String instrument vibration initiator and sustainer

An apparatus for initiating and sustaining vibrations of a string in a musical instrument. A hand-held (or permanently mounted) device senses the vibration of the string and provides an output driving signal for sustaining the vibrations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the field of devices for enhancing and sustaining 
the sounds of string instruments. 
2. Prior Art 
Initiating the vibrations of a string instrument has been accomplished 
through manual plucking, the use of standard hair bows (as in violin), 
electric motor driven bows (as in player violins), and occasionally 
through speaker feedback (as in electric guitars). Sustaining the 
vibrations of a stringed instrument has been accomplished again through 
speaker feedback (as in electric guitars), various amplifiers, compressors 
and "fuzz" boxes (distortion boosters) and electric motor driven bows. 
Each of these has its limitations including distortion; and in the case of 
some electronic means the sustained period is limited to the decay time of 
the string. 
The present invention introduces a new degree of control over sound quality 
not possible with prior art systems. As will be seen the invented device 
will smoothly initiate the vibrations in a metal string (without 
distortion), and sustain the vibrations in this string again without 
distortion, without adding noise inherent in many prior art techniques. 
However, the device may distort vibrations, if desired, and drive only 
overtones of the string, suppressing the tonic (or basic frequency of the 
string). Moreover, the vibrations of a string (or multiplicity of strings) 
may be sustained as long as desired. Unusual sounds may also be obtained 
with the disclosed system not possible with comparably priced prior art 
systems. Since the disclosed system is easily controlled (manually), the 
duration, intensity, attack-time, etc. of the sounds are easily varied. 
SUMMARY OF THE INVENTION 
An apparatus for initiating, sustaining and enhancing the vibrations of a 
string in a musical instrument is disclosed. In one embodiment, a 
hand-held device, positioned above a vibrating string in an instrument, 
senses the vibrations of the string. The sensed vibrations are 
electrically amplified, and then coupled to a coil which is used to drive 
the same string. Where the apparatus is used for a guitar, a pair of coils 
for sensing and driving a string are located within a channel defined by a 
housing. Guides for engaging other strings are disposed at the opposite 
edges of the channel allowing the channel to be readily positioned over a 
selected string. In another embodiment pickup coils and driving coils are 
permanently located adjacent to the strings of an instrument. The 
switching mechanism for activating the driving coils in this embodiment 
generally resemble the strings of the instrument. 
As will be seen the present invention provides a relatively inexpensive, 
convenient means for obtaining new and unusual sounds from a string 
instrument, such as a guitar. In one embodiment the apparatus is hand-held 
and does not require any additions or alterations to the string instrument 
.

DETAILED DESCRIPTION OF THE INVENTION 
An apparatus for initiating and sustaining the vibrations of a string or 
strings in a musical instrument is described. The presently preferred 
embodiment is disclosed in conjunction with a guitar, but as will be 
apparent, the invented system will work equally well on other string 
instruments. As the system is presently implemented steel strings, or 
ferromagnetic strings, are used in a musical instrument since the 
vibrations may be readily sensed and sustained with magnetic fields. 
Referring first to FIG. 1 and the six-stringed, electric guitar illustrated 
therein, the guitar includes generally parallel, coplanar strings 13a, 
13b, 13c, 13d, 13e, and 13f. A pickup board 42 associated with a prior 
art electric guitar is also illustrated as part of guitar 12, however, the 
presently invented system may be utilized on a non-electric guitar or 
electric guitar. Two embodiments of the invention are illustrated in FIG. 
1 (however, several other embodiments are discussed). One version of a 
hand-held sustainer 15 is shown in FIG. 1 over string 13d. This hand-held 
sustainer may be applied selectively to any string of the guitar or other 
musical instrument. Also, in FIG. 1 the guitar 12 includes a sustainer 
system, built in accordance with the present invention, which is 
incorporated into guitar 12. A sustainer base plate 44 which includes a 
plurality of input and output coils is utilized as part of this 
embodiment. 
Referring first to FIGS. 2 and 3, the hand-held sustainer 15 comprises a 
generally rectilinear housing 16 which forms a channel 20. The housing 16 
along opposite edges of the channel 20 defines a pair of parallel, 
elongated string guides 18. These spaced apart guides 18 are disposed such 
that when they engage strings of the guitar, a third string is disposed 
within the center of the channel. For example, as shown in FIG. 2 guides 
18 are engaging string 13b and 13d, while channel 20 straddles string 13c. 
In the presently preferred embodiment the housing 16 may be a molded 
plastic member adaptable for being held in the hand. 
