Modification device for string instrument pickup

Abstract: A device (20;40;50;70;100;220;220A-220D) that modifies the operating characteristics (e.g., amplitude, frequency response, "sustain") of the output signal of an electromagnetic pickup (21;51;91;221) for a stringed musical instrument, such as a guitar with steel strings (24;54;74; 94;224) ; the modification device (20;40;50;70;100) comprises a thin, flat permanent magnet (31;41;61;81;101;220;220A-220D), preferably a sheet of resin impregnated with particulate permanent magnet material, that is magnetized transversely to its thin dimension. The permanent magnet (31;41;61;81; 101;220;220A-220D) covers most or all of the top or bottom surface of the electromagnet pickup (21;51;91;221), usually the top. The signal modification device (20;40;50;70;100) may include one or more mounting elements (33;43;62-65;84,85, 90;104,105) for mounting the permanent magnet sheet on a pickup (21;51;91), if intended for addition to an existing pickup. In the simplest form the mounting element(s) may comprise a rim (33;43) on the permanent magnet or one or more steel plates (62-65;84,85,104,105) mounted on the magnet; the steel plate or plates further may modify the output signal of the pickup. For a signal modification device (220; 220A-220D) that is to be incorporated in a new pickup (221), no mounting elements may be required.

Description: Background of 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 least 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 transducer as the output of the musical instrument. That coil is customarily disposed in encompassing relation to the magnetic core or cores. This relatively simple electromagnetic structure is 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. As can be seen e.g. from US-A-4 320 681, GB-A-1 396 824, US-A-3 983 777, or US-A-4 809 578, a wide variety of individual constructions have been used for electromagnetic pickups employed with musical 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 device. This is not always the case, however; some electromagnetic pickups have been designed to give a particular distortion deemed desirable by the designer or by a musician. For electromagnetic pickups in general, as applied to musical instruments having steel or other ferromagnetic strings, there may be a problem in obtaining an output signal of sufficient amplitude. This may be a minor problem, with modern electronic 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 controlled distortion. A more pronounced problem, in most electromagnetic pickups for musical instruments, has to do with the frequency 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 signal as close as possible to the acoustic output of the instrument, at least in theory. Others, however, want to have a 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 known to musicians as "sustain"; sometimes accented "sustain" is desirable in the view of the musician using the pickup and sometimes it is not. Summary 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 electromagnetic pickup for a musical instrument having plural electromagnetic strings that produces different frequency effects in the output signal from the electromagnetic pickup. A specific object of the invention is to provide a new and improved modification device for 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 as defined by the appended claims relates to a signal modification 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. 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 strings so that vibrations of those strings generate an electrical output 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. Brief Description of the Drawings Fig. 1 is a plan view of an electromagnetic pickup for 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. 1; Fig. 3 is a detail view taken approximately as 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; 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 line 10-10 in Fig. 8; Fig. 11 is a sectional view illustrating a further embodiment of the invention; Fig. 12 is a plan view of an electromagnetic pickup for a guitar that incorporated a signal modification device 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 of Figs. 12 and 13. Description of the Preferred Embodiments Figs. 1-3 illustrate a signal modification device 20 constructed in accordance with a first embodiment of the present invention, mounted as an add-on device 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 strings 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 neck or body, depending upon where the pickup is mounted. Appropriate mounting devices 25 secure pickup 21 on the guitar body 23. 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 device 20 may be employed should include a magnetic structure for generating a magnetic field, 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 electrical output signals in the coil of pickup 21, in the usual manner. The modification device 20, one embodiment of the present invention, is quite simple in construction. It comprises a thin, flat flexible permanent magnet sheet 31. Usually, sheet 31 is formed of a resin material, preferably relatively flexible and slightly elastomeric, that is impregnated with particulate permanent magnet material. Such permanent magnet resin sheets are readily available commercially. One form of flexible permanent magnet resin material is made and sold by 3M Company under the trademark PLASTIFORM; 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 is magnetized transversely to its thin dimension; thus, sheet 31 is magnetized vertically as shown in these two figures. 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. 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 rim 33 that is affixed to three sides 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 portion 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 major 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 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, depending upon the specific construction employed in the pickup. Some 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. Device 40 comprises a thin, flat flexible permanent magnet sheet 41. Again, sheet 41 may be formed of a flexible resin impregnated with particulate permanent 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 device 40 is magnetized in a direction transverse to its thin dimension. However, the magnetization of the permanent magnet 41 is not uniform 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 is magnetized so that its upper, outer surface is a south pole and its lower, inner surface 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 pickup 21 of Figs. 1-3. It also modifies the frequency and "sustain" response characteristics of the pickup. As before, the overall effect on these response characteristics of the pickup depend in substantial part upon the construction employed in the pickup itself, as well as the construction of the modification device 40. Figs. 6 and 7 illustrate another 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 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 for the pickup (Fig. 6). The strings 54 of the instrument, which of course must also be of steel or other magnetically permeable material, extend across but are spaced from the top 53 of the pickup housing 57. The signal modification device 50 includes a thin, flat, flexible permanent magnet sheet 61 of the 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 uniformly 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 plurality 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 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 51 is mounted. The overall result is a space 69 between the two steel strips 62 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 (Fig. 