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BACKGROUND OF THE INVENTION
The present invention generally relates to musical instruments, and more
specifically to a device primarily for stringed musical instruments which
can sustain the sounds originally produced on the instrument.
While the basic principle of the present invention can be applied to most
musical instruments, as will become evident hereafter, the description
that follows is directed primarily at stringed musical instruments. As is
well known, playing a stringed instrument involves plucking the strings
and setting them into vibratory motion. The vibrations of the strings
disturb the surrounding air and these air disturbances are perceived by a
human ear as the musical sounds which are played. Under normal
circumstances, once a string has been plucked and set into motion, the
amplitude of the vibrations have an initial predetermined value and
thereafter the amplitude or magnitude of the vibrations continuously
decrease or decay until vibrations cease totally and the string reverts to
its initial stationary state. The rate of decay or the time constant
involved with each of the strings is a function of numerous factors
including, but not limited to, the density of the material from which the
string is made, its physical dimensions, the tension of the string and the
like.
Frequently, in order to produce special sound, sound effects or moods,
musicians find it necessary or desirable to sustain a musical sound
produced by, for example, a string of a musical instrument for a period of
time which is greater than that normally associated with the time
constants of the string.
With the development of electronic equipment in the mid-1930's, it was
learned that by placing an electromagnetic pick-up (microphone or
transducer) on a steel string guitar, the sound of that instrument could
be amplified. With further development of amplification equipment in the
1940's came the emergence of a new type of guitar commonly called the
"Electric" or "Solid Body" guitar. In this type of guitar the neck and
body of the instrument serve only as a means of generating the original
notes. The instrument basically has no acoustical qualities. The vibrating
strings are sensed by the magnetic pick-ups and a musician adjusts his
amplifier for volume and tonal qualities.
In about 1953, a new type of music evolved, and with it a new method of
playing the electric guitar. It was in and around that time that the
concept of sustaining the musical sounds of an electric guitar first
developed and became widely used. The music was almost of necessity loud.
By using large amplifiers and speakers, the musicians could send the notes
from their speakers back to the strings of the guitar, causing a
sympathetic vibration to occur which would reinforce the vibratory
movements of the strings and thereby sustain the sound produced by the
instrument. In effect, acoustic feedback was utilized to complete a
regenerative acoustic loop. It was the exploitation of this regenerative
effect that created what we recognize today as the electric guitar sound.
There has been, however, little progress since the above-described early
developments. The previous or older methods, as well as those used today,
which use regenerative feedback, depend on room accoustics, the type of
amplifiers and speakers used and the volume of the amplified sound. In the
prior art arrangements, then, the same external speakers that are used to
generate the sound to the listening audience are also used in the
regenerative feed-back arrangement to drive the strings. The external
speakers used, which are normally spaced a considerable distance from the
musicians and, therefore, from the strings of the musical instrument, are
of necessity played at a very high volume or loudness. The prior art
approach has not worked satisfactorily where the external speakers are
driven at a moderate or low volume since the accoustic feedback is not
sufficient in that instance to drive the strings and to sustain the sound.
Under certain conditions, and with certain room accoustics, the loudness
of the sound necessary to produce sustain on a musical instrument such as
a guitar is such as to be uncomfortable to a listener.
Since "solid body" guitars basically lack acoustic qualities, the guitar
could only be played and heard when connected to external speakers which
are normally large and bulky. The external speakers and the amplifiers
associated with most electric guitars make it difficult or at best
inconvenient to easily transport the electric guitar system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
sustaining device which does not have the disadvantages of the prior art
devices.
It is another object of the present invention to provide a sustaining
device which is simple in construction and economical to manufacture.
It is still another object of the present invention to provide a sustaining
device which is at least partially mounted on and may be self-contained
within the musical instrument whose sounds are to be sustained.
It is yet another object of the present invention to provide a sustaining
device which does not require remote external speakers.
