Sound+Waves

"Sound is a series of compression waves that moves through air or other materials. These sound waves are created by the vibration of some object, like a radio loudspeaker. The waves are detected when they cause a detector to vibrate. Your eardrum vibrates from sound waves to allow you to sense them. Sound has the standard characteristics of any waveform" (**www.school-for-champions.com** 1). =T**ypes of sound waves:**= A **Standing Wave** is shown below:
 * Audible Waves**--> longitudinal waves that lie within the range of sensitivity of the human ear = approximately 20 to 20,000 Hz.
 * Infrasonic Waves**--> longitudinal waves with frequencies below the audible range for humans.
 * Ultrasonic Waves**--> longitudinal waves with frequencies above the audible range for humans.
 * Standing Waves**--> are formed when two waves having the same frequency, amplitude, and wavelength travel in opposite directions through a medium.

A node in a standing wave is a point of no vibrations. An antinode is a place where there are vibrations.


 * Velocity, Wavelength, Frequency** - Like all waves, sound waves abide by the equation v = λf where v is velocity (m/s), λ is wavelength (m) and f is frequency (Hz).


 * Intensity** - The intensity of sound can be defined as the rate at which sound energy is transfered through a certain area. Since the rate at which energy is transfered can be defined as power the equation I = P / A where I is intensity (W/m^2), P is power (W), and A is area (m^2). It should be noted here that area in this equation refers to the area of a sphere because sound waves are emitted in all directions.


 * Relative Intensity** - The problem with the way intensity is modeled above is that it doesn't have a realistic scale. A mere 1 (W/m^2) represents the loudest sounds that the human ear can take known as the threshold of pain, while the faintest sound the human ear can detect is a miniscule 1E-12 (W/m^2) or the threshold of hearing. Fortunatly a logarithmic scale is used to model the intensity of sound relative to the threshold of hearing, the units used for this scale are decibels (dB). When a sound is emitted its intensity level in decibels can be modeled by the equation β = 10 log ( I / I(o)) where β is the decibel level, I is the intensity of the sound (W/m^2), and I(o) is the threshold of human hearing (1E-12). Going by this scale 0 dB corresponds to the threshold of hearing while 120 dB corresponds to the threshold of pain.