A property of a room or building that indicates that it will sustain sound for several seconds, letting it resonate off the usually hard surfaces in the room.

Although this is a complex topic, the main properties that contribute to the "liveness" of a room are:

• properties of the walls:
• density of the walls (including the floor and ceiling)
• degree to which the walls are parallel
• flatness of the walls (curved surfaces diffuse sound rather than reflect)
• presence of anything in the corners of the room (unoccupied corners tend to amplify bass resonances)
• amount of less dense objects in the room (i.e. people)
• humidity of the air (the dryer, the more live)