Inverse Square Law
sound level decreases -6.02dB for every doubling of distance from source
Free Field
contains NO physical barriers
Noise can be caused from which three areas?
Source, system, & environment
source distortion
origin of signal
system distortion
electronic equipment
environment distortion
surrounding sound field
produce harmonics on a vibrating string
Particle Displacement
movement of particles in a medium from a state of equilibrium
change in speed of sound when encountering mediums of differing densities
change in direction of sound when encountering boundaries
property of mass to stay in motion or at rest until acted upon by external forces (newton’s 1st law of motion)
resting state; zero state
sine wave
fundamental form of all complex waveforms; pure tone w/ all energy concentrated at one freq.
positive peak of a wave
negative peak of a wave
harmonic series
freq. that are whole number multiples above a fundamental freq. (musically pleasing)
freq. that have a mathematical relationship to a fundamental tone (naturally resonating freq.)
random particle displacement with no periodic content
Non-Linear Distortion
any change to a signal from an input stage to an output stage through a system or device
harmonic distortion
any change in amplitude of harmonic content
any distortion of a waveform usually resulting in a square wave at the extreme
the ability of one signal to cover another
summation of waves occupying same space and time
constructive interference
positive reinforcement when waves interact (amplitude increase)
destructive interference
negative reinforcement when waves interact (phase cancellation)
beat freq.
periodic changes in amplitude when two freq. are close in value
standing waves
wave pattern representing the effect of interference of waves in a medium; not a ‘true’ wave
area of minimum displacement in a standing wave
area of maximum displacement in a standing wave
waves from a direct sound that encounters a bondary
sound field
any area containing sound waves
near field
immediate area surrounding direct sound
far field
area where direct sound and reflections interact
inverse square law
for every doubling of distance from source there is a decrease of -6dB
free field
area of a sound field where inverse square law applies
4 parts of outer ear


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auditory canal (ear canal)

tympanic membrane (ear drum)

middle ear (tympanic cavity)
air filled cavity that contains the smallest bones and muscles of the human body
malleus, incus, ; stapes; the small bone chain of the middle ear
eustachian tube
small tube connected to the throat that maintains equal pressure on both sides of the tympanic membrane
sound analyzing organ
semi-circular canals
three fluid filled canals responsible for our sense of balance ; equilibrium on various axes
bundles of hair cells that sit atop nerve fibers
threshold of hearing
level of discernible difference in human hearing
threshold of feeling
level of noticeable discomfort or pain (200,000,000 x 10 (-6) pascals)
range of hearing
20Hz – 20kHz
amount of displacement from zero point (level or voltage)
length of one complete cycle of a wave
oval window
small membrane of the cochlea
round window
responds to the pressure changes
tensor tympani
small muscle ; tendon attached to the malleus that protects the auditory system from excessive sound energy
stapes (stirrup)
the movement of the stapes against the oval window of the inner ear transfers acoustic energy from air to fluid
malleus (hammer)
connected to the ear drum and transmit vibrational content it received from the ear drum to the incus through mechanical action
auditory scene analysis
ability of the auditory system to discern and localize events within a complex sound field (such as a busy restaurant)
any harmonic above a fundamental whether constant or dissonant;
number of complete cycles per second (hertz)
simple harmonic oscillator
any object with periodic vibrating or motion
simple harmonic motion
periodic motion about a point of equilibrium
peak distortion
any amplitude changes greater than maximum level
reverberant field
area of sound field where reflections tend to have a greater amplitude than the direct sound; loss of intelligibility;
haas effect
perceived localization of sound when direct sound and short reflections are combined in the ear
incidental wave
wave and angle of approach from direct sound
natural vibrational freq. of an object or environment; freq. that occurs at an antinode
super position;
intersecting wavs producing a vector sum of particle displacement;
area of audibility;
audible ranges of speech, music, and overall sound
equal loudness contours;
displays the changes in sensitivity of human hearing to freq. across the audible range
quality of sound dependent on harmonic content
fourier analysis
allows the analysis of freq., harmonic content, amplitude and phase of complex waveforms
time and phase angle relationship of interacting waves
area of a pressure wave where particles are most diffuse or spread apart as wave propagates;
pressure wave
wave motion consisting of compressions and rarefactions;
decrease in amplitude from internal and external resistive forces
critical bands
auditory filters that allow us to discern individual freq. in complex waveforms
basilar membrane
serves as a base for auditory sensory cells
once set into motion by the malleus it transmits vibrational energy to stapes;
comb filter
series of harmonically related peaks and nulls across the audio spectrum
modulating band pass filter
produce overtones across a stretched surface