Patent Publication Number: US-8969702-B2

Title: Pickup unit of electric stringed instrument

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to pickup units of electric stringed instruments, which pick up vibrations of strings and convert them into electric signals. 
     The present application claims priority on Japanese Patent Application No. 2009-133812 (Filing Date: Jun. 3, 2009), the content of which is incorporated herein by reference. 
     2. Description of the Related Art 
     Conventionally, electric stringed instruments such as electric guitars and acoustic guitars have been equipped with pickup units that pick up vibrations of saddles supporting strings so as to generate electric signals. Conventionally-known examples of pickup units of electric stringed instruments are disclosed in Patent Documents 1 and 2, as follows:
         Patent Document 1: Japanese Patent Application Publication No. H07-239684   Patent Document 2: Japanese Patent Application Publication No. H07-239685       

       FIGS. 5A and 5B  show the conventionally-known constitution of a pickup unit  50  adapted to an electric stringed instrument. The pickup unit  50  is fixed inside a recess  52 A of a lower bridge  52  attached to an exterior board  51  of an electric stringed instrument. The pickup unit  50  is constituted of a U-shaped frame  55  (having a U-shape in side view, see  FIG. 5B ) installed in the recess  52 A, a vibrator  57  which is inserted and held by the U-shape frame  55  and of which upper end supports strings  56 , a plurality of piezoelectric elements  58  which are interposed between the U-shape frame  55  and the vibrator  57  and which are disposed just below the strings  56  respectively, and a shim  59  interposed between the bottom portion of the recess  52 A and the U-shape frame  55 . 
     The vibrator  57  is constituted of a saddle  60  made of a resin, and a lead plate  61  which is fixed to the lower surface of the saddle  60  and which conducts with the upper surface of the piezoelectric elements  58 . Owing to the downward force exerted by the strings  56  which are stretched under tension, the piezoelectric elements  58  are brought into contact with the lead plate  61 . Upon playing an electric stringed instrument, vibrations of the strings  56  are transmitted to the vibrator  57  (supporting the strings  56 ) toward the piezoelectric elements  58 , which are thus deformed in shape to generate electricity. Thus, it is possible to convert vibrations of the stings  56  into electric signals. In the preparation of an electric stringed instrument, manual operation is needed to adjust the heights of the strings  56  and to adjust the projecting length of the saddle  60  above the lower bridge  52 . This manual operation is performed using a plurality of shims  59  having different thicknesses, wherein each of the shims  59  is arbitrarily selected and applied to the pickup unit  50 , thus performing the above mechanical adjustment. 
     The pickup unit  50  shown in  FIGS. 5A and 5B  is characterized in that the downward force of the strings  56  may fluctuate during the performance of an electric stringed instrument, and the saddle  60  may be inclined toward the neck of an electric stringed instrument so as to loosen the tight contact between the piezoelectric elements  58  and the lead plate  61  when the strings  56  are being stretched. This destabilizes the contact state between the piezoelectric elements  58  and the lead plate  61 , so that the piezoelectric elements  58  may not deform to readily follow up with vibrations of the saddle  60 . That is, the pickup unit  50  suffers from a great mechanical loss in transmitting vibrations to the piezoelectric elements  58 , a destabilization of vibrations of the strings  56 , and a difficulty in precisely converting vibrations of the strings  56  into electric signals. 
     In addition, the pickup unit  50  suffers from a difficulty in maintaining the uniform contact state between the piezoelectric elements  58  and the lead plate  61 , which in turn readily causes dispersions regarding the tone volume of the strings  56 . The piezoelectric elements  58  inherently possess an inclination to greatly fluctuate in electric power generation depending upon a subtle difference of the contact state with the lead plate  61 , thus easily revealing the above drawbacks. The saddle  60  of which base portion has a low precision of smoothness may induce a great fluctuation of electric power generation among the piezoelectric elements  58 , which in turn causes dispersions regarding the tone volume of the strings  56 . For this reason, a further process is needed to improve the precision of smoothness after the formation of the saddle  60  made of a thermosetting resin. 
