Section 1 Flashcards
Sound defined in physical terms
A sound is a series of disturbances of molecules within, and propagated through, and elastic medium such as air
Sounds defined in psychological terms
In a psychological sense, a sound is an auditory experience -the act of hearing something.
Define elasticity
The elasticity or Springiess of any medium is increased as the distance between the molecules is decreased. A solid is more elastic than a liquid. A liquid is more elastic than a gas.
Brownian motion
The rapid and random movement of air particles. This is affected by heat. As the heat is increased, the particle velocity is increased.
What are waves made up of?
Waves are made up of successive compressions and rarefactions.
What is a wave compression?
Molecules that are pushed close together-condensed or compressed
What is a rarefaction of the wave?
When a space exists between areas of compression-this area is said to be rarefied
What are 3 psychological aspects of sound?
Pitch
Loudness
Timbre or Quality
What are 3 Physical aspects of sound?
Frequency
Intensity
Spectrum
Undisturbed medium (air)- with exception of Brownian movement and pressure variation is in what state?
Equilibrium.
Sound definition
A disturbance in a medium caused by an external force.
T or F Sound must have a medium to pass through
True- sound cannot travel in a vacuum.
What are the qualities a medium must have for sound to pass through?
Must have elasticity (in order to vibrate)- the tendency for a material to return to its original state/form after being distorted.
Must have mass/interia- the tendency of matter at rest to stay at rest and the tendency of matter in motion to remain in motion.
T or F Sound wavve are propagated through air in all directions.
TRue
T or F Sound waves are 2 dimentional
F- 3 dimensional.
Compression or Condensation definition.
Molecules/particles pushed closer together than at equilibrium as a result of sound traveling. This creates a higher pressure than the normal atmospheric pressure.
Rarefaction definition
Particles that are farther apart than at equialibrium. Following compression, lower pressure than surrounding atmosphere.
Sound Propagation- how the sound travels
The disturbed particles exhibit a minute (tiny) forward and backward motion. The disturbance moves in a wave-like fashion NOT the air particles themselves.
Sound moving through a medium must either be:
Transverse Waves or Longitudinal waves
Transverse Waves
Displacement of the medium is perpendicular to the direction of propagation of the wave. Any medium that will support a shearing stress will transmit transverse waves.
Transverse waves cannot propagate in a gas or a liquid because there is not mechanism for driving motion perpendicular to the propagation of the wave.
** transverse aves may occur on a string, on the surface of a liquid, and throughout a solid. SOUND WAVES DO NOT PROPAGATE AS A TRANSVERSE WAVE MOTION.
Longitudinal waves
All forms of matter exhibit compressional elasticity- they will all transmit longitudinal waves. (some better than others).Each molecule will execute the same motion as the proceeding molecule. The displacement of the medium is parallel to the propagation of the wave. ( think of a slinky). **Sound waves in air are longitudinal waves*
Simple Harmonic Vibration or Simple Harmonic Motion- what does it look like?
A single tone will create a simple even wavy line. “Sine wave”
Sine Wave
A plot change in amplitude or displacement over time
The display “wave” is called the time-domain waveform, or waveform.
**Air does not actually undergo this form of excursion: the waveform is a representation.
Vibration Definition
Applies to source and air molecules-
Motion is back and forth along a bath in such a manner that there is a restoring force (potential energy), increasing with displacement, and always directed toward the position of rest.
Simple Harmonic Vibration (Simple Harmonic Motion)- 4 things about it
Waveform repeats itself over time (i.e. periodic),
is a single frequency,
pure tone,
The restoring force is proportional to the displacement
Kinetic Energy and Potential Energy- Referring to the Sine Wave
Kinetic energy-This is moving energy. On the wave- KE is at it’s max on the “equilibrium line” and is at zero when the highest and lowest points are reached.
Potential Energy is at it’s max and the top and bottom of the wave- think of a pendulum. PE is zero at the equilibrium line-zero.
Two categories of Vibration:
Free and Forced
Free Vibration
ex- tuning forks, pendulums and vibrating strings.
Vibrate at natural (resonant) frequency
- pendulum depends on length of string, strings depend on tension, length and mass, tuning forks depends of mass and stiffness.
Frequency stays constant regardless of amplitude or damping.
Resonance
Forced Vibration
An outside force is added to control the vibration. - swinging/vibration continues until the outside force is removed. When outside force is removed, the object reverts to free vibration. The human (middle ear) is highly damped.
Oscillation
One cycle of vibration. begins at any point on the wave and ends at the identical point on the next wave
Another name for a sine wave
Sinusoidal (sine like)
Pure tone
When anybody oscillates sinusodiall, showing only one frequency of vibration with no tone superimposed, it is said to be a pure tone
Cosine wave
A wave that begins at 90° rather than 0°
Damping, types
Lightly damped- Vibrations decay over time
Heavy damping-Causes the oscillations to cease rapidly
Critically damped-When oscillation ceases before a single cycle is completed
Five important measurable characteristics of vibratory motion or the sine wave:
Displacement/Amplitude Frequency Period Phase Wavelength
Displacement
The distance from equilibrium to the position of the body at that instant. Maximum displacement is reached at the extremes of the upper and lower portion of the wave.
