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151 Cards in this Set
- Front
- Back
Definition of Sound |
A condition of disturbance of the particles of a medium which is propagated in the form of a wave outward in all directions from a vibrating body. This disturbance takes the form of displacement of the particles forward and backward from their positions of rest, in the direction of the propagation of the wave. |
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Conditions for sound production |
1. Energy source (air from lungs) 2. Vibrator (vocal folds) 3. Transmitting medium (air) 4. Receiving mechanism (ears-auditory system) |
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Definition of vibration |
back and forth movement of a body or object |
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Facts about vibration |
- key factor in sound production - all types of sound involve vibrations - occurs when a body is disturbed by external force so that it moves back and forth around its original rest position |
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For vibrations to occur, a body must have certain physical properties, which are... |
1. elasticity 2. inertia 3. small damping factor |
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Types of vibration |
1. periodic a. simple b. complex 2. aperiodic
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Periodic Vibrations |
1. vibrations that occur in regular pattern so that they repeat themselves in equal (regular) intervals of time; motion of vibrating body (vibrator) occurs over and over again in the same manner
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2 types of periodic motion |
1. simple periodic motion (simple harmonic motion) - pure tones 2. complex periodic motion - complex tones (ex. some speech sound and musical tones) |
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Pure tones |
1. sounds produced by a vibrating body that moves in a simple and periodic manner 2. produced mechanically using tuning forks or electronically generated 3. are used extensively for both measurement and calibration purposes in the acoustics/psychoacoustics lab 4. are also used to determine degree of hearing impairment in audiological testing in the hearing clinic
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What is an audiometer |
a fundamental diagnostic instrument for hearing tests; it generates pure tones via oscillator and controls several properties of pure tones: amplitude, frequency, period, and phase |
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Aperiodic vibrations |
vibrations in a erratic or non-regular (non periodic) pattern; noise and some speech sounds (ex. /s/) |
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All types of vibrations have certain basic properties in common... |
amplitude, frequency, period, and phase |
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Amplitude |
- maximum displacement of a vibrator; distance that a vibrator moves during vibration - the greater the distance of vibrator from rest position, the greater the amplitude - determines physical characteristic of sound called intensity, and the perceptual aspect of sound known as loudness - the greater the amplitude, the louder the tone |
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spring-mass model |
the distance of mass from rest position at any instant in time is called its displacement; maximum displacement=amplitude of the vibration |
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Hz = |
frequency
cycles per second
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There _______ a 1:1 ratio between Hz and pitch |
IS NOT |
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Peak amplitude |
maximum momentary displacement; in sine waves, peak amplitude occur twice in 1 cycle |
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peak-to-peak amplitude |
distance between maximum displacement points in both directions around rest position; in sine waves, peak-to-peak amplitude is twice the peak amplitude |
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What is frequency? |
the number of complete vibrations made by a vibrator in a given unit of time; number of complete cycles of vibration that occur in one second |
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Cycle |
the movement of a vibrator (or particle within a vibrator) from its position of rest to maximum displacement in one direction, back through its position of rest, to maximum displacement in the opposite direction, and back again to its position of rest |
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Range of frequencies for human hearing |
20-20,000 Hz |
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Most sensitive range of frequencies to humans |
1,000-3,000 |
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The higher the frequency of the tone...the _______the perceived pitch |
higher |
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Period |
- amount of time necessary for completion of one cycle of vibration; the number of seconds for one cycle to occur - period is reciprocal of frequency of a vibrator T=1/f (ex. period of an 8,000 Hz tone is 1/8,000 sec or .0001sec; if 8,000 Hz occur in 1 sec, then it takes 1/8,000 sec. to complete 1 cycle - frequency is the reciprocal of period (ex. if the period of a vibration is .01 sec, its frequency is 100 Hz (1/.01)) |
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Phase |
-the portion of a cycle through which a vibrator has passed up to a given instant in time; that portion of a cycle that has elapsed at any instant in time relative to some arbitrary starting point -usually measured in degrees of a circle -number of degrees within one completed cycle of vibration = 360 |
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In-phase |
two waves represented by sine curves are said to by "in-phase" at any given point (instant in time) when their degree of advancement from an arbitrary zero point is equal |
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Out-of-phase |
