Note: Descriptions are shown in the official language in which they were submitted.
2~ 18
Backqround o the Invention
For many years, electromagnetic pickups have been
utilized on musical instruments having steel strings. Such
pickups have been employed with guitars, bass guitars,
banjos, mandolins, and a variety of other instruments. An
electromagnetic pickup for a musical instrument incorporates
a magnetic structure for generating a magnetic field,
including at laast one permanent magnet and at least one
high-permeability pole piece. Frequently, the pickup has a
separate pole piece for each string; on the other hand, some
- known electromagnetic pickups have a single pole that spans
a number of strings. The pickup has an electrical coil
that generates a signal that is subsequently amplified and
reproduced by a speaker or other txansducer as the output of
the musical instrument. That coil is customarily disposed
in encompassing relation to the magnetic core or cores.
This relati~ely simple electromagnetic structure i5 fitted
into a housing that may or may not be part of the magnetic
structure. Whether or not a part of the magnetic structure,
a principal purpose of the housing is to protect the pickup
from dirt and other contaminants.
A wide variety of individual constructions have
been used for electromagnetic pickups employed with musical
2~ 18
instruments such as guitars. Frequently, the efforts of the
pickup designer have been directed toward achieving an
output signal from the electrical coil that is as close as
possible to a faithful reproduction of the sound that would
. be developed by the instrument functioning as an acoustical
devi.ce. ~'his is not always the case, however~ some
electromagnetic pickups have heen des.igned to gi~e a
particular distortion deemed desira~le by the designer or by
a musiclan.
For electromagnetic pickups in general, as applied
to musical instruments having steel ox other ferromagnetic
strings, there ma~ be a problem in obtaining an output
signal of sufficient amplitude. This may be a minor
problem, with modern electxonic technology, because a very
weak signal can often be adequately amplified. On the other
hand, a reasonable output amplitude is desirable because it
reduces the necessity for subsequent amplification, and thus
reduces the likelihood of inadequately con~rolled
distortion.
A more pronounced problem, in most electromagnetic
pickups for musical instruments, has to do with the
fre~uency response. The overall "sound" derived from the
output signal is usually critical to the requirements of the
musician. Some musicians want to have the output si~nal as
close as possible to the acoustic output of the instrument,
at least in theory. Othe.rs, however, want to have a
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distortion that is acceptable to them, one that represents
their own concept or technique for interpretation of music.
The frequency response characteristics of the pickup are
critical in this regard. A similar situation is presented
by the sound characteristic lcnown to musicians as "sustain~;
sometimes accented "sustain" is desirable in the view of the
musician using khe pickup and sometimes it is not.
~umm ry of the Invention
It is a primary object of the invention,
therefore, to provide a new and improved device for
modifying at least one of the amplitude, frequency, and
"sustain~' characteristics of the output signal of an
electromagnetic pickup for a musical instrument having a
plurality of magnetic strings, which device can be employed
with a variety of different pickup constructions, either as
an addition to an existing pickup or as a component of a
pickup.
Another object of the invention is to provide a
new and improved modification device for an electromagnetic
pickup for a plural magnetic string musical instrument that
adds appreciably to the amplitude of the output signal,
despite substantial variations in the construction and
operation of the pickup itself.
Another object of the invention is to provide a
new and improved signal modification device for an
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elec-tromagnetic pickup for a musical instrument having
plural electromagnetic strings that produces different
requency effects in the ou-tput signal from the
olectromagnetic pickup.
S A sp~cific ob~ect of the invention is to provide a
new and improved modlfication device ~or an electromagnetic
pickup for a plural magnetic string instrument, particularly
a guitar, that is simple and inexpensive in construction,
that can be readily mounted upon the pickup, and that has
indefinite life, producing the effects noted above without
requiring any change in the pickup itself.
