High resolution radiation pattern measurements of a grand piano - The effect of attack velocity

Abstract

The sound radiation pattern of a grand piano is highly complex and depends on the shape of the soundboard, construction of the frame, reflections from the lid and other parts of the instrument's structure. The spectral energy generated by and emitted from the instrument is further complicated by the sound production mechanism (hammers, strings), the attack velocity, and results in independently complex behaviors depending on the register of the piano. This paper presents the acoustic measurements of the radiation pattern of a grand piano using a high spatial resolution measurement technique. Measurements of a Yamaha Diskclavier were taken using a 32-channel microphone array with a 2-inch spacing between capsules. The complex radiation patterns and overtone structure is analyzed for middle-C at three attack velocitiespianissimo, mezzo forte, and forte. Comparisons of the effect of attack strength on frequency response and radiation pattern are presented. INTRODUCTIONThe piano is a complex instrument. Capturing the sound and character of this large and complex instrument has been the subject of much debate for audio engineers. The piano's complexities are a result of the many physical and acoustical components and properties that directly affect the propagation of sound and the spatial radiation pattern of the instrument. In addition to the many physical components that make up the instrument (e.g. soundboard, frame, hammers, strings, etc.), the manner in which a piano key is struck has a significant impact on its spectral characteristic. To produce a sound, a key on a piano is pressed, the hammer lifts and strikes the string. The vibrations on the string are amplified by the soundboard and propagate through the body of the instrument. This process is further complicated by the fact that there may be sympathetic vibrations from strings other than the one that was excited. The velocity of a key determines the force from the hammer onto the strings. This force not only vibrates its intended string, but excites other portions of the piano as well. To gain an understanding of how the strength, or velocity, of the attack of a single note affects the spectral content and spatial distribution of the energy around a piano, we measured the spectral radiation pattern of the piano using keystrokes with various levels of attack strength.In this paper, we present the acoustic measurement and analysis of a densely sampled radiation pattern of the Yamaha Disklavier grand piano. Spectral characteristics are analyzed for middle C (C4), across the top of a lidless Yamaha Disklavier grand piano for three different velocities. The results of the fundamental frequency and four overtones are presented and compared against other velocities, providing insight to how the spectral and spatial distribution of the harmonic changes as a function of attack strength, and the resulting non-linearities in spectral content that arise.