The major components of the sustainer 15, in addition to the housing 16, 
are a battery 22, an input coil 27, an output coil 28, and a circuit board 
14. The coils 27 and 28 are disposed in-line within the channel 20, 
parallel with the grooves 18, such that the coils are disposed above a 
string when the guides 18 are engaging adjacent strings. For example, in 
FIG. 2 while guides 18 are engaging strings 13b and 13d, string 13c is 
disposed directly below both coils 27 and 28. As is apparent, the 
sustainer 15 may be moved such that the channel 20 is disposed above any 
of the strings 13a through 13f, however, when the channel 20 is disposed 
above either strings 13a or 13f, only a single guide 18 will be engaging a 
string. 
In the presently preferred embodiment, the circuit of FIG. 4 is fabricated 
on circuit board 14 which is disposed within housing 16 between the 
battery 22 and channel 20. The hybrid circuit of FIG. 4 includes 
integrated circuit amplifiers 30 and 40 and discrete components for the 
other circuit elements of FIG. 4. 
The circuit of FIG. 4 includes an operational amplifier 30 which may be 
anyone of a plurality of commercially available operational amplifiers. 
The input to the amplifier 30 is coupled from one terminal of coil 27 
through capacitor 31 and resistor 32. The input terminal of amplifier 30 
is also coupled to terminal 36 of the amplifier through the parallel 
combination of resistor 33 and capacitor 37. Terminal 36 is coupled to 
terminal 41 of amplifier 30 through a resistor 34. The terminal 41 is also 
coupled to one terminal of the battery 22. The output of the amplifier is 
coupled to ground through the series combination of resistor 35 and 
capacitor 39, and is also coupled to one terminal of the output coil 28. 
In one embodiment the driving signal applied to coil 28 is feedback 
through a variable gain amplifier 40 to terminal 36 of operational 
amplifier 30. The gain of amplifier 40 is controlled manually by knob 49 
shown in FIG. 3. In the presently preferred embodiment both coils 27 and 
28 include permanent magnetic cores of ALNICO-5, and the battery 22 
comprises a nine volt battery. It will be apparent to one skilled in the 
art that any one of a plurality of other amplifier circuits may be 
utilized in lieu of the circuit of FIG. 4. While in the presently 
preferred embodiment a pair of coils is used, a single coil may be used 
for both sensing the movement of the string and for driving the string. 
For applications where only the sustaining of vibrations (not initiation 
of vibrations) is desired, electrical threshold means may be placed at the 
input of amplifier 30 to prevent the feedback of small signal (or noise) 
which initiate the vibrations. The threshold means may be selectively 
coupled to the circuit by a manual switch. 
Assume that the circuit of FIG. 4 is activated within the sustainer 15, and 
that the sustainer is positioned above string 13c on the guitar as shown 
in FIGS. 2 and 3, such that the magnetic field associated with the magnets 
of coils 27 and 28 cut across string 13c. If string 13c is plucked 
causing it to vibrate, its movement will be sensed by coil 27 since its 
movement causes the magnetic field associated with coil 27 to change 
thereby inducing a current in coil 27. The electrical signal generated 
within coil 27 is amplified by operational amplifier 30 and produces a 
varying magnetic field of the same frequency in coil 28. The magnetic 
field of coil 28 drives the string 13c at its resonant frequency, thereby 
sustaining the vibrations of the string. If string 13c is not immediately 
plucked after the sustainer is in place, the sustainer (because of 
positive feedback) will cause the string to vibrate. The grooves of the 
sustainer may be used to generally align the coils with the string, and 
once this alignment is achieved the sustainer may be pressed down against 
the spring action of these strings to obtain various effects. 
Referring to FIG. 3 by moving the sustainer 25 both transverse to the 
directions of the strings as shown by arrow 24 and/or parallel with the 
strings as shown by arrow 25, the intensity and other characteristics of 
the sound produced by the sustainer 15 may be varied. Also, where 
amplifier 40 is utilized the intensity of the sound may be adjusted 
through knob 49. In one embodiment an unusual effect is produced where the 
current through the output coil 28 is reversed. In such cases it has been 
found that the fundamental frequency of the string is damped, however the 
overtones or harmonics are driven and become more pronounced. A manual 
switch may be used to permit selections of this effect. Other unusual 
sounds and effects are obtained by manipulating the sustainer 15, for 
example, in a vibrato action. 
While in FIGS. 2 and 3 the sustainer is shown having a pair of guides or 
grooves for straddling a single string; a single guide may be used. 
Moreover, more than a single string may be straddled if the grooves are so 
spaced apart and the channel between the grooves may contain a plurality 
of pickup and driving coils. 
