Absorption of blast sound close to the source

Abstract

The firing of weapons or demolitions for training purposes normally takes place at dedicated sites. Commonly used, pre-defined training scenarios result in repetitive blast emissions. In many cases, these emissions are dominated by reflections of the blast sound from surfaces close to the weapon or from obstacles that are present at the site during firing. The ground is one of these reflecting surfaces. As a consequence, sound at receiving sites can be dominated by the reflected sound at the source. Therefore, noise abatement measures applied to reflecting surfaces close to the muzzle of a gun or close to a demolition can very effectively reduce the sound at receiver sites. Close to a blast source, the acoustical levels are very high and the rules of linear acoustics do not necessarily apply for absorption phenomena. In order to develop noise abatement measures close to a blast source, tests were conducted using small demolitions (50 g) and muzzle blasts of a pistol shooting blanks. This paper reports on tests that investigated the use of mineral and steel wool for blast sound absorption. One major result is that the benefits of absorbing materials near to the source are limited by the significant reflections of the blast at the surface of the absorbing material. To reduce this effect, a pile of layered absorbers was tested with the density gradually increasing from layer to layer.