The integral equation method is applied to determine the diffracted acousti
c field about circular apertures in soft and hard baffles. To verify the ac
curacy of the numerical algorithm, the diffracted acoustic fields about sof
t and hard circular disks have been computed and compared with analytical r
esults. The same numerical method is then applied to compute the diffracted
acoustic waves about circular apertures in soft and hard baffles. The Babi
net principle has also been used to check whether the computed diffracted a
coustic wave about a soft (hard) disk is identical to that about the circul
ar aperture in a hard (soft) baffle. Finally, the effect of the wavenumber
and the location of the acoustic source on the diffraction is systematicall
y studied and analyzed. A general discussion based on a comparison of the d
iffracted acoustic fields about hard and soft baffles is given.