Accordingly, the invention relates to a signal
modificatiorl device for modifying at least one of the
amplitude, requency, and "sustain~' characteristics of the
output signal of an electromagnetic pickup for a musical
instrument having a plurality of magnetic strings. The
pickup includes a magnetic structure for generating a
magnetic field, the magnetic structure including at least
one permanent magnet, at least one pole piece (the magnet
may be the pole piece), and an electrical pickup coil
disposed in encompassing relation to the pole piece, all
mounted in a housing adapted for mounting on a musical
instrument in a position such that the pickup faces the
magnetic strings and the magnetic field of the pickup
encompasses a predetermined number of the strlngs so that
vibrations of those strings generate an electrical output
2 ~ 8
signal in the coil. The signal modification device
comprises a thin, flat, flexible permanent magnet sheet,
magnetized transversely to its thin dimension, having a
configuration corresponding generally to that of the pickup,
between the pickukp and the strings.
r.ief DescriPtLon o _he Drawinqs
Fig. 1 is a plan view of an electromagnetic pickup
fo.r a guitar, equipped with a signal modification device
constructed in accordance with one embodiment of the present
invention~
Fig. 2 is a side elevation view of the pickup and
signal modification device of Fig. l;
Fig. 3 is a detail view taken approximately as
lS indicated by line 3-3 in Fig. 2;
Fig. 4 is a plan view of a pickup signal
modification device constructed in accordance with another
embodiment of the invention;
Fig. 5 is an end view of the device of Fig. 4;
Fig. 6 is a plan view of a different embodiment of
the invention;
Fig. 7 is a sectional view taken approximately as
indicated by line 7-7 in Fig. 6;
Fig. 8 is a plan view of yet another embodiment of
the invention;
2~31 ~
Fig. 9 is a bottom view of a component that may be
employed in the device of Fig. 8;
Fig. 10 is a sectional view taken approximately as
indicated by l.ine 10-10 iII Fig. 8;
S Fig. 11 is a sectional ~iew illustrating a further
embodiment of the inventiorl;
Fig. 12 is a plan view of an electromagnetic
pickup for a guitar that incorporates a signal modification
dev.ice according to the invention;
Fig. 13 is a sectional view, on an enlarged scale,
taken approximately along line 13-13 of Fig. 12; and
Figs. 14~17 illustrate different modification
devices usable in the pickup o~ Figs. 12 and 13.
_scri~tion of the Pxeferred Embodiments
Figs. 1-3 illustrate a signal modif$cation device
20 constructed in accordance with a first embodiment of the
present invention, mounted as an add-on de~ice upon an
electromagnetic pickup 21 for a musical instrument (e.g., a
guitar). Pickup 20 has a base plate 22 that is affixed to
the top 23 of a musical instrument having a plurality of
magnetic ~trings 24. Thus, strings 24 may be the strings of
a guitar, the strings extending above and in spaced relation
to the top surface 23 of the guitar n~ck ox body, depending
upon where the pickup is mounted. ~ppropriate mounting
devices 25 secure pickup 21 on the guitar body 23.
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As previously noted, there is a wide variety of
different operating constructions that can be utilized for
the electromagnetic pickup 21. Consequently, no specific
pickup structure has been shown in Figs. 1-3. However, any
electromagnetic pickup 21 on which the signal modification
devi.ce 20 may he employed should include a magnetic
structure ~or generating a magnetic ield, that magnetic
structure including at least one permanent magnet and at
least one high permeability pole piece. For the
construction shown in Fig. 1, it is assumed that -there are
six pole pieces 26, one for each string 24 (see Fig. 1). On
the other hand, as previously discussed, a single pole piece
may serve all of the strings.
Pickup 21 includes an electrical pickup coil, not
shown, that is disposed in encompassing relation to the pole
pieces 26. Actually, in some constructions there may be six
coils all connected together. The entire pickup
construction, including the pole pieces, the permanent
magnet, and the electrical pickup coil, are all disposed in
a single housing 27. Fasteners 25 thus mount housing 27 on
the surface 23 of the guitar so that the top surface 28 of
the pickup housing faces strings 24 and the magnetic field
or fields generated by pickup 21 encompass strings 24.
Consequently, vibrations of strings 24 generate electricaI
output si~nals in the coil of pickup 21, in the usual
manner.
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The modification device 20, one embodiment of the
present invention, is quite simple in construction. It
compri.ses a thin, flat flexible permanent magnet sheet 31.
