Prediction of sound fields in a long enclosure due to a dipole source

Abstract

The speech intelligibility in long enclosures is primarily affected by two factors: The reverberation time and the signal to noise ratio. To predict the speech intelligibility, previous studies were mainly focused on predicting either the sound field or the reverberation time in long enclosures. In these predictions, the sound sources were usually assumed to be a monopole source. However, it is well known that many noise sources have distinct directional characteristics. For example, noise radiated from railway vehicles and from ventilating fans is best modeled as a dipole source. This paper presents a numerical model to predict the sound field due to a dipole source in a long enclosure. The numerical model is validated by field measurements. The experimental dipole source was built by using a pair of identical loudspeakers placed at a close distance to each other that generate sound at equal amplitude but opposite in phase. Measurements are conducted at two test sites. Tolerable agreement between numerical predictions and experimental data is obtained.