Difference between reverberation and echo? And the factors affecting both of them (unique as well as common)?

Question

Is reverberation caused by echo? Is echo the thing that we hear inside of our rooms? Or is it reverberation?

Once such definition states that -

Reverberation is the persistence of sound after the sound source has been stopped. It results from a large number of reflected waves which can be perceived by the brain as a continuous sound. On the other hand, an echo occurs when a pulse of sound can be heard twice.

Meanwhile the other one says -

An echo is a single reflection of a sound wave off a distance surface. Reverberation is the reflection of sound waves created by the superposition of such echoes.

I am also interested in knowing about what affects echo and reverberation. Like distance for echo must be around 16-17 m, right? But reverberations don't work that way right - as long as the sounds bounces off the walls? What about temperature? Surface of the reflected wall? Density of the medium? Humidity? Is that the same for reverberation as well?

Answer 1

An echo is the reflection of sound off a hard object, that your ears perceive as a single (or possibly multiple) repeat(s) of the original sound after a transit time delay.

Reverberation is the same thing, except that there are so many different reflections occurring at almost the same time that all the individual echoes blend together and you do not perceive them as discrete, individual echoes.

Echoes occur usually outside, from something like a rock cliff or wall, where the echo leaves the scene and doesn't come back. Reverberation usually occurs indoors, where the initial echo bounces off a different wall, then hits another wall, then hits the ceiling, then the floor, and so on.

Both echo and reverberation can easily be simulated electromechanically (as in spring reverb, plate reverb and tape echo devices) or purely electronically, using analog or (more commonly) digital delay lines.

Answer 2

Reverberation is the superposition of several echoes that takes place in an enclosed space. While an echo generally comprises of a primary reflection, reverberation has reflections of effectively infinite order. Of course, perceptually, we don't really notice infinite order reflections because the energy of the higher order reflections decay rapidly, due to absorption of sound by air and materials on the walls. Reverberation consists of sparsely distributed early reflections, followed by very dense echoes whose energy decays exponentially with time. In fact, this 'late reverb' is Gaussian in nature. Sabine did some fundamental work on deriving the energy profile of sound decay in enclosed spaces (Read the section 'Sound in Enclosed Spaces').