Bridge mechanism for the acoustic guitar

A bridge mechanism for an acoustic guitar for fine adjustment of the height and length of the strings. The bridge mechanism is installed on a thin installation plate that is wider laterally than the width occupied by the array of guitar strings. The installation plate is installed directly on the surface of the soundboard. The installation plate has a plurality of string stopper holes and has a concave region on its top surface. A base plate has a plurality of screw holders and is fixed in the concave region. The base plate is arranged in such a way as to correspond to the guitar strings, but does not overlap with the guitar strings. Bridge members are arranged individually and independently for each guitar string. Each has a string holder and each is freely movable back and forth via a string length adjusting screw. The bridge members are also freely movable up and down through a string height adjusting screw. A respective fixing pin fixes each guitar string in a string stopper hole.

BACKGROUND OF THE INVENTION 
1. Field of the Related Art 
This invention relates to a bridge mechanism for an acoustic guitar. 
2. Description of the Related Art 
A prior art acoustic guitar 60, such as a folk guitar, is shown in FIG. 7. 
A hollow resonant box 70 amplifies the vibrating sound of the strings 
under the table or soundboard 62 of the guitar body 61. The resonant box 
70 is completed by back 63 and side plate 64. 
Guitar strings 65 are installed at a pedestal or tailpiece 68 that is fixed 
to the surface of the soundboard 62. The end of each string is held by 
means of a wedge-like fixing pin 69. The string is rolled onto a tuning 
bolt or peg 67 at the other end of neck 66. 
In contrast to the acoustic guitar, in an electric guitar the vibrations of 
the strings are picked-up and amplified electronically, using a magnetic 
force generated by the vibrating strings. Accordingly, the body of an 
electric guitar ordinarily is solid and is equipped with a bridge 
mechanism comprising a base plate made of a metal and a plurality of 
bridge members (saddle members) made of metal as are described in the 
Official Publication of Utility Model Registration No. 2560349, to cite an 
example. 
As in the case of the above-described acoustic guitar, the guitar strings 
of the electric guitar are held at the bridge member of the bridge 
mechanism at one end and rolled onto the tuning bolt of the neck at the 
other end. In electric guitar bridge members individual adjustment of the 
string height and length are possible, as compared with the base plate. 
The string height and length normally are capable of very fine adjustment. 
In the acoustic guitar, on the other hand, it is not possible to make a 
fine adjustment of the string height and the string length. Accordingly, 
performers accustomed to an electric guitar, which has become the main 
form of guitar in use in recent years, tend to complain about this lack of 
fine string adjustment in acoustic guitars. In addition, if it becomes 
possible to make a fine adjustment of the string height and the string 
length of an acoustic guitar, the breadth of its performance capabilities 
will be expanded. 
Nevertheless, loading an acoustic guitar with a bridge mechanism that is 
capable of affording a fine adjustment of the height and the length of 
each guitar string entails the following problems: 
The surface of the soundboard of the acoustic guitar has normal curvature 
with a radius approximately in the range between 4000 and 6000 
millimeters. Variations in the curved surface stem from such natural 
conditions as the manufacturing requirements and the humidity, etc. But 
this makes it extremely difficult to adhere a base plate made of metal 
tightly to the surface of the soundboard. 
Further, if the base plate does not adhere tightly to the surface of the 
soundboard, the vibrations of the guitar strings are not transmitted 
accurately to the guitar body, and there are other undesirable sounds, 
etc. that are produced, thereby reducing the quality of the sound, for 
example. 
Even when a base plate made of metal has been tightly fixed to the surface 
of the soundboard, the soundboard tends to be deformed in the horizontal 
direction as compared with the guitar strings because of changes in the 
temperature or humidity, so that the tight adherence between the 
soundboard and base plate tending to deteriorate and deform the 
instrument. 
