1. Field of the Invention
The present invention is directed generally to musical instruments and, more particularly, to stringed musical instruments.
2. Description of the Related Art
Many stringed instruments, such as pianos, violins, double basses, and harpsichords have sound boards that help transfer vibrational energy of the strings to vibrational energy of the air as sound. One or more sound bridges in an instrument can be used, at least in part, as an intermediary between the strings and the sound board. Unfortunately, conventional approaches for coupling the strings to a sound bridge can have undesirable consequences such as overly burdensome forces being applied to the associated sound board which degrade longevity of the instrument and awkward departures in routing of the strings causing reduced sound fidelity.
Grand pianos have traditionally been designed for over a hundred years with about 230 strings tensioned and contained in a horizontal harp shaped cast metal frame. The cast frame being located on and stiffened by a wooden subframe, which in early pianos provided the only means of containing the loads arising from the tension in the strings. Demands for more powerful sound from pianos required adopting thicker heavier strings. To ensure these vibrated at the required pitch the thicker strings needed to be at higher tension. To contain the extra stresses the cast frame was introduced.
Operation of the pianos was effected by striking the strings from below by means of a series of 85 to 97 felt covered hammers to cause the strings to vibrate, each hammer striking a single, dual, tri-chord or occasionally quadric-chord groups of strings at the same tension and of the same geometry, thus sounding the same pitch. The vibrating strings have insufficient surface area to induce sound waves in the air surrounding the instrument, thus the vibrational energy is transferred via a bridge or rectangular strip of wood attached to a sound board to cause the sound board to vibrate in sympathy with the strings and thus generate sound waves in the surrounding air.
The manner of contact between the string and the top surface of the bridge highly influences the satisfactory transfer of energy in the string to the bridge and thence to the soundboard. In traditional pianos, contact between string and bridge top is maintained by two pins driven in at an angle of about 15 degrees to the vertical. These pins are so disposed that the string changes direction by about 15 degrees as it passes first clockwise then anti-clockwise round each pin in succession. The inclination of the pin plus the change of angle of the string as it passes the pin causes a resultant downward force on the string causing it to be held against the bridge top. In consequence, the string is displaced sideways as it traverses the bridge. The amount of that displacement is called the side draught. The geometry is normally arranged so that the string line on either side of the bridge is parallel. Side draught introduces an asymmetry of the string line which is considered to be a cause of loss of clarity and purity of the piano sound. The system imposes a twisting moment on the bridge and the pins are loaded cantilevers on the bridge. The sideways forces on the pins can cause cracking of the bridge top timber. If that occurs the pin becomes loose and the note pitch may change or become false.
The first bridge pin on the sounding length side of the bridge defines the termination of the sounding length of the string. It is critical that this sounding length should be identical whichever plane the string is vibrating in or the pitch of the note will vary as the plane of vibration of the string changes. For that reason the top of the bridge is typically carved so the contact point of the string with the bridge top coincides precisely with the centre of the first bridge pin. If imprecise, this carving will permit the pitch of the string to vary according to the plane of vibration of the string. This syndrome is known as falseness. Bridge carving is a skilled and costly element of piano production.
The contact force between string and bridge top generated by the above-described disposition is inadequate to retain the string in contact with the bridge top under all conditions of operation of the piano, in particular the string can part from the bridge top when struck forcefully from below. This destroys the contact path for energy transfer from string to bridge and sound power is lost. Additional contact force is traditionally developed by arranging that each string as it traverses the bridge changes angle by about 2 to 5 degrees in the vertical plane. This change of angle produces a downwards force holding the string against the bridge top. The super position of all the forces from the many strings in a piano results in a total down bearing force of around a half ton in a typical piano. That force is contained and supported by the soundboard. The soundboard must be designed to resist this load without deterioration or collapse for the life of the piano. This implies stiffening and strengthening of the soundboard which may compromise its performance as a vibrating member generating sound waves in the surrounding air. In practice the problem of soundboard collapse and loss of down bearing is common in pianos and is the most prevalent reason for the deterioration of their power and sound quality over a period of time.
It is known that piano strings not only vibrate laterally, but also vibrate longitudinally, albeit at a far higher frequency. In the traditional concept described above for retention of the strings against the bridge top, a proportion of the length of the string lies on and is held against the bridge top. Any longitudinal vibrational movement in the string is thus effectively damped by friction, and thereby the concept causes loss of energy from the string and consequent diminution of the vibrational energy available for producing sound waves.
