According to certain described aspects, an acoustic sensor is employed in a variety of beneficial ways to provide improved physiological monitoring, among other advantages. In various embodiments, the acoustic sensor may include an attachment sub-assembly including a deformable portion that enables improved coupling to a patient. Additionally, the acoustic sensor may include an adhesive layer that, in combination with the deformable portion, enables even, robust, and secure attachment of the sensor to the patient. In various embodiments, an acoustic coupler having a semi-spherical shape is provided to further improve coupling of acoustic signals from the patient to the sensor.