a condition in which a phase difference exists between vibrating sources; thus, both vibrators do not assume identical phase angles at every instant in time |
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Waves traveling through a medium of air are called... |
sound waves |
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All kinds of waves involve a.... |
disturbance -i.e. a back and forth movement, a vibration, caused by various disturbance-producing mechanisms. Differences between different wave types involve differences in vibrator, source of energy, and transmitting medium |
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Sound waves are_________ waves |
Longitudinal |
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Sound cannot be produced without a _________ between source of vibration and ear |
medium
(sound cannot be conducted in the absence of matter (sound does NOT travel through a vacuum)) |
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The most common medium through which sound is transmitted is ____________ |
air |
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Air has ___________ and_____________ and therefore can serve as a medium for transmission of waves |
-mass -elasticity |
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Air is composed of minute particles called ______________ |
molecules (there are more than 400 billion molecules in every cubic inch of air) |
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Each molecule is assumed to have some average stable position called its___________________ |
rest position |
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Sound waves _______________ transverse waves |
are NOT |
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The movement of molecules closer together in air produces a _____________________ |
wave of compression (wave of condensation) |
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Each wave of compression is followed by _______________________ |
a wave of rarefaction (wave of expansion) |
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In a state of compression there is ___________ of pressure In a state of rarefaction there is _____________ of pressure |
- increase - decrease |
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What is a sound wave? |
the movement of a disturbance though a material medium such as air without permanent displacement of molecules |
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Speed of sound wave in air is approximately... |
340 meters (34,000 cm, 1130ft) per second |
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Sine curves are used to represent... |
particle pressure, particle velocity, or particle displacement as well as the sound wave itself |
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pressure equals ________ when molecules are in rest position |
0 |
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Particle velocity increases as it approaches middle of swing and it is at its maximum value when it is in its _______ position |
rest |
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pressure is at its greatest at _______ velocity; pressure is at its least at its _______ velocity |
- lowest - greatest |
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Particle displacement |
degree of displacement of a particle to right (above line) or left (below line) as it moves away from, or toward, source of sound |
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Sound is not transmitted ______________ |
instantaneously (it takes time for a sound wave to travel from its source to listener) |
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Velocity |
distance which a sound wave will be transmitted (propagated) through a given medium in a single unit of time (velocity is measured in meters, cm, or ft per second) |
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Factors that affect velocity of sound |
- elasticity - density - temperature |
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Elasticity |
resistance to distortion offered by medium, it is the most important factor in determination of velocity |
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the greater the elasticity of a medium, the _________ transmission of wave |
more rapid (i.e. the greater the velocity of sound) |
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Density |
mass per unit of volume; it is proportional to the number of molecules in a given volume of air |
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The greater the density of a medium, the __________ the speed of wave being transmitted |
slower |
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the more molecules in a given volume of air (the greater the density) the ____________ it will take the wave to be transmitted through the medium |
longer |
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velocity of a sound wave increases when elasticity of medium ____________ and when density _____________ |
- increases - decreases |
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velocity formula |
velocity = elasticity / density
velocity = wavelength x frequency
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an increase in velocity of sound occurs with _________ in temperature of medium |
an increase |
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when temperature increases, molecules ....... |
spread farther apart |
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sounds travel ________ through steel than air because.... |
faster - steel has more elasticity |
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Normally, all sounds, regardless of pitch or loudness, travel through air... |
at the same velocity |
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Wavelength |
distance between points of identical phase in 2 adjacent cycles of a wave; distance between successive compressions (or rarefactions) in space |
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wavelength formula |
wavelength = velocity / frequency |
