Following recent advancements in the study of time-averaged properties of energy propagation in linear acoustic fields, the well established concept of power factor known from the electric AC circuits analysis, is here extended to acoustics. This allows our outline of a complete acousto-electro-mechanic analogy, where the fundamental physical concept of energy trajectory is assimilated to a continuous line network of electric circuits, and the complex intensity vector field is defined by means of three special spatial directions: the tangent, the principal normal and the binormal direction at each point of any energy path. The notions of sound energy conductance and susceptance are then introduced and their relationship with complex intensity is highlighted. Finally, the frequency distributions of the defined quantities are measured in different acoustical contexts, thus illustrating their practical utility for advanced intensimetric metrology.
A procedure for calibrating pressure-velocity (p-v) sound intensity probes using a progressive plane wave as reference field is presented here. The procedure has been checked for a microelectromechanical system technology-based Microflown(®) match-size probe by comparing the calibration results with the nominal correction curves available from the manufacturer. The reference field was generated along a wave guide by means of a dual cone loudspeaker supplying acoustic energy in the range 20 Hz-20 kHz through an impedance adaptor. Different from the current in-field procedures, the one proposed here allows the calibration of probes under test to be executed at once up to 10 kHz without any change in the experimental setup. After a detailed review of the general principles of calibration, the procedure has been finalized with three main stages: (a) determination of the full coherence calibration bandwidth of the probe, (b) comparison calibration of the probe built-in pressure microphone over the full coherence frequency range, and (c) relative calibration of the velocity sensor over the calibrated pressure one. Calibration results for the probe under test have been best fitted against the calibration filters modeled by the manufacturer and the direct comparison of the obtained data with the factory ones has been reported.
The reproduction in a given confined space - such as a cinema hall or a smaller room - of a sound event previously recorded in a completely different acoustical environment is an interesting and still open acoustical problem. A new method for hi-fi audio playback based on the general solution of the acoustic inverse problem is here pourposed. A feed-forward control based on overdetermination of conditions at active contours - i.e. loudspeakers - in order to obtain an optimal stable solution via least square approach is here proposed. This is easily possible even for complex configurations thanks to acoustic quadraphony, the application of sound intensimetry to audio technology developed in the last years within the IST-2-511316-IP European project denominated IP-RACINE. After a short explanation of the model theory, the experimental application to the simplest case of 1-D confined field is presented and some obtained results are shown.
Wide band p-v tympanometry can be defined as the measurement of the acoustic immittance of the ear, possibly in normal air pressure condition of the ear canal, and in the full audio frequency range. The most important innovation pioneered by the p-v tympanometry regards the introduction of a different principle of measurement based on the direct acquisition of, both, pressure and velocity (p-v) signals at the ear canal entrance. The measurement can be done by using a pre-calibrated couple of dedicated micro-sensors: an ordinary microphone and an acoustic velocimetric micro-device. This invited speech will report about wide band measurements of ear immittance functions carried out by means of a modified tympanometric probe hosting a pre-calibrated sound intensity micro-probe, and their comparison, with data obtained by standard 226 Hz tympanometry.
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