Large-chamber reciprocity calibration for microbarometers

Abstract

The Penn State Applied Research Laboratory (PSU) and Sandia National Laboratories (SNL) have implemented a reciprocity-based primary calibration technique in SNL’s infrasound calibration chamber. The goal in this work is primary calibration of microbarometers from 0.01 to 10.0 Hz. The National Center for Physical Acoustics at the University of Mississippi designed and built the chamber, which SNL has modified and currently operates. This chamber incorporates two moving coil loudspeakers capable of operating in receive and transmit mode. PSU developed the calibration technique and the required electronics to take advantage of these two reciprocal loudspeakers, while SNL installed this hardware and made the required test measurements. Because the chamber is large (1400 l), the chamber volume dominates the acoustical admittance thereby reducing the dependence of the calibration on the physical characteristics of the loudspeakers and reducing calibration uncertainty. However, laboratory tests have found increased uncertainty at very low frequencies ( < 0.05 Hz). This is due to reduced loudspeaker response and increasing noise within the chamber at these frequencies. This talk will discuss the large-chamber reciprocity method, important considerations for reducing uncertainty in this implementation, and limitations of this method.