SUMMARY OF THE INVENTION 
The present invention overcomes the problems of the prior art, such as 
those noted above, by providing a bridge for an acoustic guitar wherein it 
becomes possible to make a fine adjustment of the string height and string 
length for the acoustic guitar. The bridge is capable of simple and secure 
installation tightly on the surface of the soundboard, even if there are 
variations in the surface curvature. 
The invention provides a bridge for an acoustic guitar that has a hollow 
resonant box under the soundboard of a guitar. An installation plate, 
preferably wider than the guitar strings, is secured to the soundboard 
surface. A plurality of string stopper holes corresponding to the various 
guitar strings are provided in the installation plate. 
A base plate is provided in a concave portion of the installation plate. 
The base plate has a plurality of screw holding parts. The screw holding 
parts are arranged at such positions as would correspond to, and not 
overlap with, the guitar strings. 
A plurality of bridge members are arranged individually and independently 
for each guitar string. Each bridge member has a string holding part for 
the corresponding guitar string. The bridge member is held so as to be 
freely movable back and forth through an adjusting screw that has been 
inserted into the screw holding part for adjusting the length, or 
intonation, of the string. Also, the bridge members are held in such a 
manner as to freely move up and down through an adjusting screw whose 
lower end contacts the upper surface of the base plate for adjusting the 
height, or action, of the string. 
A plurality of pins fix the various guitar strings held by the string 
holding part of the bridge member integrally in the string stopper hole. 
In a preferred embodiment of the inventive bridge mechanism for the 
acoustic guitar, the installation plate and the base plate are fixed to 
the surface of the soundboard by means of a common screw member. 
Preferably, the length of the installation plate in the horizontal 
direction is more than twice the length of the base plate in the 
horizontal direction. In addition, the height of the entire bridge 
mechanism as it protrudes from the surface of the soundboard preferably 
does not exceed 15 millimeters. 
Other features and advantages of the present invention will become apparent 
from the following description of the invention which refers to the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The acoustic guitar shown in FIG. 1 generates sounds through the resonance 
of the guitar body 11. It has a hollow resonance box 15 for sound 
amplification comprised of a back 13 and a side plate 14 on the bottom 
side of the soundboard. A plurality of guitar strings S (six in the 
example shown in the drawing) are held by tuning bolts or pegs 17 of the 
neck 16 at one end. The strings are held at the other end by a bridge 
mechanism 20 arranged on the soundboard 12. 
An example of the bridge mechanism 20 according to the present invention is 
explained below. Bridge mechanism 20 holds and fixes the strings S in such 
a manner as to make it possible to carry out fine adjustment of the string 
height and string length for each of the guitar strings. As shown in FIGS. 
2-4, the bridge mechanism comprises an installation plate 21, a base plate 
31, a plurality of bridge members 41, and a plurality of fixing pins 51. 
Installation plate 21 is used to install the bridge mechanism 20 to the 
guitar body 11. Installation plate 21 is thin; and extends wider laterally 
across the soundboard as compared with the array of guitar string S. The 
back or undersurface of the installation plate is fixed adjacent to the 
upper surface 12a of the soundboard 12 of the body 11, as described 
further below. 
The flexibility of the installation plate 21 generally increases as the 
thickness of the installation plate 21 is reduced. In connection with the 
expansion of the soundboard 12 of the guitar body 11 in the lateral 
direction, due to variations in the temperature or humidity, for example, 
the installation plate 21 tends to follow the expansion of the soundboard 
12. The installation plate 21 is made of such a substance as to have some 
kind of elasticity (flexibility), and it is made of wood in this example. 
Of course, it is not limited to this. The installation plate 21 can be 
made of a plastic, as well as other natural or synthetic polymers and 
materials. 
At the bottom part of the installation plate 21, further, a plurality of 
string stopper holes 22 are provided. The stopper holes have a tapered 
surface 22a, and there is one for each guitar string S. 
There is a concave region 23 is formed in the top of the plate 21 above or 
in front of the string stopper holes 22. In this example, a plurality 
(three are shown) of fixing holes 24 are formed in the concave part 23. 
