Note: Descriptions are shown in the official language in which they were submitted.
10805~
The present invention relates to stringed
instruments and particularly to guitars. For convenience
of description reference will be made to guitars, but it
. i9 to be understood that this term is intended to include
other stringed instruments.
~' A guitar comprises a body, a head and a neck
r- interconnecting the head and bodyO A plurality of frets
are mounted transversely at spaced intervals along a
~- fingerboard or fretboard secured to the neck and extending
, 10 over the surface of the sound table to the sound hole.
Strings extend from a bridge, over a saddle, along the neck
~ and over a nut mounted at the junction of the neck and
; head to separate machine heads which are used for retaining
~; and tensioning the strings.
, 15 When a guitar is played, the strings are pressed
down by the fingers towards the fingerboard until they meet
~;, the frets and/or fretboard so that when the string is
vibrating it will produce a note of the required pitch or
frequencyO This note should be accurate to within an error
which the human ear cannot detect and should be free of
~ ~ .
spurious noises (e.g~ rattle and buzzing) which are not
directly related to the production of the required pitch or
-~ frequency and its harmonics.
The main factors which affect the notational
,' 25 accuracy and the amount of spurious noise are as followso
s (1~ The height of the string9 above the fretboard.
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1080522
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~;~ If the height of the strings above the fretboard
is too low, the vibrating string will knock against the
frets between where it is being pressed down and the
bridge, this produces an unwanted buzz or rattle. If the
` 5 string is too high, the time taken to press the string
down onto the fretboard will be undesirably long and it
will make the guitar slow and difficult to play. Also
; the string will be stretched when depressed to the
fretboard which will result in an increase in tension
and a consequent raising of the pitch of the note.
If the string is plucked gently as in finger
picking, the minimum height of the strings may be less
to avoid buzz and rattle, than if the strings are being
strummed when they will vibrate more strongly.
t2) The longitudinal flatness of the fretboard.
.
The longitudinal flatness of the fretboard is
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important because it affects the minimum height of the
j ~ strings that can be used without rattle. If the fretboard
~ curves or twists along its length the height of the
- 20 ~trings i8 determined by the minimum height above the
highest points of the curves or twists, and because of
the irregularity it is much more difficult to play.
To prevent the fretboard from curving, many
guitats have a metal rod or "truss rod" set at a slight
angle to the fingerboard inside the neck to compensate
for the upward pull of the strings. In practice the
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10805ZZ
truss rod needs constant adjwstment and i9 only partially
effective.
(3) The surface profile of the fretboard.
The surface profile of the fretboard affects
notational accuracy and also the ease of play~ When a
string is pressed onto a fret, which protrudes from the
fretboard, it will produce one note, but if it is pressed
down harder onto the fretboard behind the fret, it will
be stretched over a longer distance and the resulting
increase in the tension of the string will cause the
pitch or frequency of the note to be raised by an audible
amount.
Therefore, it is desirable to have as low a fret
height as possible, but the lower the fret height the
- 15 faster the fret will wear outO
(4) The position of the fret relative to the
scale length.
This determines the frequency of the notes
obtained when the guitar is played: if the frets are
wrongly positioned the guitar will not play in tune.
As well as having the greatest possible notational
accuracy and the minimum of spurious noise, a fretboard
should have as long a working life as possible maintaining
- these characteristics and it should also be easy to play
and offer maximum comfort to the player.
Conventional fretboards are made from hard wood,
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iO805Z~
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with frets of nickel, silver or other materialO The neck
is made of wood and the truss rod is metalO The nut is
plastics or bone, with grooves cut in the top for the
~ strings, and it determines the height of the strings above
i 5 the fretboard in conjunction with the bxidge saddleO
The disadvantages of this design are as follows:
The height of the strings above the fretboard
~- is permanently fixed by the nut, and only slight alteration
can be obtained by altering the saddle height at the bridge~
This means that the string height is best for either finger
picking or strumming, or else it may be set for Hawaiian
style (bottleneck) where the strings should be about a quarter
of an inch from the fretboard and also in a flat plane rather
than following the curvature of the fretboard. Therefore
- 15 the player is restricted to playing in the manner for which
the guitar is æt or must settle for a compromise.