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as frequency increases, wavelength ___________ |
decreases (gets shorter) |
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the greater the velocity, the ____________ the wavelength |
- longer
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frequency formula |
frequency = velocity / wavelength |
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frequency of a sound wave (does/does not) change in passing though different transmitting media; but velocity of sound wave (will/will not) vary with different transmitting media |
- does not - will |
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Types of interference in the transmission of sound waves |
reflection, absorption, refraction |
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when a sound wave impinges on any surface, result will be either ____________ or ____________ of wave's energy |
- reflection - absorption |
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Reflection |
is turning back of a wave upon itself when it encounters an abrupt change in nature of medium in which it is traveling |
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2 types of reflection of sound waves |
1. diffuse reflection 2. regular reflection |
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Diffuse reflection |
- results when reflecting surface is rough - only a small portion of sound wave energy is reflected from a rough surface |
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regular reflection |
- results when sound wave is reflected off a smooth surface - much or all of sound wave energy is reflected from a smooth surface |
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percentage of energy of a sound wave which will be reflected depends on the ___________ |
-surface (solid surfaces=up to 100% of sound wave energy;thus giving maximum reflection) (porous surfaces=minimum reflection; sometimes approaching 0%) |
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Echoes |
brief periods of reflection which are not sustained |
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Reverberation |
continual or prolonged reflection - may produce blurred sound effects, unintelligible speech, or unintelligible music |
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Absorption |
reduction in reflection of energy of sound waves by dissipation of all or some of sound energy |
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absorption coefficient |
effectiveness of a given material in absorbing sound energy; percentage of energy that is absorbed, as compared to the total energy available in sound wave ex. if a material absorbs 60% of incident energy, and reflects 40%, then its absorption coefficient is .6 |
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In general, absorption factor is __________ for lower frequencies |
lower |
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When does refraction of a sound wave occur? |
when determinants of velocity (elasticity, density, and temperature in a medium) vary |
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Plane wave |
sound waves tend to move outward from source of sound in the form of a sphere, but after about 6 feet from source, wavefront approaches a plane surface, resulting in a plane wave |
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Refraction (deflection) |
phenomenon of bending of sound waves form their path of propagation |
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Most sounds in our environment are ___________ |
complex - vibrating sources not moving in a simple back-and-forth motion |
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2 types of complex vibrations |
- complex periodic vibration - complex aperiodic vibration |
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complex periodic vibration |
a complex vibration that repeats itself over and over again in time; vowels are produced by complex periodic vibration |
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complex aperiodic vibration |
a complex vibration that does not produce repeatable patterns of vibration; fricatives are produced by complex aperiodic vibration |
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"component" of a complex wave |
each of the simple pure tones included in complex wave |
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When has the spectrum of a complex wave been described? |
when amplitude and frequency of complex wave's sinusoidal components have been specified |
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what is a spectrum? |
graphic representation of frequencies and relative amplitudes of components of a complex wave; graphic representation of the waveform - vertical axis=amplitude - horizontal axis= frequency |
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Fourier analysis |
analysis of complex periodic waves into their sinusoidal components; shows that sum of many sinusoidal waves is equivalent to a wave with a non-sinusoidal (complex) shape ex. a complex wave |
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2 general types of spectra |
- continuous - discrete |
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Continuous spectrum |
shows energy spread throughout entire frequency range; used to represent aperiodic signals |
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Discrete spectrum |
shows energy at discrete points in frequency range; used to graphically represent periodic waves |
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spectrum analysis (harmonic analysis) |
method of analyzing complex waves into their component parts |
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Waveform |
plot that shows amplitude of a sound at each instant in time - vertical axis=amplitude - horizontal axis=time (in seconds) |
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fundamental frequency |
pure tone component with lowest frequency |
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harmonics |
