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Description  |
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The present invention relates to a device for providing a sustained sound
from a musical instrument having a vibratory element such as a string.
BACKGROUND OF THE INVENTION
Musical instruments employing a vibrating mechanical element such as a
string to produce sound have been provided heretofore with transducers
commonly referred to as "pickups" for detecting the motion of the
vibrating element and producing an electronic signal representing this
vibration. This pickup signal may be amplified and converted to sound by a
loudspeaker. The sound produced from the pickup signal supplements or
replaces the sound produced by acoustical interaction of the string, the
instrument body and the air. Typically, the instrument body has little or
no acoustic response, so that the sound produced from the pickup signal
constitutes essentially the entire sound of the instrument. This is the
case in the common electric guitar, electric bass and the like.
The sound produced by instruments of this nature dies out progressively
after the string is excited. This is particularly so in the case of
instruments having little or no independent acoustic response. The sound
can be prolonged somewhat by operating the amplification and loudspeaker
system at extremely high power levels so that strong acoustic waves
representing the original vibration impinge upon the string. Such
"acoustic feedback" tends to sustain the vibration of the string, thereby
prolonging the note. However, this approach is effective only when the
sound produced by the amplification and loudspeaker system is
extraordinarily loud. Moreover, the acoustic feedback effect depends upon
the acoustic properties of the environment. Therefore, this effect will
produce different results in different concert halls.
Various attempts have been made to provide a "sustainer" or device capable
of prolonging the notes independently of acoustic feedback from the
environment. U.S. Pat. No. 4,245,540 discloses a sustainer incorporating a
loudspeaker mounted in close proximity to the strings. The amplified
signal from the pickup is passed to the loudspeaker, so that acoustic
vibrations produced by this loudspeaker will impinge directly upon the
strings. U.S. Pat. No. 4,697,491 discloses a sustainer for a stringed
instrument such as a guitar having a body and a neck projecting from the
body. An electromechanical transducer is mounted to the neck, remote from
the body. The pickup signal is passed to this electromechanical
transducer. The transducer vibrates the neck and these vibrations are fed
back into the strings. U.S. Pat. No. 3,813,473 discloses an instrument
having a "bridge" or string support linked to an electromagnet. An
electronic signal derived from the pickup signal is applied to this
electromagnet, so as to vibrate the bridge and, hence vibrate the strings.
U.S. Pat. No. 4,484,508 describes a generally similar sustainer having an
electromechanical transducer adapted to shake the instrument body
responsive to the pickup signal, and also having a circuit for
progressively reducing the amplitude of the signal so as to provide a
controlled fadeout. The fadeout circuit is arranged to provide a quicker
fadeout for higher frequency signals.
U.S. Pat. Nos. 4,137,811 and 4,181,058 provide a sustain action utilizing
magnetic interaction between a static magnetic field and electrical
currents passing through the strings themselves. Thus, a magnet is mounted
adjacent the strings, and both the strings and frets of the instrument are
electrically conductive. Circuitry is provided for directing an
alternating current feedback signal representing the pickup signal through
the strings via the frets. The alternating current in each string
interacts with the static magnetic field to produce an alternating
magneto-motive drive force on the string. U.S. Pat. No. 4,236,433
discloses a sustainer employing an electromagnetically actuated tensioning
device for each string, each such tensioning device being connected to a
feedback circuit. The signal from a pickup associated with each string is
applied through the feedback circuit to the tensioning device, so that the
tensioning device will periodically stretch and release the string. The
'433 patent also discloses an alternative arrangement wherein an
electromagnet or "driver" is juxtaposed with each string so that flux from
the electromagnet will impinge directly upon the string. Each such
electromagnet is provided with a drive signal representing the signal from
a pickup associated with the same string. Thus, variations in magnetic
flux of the electromagnet will cause variations in the flux impinging upon
the strings. This varying flux tends to excite the string in vibration,
provided the string itself is ferromagnetic. U.S. Pat. No. 4,075,921
discloses a generally similar approach, employing a magnetic pickup and a
magnetic driver arranged to directly excite a ferromagnetic string. The
sustainer may be a hand held, battery-powered device incorporating both a
pickup and a driver, and arranged so that the pickup and driver can be
aligned with one string of the instrument. Alternately, the sustainer may
be built into the instrument and may be provided with separate pickups and
drivers for the various strings. U.S. Pat. No. 3,742,113 likewise employs
a magnetic pickup and magnetic driver directly associated with each
string, with a feedback and amplification circuit connected between the
pickup and the driver. The '113 patent emphasizes that the feedback
circuit or amplifier should have "zero phase shift" so as to provide a
driving force "in phase with the string's fundamental frequency of
oscillation as transduced by the pickup" so as to reinforce the
fundamental mode vibration of the string.