The base plate 31, made of metal, is fixed in the concave region 23 of the 
installation plate 21. In this example, the base plate 31 is fixed along 
with the installation plate 21 to the surface of the soundboard 12 of the 
guitar body 11 by common screws 35. The screws are installed through 
respective fixing holes 36 formed in the base plate 31. Consequently. the 
number of parts involved is reduced, and the installation strength between 
the guitar body 11 and the bridge mechanism 20 is increased. 
In FIG. 2, the lateral width L1 of the installation plate 21 is more than 
twice the width L2 of the base plate 31 in the same lateral direction. In 
particular, the width L1 of the installation plate 21 is 150 millimeters 
while the width L2 of the base plate 31 is 63.5 millimeters. Accordingly, 
the installation plate 21 is sufficiently strong, and has increased 
flexibility (elasticity) in the horizontal direction. 
There are a plurality of screw holders 32, e.g., six provided at the bottom 
of the base plate 31 corresponding to each guitar strings S. Each screw 
holding part 32 has an opening 33 for receiving a screw. The screw holding 
parts are positioned to avoid overlap or interference with the guitar 
strings S. 
Guitar strings S are supported by bridge members 41 which are above the 
screw holding parts 32. Bridge members 41 are preferably made of a metal, 
and are provided individually and independently for each guitar string S 
on the base plate 31. Bridge member 41 has a string holding part (string 
contact part) for the guitar string S. The string holding part 42 in this 
example is provided as a groove in the shape of a curved surface. 
Moreover, each bridge member 41 is held on the base plate 31 so as to be 
freely movable back and forward through action of a respective string 
length adjusting screw 43. Each adjusting screw 43 is threaded through the 
opening 33 of the respective screw holding part 32. Each bridge member 
also is held by the base plate 31 and is freely movable up and down 
through a number of string height adjusting screws 47 (two of them in this 
example) for each bridge member, where the bottom ends of the screws 
contact the upper surface of the base plate 31. 
Referring to FIGS. 4 and 5, there is an installation part 44 for the string 
length adjustment screw. The part 44 includes screw hole 45. It is 
provided on one side of the string holding part 42 of the bridge member 
41. The string length (back and forth) adjusting screw 43 is screwed into 
the bridge member 41 through the installation part 44. 
A spring 46 around the adjusting screw 43 provides tension on that screw 43 
and biases the bridge member 41 away from screw holder 32. The 
installation part 44 accommodates the screw 43. A respective screw hole 48 
accommodates each up and down adjusting screw 47. 
Each guitar string S that is held by the string holding part 42 of the 
bridge member 41 is integrally fixed in the string stopper hole 22 by a 
fixing pin 51. Fixing pin 51 is a wedge like body, made of a plastic or 
wood, for example. In the preferred embodiment shown, a known fixing pin 
51 includes a cut 52 in the axial direction for accommodating the string. 
One end of the guitar string S is inserted into the string stopper hole 22 
along with fixing pin 51, so that the guitar string S is held between the 
tapered surface 22a of the string stopper hole 22 and the fixing pin 51. A 
bridge plate 18 (bridge pad) beneath the plate 21 is provided for 
re-enforcing the surface of the soundboard 12. 
The bridge mechanism 20 described above is installed on the surface 12a of 
the soundboard 12 of the guitar body 11 through the installation plate 21. 
Upon variations in the curved surface of the soundboard 12, due to the 
manufacturing conditions and such natural conditions as humidity, etc., 
the form of the installation plate 21 can be changed accordingly. 
Accordingly, it is possible to install the plate tightly on the surface 
12a of the soundboard 12 in a simple fashion. At the same time, the 
installation will have a high level of strength and stability. 
Even when the soundboard 12 may be deformed laterally, as compared with the 
guitar strings S, after the installation of the bridge mechanism 20 on the 
surface 12a of the soundboard 12 due to variations in the temperature or 
humidity, etc., the installation plate 21 is sufficiently flexible to 
follow the deformation. This makes it possible to prevent any 
deterioration of the tight adhesion between the bridge mechanism 20 and 
the soundboard 12. Since the base plate 31 is fixed in the concave region 
23 that has been formed on the installation plate 21, it becomes possible 
to control the maximum protrusion height above the surface 12a of the 
soundboard 12 of the bridge mechanism 20 as a whole. 
