The Collaborative International Dictionary
microphonous
microphonous \mi*croph"o*nous\ (m[-i]*kr[o^]f"[-o]*n[u^]s or m[i^]*kr[o^]f"[-o]*n[u^]s), a. Serving to augment the intensity of weak sounds; microcoustic.
Wiktionary
microphonous
a. (context archaic English) Serving to augment the intensity of weak sounds; microcoustic.