Note: Descriptions are shown in the official language in which they were submitted.
CA 02244647 1998-08-10
Title: Capo device for stringed musical instrument
Backcrround of the invention.
l.Field of the Invention
The present invention relates to a capo device for a
stringed musical instrument having series of strings extending
along a fretboard with a series of frets, i.e. an instrument
such as a guitar, lute, banjo and the like. Such an instrument
is played by plucking the strings while using fingers to stop
selected strings by holding them pressed down onto the
fretboard, the string being "stopped" by the adjacent fret.
2. Prior art.
A capo, sometimes referred to as a "capotasto", is a
device which can be used to hold strings independently of the
fingers. Simple capo devices hold all the strings at once,
usually against a particular fret, and change the basic key of
the instrument . Others are known which can be used to press
down and stop only selected strings.
Generally, capo devices do not allow different strings to
be stopped at different locations. However, in U.S.
Pat.No.5,056,397, which issued Oct.15,1991 to Leifheit, a kind
of capo device, referred to as a "fingering device", is
described for a guitar, in which a series of separate capo type
elements are provided each with a bore by which the element is
slidably mounted on one of the strings and is individually
locatable to stop a string at a particular selected location.
Each element has an undercut recess in its underside and can be
individually held in position by having this recess engage one
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of the frets, which are made to protrude from the fretboard.
The elements of the Leifheit device stop the strings directly,
rather than hold the string against an adj acent f ret , as is
more usual with capo devices.
A perceived drawback of the Leifheit device is that the
elements, when not in use, are simply pushed to the end of the
strings near to the string nut which terminates the vibrating
portion of the strings near the head of the guitar. It seems
likely that in this position the elements, although no longer
attached to the fretboard, would still vibrate with and thus
affect the vibration of the strings.
The present invention seeks to provide a capo type device
which overcomes these drawbacks, and is also easier to use than
the Leifheit device. The device of this invention is easy to
engage and disengage with the fretboard, it stops the strings
in the usual way by holding them against adjacent frets, which
are conventional frets, and it provides a storage area for the
elements when they are not in use where they cannot vibrate
with the strings.
Summarv of the Invention
In accordance with one aspect of the present invention, a
capo device for a stringed instrument of the type described,
having a series of strings extending along a fretboard, is
characterized by each string of the series passing through a
bore in an element which is slidable on the string, with each
element being dimensioned so that when held against the
fretboard the element stops the string on which it is mounted
at an adjacent fret. The elements and the fretboard have
interacting magnetic means capable of holding each element
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against the fretboard at one of a number of selected positions
during the playing of the instrument, while allowing movement
of the elements to a stored position when not in use.
The magnetic means may include permanent magnets set into
the fretboard at a series of locations adjacent individual
fret, and/or a permanent magnet mounted within each of the
elements. In a preferred embodiment, however, all the magnets
are in the fretboard, and these cooperate with capo elements of
ferromagnetic material, such as steel.
A stored position for the elements may be provided beyond
the ends of the vibrating portions of the strings, so that the
stored elements cannot affect the vibration of the strings.
Usually, the stored position will be defined either by a so-
called "string nut", or by a "zero fret" which is a large fret
terminating the vibrating portion of the strings. Both the
"string nut" and the "zero fret" will be hereinafter referred
to as an "end stop", since both define the end of the vibrating
length of the strings, when not otherwise stopped. Thus,
according to another aspect of the invention, a capo device is
characterized by the combination of the slidable elements and
fretboard with interacting means capable of holding the
elements against the fretboard during the playing of the
instrument, while allowing movement of the elements over the
frets to a stored position when not in use, along with a stored
position defined between an end stop and an auxiliary string
guide which contacts the strings between the end stop and the
usual tuning pegs. The elements are movable over the end stop
into the stored position. Where a string nut is used, a ramp
member is preferably provided on the fret side of the string
nut to facilitate movement of the elements over the nut and
into the stored position.
