first 1/3 semester Flashcards
acoustics
the study of sound
mass
what makes up all matter, it is the particles (atoms/molecules) and is commonly measured in kg
density
determined by the mass and spacing of particles (note sound travels faster in higher density
force
used to move a mass a distance; mass*acceleration
Newton
basic unit of force, it is the force required to accelerate 1kg of mass 1 meter per second/per second (kg m/s^2)
dyne
unit of force less commonly used than Newton, this is because we want to go back to our basic units: kg and m; (g cm/s^2); 1N=100,000dynes
work
applying force to move a mass for a distance
work= force*distance
energy
the ability to do work
distance vs displacement
distance=scalar meaning direction does not matter
displacement is vector meaning direction does matter
velocity
change is displacement over time
speed
change in distance over time
the three opposing forces
friction, inertia, elasticity
elasticity
the tendency of a solid material to return to its original shape after a force is removed
stiffness
the ability to resist change in shape or resistance to be set in motion
sound energy
energy that travels in a medium that has mass and stiffness; basically changes in pressure that causes perception of sound. Sound pressure is a force created by a chain reaction of high and low pressure zones
pressure
force/area; measured in Pascal or Barye; increased density increases pressure, increases heat increases pressure
Pascal
(N/m^2) and Barye= (dyne/cm^2); Pa=10Ba
Hz range humans can perceive
20-20,000Hz
decibel
expresses the intensity of sound; a logarithmic ratio of the measured and reference values. not an absolute value so 0 doesnt mean no sound, means its at reference level (measured in power or pressure)
dB power
scale is dB IL=Intensity level; refernece level is 10^-12w/m^2; humans can hear from 10^-12w/m^2 to 1w?m^2
dB pressure
scale is dB SPL= sound pressure level; reference is 20 microPa or 20x10^-6 Pa
double power
+3dB
doubling pressure
+6dB
inverse square law
deals with decrease in dB as distance from source is increased
dB change
the loss of sound intensity; 20log(original distance/new distance)
easiest way to add dB
in dB IL because power is always power but pressure changes with the wave. if adding in SPL, then you would have to calculate the phase of each wave and the amplitude at that time.
sine
opposite/hypotenuse
cosine
adjacent/hypotenuse
tangent
opposite/hypotenuse
simple harmonic motion
sound caused by vibrations that follow the mathematical shape of the sine wave
simple harmonic motion produces a:
pure tone
how are waves classified?
according to the direction of vibration of the medium relative to the direction the wave is moving
transverse wave
particle displacement is perpendicular to the direction of wave propagation
longitudinal wave
particle displacement is parallel to the direction of the wave propagation
speed of sound formula
square root of stiffness/density
+stiffness+speed, +density-speed
(frequency and intensity do not affect)
wavelength
the distance covered in a full cycle
speed of sound/frequency (c/F)
period (T)
how long does it take to complete 1 cycle (T=1/F)
measured in seconds or milliseconds
reciprocal of frequency
complex sounds
most sounds in nature; made up of many frequencies occurring at varying intensity levels; pure tones mixed together
beats
when two pure tones are close in frequency, a beating sensation occurs. when signals are in phase they will add, and when they are out of phase cancellations will occur.
Fourier analysis
spectral analysis showing the individual component parts of sound (frequency, amplitude, and phase of complex sounds) (gives phase as imaginary #)
polar plots
show freq, amplitude, and phase (phase is shown in an easier way than Fourier
distortions
unintentional changes in sound due to inaccurate production; speaker producing loud sound or poor quality speaker
harmonics
integer multiples of the lowest frequency (type of distortion)
does a pure tone have harmonics?
no, harmonics would make it a complex signal
non-linear distortions
combination tones, when two signals are presented together (a combination of tones causes different harmonics)
square wave
odd harmonics, intensity of harmonics decreases by 6dB per octave
triangle wave
odd harmonics, intensity of harmonics decreases by 12dB per octave
sawtooth wave
even and odd harmonics, intensity of harmonics decreases by 6dB per octave
noise
is aperiodic meaning vibrations do not repeat, it has a random temporal pattern
white noise
Gaussian noise; has equal energy at all frequencies averaged over time
modulated signals
gradual change in amplitude or frequency
envelope
shape of amplitude modulation
modulation rate
how often this modulation occurs
frequency modulation
a signal that had a bunch or frequencies that it goes through, they are not presented at the same time, but in sequence
ramping
rise and fall time to introduce signal and limit distortion, used in audiometer
tone burst
measured in milliseconds to rise
tone pip
measured in cycles to rise
types on envelopes from worst to best
triangular, cosine, Blackman
filters
used to control the frequencies present in a signal
cut off frequency
where you tell the filter, after this point we don’t need these, it is where power drops by 50% which is the same as a loss of 3 dB
roll-off/ slope
how fast dB drops after cutoff frequency
bandpass filter
will only allow certain range of frequencies through
high pass filter
cut low frequencies and allow all high
low pass filter
cut high frequencies and allow all low
band reject filter
allows frequencies below and above cutoff and reject anything between
diffract
wrap around a barrier
reflect
bounce off a barrier
sound going through an opening bigger than the wavelength
no significant diffraction and sound passes through
sound going through an opening smaller than the wavelength
significant diffraction and the opening functions as a new sound source, sound passes through
wavelength is longer than barrier
no sound shadow area
wavelength is shorter than barrier
sound is diffracted around barrier, sound shadow area
reverberation time
T sub 60; the interval in which the reverberating sound energy, due to decaying reflections, reaches one millionth of its initial value. Same as the time it takes for the reverb. level to drop by 60dB
doppler effect
an approaching siren sounds high in pitch, then lower in pitch as it passes; movement of sound source pushes and pulls on wave, changing perceived frequency as source moves
