Sympathetic string modes in the concert harp

The concert harp is composed of a soundboard, a cavity with sound holes and 47 strings. When one string is plucked, a number of normal modes involving the coupled motions of other strings are excited which induce a characteristic 'halo of sound'. This phenomenon, called sympathetic vibrations is due to a coupling between strings via the instrument's body. This coupling results in multiple spectral components in each partial of the resulting sound of the instrument. Resolution of Fourier analysis does not permit their identification. A high resolution Method (ESPRIT), was used to separate the spectral components which are very close one to another. Some of the measured spectral components in the analysed partials correspond to the response of sympathetic modes. The eigenfrequencies and mode shapes of these modes were investigated using a simplified model of the harp based on a waveguide approach in which bending and longitudinal motions of 35 strings connected to an equivalent beam representing the soundboard are described. Identified experimental sympathetic modes are very well captured by the model.