Cavity tone spectra have been investigated as a function of wind speed in a low noise wind tunnel, at Mach numbers below 0.2. The cavity, a cylindrical closed pipe with a rectangular slot for a mouth opening, was flush mounted in the side of a flat plate, 30-in. downstream of the leading edge. Both laminar and (tripped) turbulent boundary layer effects were explored. Contributions to tone generation from turbulent boundary layer fluctuations, acoustic background noise, sheartone feedback coupling, and cavity resonant feedback coupling are quantitatively sorted out on the basis of theoretical models. A theory of laminar pipetones, complementing an earlier model of turbulent pipetones, is used as a basis for explaining sheartone/pipetone interaction. An empirical correction curve is introduced to take into account the slowing of wave speed in thick shear layers.