Preferably, the height of the protrusion of the bridge mechanism 20 as a 
whole from the surface 12a of the soundboard 12 is to not exceed 15 
millimeters. In a preferred embodiment of FIG. 6, the thickness H2 of the 
installation plate 21 is six millimeters, the depth H3 of the concave part 
23 of the installation plate 21 is three millimeters, and the thickness of 
the base plate 31 is two millimeters. The height H5 of the highest 
position of the bridge member 41 from the top surface of the base plate 31 
to the string holding part 42 is 10 millimeters. Accordingly, the height 
H1 (=H2 +H4+H5-H3) of the protrusion of the bridge mechanism 20 from the 
surface 12a of the soundboard 12 is 15 millimeters. 
To adjust the string height or string length of each guitar string S, the 
fixing pin 51 is first loosened in its string stopper hole 22, which sets 
free the guitar string S held by the string holding part 42 of the bridge 
member 41. The string height is adjusted up and down by turning adjusting 
screw 47 accordingly. The length of guitar string S, on the other hand, is 
adjusted by turning the string length (back and forth) adjusting screw 43 
such that the screw length against the bridge member 41 is changed, 
thereby adjusting the position of the bridge member 41 along the string. 
After adjustment of the height or the back and forth position of the 
bridge member 41, the guitar string S is again fixed in the string stopper 
hole 22 by the fixing pin 51. 
The bridge mechanism 20 can be provided on various kinds of acoustic 
guitars, thereby improving the guitar's general purpose characteristics. 
The ability to carry out fine adjustment of the string height and the 
string length of the guitar strings and the fine adjustment of the string 
height, in particular, increases the breadth of the performance 
capabilities of the acoustic guitar. At the same time, the following 
advantages are achieved: 
Since the soundboard 12 in the acoustic guitar 19 is a thin plate with a 
thickness, preferably in the range between 2.5 and 3.0 millimeters, in 
accordance with its function as a resonant box, the soundboard 12 may be 
deformed in the vertical direction as compared with the guitar strings 
because of the tension of the guitar strings. As a result, the height of 
the surface 12a of the soundboard 12 and, consequently, the height of the 
guitar string S, will vary. With the present invention, however, the 
height of the guitar string S can be restored to a desired height as 
described above by the string height adjustment. 
In addition, it is possible to independently effect fine adjustment of the 
string height and string length of the guitar strings for each string. 
Therefore, an acoustic guitar can be provided which can satisfy even those 
performers who have been accustomed to an electric guitar. 
Moreover, the installation plate preferably is thin and long in the lateral 
direction as compared with the lateral array of guitar strings, and can be 
tightly installed on the surface of the soundboard in a simple fashion, 
and satisfactorily strong, even in the presence of variations in such 
natural conditions as the temperature or humidity, in addition to the 
manufacturing requirements on the surface of the soundboard. 
By providing an installation plate preferably having a lateral width that 
is more than twice the width of the base plate, moreover, it becomes 
possible not only to set the strength of the installation plate 
sufficiently high but the flexibility of the installation plate in the 
lateral direction can also be elevated, thereby further increasing the 
installation strength of the bridge mechanism on the guitar body. 
Also, by providing a bridge mechanism having a height as a whole that 
protrudes from the surface of the soundboard preferably less than about 15 
millimeters, it is possible for the bridge mechanism to be carried on 
various kinds of acoustic guitars, thereby increasing its general purpose 
capability. 
Although the present invention has been described in relation to a 
particular embodiment, many other variations and modifications and other 
uses will become apparent to those skilled in the art. It is preferred, 
therefore, that the present invention be limited not by the specific 
disclosure herein, but only by the appended claims.