1. A room or enclosure with acoustically reflective walls used in broadcasting and recording to produce echoes or similar sound effects.

2. An institution or environment in which one set of views predominates and dissenting viewpoints are squelched, ridiculed, or ignored: “Napoleon's vision of himself as a ‘superior man' had been confirmed to him time and again by events and by the echo chamber of his own propaganda machine” (David A. Bell).