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 be 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 reversal of magnet 61. The signal modification device 50, Figs. 6 and 7, has the effect 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 characteristics 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. 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 another signal modification device 70 for modifying the operational characteristics of the output signal of an electromagnetic pickup 71. It may be 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 embodiments, 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 configuration corresponding generally to that of the upper surface 73 of pickup device 71. The signal modification device 70 of Figs. 8-10, being designed for use on an existing pickup 71, includes mounting means that comprises four steel sheets or strips 82-85, all affixed to the permanent magnet sheet 81. Sheets 82 and 83 are on the top surface of permanent magnet 81; each is provided with 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. Steel sheets 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 for pickup 71 to help maintain 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 signal from the pickup 71 with which it is used. Furthermore, device 70 modifies the frequency and "sustain" characteristics of that output signal so that the overall sound produced by a transducer such as a loudspeaker, employing the pickup signal following amplification, has a different timbre and overall "sound" than would otherwise be obtained by pickup 71. Fig. 11 illustrates yet another embodiment 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 member 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 the 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. Sheet 101 may 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 configuration of the steel sheets 102-105 may be similar to those shown in Fig. 6, except that these steel sheets are wider and have no external projections. 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 configuration that may be employed for 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. Figs. 12 and 13 illustrate an electromagnetic 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 in cross-sectional configuration (Fig. 13). Transversely magnetized permanent magnets 226 are mounted in and extend for the full length of 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 each other. The sides of housing 225 are lined with an additional pair of permanent magnets 228 that are also magnetized transversely to their thin dimension as indicated by the arrows 229. Thus, from any point within the interior of housing 225, bounded by permanent magnets 226 and 228, 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 preferably 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 winding 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 232. 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 and 232. The basic magnetic construction for pickup 221 conforms to that of United States Patent No. 4,268,771. Pickup 221, however, further comprises a thin, flat, flexible sheet permanent magnet 220 that is mounted on the top of the pickup, facing strings 224. This permanent magnet 220 constitutes a signal modification 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 20 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. 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 the frequency response is also modified. Indeed, the signal modification device 220 functions, in pickup 221, in essentially the same manner as the previously described signal modification devices. For further signal modification effects, the device 220 of Figs. 12 and 13 can be magnetized in different ways as illustrated in Figs. 14-17. Thus, the signal modification device 220A of Fig. 14 is magnetized in alternate stripes 236 and 237 that are of opposed polarity, as indicated by the magnetization arrows 238 and 239. With this magnetization pattern, the frequency response characteristics of the output signal from pickup coil 234 are appreciably changed, depending on the alignment of stripes 236 and 237 relative to the musical instrument strings 224 (Figs. 12 and 13). The ratio of widths of stripes 236 to 237 is 2:1, but this ratio can be varied as desired, for varying sound effects. 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 device 220B presents north poles with a sequence of isolated south poles on each edge. Of course, to get the inverse pattern it is only necessary to turn device 220B over. A similar but different pattern is shown 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 the 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 modification 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 "O". In all of the embodiments of the invention 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 part 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 pickup due to attraction 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 described above for the individual embodiments of Figs. 1-11. Of course, composite modification devices such as those of Figs. 6-11 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 ferromagnetic 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 (0.152 cm). These dimensions may be modified to suit the demands of the user. The shapes and surface areas of the ferromagnetic steel sheets and permanent magnet sheets should be matched to some extent to the shape and size of the pickup, but precise conformity is 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 multiple poles, unified poles, single pickup coils, plural pickup coils, and hum-bucking coils. In the foregoing description, it is assumed that the guitar pickup on which the signal modification device is used includes a permanent magnet and an additional pole piece; that is not always the case. The magnet may be a part of 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 humbucker pickups.

