CDO 463 1 Basic Acoustics
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sound narrow definition
sensation for hearing

sound broad definition
physical quantity with vibration  periodic or aperiodic  and a pressure disturbance  compressions and rarefractions  and a medium  material for transmitting the sound

periodic
 regularly repeating
 ex) tone
 repeats the same frequency

aperiodic
 not reguarly repeating
 2 types  turbulent and static
 ex) noise, bullistic, release of stop consonants

Simple Harmonic Motion
tuning fork
 produces the simpliest type of sound
 tine movement : XYXZXYXZX
 one cycle: XYXZX

Period / frequency
 amount of time for one cycle / # cycles per second
 frequency = 1/period or f=1/T
 physical dimension  observable and measurable
 Hz

pitch
the perception of frequency

relationship between frequency/period and pitch
 increase in frequency = increase in pitch
 not a 1:1 change/dimension
 same physical change does not equal the same perceptual change

amplitude
 force or pressure of sound
 related to displacement of tine

loudness
 perception of amplitude
 decibel dB

relationship between amplitude and loudness
 increase in amplitude = increase in loudness
 not a 1:1 dimension

Simple Harmonic Motion
Uniform Circular Motion
 another type of SHM
 circle of radius r
 point P moves around circle at a uniform speed
 at each new P, a new radius r' is drawn that forms an angle (theta) with the original r
 by the time P goes around the circle, theta will go from 0 to 360 degrees

phase refers to
the angle of theta

period
time for one revolution

frequency
# cycles/second

amplitude
the radius of the circle

Amplitude (X) varies with
 the sine of theta
 X = r * sine

waveform
 graph of displacement as a function of time
 the waveform associated with SHM is the sine wave because the formula contains the sine function



Simple Harmonic Motion
Pendulum
 velocity is zero / movement stops at the extremes
 velcoity is at its max at the point of rest

amplitude graph vs. velocity graph
the amplitude graph is alays 90 degrees behind the velocity graph

superpositioning of sound waves
 adding sine waves together
 go point by point on the x axis and add the y axis numbers together

adding sine waves of equal frequency results in
 a sine wave with the same frequency
 creates simple waves

adding sine waves of different frequencies results in
 complex waves  any wave that is not a sine wave
 a wave with more than one frequency component

square waves are formed by
adding the odd multiples of a given frequency

the fundamental frequency is
 the lowest frequency
 largest comon multiple in a series of frequencies

harmonics
frequencies that are integer multiples of the fundamental frequency