In FIG. 5 a sustainer base plate 44 which may be a plastic, metal or wooden 
member is fastened to the upper surface of the guitar 12 and includes a 
plurality of input coils 48a through 48f, and a plurality of output or 
driver coils 47a through 47f. These coils are mounted on the sustainer 
baseplate 44 in pairs, such that a single input and a single output coil 
are in-line and beneath each string of the guitar; for example, coils 47b 
and 48b are disposed below string 13b. An amplifier means not illustrated 
which may be identical to, or substantially similar to, the circuit of 
FIG. 4 interconnects each pair of input and output coils. 
The sustainer associated with each string 13 includes an input coil 48, 
output coil 47, amplifier means, switch 52 and finger rod 57. The 
plurality of switches 52 are utilized to allow manual selection of each 
sustainer by one of the finger rods 57. The finger rods 57a through 57f 
are disposed in a general parallel in-line manner with their respective 
strings 13a through 13f. In the presently preferred embodiment each of the 
rods 57 are relatively thin such that they have the "feel" of a guitar 
string. 
A bank of the switches 52, best seen in FIG. 7, is disposed on the surface 
of the guitar between the guitar's bridge and the rods 57. Switches 52a, 
52c and 52e are mounted close to the surface of the guitar on a 
switchplate 67 while switches 52b, 52d, and 52f are mounted spaced apart 
from the other switches by a spacer 68. The switches are generally bolted 
or fastened to the guitar by bolts, or screws 50, tape, or the like. Each 
switch is used to activate its respective output coil when its finger rod 
has been selected. That is, by way of example, when rod 57f is manually 
selected, switch 57f activates coil 47f such that vibration in spring 13f 
are sustained. 
The rods 57 each include generally U-shaped coplanar ends 58 which are 
mounted within pivot blocks 60 and 61. The pivot blocks 60 and 61 which 
are mounted parallel to the bank of switches and transverse to the rods, 
include a plurality of apertures for receiving the rod ends. Referring to 
FIG. 6, rod 57f is shown with ends 58f disposed within the blocks 60 and 
61 such that rod 57f is pivotally mounted about pivot axis 70f. In FIG. 6a 
rod 57a is shown with its ends 58a disposed again in the block 60 and 61 
such that the rod 57a pivots about axis 70a. 
Each of the rods include a curved roller guide 63 which is adaptable for 
engaging a roller 55 of the switches. Referring briefly to FIG. 10 the 
guide 63e, which is an integral part of rod 57e, is shown engaging a 
roller 55e. The roller 55e is coupled to one end of the switch arm 54e. 
The switch arm 54e abuts a contact pin 65e, thereby activating switch 52e 
when the arm is moved. Referring to FIGS. 6 and 8, the roller guides 63b, 
63d, and 63f are mounted in a co-linear manner with their respective rods 
57b, 57d, and 57f in order that these guides may cooperatively engage the 
upper set of switches 52b, 52d, and 52f shown in FIG. 7. Referring to FIG. 
6a and FIG. 8, the roller guides 63a, 63c, and 63e are disposed below the 
pivot axes of rods 57a, 57c, and 57d such that these roller guides may 
cooperatively engage the lower set of switches 52a, 52c, and 52e, 
respectively. 
Referring to FIGS. 5, 8, 9 and 10 it is apparent that when a finger rod 57 
is moved in either direction about its pivot axis its switch arm 54 will 
be moved, thereby activating the associated drive coil. Referring 
specifically to FIG. 10, by way of example, when the rod 57e is moved from 
position X to position Y, the roller 55e will be urged inwardly toward 
switch 52e causing the pin 65e to move into switch 52e. The movement of 
pin 65e completes the circuit between the input coil 48e and output coil 
47e through the connecting amplifier means. Thus if 13e is set into motion 
the string will continue to vibrate as was the case with the hand-held 
embodiment of the invention. Since the finger rods activate their 
respective switch when moved in either direction, the rods have the same 
general "feel" as the strings of the instrument. Of course, more 
simplified switching means may be used if maintaining the "feel" of the 
strings is not required. 
While in FIG. 5 one switch is used for each string, this is not necessary. 
For example, a single switch may be used to activate all the 
initiators/sustainers associated with the strings. Moreover, a single 
pick-up coil may be large enough to sense movement in a plurality of 
strings. A single amplifier may also be used to replace the plurality of 
amplifiers discussed in conjunction with the embodiment of FIG. 5 and 
amplify the vibrations of more than one string. Where the threshold means 
previously mentioned is used a switch may not be necessary. The string, 
for this case, is set in motion by plucking, or the like, and manually 
clamped. 
Thus, a sustaining system for a string instrument has been disclosed in 
both a hand-held embodiment and a more permanently mounted embodiment. The 
sound of a vibrating string is enhanced and may be initiated and sustained 
with the invented system with increased control and a decrease in 
distortion, at a lower cost.