Abstract
The mean pressure over a receptor placed at a small distance from a circular source is calculated in order to estimate the effect of diffraction when the medium is transparent or slightly absorbing. The deviation relative to the propagation without diffraction is written in the form of a simple integral of the radial wave vector. The source and receiver are considered of the same size, but the expression for different diameters is given. Approximate analytical expressions are derived when the diffraction effect is small, i.e., when the source is much larger than the wavelength. The analytical expressions are used to show that diffraction corrections can easily be performed in a standard pulsed echo experiment.