1. IN COMBINATION WITH A MUSICAL INSTRUMENT HAVING MUTUALLY INDEPENDENT RESONANCE CHAMBERS FOR INDEPENDENTLY PRODUCED SOUND VIBRATIONS FROM SONAL VIBRATORS WITHIN THE DIFFERENT CHAMBERS, AN ELECTRICALLY OPERATIVE AUDIO-AMPLIFIER MEANS FEEDABLE BY A COMMON BRANCHED CONTROL CIRCUIT CONDUCTOR HAVING BRANCHES EXTENDING FROM WITHIN THE DIFFERENT CHAMBERS, MICROPHONES ASSOCIATED WITH EACH SAID CHAMBERS FOR INDEPENDENT ACTIVATION BY SOUND WAVES EMANATING FROM THE SONAL VIBRATORS IN THE DIFFERENT CHAMBERS TO CORRESPONDINGLY ENERGIZE DIFFERENT SAID BRANCHES OF SAID CONDUCTOR, MEANS IN SAID CIRCUIT BRANCHES FOR INDEPENDENTLY ADJUSTING THE VOLUMETRIC OUTPUTS OF THE DIFFERENT MICROPHONES THERETO, AND A POTENTIOMETER MEANS CARRIED BY THE INSTRUMENT AND VARIABLY COOPERATIVE BETWEEN SAID BRANCHES OF THE CONTROL CIRCUIT FOR ADJUSTMENT BY A PLAYER OF THE INSTRUMENT FOR INVERSELY VARYING THE VOLUMETRIC RATIO OF THE COMBINED MICROPHONE OUTPUTS DELIVERED TO THE AUDIO-AMPLIFIER MEANS THROUGH THE POTENTIOMETER AND THE CIRCUIT OF THE CONDUCTOR DURING A PLAYING OF THE INSTRUMENT.