Echo vs.
Reverberation
A GIF Animation
Sound is a mechanical wave which travels through a medium from
one location to another. This motion through a medium occurs as one
particle of the medium interacts with its neighboring particle,
transmitting the mechanical motion and corresponding energy to it.
This transport of mechanical energy through a medium by particle
interaction is what makes a sound wave a mechanical wave.
As a sound wave reaches the end of its medium, it undergoes
certain characteristic behaviors. Whether the end of the medium is
marked by a wall, a canyon cliff, or the interface with water, there
is likely to be some transmission/refraction, reflection and/or
diffraction occurring. Reflection of sound waves off of barriers
result in some observable behaviors which you have likely
experienced. If you have ever been inside of a large canyon, you have
likely observed an echo resulting from the reflection of sound waves
off the canyon walls. Suppose you are in a canyon and you give a
hollar. Shortly after the hollar, you would hear the
echo of the hollar - a faint sound resembling the original
sound. This echo results from the reflection of sound off the distant
canyon walls and its ultimate return to your ear. If the canyon wall
is more than approximately 17 meters away from where you are
standing, then the sound wave will take more than 0.1 seconds to
reflect and return to you. Since the perception of a sound usually
endures in memory for only 0.1 seconds, there will be a small time
delay between the perception of the original sound and the perception
of the reflected sound. Thus, we call the perception of the reflected
sound wave an echo.
A reverberation is quite different than an echo. The distinction
between an echo and a reverberation is depicted in the animation
below.
A reverberation is perceived when the reflected sound wave
reaches your ear in less than 0.1 second after the original sound
wave. Since the original sound wave is still held in memory, there is
no time delay between the perception of the reflected sound wave and
the original sound wave. The two sound waves tend to combine as one
very prolonged sound wave. If you have ever sung in the shower (and
we know that you have), then you have probably experienced a
reverberation. The Pavarotti-like sound which you hear is the result
of the reflection of the sounds you create combining with the
original sounds. Because the shower walls are typically less than 17
meters away, these reflected sound waves combine with your original
sound waves to create a prolonged sound - a reverberation.
For more information on physical descriptions of waves,
visit
The
Physics Classroom. Specific information is available there on the
following topics:
Other animations can be seen at the
Multimedia
Physics Studios. Other useful resources regarding the physics of
motion and waves is available through the
Glenbrook
South Physics Home Page.
This page was created by
Tom
Henderson of
Glenbrook South
High School.
Comments and suggestions can be sent by e-mail to
Tom
Henderson.
This page last updated on 8/17/98.