echo chamber

echo chamber (plural echo chambers)

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. (music production) 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 echoes.
3. (derogatory, by extension) An insular communication space that is of no interest to outsiders or refuses their input.
   • 2007, Susan Faludi, The Terror Dream: Fear and Fantasy in Post-9/11 America

     But it would resound in the conservative media's echo chamber.

• (communication space): groupthink

• Echo chamber (media) on Wikipedia.Wikipedia