Abstract:
A new and improved electromagnetic pickup for a musical instrument having a plurality of ferromagnetic strings includes an elongated ferromagnetic core and an elongated, annular, electrically conductive pickup coil disposed in encompassing relation to the core to enable the pickup to generate a favorable signal-to-noise ratio and to generate signals having a broad range of frequency and “sustain” characteristics.

Description:
[0001]     This application is a continuation application of U.S. Provisional patent application No. 60/702,112, filed on Jul. 25, 2005. 
     
    
     BACKGROUND  
       [0002]     Electromagnetic signal pickups are utilized on musical instruments having ferromagnetic strings. Such pickups have been employed with guitars, bass guitars, banjos, mandolins, violins and a variety of other instruments. A pickup for a musical instrument that uses ferromagnetic strings almost invariably incorporates a magnetic structure for generating a magnetic field that encompasses the strings. That magnetic structure usually includes at least one permanent magnet and may include at least one high-permeability ferromagnetic pole piece. Frequently, the pickup has a separate pole piece or permanent magnet for each string. Thus, a guitar pickup may have six pole pieces or six magnets, one for each string. On the other hand, some electromagnetic pickups have a single pole piece that spans a number of strings, often all of the strings of the instrument. The pickup may have an electrical pickup coil for each string, or it may have one electrical pickup coil that generates a composite all-string signal.  
         [0003]     The electrical signals from the coil or coils are amplified and reproduced by a speaker or other transducer that functions as the output of the musical instrument. The electrical pickup coils are customarily disposed in encompassing relation to the magnetic cores. When there are plural coils each coil usually has its own core. This electromagnetic structure is fitted into a housing that may or may not be a part of the magnetic structure. Whether or not it is a part of the magnetic structure, a principal purpose of the housing is to protect the pickup from dirt and other contaminants and to mount the pickup on the instrument.  
         [0004]     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. Many electromagnetic pickups have been designed to give a particular distortion deemed desirable by the designer or by a musician.  
         [0005]     For electromagnetic pickups in general, as applied to musical instruments having steel or other ferromagnetic strings, there may be some difficulty in obtaining an output signal of sufficient amplitude. This may be a minor problem with modem electronic technology, because even a very weak signal can often be amplified to adequate amplitude. On the other hand, reasonable output amplitude from the pickup itself is desirable because it reduces the necessity for subsequent amplification, and thus reduces the likelihood of inadequately controlled distortion. Moreover, with adequate initial amplitude of the signal generated by the pickup, the signal-to-noise ratio is increased so that a “purer” signal can be realized.  
         [0006]     A pronounced problem in many 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  
       [0007]     In order to provide a new and improved inexpensive electromagnetic pickup for a musical instrument having a plurality of ferromagnetic strings, there is provided a magnetic shield and a steel shield configured to enable the pickups to generate a favorable signal-to-noise ratio and to generate signals having a broad range of frequency and “sustain” characteristics.  
         [0008]     A particular advantage of the pickup of the present invention is the ability to provide a new and improved electromagnetic pickup for a plural ferromagnetic stringed instrument, particularly a guitar, which is quite simple and inexpensive in construction, including a core, a coil, a sensing magnet and magnetic and steel shields, yet that can be readily mounted upon the guitar and has a virtually indefinite life.  
         [0009]     Accordingly, the invention relates to an electromagnetic pickup for a musical instrument, such as a guitar, having a plurality of ferromagnetic strings disposed in substantially co-planar spaced relation to each other over a predetermined span S. The pickup includes an elongated ferromagnetic core, having a length L at least about as large as S and a substantially smaller height, and an elongated, annular, electrically conductive pickup coil disposed in encompassing relation to the core.  
         [0010]     An elongated, unitary, permanent magnet is disposed underneath the core and the pickup coil. There is no permanent magnet located immediately above the top of the core. Magnetic and steel shields are located on the elongated sides of the coil, substantially spanning the same length as the core. There are no shields on the underside of the permanent magnet.  