Claims: A signal modification device (20) to be mounted on an electromagnetic pickup unit (21) for a musical instrument having a plurality of magnetic strings (24) for modifying at least one of the amplitude, frequency, and sound characteristics of the output signal of the pickup, the pickup unit (21) including a magnetic structure for generating a magnetic field, the magnetic structure including at least one permanent magnet, at least one pole piece (26), and an electrical pickup coil disposed in encompassing relation to the pole piece, all mounted in a housing (27) adapted for mounting (25) on a musical instrument in a position such that the pickup faces the magnetic strings (24) and the magnetic field of the pickup encompasses a predetermined number of the strings so that vibrations of those strings generate an electrical output signal in the coil; the signal modification device (20) comprising: an additional permanent magnet (31) composed of a thin, flat, flexible permanent magnet sheet, magnetized transversely to its thin dimension, having a configuration permitting the device (20) to be mounted on the surface of the pickup unit (21) facing the strings (24), and mounting means (33), affixed to the additional permanent magnet sheet (31), for mounting that sheet on the pickup unit (21) so that it modifies the output signal of the pickup. A signal modification device (20) for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to Claim 1, in which the permanent magnet (31) of the device (20) is composed of a thin, flat, flexible sheet of resin impregnated with particulate permanent magnet material. A signal modification device (40) for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to Claim 1 or Claim 2, in which the permanent magnet sheet (41) is not uniformly magnetized or is magnetized transversely to its thin dimension in a pattern such that parts (44) of the surface area of that permanent magnet sheet (41) facing the pickup unit (21) have one polarity and other parts (45) of the surface area of that permanent magnet sheet facing the pickup unit have the opposite polarity. A signal modification device (40) for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to Claim 3, in which a central longitudinal part (44) of the permanent magnet sheet (41) is magnetized in one direction and at least one edge longitudinal part (45) of the permanent magnet sheet is magnetized in the opposite direction. A signal modification device (40) for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to Claim 4, in which both longitudinal edges (45) of the permanent magnet sheet are magnetized in the opposite direction from the central longitudinal part (44) of the permanent magnet. A signal modification device (220D) for an electromagnetic pickup (221) for a musical instrument having a plurality of magnetic strings (224), according to any preceding Claim, in which at least a portion of the permanent magnet sheet (220D) is unmagnetized so that parts (O) of the surface area of that permanent magnet sheet facing the pickup have no polarization. A signal modification device (220B,220C) for an electromagnetic pickup (221) for a musical instrument having a plurality of magnetic strings (224), according to any preceding Claim, in which laterally transverse parts (S) of the permanent magnet sheet (220B,220C) magnetized in one direction are interspersed with laterally transverse parts (N) of the permanent magnet sheet (220B,220C) magnetized in the opposite direction. A signal modification device (20) for an electromagnetic pickup (21) for a musical instrument having a plurality of magnetic strings (24), according to Claim 1 or Claim 2, in which the permanent magnet sheet (31) is uniformly magnetized so that the entire surface thereof facing the pickup is of one polarity. A signal modification device (20) for an electromagnetic pickup (21) for a musical instrument having a plurality of magnetic strings (24), according to Claim 1, in which the mounting means includes at least one rim element (33) on the device (20) that engages the side (27) of the pickup device housing. A signal modification device (20) for an electromagnetic pickup (21) for a musical instrument having a plurality of magnetic strings (24), according to Claim 9, in which the rim element (33) is of elongated configuration and engages a major portion of one side (27) of the pickup housing. A signal modification device (20) for an electromagnetic pickup (21) for a musical instrument having a plurality of magnetic strings (24), according to Claim 10 or Claim 10, in which there are at least two rim elements (33) engaging opposite sides of the pickup housing. A signal modification device (50) for an electromagnetic pickup (51) for a musical instrument having a plurality of magnetic strings (54), according to any preceding Claim, in which the device further comprises a thin, flat sheet (62 or 63) of ferromagnetic material, other than a permanent magnet material, affixed to and extending across a substantial part of one surface area of the