Echo is perceived reflected sound with enough time to be distinguished from the original sound; and reverberation happens when that time interval is not enough
We can say that the waves are present constantly in our daily life, because we make use of them for the communication realized both through the speech as through the music. We have seen that sound is a pressure wave propagating in material media. Thus, we can define it in two ways:
Sound is a longitudinal mechanical wave propagating in material media;
– Sound is also an auditory sensation caused by the vibration of a material medium.
Sound Effects – Echo and Reverb
The echo and reverb are two sound effects caused by the reflection of sound. So we can say that echo is the reflected sound that is perceived with enough time to be distinguished from the original sound.
When the time interval is not sufficient to distinguish the reflected sound from the original, we have the effect of reverberation . We can usually perceive the echo in places where there is some very large and massive object, such as a wall, a mountain or a cave.
In order for us to hear the sound reflected in these objects, they must be at a distance such that the round trip time of the sound is longer than its duration. For example, if you shout the word “hello” with a duration equal to 0.2 seconds, it is necessary that the distance to the object is greater than 32 meters. That way, when we finish saying hello, the “a” sound will be coming back to our ears.
In order to listen to larger words or phrases, we must be placed at greater distances, corresponding to the time it takes to pronounce them.
The ancient churches, built with stones, have remarkable sonorous characteristics. Inside it, the sound can be reflected several times between the walls, producing an effect called reverberation, that causes the original sound to be accompanied by a sequence of echoes that are attenuating as the sound is absorbed by the walls. Many musical concerts are made within churches because of these acoustic characteristics.
The echo has several technological applications, such as the ultrasound examination used to study structures inside our body.
Echo is also used, for example, to measure the distance we are from an echoing mountain: we measure the round trip time of a sound and multiply that time by the speed of sound in the air. The distance is half that value, because the sound has to go back and forth.