The reflection and absorption of sound
1. When sound waves are blocked by an object, they may be reflected or absorbed by the object.
2. An object which has hard and smooth surfaces is a good sound reflector.
Examples : Plank, glass, metal.
3. Reflected sound is known as an echo(gema). Echo does not occur in a small room because sound is
reflected very quickly.
4. An object which has soft and rough surfaces is a good sound absorber. Therefore, soft materias are
normally used reduce echo especially in a hall. Actions to reduce echo are :
(a) The floor of a hall is covered by carpets.
(b) Soft cushions and curtains are put in a hall or big room.
(c) The walls are lined by sponge or cardboard punched with holes.
5. Some equipments are invented using the principle of echo to benefit mankind.
6. Echo is used to prevent ships from colliding with rocks under the sea. Echo is also used to trace
fishes in the ocean and to determine the depth of the ocean.
Hearing Defect
1. The most common hearing defects are the inability to detect sound and the difficulty of hearing with
with ease.
2. Deafness may be caused by several factors :
(a) Damage of the ossicles.
(b) Damage of the eardrums.
(c) Damage of the cochlea.
(d) Damage of the auditory nerve.
3. Bacterial or viral infections and high fever may lead to damage of the inner ear.
4. Long exposure to loud sound may increase the chance of becoming deaf.
5. Some of the hearing limitations can be corrected by using modern devices.
(a) Hearing aids can be used to help people with hearing problems.
(b) Surgery can be carried out to replace damaged ossicles and to repair damaged eardrums.
(c) Implantation of electronic gadgets into the ears can help deaf people to hear again.
6. Nonetheless, a severe damage of the auditory nerves cannot be corrected.
7. Looking after the ears :
(a) Prevent the ears from being exposed to loud sound, especially while listening to music.
(b) Avoid digging the ears with sharp objects.
(c) Avoid from inflicting tight slaps onto the ears.
(d) Clean up the ears with cotton buds regularly so that the ear canal is not blocked.
Stereophonic hearing
(a) Hearing by using both sides of the ears is known as stereophonic hearing.
(b) Stereophonic hearing allows us to determine the direction of sound accurately.
i. A sound coming from the right side will stimulate the right ear first.
ii. The sound waves will then, reach the left ear. the impulses are sent to the brain to be
interpreted earlier than the left ear.
iii. The right ear will hear the sound louder than the left ear.
iv. The differences in the loudness or speed of the sound that reaches the ears allows us to
determine the direction or the source of sound.
(c) The direction of sound is difficult to determine using only one ear.
