Electro-mechanical transducer which couples positive acoustic feedback into an electric amplified guitar body for the purpose of sustaining

What is claimed is:

1. A transducer for a musical instrument, the musical instrument having an instrument body through which vibrations can be fed back to the instrument to sustain notes played on the instrument, the transducer comprising a core constructed from electromagnetic material, the core having a spine and a pair of legs extending away from the spine, a resilient, non-electromagnetic, non-magnetic material having two opposed side surfaces, means for mounting the core on one of said side surfaces, a conductor wound on the core so that energization of the conductor causes opposite magnetic poles to exist at the end faces of the legs remote from the spine, and means for mounting the transducer on the instrument body, a permanent magnetic pole associated with each leg, the permanent magnetic poles being opposite, means for mounting the permanent magnetic poles adjacent end faces of respective legs between the means for mounting the transducer on the instrument body and the other of said side surfaces of the resilient material, and means for feeding back electrical signals corresponding to musical note vibrations to the conductor to sustain such vibrations.

2. The apparatus of claim 1 wherein the core is somewhat E-shaped, the pair of legs comprising an end leg and a center leg, and further comprising another end leg, the transducer further comprising a third permanent magnetic pole and means for mounting the third permanent magnetic pole adjacent an end face of said other end leg between the means for mounting the transducer on the instrument body and the other of said side surfaces of the resilient material with third permanent magnetic pole being opposite to the permanent magnetic pole adjacent the end face of the center leg.

3. The apparatus of claim 2 wherein the means for mounting the transducer on the instrument body comprises a bracket, means for attaching the three permanent magnetic poles to the bracket so that opposite first and second permanent magnetic poles project away from the bracket, like first and third permanent magnetic poles project away from the bracket, and the second permanent magnetic pole lies generally between the first and third permanent magnetic poles, and means for mounting the bracket on the instrument body.

4. The apparatus of claim 1 wherein the means for mounting the transducer on the instrument body comprises a bracket, means for attaching the permanent magnetic poles to the bracket so that opposite permanent magnetic poles project away from the bracket, and means for mounting the bracket on the instrument body.

5. In combination, a musical instrument and a transducer comprising a core constructed from electromagnetic material, the core having a spine and first and second legs extending away from the spine, a generally flat sheet of a non-electromagnetic, non-magnetic resilient material, means for mounting the core on a surface of the resilient material, a conductor wound on the core so that energization of the conductor causes opposite magnetic poles to occur at end faces of the first and second legs remote from the spine, first and second permanent magnetic poles for the first and second legs, respectively, means for mounting the permanent magnetic poles adjacent the end faces of respective legs on a surface of the resilient material opposite the surface on which the core is mounted with the permanent magnetic poles poled in opposite directions, means for mounting the transducer upon the musical instrument, and means for feeding back electrical signals corresponding to musical note vibrations to the conductor to sustain such vibrations.

6. The combination of claim 5 wherein the core further comprises a third leg extending away from the spine making the core somewhat E-shaped, a third permanent magnetic pole and means for mounting the third permanent magnetic pole adjacent the end face of the third leg on the surface of the resilient material opposite the surface on which the core is mounted with the third permanent magnetic pole poled in the opposite direction to its nearest neighbor of the first and second permanent magnetic poles.

7. The combination of claim 6 wherein the means for mounting the transducer upon the musical instrument comprises a mounting plate, means for attaching the three permanent magnetic poles to the mounting plate so that the first and second magnetic poles are opposite and project away from the mounting plate, the first and third magnetic poles are like and project away from the mounting plate, and the second magnetic pole lies generally between the first and third magnetic poles, and means for mounting the mounting plate on the musical instrument.

8. The combination of claim 5 wherein the means for mounting the transducer upon the musical instrument comprises a mounting plate, means for attaching the permanent magnetic poles to the mounting plate so that opposite first and second permanent magnetic poles project away from the mounting plate, and means for mounting the mounting plate on the musical instrument.

