It has previously been shown that a three-dimensional mapping of an acoustic field's amplitude and phase may be calculated from a set of TV-holography measurements by use of tomographic techniques. In this paper a thorough mathematical description of this measuring technique is given. An increased number of measured projections improves the tomographic reconstructions significantly. Techniques for obtaining quantitative data for the pressure amplitude of the acoustic field are implemented. The technique is demonstrated by measurements of the near field of a loudspeaker and these measurements are shown to agree well with measurements obtained with a microphone.
In this investigation a multi-channel MLS (maximum length sequence) measurement system is used for vibrational and acoustical measurements on the violin. MLS measurements are useful since both phase and magnitude can be measured with great accuracy. In these measurements, both the phase and magnitude influence of the transducers are corrected. Using this tool, the input admittance, the velocity at the feet of the bridge, and the sound pressure at the far field of the violin are measured simultaneously. These parameters give important information about the vibrational and acoustical properties of the violin. A more extensive investigation is also performed. The sound level pressure and phase are measured in several equally spaced positions in the far field of the violin situated in an anechoic chamber. Radiation patterns are found for each mode and the radiated power is calculated. Optical holography is then used to measure the vibrational pattern for the most important modes of the violin body. These acoustical and vibrational measurements are correlated to determine which modes are most important to the radiated sound power.
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