Usually, sheet 31 is ormed of a resin material/ preferably
relatively flexible and slightly elastomeric, that is
impregnaked with particulate permanent magnet ~aterial.
Such permanent magnet resin sheets are readil~ available
commercially. One form of flexible permanent magnet resin
material is made and sold by 3M Company undar the trademark
PL~STIFORM; another flexible resin permanent magnet material
that may be utilized in device 20 for the permanent magnet
31 is made and sold by B.F. Goodrich Company under the
trademark KOROSEAL.
As indicated in Figs. 2 and 3, the permanent
magnet strip or sheet 31 i5 magnetized transversely to its
thin dimension; thus, sheet 31 is magnetized vertically as
shown in these two igures. The permanent magnet strip has
a configuration corresponding to that of the top surface 28
of pickup housing 27. The permanent magnet sheet 31 covers
most of the top surface of pickup 21 and preferably covers
all of that part of the pickup surface 28 that is located
below strings 24. In the modification device 20, the
permanent magnet 31 is shown as being slightly narrower than
pickup housing surface 28; it should be nearly as wide as
the housing and, indeed, may exceed the housing width
slightly.
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The modification device 20, being designed for
addition to an existing pickup, includes mounting means,
affixed to the permanent magnet sheet 31, for mounting that
sheet on the top surface 28 of a pickup housing, such as the
housing 27 of pickup 21. In the construction shown in
Figs. 1-3, the mounting means comprises an edge portion or
r.im 33 that is affixed to three side~ of the permanent
magnet sheet 31. This edge portion 33 of device 20 may be
formed of molded or extruded resin and is joined to the
edges of permanent magnet sheet 31 by adhesive bonding,
ultrasonic welding, or any other desired bonding technique.
The edge poxtion 33 of device 20 extends down along the side
walls of housing 27 for pickup 21 and serves as an aid to
anchoring permanent magnet sheet 31 of device 20 on the top
28 of pickup 21. The magnetic field of permanent magnet 21
also plays a ma~or part in maintaining the permanent magnet
sheet 31 on the top of housing 27, due to magnetic
attraction between poles 26 and the add-on magnet. For this
purpose it may be necessary to magnetize sheet 31 in the
opposite direction to that illustrated, depending upon the
orientation of the permanent magnet fields in poles 26 of
pickup 21.
The operational effect of the signal modification
device 20 on pickup 21 depends in part on the normal
construction and operation of the pickup. For virtually any
pickup construction, device 20 materially increases the
2~ 3~8
amplitude of the output signal. In addition, the
modification device usually affects the frequency response
of pickup 21 so that its output signal places greater
emphasis upon either high or low frequency components,
S depending upon the specific constrllction employed in the
pickup. SomQ experimentation may be necessary in this
regard. In addition to altering the frequency response, in
most instances, device 20 modifies the "sustain"
characteristics for the output signal from electromagnetic
pickup 21.
Figs. 4 and 5 illustrate another signal
modification device 40 constructed in accordance with the
invention. Device 40 can be substituted directly for device
20 in Figs. 1-3. The overall effect on the output from
electromagnetic pickup 21 may be appreciably different,
however, when device 40 is used, from that afforded by the ~-
previously described modification device 20.
Davice 40 comprises a thin, flat flexible
permanent magnet sheet 41. Again, sheet 41 may be formed of
a flexible resin impregnated with particulate permanen$
magnet material. That is, sheet 41 may be formed of the
same kinds of permanent magnet materials as the sheet 31 of
device 20. Again, the permanent magnet sheet 41 of
modification devicP 40 is magnetized in a direction
transverse to its thin dim0nsion. However, the
magnetization of the permanent magnet 41 is nat uniform
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throughout its surface. Thus, the central portion 44 of the
permanent magnet strip or sheet 41 is magnetized so that its
upper, outer surface constitutes a north pole and its inner,
lower surface is a south pole. On each side of sheet 41,
however, there is a narrow strip 45 that is magnetized in
the opposite direction. Thus, each side strip 45 of sheet
41 i9 magneti~e~ so that its upper, outer surface is a south
pole and its lower, inner surace is a north pole. As
before, the permanent magnet sheet 41 may be provided with a
rim 43 to aid in mounting the sheet on an electromagnetic
musical instrument pickup (e.g., pickup 21, Figs. 1-3).
