The term 'SOUND BOUNCE' can be broken down into two crossword solutions: ECHO (4 letters) and BOUNCE (6 letters). ECHO is a phenomenon in which sound waves are reflected off of a surface and return to the source, creating an audible effect. Bouncing is the act of rebounding off of a surface, usually with some force. Together, these two terms describe the process of sound bouncing off of a surface and returning to its source.