It is a further object of the present invention to provide a sustaining
device which can sustain musical sounds substantially independently of the
volume of the musical sounds produced by the musical instrument.
It is still a further object of the present invention to provide a
sustaining device for sustaining the sounds of a stringed musical
instrument, with the sustaining device being mounted on the musical
instrument and proximate to the strings thereof to permit driving of the
strings into a sustained condition substantially independently of the
volume at which the musical instrument is played.
It is yet a further object of the present invention to provide a sustaining
device which is light in weight and may be self-contained within the
musical instrument to make the same readily portable and transportable.
It is an additional object of the present invention to provide a sustaining
device which includes signal processing means for modifying the original
sounds produced, including modifying the low and high frequency contents
of the audio ranges and modifying the phase of the signals to be
reproduced, prior to amplification and reproduction.
It is still an additional object of the present invention to provide a
sustaining device which includes a transducer mounted proximate to the
strings of the electric guitar or the like which is used to drive the
strings of the guitar and which permits the guitar player a freedom of
movement without compromising the sustaining characteristics of the
guitar.
It is yet an additional object of the present invention to provide a
sustaining device which includes control means for adjusting the degree of
sustain and for sustaining one or more musical notes substantially
indefinitely.
In order to achieve the above objects, as well as others which will become
apparent hereafter, a sustaining device in accordance with the present
invention for sustaining musical sounds produced by a stringed musical
instrument cooperates with at least one pick-up transducer associated with
the strings of the musical instrument for generating electrical signals
having frequencies corresponding to the frequencies of vibrations of the
strings of the musical instrument. The sustaining device comprises
amplifying means connected to said pick-up transducer for amplifying said
electrical signals generated by said pick-up transducer. Output transducer
means is provided connected to said amplifying means for converting said
amplified electrical signals into mechanical vibrations and for imparting
movements to said strings to correspond to the amplified electrical
signals. An output transducer means is mounted on said stringed instrument
and arranged proximate to the strings of the musical instrument. Said
amplifying means, said strings, said pick-up transducer, and said output
transducer means together form a regenerative system for sustaining a
musical sound substantially independently of the volume of the musical
sounds produced by the stringed musical instrument.
In accordance with one presently preferred embodiment, wherein the
sustaining device is incorporated in a guitar, an audio amplifier is
connected to electromagnetic pick-ups for amplifying the electrical
signals generated in the pick-ups due to the vibratory movements of the
strings. The output of the amplifier is fed to a loudspeaker which is
disposed in a cavity or cut-out portion of the guitar just beneath the
strings. The loudspeaker is positioned in such a way that the air
movements caused by the cone of the speaker are directed at the strings,
such air movements constituting mechanical vibrations which reinforce the
initial vibratory movements of the strings. The speaker is advantageously
resiliently mounted on the guitar and is at least partially shielded with
a suitable magnetic shielding material to minimize direct coupling between
the loudspeaker and the electromagnetic pick-ups. In this manner, the
regenerative loop is through the strings and can be controlled by
controlling the level of the signals which drive the loudspeaker. The
distance of the speaker from the strings may be on the order of magnitude
of the thickness of the body of the guitar. By mounting the speaker or
string driving mechanism directly on the guitar and in close proximity to
the strings, the level or degree of sustain can be accurately controlled
and any desired sustain is possible without excessively increasing the
level of the audio sounds as heretofore required.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages of the invention will become apparent from a reading of
the following specification describing illustrative embodiments of the
invention. The specification is to be taken with the accompanying drawings
in which:
FIG. 1 is a top plan view of an electric or "solid body" guitar
incorporating the sustaining device in accordance with the present
invention;
FIG. 2 is an enlarged top plan view of a control panel of the sustaining
device shown in FIG. 1, showing the various controls and adjustments which
can be used to modify the sounds or musical effects obtainable with the
sustaining device;
FIG. 3 is a fragmented cross-sectional view of the guitar shown in FIG. 1,
and showing diagrammatically one presently preferred embodiment of the
sustaining device of the present invention;
FIG. 4 is an enlarged cross-sectional view of an electromagnetic pick-up
shown in FIG. 3; and
FIG. 5 is a diagrammatic and electrical schematic representation of another
presently preferred embodiment of the sustaining device of the present
invention, showing additional and optional features with which the
sustaining device may be provided.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now specifically to FIGS. 1 and 2, wherein the identical or
similar parts are designated by the same reference numerals throughout, an
electric guitar 10 is shown which is of the type commonly known as a
"solid body" guitar. Such a guitar has little acoustical qualities and
relies substantially entirely upon an electronic pick-up and reproduction
system which monitors the vibrations of the strings and converts the same
into electrical signals which are amplified and used to drive external
speakers. The prior art electrical guitars, therefore, could not properly
be played without the associated electrical components, and namely the
external amplifiers and speakers.
