The two-microphone sound intensity method is potentially a valuable tool for noise source identification, sound power determination, and for other measurements (e.g., transmission loss) that are based on sound intensity measurements. An essential ingredient in an accurate sound intensity measurement is the accurate measurement of the phase between the two microphones. Because the phase is generally small, on the order of a few degrees, the microphones must either be "phase matched," or a phase calibration procedure must be used. This paper outlines the design and test procedures for using a plane-wave tube to perform a microphone phase calibration with an uncertainty of less than approximately 0.2 deg. The phase calibration procedure is illustrated for a pair of condenser microphones and for a pair of miniature crystal microphones typically used in hearing aids.10:05 S103

Axial profiles of three piezoelectric, nonfocused, immersion pulse-echo transducers were measured using a small spherical reflector and an automatic scanning device. The scanning distance range included the first and second maxima. Measured data were compared with rigid disk radiation theory. The frequency-dependent active radius was used as a parameter in the curve fitting. In addition, three different approaches were used in the curve fitting. These included (1) fitting the entire range of the scanning distances, (2) fitting the first maximum, and (3) fitting the second maximum. The results of fitting the first maximum agree extremely well with the entire curve fitting, while the results obtained from the second maximum contain more errors. The results of modeling the transducers will be discussed in terms of the active radii and spatial sensitivity functions. In general, good agreement between the theoretical and experimental results was obtained. [Work supported by Center for NDE, Ames, Iowa.]

No abstract

Two-microphone finite difference errors for velocity, intensity, and radiated power were analyzed in the near- and farfield of a vibrating piston in a baffle. Since a closed form solution is not available for nearfield radiation, numerical solutions were used to obtain the sound pressure, velocity, and intensity. Newton's method was used for the numerical integration. The finite difference errors were calculated for two different intensity probe locations. These locations were in a plane parallel to the surface of the piston and on a sphere centered around the piston. The results were analyzed in terms of sound intensity and sound power measurements. In addition, experimental data were measured for comparison purposes.

Modern digital signal processing systems require substantial hardware and software flexibility at a sufficiently low cost. The cost of configuring the hardware and developing the software should be low, and it should be easy to make revisions as requirements such as the number of channels and data rates change. Also important is efficiency for both numerically intensive operations, such as FFT and filter operations, and logical and symbolic manipulation intensive operations such as decision making and display generation. This mixture of computationally intensive operations is ideally suited to concurrent parallel processing. The BBN Butterfly multiprocessor provides a general purpose parallel processor which may be configured for a wide range of applications. It contains up to 256 simultaneously operating asychronous processor nodes, each containing a general purpose microprocessor, local memory, and optional floating-point accelerator, optional high-speed auxiliary processors, and a unique expandable inter-processor communication system. The tight processor coupling and global memory sharing provided by the communication system allows the necessary coordination of the operations in the independent processor nodes, and provides a software environment which dramatically facilitates the ease of programming.