         [0011]     A housing encompassing the core, the coil, the permanent magnet and the shields, is provided for mounting the pickup on the musical instrument with the core and the coil spanning the ferromagnetic strings in spaced relation thereto and with all strings passing through a magnetic field afforded by the permanent magnet means and the core so that movement of any string (or combination of strings) generates an electrical signal in the coil. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a plan view of an electromagnetic musical pickup, specifically a guitar pickup, of the kind to which the invention is directed;  
         [0013]      FIG. 2  is a side elevation view of the apparatus of  FIG. 1 ;  
         [0014]      FIG. 3  is a section view taken approximately along line  3 - 3  in  FIG. 2 ;  
         [0015]      FIG. 4  is a plan view, with the housing omitted, of an electromagnetic musical pickup such as for an electric guitar, constructed in accordance with one embodiment of the invention;  
         [0016]      FIG. 5  is a longitudinal sectional view taken approximately along line  5 - 5  in  FIG. 4 ;  
         [0017]      FIG. 6  is a transverse sectional view taken approximately along line  6 - 6  in  FIG. 4 ;  
         [0018]      FIG. 7  is a transverse sectional view, like  FIG. 6 , of an alternate embodiment of the invention;  
         [0019]      FIG. 8  is a transverse sectional view, like  FIG. 7 , of another alternate embodiment of the invention;  
         [0020]      FIG. 9  is a transverse sectional view, like  FIG. 4 , illustrating the magnetic fields generated by the electromagnetic musical pickup in accordance with an embodiment of the invention;  
         [0021]      FIG. 10  is an isometric view of the electromagnetic musical pickup in accordance with an embodiment of the invention; and  
         [0022]      FIG. 11  is an exploded view and a top view of the electromagnetic musical pickup of  FIG. 10 . 
     
    
     DESCRIPTION  
       [0023]      FIGS. 1-3  illustrate an electromagnetic guitar pickup  30  that may be deemed generally representative of prior art pickups but that also applies generally to the electromagnetic musical pickups of the present invention. Typically, pickup  30  comprises a housing  31  having a base plate  32  that may be integral with the housing. Housing  31  may be made of steel or of a permanent magnet material if it is used as an operating component of pickup  30 . The housing may be of a magnetically inert plastic if it is not a working electromagnetic component of the pickup. Pickup  30  is mounted on the top  33  of a musical instrument having a plurality of ferromagnetic strings  34 . As illustrated, strings  34  are the strings of a guitar and extend across but in spaced relation to the top surface  33  of the guitar neck or body, depending upon where the pickup  30  is mounted. Strings  34  are distributed across a total span S ( FIG. 1 ), usually with approximately equal spacing between the strings. Screws or other appropriate mounting devices  35  are utilized to mount pickup  30  on guitar body  33 .  
         [0024]     A wide variety of different electromagnetic sensing devices have been utilized in prior art embodiments of pickup  30 . Consequently, no specific pickup structure is shown in  FIGS. 1-3 . On the other hand, it may be noted that any known construction for electromagnetic pickup  30  would include a magnetic structure for generating a magnetic field that encompasses the ferromagnetic strings  34 . A structure of this sort, in any of the known prior art devices, customarily includes at least one permanent magnet and may include at least one high permeability ferromagnetic pole piece. For the electromagnetic pickup  30  shown in  FIGS. 1-3 , utilizing known constructions, there could be six pole pieces, or six magnets, one for each string  34 . On the other hand, some forms of electromagnetic pickup have utilized a single pole piece or core that extends the length of the pickup, beneath all of the musical strings  34 .  
         [0025]     In any of the known forms of electromagnetic pickup there is at least one electrical pickup coil (not shown). There may be separate coils for each of the strings  34 , usually with all of those coils electrically connected together. The entire pickup construction, including the pole piece or pieces, the permanent magnet or magnets, and the electrical pickup coil or coils, is disposed in housing  31 . Vibrations of the musical instrument strings  34 , both vertically and horizontally, generate electrical signals in the coil or coils within housing  31 , and it is those signals that are amplified and reproduced, as by one or more speakers, to afford an output from the musical instrument in conventional manner.  
         [0026]     As mentioned above, all pickups used on guitars have a magnet and a coil of wire that are appropriately positioned to generate a voltage when the guitar string is moved. However, the improved pickup of the present embodiment includes vastly different sonic and physical properties.  