It is long established practice for the strings of pianos to pass from tuning pin via a fixed point normally on the frame which defines the beginning of the sounding length, and thence over the bridge with which the string is held in contact and through which the vibration energy in the string is transferred to a sounding board. In a grand piano the string is set in vibration by striking it from beneath by a felt covered hammer. The blow tends to lift the string and thus imparts a separating force between the string and the bridge cap. It is therefore necessary to provide a downwards force on the string, called down bearing, to ensure it remains in contact with the bridge cap or vibration energy transfer would be interrupted if the string parts from the bridge cap. Since the surface area of the strings is inadequate to excite significant sound waves in the air surrounding the instrument, no substantial sound would be heard unless the sound board itself receives the vibration energy input.
Two principal means are conventionally used to keep the string in firm contact with the bridge cap. The string changes angle in the vertical plane as it passes over the bridge cap. Thus it creates a downwards pressure onto the bridge cap. The change of angle is typically about 1 to 5 degrees and may be varied across the registers of the piano so that optimum contact force is developed for best sound in each register. Each string is located in the horizontal plane on the bridge by two bridge pins so positioned that the string is wrapped around each pin in the horizontal plane. The first pin defines the end of the sounding length. The two pins are so positioned that the string line is displaced sideways as it traverses the bridge. The string changes angle by about 15 degrees in the horizontal plane which is the amount of wrapping round the bridge pin. This change of angle combined with the tension in the string creates a lateral force against each bridge pin. The bridge pins are inserted in the bridge cap at about 15 to 20 degrees to the vertical at an angle which causes the string to tend to slide down the pin and thus press against the bridge cap. This develops an additional pressure contact between string and bridge cap without, in this case, causing a down bearing load on the soundboard.
This traditional system has consequent disadvantages that affect the performance and durability of the piano. The down bearing force resulting from the change of angle of the string in the vertical plane as it passes over the bridge from about 200 strings in a typical piano amounts to approximately a half ton. That force is applied constantly throughout the life of the piano to the sound board. The sound board must therefore be so designed to withstand the load for the life of the piano. This entails creating a sound board stronger and stiffer than would be ideal for optimum acoustic performance. If the designer creates a thin light sound board he can enhance the piano acoustic performance at the expense of a shorter instrument life. As the crowning of the soundboard sinks with time due to this load, the contact force between strings and sound board decreases and the efficiency of the transfer of vibration energy from strings to sound board becomes compromised. The piano as a consequence loses its acoustic performance. In extreme cases the string may part from the bridge cap when the hammer strikes and then buzzing sounds develop.
The downwards loads from the strings to the sound board may also compromise the freedom of the soundboard to respond to the vibrational energy from the strings and this may result in degraded sound volume and quality, the duration and the harmonic content of the sound developed is spoiled. It is for example well established that down bearing load on the bass bridge of a piano will suppress the performance of the middle treble range of the registers because the bass bridge is located near the soundboard zone that needs to respond to the middle treble register frequencies.
Because the strings are struck from underneath it is found that with forceful playing they tend to slide up the inclination of the bridge pins and be held away from firm contact with the bridge cap by friction between the pin and the string. Piano technicians will need to tap them down again after vigorous playing or the sound performance will suffer.
The bridge pins are inserted in the bridge by drilling inclined pilot holes of controlled depth. It is critically important that each pin is firmly located and the hole into which it is fitted is not bell mouthed which would allow the pin to flex at its upper end. An insecure pin may result in a badly defined length of the sounding portion of the string. In that case each string may produce a varying frequency known as a false note.
The two sets of bridge pins are mounted about 20 mm apart. Because of the wrap angle round the pins the string line is displaced sideways where the string traverses the bridge. In consequence of this asymmetry it is found that a piano string that is initially excited to vibrate in the vertical plane will begin to develop a component of vibration in the horizontal plane. The plane of vibration rotates with time. The quality and volume of sound when the string is vibrating horizontally is degraded and the overall sound quality of the instrument may be compromised by a weak or variable note quality.
Where the string traverses the bridge cap it lies in contact with the bridge cap surface. When the string is excited by striking with the hammer, most of the vibration energy is in transverse movement, but a proportion also appears as longitudinal vibration. Longitudinal rubbing between the string and the bridge cap results in loss of vibration energy in the string and reduction in the efficiency of use of the available vibrational energy produced in the string.
As will be discussed in greater detail, a string-bridge interface system including a plurality of string-bridge interface units is disclosed herein to provide coupling between the strings and one or more sound bridges, which are further coupled to the sound board of a musical instrument. Such coupling provided by the interface units can allow benefits such as significantly reduced loading of the sound board and more direct routing of the strings.