9. A transducer for a musical instrument through which vibrations can be fed back to the instrument so that notes played on the instrument can be sustained, the transducer comprising a bracket for mounting the transducer to the instrument, a first permanent magnetic pole, means for mounting the first permanent magnetic pole so that it projects away from the bracket, a second permanent magnetic pole, means for mounting the second permanent magnetic pole so that it projects away from the bracket, the second permanent magnetic pole being opposite to the first, a sheet of a non-magnetic, non-electromagnetic resilient material, means for attaching a first surface of the sheet of resilient material to the projecting first and second magnetic poles, an electromagnetic core having a spine and first and second legs originating at, and extending away from, the spine and terminating at first and second end faces, respectively, a conductor wound on the core, varying current flow in the conductor inducing flux variations in the core, and means for attaching the first and second end faces to a surface of the sheet opposite the surface of the sheet to which the permanent magnetic poles are attached, with the first face adjacent the first permanent magnetic pole and the second face adjacent the second permanent magnetic pole.

10. The apparatus of claim 9 and further comprising a third permanent magnetic pole, means for mounting the third permanent magnetic pole so that it projects away from the bracket, the third permanent magnetic pole being like the first permanent magnetic pole, means for attaching the first surface of the sheet of resilient material to the projecting third magnetic pole, the electromagnetic core further including a third leg originating at, and extending away from, the spine and terminating at a third end face, and means for attaching the third end face to the surface of the sheet opposite the surface to which the permanent magnetic pole are attached, with the third face adjacent the third permament magnetic pole.

11. The apparatus of claim 10 wherein the first and third magnetic poles are mounted on the bracket in spaced orientation with the second permanent magnetic pole mounted on the bracket generally between them.

12. A system for feeding back musical note vibrations to a musical instrument to sustain the playing time of the musical note on the instrument, the instrument being sensitive to the phase of the vibrations fed back to it, the system comprising means for conditioning an electrical signal corresponding to the played note to provide a conditioned electrical signal at a level at which the conditioned electrical signal can be fed back to the musical instrument to sustain the playing time of the musical note, means for coupling the musical instrument to the conditioning means, and means for coupling the conditioning means to the musical instrument, the conditioning means including a digital shift registor having an input terminal and an output terminal, an A/D converter, a D/A converter, means for coupling the A/D converter to the input terminal of the digital shift register and means for coupling the output terminal of the digital shift register to the D/A converter, at least one of the input terminal to the digital shift register and the output terminal from the digital shift register being selectively variable for providing a selectively variable time delay for controllably and selectively varying the phase between the played note and the conditioned electrical signal.

13. A system for feeding back musical note vibrations to a musical instrument to sustain the playing time of the musical note on the instrument, the instrument being sensitive to the phase of the vibrations fed back to it, the system comprising means for conditioning an electrical signal corresponding to the played note to provide a conditioned electrical signal at a level at which the conditioned electrical signal can be fed back to the musical instrument to sustain the playing time of the musical note, means for coupling the musical instrument to the conditioning means, and means for coupling the conditioning means to the musical instrument, the conditioning means including a series of CCDs having an input terminal and an output terminal, at least one of the input terminal to the series of CCDs and the output terminal from the series of CCDs being selectively variable for providing a selectively variable time delay for controllably and selectively varying the phase between the played note and the conditioned electrical signal.

14. A system for feeding back musical note vibrations to a musical instrument to sustain the playing time of the musical note on the instrument, the instrument being sensitive to the phase of the vibrations fed back to it, the system comprising means for conditioning an electrical signal corresponding to the played note to provide a conditioned electrical signal at a level at which the conditioned electrical signal can be fed back to the musical instrument to sustain the playing time of the musical note, means for coupling the musical instrument to the conditioning means, and means for coupling the conditioning means to the musical instrument, the conditioning means comprising an audio amplifier, a splitter, a loudspeaker, a transducer, means for coupling the musical instrument to the audio amplifier to amplify the level of the electrical signal, means for coupling the audio amplifier to the splitter to split the amplified signal into two channels, means for coupling the splitter to the loudspeaker to provide an audio signal corresponding to the musical note, means for coupling the splitter to the transducer and means for coupling the transducer to the musical instrument to feed back to the musical instrument mechanical vibrations corresponding to the musical note, the conditioning means controllably and selectively varying the phase between the played note and the conditioned electrical signal to sustain the playing time of the musical note.

