U.S. patent number 3,656,395 [Application Number 05/044,202] was granted by the patent office on 1972-04-18 for guitar construction.
This patent grant is currently assigned to Kaman Corporation. Invention is credited to Charles H. Kaman.
United States Patent |
3,656,395 |
Kaman |
April 18, 1972 |
GUITAR CONSTRUCTION
Abstract
A guitar includes a body comprised of a one-piece curved bowl of
fiberglass material forming the back and sides of the body and a
flat wooden soundboard forming the top of the body. A unique
arrangement of braces secured to the interior surface of the
soundboard causes it to be tuned to a large number of different
frequencies over the fully frequency and produces a full rich sound
when the instrument is played.
Inventors: |
Kaman; Charles H. (Simsbury,
CT) |
Assignee: |
Kaman Corporation (Bloomfield,
CT)
|
Family
ID: |
21931046 |
Appl.
No.: |
05/044,202 |
Filed: |
June 8, 1970 |
Current U.S.
Class: |
84/267; 84/291;
984/106; 984/112 |
Current CPC
Class: |
G10D
3/02 (20130101); G10D 1/08 (20130101) |
Current International
Class: |
G10D
3/02 (20060101); G10D 3/00 (20060101); G10D
1/08 (20060101); G10D 1/00 (20060101); G10d
001/08 (); G10d 003/00 () |
Field of
Search: |
;84/267,268,274,275,291,294 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Gonzales; John F.
Claims
I claim:
1. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, a bottom main brace also arranged obliquely to said
vertical center-line of said soundboard and extending across said
soundboard from its bass side to its treble side, the treble-side
end of said bottom main brace being located at approximately the
level of said bridge and the bass-side end of said bottom main
brace being located at a level considerably below that of said
bridge, and a plurality of other braces extending generally
longitudinally of said soundboard and spaced from one another
transversely of said soundboard, said other braces being located
between said top main brace and said bottom main brace.
2. A guitar as defined in claim 1 further characterized by said
soundboard being tapered from a first thickness at its top to a
smaller thickness at its bottom.
3. A guitar as defined in claim 1 further characterized by said
body in addition to said soundboard including means defining side
and rear walls for said body, said rear wall of said body being
curved in two dimensions to provide a correspondingly curved sound
reflecting surface in the interior of said body spaced rearwardly
from said soundboard.
4. A guitar as defined in claim 1 further characterized by said
other braces each having a transverse cross-sectional size and
stiffness substantially less than that of said top main brace and
said bottom main brace.
5. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, and a bottom main brace also arranged obliquely to
said vertical center line of said soundboard and extending across
said soundboard from its bass side to its treble-side, the
treble-side end of said bottom main brace being located at
approximately the level of said bridge and the bass-side end of
said bottom main brace being located at a level considerably below
that of said bridge, the bass-side end of said top main brace being
located in the vertical region of said soundboard defined by the
center and said lowermost extent of said sound opening.
6. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, and a bottom main brace also arranged obliquely to
said vertical center line of said soundboard and extending across
said soundboard from its bass side to its treble side, the
treble-side end of said bottom main brace being located at
approximately the level of said bridge and the bass-side end of
said bottom main brace being located at a level considerably below
that of said bridge, said soundboard having a depression in its
interior surface below said bottom main brace so as to render said
soundboard thinner in a given area below said bottom main brace
than it would be if said interior surface were truly planar.
7. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, and a bottom main brace also arranged obliquely to
said vertical center line of said soundboard and extending across
said soundboard from its bass-side to its treble side, the
treble-side end of said bottom main brace being located at
approximately the level of said bridge and the bass-side end of
said bottom main brace being located at a level considerably below
that of said bridge, said soundboard having a depression in its
interior surface above said top main brace so as to render said
soundboard thinner in a given area above said top main brace than
it would be if said interior surface were truly planar.
8. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, a bottom main brace also arranged obliquely to said
vertical center line of said soundboard and extending across said
soundboard from its bass side to its treble side, the treble-side
end of said bottom main brace being located at approximately the
level of said bridge and the bass-side end of said bottom main
brace being located at a level considerably below that of said
bridge, and a plurality of fan braces spaced relative to one
another transversely of said soundboard and located between said
top main brace and said bottom main brace, each of said fan braces
having an upper end located adjacent said top main brace and
extending generally downwardly relative to said soundboard from
said top main brace.
