 The phenomenon is described as occurring in resonators of instruments;

First proposed by Zarlino in "Instituzione armoniche" (1558), the undertone series has been appealed to by theorists such as Riemann and D'Indy to explain phenomena such as the minor chord, that they thought the overtone series would not explain.However, while the overtone series occurs naturally as a result of wave propagation and sound acoustics, musicologists such as Paul Hindemith considered the undertone series to be a purely theoretical 'intervallic reflection' of the overtone series.This assertion rests on the fact that undertones do not sound simultaneously with its fundamental tone as the overtone series does.