Description Submit all comments and votes

The invention has been described in the context of an electric guitar and its related components. However, the invention is believed to be useful with other types of musical instruments, notably stringed instruments, whether fretted or not.

Since its inception in the late 1940's, the electric amplified guitar has become a very popular musical instrument. Many playing styles have evolved, and some have reached high levels of sophistication. No other instrument has had a greater impact on the development of rock music than the electric guitar.

One technique used by many rock guitarists is sustaining or prolonging the time duration of a played note. This is usually referred to simply as "sustain". It is often considered desirable to utilize the sustain effect during guitar solos in rock music.

It was recognized early in the evolution of rock music that by increasing the volume setting on guitar amplifiers, a plucked note would sustain its original volume level for a significant period of time (often several seconds) before beginning to "die out," even though the vibration amplitude of the string might immediately begin its natural logarithmic decay due to mechanical damping losses.

There are several techniques which use high volume level settings on guitar amplifiers to cause notes to sustain. Two of these involve non-linear compression of waveform peaks.

The first of these techniques is so-called amplifier "clipping". Most musical instrument amplifiers comprise several voltage gain stages in cascade, with a final output stage which may or may not have voltage gain. Most of the vacuum tube amplifiers made in the 1950's and 1960's were constructed in this manner, wherein the individual pre-amp voltage gain stages were cascaded, and were not contained within an overall feedback loop. By increasing the input voltage level beyond some reference voltage amplitude, the dynamic range of such an amplifier is exceeded, that is, the amplifier saturates, and clipping occurs in one or more of the voltage gain stages. The clipping amplitude is normally approximately equal to the D.C. power supply voltage of the amplifier, minus voltage drops across amplifier components. If the input signal voltage is increased further (FIG. 1a), output voltage peaks cannot increase, due to the clipping (FIG. 1b).

This is a crude form of waveform compression, which imparts some harmonic distortion to the aplified signal appearing across the amplifier output terminals. It produces a sustain effect if the amplifier is overdriven a considerable amount. This occurs because, although the plucked string vibration naturally decays in amplitude, the corresponding amplified peak voltage amplitude at the amplifier output does not decay until the amplifier comes out of clipping. This is best illustrated at time t.sub.1 of FIG. 1b. The perceived change in volume as the string vibration decays is difficult to detect until clipping ceases.

A similar effect occurs at high loudness levels due to non-linear loudspeaker operation, assuming conventional magnetic voice coil cone-type loudspeakers. The acoustic "clipping" that results is normally less harsh sounding than amplifier overdrive because there is less harmonic distortion with this form of "sustain" than with amplifier overdriving and the resulting "clipping" distortion. Two factors combine to produce this phenomenon of non-linear loudspeaker operation. They are non-linear suspension compliance, and non-linear magnetic force on the voice coil. Considering non-linear suspension compliance first, at normal design playing levels for a typical loudspeaker, the restoring forces exerted by the cone suspension and voice coil suspension are linear and proportional to the cone excursion. Larger excursions produced by louder playing levels stretch the cone suspension. Larger force is therefore required to move the cone a given distance. Consequently, a compression (and resulting sustain of plucked notes) occurs. Next considering non-linear magnetic force on the voice coil, at normal playing levels, the voice coil of a typical loudspeaker moves through a relatively constant magnetic flux, resulting in the magnetic force on the voice coil being essentially proportional to current through it. At the ends of the magnetic voice coil gap, however, the flux density decreases, due in some part to flux leakage. Large excursions produced by loud playing cause portions of the voice coil to move in these areas of low flux density. The result is a non-linear relationship between voice coil current and force on the voice coil, causing reduced cone excursion and reduction of acoustic output during waveform peaks. Once again, a compression, with resulting sustain, occurs.