The electrical guitar 10 has a guitar body 12 which, as suggested above, is
frequently made out of a solid material such as wood and does not have the
resonant or acoustical qualities of conventional guitars. A finger board
14 extends from the guitar body 12 and a plurality of strings 16 are
spaced from each other along the finger board 14. The steel strings 16 are
in a state of tension, being anchored at an anchoring or holding member 18
at one end and tensioned at the other end by a series of tuning pegs 20.
In order to elevate the strings above the guitar body 12, conventional
bridges 22 and 23 are used which also space the strings from a pair of
spaced electromagnetic pick-ups 24 and 26, as best shown in FIG. 3. The
electromagnetic pick-ups 24 and 26 may be conventional and will be
discussed more fully hereafter in connection with FIG. 4.
The sustaining device in accordance with the present invention, to be more
fully described hereafter in connection with FIGS. 3 and 5, includes a
loudspeaker 28 which is shown disposed in a recess or cavity formed in the
guitar body 12 and directly below the strings 16. The loudspeaker 28 is
positioned proximate to the strings and is oriented to direct the sound
which emanates therefrom in or towards the direction of the strings so as
to be capable of sympathetically driving the strings in a manner which
will be more fully described hereafter.
The sustaining device of the present invention also includes a control
panel 30, best shown in FIG. 2, which includes various controls, to be
described below, for modifying the electrical characteristics of the
sustaining device and, therefore, also of the audio out-puts which are
produced by the guitar 10.
Referring to FIG. 3, there is shown the general arrangement of components
in a solid body guitar which has been modified to incorporate the
sustaining device of the present invention. The circuitry shown is
diagrammatic and presents a basic arrangement of the sustaining device. A
more versatile embodiment of the sustaining device having more controls
and features will be described in connection with FIG. 5.
Referring to FIG. 3, the electromagnetic pick-ups 24 and 26 are shown
mounted on the guitar and spaced from each other along the general
direction of the strings 16. While two pick-ups 24, 26 are shown, it will
become evident from the description that follows that one, two or more
pick-ups may be used. Electric guitars are conventionally supplied with
pick-ups of the type which may be used in connection with the sustaining
device of the present invention. When the basic guitar has been provided
with pickups, then these need not be provided since the pick-ups provided
with the guitar can be used. However, where a guitar or other stringed
instrument is not initially provided with pick-ups, then such pick-ups
must be provided and generally arranged or positioned to pick-up the
mechanical vibrations of the strings and convert the same into
corresponding electrical signals. The use of pick-up transducers, such as
electromagnetic pick-ups, is well known in the art, as is their selection
and positioning or arrangement with reference to the strings.
