M.E.’s Finest

Acoustic Intensity Probe Calibrator by M.E.’s Finest

Sponsored by Dr. Yiming Liu of KCF Technologies

Team Members: Jason Albright, Jim Gaida, Tim Pallozzi, Venki Prabhu, Dan Rosenkrantz

Faculty Coach: Dr. Gary Koopmann – Mechanical Engineering

Date: Spring 2007

Executive Summary:

Quite often in designing machinery, manufacturers contract KCF Technologies to test their product for sources of excess noise patterns. A sound intensity probe, which is a series of three in-line microphones with variable spacing, is commonly used to measure sound intensity emitted by loud machinery such as a compressor. The goal of our team is to design a way to calibrate this probe without having to disassemble it and calibrate each microphone individually. To calibrate the microphones, our team must verify that the three microphones are in phase. Acoustically, some design parameters include properly constructing the geometry of the calibrator to avoid standing and/or clipping sound waves and ensuring that each microphone receives the same sound intensity from the sound source. It is also necessary that the design be easily and securely fastened to the probe. Once the important parameters were established and a solution concept selected, the team will focused on constructing a prototype. It was also essential during the physical design process that the team focused on creating an electronic interface where the sound intensity could be measured and plots can be generated to determine the phase of each microphone. Through prototyping and testing, the team achieved its goal to design an easily portable and attachable calibration device operating over the audible frequency range so that companies can more efficiently maintain sound intensity equipment.

Wide-Band Acoustic Intensity Probe

Final Design Concept and Prototype:

The team chose to calibrate the microphones separately, by creating a transfer function for each one. To do so, a tight-fitting cavity was designed to house the microphones and holes bored to accommodate that pressure source; a small headphone driver.

The transfer function was attained by using a real time analyzer to send a chirp signal to the amplifier, which powered the speaker to excite the microphones. The signal was sent to the real time analyzer so it could perform a Fast-Fourier Transform and create a transfer function from the speaker signal to the microphone signal. The phase diagrams for each microphone were plotted and compared to reveal any differences among them.

SolidWorks 3D Model of Prototype Final Prototype of Acoustic Intensity Probe Calibrator