Eventually, with the construction of valve instruments, the interest for these great, natural main intervals faded, and the “new sound” composers of the 20th century turned to even finer intervals of the major and minor second - that is, the space between the seventh and eighth overtone, the eighth and ninth overtone; or the space between the ninth and tenth overtone, and the tenth and eleventh overtone respectively.

At this point, however, the new composers began to intimidate the music lover; for, even to the uneducated ear, the discrepancy of the “forced marriage” between the microcosm and the macrocosm of music became clear; a marriage, in which the microcosm produces shrill dissonances due to the lack of sensitivity of the macrocosm.

The continuous playing of tones at too small intervals causes a friction between their high overtones, which are too closely spaced, and creates a strange sharpness of shrill dissonances, thus destroying the comprehension of the inner content of a composition - since they shift the attention of the listener, and even that of the musician, incessantly from the immanent logic of the composition to the gross combat of overtones. Thus, each overtone fights its neighbour for superiority, something we perceive as shrill, and reject as unpleasant.

This leads us to twelve-tone music and to the technique of serial composition of the 20th century - the so-called avantgarde.

Not that the great classics had been unable to write in seconds or to produce dissonances, but in the mixture of the outer-musical macrocosm and the inner-tonal microcosm they rather knew the natural limits, which exist as long as the musician does not master the microcosm of music.

Therefore, the great classical composers from Bach to Wagner only approached, but never crossed, the border to disharmony, and thus created mostly harmonious music.

This indicates that they were guided by their natural inner hearing, and that to them a lined sheet of paper was not a drawing board for the construction of music.
With perfect confidence the great classical musicians simply brought to paper what they heard within.