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As an alternative, the conventional string nut or zero
fret may be dispensed with, and a series of storage recesses or
pockets may be provided which locate the elements in stored
positions in which they act to terminate the maximum vibrating
length of the string. Unlike in Leifheit, the elements in this
position are positively located and held against movement, and
cannot vibrate with the string, so that the strings have a
properly defined maximum length of vibration.
Brief Description of the drawing
Preferred embodiments of the invention will now be
described by way of example with reference to the accompanying
drawings, in which;
Fig.l is a top view of the fretboard portion of a guitar
incorporating the invention;
Fig.2 is a side elevation of the same parts as shown in
Fig. l,
Fig.3 is an enlarged, perspective view of one slidable
capo element;
Fig.4 is a side view of the same element and associated
parts,
Fig.S is an enlarged top plan view of an alternative
construction of the head end of the guitar;
Fig.6 is a view similar to Fig.5 of another alternative,
and preferred, form of the invention;
Fig.7 is a side elevation of the same parts shown in
Fig.6; and
Figs.8 and 9 are views similar to Figs.3 and 4 of the
preferred embodiment of Figs.6 and 7.
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Detailed Description.
Figs.l and 2 show the neck 10 of a guitar, this neck
extending between the guitar body 11 and head 12. The body, and
the parts mounted on the body, are conventional, and include a
bridge (not shown) which anchors inner ends of the six strings
14. The strings extend along a fretboard 16 on the front face
of the neck, having a parallel series of frets 17, and have
their outer ends held by spindles 18 rotatable by tuning pegs
19, these parts also being conventional. The frets 17 are also
generally conventional, having semi-cylindrical protruding
portions which stand just over 1 mm above the planar surface of
the fretboard.
As is also usual, the vibrating portions of the strings
terminate at a "string nut" 20, and pass from the nut onto the
spindles 18. Usually, the strings diverge after passing over
the nut. Here, however, the strings remain parallel and
substantially unbent until they pass over an upstanding
auxiliary guide 22, after which they slope down towards the
head and diverge towards the spindles . In the space between the
nut 20 and the guide 22 is a platform 24, spaced a few
millimeters below the strings . This platform has the same width
as the neck and a length of about 1.5 cm; it provides a stored
position for the capo elements to be described. On the
fretboard side of the nut 20 a ramp member 26 provides a
transition between the fretboard and the nut which facilitates
movement of the elements into the stored position.
The fretboard 16 is modified, in accordance with the
invention, by the provision of several rows of small
cylindrical magnets 30, these magnets being each fitted into a
cylindrical recess drilled into the fretboard and aligned with
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one of the overlying strings. The magnets are centered about 6
to 8 mm on the outerside (i.e. on the head side) of each of the
frets 17. The magnets are so-called "rare earth" permanent
magnets, specifically neodymium-iron-boron magnets, preferably
of N-35 strength or greater; suitable magnets have a diameter
of about 1/4 inch (about 6 mm). Usually, the rows of magnets
are provided at the outside of the outermost seven frets, but
could be provided for more of the frets if desired.
The magnets 30 cooperate with slidable capo elements 32,
best shown in Figs.3 and 4. Each element is rectangular when
seen is plan view; in side view (Fig.4) it is generally
rectangular but has rounded or bevelled lower corners 32a
providing ramp means which enable it to move over the frets.
The element has a length of about 11 mm, which is slightly less
than the narrowest gap between adjacent frets, and has a width
and height of about 7 mm. It is preferably formed of hard wood
such as ebony, or plastic . The lower portion of the element has
a longitudinal bore 34, laterally centered and spaced less than
1.0 mm from its lower surface, and which has a diameter,
usually about 1/16 or 3/64 inch (1.2 to 1.5 mm), by which it
has a snug but readily sliding fit on the respective string 14.
Although it is not essential, the bore may have a bushing or
liner of soft material to avoid any vibration of the element on
the string.
