  Using a nonlinear sound wave equation for a bubbly liquid in conjunction with
an equation for bubble pulsation, we predict and experimentally demonstrate the
appearance of a gap in the frequency spectrum of a sound wave propagating in a
cavitation cloud comprising bubbles. For bubbles with an ambient radius of 100
{\mu}m, the calculations revealed that this gap corresponds to the phenomenon
of sound wave localization. For bubbles with an ambient radius of 120 {\mu}m,
this spectral gap relates to a forbidden band of the sound wave. In the
experiment, we observed the predicted gap in the frequency spectrum in soda
water; however, in tap water, no spectral gap was present because the bubbles
were much smaller than 100 {\mu}m.
