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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates generally to electrical pickups, more
particularly to a musical instrument pickup and specifically to a pickup
for mounting within the interior of a hollow-body instrument such as a
guitar.
2. Description of the Prior Art
Transducers for converting acoustic energy to electrical energy are well
known and a variety of different types have heretofore been proposed to
meet the requirements of particular applications. For amplifying the
sounds of musical instruments, microphones and pickups connected to power
amplifiers are commonly used.
Acoustic stringed instruments generally include hollow bodies enclosed by a
panel, referred to as a "soundboard" to which the strings are attached.
Sound holes are often provided in the soundboard to emit the sound from
the interior of the hollow instrument body. The configuration, material,
sound hole location, string material and other characteristics of the
musical instrument all affect the tonal qualities of the sound.
Electric stringed instruments, on the other hand, often have solid bodies.
Electric guitars comprise a common type of electric, stringed musical
instrument and include ferromagnetic strings. Pickups are mounted in
proximity to the strings of electric guitars and generally include coils
and magnets which move relative to each other in synchronization with the
vibration of the strings when the instrument is played. The pickup
converts the vibration of the strings to alternating current electrical
signals which can be amplified.
Electric guitars are often designed with solid bodies that are acoustically
inert so that a relatively "pure" signal is produced. The sound produced
by amplified, solid-body electric guitars differs considerably from the
sound produced by acoustic guitars, and musicians tend to select guitars
appropriate for their musical styles and the desired sound
characteristics. For example, acoustic guitars are generally thought of as
having more "resonant" tonal qualities, whereas notes and chords played on
electric guitars can be sustained longer by the pickup and amplification
circuitry.
Hybrid types of guitars include hollow-body electric guitars and acoustic
guitars fitted with various types of microphones and pickups. For
performing, recording and playing with other musicians, acoustic guitar
players often require amplification of their instruments. To this end,
acoustic guitars are often "miked" by placing a microphone in proximity to
the instrument body. The microphone is connected to an amplifier. A
disadvantage with this arrangement is that the instrument body must remain
in proximity to the microphone. Many musicians prefer not to be so
restricted while performing. Another possible disadvantage is that the
microphone may pick up extraneous sounds in addition to those of the
acoustic guitar.
The prior art pickups for acoustic guitars, on the other hand, provide more
mobility for the performer but usually at a sacrifice of resonant tonal
quality. Many prior art acoustic guitars with pickups tend to sound
"tinny", "bassy" or too much like an electric guitar. In general they fail
to provide the resonant tonal qualities preferred by acoustic guitar
players.
Heretofore there has not been available an electrical pickup which
faithfully reproduces the tonal qualities of hollow-body instruments with
the advantages and features of the present invention.
SUMMARY OF THE INVENTION
In the practice of the present invention, an electrical pickup is provided
for a stringed musical instrument having a hollow body with an interior at
least partially enclosed by a soundboard panel mounting the strings. The
pickup includes a coil assembly with a winding having opposite ends. A
coil mounting assembly is adapted for mounting the coil within the
instrument body interior and includes telescopically connected inner and
outer tubes. The outer tube is mounted on the guitar body and the inner
tube is connected to the coil assembly. A magnet assembly includes a
magnet with opposite poles and a lens with a concavity receiving the
magnet. The lens is adapted for mounting on an inside surface of the
soundboard panel with a pole of the magnet aligned with the coil.
Electrical leads are connected to the coil winding ends and are adapted
for connection to a power amplifier.