         [0027]      FIGS. 4-6  and  9 - 11  illustrate the operating components of an electromagnetic-musical pickup  130  constructed in accordance with one embodiment of the present invention. The pickup  130  includes an elongated central ferromagnetic core  141  that extends for a length L that is larger than the string span S. Thus, the core  141  spans all of the ferromagnetic strings  134  of the musical instrument. In this instance, it is assumed that the pickup  130  is used for a six string guitar. However, the pickup  130  easily may be adapted for use with stringed musical instruments having fewer or greater numbers of strings.  
         [0028]     As illustrated, the core  141  is made of eight thin sheet steel stabilized magnetic tone alloy laminations. However, the number of laminations may vary. Six or even eight thin steel laminations are frequently utilized. However fewer or greater laminations also may be used to change the tonal characteristics of the sound output from the pickup  130 . A coil form or bobbin  142  is mounted on the central laminated core  141  and an electrical pickup coil  143  is mounted in a coil form  142 , thus being disposed in encompassing relation to core  141 . The pickup coil  143  generates an electrical signal representative of movements of the strings  134  and is a precision wound coil that is calibrated to control output and tone.  
         [0029]     An elongated permanent magnet  144  is mounted in the outer edges of the coil form  142  to function as a unique anisotropic flux deflecting magnetic shielding system. More particularly, as shown in  FIG. 9 , the shielding system includes a thin magnet  144  wrapped around the coil  143 , having the same polarity on the coil side as the laminated pole. This configuration causes the magnetic field to become focused and directed at the string  134 , resulting in a field pattern  400  that causes far greater accuracy and quality in the reproduced sound. Shaping the magnetic field in this way enables the higher harmonics in the string to be sensed by the pickup  130 . Usually, because the harmonics are shorter in wavelength than the fundamental tone and because a magnetic sensor is unable to pickup wavelengths shorter than its window, signal loss is experienced. The pickup  130  of the present invention eliminates such signal loss and produces a much cleaner and fuller sound.  
         [0030]     In addition, another advantage of the above described configuration is the increase in the amplitude of the output signal, resulting in greater sound. Furthermore, a major consideration of pickups is the amount of hum, which is also picked up from the ever-present noise fields caused by AC lines etc. Effectively, the use of the magnet  144  wrapped around the coil  143  results in an output increase of about 6 dB, without any increase in hum.  
         [0031]     As shown in  FIG. 10 , in addition to the shielding magnet  144 , a steel shield  145  may be placed in contact with the outside of the shielding magnet  144 . It should be noted that the steel shield  145  does not extend to the underneath of the pickup  130 , but may be configured with a curve to cover the ends of the coil  143 . This results in considerable reduction in the hum, with a corresponding increase in the quality of sound. It should further be noted that, as shown in  FIG. 11 , there is no requirement that the steel shield  145  and the shielding magnet  145  be in contact with the coil  143 . It is also to be noted that plastic with metal based plating or plastic with impregnated metal also may be used.  
         [0032]     Advantageously, when the steel shield  145  is made out of material with a total cross-section area equal to the laminated pole there is a great reduction of pickup hum. The effective cross-section of the lamination is also influenced by the effective length of the magnet and the effective permeability of the magnet. As such, there is an almost complete overall reduction in hum.  
         [0033]     The use of shields, like the steel shield  145 , stops the magnetic field from going beyond the coil perimeter, thereby eliminating the effect of any coils outside the steel shield  145 . Increasing the vertical height of the steel shield  145  increases its influence. Increasing the thickness of the steel shield  145  yields a similar effect. Furthermore, hum reduction is further slightly increased with an increase in the shield area. The use of the shields also reduces the effect of any shorted turns outside the coil system. For example, the use of a brass cover over a pickup without the magnetic and steel shields has the same effect as almost 1000 shorted turns, which results in a considerable loss of output and a decrease in tonal quality. Significantly, with the shields the effect is zero. That is, the brass cover has no discernable influence on the pickup output, either tonally or sonically. This is the result of the variable magnetic gap being isolated to only the area over the core ( FIG. 9 ). If a brass cover is used, a separate ground wire may be provided to allow ease of phase reversal of the pickup.  