A third technique by which sustain can be achieved is acoustic feedback from guitar loudspeakers to guitar body and strings. Depending upon the amplifier acoustic power output available, guitar body construction, distance between amplifier loudspeakers and guitar, and ambient acoustic conditions, sufficient energy can be coupled from loudspeakers to guitar to excite the strings into sustained vibration by means of positive acoustic feedback. The amount of coupled energy can be so great as to cause the string vibration amplitude to increase to a point at which a runaway oscillatory condition occurs, limited eventually by amplifier clipping and/or loudspeaker compression.

A fourth technique closely akin to the third is for the guitarist to bring some structural component of his guitar, illustratively the headstock, into contact with some component of the speaker enclosure, such as a speaker baffle, when he wants to sustain a note. Mechanical vibration of the baffle is fed back through the heatstock into the guitar, causing positive feedback of string oscillations under appropriate conditions, resulting in sustain. Again the amount of energy fed back can be enough to drive the amplifier into clipping.

Many modern guitar amplifiers are equipped with circuitry designed to produce deliberate clipping. The typical circuitry consists of voltage gain stages and spectral shaping circuits. Controls are usually provided to control the amount of overdrive. A number of accessory "sustainer" or "distortion-substainer" products are also available which contain signal-level circuitry to accomplish the same purpose. These are usually inserted into the signal path between guitar and amplifier. Other types of circuits are manufactured and sold for the purpose of sustaining guitar notes. These include linear compressors which are essentially linear voltage aplifiers containing DC voltage-controlled gain stages. The gain control device is usually a voltage-controlled resistor, either a field effect transistor (FET--see FIG. 2a) or a cadmium sulfide (CdS--see FIG. 2b) photocell. A DC voltage having an amplitude which is proportional to the voltage output of the guitar is formed by rectifying and filtering an amplifier guitar output signal. The DC voltage is then applied to the gain element which is configured to reduce the voltage gain of the stage as the guitar signal level increases. In the case of a photocell, the DC voltage powers a lamp which shines on the CdS cell. The result of an input signal such as the signal of FIG. 3a from a guitar is a relatively constant output voltage as the input signal dies out, as shown in FIG. 3b. The main difference in the output signals of FIGS. 1b and 3b is that less harmonic distortion is present in the output signal of FIG. 3b, since no clipping has occurred. In reality, however, voltage gain devices of the type discussed here and illustrated in FIGS. 2a-b do exhibit some distortion due to non-linear transfer characteristics.

A more recently available sustain circuit, the Boss super distortion feedback model DF-1 manufactured by Roland Corporation, 7200 Dominion Circle, Los Angeles, Calif. 90040, (FIG. 4) "locks on" to a note utilizing a phase-locked loop. An internal voltage-controlled oscillator is phase-locked to a played note when a switch is closed, e.g. by depressing a foot pedal. The phase-locked oscillator locks onto the frequency of the played note and remains at that frequency until the switch is opened. If a new note is plucked at the guitar, or if the original note is modified by some pitch change technique by the guitarist, such as string bending or mechanical vibrato, the phase-locked oscillator signal will not respond accordingly until the switch is opened and closed again. The serious limitations described in this discussion of the prior art do not exist with the present invention.

According to one aspect of the invention, a transducer is provided for a musical instrument. The musical instrument has an instrument body through which vibrations can be fed back to the instrument to sustain notes played on the instrument. The transducer comprises a core constructed from electromagnetic material, the core having a spine and a pair of legs extending away from the spine, a resilient, non-electromagnetic, non-magnetic material, a conductor wound on the core so that energization of the conductor causes opposite magnetic poles to exist at the end faces of the legs remote from the spine, and means for mounting the transducer on the instrument body. A permanent magnetic pole is associated with each leg and means for mounting the permanent magnetic poles adjacent end faces of respective legs between the means for mounting the transducer on the instrument body and the resilient material with the permanent magnetic poles being opposite.

According to another aspect of the invention, a combination includes a musical instrument and a transducer. The transducer comprises a core constructed from electromagnetic material, the core having a spine, and first and second legs extending away from the spine, a generally flat sheet of a non-electromagnetic, non-magnetic resilient material, means for mounting the core on a surface of the resilient material, a conductor wound on the core so that energization of the conductor causes opposite magnetic poles to occur at end faces of the first and second legs remote from the spine, first and second permanent magnetic poles for the first and second legs, respectively, means for mounting the permanent magnetic poles adjacent the end faces of respective legs on a surface of the resilient material opposite the surface on which the core is mounted with the permanent magnetic poles poled in opposite directions, means for mounting the transducer upon the musical instrument, and means for feeding back electrical signals corresponding to musical note vibrations to the conductor to sustain such vibrations.

