The lines telling of the great bell stirred by the note of a flute played at the proper pitch suggest the moving power that lies in sympathetic vibration. The first time a military body crossed the Brooklyn Bridge, the spectators were surprised to hear the order given for the soldiers to march out of step. They had expected to be thrilled by the sight of a thousand men crossing the great structure in measured tread, with band playing and colors flying. They did not know that the structure, being a suspension bridge, might have been weakened
and possibly destroyed by the force of rhythmic oscillation. Yet the accumulated force in the tramp of a thousand men is no greater than that which lies in the sympathetic vibrations of a musical note. Every metal structure has its note, and it is an old engineering saw that a huge structure like the Brooklyn Bridge eventually could be destroyed by the cumulative force of sympathetic vibration evoked by a musical instrument constantly reiterating the note of the bridge.
Sound has three dimensions: pitch, loudness and timbre.
Pitch depends upon the frequency of vibrations. The more rapid the vibrations, the higher the pitch.
Loudness is determined by the amplitude of the vibrations. As their length or "excursion" increases, so does the sound gain in loudness. Conversely, the diminution in the size of vibrations causes corresponding decrease of loudness.
Differences in the shapes of vibrations cause differences in quality or timbre.
After voice has originated within the restricted limits of the larynx, its power, its carrying quality is much augmented by the sympathetic vibrations within the resonance cavities above the larynx. These include the pharynx, nasal passages, mouth, bone
cavities of the face—in fact pretty much every hollow space in the head, every space that will resound in response to vibration and assist in multiplying it. Moreover, the cavities of resonance by their differences in shape in different individuals determine the timbre or quality of individual voices. The chest, although situated below the larynx, is a resonance cavity of voice. In fact, in a certain register its vibration is felt so distinctly that we speak of these notes as being sung in the "chest register," which, so far as it implies that the tones are produced in the chest, is a misnomer. The same is true of "head register," in which vibration is felt in the head where, however, it is needless to say, the "head tones" do not originate.
Expiration—breath-emission—is the motor function of the vocal organs; and there are two other physical functions of the organs—vibratory and resonant.
Added to these is the sensory function, to which I attach great importance; and I call it a psychological function because it acts through the nerves upon the physical organs of voice. Without it the three physical functions—motor, vibratory and resonant combined—would remain ineffectual. They could generate voice, but it would be voice lacking