Spreading factor for waves?

Question

I am doing a lab report on wave propogation, and the lab manual and the textbook both say that "a spherical wave has a spreading factor of 1/r", however everything I know about physics tells me that it should be 1/r^2. The lab question asks "what is the spreading factor for a 1-D wave? 2-D? 3-D?", which I would think would be 1, 1/r, and 1/r^2 respectively. Am I missing something here or is the book wrong?

Answer 1

The wave energy intensity is proportional to 1/r^2, but the wave amplitude is proportional to 1/energy^2 and thus to 1/r. The ref. describes the relation between sound intensity and amplitude (pressure).