Aspects include retaining the strings in grand pianos against the bridge top, without need for conventional uncompensated down bearing of the string on the bridge top or for the use of bridge pins and sidedraught. In consequence, the sound board can have greater freedom to respond to vibrational input from the strings and can be designed to enhance acoustic response to the vibrational energy input via the sound bridge. Aspects can also reduce or eliminate the need for bridge carving. Side draught can be reduced or eliminated, and its disadvantage of introducing loss of clarity and purity of sound can be reduced or eliminated. Aspects can reduce or eliminate twisting moment on the bridge and can reduce or eliminate risk of cracking around the bridge pins since bridge pins are not used in implementations.
It has been demonstrated that by removal of the bass strings from a traditional design piano, the performance in terms of sound power and sustain of the middle registers of the piano were substantially improved. This was attributed to the freeing of the response of the soundboard resulting from removal of down bearing loads from the bass bridge. Aspects permit little or no conventional uncompensated down bearing on the bass bridge of a piano, which similarly can afford enhancement of the middle registers of a piano.
The continuous subjection of sound boards of traditional design pianos to down bearing forces inevitably and ultimately leads to collapse of the soundboard and consequent loss of effective contact between strings and sound bridge top. At that point the piano loses its performance and sound quality. Effectively useful life of a piano is ended unless skill and money is expended on renovation which usually is difficult to justify. Aspects reduce or eliminate this cause of degradation of piano performance.
Greatly minimized or absent conventional uncompensated down bearing load on the bridge that would otherwise be transferred onto the sound board opens the possibility of using materials other than wood for soundboard construction. In particular, sound boards of carbon fiber may be used. General observations have suggested that carbon fiber sound boards in thicknesses more than 4 mm tend to produce harsh sound in a piano. Aspects can enable carbon fiber boards of approximately 2 mm thicknesses to be used in pianos. Such carbon fiber sound boards offer both enhanced sound power and resistance to adverse climatic conditions.
Aspects include provision for an adjustable amount of contact pressure between the string and the bridge cap without applying any sizeable or without applying any conventional uncompensated down bearing load on the bridge and thus not transferring such loading to the sound board. Strings pass first over an angulated edge of a contact member, which is retained in position in a horizontal plane by location in a slot of a support member base. The angulated edge is however free to slidably move in the vertical plane. Contact pressure is developed between the angulated edge and a bridge by change of angle in the string line in the vertical plane as it passes over the angulated edge. The string is deflected downwards by a depressor member, or roller, located under a clip in the support member, enhanced bridge agraffe.
Downward deflection of the string by the roller causes the change of angle of the string as it passes over the angulated edge. The amount of string deflection and thus the load on the angulated edge can be adjusted by changing the diameter of the roller. Depression of the string by the roller causes an upwards force on the roller and therefore the support member, or agraffe body, which is substantially equal to the sum of the downward forces on the two angulated edges. It is therefore necessary to provide an equal and opposite force to retain the agraffe in contact with the bridge cap. This is done by a screw, which attaches the base of the support member to the bridge cap. The screw is secured in the bridge cap using an insert in the wood of the bridge cap to ensure the load. In some implementations, approximately 75 kgms can be held per string. In other implementations, other loading levels can be employed. Because the angulated edges are independent of the support member, the upwards pull of this screw on the bridge cap substantially or exactly equals the downwards force applied to the two angulated edges. There is, therefore, little or no resulting down bearing load on the bridge cap in these implementations to transfer to the sound board, as is present to transfer to the sound board with conventional approaches. Implementations provide adjustable height hitch pins in order that the plane of the strings on either side of the bridge cap is substantially the same to greatly reduce or eliminate the conventional uncompensated down bearing loading of the bridge, which would otherwise be transferred to the sound board as found in conventional approaches.
In practice, a small amount of down bearing force onto the sound bridge may sometimes be advantageous and may be used to match the note quality on adjacent notes. Use of height adjustable hitch pins allow for an introduction of this slight down bearing force. It is also found that by changing the roller diameter and thus the pressure between the angulated edge and the bridge cap, the note quality can also be modified advantageously.
Implementations include little or no side draught in the horizontal plane of the strings. In consequence, the strings have reduced tendency to develop a rotation of the plane of vibration. The clarity and purity of the note thus can be improved. It also can be observed that the symmetry of termination of the sounding length at surfaces in the same plane is advantageous in this respect. Further aspects include implementations that do not incorporate bridge pins. The tendency for development of falseness due to insecure bridge pins is thus eliminated.
