An evaluation of piano sound and vibration leading to improvements through modification of the material properties of the structure

Abstract

A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber.

Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone.

A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands.

A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved.