Method and apparatus for amplifying vibrations produced from musical instruments

Claim 2

In a musical instrument having a number of independently vibrating members, the combination including a corresponding number of metal resistive strain gauges secured to the respective members, means for passing exciting current through each strain gauge to produce a voltage thereacross, means for electrically summing the strain gauge voltages to produce a resultant voltage, an alternating current amplifier, a loudspeaker, means responsive to the resultant voltage for driving the amplifier, and means coupling the amplifier to the loudspeaker.

Claim 3

A musical instrument as in claim 1 wherein the exciting means comprises a high impedance source and wherein the summing means comprises means for connecting all strAin gauges in series across the source.

Claim 4

A musical instrument as in claim 1 wherein the exciting means comprises a low impedance source and wherein the summing means comprises means for serially connecting two strain gauges across the source.

Claim 5

A musical instrument as in claim 1 wherein the exciting means comprises a low impedance source and wherein the summing means comprises means for connecting the strain gauges in a balanced bridge circuit.

Claim 6

A musical instrument as in claim 1 wherein the number of strain gauges is more than four; wherein the exciting means comprises a low impedance source; and wherein the summing means comprises means for connecting the strain gauges in a plurality of balanced bridge circuits each providing an output, a corresponding plurality of transformers each having a primary and a secondary winding, means coupling the output of each bridge circuit to a corresponding primary winding, and means connecting all secondary windings in series.

Claim 7

A musical instrument as in claim 1 wherein one vibrating member is a tuned bar simply supported adjacent its ends and adapted to sustain up-and-down flexural vibration when its upper surface is struck with a mallet and wherein one strain gauge is secured to the under surface of the bar.

Claim 8

An instrument as in claim 6 wherein said strain gauge is secured to the bar intermediate its supports.

Claim 9

An instrument as in claim 6 wherein said strain gauge is secured to the bar closer to one support than to the other support.

Claim 10

In a musical instrument having a vibrating member, the combination including a metal resistive strain gauge secured to the member, means for passing exciting current through the strain gauge to produce a voltage thereacross, an alternating current amplifier, a loud speaker, means responsive to the voltage across the strain gauge for driving the amplifier, means coupling the amplifier to the loud speaker, said exciting means comprising a low impedance source and means including three resistors for coupling the source to the strain gauge in a balanced bridge circuit.

Claim 11

In a musical instrument having a vibrating member, the combination including a metal resistive strain gauge secured to the member, means for passing exciting current through the strain gauge to produce a voltage thereacross, an alternating current amplifier, a loud speaker, means responsive to the voltage across the strain gauge for driving the amplifier, means coupling the amplifier to the loud speaker, said exciting means comprising a low impedance source and means including three resistors for coupling the source to the strain gauge in a balanced bridge circuit.

Claim 12

In a musical instrument having a vibrating member, the combination including a metal resistive strain gauge secured to the member, means for passing exciting current through the strain gauge to produce a voltage thereacross, an alternating current amplifier, a loud speaker, means responsive to the voltage across the strain gauge for driving the amplifier and means coupling the amplifier to the loud speaker, said means coupling the amplifier to the loud speaker comprising a controllable voltage divider.

Claim 13

In a musical instrument having a vibrating member, the combination including a metal resistive strain gauge secured to the member, means for passing exciting current through the strain gauge to produce a voltage thereacross, an alternating current amplifier, a loud speaker, means responsive to the voltage across the strain gauge for driving the amplifier and means coupling the amplifier to the loud speaker, said means coupling the amplifier to the loud speaker comprising a controllable voltage divider.

Claim 14

An instrument as in claim 10 wherein the voltage divider comprises a field-effect transistor having a gate, a combination further including an amplitude detector, means coupling the amplifier to the detector, and means coupling the detector to the gate.

Claim 15

In a musical instrument comprising a plurality of bars which are to be struck to produce various tones which may yield beat frequencies in the range between one and ten cycles per second and in which the beat frequency amplitude fluctuation is superposed on an exponential decay of tone amplitudes due to internal damping of the bars and having a time constant on the order of 10 seconds, a preamplifier, means for electrically transmitting signals from said bars to the preamplifier, the signal output of the preamplifier fluctuating at said beat frequency above and below the threshold value of the signal amplitude, a capacitor electrically connected to the preamplifier means providing a control bias across said capacitor which rapidly changes from a first potential to a second potential when a bar is struck and which thereafter changes slowly from the second potential to the first potential, the time constant of said rapid change being not more than approximately 0.1 millisecond, and the time constant of the slow change being not less than approximately 0.1 seconds.

Claim 16

In a musical instrument comprising a plurality of bars which are to be struck to produce various tones which may yield beat frequencies in the range between one and ten cycles per second and in which the beat frequency amplitude fluctuation is superposed on an exponential decay of tone amplitudes due to internal damping of the bars and having a time constant on the order of 10 seconds, a preamplifier, means for electrically transmitting signals from said bars to the preamplifier, the signal output of the preamplifier fluctuating at said beat frequency above and below the threshold value of the signal amplitude, a capacitor electrically connected to the preamplifier means providing a control bias across said capacitor which rapidly changes from a first potential to a second potential when a bar is struck and which thereafter changes slowly from the second potential to the first potential, the time constant of said rapid change being not more than approximately 0.1 millisecond, and the time constant of the slow change being not less than approximately 0.1 seconds.