9. A guitar as defined in claim 8 further characterized by said
soundboard assembly including at least one additional brace
supplementary to said two main braces and said fan braces, said at
least one supplementary brace being disposed outside of that area
of said soundboard located between said two main braces.
10. A guitar as defined in claim 9 further characterized by said at
least one additional brace being a supplemental brace located above
said sound opening and extending across a substantial portion of
both said bass side and said treble side of said soundboard.
11. A guitar as defined in claim 10 further characterized by said
supplemental brace being inclinded relative to said center line of
said soundboard in such a direction that its bass side end is lower
than its treble side end.
12. A guitar as defined in claim 8 further characterized by said
fan braces including a first plurality thereof located on said bass
side of said soundboard and a second plurality thereof located on
said treble side of said soundboard, each of said fan braces of
said first plurality being inclined in one direction relative to
said vertical center line of said soundboard and each of said fan
braces of said second plurality being inclined in the opposite
direction so that each of said fan braces has its upper end located
closer to said center line than its lower end.
13. A guitar as defined in claim 12 further characterized by said
fan braces being so arranged that those located closer to said
center line of said soundboard are inclined at smaller angles to
said center-line than those which are located further from said
center-line.
14. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, and a bottom main brace also arranged obliquely to
said vertical center line of said soundboard and extending across
said soundboard from its bass side to its treble side, the
treble-side end of said bottom main brace being located at
approximately the level of said bridge and the bass-side end of
said bottom main brace being located at a level considerably below
that of said bridge, said top main brace having its treble-side end
spaced above the treble-side end of said bottom main brace.
15. A guitar as defined in claim 14 further characterized by said
soundboard assembly including a plurality of fan braces spaced
relative to one another transversely of said soundboard and located
between said top main brace and said bottom main brace, each of
said fan braces having an upper end located adjacent said top main
brace and extending generally downwardly relative to said
soundboard from said top main brace.
16. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, a bottom main brace also arranged obliquely to said
vertical center line of said soundboard and extending across said
soundboard from its bass side to its treble side, the treble-side
end of said bottom main brace being located at approximately the
level of said bridge and the bass-side end of said bottom main
brace being located at a level considerably below that of said
bridge, said top main brace having its treble-side end in
engagement with the treble-side end of said bottom main brace, and
a plurality of fan braces spaced from one another transversely of
said soundboard and located between said top main brace and said
bottom main brace, each of said fan braces having an upper end
located adjacent said top main brace and extending generally
downwardly relative to said soundboard from said top main
brace.
17. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, a bottom main brace also arranged obliquely to said
vertical center-line of said soundboard and extending across said
soundboard from its bass side to its treble side, the treble-side
end of said bottom main brace being located at approximately the
level of said bridge and the bass-side end of said bottom main
brace being located at a level considerably below that of said
bridge, and a plurality of fan braces spaced relative to one
another transversely of said soundboard and located between said
top main brace and said bottom main brace, said fan braces
consisting of two fan braces located on said treble side of said
soundboard and three fan braces located on said bass side of said
soundboard, the two of said treble-side fan braces and the one of
said bass-side fan braces which is closest to said center line of
said soundboard extending substantially the entire distance from
said top main brace to said bottom main brace so that their upper
ends are located adjacent said top main brace and their lower ends
are located adjacent said bottom main brace, the other two of said
bass-side fan braces having their lower ends spaced laterally
farther from said center-line than the bass-side end of said bottom
main brace.
18. A guitar having a body with a soundboard assembly, said
soundboard assembly including a soundboard with generally planar
interior and exterior surfaces and a sound opening passing
therethrough, a bridge attached to said exterior surface of said
soundboard below said sound opening, and bracing secured to said
interior surface of said soundboard, said bracing including a top
main brace arranged obliquely to the longitudinal center line of
said soundboard and extending across said soundboard from its bass
side to its treble side, the treble-side end of said top main brace
being located at a lower level than its bass-side end and within
the vertical region defined by the lowermost extent of said sound
opening and a lower limit located approximately at the level of
said bridge, a bottom main brace also arranged obliquely to said
vertical center line of said soundboard and extending across said
soundboard from its bass side to its treble side, the treble-side
end of said bottom main brace being located at approximately the
level of said bridge and the bass-side end of said bottom main
brace being located at a level considerably below that of said
bridge, and a plurality of fan braces spaced relative to one
another transversely of said soundboard and located between said
top main brace and said bottom main brace, said fan braces
consisting of three fan braces located on said treble side of said
soundboard and three fan braces located on said bass side of said
soundboard, the three of said treble-side fan braces and the one of
said bass-side fan braces which is closest to said center-line of
said soundboard extending substantially the entire distance from
said top main brace to said bottom main brace so that their upper
ends are located adjacent said top main brace and their lower ends
are located adjacent said bottom main brace, the other two of said
bass-side fan braces having their lower ends spaced laterally
farther from said center-line than the bass-side end of said bottom
main brace.
