Acoustical measurements enabled by low cost electronics and digital oscilloscopes

The advent of low-cost impedance analyzers and digital oscilloscopes have enabled the realization of cost-effective measurement systems for research, development, calibrations, and classroom/laboratory demonstrations. Traditionally, we have relied on HP/Agilent 4194 impedance anyalzers for laboratory use, but these units are heavy and expensive, originally costing about $30,000. Over the years, we have acquired and repaired many used units from ebay but recently found an alternative. Digilent offers a PC-based impedance measurement ($30) as add on to the Discovery logic Analyzer and Waveforms software, costing less than $300 that is lightweight and ideal for field or classroom use. Digital PC-based oscilloscopes and data acquisitions systems (e.g., TiePie, Cleverscope, Digilent) have also enabled the development of comprehensive low-cost acoustic calibration systems. We have developed such a system based on the TiePie Digital Oscilloscope (DIFF 1000MS/s), PC based signal generation and acquisition systems, a power amplifier, a preamplifier, and a stepper motor. The transmit signal is from a TiePie HS5-540XM 5 (500 MHz, 1-channel generator, 2-channel acquisition). The calibration and data display are controlled throught a MATLAB (GUI). Measurements of Transmit Pressure Response per Volt (TR/V or TVR), Free Field Voltage Sensitivity (FFVS), and Beam Pattern measurements and dependence on environmental pressure and temperature will be presented.