yg/7yh are partially cut along lines 7ym/7yn and 7yo/7yp. The inner PE insulating layer 7t, the outer conductive line 7u and the outer PVC insulating layer 7v are covered with the tongue portions 7yd/7ye/7yj/7yk. Thus, the laminated structure of substrate/piezoelectric element/ground electrode 7d/7e/7f and the coaxial cable 7c are shielded in the shield tape 7y, and the shield tape 7c prevents the piezoelectric converting unit 7a from external electromagnetic wave. The connecting portion of the coaxial cable 7c is further covered with a protective tube 7za of heat shrinkable resin, and the protective tube prevents 7za the shield tape 7y from friction on the body 1. The coaxial cable 7c is branched at the other end into two end portions 7yr/7ys. The conductive core line 7s coated with an insulating layer form the end portion 7yr, and a connector 7yt is attached to the end portion 7yr. On the other hand, the conductive outer line 7u coated with an insulating layer form the other end portion 7ys, and another connector 7yu is attached to the other end portion 7ys. The connectors 7yt/7yu are connected to the filter/amplifier circuit 7b As will be understood from the foregoing description, the coaxial cable 7c electrically connects only the conductive strip 7o on the upper surface of the piezoelectric element 7e and the conductive layer 7q on the lower surface of the piezoelectric element 7e to the filter/amplifier circuit 7b, and the partition area 7p electrically isolates the conductive strip 7n on the upper surface of the piezoelectric element 7e from the conductive strip 7o. For this reason, the coaxial cable 7c provides the potential level on the upper surface of the right portion of the piezoelectric element 7e and the potential level on the lower surface of the piezoelectric element 7e to the filter/amplifier circuit 7b. The leg portions 6a and 6b are located over the conductive strips 7n and 7o, and the vibrations of strings 5a to 5d are propagated through the leg portions 6a/6b to the left portion of the piezoelectric element 7e and the right portion of the piezoelectric element 7e. Thus, although the vibrations are propagated to the entire upper surface of the piezoelectric element 7e, the filter/amplifier circuit 7b receives the electric signal S2 representative of the vibrations propagated through only the right portion of the piezoelectric element 7e. For this reason, the piezoelectric converting unit 7a equally affects the vibrations propagated through both leg portions 6a/6b; however, the piezoelectric converting unit 7e converts the vibrations propagated through the leg portion 6b to the electric signal S2 only. In this situation, even if one of the leg portions 6a/6b supplies the vibrations anti-phase to the vibrations propagated through the other leg portion, the electric signal S2 is never affected by the cancellation between the vibrations through the leg portions 6a/6b, and the electric system 7 faithfully produces the electric sounds to be expected. The vibrations pass through the piezoelectric converting unit 7a, and the piezoelectric converting unit 7a does not change the vibration characteristics of the bridge 6. Moreover, the coaxial cable 7c is integrated with the laminated structure of substrate 7d/piezoelectric element 7e/ground electrode 7f, and makes the assembling work and the repairing work easy. Modifications Although one particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. For example, the coaxial cable may be connected to an electronic sound generating system. In this instance, the electronic sound generating system extracts the pitch and the amplitude of the electric signal S2 after the amplification, and formats these pieces of music data information to a digital music data code. The digital music data codes are supplied to a tone generator, and the tone generator produces the audio signal S1 from the digital music data codes and another piece of music data information representative of a timbre of electronic sounds. The electric signal S1, the digital music data codes or the audio signal may be supplied to another electronic system or recorded into a data storage medium. The conductive layer 7q may be separated into two conductive strips as similar to the conductive strips 7n/7o. In this instance, the conductive strips 7n/7o may be not separated. When the conductive layer 7q is separated into two conductive strips without integration of the conductive strips 7n/7o, not only the vibrations through the leg portion 6a but also the vibrations through the other leg portion may be independently converted to two electric signals. One of the electric signals is mainly used in the filter/amplifier circuit 7b, and the other electric signal may be used for enhancement of control or in a trouble such as disconnection of the cable for the one electric signal. If the conductive strips 7j/7n are thin enough not to affect the vibration characteristics of the bridge 6 and the mechanical strength, only the conductive strips 7h/7o are formed on the