The signal modification device 40 of Figs. 4 and
5, like device 20 of Figs. 1-3, usually increases the
amplitude of the output signal from an electromagnetic
musical instrument pickup with which it is associated, such
as pic]cup 21 of Figs. 1-3. It also modifies the frequency
and "sustain" response characteristics of the pickup. As
before, the ovexall effect on these response characteristics
of the pickup depend in suhstantial part upon the
construction employed in the pickup itself, as well as the
construction of the modification device 40.
Figs. 6 and 7 illustrate ano~her signal
modification device 50, used as an add-on device for
modifying operating characteristics of the output signal
from an electromagnetic pickup 51 for a stringed musical
instrument. In Figs. 6 and 7 device 50 is mounted on top of
11
the electromagnetic pickup 51, which is secured to the
surface of a guitar, banjo, or other like musical instrument
by appropriate fasteners 55 that extend through a base plate
52. ~ox the pickup (Fi~. 6). The strings 54 of the
S instrument, whi.ch of course MUSt also be of steel or other
magnetically permèablè material, extend across but are
~paced ~rom the top 53 o~ the pickup housing 57.
The signal modification device 50 includes a thin,
flat, flexible permanent magnet sheet 61 of ~he same type as
used in previously described embodiments. Permanent magnet
61 is magnetized transversely to its thin dimension and has
a configuration approximately corresponding to that of the
top surface 53 of pickup 51. Like permanent magnet 31 of
the embodiment of Figs. 1-3, permanent magnet 61 is
unifoxmly magnetized throughout its area.
Pickup device 50, however, includes four steel
strips 62, 63, 64 and 65. Each of these steel strips 62-65
should be formed from ferromagnetic stock. Each includes a
multiplicity of external projections 66 along the edge of
the strip. Each of the steel strips also includes a
plurality of central projections 67 that are received in
indentations 68 in the mating steel strip. Thus, as shown
in Fig. 6, the ferromagnetic strip 62 has a plurali~y of
projections 67 that fit into indentations 68 in the strip 63
that is aligned with strip 62 on top of permanent magnet 61.
Similarly, strip 63 has a plurality of projections 67 that
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fit into indentations 68 in strip 62. Each projection 67 is
aligned with one of the strings 54 of the musical instrument
on which pickup S1 is mounted. The overall result is a
space 69 between the two steel strips 6~ and 63 that extends
for the full length of the signal modification device 50,
with one of the projections 67 under each string 54 (Fig.
6). The strips 64 and 65 on the opposite side of permanent
magnet 61 (~ig. 7) have the same configuration as the upper,
outer strips 62 and 63 and are preferably aligned with the
upper, outer strips. Thus, except for a change in
polarization for permanent magnet 61, device 50 can ~e
mounted with strips 62 and 63 facing strings 54, as shown,
or may be mounted with strips 64 and 65 facing the strings
if the polarity of the pickup poles 56 requires xeversal of
magnet 61.
The signal modification device 50, Figs. 6 and 7,
has the efect of increasing the amplitude of the pickup
output signal; in that respect, it is similar to the
modification devices of previous figures. For a pickup with
individual magnet poles for the individual instrument
strings 54, such as poles 56 (Fig. 6), steel plates 62-65
modify overall operation so that the output signal from
pickup 51 exhibits chara~teristics more closely simulating
those of a single-core electromagnetic pickup as in U.S.
Patent No. 4,809,578, even though the pickup itself may be a
multi pole device like that shown in U.S. Patent No.
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2 3 i) ~1 ~ 8
3,236,930. Stated differently, the ferromagnetic plates 62-
65 function as a mounting means to aid in affixing permanent
magnet 61 to pickup 51 and also have a substantial effect on
the frequency and "sustain~ response characteristics of the
output signal from pickup 51.
