TESTING THE NONLINEARITY OF PIANO HAMMERS USING RESIDUAL SHOCK SPECTRA

Force pulses and residual shock spectra of voiced, unvoiced (soft), an d used (hard) piano hammers are compared. The peak frequency f(max) of the residual shock spectrum is related to the frequency range over wh ich the hammer will be most effective in exciting string modes. Hammer speeds of 1 to 6 m/s, used in these experiments, span the normal dyna mic range of the piano. Peak force is related to pulse duration an d a lso to a nonlinearity exponent in the equation relating force to compr ession of the felt. For lower notes on the piano, f(max) is well above the fundamental frequency which helps to explain the dominance of hig her partials in the bass notes. At the treble end, however, f(max) is comparable to the fundamental frequency, resulting in a strong fundame ntal and few partials in these notes on a piano. In addition to its us efulness in piano research, the residual shock spectrum could serve as a useful guide in the production and voicing of pianos.