The aforementioned '921, '433 and '113 patents utilize pickups and drivers
having a separate ferromagnetic pole piece disposed beneath each string,
so as to provide a substantially concentrated magnetic field from each
pole piece at normal, undistorted position of the associated string.
Separate coils may be provided for each pole piece. U.S. Pat. Nos.
4,580,481 and 4,535,668 disclose a pickup having a unitary, oblong coil
and ferromagnetic core extending laterally across the string array.
Movable permanent magnets are also provided. By repositioning the
permanent magnets, the field direction can be varied so as to provide
different phase relationships among the signals induced in the coil by the
various strings. U.S. Pat. No. 3,983,777 suggests a pickup having a
uniform magnetic field strength across the lateral extent of the string
array to suppress variations in pickup response caused by lateral movement
of the strings. Other unitary pickups having a single coil and a single
ferromagnetic pole piece extending across the string array are shown in
U.S. Pat. Nos. 4,364,295 and 4,151,776.
Despite the extensive efforts of the art heretofore, there have been
substantial, unmet needs for further improvement. The sustainers available
heretofore generally have been inefficient, in that they require
substantial electrical power to the drive coil in order to produce an
appreciable sustain effect. This high power consumption poses a
significant problem where the sustainer draws its power from a battery
mounted on the instrument.
Moreover, application of high power to an electromagnetic drive coil in a
sustainer tends to produce substantial electromagnetic emissions.
Electromagnetic fields radiated from the drive coils impinge upon the
pickup and induce unwanted signals. Although the pickups used in
electronic musical instruments typically incorporate features for
suppressing the effect of stray electromagnetic radiation, these measures
are not always perfectly effective. Radiation from the driver can be
suppressed to some degree by shielding, but such shielding adds weight,
bulk and cost. Thus, there has been a substantial need heretofore for an
efficient sustainer capable of providing a powerful sustaining effect with
only a modest power input to the driver. There has been a further need for
a sustainer which would permit the musician to adjust the action of the
sustainer to provide varied artistic effects.
SUMMARY OF THE INVENTION
The present invention addresses these needs.
A sustainer according to one aspect of the present invention is adapted for
use with a musical instrument having at least one vibratory element, which
may be a string or the like. The sustainer includes drive means for
applying a drive force to a vibratory element of the instrument responsive
to the drive signal so that the drive force bears a predetermined phase
relationship to the drive signal. Feedback means are provided for
accepting a pickup signal representing vibration of the vibratory element
of the instrument and having a predetermined phase relationship to the
vibration. The feedback means are arranged to provide a drive signal to
the drive means such that the drive force applied by the drive means will
be substantially in phase with the vibration of the vibratory element. The
sustainer may further include a pickup for providing the pickup signal in
response to the vibration of the string.
One or both of the pickup means and the drive means typically will have a
non-zero phase shift. That is, the pickup signal produced by the pickup
means may lag or lead the actual movement of the vibratory element,
whereas the drive force applied by the drive means may lag or lead the
drive signal. The feedback means preferably is arranged to provide a phase
shift which is substantially inverse to the combined phase shift of the
pickup means and the drive means, taken together. Thus, the combined
overall phase shift of the entire sustainer will be approximately zero and
the drive force will be applied in phase with the vibratory motion of the
string itself, i.e., in phase with the sustainers according to this aspect
of the invention can provide a powerful, sustaining action to prolong the
fundamental mode vibration of a string or other vibratory element with
only modest power input to the driver. Such sustainers according to the
invention can provide sustaining action suitable for prolonged, continuous
use, as in a concert environment, while employing only small,
self-contained batteries as a power supply. Although the present invention
is not limited by any theory of operation, it is believed that the
enhanced results achieved arise at least in part from better phase
matching of the force applied to the vibratory element and the actual,
fundamental mode vibration of the vibratory element.
As set forth in our aforementioned U.S. Pat. No. 4,907,483, the feedback
means may be arranged so that for at least some frequencies of the pickup
signal, the drive signal differs in phase from the pickup signal and this
phase difference varies with frequency. As also set forth in our U.S. Pat.
No. 4,907,483, desirably, such variation in the phase difference between
the pickup and drive signals is towards a drive signal leading phase
difference with increasing frequency. One aspect of the invention claimed
in the present application is to provide a sustainer having feedback
means; is operative to provide the drive signal so that for at least some
frequencies, the drive signal leads the pickup signal.