Efficiency of conversion of finger energy to sound energy is an important matter in determining the acceptability of the artist/instrument interface of any piano or other stringed instrument. The efficiency of transfer of vibration energy is affected, inter alia, by the compliance of the contacting surfaces, the pressure of contact between the surfaces, and the area of the surfaces. Implementations allow for enhancement of the factors affecting energy transfer. Conventional practice of a wire lying on the comparatively soft wood surface of a bridge cap is not as favorable to efficient energy transfer. The relatively larger area of the base of the contact member aids significantly in energy transfer.
Experience has demonstrated that as the compliance of the contacting surfaces is reduced there is a tendency for enhancement of higher harmonics in the piano sound. Implementations incorporate a harmonic moderator pad under each contact member which is conveniently applied in some versions by a complete covering over the top surface of the bridge cap, to permit adjustment of the compliance for sound enhancement. This pad may be made of fiber, rubber, metal, wood, plastic, felt or any combination of these materials. As a note, the softer the material the less the enhancement of higher harmonics in the instrument sound and the lower the efficiency of transfer of vibration energy to the soundboard.
Implementations can be applied to other stringed instruments with bridge systems besides pianos including, for example, violins, double basses, or harpsichords. Such instruments are particularly adversely affected by conventional uncompensated down bearing loads from the bridge onto their resonance boxes.
A portion of a string-bridge interface system 100 is shown in
The support member 110 is shown to include a base portion 116 with a first opening 118 sized to receive and position the first contact member 112 and a second opening 119 sized to receive and position the second contact member 113. The base portion 116 includes a first edge 120 and a second edge 122 that straddle the strings 108 as the strings pass through the interface unit 102. The support member 110 includes a first side 124 extending substantially perpendicular to the base portion 116 from the first edge 120 of the base portion and having a first slot 126. The support member 110 includes a second side 128 extending substantially perpendicular to the base portion 116 from the second edge 122 of the base portion and having a second slot 130.
The depressor member 114 has a first head portion 132, a second head portion (not shown), and a body portion 134 extending therebetween. The second head portion has the same construction and appearance as the first head portion 132. The depressor member 114 is shown to have indentures 136 spaced apart and circumscribed in the body portion 134 of the depressor member. When the depressor member 114 is engaged with the support member 110, the first head portion 132 of the depressor member is engaged with the first slot 126 of the first side 124 of the support member and the second head portion of the depressor member is engaged with the second slot 130 of the second side 128 of the support member. The support member 110 is coupled to a sound board 138 as shown in
The depressor member 114 is shown engaged with the support member 110 with the strings 108 positioned to contact the first contact member 112 and the second contact member 113. The first slot 126 and second slot 130 of the support member 110, and the first head 132, second head, and the indentures 136 in the body portion 134 of the depressor member 114 are so sized and positioned that each of the indentures receives a different one of the strings 108 and the strings are deflected to a desired amount by the depressor member between where the strings contact the first contact member 112 and the second contact member 113 (better shown in
Further shown in
Implementations provide greater contact area between the first contact member 112 and the sound bridge 138 and the second contact member 113 and the sound bridge than a conventional string lying on the bridge surface. This greater contact area can improve efficiency of energy transfer from the strings 108 to the sound bridge 138 and thus reduce the finger energy needed to produce the sound power required by the artist. In consequence, the artist instrument interface can be improved and the artist can have improved control over the performance. Consequent conservation of energy can also enhance the length of time the note can be sustained. As shown, after passing under the depressor member 114, the string 108 then traverses the second contact member 113 on the back length of the scaling on toward the hitch pin 106. This can reduce or eliminate residual twisting, overturning, or moment that could otherwise be applied to the sound bridge 138.
The base portion 116 of the support member 110 is shown in
The support member 110 can be made in precision cast manganese bronze or other materials. The first contact member 112 and the second contact member 113 can be made of beryllium bronze or other materials. The depressor member 114 and the screw 142 can be made of 316 stainless steel or other materials. The thread on the screw 142 can be a special thread used for conventional agraffes in pianos.
Just as each of the first forces, F1, and the second forces, F2, may vary for each of the strings 108 due to various factors, each of the third forces, F3, may vary for each of the strings 108 for similar or other reasons. For each of the strings 108, the third force, F3, has a magnitude that is substantially the sum of magnitudes of the first force, F1, and the second force, F2 and the direction of the third force, F3, is substantially opposite to the direction of the first force, F1, and the second force, F2. As a consequence, for each of the strings 108, the third force, F3, substantially cancels potential loading forces resulting from the first force, F1, and the second force, F2, that might otherwise be imparted onto a sound board so coupled to the sound bridge 138 and thus the loading force of the first force F1 and second force F2 is thereby compensated by the third force F3.