     The pickup unit  50  of  FIGS. 5A and 5B  is simply assembled such that the piezoelectric elements  58 , the lead plate  61 , and the saddle  60  are sequentially mounted in the recess  52 A of the lower bridge  52  on the exterior surface  51  of an electric stringed instrument. For this reason, even when the surface of the lead plate  61  is smoothed, it is difficult to practically secure the same contact state among the piezoelectric elements  58  with the lead plate  61 . Since the contact pressure of the piezoelectric elements  58  normally fluctuates owing to vibrations of the strings  56 , the piezoelectric elements  58  partially contacts with the lead plate  61  with respect to micro-time. This degrades the sound quality and tone color of an electric stringed instrument. Since the tone color of an electric stringed instrument is inherently correlated to the initial plucking period, fluctuations of contact pressure greatly affect the tone color of an electric stringed instrument as they are apt to increase in the initial plucking period. 
     Furthermore, the shim  59  disposed in the bottom portion of the recess  52 A of the lower bridge  52  causes a mechanical loss in transmitting vibrations to the lower bridge  52  and the body of an electric stringed instrument. For this reason, it is difficult to reproduce a live sound of an electric stringed instrument with the conventionally-known constitution of the pickup unit  50 . 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a pickup unit of an electric stringed instrument, which is able to efficiently transmit vibrations of strings to piezoelectric elements and which improves the tone color and sound quality by minimizing dispersions regarding the tone volume of strings. 
     It is another object of the present invention to provide a pickup unit of an electric stringed instrument, which guarantees the smooth height adjustment of strings and which markedly reduces a mechanical loss in transmitting vibrations to a lower bridge. 
     It is a further object of the present invention to provide a pickup unit of an electric stringed instrument, in which piezoelectric elements can be easily disassembled from support members. 
     The present invention is directed to a pickup unit installed in a lower bridge of an electric stringed instrument. The pickup unit is constituted of a vibrator supporting a plurality of strings, a support which is installed in the lower bridge so as to support the vibrator, a plurality of piezoelectric elements which covert vibrations of the strings transmitted thereto via the vibrator into electric signals, and at least one presser member which is interposed between the support and the vibrator so as to apply a pressure pressing the piezoelectric elements onto the vibrator. 
     In the above, the presser member is adjusted in the pressure applied to the piezoelectric elements. The support is constituted of a frame holding the vibrator and a base which is fixed to the frame and is mounted inside the lower bridge, wherein the lower surface of the base has a processability in cutting. The piezoelectric elements are each coupled with tuning plates via conductive bonds and are interposed between the vibrator and the support. The support includes at least one positioning projection which regulates the positioning of the piezoelectric element in the alignment direction of the strings. The vibrator includes a printed circuit board which is connected to a lead via a connector detachably attached to the vibrator. 
     The pickup unit of the present invention is designed such that the presser member (e.g. screws) presses the piezoelectric elements onto the vibrator, hence, it is possible to prevent the contact state between the vibrator and the piezoelectric elements from fluctuating when the downward force of the strings applied to the vibrator fluctuates or the vibrator is forced to incline during a rendition of an electric stringed instrument. This makes it possible for the piezoelectric elements to readily deform to follow up with vibration of the vibrator, thus achieving various effects. For example, it is possible to efficiently transmit vibrations of strings to the piezoelectric elements without any transmission loss, thus reproducing a rich and live sound. In addition, it is possible to improve the tone color and sound quality of an electric stringed instrument by way of the precise detection and rendition of vibrations of strings. 
     The presser member uniformizes the pressure applied to the piezoelectric elements and thereby uniformizes the contact state between the piezoelectric elements and the vibrator. Even when the lower surface of the vibrator has a low degree of smoothness, it is possible to reliably prevent the piezoelectric elements from unexpectedly fluctuating in terms of the electric power generation; hence, it is possible to prevent the occurrence of dispersions among the tone colors of the respective strings. 
     Using the “adjustable” presser member, it is possible to apply the optimum contact pressure to the piezoelectric elements generating electric signals. 
