The paper discusses the detection of high-frequency gravitational waves (HFGWs) using resonant cavities, particularly in the context of primordial black hole (PBH) mergers. The authors derive the sensitivities of existing and planned resonant cavities to detect HFGW backgrounds, focusing on the collective signals from PBH mergers within the asteroid mass range. They quantify the loss in experimental reach due to the actual coherence of the source, which is a significant factor in the detection of coherent binary mergers. The study highlights that the actual reach is significantly worse than previously discussed in the literature, with a discrepancy of about eight orders of magnitudes for BH mergers. The authors also provide a recipe for estimating the stochastic background, emphasizing the presence of the signal in the cavity at all times. They conclude that while the current experimental reach is limited, the search for HFGWs using resonant cavities remains promising due to the unexplored frequency band and the potential for new physics.The paper discusses the detection of high-frequency gravitational waves (HFGWs) using resonant cavities, particularly in the context of primordial black hole (PBH) mergers. The authors derive the sensitivities of existing and planned resonant cavities to detect HFGW backgrounds, focusing on the collective signals from PBH mergers within the asteroid mass range. They quantify the loss in experimental reach due to the actual coherence of the source, which is a significant factor in the detection of coherent binary mergers. The study highlights that the actual reach is significantly worse than previously discussed in the literature, with a discrepancy of about eight orders of magnitudes for BH mergers. The authors also provide a recipe for estimating the stochastic background, emphasizing the presence of the signal in the cavity at all times. They conclude that while the current experimental reach is limited, the search for HFGWs using resonant cavities remains promising due to the unexplored frequency band and the potential for new physics.