How is Time represented on a sine wave?
Runs from left to right (the X axis) and is called “abscissa”
How is pressure represented in a sine wave?
Runs up and down (the y axis). Above equilibrium is high pressure and below equilibrium is low pressure. Also called “ordinate”
Amplitude
HOw much energy or force is imposed on the medium. The maximum displacement of the body from its equilibrium. equal to half the total of the vibration. Also called peak amplitude.
Peak to peak amplitude (pp amplitude)
Is the total displacement of the upper and lower peak. Twice the amount of peak amplitude.
Peak amplitude
The amount of displacement for one side/peak of a sine wave. Peak amplitude in most cases is half the amount of peak to peak amplitude.
Loudness is the
impression we get from the strength of the amplitude. Our subjective impressions at various frequencies vary. As a general rule, the larger the amplitude the louder it sounds to us.
T or F Greater density and air pressure is created by compression/condensation with higher amplitude sine waves
TRUE
Frequency f
the number of complete vibrations or cycles per unit of time.
- usually measured in cycles per second (cps)
- cps in generally represented by Hertz (hz)
- 100 CPS=100 Hz (SAME MEASUREMENT:) )
- frequency and pitch are different. Frequency can be measured and pitch is perceived.
High frequency wave- what does it look like?
More cycles per second. wave is closer together.
Low frequency tone- what does it look like?
Less cycles per second. Wave is more spread out.
Mass and Stiffness- what creates a higher or lower frequency?
Greater mass in an oscillating system results in a decrease of the frequency of vibration. (ex- thicker strings, lower pitch/frequency)
Systems that have more stiffness (less compliance) will vibrate better at higher frequencies. (ex- tighter strings on a violin)
Human hearing- what frequencies can humans typically hear?
Low- 20 Hz
High- 20k Hz
This is about 10 octaves.
After teens the highest frequency changes to about 10k hz. Most common range of sounds 100 hz (deep male adult) to 6k hz (s sounds in some females).
Most common range of hearing after childhood/teenage years. And most common range of sounds?
After teens the highest frequency changes to about 10k hz. Most common range of sounds 100 hz (deep male adult) to 6k hz (s sounds in some females).
Sounds above our normal range of hearing are called:
Sounds below our normal range of hearing are called:
Above: ultrasound
Below: Infrasound
fun fact- dogs can hear 45k hz
Porpuses can hear up to 150k hz!
Resonant Frequency
The natural rate of vibration for an object. When set into vibration- an object will revert to its’ resonant vibration after the force is discontinued until it is damped- some object like a desk damp very quickly.
Period
aka T- the time that elapsed during a single complete vibration.
*Frequency and period are reciprocals… T=1/f f=1/T
Low frequency sound have a relatively long period and high frequency sounds have a relatively short period.
Phase
describes vibratory and wave motion. Useful in describing the relationship between two or more vibrations or wave motions.
Definition: The portion of a cycle through which a vibrating body has passed up to a given instant. Expressed in terms of a degree of a circle.
Phase change in a complete vibratory cycle:
360 degrees
Starting phase:
The point at which an object begins its vibration. It can be at zero or any other point where the sine wave starts.
How is phase expressed? / the sign of phase
Theta θ
Sound Velocity
The speed at which sound travels from the source to another given point.
- dependent on medium density- higher atmos. pressure=greater velocity
- dependent on medium pressure- higher temp= increases sound velocity
- the closer the molecules are together, the closer the molecules are the quicker the displacement travels.
Constant Sound Velocity used for class
At sea level 20 degrees C
344 m/sec OR 1130 ft/sec
Velocity sound travels through gas (air)
1130 ft/sec
Speed sound travels through Fluid (water)
4500 ft/sec
speed sound travels through some solids
15000 ft/sec
Wavelength
The distance in feet between identical points on two adjacent waves.
Wavelength (λ) = C/f
C= constant/velocity speed of sound 1130 ft/sec 344m/sec?
f= frequency
KNOW THIS__!!
What is the constant C in W (λ)= C/f
344 m/sec 1130 ft/sec
Short wavelength means:
lots of wave, high frequency, high sound
Long wavelength means:
fewer waves, low frequency, low sound
T or F short wavelengths travel faster than long wavelengths
false- all sound travels at the same speed. short wavelengths hit your ear more often than long wavelengths.
Why do you most often hear bass from your neighbor’s house and not higher frequency notes?
Longwave lengths can bend around an object shorter than their wavelength. High frequency sounds are impeded by objects longer than their wavelength.
frequency and wavelength relationship
as frequency increases, wavelength decreases.
as frequency decreases, wavelength increases.
w=v/f or lambda=C/f (SAME THING)
What is the wavelegth of a 113 Hz tone?
