1. BY QingjieBao

2.  A sound wave is the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water, or any other liquid or solid matter) as it propagates away from the source of the sound. The source is some object that causes a vibration, such as a ringing telephone, or a person's vocal chords. The vibration disturbs the particles in the surrounding medium; those particles disturb those next to them, and so on. The pattern of the disturbance creates outward movement in a wave pattern, like waves of seawater on the ocean. The wave carries the sound energy through the medium, usually in all directions and less intensely as it moves farther from the source.

3.  All sound is the same, just at different frequencies and volume. However sound is often categorised into three groups. Subsonic - Low frequency, below the threshold of human hearing. 25 hertz or less. Audible - Any sound a normal human being can hear. 25 Hertz - 18 Kilo Hertz. Ultrasonic - High frequency sound, above the threshold of human hearing. 18 Kilo hertz and above. It should be noted that some animals such as dogs and bats can hear much higher frequencies than humans. Also note, the upper limit of human hearing varies from person to person, and decreases with age. 18 - 18.5 kilo hertz is normally the upper limit for most people.

4.  Look at the diagram above. The compressions, in which particles are crowded together, appear as upward curves in the line. The rarefactions, in which particles are spread apart, appear as downward curves in the line. Three characteristics are used to describe a sound wave. These are wavelength, frequency, and amplitude.

5.  This is how high or low a sound seems. A bird makes a high pitch. A lion makes a low pitch.

6.  Sounds also are different in how loud and how soft they are. The more energy the sound wave has the louder the sound seems. The intensity of a sound is the amount of energy it has. You hear intensity as loudness.  Remember the amplitude, or height of a sound wave is a measure of the amount of energy in the wave. so the greater the intensity of a sound, the greater the amplitude.

7.  Pitch and loudness are two ways that sounds are different. Another way is in quality. Some sounds are pleasant and some are a noise.  Compare the two waves on the right.  A pleasant sound has a regular wave pattern. The pattern is repeated over and over. But the waves of noise are irregular. They do not have a repeated pattern.

8.  Wavelength; this is the distance from the crest of one wave to the crest of the next.  Frequency; this is the number of waves that pass a point in each second.  Amplitude; this is the measure of the amount of energy in a sound wave.

9.  The most simple experiment I take a piece of paper into the hole to put the bass of the subwoofer paper vibration can be proved