Figs. 8-10 illustrate anot}ler signal modification
device 70 for modifying the operatio.nal characteristics of
the output signal o~ an electromagnetic pickup 71. It may
~e assumed that pickup 71 employs an internal construction
of the kind described in U.S. Patent No. 4,809,578, which
has a single elongated central core or pole piece that spans
all of the strings 74 of a guitar or other musical
instrument on which pickup 71 is mounted. Pickup 71 has a
base 72 ~Fig. 8) with fasteners 75 used to mount the base on
the surface of a guitar or like instrument (not shown).
Modification device 70 is mounted on the top of pickup 71;
see Fig. 10.
Device 70 includes a thin, flat flexible
permanent magnet 81 (Fig. 10). This permanent magnet is
preferably formed from a sheet of resin impregnated with
particulate permanent magnet material, such as the
aforementioned PLASTIFORM and KOROSEAL materials. As in the
previously described em~odiments, the permanent magnet sheet
81 is magnetized in a direction transverse to its thinnest
dimension. Furthermore, as is apparent from Figs. 8 and 10,
the permanent magnet sheet 81 has a configuratlon
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corresponding generally to ~hat of the upper surface 73 of
pickup device 71.
The signal modification device 70 of Figs. 8-10,
being desi.gned for use on an existing pickup 71, includes
mounting means that comprises ~our steel sheets or strips
82-85, all affixed to the permanent magnet shee~ 81. Sheets
82 and 83 are on the top surface of permanent magnet 81;
each is provided wi.th a pattern of apertures 86
corresponding to a multiplicity of projections or teeth on
the central core of pickup 71 as described in the
aforementioned U.S. Patent No. 4,809,578. The steel plates
or sheets 82 and 83 do not contact each other; instead,
there is an elongated gap 88 between the two steel sheets.
SteeI she~ts 84 and 85, on the other hand, are mounted on
the bottom surface of permanent magnet 81. Each is provided
with a plurality of indentations or slots 87 that are
aligned with the apertures 86 in the two.top steel strips 82
and 83. Again, the steel strips 84 and 85 do not engage
each other; they are separated by a longitudinal gap 89.
Modification device 70 may also includes a plurality of tabs
90 affixed to the permanent magnet 81 or to the upper steel
- strips 82 and 83. Tabs 90 project downwardly, engaging the
sides of the housing ~or pickup 71 to help malntain device
70 in place on the top surface 73 of the pickup.
The signal modification device 70, like previously
described embodiments, enhances the amplitude of the output
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signal from the pickup 71 with whLch it is used.
Furthermore, device 70 modifies the frequency and ~sustain~
characteristics of that output signal so that the overall
sound produced b~ a transducer such as a loudspeaker,
S employin~ the pickup ~ignal ollowing amplification, has a
diffe~rent timbre and overall "sound" than would otherwise be
obtained by pickup 71.
Fig. 11 illustrates yet another embadiment of the
present invention in the form of a signal modification
device 100 mounted upon and utilized to modify the output of
a pickup generally indicated at 91. Pickup 91 is of the
type, such as the pickup shown in U.S. Patent No. 3,236,930,
that has an individual permanent magnet or permanent magnet
pole for each string 94 of the musical instrument. In Fig.
11 only one of these poles or magnets 96 is shown. In this
pickup construction, however, each pole 96 projects above
the top wall 93 of pickup 91. As a consequence, if the
signal modification device 100 were mounted only on the
tops of poles 96, it would be quite unstable.
In pickup 100 this situation is obviated by a
support mem~er 106, preferably formed of molded resin
material, that fits onto the top 93 of pickup 91. Support
106 may have rim elements 107 that engage the side walls of
tha pickup housing to further stabilize the mounting of
device 100 on pickup 91. The modification device 101 itself
comprises a thin, flat, flexible permanent magnet sheet 101.
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Sheet 101 ~ay be a resin impregnated with permanent magnet
material so that the sheet is itself an effective permanent
magnet. On top of sheet 101 there are two steel elements
102 and 103 separated by a gap 111. On the bottom of
permanent magnet 101 there are two similar steel elements
104 and 105 spaced from each other by a gap 112. The
con~iyuration of the steel sheets 102~105 may be s.imilar to
those shown in Fig. 6, except that these steel sheets are
wider and have no external pro~ections. On the other hand,
these steel sheets 102-105 could be like the similar steel
elements 82-85 of Figs. 8-10. Yet a further conf.iguration
that may be employed or steel elements 102-105 would
conform to the overall surface configuration of permanent
magnet 101 except for a gap having a configuration like gap
69 in Fig. 6.