Referring to FIG. 4, there is shown one typical pick-up transducer in the
nature of an electromagnetic pick-up 24. The pick-up 24 generally
comprises a permanent magnet 24a substantially enclosed within a housing
24b and having at least a portion thereof extending beyond the housing. A
coil 24c is wound about the magnet 24a and has a pair of output terminals
24d. The exposed end of the magnet 24a is spaced a distance "d" from the
steel strings 16. The permanent magnet establishes a magnetic field in the
region of the steel strings. The vibrations of the steel strings 16 bring
the strings closer and further away from the permanent magnet to modify
the magnetic field. The changes in the magnetic field induce electrical
signals in the coil 24c which are made available at the output terminals
24d.
While electromagnetic pick-ups are the conventional pick-up transducers
used on electric guitars, the present invention also contemplates the use
of other types of pick-up transducers. Almost any type of pick-up
transducer may be utilized which monitors the vibrations of the strings,
in the case of stringed instruments, and converts those vibrations to
electrical signals to correspond to the vibrations. By way of example
only, the pick-up transducer may be electromagnetic, electrostatic,
piezoelectric, electromechanical, proximity or capacity sensitive,
velocity sensitive, or any other transducer which converts physical
movements to electrical energy. Photoelectric arrangements utilizing a
source of light and a photocell or phototransistor may be used. It is also
possible to use magneto-restrictive materials which exhibit a relationship
between the physical length or dimensions thereof and the electrical
potentials which they produce. For example, a nickel bar or other similar
material may be used for the bridge 22, the vibrations of the strings
generating electrical potentials which can be amplified. In effect, almost
any material which converts physical movements to electrical signals may
be used, such as rochelle salts, and materials used in contact, ceramic,
ribbon, and carbon microphones. As suggested above, when a musical
instrument is not initially provided with a pick-up transducer, any one of
the above-described transducers may be utilized. However, when the
instrument is provided with pick-ups of any type, these may be used in
conjunction with the sustaining device of the present invention.
The specific positions of the pick-up transducers along the length
directions of the strings 16 is not critical. In the embodiment shown in
FIGS. 1 and 2, the pick-up 24 is positioned near the bridge 22 while the
pick-up 26 is positioned near the fingerboard 14. As will become evident
from the description that follows, either one of these two pick-ups can be
used individually. Additionally, the pick-ups 24 and 26 can be spaced
closer together or further apart, limited only by the dimensions of the
guitar body 12 and the size and position of the speaker 28. However, it
has been found that the positions of the pick-ups along the length of the
strings influence the frequency content of the picked-up signals. For
example, the closer the pick-up is to the bridge 22, the more harmonics
that will be picked up by the pick-up 24. On the other hand, the pick-up
26, being spaced further away from the bridge 22, picks up predominantly
the fundamental and, therefore, lower frequencies in the audio range.
The pick-ups 24 and 26 are connected by means of leads 32a and 32b to the
input terminal of an amplifier 34 through a sustain control 36. The
sustain control may comprise an adjustable potentiometer which can be used
to modify or adjust the level of the signals which are fed to the
amplifier 34.
The amplifier 34 is energized by a battery 38 which is housed within the
guitar body 12. An external AC power supply may be used in lieu of or in
addition to the battery 38 to power the amplifier 34. An on-off power
switch commonly denominated as a "juice" switch in the music trade, is
shown in FIG. 2 but not in FIG. 3. By using an internal battery to drive
an advantageously low drain amplifier 34, a guitar which incorporates the
sustaining device of the present invention is completely portable and may
be played anywhere without the usual bulky and heavy auxilliary equipment.
The amplifier 34 may be a relatively low power output audio amplifier. It
has been found that a three watt audio amplifier is satisfactory for the
purpose to be described. One example of an amplifier which may be used is
the Universal Type three watt audio amplifier manufactured by Midland
Electronics. Another amplifier which is suitable for this purpose is a
three watt solid state push-pull audio amplifier No. AA 900 manufactured
by Philmore Manufacturing Co., Inc. While the amplifier 34 should have
enough power output to drive the string 16, as to be described, and to
permit listening of the electric guitar 10, it need not provide the very
large power inputs that are typical of external amplifiers used to drive
the external speakers commonly used with electric guitars. To drive
external speakers, the outputs of the pick-ups 24, 26 can be connected to
the inputs of external amplifiers as was the practice heretofore.