19. A guitar as defined in claim 18 further characterized by said
soundboard assembly including a supplementary bottom brace arranged
generally perpendicular to said bass-side fan braces and located
near the lower ends of said bass-side fan braces.
20. A guitar as defined in claim 19 further characterized by said
supplementary bottom brace being arranged to directly engage and
extend between said bottom main brace and the laterally outermost
one of said three bass-side fan braces.
21. A guitar as defined in claim 18 further characterized by said
soundboard assembly including an upper supplementary brace located
generally above said sound opening and extending between the bass
side and the treble side of said soundboard.
22. A guitar as defined in claim 21 further characterized by said
soundboard having a first depression in its interior surface below
said bottom main brace and a second depression in its interior
surface between said top main brace and said upper supplementary
brace so as to render said soundboard thinner in a given area below
said bottom main brace and in another given area between said upper
main brace and said upper supplementary brace than it would be if
said interior surface were truly planar.
Description
BACKGROUND OF THE INVENTION
This invention relates to guitars, and deals more particularly with
a guitar construction for producing an improved character of sound
from the instrument.
The guitar construction of this invention is intended primarily for
use in acoustic guitars, and is shown and described herein in
connection with such guitars. However, the scope of the invention
is not necessarily so limited and where applicable it may, if
desired, also be applied to electric guitars. In any guitar, the
fundamental source of sound is a vibrating string or strings. These
vibrating strings, however, by themselves emit only very low levels
of sound, and to render the sound acceptably audible, it is
necessary to amplify it, or more precisely to increase the coupling
between the vibrations and the surrounding air. In an acoustic
guitar this amplification is achieved by transmitting the
vibrations of the strings through a bridge to the top of the
instrument body, referred to herein as the soundboard and forming
part of a soundboard assembly including in addition to the
soundboard a plurality of interior braces which modify the acoustic
response of the soundboard. Of course, when a particular musical
note is played by plucking a string the tone produced consists not
only of the fundamental frequency of the note but also various
overtones or harmonics of such note, and the degree to which the
note is amplified by the soundboard assembly, as well as its tonal
character or timbre, will depend on the response of the soundboard
assembly to the fundamental frequency and to its various harmonic
frequencies.
In previous guitar constructions, the soundboard assembly tends to
emphasize certain frequencies and to de-emphasize other frequencies
over the audible range. This is due to the soundboard assembly
having the characteristic of being resonant to certain frequencies,
which are emphasized, and substantially non-resonant to other
frequencies, which are not emphasized. The result is that if the
frequency response characteristic (frequency vs. volume of emitted
sound for a fixed excitation) of the soundboard assembly is plotted
the response curve will be found to have several spaced peaks
representing frequencies that are emphasized and alternating with
spaced valleys representing frequencies which are not emphasized.
When a guitar with such a soundboard assembly is played,
particularly in loud chords, the sound tends to "break-up" and to
become unpleasing to the ear. This is because the energy of the
emitted sound is concentrated at the few resonant frequencies of
the soundboard assembly and as the chordal structure becomes more
complex and the vibrations of the strings become more intense the
contrast between these resonant frequencies and the missing or
de-emphasized frequencies becomes more material so as to produce a
more unpleasant sound.
