Definition.com
Echo is a always a play against the inertness or voicelessness of matter; Just watch how echoes rise and lower in an auditorium according to the attention of the audience.
Definition.com
Echo is the effect of the voicelessness of matter. The more inert a substance, the louder will echo thunder against its walls
Definition.com
Echo is always a play against the inactivity of matter — echoes cover more space on still than on running water. The voice ricochets more in a rock-strewn woodland. Hardwood buildings are more resonant than softwood buildings.
See also
.com