OBJECTS AND ADVANTAGES
The objects and advantages of the present invention include: providing a
pickup for a musical instrument; providing such a pickup for a
hollow-body, acoustic musical instrument; providing such a pickup with
good tonal qualities; providing such a pickup which transduces acoustic
energy to electrical energy; providing such a pickup which is adapted for
connection to an amplifier for faithfully amplifying the sound of an
acoustic instrument; providing such a pickup which, when coupled to an
amplifier, provides an amplified sound with the resonant tonal
characteristics of the acoustic instrument; providing such a pickup which
is well adapted to the needs of performing and recording musicians;
providing such a pickup which is relatively unobtrusive when mounted in a
hollow-body instrument; providing such a pickup which is relatively easy
to install in a hollow-body instrument; providing such a pickup which may
be installed with minimal modifications to a hollow-body instrument;
providing such a pickup which is adjustable to achieve optimum
performance; providing such a pickup which is adaptable for classical,
steel-string, jumbo and other types of acoustic guitars; providing such a
pickup with a pair of coils wound concentrically in opposite directions;
providing such a pickup with a pair of coil leads and a separate ground
shield for a balanced system; providing such a pickup which, when
installed n an acoustic guitar, is not likely to subject a musician
playing the guitar to electrical shock; and providing such a pickup which
is economical to manufacture, efficient in operation, capable of a long
operating life and particularly well adapted for the proposed uses
thereof.
Other objects and advantages of this invention will become apparent from
the following description taken in conjunction with the accompanying
drawings wherein are set forth, by way of illustration and example,
certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary
embodiments of the present invention and illustrate various objects and
features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an acoustic guitar with a pickup embodying
the present invention shown in phantom.
FIG. 2 is an enlarged, fragmentary, sectional view of the guitar taken
generally along line 2--2 in FIG. 1 and showing a side elevation of the
pickup.
FIG. 3 is a horizontal, cross-sectional view of the pickup taken generally
along line 3--3 in FIG. 2.
FIG. 4 is an enlarged, fragmentary, vertical, cross-sectional view of the
pickup, particularly showing coil and magnet assemblies thereof.
FIG. 5 is a horizontal, cross-sectional view of the pickup taken generally
along line 5--5 in FIG. 4 and particularly showing a bottom plan view of a
magnet assembly.
FIG. 6 is a horizontal cross-sectional view of the pickup taken generally
along line 6--6 in FIG. 4 and particularly showing a schematic diagram of
the coil windings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As required, detailed embodiments of the present invention are disclosed
herein; however, it is to be understood that the disclosed embodiments are
merely exemplary of the invention, which may be embodied in various forms.
Therefore, specific structural and functional details disclosed herein are
not to be interpreted as limiting, but merely as a basis for the claims
and as a representative basis for teaching one skilled in the art to
variously employ the present invention in virtually any appropriately
detailed structure.
Without limitation, vertical orientational references (e.g. up, down, top,
bottom, etc.) apply to the pickup and guitar as oriented in FIG. 1).
I. Introduction and Environment
Referring to the drawings in more detail, the reference numeral 10
generally designates a pickup embodying the present invention which may be
mounted substantially within a hollow-body musical instrument, such as an
acoustic guitar 11. The guitar 11 includes a hollow body 12 with a
soundboard panel 13 having sound hole 14 and partially enclosing a body
interior 15. The body includes a butt block 16 to which a strap 17 may be
attached at one end. A bridge 18 is mounted on an exterior surface of the
soundboard panel 13 between the sound hole 14 and the butt block 16.
Strings (e.g. numbering six for a guitar) 19 are each attached at one end
to the bridge 18. A neck 20 extends from the body 12 and mounts the other
ends of the strings 19. The other end of the strap 17 may be attached to
the neck 20 as shown or to the body 12.
The acoustic guitar 11 described thus far is generally of a type which is
commonly available in different sizes, styles, price ranges, etc.
The pickup 10 generally comprises a coil assembly 21, a coil mounting
assembly 22 and a magnet assembly 23.
II. Coil Assembly
The coil assembly 21 includes a bobbin 28 with parallel, spaced, upper and
lower bobbin disks 29, 30 each concentrically mounted on a bobbin center
post 31 with upper and lower ends 33, 34. The upper bobbin disk 29 is
mounted adjacent to the bobbin center post upper end 33, and the lower
bobbin disk 30 is positioned slightly below and in close proximity to the
bobbin center post upper end 33. An annular winding groove 32 encircles
the bobbin center post between the disks 29, 30. The upper and lower
bobbin disks 29, 30 include perimeters 39, 40 respectively.