To produce a fuller and richer tone, and to overcome the tendency
of the sound to break-up when the instrument is played in loud
chords, the soundboard assembly of this invention is constructed so
as to be resonant or tuned to a large number of different
frequencies over the audible range of frequencies, thereby
producing a smoother response curve having less contrast between
its peaks and valleys and tending to emphasize practically all
frequencies to a considerable extent. In particular, the soundboard
assembly of a guitar made in accordance with this invention
includes braces on its interior surface so arranged as to cause the
soundboard to have a number of different resonant areas for each
particular frequency of the audible range. That is, for a
particular fundamental frequency, the soundboard has distributed
over its surface a number of different small areas which tend to
vibrate in a substantially resonant fashion in response to such
frequency. At another fundamental frequency, the soundboard
includes a number of other differently located areas which tend to
vibrate in a substantially resonant fashion in response to such
frequency. The size, the pattern, the shape, the number and the
location of the resonant areas all shift and change as the
frequency of the fundamental tone changes, but as a general rule
for any given excitation frequency the soundboard surface includes
at least some area which responds in a generally resonant manner to
amplify such frequency. Accordingly, although the response curve
may include some peaks at frequencies which are emphasized somewhat
more than others, the response between such peak producing
frequencies is more filled in and contains less deep valleys or low
response frequencies than heretofore. In addition to this giving
the guitar a more pleasant tone, it also tends to give it more
volume, better carrying power and long sustained notes due to the
fact that the soundboard assembly tends to readily resonate at any
frequency with small excitation of the string or strings.
An added benefit of the invention is that the particular bracing
employed greatly improves the sound produced by practically all
soundboard materials and therefore not only permits one to obtain a
highly superior sound from the better and more expensive grades of
soundboard materials but to also obtain a very acceptable sound
from less expensive soundboard materials such as plywood.
SUMMARY OF THE INVENTION
The present invention resides in a guitar having a body with a
soundboard assembly including a soundboard, a bridge attached to
the exterior surface of the soundboard below the sound opening, and
bracing secured to the interior surface of the soundboard for
modifying the frequency response of the soundboard and more
particularly for causing it to resonate and produce a significant
response at almost any excitation frequency. The bracing consists
of a main top brace and a main bottom brace both arranged obliquely
to the center line of the soundboard, in different directions of
inclination, and extending across the bass and treble sides of the
soundboard to form a generally V-shaped figure having an apex on
the treble side of the soundboard. The upper or treble-side end of
the bottom main brace is located at approximately the level of the
bridge and the lower or treble-side end of the top main brace may
be located directly adjacent thereto or may be spaced some distance
upwardly therefrom. The area of the soundboard located between the
two main braces comprises essentially a diaphragm in approximately
the center of which the bridge is located. The bracing further
includes a plurality of fan braces, of smaller cross-section than
the main braces, having upper ends located adjacent the top main
brace and extending generally downwardly toward the bottom main
brace, the fan braces being spaced from one another transversely of
the soundboard and being inclined relative to the soundboard center
line so that each has its upper end located closer to such center
line than its bottom end. Preferably, an additional brace is
located above the sound opening and is inclined relative to the
soundboard center line in the direction opposite to the inclination
of the top main brace. Another brace may be applied in some cases
to extend generally perpendicularly to and across the lower ends of
some of the bass-side fan braces. The soundboard is preferably
tapered in going from its top to its bottom so as to be thicker at
its top than at its bottom, and on its interior surface the
soundboard may be additionally thinned out in areas located below
the bottom main brace and/or above the top main brace. In addition
to the soundboard assembly, the body of the guitar includes side
and back walls and preferably these latter walls are part of a
one-piece back having a rounded back wall curved both in the
longitudinal and transverse directions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of a guitar embodying the
present invention, part of the lower right-hand corner of the
soundboard being broken away to show other details.
FIG. 2 is a side elevational view of the guitar of FIG. 1 with part
of the bowl of the body being shown broken away to reveal other
details.
FIG. 3 is a transverse sectional view taken on the line 3--3 of
FIG. 1.
FIG. 4 is a plan view, drawn on a slightly enlarged scale from that
of FIG. 1, showing the interior surface of the soundboard of the
FIG. 1 guitar and the bracing secured thereto.
FIGS. 4A through 4H are side elevational views of the various
braces of FIG. 4.
FIG. 5 is a plan view generally similar to FIG. 4 but showing
bracing arranged slightly differently from that shown in FIG.
4.
FIG. 6 is a front elevational view of another guitar embodying the
present invention.
FIG. 7 is a plan view, drawn on a slightly enlarged scale from that
of FIG. 6, showing the interior surface of the soundboard of the
FIG. 6 guitar and the bracing secured thereto.
FIGS. 7A through 7J are side elevational views of the various
braces of FIG. 7.
FIG. 8 is a plan view generally similar to FIG. 7 but showing a
soundboard additionally including thinned areas.