Alternately, the output of the amplifier 34 can be fed to the external
amplifiers and constitutes a pre-amplified output. As to be described more
fully to FIG. 5, the direct outputs from the pick-ups and the
pre-amplified output from the amplifier 34 can be materially different
depending on whether the amplifier 34 is operating linearly or is in
saturation.
The amplifier 34 output is connected by means of a lead or electrical
conductor 40 to the loudspeaker 28. The loudspeaker 28 is thereby driven
in a conventional manner, the electrical signals causing the loudspeaker
28 cone to vibrate and produce air movements which manifest themselves in
audio sounds.
The guitar body 12 is provided with a suitable opening for receiving the
loudspeaker 28 which may be mounted on the guitar body 12 in any
conventional manner. For example, the loudspeaker 28 may be mounted by
means of screws as shown in FIG. 3 with rubber grommets 42 being
interposed between the loudspeaker 28 frame and the guitar body 12.
Rubber, foam or any other resilient material may be used to acoustically
decouple the loudspeaker 28 from the guitar body 12 for reasons to be
described. Additional acoustic shielding in the nature of foam 44 may be
used to further acoustically decouple the loudspeaker 28 from the guitar
body 12 and the pick-ups 24 and 26.
The loudspeaker 28 serves an an output transducer means for converting the
amplified electrical signals into mechanical vibrations and for imparting
movements to the strings 16 to correspond to the magnified electrical
signals as to be described below. While the output transducer has been
described as being a loudspeaker, it will become evident to those skilled
in the art that any output transducer which is capable of converting
electrical signals into mechanical vibrations which may be coupled to the
strings 16 may be used. For this purpose, most of the transducers
described with respect to the pick-up transducer could also be used for
the output transducer. Thus, if a nickel bar or other magneto-restrictive
material were used, a coil could be wound around the nickel bar. When the
amplified signals are applied to the coil, the nickel bar instantaneously
changes dimensions to correspond to the electrical signals. The nickel bar
could be used, for example, in place of the bridge 22 so that the nickel
bar is in contact with the strings 16 and the instantaneous changes in
dimensions of the nickel bar are equivalent to vibrations which are
coupled to the strings 16. Other output transducer arrangements which can
couple vibrations to the strings 16 in accordance with the amplified
signals will become readily evident to those skilled in the art.
When the output transducer is in the nature of a loudspeaker or other
electromagnetic device, electromagnetic fields are established in the
vicinity of the electromagnet 28a in addition to the generation of
vibrations. While the grommets 42 and the acoustic shield 44 are intended
to acoustically decouple the loudspeaker 28 from the pick-ups 24 and 26,
there is also advantageously provided magnetic shields 46 which
substantially surround or enclose the electromagnetic pick-ups 24 and 26.
Such magnetic shields 46 assist in electrically decoupling the loudspeaker
28 from the electromagnetic pick-ups 24, 26 so that direct acoustic and
electrical coupling between the loudspeaker 28 and the magnetic pick-ups
24, 26 are minimized. To still further reduce the amount of electrical or
magnetic coupling between the loudspeaker 28 and the pick-ups 24, 26,
there is advantageously provided a further magnetic shield which
substantially, if not fully, encloses or surrounds the loudspeaker 28 and
is interposed between the pick-ups 24, 26 and the loudspeaker 28. The
magnetic shields 46 and 48 may be made from any highly permeable magnetic
or ferrous material, such as tin or Mumetal. Where the magnetic shield 48
substantially encloses the loudspeaker 28, and particularly the cone area
through which the sound emanates, the magnetic shield 48 is advantageously
provided with an array of holes or apertures 48a to form a grill or mesh
through which the air movements may propagate in the direction of the
strings 16.
