Releated to echo distance

We hear echo in empty room or in small room just because of reverberation of sound. Persistence of sound wave for long time because of repeated (multiple) reflections of sound by the reflecting surface in blank room, are called reverberation of sound. As we put undesirable sound absorbing materials like sofa, curtains, plant fibers, carpet and press fire board etc in the room we will not hear the multiple echo of sound.