FIG. 9 is a sectional view taken on the line 9--9 of FIG. 8.
FIG. 10 is a sectional view taken on the line 10--10 of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and first particularly to FIGS. 1 to
4, these figures illustrate one embodiment of a guitar made in
accordance with the present invention. The guitar is indicated
generally at 10 and includes a hollow body or sound box 12
comprised of a one-piece curved bowl 14 and a soundboard assembly
16 including a flat top plate or soundboard 18. The bowl 14 is
preferably made of a resin impregnated fabric such as plies of
fiberglass fabric impregnated with an epoxy resin and laminated to
an appropriate thickness. The bowl has a generally inwardly curving
waist characteristic of a conventional acoustic guitar. It
terminates in a forward edge 20 and, as shown best in FIGS. 2 and
3, has a two-dimensionally curved rear wall which produces a
correspondingly curved acoustically effective inner surface 22
which tends to reflect sound more clearly and project it farther
than a more conventional flat surface. The side portion of the
bowl, which terminates in the forward edge 20, includes generally
U-shaped upper and lower bouts, respectively indicated at 24 and
26, connected by inwardly curved central bouts 28, 28 which form
the waist of the instrument. The side portion of the bowl adjacent
the forward edge 20 is substantially perpendicular to the
soundboard 18, and the soundboard is attached thereto by an
L-shaped strip 30 having one leg bonded to the bowl 14 and its
other leg bonded to the soundboard 18, as by adhesive. Included in
the soundboard 18 is a sound opening 32 of circular shape having
its center located on the longitudinal center line of the
soundboard slightly above the level at which the waist of the
instrument is of a minimum transverse dimension.
Also included in the guitar 10 is a neck 34, connected to the body
12, terminating in a peghead 36 and carrying a fret board 38 having
a plurality of frets 40, 40. The illustrated peghead 36
accommodates six strings 42, 42 which at their lower end are
attached to a bridge 44 including an upright transversely extending
bridge member 45. There are fourteen frets 40, 40 on the
illustrated fret board 38 between the peghead 36 and the top of the
body 12, and this is a characteristic common to so-called "folk"
guitars. Except for the soundboard assembly 16, which is
hereinafter described in more detail, the guitar 10 is or may be
identical to the one shown in U.S. Pat. No. 3,474,697 to which
reference may be had for further details of its construction.
The soundboard assembly 16 includes the soundboard 18, the bridge
44 and a unique arrangement of bracing secured to the interior
surface 46 of the soundboard. It may also include, on the exterior
surface 50 of the soundboard, a rosette or purfling ring 48
surrounding the sound opening 32 and possibly a band of purfling or
other edge trim extending along the outer edge of the soundboard,
but these details do not form any part of the present
invention.
The soundboard 18 is preferably made of a single thickness of wood,
such as spruce, and also, as shown best in FIG. 2, is preferably
tapered from top to bottom so as to have a greater thickness at its
top than at its bottom. This provides the body 12 with maximum
strength at its upper end where it is attached to the neck 34 while
providing the soundboard with greater freedom of vibration in its
lower region. It should be noted, however, that this tapering is
not absolutely necessary to the broader aspects of the invention
and if desired the soundboard may be made with a uniform thickness
from top to bottom. In fact, one of the benefits of this invention
is that the bracing applied to the interior surface of the
soundboard enables what were previously considered to be poor
soundboard materials to produce greatly improved tonal results; and
by using the present invention very good sounding guitars may be
made using untapered soundboards of relatively low cost material
such as plywood.
The present invention involves primarily the arrangement of the
bracing applied to the interior surface of the soundboard of a
guitar. Before considering in detail the particular bracing applied
to the guitar 10 of FIGS. 1 to 4, it should be understood that the
arrangement of the bracing may vary slightly from one instrument to
another, without departing from the invention, in order to best
suit other design parameters of the guitar and/or to produce a
desired tonal effect such as increase or decrease in the bass or
treble response. As to the other design parameters, the more
important ones involve the style of the guitar, its number and type
of strings and the size of its body. Conventionally, acoustic
guitars are made in either a "folk" style or a "classic" style, and
the strings may be either metallic or non-metallic. Also, the size
of the body and consequently its volume and the size of its
soundboard may vary slightly from model to model. The "folk" style
is characterized by a long neck having a fret board with fourteen
frets between the peghead and the instrument body, and the
"classic" style is characterized by a shorter neck with a fret
board having 12 frets between the peghead and the instrument body.