substrate 7d and the piezoelectric element 7e, respectively. In this instance, the piezoelectric converting element 7a can detect the vibrations propagated through the leg portion 6b only. Even if one of the leg portions 6a/6b propagates the vibrations anti-phase of the vibrations of the other leg portion 6b/6a, the cancellation does not take place. The conductive strip 7q and the ground electrode 7f may be provided under one of the leg portions 6a/6b, only, so as to detect a potential difference between the conductive strip 7n/7o and the conductive strip 7q. Two piezoelectric converting units may be separately provided under the leg portions 6a/6b. In this instance, the electric signal may be supplied from one of the piezoelectric converting units to the filter/amplifier circuit 7b. Each of the piezoelectric converting units may have the laminated structure, i.e., the upper conductive strip/ the piezoelectric element/lower conductive strip. The above described changes may be applied to the piezoelectric converting units. For example, one of the upper and lower conductive strips may be deleted from one of the piezoelectric converting units. Two coaxial cables may be connected to the piezoelectric converting units, respectively, and the electric signals are used as described hereinbefore. The pickup may be incorporated in another kind of bowed stringed musical instrument such as, for example, a viola or a plucked stringed musical instrument such as guitar in so far as a bifurcated bridge is provided between the strings and the body.

Claims: A silent stringed musical instrument comprising a body structure (1/2/3/4a-4d/6) including a body (1) having an upper surface and a bridge (6) having a supporting bridge portion (6c) and two leg portions (6a/6b) projecting from said supporting bridge portion to said upper surface, at least one string (5a to 5d) stretched over said upper surface of said body and held in contact with said supporting bridge portion so as to propagate vibrations thereto, and a vibration-to-electric signal converter (7a) for converting said vibrations to an electric signal (S2), characterized in that said vibration-to-electric signal converter is located between said two leg portions (6a/6b) and said body (1), and converts said vibrations propagated through one of said two leg portions to said electric signal, and does not convert vibrations progagated through the other one of said two leg portions to an electric signal. The silent stringed musical instrument as set forth in claim 1, in which said vibration-to-electric signal converter includes a piezoelectric element (7e) formed of piezoelectric material and having a first surface and a second surface reverse to said first surface, said first surface having a first area provided under one of said two leg portions (6a/6b) and a second area provided under the other of said two leg portions (6b/6a), a first conductive layer (7n/7o) attached to said first surface, a second conductive layer (7q) attached to said second surface, and a first conductive line (7s) and a second conductive line (7u) electrically connected to said first conductive layer and said second conductive layer, respectively, in such a manner as to propagate said electric signal The silent stringed musical instrument as set forth in claim 2, in which said first conductive layer is separated into a first conductive strip (7n) located under one of said two leg portions and a second conductive strip (7o) located under the other of said two leg portions. The silent stringed musical instrument as set forth in claim 3, in which said vibration-to-electric signal converter further includes a substrate (7d) having a lower surface, a third conductive strip (7j) attached to said first conductive strip and located under one of said two leg portions, a fourth conductive strip (7h) attached to said second conductive strip, located under said other of said two leg portions and electrically isolated from said third conductive strip, and a conductive electrode (7f) connected to said second conductive layer. The silent stringed musical instrument as set forth in claim 4, in which said first conductive line (7s) is fixed to one of said first and second conductive strips (7n/7o), and said second conductive line is fixed to said conductive electrode (7f). The silent stringed musical instrument as set forth in claim 2, in which said piezoelectric material is polyvinylidene. The silent stringed musical instrument as set forth in claim 5, in which said vibration-to-electric signal converter further includes a shield layer (7y) covering said first and second conductive strips, said piezoelectric element, said conductive layer and the connection between said first conductive line and said one of said first and second conductive strips and the connection between said second conductive line and said conductive electrode.

Inventors: YAMADA TOSHIYA, YAMADA, TOSHIYA
Applicants: YAMAHA CORP, YAMAHA CORPORATION
Application year: 1997
Main classification: G10H3
IPC codes: G10H1, G10H3