The term 'acoustical bounce' is a phenomenon that occurs when sound waves are reflected off of a surface, creating an ECHO. The crossword solution for this term is 'ECHO, ' which is a four-letter word. An ECHO is the repetition of sound caused by the reflection of sound waves off of a surface. This phenomenon is often heard in large, open spaces such as canyons or caves, where sound waves can travel long distances and be reflected multiple times.