[BU3] Module 4: Sound Intensity, Inverse Square Law, Sound Pressure, Sound Pressure Level & Intensity Level

sound intensity

also known as acoustic intensity

sound intensity

defined as the mean value of acoustic energy which crosses a unit area perpendicular to the direction of propagation in unit time

sound wave intensity

amount of energy transported past a given area of the medium per unit of time

true

the greater the amplitude of vibrations of the particles in a medium, the greater the rate at which energy is transported through it and the more intense that the sound wave is

power/area

intensity formula

watts/meter^2

typical units for expressing the intensity of a sound wave

sound intensity level

level of intensity of a sound relative to a reference value

inverse square relationship

the mathematical relationship between intensity and distance is sometime referred to as _____

inverse square law

states that a specified physical quantity is inversely proportional to the square of that physical quantity

50%

in acoustics, the sound pressure of a spherical wave front radiating from point sources decreases by ____% as distance r is doubled

sound field

technical name given to dispersion of sound energy with given boundaries

reverberant field

a steady state situation where the rate at which sound energy is being lost is exactly balanced by the rate at which the loudspeakers add energy

free field

region where the acoustic waves can propagate free from obstructions that would otherwise interfere with the sound path

reflections

in an acoustic free field there are no _________

free field

sound source is far enough away that it appears as a single point source, far in the distance

free field

airplaine flying high overhead on a clear day

anechoic chamber

special facility constructed to approximate an acoustic free field by using materials to absorb sound waves before they can be reflected

diffuse field

opposite of free field

diffuse field

describes an acoustic field where sound waves reach the observer from all directions

diffuse field

reflected sound is of similar magnitude to the direct sound when it reaches the observer, and as a result, does not appear to have a single source

near field

region of space close to the emitting source

evanescent waves

waves that circulates back and forth with the vibrating surface of the source, never escaping or propagating away

far field

the source can be treated as a point source

far field

defined as the region where the sound pressure and acoustic particle velocity are in phase, and where the sound pressure level decreases by 6db for each doubling of the distance from the source

sound pressure

force of sound on a surface perpendicular to the propagation sound

N

unit of sound force acting on the surface area

m2

unit of surface area

Pa or N/m2

unit for sound pressure

sound pressure

result of sound sources radiating sound energy that os transferred into a specific acoustical environment and measures at a specific location

sound pressure

ultimately what our ears hear

sound pressure level

most commonly used indicator of the acoustic wave strength

sound power

energy rate, or energy of sound per unit of time emitted by a source

sound power

when sound propagates through a medium acoustic sound power is transferred

sound power

total airborn sound energy radiated by sound source per unit of time

sound power level

measure of energy output of a sound source

sound power level

measure of the acoustic energy emitted from a source of noise, expressed in decibels