The string lengths are, however, the same for both styles with the
requirement therefore that the bridge be located lower on the
soundboard in the classic style than it is in the folk style. Metal
strings are held at a higher tension when tuned than are
non-metallic strings and therefore the bridge in a metal stringed
guitar absorbs a higher string load than does the bridge of a
guitar with non-metallic strings. Also, the bridge of a 12 -string
guitar obviously has approximately twice the string load applied
thereto as does the bridge of a six-string guitar. It is therefore
seen that the location of the bridge and the string load imposed
thereon, as well as the size of the soundboard and the volume of
its body, may vary from one guitar to another, and in order to
obtain optimum results from such different guitars it may be
necessary to use in them slightly different variations of the
bracing of this invention. By way of example, several different
variations of the bracing falling within the scope of the invention
are illustrated by the various figures presented in this
application.
Turning next specifically to FIG. 4 and to FIGS. 4A to 4H, these
figures show a presently preferred arrangement of bracing for the
guitar 10 of FIG. 1 which is a six-string folk style guitar having
a relatively large bowl. In referring to these figures, the bracing
includes a number of individual braces, 4A to 4H, all of which are
bonded to the interior surface 46 of the soundboard by adhesive and
all of which are made of wood such as spruce. Also all of the
braces, except for the brace 4E preferably have their end portions
tapered by concave scallops 56, 56. The scalloping is provided
primarily to produce a thin section on each brace end to which it
is applied. The manner of achieving this end thinning is not
however extremely critical and if desired, particularly with the
fan braces, other shaping of the braces may be used such as a
gradual feathering as used on the braces 7E to 7I hereinafter
discussed. The braces consist of a top main brace 4G and a bottom
main brace 4F, both of which are inclinded relative to the
longitudinal center-line 52 of the soundboard and extend across
both the bass and treble side of the soundboard to form a generally
V-shaped figure having an apex on the treble side. As shown in FIG.
4, the bass side of the soundboard is the right hand side and the
treble side the left hand side, the bass side being the side
underlying the lower pitched strings 42, 42 and the treble side
being the side underlying the higher pitches strings 42, 42 in the
completed instrument. All four ends of the top main brace 4G and
the bottom main brace 4F terminate slightly short of the outer edge
54 of the soundboard. The top main brace 4G is arranged so that its
bass-side end 58 is located within the vertical region of the
soundboard defined by the center and the lowermost extent of the
sound opening. In FIG. 4, the line 60 indicates the level of the
center of the sound opening and the line 62 indicates the level of
the lowermost extent of the sound opening, the region containing
the end 58 being the region between the lines 60 and 62. The
treble-side end of the top main brace 4G is located at a lower
level than its bassside end and within the vertical region defined
by the lowermost extent of the sound opening and a lower limit
located approximately at the level of the bridge. In FIG. 4, the
approximate level of the bridge is indicated by the line 66 and the
region containing the end 64 is therefore the region between the
lines 62 and 66. The exact location of the end 64 in FIG. 4 is, in
fact, a spot spaced some distance above the level 66 of the
bridge.
The bottom main brace 4F is arranged so that its treble-side end 68
is located at approximately the level of the bridge and with its
bass-side end 70 located a considerable distance therebelow. The
location of the treble-side end 68 of the bottom main brace at
approximately the level of the bridge has been found to be fairly
critical and is one standard which should be maintained in making
slight variations of the bracing for different guitars.
The top main brace 4G and the bottom main brace 4F are the primary
braces of the invention and, except for the brace 4H, are of
relatively larger cross-section and stiffness than the other
braces. The arrangement of the braces 4I and 4G defines an area of
the soundboard located therebetween which acts somewhat as a
diaphragm and in approximately the middle of which the bridge
resides. As this diaphgram-like portion of the soundboard is
vibrated by the bridge, the main braces tend to transmit these
vibrations to other portions of the soundboard located above and
below such braces to also bring them into vibration.