other higher component frequencies in complex tone; they are integral (whole-number) multiples of fundamental |
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timbre |
quality of musical tones; derived from varying amplitude patterns of harmonics (amplitude of harmonic varies in relative intensity from one instrument to another) -number, distribution, and relative amplitude of harmonics determine quality/timbre |
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Partial tones (partials) |
component pure tones of a complex periodic signal |
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Overtones |
partials with frequencies higher than that of fundamental |
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In general, the more harmonics a tone contains, the _________ and __________ it sounds |
fuller and richer |
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3 factors that influence the shape of a complex wave |
1. frequency 2. amplitude 3. phase |
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All harmonics are ________________ Not all overtones are ___________ |
- overtones - harmonics |
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cross hearing |
when test signal is heard in ear not being tested (white noise or narrowband noise, a complex aperiodic vibration, are used to eliminate this) |
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Resonance |
the phenomenon whereby a body, which has a natural tendency to vibrate at a certain frequency (its resonant frequency) will exhibit greater amplitudes of vibration when set into vibration by another body whose frequency of vibration is identical, or similar, to the natural frequency of the first body; the closer the frequency of the driving system to the natural frequency of the resonator, the greater the amplitude of the vibrations |
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it is important to note that a resonator gives no tone unless... |
impulses are received from some other vibrator which, in turn, is activated by a generator |
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The principle of resonance is applied in 3 different ways |
1. sympathetic vibration 2. "sounding-board" effect 3. cavity resonance |
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Sympathetic Vibration |
if two tuning forks of equal frequency are placed near each other, and one fork is struck and if its vibration is stopped, a sound will be heard from the second, unstuck tuning fork |
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Sounding Board Effect |
- a vibrating body (ex. a tuning fork) is placed in direct contact with some large resilient surface - ex. waves of a oscillating tuning fork are of low amplitude; they only disturb the air a little. But if a stem of fork is placed on a table or some other resilient surface of considerable dimensions, it can set a second tuning fork into vibration, and these vibrations will involve disturbance of the air particles over a larger area |
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Cavity Resonance |
- a vibrating tuning fork held in the hand will give out a barely audible tone - but if it is held over open end of a tube of proper length, or over mouth of a jar or bottle of proper size, the resulting tone will be quite strong - tube or bottle or jar acts as a resonator (waves from fork are added to those from body of air in resonator, thus providing a resultant wave of much greater amplitude than original waves from tuning fork |
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Principle of Frequency Response Curve |
- if a vibrating tuning fork is placed over one end of a tube that has two open ends (but one is immersed in water) by moving the tube up and down, a point will be reached where maximum amplitude of sound from fork will be heard |
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Resonant (natural) frequency |
- point of maximum amplitude of the sound |
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Frequency response curve (resonance curve) |
-spectrum of a complex sound also provides a description of the natural frequencies of vibration of the sound - frequencies to which a resonator will respond - shows not only the component (pure tone) frequencies of the complex wave, but also the frequencies at which the wave resonates - graphic representation |
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damped resonator |
can be set into vibration by a wide range of frequencies - damped resonators are described by flat frequency response curves - sound source whose vibrations die away quickly - ex. sounding board of a piano and the body of a violin |
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undamped resonator |
requires a long time for its vibrations to build up and die away; undamped resonators can be set into vibration by only a limited range of frequencies - ex. tuning forks |
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bandwidth |
- the range of frequencies to which a resonator will resonate - effective frequency range of a resonator |
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cavity (acoustical) resonance is analogous to... |
the air in the vocal tract the air in the external auditory meatus |
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Acoustic filter |
a resonator used to transmit or pass on sound - when a resonator behaves in this manner of making some vibrating forks and not making others audible - selective with respect to frequency; it transmits some frequencies with greater efficiency than other frequencies |
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a tube with uniform cross-sectional dimensions throughout its length has______________________________________; the values of these resonant frequencies depend on ___________ of tube |
- regularly spaced resonant frequencies - length |
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For a tube that is closed at one end and open at the other end, the lowest resonant frequency (natural frequency) is equal to the frequency of a sound wave whose wavelength is ..... |
