Acoustic intensity measurement of the sound field radiated by a concert harp

An experimental study of the acoustic radiation of a concert harp is presented. Using a stationary mechanical excitation placed at one string location, the acoustic radiation of the complete instrument is investigated. Two main acoustic radiation sources are identified: the soundboard and the soundbox holes. Acoustic intensity vectors are measured in two planes located in the near field of these two sources, making use of a 3D intensity probe. A detailed description of the acoustic intensity field radiated by these two sources is given. Calculations of acoustic power radiated by the soundboard surface and by the soundbox holes allow us to quantify the relative importance of these two sources. In three frequency ranges, it is shown that the soundbox holes radiate more than the soundboard. In the first range, it is suggested that the acoustic radiation of the instrument can be described by two point sources of sound implying that in this range the harp acts as an equivalent elastic Helmholtz resonator.