As further recited in our U.S. Pat. No. 4,907,483, control means may be
provided for determining the frequency content of the pickup signal and
altering the phase transfer function of the feedback means, the phase
transfer function of the drive means or both depending upon this frequency
content. Thus, the control means may include means for adjusting the phase
transfer function of the feedback means towards a drive signal leading
condition as the predominant or highest amplitude frequency of the pickup
signal increases.
The drive means may include an inductive coil and means for applying the
drive force to the vibratory element responsive to magnetic flux produced
by the coil. The force applied by drive means employing an inductive coil
tends to lag behind the drive signal or voltage applied to the coil. A
further aspect of the invention as claimed herein provides a sustainer
with means for providing capacitance in series with the drive coil and
means for selectively changing said capacitance. The capacitance tends to
counteract the lag caused by the inductive drive coil.
A further aspect of the present invention is directed generally to the
concept of a sustainer having automatic gain control means for controlling
the feedback means to maintain the drive signal at a predetermined
magnitude. By contrast, our aforementioned U.S. Pat. No. 4,907,483
discloses this concept but only claims the concept in conjunction with
certain other features.
Additionally, although our aforementioned U.S. Pat. No. 4,907,483 discloses
the combinations of the various sustainers claimed therein with the
musical instrument itself, the specific claims directed to combinations of
sustainers and musical instruments in the '483 patent are not fully
commensurate with the claims directed to the sustainers themselves.
Accordingly, the present application claims combinations of musical
instruments and sustainers in scope more closely commensurate with the
broad scope of the claims directed to sustainers in the '483 patent.
The foregoing comments as to the presently claimed invention and the
invention claimed in the '483 patent and provided solely to facilitate
understanding of the differences therebetween, but should not be taken as
limiting or restricting the scope of either the '483 patent or the present
claims.
These and other objects, features and advantages of the present invention
will be more readily understood from the detailed description of the
preferred embodiment set forth below, taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view of a sustainer in accordance with
one embodiment of the present invention, in conjunction with a musical
instrument.
FIGS. 2 and 3 are fragmentary, schematic sectional views taken along lines
2--2 and 3--3 respectively in FIG. 1.
FIG. 4 is a functional block diagram of the sustainer and instrument shown
in FIG. 1.
FIG. 5 is a schematic circuit diagram showing a portion of the sustainer of
FIGS. 1-4.
FIG. 6 is a graph of certain variables associated with the sustainer of
FIGS. 1-5.
FIG. 7 is a fragmentary schematic circuit diagram depicting a portion of a
sustainer according to a further embodiment of the invention.
FIG. 8 is a schematic, fragmentary perspective view depicting a portion of
a sustainer in accordance with another alternate embodiment of the
invention.
FIG. 9 is a fragmentary, schematic sectional view taken along lines 9--9 in
FIG. 8.
FIG. 10 is a fragmentary perspective view similar to FIG. 8 but depicting a
sustainer in accordance with embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A conventional electric guitar 20 has a structure including a body 22 and
an elongated neck 24 projecting from the body. A conventional tailstock 26
and bridge 28 are secured to body 22, whereas a headstock 30 is secured to
the end of neck 24 remote from head 22. Frets 25 are arranged along neck
24. Six ferromagnetic, typically steel strings 32 are held under tension
by tailstock 26 and headstock 30, and engaged with bridge 28 so that each
string extends generally in the same, longitudinal direction from the
tailstock to the headstock, the strings being disposed side-by-side above
the neck 24 and body 22. The strings thus define an array having a
widthwise direction transverse to the longitudinal direction and generally
parallel to the top or string-facing surfaces of the neck and body. As
used in this disclosure the terms "widthwise" and "laterally" should be
understood as referring to this widthwise direction of the string. Also ,
the terms "up" and "down" should be understood as referring to the
directions from the strings away from and towards the surface of the
guitar body, respectively. As seen in FIG. 2, the directions to the left
and to the right are widthwise or lateral directions, whereas the
directions towards and away from the top of the figure are upward and
downward, respectively.
Guitar 20 incorporates a pickup 34 of the type known in the art as a
"hum-bucking" pickup. mounted to body 22 adjacent bridge 28. Pickup 34
incorporates a permanent magnet 36 extending along the top surface of body
22, magnet 36 having its northseeking pole facing rearwardly, towards
headstock 30 and its south-seeking pole facing forwardly, towards
tailstock 26. The pickup also includes six ferromagnetic prongs or
projections 38 adjacent the north-seeking pole of magnet 36 and six
similar prongs or projections 40 adjacent the south-seeking pole. These
projections 38 and 40 are disposed in pairs. Each such pair includes one
projection 38 adjacent the north-seeking pole and one projection 40
adjacent the south-seeking pole. Both projections of each pair are aligned
with one string 32. The projections tend to concentrate the flux from the
magnet on the strings.