     Owing to the processability in cutting on the lower surface of the base of the support, it is possible to adjust the projecting length of the vibrator above the lower bridge and to adjust the heights of the strings with ease. This eliminates the shim which is conventionally used for the pickup unit of an electric stringed instrument; hence, it is possible to suppress the mechanical loss of transmitting vibrations of strings to the lower bridge and the body of an electric stringed instrument, thus reproducing a good live sound. 
     In addition, it is possible to reliably prevent the piezoelectric elements coupled with the tuning plates from partially contacting with the vibrator in the initial plucking period in which strings are plucked to vibrate with maximum amplitudes; hence, it is possible to improve the fidelity of piezoelectric elements generating electric signals. This prevents unwanted fluctuations of the tone color and degradation of the sound quality in reproduction. The tuning plates may serve as a tuning filter rectifying vibrations transmitted to the lower bridge from strings, wherein it is possible to suppress or eliminate unwanted components of vibrations (e.g. vibrations of a certain register) and noise. In addition, the tuning plates are not necessarily placed in direct contact with the vibrator and are thereby physically separated from the vibrator; this makes it possible for the technician (or engineer) to easily disassemble the piezoelectric elements and the vibrator. 
     Furthermore, the positioning projection of the support makes it easy for the technician to establish the precise positioning with respect to the piezoelectric elements relative to the support; this facilitates the setting operation, reduces the workload, and speeds up the assembling operation. 
    
    
     
       BRIEF DESCRIPTION OF DIE DRAWINGS 
       These and other objects, aspects, and embodiments of the present invention will be described in more detail with reference to the following drawings. 
         FIG. 1  is a traverse sectional view showing the constitution of a pickup unit of an electric stringed instrument according to a preferred embodiment of the present invention. 
         FIG. 2  is an exploded view partly in cross section showing the assembly of constituent parts of the pickup unit. 
         FIG. 3  is an enlarged cross-sectional view taken along line A-A in  FIG. 1 . 
         FIG. 4  is an enlarged cross-sectional view take along line B-B in  FIG. 1 . 
         FIG. 5A  is a traverse sectional view showing the constitution of a conventionally-known pickup unit adapted to an electric stringed instrument. 
         FIG. 5B  is a cross-sectional view taken along line C-C in  FIG. 5A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described in further detail by way of examples with reference to the accompanying drawings. 
     As shown in  FIGS. 1 to 4 , a pickup unit  10  according to a preferred embodiment of the present invention is installed in an electric stringed instrument such as an electric guitar or an acoustic guitar. The pickup unit  10  is installed in a lower bridge  12  formed on an exterior surface  11  (see  FIG. 1 ) constituting the body of an electric stringed instrument. The pickup unit  10  is constituted of a vibrator  15  of which an upper end supports six strings  13 , a support  16  which is fixed inside a recess  12 A of the lower bridge  12  so as to support the vibrator  15 , a plurality of piezoelectric elements  18  which convert vibrations of the strings  13 , transmitted thereto via the vibrator  15 , into electric signals, and a plurality of presser members  19  which are interposed between the vibrator  15  and the support  16 . 
     The vibrator  15  is constituted of a saddle  21 , which is made of a resin and elongated in the alignment direction of the strings  13 , and a printed circuit board  22  disposed on the lower surface of the saddle  21 . The upper surface of the printed circuit board  22  is entirely fixed to the lower surface of the saddle  21  via the adhesive. The upper surface of the printed circuit board  22  serves as a ground surface, while the lower surface serves as a lead-fabricated surface. Near the left-side position of the support  16 , a connector  24  is detachably attached to the lower surface of the vibrator  15  via a screw  25 , which is screwed into the lower surface of the saddle  21 . A pair of lead terminals is integrally formed in the connector  24 , wherein one lead terminal is connected to the lead-fabricated surface of the printed circuit board  22  and is soldered with the lead terminal of a lead  26 , while the other lead terminal is connected to the ground surface of the printed circuit board  22  and is soldered with the ground terminal of the lead  26 . That is, the printed circuit board  22  is connected to the lead  26  via the connector  24 . 
     The support  16  is constituted of a frame  28  made of a metal supporting the lower end of the vibrator  15  and a base  29  made of a resin (e.g. a urea resin) fixed to the frame  28 . The support  16  is formed by unifying the frame  28  and the base  29  together. 