Illustratively, according to these aspects of the invention, the core is somewhat E-shaped, the pair of legs comprising an end leg and a center leg. The transducer further comprises another end leg, a third permanent magnetic pole and means for mounting the third permanent magnetic pole adjacent an end face of said other end leg between the means for mounting the transducer on the instrument body and the resilient material with the third permanent magnetic pole being opposite to the permanent magnetic pole adjacent the end face of the center leg.

Additionally according to illustrative embodiments of these aspects of the invention, the means for mounting the transducer on the instrument body comprises a bracket, means for attaching the three permanent magnetic poles to the bracket so that opposite first and second permanent magnetic poles project away from the bracket, like first and third permanent magnetic poles project away from the bracket, and the second permanent magnetic pole lies generally between the first and third permanent magnetic pole, and means for mounting the bracket on the instrument body.

According to yet another aspect of the invention, a transducer is provided for a musical instrument so that vibrations can be fed back to the instrument so that notes played on the instrument can be sustained. The transducer comprises a bracket for mounting the transducer to the instrument, a first permanent magnetic pole, means for mounting the first permanent magnetic pole to the bracket, the first permanent magnetic pole projecting away from the bracket, a second permanent magnetic pole, and means for mounting the second permanent magnetic pole to the bracket, the second permanent magnetic pole projecting away from the bracket, the second permanent magnetic pole being opposite to the first. The transducer further includes a sheet of a non-magnetic, non-electromagnetic resilient material, means for attaching a first surface of the sheet of resilient material to the projecting first and second magnetic poles, an electromagnetic core having a spine and first and second legs originating at, and extending away from, the spine and terminating at first and second end faces, respectively, and a conductor wound on the core. Varying current flow in the conductor thus induces flux variations in the core. The transducer further includes means for attaching the first and second end faces to a surface of the sheet opposite the surface of the sheet to which the permanent magnetic poles are attached, with the first face adjacent the first permanent magnetic pole and the second face adjacent the second permanent magnetic pole.

Illustratively according to this aspect of the invention, the transducer further comprises a third permanent magnetic pole, means for mounting the third permanent magnetic pole to the bracket with the third permanent magnetic pole projecting away from the bracket, the third permanent magnetic pole being like the first permanent magnetic pole, means for attaching the first surface of the sheet of resilient material to the projecting third magnetic pole, the electromagnetic core further including a third leg originating at, and extending away from, the spine and terminating at a third end face, and means for attaching the third end face to the surface of the sheet opposite the surface to which the permanent magnetic poles are attached, with the third face adjacent the third permanent magnetic pole.

Additionally according to an illustrative embodiment of this aspect of the invention, the first and third magnetic poles are mounted on the bracket in spaced orientation with the second permanent magnetic pole mounted on the bracket generally between them.

According to another aspect of the invention, a splitter is provided for splitting a high level voltage signal and for providing a selected first portion of the split signal to a first channel characterized by an inductive load and for providing a selected second portion of the split signal to a second channel. The splitter comprises a pair of input terminals for coupling a high level voltage signal source to the splitter, a first pair of output terminals for coupling the splitter to the first channel, a second pair of output terminals for coupling the splitter to the second channel, a first resistor, and means for coupling the first resistor in series between one of the input terminals and one of the first pair of output terminals. The means for coupling the first resistor in series between one of the input terminals and one of the first pair of output terminals includes first and second switches which are alternately actuable. Actuation of the first switch couples said one of the input terminals to a first of the first pair of output terminals. Actuation of the second switch couples said one of the input terminals to a second of the first pair of output terminals.

According to an illustrative embodiment of this aspect of the invention, the splitter further comprises means for indicating whether the first switch or the second switch is actuated. Illustratively, the indicating m