echo chamber

noun3

1. •
   A room or other enclosed space that is highly conducive to the production of echoes, particularly one that has been designed and built for this purpose.
2. •
   (figurative) An environment in which a person is exposed to only those beliefs and opinions that agree with their own, so that their existing views are magnified and reinforced while alternative ideas are not expressed or considered.

   • But it would resound in the conservative media's echo chamber. — 2007
3. •
   A sound effect that may be applied to live or recorded sounds through a sound editing process, which creates the impression that the sounds originated in an enclosed space which was conducive to producing echoes or echoing.