An inner coil winding 35 is wound concentrically around the bobbin center
post 31 within the winding groove 32 in a first direction, e.g. clockwise
as shown in FIG. 6, and includes first and second ends 36, 37. An outer
coil winding 38 is wound concentrically around the inner winding 35 in a
second direction, e.g. counterclockwise as shown in FIG. 6, and is located
between the bobbin disk perimeters 39, 40 and the inner winding 35. The
outer winding 38 includes first and second ends 41, 42. The windings 35,
38 may comprise copper wire, for example, forty-two gauge or finer.
The inner and outer windings 35, 38 are substantially equal in length, and
their respective first ends 36, 41 and second ends 37, 42 are connected
together at first and second winding terminals 45, 46. The windings 35, 38
may be wound to achieve a desired impedence, for example about three
hundred and forty ohms each for a total, parallel-connected impedence of
one hundred and seventy ohms. The impedence of the coil windings 35, 38
may be adjusted by varying their respective lengths, by using different
wire gauges and materials, etc. The bobbin center post 31 may comprise a
nonferromagnetic material, such as brass.
The inner and outer windings 35, 38 collectively have a thickness "T" (FIG.
4) equal to the spacing between the bobbin disks 29, 30 and a diameter "D"
which may be slightly less than the diameter of the disks 29, 30. The
winding diameter D is preferably at least four times greater than the
winding thickness T.
A coil housing 49 may comprise a nonferromagnetic material, such as brass
sheet metal, and may include a square top 50, a square bottom 51 and
generally rectangular sides 52. The bobbin center post 31 extends through
the center of the housing bottom 51 in proximity to the post upper end 33.
The disks 29, 30 and the windings 35, 38 are sandwiched between the coil
housing top and bottom 50, 51.
The coil assemby 21 includes a grounded, shielded cable 43 with first and
second (e.g. positive and negative) leads 47, 48. A grounding shield 44 of
the cable 43 is electrically connected to the coil housing 49 by a jumper
53. The leads 47, 48 are electrically connected to the first and second
winding terminals 45, 46 respectively.
III. Coil Mounting Assembly
The coil mounting assembly 22 includes a grounded, three-conductor (i.e.
positive, negative and ground) jack subassembly 55 including an
externally-threaded tube 56 with inner and outer ends 57, 58. The tube 56
threadably receives a bezel nut 59. An end cap 62 includes a coaxial,
internally-threaded receiver 63 threadably receiving the jack subassembly
tube 56. An outer, tubular guide member 67 includes an outer end 68
mounting the end cap 62 and an open, inner end 69 with a set screw 70.
An inner tubular member 74 is telescopically received in the outer guide
member 67 and includes proximate and distal ends 75, 76. A variable-length
section of the inner tubular member 74 adjacent to its proximate end 75 is
slidably and telescopically received in a section of the outer guide
member 67 adjacent to its inner end 69. The inner tubular member 74
includes a coaxial bore 77 extending between its opposite ends 75, 76.
In proximity to its distal end 76, the inner tubular member 74 includes a
passage 79 extending therethrough and intersecting the inner tubular
member bore 77 at approximately right angles. A cable opening 80 is formed
in the inner tubular member 74 and may be located slightly outwardly from
the vertical passage 79. A set screw 81 extends into the inner, tubular
member 74 at approximately the intersection of its bore 77 and its
vertical passage 79.
A coil mounting column subassembly 84 includes a sleeve 85 slidably
received in the vertical passage 79 whereby it extends vertically and is
approximately perpendicular to the telescopic members 67, 74. The sleeve
85 may comprise a nonferromagnetic metal such as brass. Within the sleeve
85 a column insulator 86 is positioned and includes a vertically extending
bore 87. The column insulator 86 is fluted (FIG. 3) and preferably
comprises a resilient, elastomeric material, e.g. rubber, which is
compressed slightly to fit snugly within the sleeve 85. The coil mounting
column subassembly includes upper and lower ends 88, 89. The column
insulator bore 87 receives the coil post 31 and mounts the coil housing 49
adjacent to the coil mounting column subassembly upper end 88.