As the neck and fretboard are made from wood, and
are being subjected to the pull of the strings, they tend
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to bend or twist and therefore cause the height of the
strings above the fretboard to increase, which is
undesirable. Also, as the humidity and temperature of the
-~ wood changes, so further stresses are set up and increase
:
this effect~ Due to these changes, al~hough the fretboard
j may start off straight, the straightness does not last and
t 25 usually needs lengthy repairsO
;~ Further the fret material is, of necessity, a soft
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108VSZZ
metal and therefore it is subject to a high rate of wear.
As the frets wear so the profile flattens and produces a
condition wherein the frequency can increase by a quartertone
to a semitone in the pitch of a note selected.
According to the present invention, there is
provided a fretboard adapted to be fitted to the neck of a
stringed instrument, the fretboard comprising a unitary,
elongate body having first and second longitudinally spaced
ends to be arranged adjacent the body and head ends,
respectively, of a stringed instrument, and a plurality of
integrally formed frets in the normal fret positions, said
frets comprising transversely extending crests of a
plurality of triangular shaped ridges arranged in succession
along a surface of said body from said first end to said
second end, each said ridge comprising a relatively short
side steeply inclined to the longitudinal axis of said body
and a relatively long, substantially planar side sloping
from the top of said short side to the base of the short
side of the next following ridge in the direction of said
second end, the top of each said short side where it meets
its associated relatively long side, being rounded with the
centre of curvature located on an imaginary line extending
substantially at right angles to the longitudinal axis of
said body and passing through the crest of the associated
ridge, at least the crest of each ridge having a hard, wear
resistant surface. By having the steeply inclined faces of
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10805Z2
the ridges face towards the body of the guitar and the
opposite longer faces slope gently back to the base of the
fret behind, there i9 a reduction, as compared with
conventional fretboards, of the frequency deviation caused
when the string is fretted, and also there is a reduction
in the force opposing fretting movement of the fingers when
the hand is being moved rapidly up the fretboard.
. .
The present invention also relates to a stringed
instrument having such a fretboard.
The fretboard should preferably be made of a
light, strong substance with a hard surface, so that it will
not wear in use, nor bend or twist under the tension of the
strings. Suitabl~ substances may be high impact plastics,
~ magnesium alloy, aluminium alloy with a hard anodised
; 15 surface, pla~tics or aluminium alloy with hard strips set
!. l
into the crests of the ridges, e.g. tungsten carbide, or
be
any other suitable substance which may/either machined,
cast, moulded or a combination of these. The front face
- of the frets may be marked in a different colour of hard
i~l 20 anodising or by any other method for ease of fret
identification.
The fretboard may be screwed or glued to the neck
,; in the conventional manner. If desired, an elongate
stiffening bar may be formed in the underside of the
,;
~ 25 fretboard, being located in a groove formed in the neck of
:;
;~ a guitar to which it is fitted.
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1080522
Further the elongate stiffening bar may be made
in a male dovetail form, and the slot in the neck may be
made in a female dovetail form. If the female is tapered
slightly at the body end of the neck the fretboard may be
attached to the neck simply by slotting the male dovetail
bar into the female dovetall groove formed in the neck and
; tapping them tight, thereby forming a friction fit.
If desired the fret may be of convex shape as
viewed in a cross-section transverse to the longitudinal
axis of the fretboard.
Further, the neck may be formed of plastics,
glassfibre, or other synthetic material that would have the
advantage of increasing the strength whilst not being
affected by humidity or age, or the neck and fretboard may
be made as a single unit. A wooden neck would also be
suitable provided that the fretboard is designed to accept
the total string load
Apart from the simplicity of fitting such fret-
boards, or replacing them, the working life should be
considerably extended d~e to the surface wearing at a slower
rate than conventional frets. Also the position of the frets
- may be determined with a precision accuracy which will not
` change with wear~ The fretboard with an elongate stiffeningbar will maintain its original flatness far better than
conventional fretboards and will not be subject to changes
. .
due to humidity or temperature as much as conventional
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108~5ZZ
fretboards~ The truss will not be needed, so adjustment
and manufacture should be simplified.