In addition to the main braces 4G and 4F, the bracing of FIG. 4
also includes five fan braces 4A, 4B, 4C, 4D and 4E. The two fan
braces 4A and 4B are located on the treble side of the soundboard
and the three braces 4C, 4D and 4E are located on the bass side of
the soundboard. All of the fan braces are spaced transversely of
the soundboard from one another, and they are arranged in a fan
fashion so that each is inclined relative to the longitudinal
center line 52 with its upper end located closer to such
center-line than its bottom end. The upper end of each fan brace is
located adjacent the top main brace 4G and each extends downwardly
toward the bottom main brace 4F. The three fan braces 4A, 4B and 4C
have their bottom ends located adjacent the bottom main brace 70,
but the lower ends of the braces 4D and 4E are spaced laterally
outwardly beyond the lower end 70 of the bottom main brace and
terminate slightly short of the outer edge 54 of the soundboard.
The brace 4E is scalloped at only its lower end and at its upper
end engages the top main brace and is preferably bonded firmly
thereto. The fan braces, 4A to 4E, have a substantial effect on the
sound produced by the soundboard and in addition to aiding in
transferring vibrations from the diaphragm area to other portions
of the soundboard also appear to have the effect of breaking up the
area of the soundboard into a larger number of potential resonating
areas.
It has been found that the tone or sound of the instrument is also
usually improved by placing a brace, such as the one shown at 4H,
above the sound opening and arranged to extend across a major part
of both the bass and treble sides of the soundboard with its
longitudinal axis inclined relative to the soundboard center line
oppositely to the inclination of the top main brace 4G so that its
bass side end is lower than its treble side end. The brace 4H is
preferably relatively thick in both its cross-sectional dimensions
so as to be relatively stiffer than the fan braces 4A to 4E.
With regard to the arrangement of the top main brace 4G and the
bottom main brace 4F, it has been found that by varying the spacing
between their treble-side ends 64 and 68 the tonal response of the
instrument may be controlled to some extent. In particular,
increasing the spacing between these ends tends to de-emphasize the
bass frequencies, and bringing them closer together tends to
emphasize the bass frequencies. The volume of the bowl generally
has a similar effect on the response of the instrument. That is, a
large volume bowl tends to emphasize the bass frequencies and a
smaller volume bowl tends to de-emphasize the bass frequencies. In
the instrument 10 of FIGS. 1 to 4, the body is one having a
relatively large volume and, therefore, the treble-side ends 64 and
68 of the main braces 4G and 4F are spread a substantial distance
since the large volume of the bowl already produces a sufficient
bass response and no enhancement of it is required. In a smaller
volume bowl, however, the ends 64 and 68 of the main braces 4G and
4F may be placed closer together to obtain a greater bass response
to compensate for the smaller volume of the bowl which normally
produces less emphasis of the bass frequencies.
FIG. 5 illustrates a soundboard assembly generally similar to that
shown in FIG. 4 but wherein the bracing has been arranged to
achieve a greater bass response, thereby in general rendering it
suitable for use on a guitar having a smaller volume body than that
of the guitar 10. In FIG. 5, the various illustrated parts are
substantially identical to those of FIG. 4 and therefore the same
reference numerals have been used as in FIG. 4, except for being
primed, and the various parts need not be redescribed in detail. It
should be noted in FIG. 5, however, that the bottom main brace 4F'
is arranged at approximately exactly the same location as the
bottom main brace 4F of FIG. 4 so that its treble side end 68'
remains at the spproximate level of the bridge. The closing of the
space between the ends 64' and 68' is accordingly achieved by
moving the end 64' of the top main brace 4G' downwardly from the
position occupied by the corresponding end 64 of FIG. 4. Also, the
treble-side end portions of the main braces 4G' and 4F' are not
scalloped in the construction of FIG. 5 and are brought into direct
contact with one another and bonded together by an adhesive.
Referring next to FIGS. 6, 7 and 7A through 7J, these figures
relate to a guitar, indicated by the reference numeral 72, which in
contrast to the guitar 10 of FIG. 1 is of a "classic" style rather
than of a "folk" style. That is, it includes a fret board 74 having
twelve frets 76, 76 between the peghead 78 and the body 80, and
consequently its bridge 82 is located lower on its soundboard 84
than is the bridge 44 of FIG. 1. Except for this difference and the
difference in the bracing applied to the interior surface of the
soundboard 84, the guitar 72 of FIG. 6 is basically similar to the
guitar 10 of FIG. 1 and, except for its bracing, need not be
described in further detail.
