A series of measurements is taken on two concert grand pianos in seven different stages of production, starting with the glue-laminated soundboard planks and ending with the completely assembled piano in concert tuned state. Due to the large size of the soundboard as well as its irregular shape, measuring deflection shapes is a nontrivial task. Common measurement tools such as piezoelectric accelerometers can affect the acoustic vibrations of the soundboard due to the added mass. To this end, a noninvasive microphone array method is utilized for the present work. The array consists of 105 microphones successively placed parallel to the soundboard, resulting in a total number of 1289 microphones covering the entire surface. The Soundboard is excited using an acoustic vibrator at 15 positions associated with string termination points on the bass and main bridge. Impulse responses are obtained using the SineSweep technique. The measured sound pressure can be back-propagated to the radiating soundboard surface using a minimum energy method. Based on the measured vibrational and acoustical data a set of signal features is derived which cover direct physical behavior (e.g., driving point mobility, damping, radiation efficiency) as well as perceptive parameters (e.g. attack time, spectral centroid). The empirical findings will contribute to a software tool (based on a real time physical model) to help piano makers estimate the impact of design changes on the generated sound.

Instruments working with stick-slip interactions not using a string were popular in the West since the invention of the glass harmonica by Benjamin Franklin in 1751. The Terpodion investigated was built by Buschmann in the mid-19th century as a friction instrument with a keyboard, where bars are pressed against a wooden rotating cylinder producing a sound. Using high-speed camera recordings, the only playable instrument today at the Viadrina museum in Frankfurt a.O. shows sinusoidal vibrations of the bars determining the played pitch while the radiated sound is highly complex. Therefore the instrument shows a fundamentally different stick-slip action compared to bowed instruments. Friction instruments of the East, like the singing bowls also show very sinusoidal-like sounds again caused by the stick-slip interaction. The New Ireland Lounuet, a finger-rubbed wooden block has both, a sinusoidal motion as well as a highly complex one which is to imitate bird and frog sounds. A systematic view on the different stick-slip interactions is suggested.