         [0034]     As particularly shown in  FIG. 10 , the lower elongated edge of the laminated steel core  141  engages the top surface of an isotropic main permanent magnet  146 . The main permanent magnet  146  may be constructed of several layers of permanent magnet material commercially available in thin sheets or of unitary construction (as illustrated). If made of several layers, all the layers of the permanent magnet  146  are magnetized in the same direction, transverse to the height of the core  141 . This enables a continuous south pole facing upwardly of the magnet  146  and engaging the lower edge surface of the laminated core  141 . The entire pickup  130  may be encompassed in a housing  131  and supported upon a base  132 . The housing  131  and base  132  may constitute plastic moldings, since the housing is not a part of the magnetic structure in the pickup  130 .  
         [0035]     The preferred permanent magnet material, for the shield magnet  144  as well as the main permanent magnet  146 , comprises 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 Arnold Company under the trademark PLASTIFORM. Another flexible resin permanent magnet material that may be utilized in the device  130  for the permanent magnets is made and sold by RJF International Corporation under the trademark KOROSEAL. Yet another such material is available from The Electrodyne Company under the designation PLASTALLOY for material with a moderate induction level. Similar material with a higher induction level (maximum energy product is sold by that company under the designation REANCE  90 . The preferred wire size for the coil  143  ranges from 38 to 44 gauge copper wire. Larger wire sizes result in better high frequency response. For the core  141 , No. 1008 steel is satisfactory.  
         [0036]     The electromechanical musical pickup  130  of  FIGS. 4-6  and  9 - 11  produces a rather surprisingly high amplitude output signal, usually three to four times the amplitude obtainable with previously known pickups, particularly guitar pickups. All of the materials employed in the pickup  130  are commercially available, although the coil  141  is usually wound to a particular specification and the dimensions of the core laminations must also be established. Typically, the laminations of the core  141 , in a guitar pickup, may have a length L of 2.22 inches (5.64 cm), a height of 0.34 inches (0.86 cm) and a thickness of 0.02 to 0.025 inches (0.125 cm). Typically, the permanent magnet layers are No. 1008 steel, approximately 0.03 inches (0.075 cm) in thickness.  
         [0037]      FIG. 7  illustrates another electromagnetic musical pickup  230  constructed in accordance with the invention, in a view similar to  FIG. 6  but omitting the housing. In many respects pickup  230  of  FIG. 7  is a dual coil or “humbucker” version of the construction illustrated in  FIGS. 4-6 . Thus, it includes two laminated ferromagnetic cores  241  on which two coil forms  242  are mounted. There are two electrical pickup coils  243  in the pickup  230 . In each side of the humbucker pickup  230  there is an elongated permanent magnet  244 , used as a shield magnet and mounted in the outer portion of the coil form  242  for one side of the pickup. A steel shield  245  is also mounted along the outside of the permanent magnet  244 , but specifically is not wrapped around the bottom of the permanent magnet. The permanent magnet  244  of the pickup  230 , as seen in  FIG. 7 , is magnetized transversely so that the surface of the permanent magnet shield facing the coil  243  on this side of the pickup presents a continuous south pole facing toward the coil. The construction is the same but the polarization of the permanent magnets is opposite on the right-hand side of the humbucker pickup  230 , so that the coil  243  on this side of the device faces a north pole for the shield magnet  244 .  
         [0038]     Immediately below each of the laminated sheet steel cores  241  in the pickup  230  as shown in  FIG. 7 , there is a permanent magnet  246 . The permanent magnets  246  are shown as each having two layers of permanent magnet material. They could be three layers as shown in  FIG. 6  or, when thicker permanent magnet material is available, each of the permanent magnets  246  may be of unitary, integral construction. The permanent magnet  246  at the left-hand side of the pickup  230  is magnetized to present a continuous south pole on the upper surface of the magnet that engages the lower longitudinal edge of the core  241  at this side of the pickup. The other main permanent magnet  246 , at the right-hand side of pickup  230 , is of similar construction but is magnetized so that its upper surface, engaging the lower edge of the associated core  241 , is a north pole. The steel sheet  245  extends across only the sides of the pickup and does not cover either the bottom of the pickup  230  or the permanent magnets  246 . Coil bobbins  242  may be provided with depending projections  248  to facilitate alignment of the magnets  246  with their associated laminated cores  241 .  