permanent magnet sheet (61). A signal modification device (50) for an electromagnetic pickup (51) for a musical instrument having a plurality of magnetic strings (54), according to Claim 12, in which the further ferromagnetic sheet comprises two ferromagnetic sheet members (62,63) aligned with each other and spaced from each other by a short air gap (69) extending transversely to the strings (54). A signal modification device (50) for an electromagnetic pickup (51) for a musical instrument having a plurality of magnetic strings (54), according to Claim 13, for use with a pickup (51) having a plurality of magnetic poles, one for each string (54), in which each further ferromagnetic sheet member (62,63) includes a plurality of apertures (67,68), each aperture aligned with one pickup pole. A signal modification device (50) for an electromagnetic pickup (51) for a musical instrument having a plurality of magnetic strings (54), according to Claim 14, for use with a musical instrument having n strings (54) and a pickup (51) having n poles, in which each ferromagnetic sheet member (62,63) incudes n /2 apertures. A signal modification device (50) for an electromagnetic pickup (51) for a musical instrument having a plurality of magnetic strings (54), according to Claim 15, in which each ferromagnetic sheet member (62,63) also includes n /2 projections aligned with and extending into the apertures in the other ferromagnetic sheet member (62,63). A signal modification device (70) for an electromagnetic pickup (71) for a musical instrument having a plurality of magnetic strings (74), according to Claim 16, in which each of the two ferromagnetic sheet members (84,85) is appreciably smaller than the permanent magnet sheet (81) and includes a multiplicity of peripheral projections (between slots 87) extending from the ferromagnetic sheet member (84,85) toward one side edge of the permanent magnet sheet (81). A signal modification device (70) for an electromagnetic pickup (71) for a musical instrument having a plurality of magnetic strings (74), according to Claim 12 or Claim 13, in which the further sheet of ferromagnetic material (82,83,84 or 85) includes a multiplicity of apertures (86 or 87), plural apertures for each string (74). A signal modification device (50) for an electromagnetic pickup (51) for a musical instrument having a plurality of magnetic strings (54), according to any preceding Claim, in which the device further comprises two thin, flat sheets (62,63 and 64,65) of ferromagnetic material, other than permanent magnet material, affixed to and extending along opposite sides of the permanent magnet sheet (61), one ferromagnetic sheet engaging the top surface (53) of the pickup (51) and the other facing the strings (54), each ferromagnetic sheet covering a substantial portion of a surface of the permanent magnet sheet (61). A signal modification device (100) for an electro magnetic pickup (91) for a musical instrument having a plurality of magnetic strings (94), according to any of Claims 1 through 19, for use with a pickup (91) having at least one magnetic pickup pole (96) projecting a given height above the pickup housing (93), in which the mounting means includes a support member (106) having a thickness approximately equal to that given height, through which the pickup pole projects, for supporting the permanent magnet (101) above the top of the pickup pole (96). An electromagnetic pickup for a musical instrument having a plurality of magnetic strings (24,54,74,224), of the kind comprising: a principal magnetic structure of predetermined configuration for generating a principal magnetic field, the principal magnetic structure including at least one permanent magnet (226,228) and at least one pole piece (26,56,96,231,232); an electrical pickup coil (234) disposed in encompassing relation to the pole piece (231,232); and a housing (27,57,225) for the magnetic structure and the coil, the housing being adapted for mounting on a musical instrument in a position which that the pole piece (26,56,96,231,232) faces the magnetic strings (24,54,74,224) and the principal magnetic field encompasses a predetermined number of the magnetic strings so that vibrations of those strings generate an electrical output signal in the coil (234); characterized by: a signal modification device comprising an additional permanent magnet (31,41,61,81,101,220) formed by a thin, flat, flexible sheet of permanent magnet material, magnetized transversely to its thin dimension, and having a configuration corresponding generally to that of the top surface of the principal magnetic structure, toward the strings, interposed between the principal magnetic structure and the strings (24,54,74,224). An electromagnetic pickup according to claim 21, including a signal modification device (20, 40, 50, 70, 220) according to any one of claims 2 to 20.

Inventors: LACE MELVIN A, LACE, MELVIN A.
Applicants: DORN THOMAS E, LACE MILDRED A, DORN, THOMAS E., LACE, MILDRED A.
Application year: 1991
Main classification: G10H3
IPC codes: G10H3