Due to the cumulative effects of these factors,
the height of the strings above the fretboard may be kept
to a minimum for any mode of play, This will improve both
the notation and the ease of play.
The accuracy of the fret positioning and the
reduction in notational deviation caused by the string
bending over the fret when it is being played will make
any inaccuracy in frequency inaudibleO
If desired the stringed instrument may be
provided with a rotatable string supporting nut. The
- rotatable nut may be of substantially cylindrical form with
circumferential grooves therein through which strings extend
in use, the nut being so mountable or the grooves being so
shaped that the height of the strings above the surface of
a fretboard of a stringed instrument to which the nut is
-~ fitted may be varied by rotating the nut.
i~ Prefe~ably, the sides of the grooves are so formèd
that when a groove is viewed in section its sides diverge
outwardly O This permits the string supported by, and
extending tangentially from, the bottom of the groove to
vibrate freely without contacting the sides of the groove.
Preferably the shape of each groove is that of a
,~
plane spiral so that the scale length is not varied when the
nut is rotated about its longitudinal axis, therefore any
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~08~5~Z
height of the strings above the fretboard can be selected by
the player to suit the mode of play.
Further, by having slightly different dimensions
on the plane spirals, the strings may follow the curvature
of the fretboard in the low position suitable for finger
picking or strumming and in the high position may be in a
flat plane suitable for Hawaiian or "bottlenedk" style.
The cylindrical nut may be rotatably mounted in
brackets at each end or in any other way so that it can
rotate. It may be driven by a lever, or a worm gear and
cog mounted at either end~ The cog may be made as an
integral part of the cylinder between the grooves, with the
~; worm gear coming up through the base of the neck so that it
~ meshes with the cog. This would have the advantage of
f 15 keeping the weight down to a minimum, and it would reduce
~ the chance of accidental damage and make the drive mechanism
i as compact and efficient as possible~
A device similar to the cylindrical nut may be
used in place of the bridge saddle, with arrangements for
longitudinaljdisplacement and adjustment.
~ I~ desired, the mounting for the nut may be formed
f~ as an integral part ofi the fretboardO
,; Reference is made to the accompanying drawings in
~ which Figures 1 to 3 show a portion of a conventional
; 25 fretboard and Figures 4 to 12 illustrate an exemplary
embodiment of the present invention~
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~08052Z
In the drawings:
Flgures l and 2 illustrate a portion of a
:~ conventional fretboard including the eleventh and twelfth
frets and the fingering thereof,
Figure 3 is a view similar to Figure 2 showing
~- the effect of worn frets;
Figures 4 and 4A are the plan view and side
elevation view of a fretboard made in accordance with the
present invention:
Figure 4B is an enlarged segment of Figure 4A
showing a cross-sectional side elevation of one fret:
the vertical line shows the actual point of the fret
position:
:~ Figure~ 5A and 5B are left and right end views
of the fretboard shown in Figure 4:
Figures 6 and 7 are the side and end elevations
.,
. of a nut for use in a stringed instrument provided with a
;- : fretboard in accordance with the present invention, showing
; the grooves for the strings, the integral cog and the axles
which locate in the brackets shown in
.,
: Figures 8 and 8A which are the side and end
~ elevation of the brackets:
~j
~ Figures 9, 10 and 11 are views showing various
.
shapes of groove formed in the nut of a six string guitar:
: 25 Figure 12 is a cros~ sectional side elevation
of the end of the neck and fretboard, showing one machine
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1~38V52~
head and an embodiment of one driving mechanism for the nut.
Referring to Figures 1 and 2, the surface profile
of a conventional fretboard 100 i~ a flat surface with
ridges or fretq 101 at calculated intervals along its
S length. Notional or frequency deviation occur~ when a
string 102 is pre~sed from its rest or unfretted position
shown by broken line 103 onto the fret by an instrument
: player's finger 104. Factors governing the frequency of
the required note are ~hown in the following equation
f = 2 1 ~ m
where f is the pitch or frequency
1 i8 the vibrating length of a string
T is the tension on the string, and
m iS the mass per unit length of the string.
