Measuring the motion of the piano hammer during string contact

The motion of the striking point on the piano hammer was measured before and during string contact by means of an optical equipment. The measurements resolved the motion in two perpendicular components; in the striking direction (vertical), and in the string direction (horizontal). The influence of dynamic level and touch on the hammer motion was studied. Three different types of touch were evaluated; legato, staccato, and " strained" touch. In addition, two different hammer shanks were tested, normal and soft. Key questions tried to answer included changes in the initial horizontal displacement of the striking point, and the presence of a horizontal hammer motion during string contact. INTRODUCTION This study deals with the motion of the piano hammer immediately before and during string contact, and a possibly connection with the pianist's "touch." In particular, the influence of hammer resonances on the free motion of the hammer, and the following interaction with the string are examined. HAMMER VIBRATIONS Previous studies have shown that the shank of the piano hammer bends during the acceleration towards the string (Suzuki, 1982). It is also well known that the hammer can be set in vibrations for certain types of touch (see Fig. 1). The results have been confirmed in independent studies by Suzuki (1983) using computer simulations, as well as by measurements (Askenfelt & Jansson, 1982; 1991; Boutillon, 1988), The vibrations, which mainly consists of a mixture of the two lowest hammer modes at about 50 and 250 Hz, respectively, are excited only for a relaxed, "pianistic," type of touch. The second mode features a pronounced horizontal motion of the hammer head, i.e., in the string direction (see Fig. 2). At string contact, the boundary conditions change, and modes of other shapes and frequencies will come into play. An example of the vertical and horizontal components of the hammer motion during string contact is shown in Fig. 3, as measured on the wooden hammer moulding. The horizontal motion involves a full period of vibration at approximately 800 Hz. The displacement amplitude at the top of the hammer head could be estimated to 0.1 mm, approximately. Also included is a higher component at about 2100 Hz, caused by repeated impulses on the hammer from reflections on the short string segment hammer-agraffe (Hall & Askenfelt, 1988; Askenfelt & Jansson, 1988). The present study aimed at a direct measurement of the motion of the striking point at the top of the hammer, before and during string contact. The motion was measured in two perpendicular directions, vertically (in the striking direction), and horizontally (in the string direction).