Acoustical characterization of a portable pneumatic infrasound source.

A portable infrasound source based on a pneumatic siren design is described. The source is capable of producing narrowband tone bursts over a frequency range of approximately 0.25-10 Hz. The acoustical characteristics of the infrasound source are presented, including measured sound pressure levels and horizontal directivity. The methodologies for processing the received acoustic signals are reported, and comparisons of measurements are made with a simple multipole model of the source. Measurements indicate that the pneumatic infrasound siren can be useful for a variety of applications for which a controlled, known infrasound source is required.

Acoustic radiation from an infrasonic ball-valve siren.

The concept of a ball-valve siren is developed through experimentation and theoretical modeling. The ball-valve siren is a source transducer developed for the purpose of establishing the concept of infrasound generation through the modulation of compressed air flowing through a rotating ball valve and released into the atmosphere, in the context of a siren. Directivity, frequency response, and propagation experiments were performed for the fundamental frequency component, and the results compare favorably to an empirical model based on monopole and dipole radiation. The results show that a small ball-valve siren can generate useful infrasound radiation with nominal directivity at frequencies in the range 1 to 8 Hz.