When a ~tring is in its rest or unfretted position
103, it i8 under a predetermined tension "t" in order that the
correct frequency "f" be obtained. When the string is pres-~ed
down from it8 rest position into contact with the fret there
i~ a corresponding increase in the value sf "t" and therefore
.~ 20 an increase in "f". This error is shown as El in Figure 1.
In practice, when the string 102 i8 pu~hed down
~dr frétted) the situation shown in Figure 2 is likely
t~ o~cur. ~e ~trin~ 102 i~ pushed a greater diAtance
fr~m it~ rèst p~sition and the error E2 in Figure 1 further
incre~e~ the v~lue of "t" leading to a further increase of ~Ifu. :
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10~3~5Z2
i Although the distance of El in Figure 1 is greater
than E2, the effect of E2 on the tension is far greater.
This is because the string i8 forced to bend around the
fret 101 and under the finger 104, as shown in Figure 2,
causing it to follow a longer path, which results in an
f~ ~ increase in "t" and hence in "f". This second error in
practice tends to be approximately ten times that of the
first error, and in practical tests the second error was
, . ,
seldom less than a quartertone~
Figure 3 indicates the situation in which the
frets 101 are worn, the vertical lines "A" indicate the
points from which the vibrating length "1" is calculated.
Due to the flattening of the fret, the string
, now leaves the fret at point B, causing the error E4
which decreases "1" which in turn increases "f" still
further.
The sum of E3 plus E4 all working to increase
the value of "f" cause changes of a quartertone to a
~; semi tone in the pitch of a note selected~
¦ 20 Referring to the above equation it must be
noted that, due to the frequency doubling effect of a
guitar top or resonator, the string is arranged to
vibrate at half the frequency "f" of the required note.
For example, an "A" string fretted at the 12th fret
~; . .
vibrates at 21905 Hz but the body of the instrument
produces a note of 439 Hz. Therefore, any error in the
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1()8052Z
vibrating freq~lency of the string due to errors in fretting
will be doubled in the same manner.
These changes in pitch represent a significantly
audible deviation from the required note. Hence it is
desirable to reduce or eliminate these errors in fretting.
Figures 4, 4A, 4B, 5A and 5B show a plan, side
elevation, an enlarged section of the side elevation
and an end elevation of a fretboard 12 made in accordance
with the present invention. The fretboard i9 made of a
material which is both light and strong (such as the
materials mentioned earlier) which must withstand the
string tension without bending. As can be seen from the
side and end views of the fretboard, an elongate bar 13
extends along part of the undersidé of the fretboard for
increa~ed strength and rigidity.
The elongate bar is set into a groove in the neck
of the guitar (not shown,). The fretboard may be screwed
or glued to the neck. To speed up and simplify the
assembly or removal of the fretboard from the neck, the
- 20 elongate bar 13 may be made in the form of a male dovetail
as shown in Figures 5A and 5B, and slotted into a female
dovetail in the neck. By making the female dovetail smaller
at the end of the neck nearest the guitar body, the fret-
board may be held in position by a friction fit. If
necessary small barbs may be incorporated on the sides of
the elongate dovetail bar to prevent the fretboard from
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1~)8052'~
sliding along the neck away f:rom the body.
The upper surface of the fretboard has a plurality
of ridges 15 of a sawtooth shape when viewed in the side
elevationO The ridges are of increasing pitch from 16 to
the end 17 which is attached to the body of the guitarO
The ridges 15 are substantially triangular shaped when the
fretboard is viewed in cross section with the frets
comprising transversely extending crests of a plurality of
the triangular shaped ridges arranged in succession along
a surface of the body, each ridge 15 comprising a relatively
short side steeply i.nclined to the longitudinal axis of the
fretboard and a reIatively long, substantially planar side
sloping from the top of the short side to the base of the
short side of the next following ridge along the length of
the fretboard~ As shown in Figure 4B the steeply inclined
short face of each ridge is rounded. In particular t.he
top of each short face, where i.t meets the associated long
face of the ridge, is rounded with the centre of curvature
being located on an imaginary line extending substantially
: 20 at ri'ght angles to the longitudinal axis of the fretboard
and passing through the crest of the ridge.