FIG. 7 shows the bracing applied to the interior surface 86 of the
soundboard 84 of the guitar 72, and FIGS. 7A through 7J show the
side elevations of the various individual braces employed. The
bracing shown in FIG. 7 includes a top main brace 7B and a bottom
main brace 7C. The top main brace 7B is located and arranged
approximately similarly to the top main brace 4G of FIG. 4, but the
bottom main brace 7C is located somewhat lower than the bottom main
brace 4F of FIG. 4 so as to accommodate the lower location of the
bridge and to maintain its treble-side end 88 at approximately the
level of the bridge 82, such approximate level being indicated by
the line 90.
Between the top main brace 7B and the bottom main brace 7C the
bracing of FIG. 7 includes six fan braces, 7D to 7I, located in the
area between the main braces and spaced transversely from one
another relative to the soundboard. Each of the fan braces, 7D to
7I, has its upper end located adjacent the upper main brace 7B and
extends downwardly from such upper main brace toward the bottom
main brace 7C. Three of the fan braces, 7D, 7E and 7F, are located
on the bass side of the soundboard 84 and the three other of the
fan braces, 7G, 7H and 7I, are located on the treble side of the
soundboard. They are collectively arranged in a fan fashion so as
to be inclined relative to the center line of the soundboard with
each having its upper end located closer to the center-line than
its bottom end. As shown, each of the fan braces has its upper end
tapered by a gradual feathering, except for the one brace 7D which
has an untapered upper end, and all the fan braces are shaped to
gradually taper to a small thickness at their lower ends.
In addition to the two main braces and the fan braces, it has also
been found to be generally beneficial to add a supplementary bottom
brace, such as shown at 7J, to the bracing arrangement of FIG. 7.
This supplemental bottom brace 7J is located near the lower ends of
and arranged generally perpendicular to the bass-side fan braces
7D, 7E and 7F, and in the illustrated case extends between and
directly contacts the sides of the bottom main brace 7C and the
outermost bass-side fan brace 7D. It has still further been found
that usually an improved sound may be produced with the above
described bracing of FIG. 7 by also including in the soundboard
assembly an upper supplemental brace, indicated at 7A and generally
similar to the brace 4H of FIG. 4, located above the sound opening
90 of the soundboard and arranged to extend between the bass side
and the treble side of the soundboard with its bass side end lower
than its treble side end.
As another refinement of the present invention, it has been found
that, when desired, increased treble response of the soundboard may
usually be obtained by thinning out areas of the interior surface
of the soundboard located either below the bottom main brace, above
the top main brace or both. Referring to FIGS. 8, 9 and 10, these
figures show a soundboard assembly 83' identical to the soundboard
assembly 83 of FIG. 7 except for including thinned areas in the
soundboard for increasing the treble response. In these figures
parts which are identical or similar to corresponding parts of FIG.
7 have been given the same reference numerals as in FIG. 7, except
for being primed, and need not be redescribed. As shown in FIG. 8
the soundboard 84' in its interior surface 86' includes a first
depression 92 located below the bottom main brace 7C' and a second
depression 94 located between the top main brace 7B' and the upper
supplemental brace 7A'. These depressions 92 and 94 may be made by
making the soundboard with initially planar interior and exterior
surfaces and then cutting away material from the interior surface
in the areas 92 and 94 so that the resulting soundboard in the
areas 92 and 94 is thinner than it would be if the interior surface
were truly planar.
As previously explained, the accompanying drawings and the
foregoing explanation thereof relate to several specific examples
of this invention, and it is intended that the bracing may be
varied somewhat from these examples without departing from the
broader aspects of the invention. In particular, it should be noted
that the number and arrangement of braces supplementary to the two
main braces, and located outside of the diaphragm-like area of the
soundboard defined by the two main braces, may vary widely. As to
these supplemental braces, it has been found in general that
increasing their number tends to emphasize the treble response and
to decrease the bass response. Also, if it is desired to modify the
response of the soundboard to a particular frequency of vibration
this can be done by exciting the soundboard at such frequency and
locating on its surface various nodes and anti-nodes, nodes being
points at which the soundboard has a low or zero amplitude of
vibration and anti-nodes being points at which the soundboard has a
high amplitude of vibration. Then, placing a supplemental brace at
a node tends to increase the response of the soundboard to the
frequency in question and placing a supplemental brace at an
anti-node has the tendency of reducing the response of the
soundboard to the frequency in question.
* * * * *