The cable 43 extends from the coil assembly 21, through the cable opening
80, through the coil mounting assembly telescopic members 67, 74 and is
electrically connected to the jack subassembly 65.
IV. Magnet Assembly
The magnet assembly 23 comprises a magnet 100 with first and second (e.g.
north and south) poles 101, 102. The magnet 100 may comprise, for example,
a lightweight magnetic material such as neodymium ferrite or samarium
cobalt. A circular lens 105 comprising a ferrous material is provided with
a lower, inner concave surface 106; an upper, outer convex surface 107;
and a downwardly, inwardly projecting rim 108. The magnet 100 is attached
(for example, by adhesive) with a pole 101 or 102 against the lower, inner
surface 106 substantially in the center of the lens 105. Although the
second (south) pole 102 is shown against the concave lower surface 106,
the orientation of the magnet 100 could be reversed, which of course would
reverse the polarity of the magnet assembly 23. The lens 105 is attached
(for example, by adhesive 109) to an inside surface of the guitar
soundboard panel 13 so that its rim 108 and the magnet first (north) pole
101 face downwardly into the guitar body interior 15. The lens 105 is
preferably located in a central area of the soundboard panel 13, for
example below the edge of the bridge 18 located closest to the guitar butt
block 16.
The magnet assembly lens 105 functions to mount the magnet 100 and also to
direct the flux to its upper (south) pole 102 from the outer coil winding
38. The approximate orientation of the flux from the magnet 100 is
represented by the flux lines FL. As shown in FIG. 4, the lens rim 108 is
positioned approximately above the outer perimeter of the coil outer
winding 38 whereby the lens 105 has a diameter approximately equal to the
diameter D of the coil outer winding 38.
V. Installation
The pickup 10 of the present invention is designed for relatively easy
installation in a hollow-body musical instrument, such as the acoustic
guitar designated 11. In particular, the pickup 10 is designed for
installation with a minimum of modifications to the instrument. Most
acoustic guitars include a knob screwed into the butt block for attachment
of a guitar strap. A process of installing the pickup 10 in the guitar 11
includes the step of removing the knob (not shown) from the butt block 16.
Using the screw hole (not shown) for the knob as a guide, a jack receiver
112 is drilled through the butt block 16. The jack receiver 112 may have a
diameter approximate equal to the diameter of the jack subassembly tube
56.
The guitar strings 19 are either loosened or removed to provide access to
the body interior 15 through the sound hole 14. The magnet assembly 23 may
be mounted next, and the coil and coil mounting assemblies 21, 22 may be
utilized to properly position the magnet assembly 23 within the body
interior 15. The coil mounting assembly 22 is adjusted to an appropriate
length whereby the coil assembly 21 will be located below a central area
of the soundboard panel 13 (FIG. 2). The length of the coil mounting
assembly 22 is adjustable by telescopically sliding the members 67, 74
thereof with respect to each other. The telescopic members 67, 74 may be
secured with respect to each other at a desired length with the set screw
70.
The coil mounting column subassembly 84 is normally adjusted with respect
to the inner tubular member 74 so that the coil assembly 21 is positioned
slightly below and in spaced relation from the magnet assembly 23.
However, for purposes of mounting the magnet assembly 23, the coil
mounting column subassembly 84 may be slightly raised. The magnet assembly
23 may then be temporarily attached to the coil assembly 21, for example,
with two-sided tape. The adhesive 109 may then be applied to the upper
(outer) convex surface of the lens 105.