As illustrated in FIG. 3, considering the generally accepted convention for
magnetic flux direction, the flux emanates from each projection 38
upwardly through the aligned string 32 and returns, in the downward
direction again through the string to the associated projection 40. A coil
42 wound in a first predetermined direction extends around all of the
projections 38, whereas a coil 44 wound in the opposite direction extends
around all of the projections 40. Coil 42 is in series with coil 44.
Upward and downward motion of a string 32 associated with a particular
pair of projections 38 and 40 will change the distance between the string
and the projections 38 and 40 and hence will alter the magnetic reluctance
between the projections. As the string approaches the projections
(downward movement) the reluctance will decrease so that there will be an
increase in upwardly directed flux through the projection 38 and an
increase in downwardly directed flux through projection 40. The opposite
will occur for upwardly directed movement of the string. For any
particular upward or downward string movement, the voltages induced by the
oppositely directed changes in flux in the oppositely wound coils will
reinforce one another, and hence will produce an appreciable output
voltage. As all of the strings cause similar flux changes, the output of
pickup 34 will be a composite signal representing the upward and downward
motions of all of strings 32. Stray electromagnetic signals will induce
oppositely directed voltages in coils 42 and 44. Thus, stray
electromagnetic fields produce little or no output signal.
The output or pickup signal may be sent to a conventional amplifier 46 and
loudspeaker 48 (FIG. 4), desirably via a conventional free space
communications link 50 such as a radio frequency link or the like.
Preferably, the free space communication link and pickup are arranged to
operate without any wired connection to either a fixed power supply or to
the amplifier 46. Thus, those portions of the free space communication
link 50 mounted to guitar 20 may be powered by a battery likewise mounted
to the guitar. Pickup 34 desirably is connected to free space
communications system 50 via the preamplifier 74 of the sustainer, further
discussed hereinbelow.
The sustainer includes a driver 52. Driver 52 incorporates an elongated
generally rectangular ferromagnetic element 54 (FIG. 3). Element 54 is a
permanent magnet composed of a ceramic ferromagnetic material such as the
material commonly available in the magnet trade under the designation
"Ceramic-B". The magnetization of element 54 is directed so that the
north-seeking pole of the element extends along one relatively long,
narrow face 56 of the element and the south-seeking pole extends along the
opposite face 58. Driver 52 also includes a drive coil 60 encircling
element 54. Coil 60 is generally helical, the shape of the helix being
distorted to fit closely around element 54. The axis of helical coil 60
extends in the pole to pole direction of element 54, i.e., between faces
56 and 58. Drive coil 60 has a ground connection 62, an end connection 64
opposite from the ground connection, and a center tap 66.
Appropriate means such as screws 66 or other conventional securement
devices are provided for mounting driver 52 to the structure of instrument
20 at a preselected drive location along the longitudinal extent of
strings 32. The drive location is preferably remote from bridge 28 and
from headstock 30, and may be approximately midway between the bridge and
the headstock. Thus, the drive location may be adjacent the juncture
between body 22 and neck 24. The mounting means are arranged to secure
driver 52 to the instrument structure so that the long dimension Z (FIG.
2) of element 54 extends in the lateral direction of the string array, and
so that the north-seeking pole face 56 of element 54 faces upwardly
towards the array of strings 32. As the long dimension Z of ferromagnetic
element 54 is greater than the lateral extent W of the string array 32,
the ferromagnetic element protrudes laterally beyond both edges of the
string array.
With driver 52 is secured to the body, magnetic flux resulting from the
permanent magnetism of element 54 impinges on strings 32. As best seen in
FIG. 3, the permanent flux from ferromagnetic element 54 is generally
co-directional with the flux in each rearward projection 38 on pickup 34.
The flux in element 54 and in each projection 38 is upwardly directed.
Stated another way, the flux in the driver ferromagnetic element is
co-directional with the flux in the closest active portion or projection
of the pickup. As best seen with reference to FIG. 2, the upwardly facing,
north-seeking pole face 56 of ferromagnetic element 54 extends
substantially parallel to an imaginary surface 68 defined by strings 32 at
the driver location. Thus, the upper or string-facing surface 56 of
element 54 has a slight upward bow adjacent its midpoint. This slight
curvature matches the curvature of the imaginary surface 68 defined by
strings 32 at the drive location, also visible in FIG. 2. Thus, the
distance between the string facing surface 56 and the imaginary surface 68
defined by the strings is substantially constant across the entire lateral
extent of the string array. Surface 56 of the ferromagnetic element is
substantially devoid of appreciable projections extending towards the
strings or notches extending away fro | | |