The element 32 also has a wide cylindrical bore normal to
and passing through the center of its top surface, which
receives a magnet 36 which may be the same as, or similar to,
one of the magnets 30 in the fretboard, and which has its lower
end close to the bore 34. Between the bottom of the magnet and
the bottom face of the element is a steel disc 38, through the
lateral and axial center of which passes the bore 34. Use of
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the steel disc avoids the need to drill through the magnet 36,
which requires special equipment.
The magnets 30 and 36 are of suitable strength that when
an element 32 is located with its magnet aligned with a magnet
30 it is pulled into contact with the fretboard, in which
position, as shown in Fig.4, it holds the string on which it is
mounted against the adjacent fret, effectively stopping this
string in the same manner as a player's finger. The disc 38
completes the magnetic circuit between the two magnets.
However, the magnetic force can easily be overcome by the
player using a finger to push the element along the string when
this is to be repositioned, the sloping corners 32a allowing
the element to ride over the frets. This action is believed to
be much easier than that involved in the Leifheit construction,
and allows for easy rearrangement between songs. When the capo
elements are not needed, they can be simply pushed to the end
of the fretboard, with the ramp 26 allowing them to pass over
the nut 20 into the stored position above the platform 24,
where they cannot affect the vibration of the strings.
Fig.5 shows an alternative arrangement at the head of the
guitar, in which the nut 20 and ramp 26 have been dispensed
with, and instead a fitting 40 is provided having recesses or
pockets 41 spaced across the fretboard at its head end, each
recess underlying one string end and providing a storage
position for one of the capo elements. Each recess 41 is made
to fit its element precisely, so that the element in this
position is firmly located and cannot vibrate, and its string
is stopped at the end of the element, which is close to the
normal string nut position. For precisely locating the
elements, the recesses may be lined with shims of veneer.
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Figs . 6 to 9 show a preferred construction in which all the
magnets 30' are in the fretboard, and the capo elements 32' are
of ferromagnetic material, preferably steel, and have no
magnets. This construction has the advantage that the capo
elements do not tend to attract and stick to each other, as
sometimes happens with the embodiments previously described. To
give the required attractive force between the capo elements
and the magnets, the magnets are provided in pairs, the magnets
of each pair being aligned longitudinally, i.e. along the
string direction, and the magnets of each pair being closely
spaced so that they can attract the same capo element.
As shown in Figs.6 and 9, the pairs of magnets are
preferably mounted on the fretboard by means of transverse
mounting strips 50, each having a length equivalent to the
fretboard width, a width of about 16 mm or 5/8 inch, and a
thickness of about 3 to 4 mm. The strips are arranged to be
glued in correspondingly sized mating grooves extending across
the fretboard on the outer sides of the first seven or more
frets. The strips may be of wood, and wood-type adhesives such
epoxy glue may be used to secure these in place. Each strip has
six pairs of magnets along its length, each located in relation
to an overlying string, the magnets each having a diameter of
about 1/4 inch or 6 mm, and being closely spaced, separated by
say about 2 mm. Each pair of magnets has one magnet with its
south pole uppermost, and one with its north pole uppermost.
The capo elements are simple slugs of steel, about 8 to 10 mm
in length, i.e. having a length which at least spans the major
part of the overall length of a magnet pair, and which
completes a magnetic circuit when the element bridges the
surfaces of a magnet pair. The height of the capo elements is
less than in the previous embodiment, and is typically about 4
mm. The elements have a horizontal bore for receiving a string,
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i
as in the previous embodiment, and preferably have a liner to
prevent vibration on the string.
The rest position of the elements is in this case provided
by an end series of pairs of magnets, held by a transverse
strip 50' between the string guide 22, which is similar to that
of Figs.1-4, and a "zero fret" 20' which acts as an end stop
preventing vibration of the strings beyond this position and
thus defines the end of the vibrating string length. The zero
fret is of similar height to the nut 20, but since it is
rounded, it does not require the ramp member used with the
string nut of the first embodiment.
While the description above has concentrated on permanent
magnets which are suitable for use with a conventional acoustic
guitar, nevertheless with an electric guitar, electro-magnets
may be used, and the term "magnetic means" is of course broad
enough to cover such electro-magnets.
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