I am confused after reading the Photoacoustic Waveforms in 1D, 2D, and 3D example, and I was wondering if anyone could explain this to me. Why is the 1D waveform compact supported while the 2D waveform is not. The 1D waveform is also infinitely long but in two directions as a plane wave in 3D, so I don't understand the line source analogy in 2D. Why does the pressure in 1D never go below zero?