This contribution presents the rationale, basis, and potential for continuous and event-driven online chromatic acoustic monitoring of transformers and their tap changers. Illustrations are given from a feasibility project for monitoring transformers at several substation sites in the Manchester and Stoke regions of the U.K. Examples of monitoring outputs are presented in a top-down order of information compression, representing an approach that is tailorable to substation operators' information requirements for tracking and tracing overall and individual tap change quality. It is concluded that the approach is feasible for trend sampling and continuous monitoring regimes. Ongoing work includes the evaluation of overall transformer acoustic behavior patterns and individual internal tap-change elements. The monitoring is being rolled out to 50 transformers.