Page 42 - Curriculum Visions Dynamic Book. To close the book, close the tab.

Soundproofing
Sound waves represent a pattern of zones where the air has been compressed.
 Sound waves – Sound waves are compression waves.
The waves move this way.
The air particles move to and fro.
Wave crest or peak
This horizontal line represents still conditions when the air is not disturbed by sound.
Soundproofing
Reducing the sound that is transmitted through walls and windows so that the source of sound is contained in a room as well as possible.
When sound waves travel through the air and strike a room wall, floor, or ceiling, the partition then acts like a diaphragm and transmits the sounds to adjoining rooms.
Soundproofing efficiency depends on the density of the wall material. A wall made from masonry will
act as a better soundproof barrier than one made of wallboards on
a wooden frame. To increase soundproofing in hollow walls, a sound-absorbing filler can be added.
Materials with small holes (porous materials) absorb sound energy much more effectively than flat materials. Fibre tiles and panels, special acoustical plasters and polyurethane foam are all effective soundproofing materials. (See also: Damping.)
The wavy line represents the sound wave and shows where particles are being compressed (crests or peaks), and where they are spread apart (troughs).
of the time. In still air the molecules move around randomly, each molecule colliding with its neighbours about 5 billion times
a second. The amount of energy
of movement of these molecules
is amazing, being greater than the energy used by four large cars travelling at top speed. And all this in a still room!
The pressure of air molecules on a human eardrum is about 300kg per square metre (the same as four large people). However, this great pressure does not destroy the eardrum because there is an equal pressure from molecules inside the ear.
If a sound is played in the room, the air molecules no longer move randomly. A note like an A, which is about 400 cycles per second, sets up 400 waves per second travelling across the room, each about a metre apart, at a speed of 12,000km/h – the speed of sound.
You don’t get bombarded by
Wave trough
Each dark band represents where air is compressed.
Each light band represents where air expands.
Sound waves
A travelling pattern, or wave, consisting of regions of high
and low pressure through air
or some other medium that can
be detected by our ears. The changes in pressure are caused by places where molecules become compacted and regions where they are relatively scarce.
Every space contains a vast number of air molecules. The living room of a house might contain over one billion billion billion (10 followed by 20 zeros, or 1020) air molecules. If you could weigh them, you would find they weighed about 70 to 80kg. Nevertheless, there is much more empty space between the air molecules than is taken up by the molecules themselves, and so the molecules are still free to move around.
Air molecules look like small spinning dumbbells and are moving around at about 1,600km/h, colliding with one another all
42