Fiss. 12 and 13 illustrate an electr~magnetic
pickup 221 for a guitar or other plural-string musical
instrument that utilizes steel strings or other
electromagnetic strings. Pickup 221 includes a base plate
222 preferably formed of aluminum or other non magnetic
material, with appropriate means (not shown) for mounting on
a guitar or other musical instrument in alignment with a
plurality of magnetic strings 224. Pickup 221 comprises a
housing 225 that is U-shaped ln cross-sectional
configuration (Fig. 13). Transversely magnetized permanent
magnets 226 are mounted in and extend for the full length of
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the base of housing 225; two are shown but one, three, or
even more base permanent magnets may be used. The permanent
magnets 226 are transversely magnetized, both in the same
direction, as indicated by arrow 227 in Fig. 13, so that
they aid ~ach other. The sides of housing 225 are lined
w.ith an additional pair of perman~nt magnets 228 that are
a.lso magnetized transversely to their thin dimension as
indicated by the arrows 22~. Thus, from any point within
the interior of housing ~25, bounded by permanent magnets
226 and 2~8, only north pole magnetization is apparent.
The magnetic structure of pickup 221, Figs. 12 and
13, further includes a pair of back-to-back C shaped pole
pieces 231 and 232 preferably separated by an electrical
insulator 233. Pole pieces 231 and 232 are prefexably
lS mounted on and supported by the upper most one of the base
permanent magnets 226. They conjointly afford a support for
an electrical pickup coil or wlnding 234. It should be
noted that insulator 233 has little or no effect on the
magnetic structure of pickup 221; it is the equivalent to an
air gap of little or no consequence between the two pole
pieces 231 and ~32. However, it is convenient for making
electrical connections to coil 234.
As thus far described, pickup 221 is basically
similar to the pickup described in United States Patent No.
4,809,578, except that it does not utilize multiple
projections on the magnetic core or pole piece members 231
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and 232. The basic magnetic construction for pickup 221
conforms to that of United States Patent No. 4,268,771.
Pickup 2~1, however, further comprises a thin,
flat, flexible sheet permanent magnet 220 that is mounted on
S the top of the pickup, facing strings 224. I'his permanent
magnet 220 constitutes a signal modiication device that
materially alters the operating characteristics that would
otherwise be obtained with pickup 221. In its simplest
form, this signal modification device 220 may have the same
construction as the signal modification device ?0 of Figs.
1-3, but without rims 33. Device 220 is uniformly
magnetized transversely to its thin dimension, as indicated
by arrow 230. The entire pickup may be enclosed by a cover
235, usually nylon or other plactic, as indicated in Fig.
lS 12.
In pickup 221, Figs. 12 and 13, it would seem that
the signal modification device 220, constituting the thin
transversely magnetized permanent magnet disposed on top of
the pickup 221, would materially reduce the signal amplitude
output from coil 234 by effectively shorting out the
magnetic circuits of the pickup. But this does not happen.
Instead, the amplitude of the electrical signal output from
coil 234 is perceptibly increased. Furthermore, the
"sustain~' characteristics of the output signal are altered
in most instances and ~he frequency response is also
modified. Indeed, the signal modification device 220
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functions, in pickup 221, in essentially the same manner as
the previously described signal modification devices.
For further signal mo~ification effects, the
device 220 of Figs. 12 and 13 can b~ magnetized in different
ways as illustrated in Figs. 14-17. Thus, the signal
modification device 220A of F.ig. 14 is magnetized in
alterna~ stripQs 236 and 237 that are of opposed polarity,
as indicated by the magnetization arrows 238 and 239. With
this magnetization patternl the frequency response
characteristics of the output signal ~rom plckup coil 2~4
are appreciably changed, depending on the alignment of
stripes 236 and 237 relative to the musical instrument
strings 224 (Figs. 12 and 13). The xatio of widths of
stripes 236 to 237 is 2:1, but this ratio can be varied as
desired, for varying sound Qffects. Of course, to get the
direct inverse of the magnetization pattern illustrated in
Fig. 14, it is only necessary to turn device 220A over. In
that way, the broad stripes 236 show south poles and the
narrow stripes show north poles.