         [0039]     With the coils  243  connected to each other in a conventional coplanar humbucker configuration, as shown, the signal-to-noise ratio of the pickup  230  is high and there is virtually no hum in the output signal from the pickup coils  243 . The desired signal output from the device  230 , however, produced by vibration of one of the ferromagnetic strings  234  in the magnetic field of the pickup, is appreciably higher in amplitude than with conventional humbucker pickups. Indeed, an increase in amplitude of three to four times is readily realized. Moreover, the pickup  230  is protected against internal vibrational feedback and microphone effects by the auxiliary shield magnet  244 . A steel sheet is mounted on the outside of the shield magnet  244 , as described in regards to the pickup  130  mentioned above. The base  247  may constitute plastic moldings.  
         [0040]     A further modification of pickup  230 ,  FIG. 7 , entails reversing of one main permanent magnet  246  to have the same polarization as the other main magnet. The outer shield magnet for that same side of the pickup should also be reversed in polarization. A steel shield is also provided on the outside of the shield magnet. The result is a pickup that still has a higher amplitude output and is still protected against vibrational feedback and microphonic effects by the shield magnets  244  and  245 .  
         [0041]     Yet another electromagnetic musical pickup  330 , constructed in accordance with a further embodiment of the invention, is shown in  FIG. 8 , again in a view comparable to that of  FIGS. 6 and 7 . In the pickup  330 , which is shown as a humbucker pickup, there are again two elongated laminated ferromagnetic cores  341  each encompassed by a coil form or bobbin  342  with an electrical pickup coil  343  mounted in the bobbin at each side of the pickup. The pickup  330  is disposed within a sheet steel casing  347  that is open at the top and the bottom sides. The casing  347  may constitute a part of the pickup housing, requiring only a lid (not shown) to enclose the entire pickup. A permanent magnet shield  344  is mounted in the right-hand side of the pickup  330 , between the vertical wall of the casing  347  and the coil  343 . Similarly, a permanent magnet shield  345  is disposed adjacent to the left vertical wall of the casing  347 , between the casing and the second coil  343 . The permanent magnets  344  and  345  are polarized so that one of the magnets  344  presents a continuous south-pole face to the coil  343 , whereas the other permanent magnet  345  presents a continuous north-pole face immediately adjacent its coil  343 .  
         [0042]     The pickup  330  further includes two main permanent magnets  351  and  352  in the base of the pickup. One of the permanent magnets  351  is located at the left-hand side of the pickup, as shown in  FIG. 8 , immediately below the laminated ferromagnetic core  341  at the left-hand side of the pickup. This permanent magnet  351  is polarized, as shown, to present a north-pole surface engaging the lower surface of the core  341 . The other permanent magnet  352  is similar except that it engages the other laminated core  341  at the right-hand side of the pickup  330  and presents a continuous south-pole surface in engagement with that core. Thus, the pickup  330  is a “humbucker” pickup.  
         [0043]     At the center of the pickup  330  there is one more permanent magnet  348 . This permanent magnet is magnetized transversely to present a continuous north pole facing toward the left-hand half of the pickup and a continuous south pole facing the right-hand portion of the pickup.  
         [0044]     Like the previously described dual coil humbucker pickup of  FIG. 7 , the humbucker pickup  330  of  FIG. 8  generates a high amplitude output signal from its interconnected coils  343 . If those two coils are connected in the usual humbucker configuration so that they cancel extraneous hum or noise, the output signal developed in response to vibration of any of the ferromagnetic strings  334  is of substantial amplitude but has little or no hum content. The signal-to-noise ratio is excellent. As in the case of the pickup shown in  FIG. 7 , the auxiliary or shield permanent magnets  344 ,  345  and  348  shield the two coils  343  of the pickup. Also, the entire pickup  330  may be encompassed in a housing  347 . The housing  347  may constitute plastic moldings, since the housing is not a part of the magnetic structure in the pickup  330 .  
         [0045]     It will be apparent to those skilled in the art that various modifications and variations can be made in the electromagnetic pickup of the present invention without departing from the scope or spirit of the invention.