2a.1 Testing Modes of Vibration in Agraffe Bridge and Pinned Bridge Coupling – Peter Phillips.
Testing the vibrational modes of piano strings of agraffe bridge and pinned bridge pianos, to see if the vibrations directly correspond to the type of string coupling on the bridge of Stuart and Steinway.
The horizontal and vertical excursions in both the Stuart and Steinway piano string oscillations were measured using sensors at both horizontal and vertical angles positioned close to the strings. This research is influenced by Gabriel We inriech’s study Coupled Piano Strings, which established evidence for the actuality of two polarizations in the piano string motion, Vertical and Horizontal, with respective decay rates. To do this, We inriech constructed a vibration probe for piano strings that recorded the two independent projections of the string’s motion.543
These research tests involved the expert contributions of mathematician Peter Phillips, and photographer Hideki Isoda.
The purpose of the tests described here are to establish data to identify the manner in which a piano string vibrates when struck at a particular force. The results of the tests provide insight into the behaviour of two different strings, coupled differently to the bridge, the Stuart-Paulello and the Steinway-Roslau string, and allow a comparison between their behaviour. From the results obtained it has been concluded that the strings demonstrate significantly different vibrational characteristics, and that this is primarily due to the manner in which they are attached.
Summary of conclusions
The Stuart string has a greater tendency to oscillate vertically, and a lesser tendency to oscillate horizontally compared to the Steinway string. Its oscillations resolve into a narrow elliptical pattern, where the Steinway string resolves into a much wider elliptical pattern. Furthermore the Steinway string begins horizontal motion much sooner in the cycle than the Stuart string.
Equipment
1. Wayne Stuart provided a rig comprising two piano strings tuned to C2 (65.406Hz), one attached to the sound board as per PB design, the other as per AB design. The PB string is wound with copper, the AB with stainless steel. Wayne Stuart also provided a single hammer piano action from a Yamaha C3 grand, with the rig designed to work with this action.
2. To establish a reliable means of striking the piano key with a fixed velocity, Peter Philips developed a piano key striker powered by a solenoid typical of that in a MIDI mechanical piano. When a button is pressed, the electronics provides a pulse of power at 40V DC to the solenoid of a certain duration and via a certain value of resistance, with a range of six velocity settings. The unit was calibrated by making it play middle C on Peter Phillip’s Disklavier at each velocity setting, and recording the results. The MIDI values on the control box are the values obtained in this way, but cannot be regarded as absolute, rather as relative values, where MIDI 20 is PPP, and MIDI 81 is FF.
543 9Weinreich.
