Science of Sound Video

This video is an introduction to the science of sound.

What is Sound?
• Sound is created by a vibrating object.
• Sound travels as a wave through a medium.
• A sound wave is an example of a compressional or longitudinal wave.
• The particles in a longitudinal wave move parallel to the direction in which the wave is traveling.
• A sound wave alternately compresses (areas of high pressure) and expands (areas of low pressure) whatever medium it is traveling through.

Characteristics of Sound

• A sound wave’s amplitude relates to amount of energy it carries.
• As amplitude increases, a sound is perceived to be louder; as amplitude decreases, a sound is perceived to be softer.
• The average amount of energy passing through a unit area per unit of time in a specified direction is called the intensity of the wave. Sounds with higher intensities are perceived to be louder.
• Relative sound intensities are often given in units named decibels (dB).
• One complete repetition of a wave is called a [wave] cycle.
• Frequency is the number of cycles per second.
• If the frequency of a sound is increased (there are more cycles in a second), a higher pitched sound is produced. If the frequency is decreased, a lower pitched sound is produced.
• A high-frequency sound has a shorter wavelength than a low-frequency sound. The wavelength is the distance from a point on one wave to the corresponding position on the next wave.
• Phase specifies the location of a point within a wave cycle of a repetitive sound. When two sounds of the same frequency are in phase, their amplitudes combine. When they are out of phase, they cancel each other out.

Sound Movement

• Sound travels about 1500 meters per second in seawater. Sound travels much more slowly in air, at about 340 meters per second.
• Sound level decreases as a sound moves away from its source. A sound wave gets smaller (loses energy) because it spreads out, or spreading loss occurs, and because some of the wave’s energy is absorbed.

Source Levels/Ambient Noise

• Background sound is the sum of all distance sounds in the ocean, called ambient noise.
• The primary sources of ambient noise varies in different regions of the ocean and can be categorized by the frequency of the sound.
• Source level is the intensity level of a sound source, at a distance of 1 meter. It has units of decibels.