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anxiety, stress, sleep disturbance and damage As a sound wave reaches the end of its
temporary or permanent to our hearing. It is medium, it undergoes certain characteristic
the loudness of the sound which decides behaviors. Whether the end of the medium is
whether the sound is pleasing or unpleasing. marked by a wall, a closed tunnel, a hill or the
The sound that is too loud is termed as noise interface with water, there is likely to be some
pollution. Even the music being played too absorption and some reflection or echo of the
loudly causes noise pollution. The loudness of sound wave.
the sound is measured in decibel(db) Echo is the faint sound resulting from the
SOUND PITCH original sound. When you speak loudly in front
Shrill voice is a pitched sound. It depends on of a hill or a large building at some distance.
frequency of vibrations and does not depend Reflection of the sound occurs in the same way
on amplitude of vibrations. as the ball bounces from the wall.
High pitch sound is produced by high Surfaces reflect sound whether they are far or
frequency sound and low pitch or shallow near. Then why do we hear an echo only when
the surface is far away? This is because if the
echo reaches our ears very quickly we are not
able to distinguish it as a separate sound. In
fact, ears are able to distinguish the two
(a) Softer (b) Louder (c) Dull (d) Shrill
sound-low sound-high sound-low sound-high sounds clearly only when the second sound is
th
amplitude amplitude frequency frequency received after 1/10 of a second or more from
Representation of sound
the first sound.
voice is produced by low frequency sound.
Just like reflection sound also shows the
AUDIBLE AND INAUDIBLE SOUNDS
property of absorption. As we speak sound
Audible Sounds : The sound that can be heard always gets partly reflected and partly
by us is known as audible sound. It is in the absorbed. Hard surfaces are better reflectors
range of 20– 20,000 Hz (Hertz) for human of sound while soft surfaces are better
beings. absorbers of sound. Sound absorbing material
Inaudible Sounds : The sounds that can not be is used in walls of auditoriums to stop undue
heard by us are known as inaudible sound. It is reflection and echo of sound. It is also common
in the range of less than 20Hz (called infrasonic in voice recording studios to make them sound
sounds) or more than 20,000 Hz (called proof and cut down any sort of extra noise.
ultrasonic sounds) which cannot be heard by Applications of echo
human ears.
· Echo is used to locate underwater objects.
Infrasonic waves can be detected by
· Doctors use echo to get a picture of the
elephants, whales etc. Earthquake's sound is
internal organs of the body.
of this frequency only. Ultrasonic sounds are
used in ultrasound which is used for medical · Bats use echoes to locate their prey.
activities or treatment. Quality of sound
REFLECTION AND ABSORPTION OF SOUND The quality of sound is determined by the
frequencies present in it and their relative
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