Listed only by Irwin, who says: An Octave Diapason of smaller than normal [scale?] and less than average volume of sound, at 4' on the manuals or 8' on the pedals. It may sound in contrast to a louder Octave or imply a Principal Octave 4'. It may also appear on the Choir as its only Octave stop. The name Minor Principal is also used as a synonym for Minor Diapason.

Minor Octave 4', Enclosed Great; Cadet Chapel, United States Military Academy, West Point, New York, USA; Moller 1911. This is the only known example of this name.