The evidences of tonal difference which defined the characteristics of the Stuart piano sound were established in this research by evaluating the transient qualities found in the partial tones of each piano tone.

Composite Tones

Composite tones also described as complex tones, are the superposition of the partial tones related by the resonance and frequency of the fundamental tone. A composite tone is perceived as an instrumental tone, shaped in its composite complexity by the dimensions of the vibrating system or instrument.

A vibrating piano string simultaneously oscillates multiple modes of vibration, known as partials or overtones, which combine to produce the composite tonal sound of one note. The result is a superposition of sound waves, blended together into one complex wave. The frequency of the 1st harmonic, known as the fundamental, represents the repetition rate of the resulting complex vibration.¹⁸⁰

In his treatise, On The Sensations of Tone , acoustic physicist Herman Helmholtz described a musical tone as a complex periodic vibration which consists of a series of partial tones he names as ‘upper partials’, all governed by the same periodic vibration, that of the fundamental partial tone, or the prime. He surmises musical tones as being dependent on three elements, force, pitch and quality.

………. we found that difference in the quality of musical tones must depend on the vibration of the air. The reasons for the assertion were only negative. We had seen that force depended on amplitude, and pitch on rapidity of vibration: nothing else was left to distinguish quality but vibrationalform. We then preceded to show that the existence and force of upper partials tones which accompanied the prime depend also on the vibrational form, and hence we could not but conclude that musical tones of the same quality [timbre] would also exhibit the same combination of partials, seeing that the peculiar vibrational form which excites in the ear the sensation of a certain quality of tone, must always evoke the sensation of its corresponding upper partials.¹⁸¹

Helmholtz also suggests that it is not only the compound musical note we are hearing, but collectively with it the sympathetic resonant oscillations within the instrument which combine to produce the qualities of the sound. This is a relevant observation for piano sound, as many sections of the resonating system of the piano vibrate in sympathy. The sustain pedal is ‘on’ for the piano sounds tested in this study, so the sound is representative of the whole resonating system. This includes the vibrations of strings that are not struck by the hammer. These unstruck strings are said to vibrate in sympathy, in a syntonic vibration.

When one resonant object is caused to vibrate, any other resonant object in its vicinity which has the same natural frequency will also vibrate; two bodies need not be touching, since vibration is passed on through such media as air. For example, if a tuning fork is sounding in air and a second tuning fork of identical frequency is placed close to it; then the second fork will begin to vibrate ‘in sympathy’.182

^{180     2}Roederer,126.
^{181     2} Hellmholtz ,65.
¹⁸²Foulcher, T. L. Fundamental Notes For Piano Technicians. (Sydney: School Of Piano Technology, State Conservatorium of Music, N.S.W 1981), 47.