# sound intro

```Introduction- Sound is formed as a result of matter vibrating back and forth1. The human
ear, however, cannot always hear all sound vibrations. It can usually respond to vibration
rates between 20 and 20,000 per second. With the addition of modern technologies,
several characteristics of sound can be modified. There are several other factors that also
determine why humans cannot hear certain sounds1.
Because sound travels spherically from its origin, it becomes less intense as it
travels2. Sound pressure is inversely proportional to distance from the source as long as
the sound does not encounter obstacles. Obstacles, which create a change in the medium,
impede or resist the propagation of sound. There are several materials in which sound
cannot travel through as easily. Cork, for example, is one material in which sound has
trouble traveling through. When a sound waved encounters an obstacle or change in
medium, a portion of the sound wave is reflected from the surface. That portion of a
sound wave not reflected from an obstacle is absorbed and continues to be propagated
through the new medium2.
The speed of sound is affected by several items. One item that affects the speed
of sound is the current temperature3. This occurs because temperature changes the
density of the air without necessarily changing the pressure. Sound speed difference is
also related to the difference in the elasticity and density of the media in which the sound
is traveling through. The speed of sound is based on the number system of mach. Mach
1
http://www.neurophys.wisc.edu/~ychen/textbase/s1-p3.html
2
http://www.bwk.kuleuven.ac.be/bwf/articles/ib01.htm
3
http://www.saflex.com/Acoustic/sountran.htm
1 is equal to a speed of 1200 kilometers per hour. When an object reaches this speed it is
said to have broken the sound barrier. The object has caught up with its own sound3.
The intensity (or energy flow) of a sound wave is the power (in energy/sec)
transmitted through an area oriented perpendicular to (normal to) the propagation
direction of the wave4. The sensation of loudness is determined by the intensity. The
greater the intensity the greater is the perceived loudness.
The frequency of sound is the number of complete waves or oscillations or cycles
of a periodic quantity occurring in unit time (usually 1 second). The pitch of sound is
measured in Hertz (Hz), where 1 Hz is equal to 1 vibration per second. The pitch can be
described through the example of a musical scale. As the musical scale increases, so
does the pitch. When in comparison to vibrations, the pitch will be higher with a greater
number of vibrations per second4.
4
http://online.anu.edu.au/ITA/ACAT/drw/PPofM/
```