Speaker
Description
The impulsive sound of large caliber weapons or explosions can travel over long distances. To calculate the sound levels at some distance from the source, a linear propagation model and therefore a linear acoustic source strength is used, in general. Nonlinear propagation effects for the shock wave, relatively close to the source, are not taken into account. By measuring the source strength at a larger distance, typically 100 to 200 meters the linear acoustic source strength can be determined.A new method to determine the linear acoustic source strength has been developed, based on using closer measurements. At shorter distances, typically 50 meters or less from the source, deploying microphones around the weapon is simpler and faster. Also, less space is required for the measurement setup.In a validation setup, sound measurements were carried out at two distances from a large caliber weapon: at 150 and at 50 meters. At 50 meters nonlinear effects can be observed; i.e. a faster than linear decrease of the peak sound pressure over distance and a broadening of the shockwave in time resulting in a frequency shift of the corresponding spectrum. An analytical nonlinear model is used which allows to estimate the shock wave in the time domain at various distances. Special attention is paid to the influence of the ground, as this can require to correct with several dB’s in certain octave bands when determining the source strength.