Music – Instruments – Electrical musical tone generation
Reexamination Certificate
2000-04-27
2002-05-21
Donels, Jeffrey (Department: 2837)
Music
Instruments
Electrical musical tone generation
Reexamination Certificate
active
06392137
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed towards transducers. These devices are used to convert the physical energy of a vibrating ferromagnetic object into an electrical signal. The pickup of an electric guitar is a transducer that converts the kinetic energy of a vibrating guitar string into an electrical signal in the form of an oscillating voltage. Generally, guitar pickup transducers utilize permanent magnets and electrical coils that are formed by winding insulated copper wire around pole pieces. The transducer's magnet and coil winding system are mounted on the body of a guitar so that the guitar strings pass through the magnet's flux field and alter the shape of the magnetic field when the string vibrates. The changing flux induces an electrical signal in the windings of the pickup. The guitar amplifier converts this voltage into sound.
The traditional guitar has a plurality of guitar strings that are secured at each end and held under tension to vibrate at the appropriate frequency. The guitar strings are supported on a bridge over a transducer. On electric guitars with magnetic pickups, the guitar strings normally do not touch the pickup/transducer, but instead lie in close proximity thereto. This is also the case for tone-hole pickups used in acoustic guitars. The transducer includes a magnet that emits a magnetic field and an electrical coil that is placed within the effects of the magnet field. The strings are constructed from magnetically permeable material and are placed so that they pass through the transducer's magnetic field. When plucked or strummed, the magnetically permeable material of the vibrating guitar strings produce a corresponding oscillating magnetic flux at the windings of the coil. Thus, through magnetic induction, the vibration of the guitar strings moving within the lines of magnetic flux emanating from the pickup causes an electrical signal to be generated within the coil of the pickup.
Often, during music performance or recording, the pickup signal is processed to create a desired effect. Among the most common effects are added harmonic distortion, chorus and reverberation. For some of the more sophisticated effects, such as polyphonic fuzz, it is preferred, and sometimes required, that a separate signal be obtained from each string. For this purpose, polyphonic pickups are used. A polyphonic pickup contains multiple sensors, each one being particularly sensitive to the vibrations of one string and relatively insensitive to the vibrations of other strings. A polyphonic pickup for a six-string guitar has six sensors, and is sometimes referred to as a hexaphonic pickup or a hex pickup. Polyphonic or hexaphonic guitar pickups are also used in systems where the guitar is interfaced with a digital signal processor or synthesizer where the final sound is created.
In a hexaphonic pickup, each sensor is dedicated to a different string of a six-string guitar. The two common types of pickups used for this purpose are piezoelectric and magnetic pickups. The magnetic pickup generally consists of variable reluctance type magnetic field sensors with permanent magnets and sensor coils located under the strings. This type of pickup produces output voltages in its coils in response to the velocity of the vibration of the parts of the strings that are in its magnetic field.
Variable reluctance type transducers are often used to measure or detect the velocity of a moving ferromagnetic target. When the target can move only along a predetermined path, the direction of velocity can be determined from the polarity of the voltage induced at the sensing coil of the transducer. However, if the target can move along an arbitrary path, as in the case of a section of a vibrating guitar string, the direction of movement cannot be determined from the induced voltage polarity, nor does the magnitude of the induced voltage accurately represent the magnitude of the target's velocity.
As previously noted, polyphonic guitar pickups are often used in combination with signal processors that are designed to create different sounds depending on certain characteristics of string vibrations. This gives the guitar player a degree of expression not possible with signals obtained from monophonic pickups. Sometimes the sound may be digitally synthesized or modified using information obtained from the pickup signal. In such systems, inadequate or inaccurate conversion of string vibrations into pickup signals result in poor digital pitch tracking and unwanted sounds. It is therefore desirable for a polyphonic pickup to produce signals that are as accurate a representation of all aspects of the vibrating string as possible. Signal components caused by other sources, such as vibrations of adjacent strings, vibrations of other parts of the guitar, noises created by inadvertent impacts on the guitar body, fret noise, etc., are to be avoided as much as possible. Generally, piezoelectric pickups are more sensitive to such extraneous unwanted effects than magnetic pickups are. On the other hand, magnetic polyphonic pickups may suffer from magnetic cross talk between the strings. Cross talk can occur when a each transducer senses the vibration of adjacent strings in addition to the one immediately overlying the transducer in question. This may be caused by the second string's vibration affecting the magnet field at the coil of the first transducer, and may also be caused by stray magnetic flux of the second transducer affecting the readings of the first transducer's coil
When a guitar string is plucked and released, a given point on the string vibrates in multiple directions in the transverse plane. The transverse plane is the plane perpendicular to the axis of the string. The path of string vibration may be, for example, a precessing ellipse in the transverse plane. Conventional magnetic polyphonic guitar pickups respond primarily to string vibrations occurring along the vertical axis, i.e., towards and away from the pickup. They also respond, but with less sensitivity, to string vibrations occurring along the horizontal or axis, i.e., in the plane defined by the strings. As a result of this cross-axis sensitivity, string vibrations in different directions induce differently scaled voltages in the sensing coil that are inseparably mixed in the output signal. This drawback of conventional magnetic pickups limits the tracking speed, pitch accuracy, and other performance characteristics of the electronic systems that interpret the signal. As a demonstrative example, string vibrations with large amplitude in a near-horizontal direction may be indistinguishable from those with small amplitude in a near-vertical direction. Conversely, the pickup may respond with different sensitivities to string vibrations of equal amplitudes in different directions.
The insufficiency of conventional guitar pickups to determine transverse string vibration in all planes has been recognized by other inventors in the prior art. An example of a multiple pole pickup for a single string is shown in U.S. Pat. No. 4,348,930 issued to Chobanian et al. on Sep. 14, 1982 entitled Transducer For Sensing String Vibrational Movement in Two Mutually Perpendicular Planes. This patent teaches separate dedicated pole pieces and coils that are sensitive to vibration in two separate and mutually perpendicular planes. This patent is directed towards the use of a first magnetically permeable pole piece with a first coil for supplying a first electrical signal and a second magnetically permeable pole piece with a second coil for supplying a second electrical signal. The design uses a first pole piece where the vibrational movement of the string in a first plane induces minimal or insignificant flux changes in the second coil, and vice versa. Thus, the vibrational movement of the string in one plane is sensed independently of, and with minimal influence over, the sensing of the vibrational movement of the string in the other mutually perpendicular plane. Thus, Chobanian describes a polyphoni
Beavers Lucian Wayne
Donels Jeffrey
Gibson Guitar Corp.
Waddy & Patterson
LandOfFree
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