Abstract: An electronically controlled swell shutter operator for pipe organs includes an electric motor driving a speed reducer whose output is connected to move the shutters of a pipe organ swell chamber, in order to control the volume of sound heard by the listeners. A swell pedal controlled by the organ player operates a first potentiometer and establishes a first voltage of a given polarity, the magnitude of which represents the exact position that the shutters should be in. The output of the speed reducer operates a second potentiometer which establishes a second voltage of a polarity opposite to that of the swell pedal potentiometer, the magnitude of this second voltage being dependent on the position of the swell shutters. A system of integrated circuit comparators compares the above-mentioned first and second voltages to produce an error signal.

Abstract: A compact hybrid pipe organ, wherein certain bass notes are electronically produced, and wherein the remaining notes utilize a compact and portable swell box to produce the characteristics pipe organ tones, is disclosed. The swell box is just large enough to encompass a selected number of ranks of organ pipes, the pipes being oriented to have their opening facing toward an open side of the swell box so that the tones are directed outwardly away from the back surface of the box. The open front of the box is selectively closable by means of a plurality of pivotally mounted shutters which rotate under the control of the organist. At least the rear wall of the swell box is covered with a sound-absorbent material to prevent rearwardly-directed sound waves from being reflected in a forward direction, and thus, to prevent the production of standing waves within the swell box. The shutters may be of a non-sound-absorbent material, and thus may be of wood, or in a preferred form, may be glass plates.