Given this substantial cancelation or compensation of potential loading by the third force F3, the first force, F1, and the second force, F2, imparted through the first contact member 112 and the second contact member 113, respectively, by each of the strings 108 to the sound bridge 138 can be significant to the extent that efficient transfer of sound energy from each of the strings 108 to the sound bridge 138 and onto a sound board coupled to the sound bridge can be accomplished without danger of exposing the sound board to loading issues. Since the efficiency of transfer of energy from the string to the bridge top is dependent on that force being adequate, implementations can include effective contact forces in ranges of less than six times to greater than six times more than that developed in a conventional piano by conventional angled bridge pins and conventional down bearing.
As shown in
Furthermore, although each of the strings 108 are deflected in the first plane between the first contact member 112 and the second contact member 113, the first contact member and/or the respective tuning pin 104 can be sized, positioned, and/or height adjusted to maintain a desired elevation for the string in the first plane between the tuning pin 104 and the first contact member. Also, for each of the strings 108, the second contact member 113 and/or the respective hitch pin 106 can be sized, positioned, and/or height adjusted to maintain a desired elevation for the string in the first plane between the respective hitch pin and the second contact member.
Most pianos, including grand pianos, use a different set of a plurality of different ones of the strings 108 to produce a different note. For instance, many pianos use a different set of three different ones of the strings 108 for each of notes to be produced. Consequently, in implementations, each of the interface units 102 are coupled to a different set of different ones of the strings 108, shown in
As shown in
The second implementation is shown in
The support member 110 is placed adjacent the attenuating pad 156 and coupled to the attenuating pad, the bridge cap 154, and the sound bridge 138 with the screw 142 being received by the threaded insert 158. In the second implementation, the first contact member 112 and the second contact member 113 are positioned to contact the attenuating pad 156 by the support member 110.
As shown in
As shown in
As shown in
As shown in
Aspects include:
1. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a method comprising:
2. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a method comprising:
3. The method of aspect 2 wherein the first location defines a first speaking length for the piano and the second location defines a second speaking length for the piano.
4. The method of aspect 2 wherein the first portion of the first string force is the entire first string force, the second portion of the second string force is the entire second string force, and the third portion of the third string force is the entire third string force.
5. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a method comprising:
6. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a method comprising:
7. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a method comprising:
8. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
9. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
10. The system of aspect 9 wherein the first location defines a first speaking length for the piano and the second location defines a second speaking length for the piano.
11. The system of aspect 9 wherein the first portion of the first string force is the entire first string force, the second portion of the second string force is the entire second string force, and the third portion of the third string force is the entire third string force.
12. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
13. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
14. For coupling each of a plurality of strings with a sound bridge of a piano, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
15. For coupling with a plurality of strings of a piano and with a sound bridge, wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
16. The system of aspect 15 wherein the elongated body portion of the depressor member includes spaced indentures, each to receive a different one of the plurality of strings
17. The system of aspect 15 wherein the base portion has a screw hole to receive a screw for coupling with the surface
18. The system of aspect 17 wherein the system further comprises a threaded sleeve to couple with the sound bridge and to receive the screw.
19. The system of aspect 15 wherein the first contact member and second contact member each have an angulated edge for contact with the strings.
20. The system of aspect 15 wherein the first end and the second end of the body portion of the depressor member each have heads and the first side portion and the second side portion each has a slot to each receive one of the heads to couple the depressor member with the support member.
21. The system of aspect 15 further comprising an attenuating pad couplable to the sound bridge and sized and configured to receive the base portion of the support member thereon.
22. The system of aspect 16 further comprising height adjustable hitch pins.
23. The system of aspect 16 wherein the depressor member is a pin.
24. The system of aspect 16 wherein the depressor member is a roller.
25. For coupling with a plurality of strings of a piano and with a sound bridge, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
26. For coupling with a plurality of strings of a piano and with a sound bridge, wherein the piano includes a plurality of tuning pins and a plurality of hitch pins, each string being coupled to one of the plurality of hitch pins and to one of the plurality of tuning pins, and extending therebetween, and wherein the piano includes a sound board coupled to the sound bridge, a system comprising:
Number | Date | Country | |
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61148320 | Jan 2009 | US |