Acoustic and performance studies of an expressive keyboard: the clavichord
Résumé
The aim of the present research is to measure a number of acoustical and mechanical features that are associated with the sound (dynamics, duration) and playability (dynamic range, key velocity) of the clavichord. Several instruments are studied (copies of XVth, XVIIth, XVIIIth models). Four aspects of the sounded tones are analyzed: SPL and its relationship to tangent velocity, spectral slope, pitch variations, and sympathetic string vibration. These results indicate a linear relationship between sound pressure level and tangent peak log velocity. Spectral slope seems almost constant independent of tangent velocity and dynamic level. Both tangent velocity and finger pressure are shown to influence the fundamental frequency. The sympathetic strings of the clavichord respond as a type of reverberation, being mainly effective above 500 Hz. There is also a noticeable reverberant effect from the lowest played notes, which are not well damped. Controlling both finger velocity and finger pressure may prove challenging for the player, and this may explain why the sound quality of the clavichord depends so much on the players ability. A comparison between the clavichord and the early square fortepiano, two instruments that are in some cases almost identical in shape and dimensions, will also unveil the specific expressive features of both types of instruments.