A device into which an electro-acoustic transducer is incorporated has at least two audio signal conductors through which the device may be coupled to another device to convey analog audio signals representing sounds at a time when the other device places a relatively low DC bias voltage across the at least two audio signal conductors, and to be operated as either a digital serial bus to exchange pieces of digitally-encoded data concerning the electro-acoustic transducer or as a trigger to cause the electro-acoustic transducer to be bypassed to enable another electro-acoustic transducer to be tested at a time when the other device places a relatively high DC bias voltage across the at least two audio signal conductors.