echo chamber

Noun

• 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.
• 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.
• An insular communication space or community that shows no interest towards outsiders or their input or opinions.