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• Phononic crystal (PC) point defects coupled with Helmholtz resonators is proposed. • Coupled resonator (CPCR) can realize acoustic enhancement and directional sensing. • The CPCR helps overcome the detection limit of conventional acoustic systems. • The CPCR can be used for sound source localization. The detection and localization of acoustic signals play a vital role in many areas, such as structural health monitoring, gas pipeline leakage detection and underwater acoustic communication. However, the realization of both high-sensitivity and high-directivity acoustic systems at the same time remains a slippery subject. Besides, the detection limit, namely the detection capability of minimal detectable pressure, of sensitivity and directivity still hinders the performance of ordinary acoustic sensors where weak signals or low signal to noise ratios (SNRs) exist. Here, we propose a structure that couples phononic crystal (PC) point defects with four-sided Helmholtz resonators (HRs) to realize acoustic enhancement and directional sensing simultaneously in a high energy density cavity. The proposed coupled PC resonator (CPCR) shows a much better acoustic enhancement performance than PC point defects or four-sided HRs individually. Meanwhile, the remarkable directional response of the CPCR ensures the success in directional sensing. Furthermore, both in numerical and experimental studies, we demonstrate that the CPCR can be regarded as an acoustic device or sensor to detect harmonic signals and Gaussian pulse signals effectively. This work breaks through the detection limit of conventional acoustic sensing systems and provides a new routine for the development of coupled acoustic sensing devices that are highly desirable in practical engineering applications. [ABSTRACT FROM AUTHOR]