1130 tone?
11300 tone?
10 ft
1 foot
.1 foot
Damping
Sound energy dissipates with distance from a source. i.e a person talking from across the room. reduction of amplitude during successive oscillations. It is result of frictional resistance or absorption. Does not affect the frequency.
Complex Sounds- speech and music
build from a number of sinusoidal components that are taking place at the same time.
Complex Periodic sounds
Waves that repeat themselves over time- sound more music. This is true for pure tones and complex sounds.
Aperiodic
Complex sounds perceived as noise. Does not repeat itself.
Fundamental Frequency Fo
A periodic wave, however complex, has a fundamental frequency Fo at which the wave repeats itself.Fo is the first harmonic in the harmonic series and the series of harmonics are simple whole number ratios.
Fundamental Frequency
The lowest frequency- also called the 1st harmonic
First Overtone
Also called the 2nd harmonic, 1st octave. it is 2xFo
Octave
First octave found by Simply the doubling the fundamental frequency.
2nd octave found by doubling the 1st octave frequency.
2nd overtone
aka 3rd harmonic. 3xFo
Third overtone
aka 4th harmonic, 2nd octave. 4xFo
Harmonics and partials
labeled the same as harmonic pretty much
fundamental-1st partial
2nd harmonic-2nd partial
3rd harmonic- 3rd partial
Jean Baptiste Fourier
1786-1830
Studied heat-discovered complex waves are built up of harmonic sine waves
Discovered a Mathematical prism technique that allows us to decompose a complex wave into frequencies
Fourier Analysis
Acts like a prism- decomposes a complex wave into it’s pure frequencies. Determines if a sound wave is a pure tone or various harmonics.
Fourier analysis continued.. how is it represented?
In graph from, showing the frequency and the corresponding amplitudes. Called a spectrum of sum..can also show the starting phase of the wave.
Steady-state sound
has to do with music mostly, not speech. Usually periodic. Frequency, composition, amplitude and phase relationshipof the partials of a tone are constant over time.
Transient Sound
Usually aperiodic- speech. A change in steady state- speaking.
Interference
Whenever more than one tone is introduced at the same time or the same frequency is introduced at different phases. When two or more waves come together, they can either add together or partially/fully cancel each other out.
Constructive Interference
Can be upwards or downwards. At any location when two waves are displaced in the same direction.
Destructive Interference
Occurs when two waves have a displacement in the opposite direction. Cancels each other out depending on amount of displacement. After overlapping the wave continues in their own directions.
Phase interference- review
two waves are “ in phase”with equal frequency and amplitude- it results in a summation of the two waves (doubles)- constructive interference.
If the same two aves are 180 degrees out of phase the to tomes will cancel each other out.- destructive interference.
Beats
When two tones of almost identical frequency are presented. Creases a noticeable increase and decrease in amplitude- this rapid fluctuation sounds like beats. its constructive and destructive interference.
Noise
A sound that has little or no periodicity. not always “bad”
- can mean a sound with an instantaneous amplitude that varies over time in a random manner.
- can be generated in many ways
- defined as any undesirable sound- not rigidly defined.
White Noise
All frequencies within a specified range are present, without regard to phase and the intensity is all the same.
Pink Noise
Intensity decreases by one half with each doubling of frequency. (3dB per octave).
Passive Filter
3 types can be applied to filter out white noise
low pass filter
high pass filter
Combination
Low pass filter
Attenuates high frequency energy but passes low frequency energy
High pass filter
attenuates low frequency but passes high frequency
Combination Filter
Results in a filter that will pass signals within a certain frequency band, but attenuate others. used in testing to mask some of the pure tones. ex. Narrow Band noise.
Resonant frequency
The natural rate of vibration of a mass
Instantaneous velocity
The velocity of sound determined at any specific moment
In phase with the standard
An oscillation that has the beginning of zero or 360°
Two sine waves maybe contrasted by their differences in
Frequency, intensity, phase
Dyne
A unit of measurement for quantifying small changes in force
Decibel
A ratio between two sound powers. It doesn’t mean anything by itself. It mathematically reflects the magnitude of a ratio in a logarithm. It’s exponential. Usually measured 0-140 dB. We use it for Sound pressure measurement but dB can be used in other applications. Anytime dB is used it needs to have a reference.
Logarithmic scale
No true zero. Compares ratios.
Threshold
The lowest point in intensity that a person can hear
0dB reference point
The lowest stimulus a young normal hearing person can perceive.
IL
Intensity level
SPL
Sound pressure level
Intensity Level
Used exclusively for the measurement of sound in watts/meter2.
Diff than pressure.
Usual intensity reference IR=10^-12 watt/m^2 or 10^-16 watt/cm^2
Sound pressure Level
Pressure is force per unit area Unit of force: Dyne-calculates small units of force 1g 1 cm/sec Newton- 1kg of mass 1m/s Unit of sound pressure: Pascal pa=1N/M^2
