Decoupling of seismic and infrasonic sources based on the orientation of a low-frequency electret condenser microphone

Membrane-based microphones are subject to seismic excitation, which interferes with signals from propagating infrasound. An experiment was designed to decouple seismic and infrasonic signals. The microphone was rigidly attached to a base plate on the ground with a fixture that permitted the orientation of the microphone axis to be varied. An accelerometer was mounted to respond to seismic stimuli normal to the base plate. Subsequent field testing included the dropping of various weights from a height of 2–3 m vertical drop at distances of 2 to 15 m from the system. In addition, a low frequency Helmholtz resonator (17 Hz) was used to provide an acoustic test signal. The intent of the experiment was to identify the best microphone orientation to reduce the effects of local seismic disturbances in the presence of low-frequency acoustic monitoring. Additional experiments were performed in the laboratory using a vibration exciter. The results of decoupling of seismic and infrasonic sources, based upon laboratory and field experiments, will be presented.