4 times the length of the tube |
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Coupling |
occurs when two or more resonators, each capable of resonance, are joined together; when any part of the system vibrates, force will be exerted on the other part(s) of the system, and it (they) will also vibrate |
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loosely coupled system |
one in which the force that one part of the system exerts on the other part(s) is small |
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tightly coupled system |
one in which the force that one part of the system exerts on the other part(s) is great |
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Sound frequency is determined by... |
number of complete cycles per second of sound wave |
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range of audible frequencies that human ear can perceive |
20-20,000 Hz |
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ultrasonic sounds |
sounds above 20,000 Hz (in medicine and industry) |
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subsonic sounds |
sound below human audibility (below 20 Hz) - often felt via their vibration |
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frequencies important in speech signal |
100-8,000 Hz |
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There is a very strong relationship between speech production and______________ |
speech perception |
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Doppler Effect |
-stationary listener & moving sound source (vice versa) - train moving toward stationary observer the pitch seems to get higher because more sound waves per second reach listener's ear as train gets closer - train moves away from stationary listener, pitch is perceived as getting lower because fewer sound waves are reaching observer's ear per second - FREQUENCY OF SOUND REMAINS CONSTANT - CHANGE IN PERCEIVED PITCH |
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Sound intensity |
physical measurement related to perception of loudness of a sound; the greater the intensity of a sound, the louder is its perception - rate at which energy is given off by a sound source, or energy with which a sound wave strikes an object |
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Energy |
capacity for doing work (force X distance) |
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amount of energy produced depends on what 2 factors? |
-amplitude - frequency |
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intensity of a sound is most often measured in _________ and ___________ |
-power -pressure |
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Pressure |
force per unit area - measured in dynes/cm 2 or microbar or Pascal (Pa) - created when a force is distributed over an area - .0002 dyne/cm 2 or Pa |
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Pascal |
most current unit of measurement for sound pressure - equivalent t dyne/cm 2 or microbar |
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Power |
amount of work done per unit of time (or rate at which energy is used) - expressed in watts
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Intensity is usually measured in.... |
sound pressure - but it can also be measured in power |
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The energy of individual speech sounds is very small or large? |
-small - estimated it would take 4 million people all talking at once to light a single 40-watt light bulb - however, the human ear is capable of hearing a very wide range of sound intensities |
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Loudest sound that can be heard without pain ________ dynes/cm 2 Softest sound that can be heard ______ dynes/cm 2 |
- 2000 (10 million times the softest intensity) - .0002 |
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Clinical practice intensity of sound is expressed as a ________ rather than as an absolute magnitude |
ratio |
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Linear Scale |
all units on the scale are the same size (10 to 11 inches on a ruler is exactly the same distance as 50 to 51 inches) - inches and pounds are linear scales |
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Logarithmic scales |
each unit in the scale is larger than the preceding unit - in the numbers 1, 2, 4, 8, 16, 32, 64 the distance between the numbers is not equal; distance between units gets progressively larger |
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Decibel (dB) scale |
a logarithmic scale (not linear) - cannot be added and subtracted in a conventional manner - 1 to 2 dB is smaller than from 2 to 3 dB |
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Doubling of sound pressure involves the addition of _____ DB |
6 |
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Decibel scale is a ________ scale not an absolute scale |
relative (ratio) (it measures intensity of sound in comparison to some other sound) |
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Absolute Scales |
- zero point of scale represents absence of what is being measured - a true zero point - no negative numbers ( ex. 0 inches represents absence of distance; something cannot be -5 inches long) |
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Relative Scale |
- no true zero point - zero value is arbitrarily and unanimously selected by users of the scale - zero point does not mean absence of measure, but rather the base of the scale (ex.decibel and temperature) |
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Logarithmic scale uses _________ of some constant number |
exponents |
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constant number = |
base
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Logarithm |
value to which a base must be raised to equal desired number - exponent |
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Inverse square law |
describes relationship of intensity and distance: intensity varies inversely as the square of the distance from the sound source |