Analysis of an acoustic propagation model for sources of noise with directivity in indoor environments

Abstract

Small caliber firearm (SCF) noise sources are typically impulsive in nature, possess a large amount of acoustic energy (consequently a large hearing damage risk), and are not omnidirectional. These sources are often operated in indoor shooting ranges where the potential for noise exposure risk is greater due to the reflective surfaces in the room. Indoor sound propagation models require inputs such as geometry, wall material properties, and some quantified source level description. One such room acoustic modeling technique is the Image-Source Method (ISM). ISM typically assumes specular reflections off the walls and represents those reflections as image sources. Many ISM algorithms can operate with high computational efficiency for simple omnidirectional source models, usually represented by a single quantity: sound power. However, ISM models using an omnidirectional source assumption can produce high errors in some scenarios involving highly directional sources, such as SCFs. In this work, an ISM algorithm has been modified to predict listener exposure levels from non-omnidirectional sources in complicated room designs, and has been validated against measured data from an SCF on an indoor Air Force shooting range.