The temporary assemblage comprising the coil assembly 21, the coil mounting
assembly 22 and the magnet assembly 23 may then be inserted in the body
interior 15 through the sound hole 14, and the jack subassembly tube 56
inserted through the jack receiver 112 and secured by the bezel nut 59. In
this temporary configuration, the magnet assembly 23 will be pressed
against the inner surface of the soundboard panel 13 whereby the adhesive
109 can be given sufficient time to properly set up.
Having served its purpose of temporarily attaching the magnet assembly 23
to the coil assembly 21, the two-sided tape may then be removed and the
magnet assembly 23 will remain more or less permanently attached. The coil
and coil mounting assemblies 21, 22 may then be withdrawn from the body
interior 15 through the sound hole 14. The coil mounting column
subassembly 84 may then be repositioned on the inner tubular member 74 to
achieve the proper spacing between the coil and magnet assemblies 21, 23.
The spacing between the coil and magnet assemblies 21, 23 greatly affects
the flux linkage therebetween, which in turn affects the sound
reproduction with the pickup 10. Generally, greater bass response is
achieved by placing the coil and magnet assemblies 21, 23 closer together,
and greater treble response is attained when they are further apart. The
adjustability features of the present invention permit a musician to
experiment with different settings to obtain optimum performance.
VI. Operation
With forty-two gauge copper wire comprising the windings 35, 38, and with a
coil diameter-to-thickness ratio (D/T FIG. 4) of at least of four-to-one,
the pickup 10 may be configured for a relatively low impedence of under
six hundred ohms. For electrical instrument amplifiers, impedence values
under six hundred ohms are considered relatively low. If the pickup 10 is
to be connected to an amplifier with a higher input impedence rating, an
impedence matching device, such as a transformer, may be provided. The
pickup 10 of the present invention may be connected to an amplifier (not
shown) by a cable 114 with a three-conductor (i.e. positive, negative and
ground) plug 115 adapted for insertion in the jack subassembly 55 as shown
in FIG. 2.
The pickup 10 described above provides balanced power output for a balanced
system wherein a pair of coil leads 47, 48 are provided and are
electrically isolated from a grounding shield 44. Thus, the amplifier
power is isolated from the coil leads 47, 48, which are shielded by the
shield 44 from interference.
Unlike many electric guitars wherein the metal strings are grounded to the
amplifier, a musician playing an instrument equipped with the pickup 10 of
the present invention would not normally be in contact with any
electrically conductive parts of the system. Thus, the likelihood of a
musician receiving an electrical shock while playing an instrument
equipped with the pickup 10 of the present invention may be accordingly
reduced.
The balanced coil assembly 21 of the present invention, with its
substantially equal-length windings attached to separate leads and the
windings being wound in opposite directions for interaction with the
opposite magnet poles 101, 102, provides what is sometimes referred to as
a "Humbucking" effect. The concentric, oppositely-wound coils thus link
flux with the opposite magnet poles 101, 102. The result is a relatively
true, faithful reproduction of the musical instrument sound.
When the guitar 11 is played, the strings 19 vibrate at their respective
harmonic frequencies or pitches, which vibrations are transmitted to the
soundboard panel 13. The magnet assembly 23 thus vibrates with resect to
the coil assembly 21. The flux linkage between the magnet 100 and the coil
windings 35, 38 changes as the distance therebetween changes, whereby
current flow is induced in the windings 35, 38. The current is conducted
through the windings 35, 38; through the terminals 45, 46; through the
leads 47, 48; through the jack subassembly 55 to the plug 115; and thence
to an amplifier (not shown) or other device.
The guitar strap 17 may be attached to the bezel nut 59. The column
insulator 86 of the coil mounting column subassembly 84 tends to isolate
the coil assembly 21 from its mounting assembly 22 and tends to dampen
unwanted vibrations.
It is to be understood that while certain forms of the present invention
have been illustrated and described herein, it is not to be limited to the
specific forms or arrangement of parts described and shown.
For example, a two-conductor system with a coil having a single winding
could be employed with the pickup of the present invention.
* * * * *
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