An important feature of the present invention is that the output
transducer, or the loudspeaker 28 in the embodiment being described, is
mounted on the instrument and arranged proximate to the strings 16 of the
guitar 10. In FIG. 3, the loudspeaker 28 is shown spaced from the strings
16 a distance "D". While the distance "D" is not critical, it is
substantially smaller than the distances which heretofore existed between
the strings of an electrical guitar and the external speakers. Where the
guitar 10 has a thickness of the body 12 equal to a predetermined value,
the spacing "D" between the loudspeaker 28 and the strings 16 is
advantageously on the order of magnitude of the predetermined thickness of
the guitar body 12.
Where the output transducer such as the loudspeaker 28 is mounted below the
strings 16, the distance "D" is typically on the order of magnitude of the
thickness of the guitar body 12. However, the output transducer need not
be located beneath the strings as shown in the Figures, but may be
disposed anywhere on the musical instrument. Thus, for example, the output
transducer may be positioned on the guitar body 12 beyond the anchor or
holding member 18 for the strings 16, or on either side of the strings.
With the latter arrangement, however, there is advantageously provided air
ducts which extend between the output transducer and the strings to couple
the air movements and vibrations of the output transducer to the strings.
With such an arrangement, the distance which must be primarily considered
is the distance between the output of the air duct and the strings 16,
which distance could be approximately equal to the distance "D" above
described.
The output of the amplifier 34 may, as suggested above, constitute a preamp
output to an external amplifier. The lead or conductor 50 may be connected
to an output jack or to an output selector switch as described in
connection with FIG. 5. Similarly, the lead or conductor 52 is connected
to the pick-ups 24, 26 directly and may similarly be connected to an
output jack or to an output selector switch.
Referring to FIG. 5, there is shown a further embodiment of the sustaining
device in accordance with the present invention, which includes more
features and is more versatile than the device shown in FIG. 3. There is
provided, for example, a phase reversing switch 54 connected by way of
leads 24d to the treble pickup 24. A pick-up selector switch 56 is
provided which has a movable or sliding contact 56a and fixed contact 56b
and 56c. The phase or reversing switch 54 is connected to the stationary
contacts 56b by means of lead 32a while the fixed contact 56c is connected
to the pick-up 26 by means of lead 32b. The pick-up selector switch 56
advantageously has three positions so that the individual or the combined
outputs of the pick-ups 24, 26 may be selected. Only one phase reversing
switch 54 is shown to permit changes in relative phase of the signals
generated by the pick-ups 24,26. However, a second phasing switch for
pick-up 26 may be provided.
The moveable contact 56a of the pick-up selector switch 56 is connected to
a direct output volume control 58 which may be in the nature of a
potentiometer having a sliding contact 58a. The sliding contact 58a is
connected to a fixed terminal 60 of an output selector switch 66. The
output of the amplifier 34 is connected to a pre-amp output level control
62 which may be in the nature of a potentiometer having a sliding contact
62a. The sliding contact 62a is connected to another fixed contact 64 of
the output selector switch 66. The moveable contact 66a of the output
selector switch 66 is connected to an output terminal jack 68 suitable for
use in conjunction with an external amplifier. With this arrangement, the
musician may select the output which he desires to have amplified by the
external amplifiers and reproduced by the external speakers.
When the amplifier 34 operates in the linear range, such as when the
signals at the input to the amplifier 34 are relatively small, the outputs
at the terminals 60 and 64 are substantially equivalent except for
magnitude. However, when the input signals to the amplifier 34 exceed a
predetermined value, the output signals become clipped or otherwise
distorted due to the saturation of the amplifier. The signals which then
appear at the pre-amp output terminal 64 are substantially different in
harmonic overtone content than the original signals which are generated by
the pick-ups 24, 26 and available at the direct output terminal 60. In
some instances, musicians may prefer to use the somewhat distorted output
signals appearing at the terminal 64 as opposed to the direct output
signals appearing at the terminal 60 in order to obtain special sounds or
effects.
