title: Design and optimization of a noise reduction system for infrasonic measurements using elements with low acoustic impedance.
abstract: The implementation of the infrasound network of the International Monitoring System (IMS) for the enforcement of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) increases the effort in the design of suitable noise reducer systems. In this paper we present a new design consisting of low impedance elements. The dimensioning and the optimization of this discrete mechanical system are based on numerical simulations, including a complete electroacoustical modeling and a realistic wind-noise model. The frequency response and the noise reduction obtained for a given wind speed are compared to statistical noise measurements in the [0.02-4] Hz frequency band. The effects of the constructive parameters-the length of the pipes, inner diameters, summing volume, and number of air inlets-are investigated through a parametric study. The studied system consists of 32 air inlets distributed along an overall diameter of 16 m. Its frequency response is flat up to 4 Hz. For a 2 m/s wind speed, the maximal noise reduction obtained is 15 dB between 0.5 and 4 Hz. At lower frequencies, the noise reduction is improved by the use of a system of larger diameter. The main drawback is the high-frequency limitation introduced by acoustical resonances inside the pipes.
authors.affiliation: CEA/DASE-LDG, BP12, 91680 Bruyères-le-Châtel, France. benoit.alcoverro@antigone.cea.fr
authors.forename: Benoit
authors.initials: B
authors.lastname: Alcoverro
authors.forename: Alexis
authors.initials: A
authors.lastname: Le Pichon
mesh_terms: D000158:Acoustic Impedance Tests; D004784:Environmental Monitoring / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D007391:International Cooperation; D008962:Models, Theoretical; D009622:Noise / Q000517:prevention & control*; D009689:Nuclear Warfare / Q000517:prevention & control*; D013018:Sound Spectrography; D014919:Wind