One way that I think about impedance matching is with the idea of resonant coupling. If one wants to record a heartbeat, the microphone needs to resonate and couple with the heart. But since sound waves don't transfer well across gaps of materials with different impedance, to enhance resonant coupling, the microphone is embedded within another device that can better couple with the skin -- e.g., through increased surface area or with material that is acoustically similar to the skin. The use of acoustically similar materials is also called impedance matching.
One way that I think about impedance matching is with the idea of resonant coupling. If one wants to record a heartbeat, the microphone needs to resonate and couple with the heart. But since sound waves don't transfer well across gaps of materials with different impedance, to enhance resonant coupling, the microphone is embedded within another device that can better couple with the skin -- e.g., through increased surface area or with material that is acoustically similar to the skin. The use of acoustically similar materials is also called impedance matching.
This article is nice, especially the illustration of how air ducts can be used to create low/high-pass and bandpass filters. https://www.britannica.com/science/sound-physics/Impedance