     As shown in  FIGS. 3 and 4 , the frame  28  is constituted of a base portion  31  and a pair of side portions  32  vertically interconnected to left and right ends of the base portion  31 , wherein the frame  28  is formed in a U-shape in side view, partially holding the lower end of the vibrator  15 . A plurality of holes  31 A is formed in the base portion  31  of the frame  28 , wherein each hole  31 A is positioned just below the midpoint between the adjacent strings  13 . A ground screw  33  is put into the right end of the frame  28  which horizontally projects from the right end of the base  29 . The ground screw  33  is screwed into the lower surface of the saddle  21  so as to nm through the frame  28  and the printed circuit board  22  as well as a spacer  34  interposed between them. The spacer  34  is connected to the ground surface of the printed circuit board  22  via a through-hole, so that the frame  28 , the spacer  34 , and the ground surface of the printed circuit board  22  are electrically conducted with each other via the ground screw  33 . 
     The base  29  is positioned beneath and along the lower surface of the bottom portion  31  of the frame  28  and is constituted of a foot portion  36  mounted on the bottom portion of the recess  12 A and a plurality of positioning projections  37  which project above the foot portion  36 . The lower surface of the foot portion  36  of the base  29  possesses a processability in cutting, wherein it is subjected to cutting using an appropriate tool so as to change the distance from the bottom portion of the recess  12 A to the upper end of the saddle  21 , thus adjusting the heights of the strings  13 . It is preferable that the maximum cutting thickness in the foot portion  36  of the base  29  be set to 1.5 mm. In this connection, a gap is formed between the bottom portion of the recess  12 A and the connector  24  so as to prevent the connector  24  from contacting the bottom portion of the recess  12 A irrespective of the cutting of the foot portion  36  of the base  29 . 
     The positioning projections  37  are formed to adjoin together in the alignment direction (i.e. the left-right direction) of the strings  13  in connection with the piezoelectric elements  18 , thus regulating the lateral movements of the piezoelectric elements  18 . Each of the positioning projections  37  is disposed around each of the holes  31 A above the left and right ends of the base portion  31  of the frame  28 . The positioning projections  37  are unified with the frame  28  together with the foot portion  36  by way of the outsert molding using a resin material. 
     Six piezoelectric elements  18  are aligned just below the six strings  13 . The piezoelectric elements  18  are arranged inside the frame  28  in the same polarization direction, in which each piezoelectric element  18  is polarized in the thickness direction so that charges are generated on both the upper and lower faces thereof. The upper faces of the piezoelectric elements  18  are bonded onto the lower surface of the printed circuit board  22 . Tuning plates (or plate members)  39  are attached to the lower faces of the piezoelectric elements  18 ; hence, the piezoelectric elements  18  bonded together with the tuning plates  39  are interposed between the saddle  21  and the support  16 . Herein, non-hardening materials having conductivity and adhesiveness are used as bonds applied to the upper and lower faces of the piezoelectric elements  18 . That is, the piezoelectric elements  18  are connected to the vibrator  15  and the tuning plates  39  with the adequate adhesiveness. This guarantees that a certain level of the contact state is maintained between the piezoelectric elements  18  and the printed circuit board  22  over a lapse of time even when the strings  13  are plucked with a relatively strong force. In this connection, the above bonds may embrace both-side adhesive tapes having the above property. The height of the positioning projection  37  projecting above the base portion  31  of the frame  28 , is smaller than the overall thickness of the piezoelectric element  18  and the tuning plate  39  unified together, so that a small gap is formed between the upper end of the positioning projection  37  and the lower surface of the printed circuit board  22 . 
     The tuning plates  39  are composed of a metal such as a brass. The tuning plate  39  collectively serve as a tuning filter suppressing or eliminating unwanted harmonics and noise, while they are devoted to effects of firming up median and base tones and effects of sustaining sound by appropriately changing the material and thickness thereof. The timing plates  39  are not necessarily fixed to but simply mounted on the base portion  31  of the frame  28 ; hence, it is possible to easily disassemble them from the support  16  and to easily perform maintenance of the piezoelectric elements  18 . 
