In his book Theory of Harmony from 1911, Schönberg wrote:
“the student can perform the phenomenon of overtones for himself, at least partly, by silently depressing the piano keys c’, e’, g’ and then quickly and forcefully striking (without the use of pedal) the great C and possibly the contra C an octave lower. Then the harmonic-like sound of the tones c’, e’, g’, the overtones, can be heard.”
The procedure described here is a reliable teaching method both for explaining the harmonic series and for demonstrating the phenomenon of resonance: carefully depressing the higher keys does not cause the hammers to strike, rather, it only lifts the dampers of the corresponding strings. These strings are then stimulated to move in sympathetic vibration with the hammered lower strings by means of sound waves carried by the bridge, the soundboard, and the surrounding air.
Schönberg’s first musical work to use this technique of “harmonics created by silently depressing the keys“ [Flag. durch tonlos Niederdrücken der Tasten] was his song for voice and piano Am Strande [At the Beach] from 1909. Here, the sound of the resonating strings symbolizes the distant sound of the sea.
Other works with text, such as Pierrot lunaire op. 21 and Ode to Napoleon Buonaparte op. 41, make use of this technique in similar contexts of sound and expression: a sound that symbolizes ethereal, incorporeal transcendence and dissolution, which epitomizes a “fantastical moonbeam,” [phantastischen Mondstrahl] “fearful souls,” [bange Seelen] or the disintegration of a corpse into dust.
Schönberg employed this timbral expansion of the piano not only programmatically, but also as a structural device: in the Piano Piece op. 11/1, the “flageolet” [harmonic] functions as a hinge joining brief, athematic timbral passages with solidly established sections that develop motivic and thematic ideas.
He understood this sympathetic resonance as a pianistic counterpart to the harmonics of stringed instruments. This can be gleaned from his instructions and the notation of his scores as well as from his application of the piano sound in combination with other instruments. Today, the term "piano harmonic" refers to a different sound effect, one which is produced in a manner clearly more similar to the harmonics of stringed instruments: that is, by lightly touching the string on the nodal points.
Le Livre des Serenades by Jules Burgmein, alias Giulio Ricordi, contains what is likely the first use of sympathetic vibrations resulting from silently depressed piano keys.
Video: Theory of Harmony; Piano Piece op. 11/1, 12-18; Pierrot lunaire op.21/3 – Der Dandy, 25-31;
Historical recordings and documents: Arnold Schönberg Center, Wien
Visit also the Online-Exhibition - Into Nature with Schönberg: Object #38 - An Strande/At the Beach