How to define a acoustic point source

Hi all,

I have a problem with Comsol. I defined a point source from 1m away from a acoustic lens, but it seems that there is no convergent behind the acoustic lens. Normally, if I use a plane wave as the sound source, the sound can be converged behind the acoustic lens at the focal point.
Does anyone know how to define point sources (2D) in the Acoustic module in COMSOL?

Thanks a lot.
Tran Quang Dat