The level of the signals at the direct output terminal 60 are initially
adjusted by means of the direct output volume control 58 while the level
of the signals at the pre-amp output terminal 64 are adjusted by means of
the pre-amp output level control 62.
The level of the signals appearing at the input to the amplifier 34 are
primarily determined by the sustain control 36 which is in the nature of a
potentiometer, with a sliding terminal 36a thereof connected to the input
terminal of the amplifier 34. With this arrangement, and with the gain of
the amplifier 34 substantially fixed, the level of the signals at the
output of the amplifier 34 are primarily determined by the levels of the
signals at the input thereto. The input levels to the amplifier 34 are, of
course, determined by the activity of the steel strings 16 as well as the
efficiency of the pick-ups 24, 26. Additionally, slight changes in level
may result between the different positions of the pick-up selector switch
56. The levels of the signals at the output terminal of the amplifier 34
can be effectively controlled by adjusting the sustain control or
potentiometer 36. The sustain control 36 can be effectively adjusted to
provide relatively low level or high level signals at the output of the
amplifier 34.
The greater the electrical input levels to the loudspeaker 28, the greater
the vibratory movements of the loudspeaker cone and the greater the air
movements created by the loudspeaker. The louder the audio from the
loudspeaker 28 or the greater the air movements which propagate therefrom,
the more the loudspeaker 28 drives the steel strings 16 into sympathetic
vibratory modes.
An optional tone control 70 is provided which includes a capacitor 70a and
potentiometer 70b connected as shown in a conventional manner.
Additionally, a base filter generally designated by the reference numeral
72 may be provided which includes a switch 72a connected in parallel with
the capacitor 72b as shown in FIG. 5. Both the tone control 70 and the
base filter 72 are connected between the pick-ups and the input to the
amplifier 34 so that the frequency content of the input signals can be
modified prior to amplification.
It should be evident from the above description that the basic principle of
operation involves provision of a regenerative acoustic feedback loop
which at least comprises the amplifier 34, the strings 16, the pick-up
transducers 24, 26 and the output transducer or loudspeaker 28. However,
to control the degree of regeneration and to prevent spurious
oscillations, it is important that the direct coupling between the output
transducer or loudspeaker 28 and the pick-up transducers 24, 26 be
minimized. It is for this reason that the acoustic shielding means 42, 44
and the magnetic shielding means 46,48 are provided. Under ideal
conditions, there is litte or no coupling between the loudspeaker 28 and
the pick-ups 24, 26 and all coupling between these transducers takes place
only through the strings 16 themselves.
As described above, the time constants of the steel strings 16 will have a
tendency to cause the vibrations thereof to decay with time. Driving the
strings with relatively low audio levels at least partially compensates
for the tendencies of the strings to decay and causes the decay to be more
gradual, thereby increasing the sustain of the notes. Driving the strings
harder with greater audio outputs may fully or over-compensate for the
tendency of the steel string vibrations to decay. Accordingly, adjustment
of the sustain control potentiometer 36 can be used to adjust the degree
of sustain or the length of time during which a note is played. Increasing
the signals excessively at the input of the amplifier 34 may over
compensate the tendency of the strings 16 to come to rest and the strings
will continue to vibrate more vigorously with time to thereby cause an
increase rather than a decrease in volume at the output of the guitar with
time. This can also be used by a musician to produce special musical
effects.
To operate the guitar 10, the power or "juice" switch 74 is moved to the
"on" position. The other various controls, switches or adjustments shown
on the control panel 30 in FIG. 2 are then moved to the required positions
to provide a desired musical effect. Depending on how long the notes are
to be sustained, the sustain control 36 is adjusted to increase or to
decrease the sustain time. The guitar 10 can be played at this point. It
may be pointed out that the various controls discussed above and shown in
FIG. 2 may be changed during play of the guitar and, in fact, even while a
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