Another magnetization pattern for the signal
modification device is shown by device 220B of Fig. 15. In
this instance, in the alignment shown the major portion of
the surface area of de~ice 220B presents north poles with a
sequence of isolated south poles on each edge. O-f course,
to get the inverse pattern it is only necessary to turn
device 220B over. A similar but different pattern is shown
2 ~ ~J~ 1 8
for device 220C, Fig. 16. Again, with the signal
modification device in the alignment shown the major central
area appears as a large north pole, with smaller south pole
areas along each edge of khe device and individual smaller
projections constituting south poles extending into the
central north pole space. Again, the inverse pattern can be
obtained simply by turning the signal modiication device
220C over. It should be noted that it is not necessary to
magnetize all of the thin, flat, flexible sheet permanent
magnet that constitutes each of the signal modification
devices. Thus, device 220D, Fig. 17, has a central area
which, in the alignment shown, constitutes a north pole,
with edge areas of south poles, and particularly with
individual unmagnetized areas designated by 'lOI'.
In all of the embodiments of the in~ention
described above, the signal modification device affords some
enhancement of the amplitude of the output signal from the
pickup. Furthermore, all embodiments of the invention
modify the frequency response and "sustain" characteristics
of the pickups with which they are employed, regardless of
whether the signal modification device is used as an add-on
to an existing pickup or as an integral p~rt of a new
pickup. For add-on devices, the mounting means in each
instance includes the permanent magnet signal modification
device itself, because the magnetic field of the permanent
magnet pulls the magnet tightly against the electromagnetic
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pickup due to at~raction of that field for the pole pieces
in the pickup. Each add-on device, as applied to an
existing pickup, may also include further mounting means,
such as the steel plates or rims descrihed above for the
individual embodiments of Figs. 1-11. Of course, composite
modification devices such as those of Figs. 6-ll can be
incorporated in a pickup structure as in Figs. 12 and 13.
In all described embodiments of the invention
there can be appreciable variation in the dimensions of the
permanent magnet sheets comprising the basic signal
modification devices and of the ferromagnetic steel sheets
when used in the modification devices. Typically, the
permanent magnet signal modification members (e.g., members
31, 41, 61, 81, 101 and 220-220D) may have a thickness of
about 0.030 inch (0~076 cm). The fe.rromagnetic sheets
(e.g., steel members 62-65, 82-85, and 102 105) may be about
0.010 inch (0.025 cm) thick. In the pickup 221 of Figs. 12
and 13, housing 225 may be formed of steel of about 0.04 to
0.05 inch (0.101 - 0.127 cm) thickness; the C-shaped pole
pieces 231 and 232 can be fabricated from 0.024 inch (0.061
cm) steel. The magnets 226 and 228 in pickup 221 typically
have a thickness of 0.06 inch (G.152 cm). These dimensions
may be modified to suit the demands of the user. The shapes
and surface areas of the ferromagnetic steel sheets and
permanant magnet sheets should be matched to some extent to
the shape and size of the pickup, but precise conformity is
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not required, as will be apparent from the drawings. The
signal modification device of the invention is applicable to
virtually any electromagnetic pickup, including those with
multipl.e poles, unified poles~ single pickup coils, plural
. pickup coils, and hum-bucking coils.
In the foreyoing description, i.t is assumed that
thQ guitar pickup on which the signal modification device is
used includes a permanent magnet and an additional pole
piece; tha~ is not always the case. The magnet may be a
part o~ or all of the pole piece for the pickup coil. The
device of the invention works or pickups with permanent
magnet pole pieces as well as on those with pole pieces that
are not themselves permanent magnets. Of course, the
modification device can also be applied to plural coil
pickups, including humbacker pickups.
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