     The presser members  19  are constituted of three screws which are put into the lower surface of the vibrator  15  from the lower surface of the support  16  and which are aligned in the alignment direction (i.e. the left-right direction) of the strings  13 . The screws of the presser members  19  run through the positioning projections  37  which are formed via the holes  31 A of the base portion  31  of the frame  28 , wherein a first screw is positioned just below halfway between the lowest-pitch string  13  and its adjacent string  13 , a second screw is positioned just below halfway between the highest-pitch string  13  and its adjacent string  13 , and a third screw is positioned just below halfway between the two strings  13  in the middle of the six strings  13 . Screwing the presser member  19  makes the base portion  31  of the frame  28  approach the lower surface of the vibrator  15 , thus producing the upward pressure pressing the piezoelectric elements  18  toward the vibrator  15 . The piezoelectric elements  18  are tightly held between the lower surface of the printed circuit board  22  and the base portion  31  of the frame  28  and are subjected to upward/downward compressive forces independently of the downward pressure produced by the strings  13  being stretched under tension. In other words, the present embodiment is able to apply compressive forces to the piezoelectric elements  18  before the strings  13  are stretched. It is possible to arbitrarily adjust the pressures by changing the screwing torques of the presser members  19 , wherein a torque driver or the like is used to apply a preset torque to the presser members  19 , thus uniformizing the compressive pressures applied to the piezoelectric elements  18 . 
     In a rendition of an electric stringed instrument of which strings  13  are being plucked, vibrations of the strings  13  are transmitted to the piezoelectric elements  18  via the vibrator  15  so that the piezoelectric elements  18  convert them into electric signals. Electric signals of the piezoelectric elements  18  are output to an external device (not shown) via the printed circuit board  22  and the lead  26 , so that the corresponding sound (or an artificial electronic sound) is reproduced. 
     The present embodiment is designed such that the piezoelectric elements  18  are pressed onto the printed circuit board  22  by means of the presser members  19 ; hence, it is possible to prevent the contact state between the piezoelectric elements  18  and the printed circuit board  22  from being unexpectedly altered. Thus, it is possible to efficiently transmit vibrations of the strings  13  to the piezoelectric elements  18 , thus achieving a high sound quality. In addition, it is possible to establish the uniform contact state between the piezoelectric elements  18  and the printed circuit board  22  and to uniformize the compressive pressures applied to the piezoelectric elements  18 . In short, it is possible to suppress unwanted fluctuations of electric power generation of the piezoelectric elements  18  and to maintain a good balance in tone volume between the strings  13 . 
     The present embodiment is designed such that the piezoelectric elements  18  are bonded to the printed circuit board  22  and the tuning plates  39  by use of the above bonds; hence, it is possible to prevent them from partially contacting each other with respect to micro-time in the initial plucking period significantly affecting the tone color of an electric stringed instrument. Thus, it is possible to precisely transmit vibrations of the strings  13  to the piezoelectric elements  18 , and it is therefore possible to reproduce rich and live sounds of an electric stringed instrument. In addition, the connector  24  is formed independently of the support  16  and is connectible to the printed circuit board  22 ; hence, it is possible to prevent the connector  24  and the lead  26  from disturbing the adjustment of the thickness of the foot portion  36  of the vibrator  15  via cutting. 
     The present invention is not necessarily limited to the above embodiment and examples, which can be appropriately modified in various ways within the scope of the invention as defined in the appended claims, since the skilled person in the art may be able to readily alter the names, shapes, sizes, arrangements, and illustrations of the constituent parts of the pickup unit of an electric stringed instrument. 
     For example, it is possible to change the number of the presser members  19  and their positions such that the presser members  19  are positioned just below all the midpoints of the adjacent six strings  13 , they are positioned at both the left and right ends of the saddle  21 , or one presser member  19  is arranged at the intermediate position between the left and right ends of the saddle  21 . 
     In addition, it is possible to modify the presser members  19  in terms of the structure or mechanism as long as they are able to press the piezoelectric elements  18  onto the vibrator  15 ; for example, it is possible to employ a rod and a lock mechanism regulating the retractable motion of the rod instead of the screw of the presser member  19 .