ABSTRACT
This chapter explores the prediction of ground effect for dipole and quadrupole sources. It discusses with the study of the sound field due to a dipole source near to a ground surface with normalized effective admittance. The source strength for the dipole is normalized to give the same sound level as the vertical dipole at 0 m range. Most electrically hauled trains radiate sound with dipole source characteristics. Having gone through the analyses for the sound field due to a horizontal and vertical dipole, it is natural to expect that the Green’s function for an arbitrarily orientated dipole is a combination of these two fundamental building blocks. It is natural to ask whether a similar asymptotic solution can be developed for an arbitrarily orientated quadrupole because it can be imagined as two closely spaced dipoles with equal but opposite dipole-moment amplitude vectors.