The surface of at least the crest of each ridge
of the fretboard must be hard and smooth so that it is
pleasant to play and wear is kept to a minimum, e.gO hard
anodising on aluminium, or high carbon steel strips may
be inserted into the crests of the ridgesO
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108VS~Z
~y using the sawtooth shaped profile, of the
above con~truction,the height of the strings above the
fretboard may be permanently kept at the lowest and hence
the fastest level regardless of normal humidity or
temperature fluctuations. Notational deviation will be
outside the range of human hearing, string wear will be
reduced due to a greater area of string being in contact
with the sawtooth profile, which allows the stress to be
distributed over a wider area of both string and sawtooth
fret; there will also be less opposition to the player's
fingers when moving swiftly up the fretboard.
Figure 6 shows details of a nut 26 which is
preferably made from stainless steel, or a material having
a similar degree of surface hardness and durability, and is
formed from a cylindrical length of rod. The nut is
rotatably mounted in end brackets shown in Figures 8 and 8A
and ha$ a cog 22 machined or cast into it ~o that it can be
driven. The nut has six helical grooves numbered l to 6 for
the strings (not shown), which grooves diverge in a radially
outwards direction to prevent the strings vibrating against
the sides of the grooves. The bases of the grooves are of
various widths, as shown in Figure 1, to accommodate various
widths of strings, the groove l being the narrowest and
the groove 6 being the widest. The cross-sectional shape
of the root forming the base of each groove l to 6, that is,
a section transverse to the longitudinaI axis of the nut 26,
,
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10~3V5~2
is in the form of a plane spiral or snail cam in that the
root of each groove increaseis progressively from a minimum
to a maximum radius. The roots of the grooves are arranged
in matched pairs, and on the drawings the matched pairs are
the grooves 1 and 6, 2 and 5, and 3 and 4. Although the
pairs of grooves have similar shapes they have different root
dimensions and taking the cross-sectional views shown in
Figures g to 11 as a specific example the dimensions in
millimetres are as follows, starting at the maximum radius
and taking the radii at three other positions indicated at
X, Y, Z in each of the Figures, the positions X, Y and Z being
angularly spaced from the position of maximum radius and from
each other in a clockwise direction about the axis of the
nut by 90.
Figure Grooves R~dii Posn. X Posn. Y Posn. Z
.__ ...
9 3,4 S.8 5.132 4.466 3.8
.
2,5 5.8 5.067 4.334 3.6
11 1,6 5,8 4.9 4.0 3.1
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The overall d~ameter of the nut is 13O6 mm.
Although the ~ut 26 is preferably made as a
unitary member from a single length of stainless steel rod,
it may comprise a splined shaft having a plurality of
snail cams of suitable shape which are spaced apart on the
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10~305ZZ
shaft by spacer members non-rotatably mounted on the shaft.
In a further embodiment of the nut it may comprise a
grooved cylinder which is eccentrically mounted whereby
rotation of the nut will cause the height of the strings
to be variedO
At each end of the nut is a 4tub axle 8 which
fits rotatably in the brackets 9 which are shown in side
and end elevation in Figures 8 and 8A.
The nut 26 is driven by the cog 22 which meshes
with a worm gear 23 as shown in Figure 12. The worm gear
23 is mounted on the head of a shaft 20 running up through
a sleeve 21 which is set at an angle through the head 19 ;~
of a guitar. Thus the nut 26 may be rotated by turning
the turn pin or head 24 on the end of the shaft 20. A
shoulder 25 is provided on the shaft 20, the shoulder 25
bears against the lower end of the sleeve 21. For
convenience the turn pin 24, the shaft 20 and the shoulder
25 may be formed as a single unit. The turn pin may also
be formed as a crank handle for faster adjustment.
Although other methods of driving the nut may be
used, such as a lever on the end of the nut, or a worm
gear and cog mounted at either end of the nut, the advantages
` of the above method are that the player has a fine adjustment
of the string height, and the nut will then be held securely
in positionO Also there is nothing at either end of the nut
to obstruct the player's hand.
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By using the rotating cam nut 26 in conjunction
with a fretboard having a sawtooth profile a player may
easily adjust the height and plane of the strings relative
to the fretboard for the optimum in any mode of play and
at the same time obtain great notational accuracy.
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