A common method of amplifying the sound produced by a bar percussion instrument is to place each bar directly above a resonator tube tuned to one quarter wavelength of the bar's fundamental frequency. This research explores the changes in timbre and directivity produced when a resonating structure is placed near a vibrating bar. These changes are observed through measurement of an aluminum bar and resonator tube from a vibraphone and by a computer model of the system.
Both nearfield and farfield measurements are made of the frequency spectra and directivity of the bar with and without the resonator tube. The surface velocity of the bar is measured with laser vibrometry to show the dominant modes of vibration. The system is modeled computationally using a finite element method for the structural vibrations of the bar and a boundary element method to show the sound radiated from the bar and resonator tube. With this computational method, different shapes and positions of the resonating structure may be modeled, and the resulting changes in timbre and directivity may be observed.