- Concepts -
The time rate at which sound energy flows through a defined area.
Since the flow of energy is power, the dimensions of sound intensity are
power/area. Usually, sound intensity is measured in watts/meter^2.
Intensity is perceived as loudness.
Generally, interference is a synonym for superposition.
Constructive Interference - The amplitude of the combined wave created by superposition is greater than the amplitude of either component wave.
Destructive Interference - The amplitude of the combined wave created by superposition is less than the amplitude of either component wave.
Inverse Square Law -
The decrease in the intensity of a sound wave is proportional to the inverse
square of the distance from the source.
The phase of a wave is an expression of how far through its cycle of oscillation
it has progressed. Because the mathematical description of wave motion is similar to
the mathematical description of motion in a circle, wave phase is expressed in degrees
or radians. A wave completes its cycle in 360°, just as a circle is completed in 360°.
Half a cycle is 180°, and a quarter cycle is 90°.
The relative phase of two similar waves is a measure of how synchronized they are.
In phase - Similar waves whose peaks (maxima) coincide are said to be in phase. Their phase difference is 0°.
Out of phase - Similar waves whose peaks (maxima) do not coincide are said to be out of phase. If the peaks of one coincide with troughs (minima) of the other, the two waves are said to be 180° out of phase.
This concept describes the way in which sound waves, and waves
more generally, interact. In essence, two waves passing through the same point
in space at the same time combine in a linear fashion to create a single new
wave. If the displacement from equilibrium caused by the first wave equals "a"
and the displacement from equilibrium caused by the second wave equals "b", the
resulting displacement from equilibrium for the combined wave will be "a + b".
This is an algebraic addition. Since "a" and "b" can be positive, negative, or
equal to zero, the resulting sum can also be positive, negative, or equal to