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COMD 451
Chapters 3-6 Vocab
118
Audiology
Undergraduate 4
02/22/2010

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Term
Period
Definition
The time required for the completion of one cycle of a periodic motion.
Term
Frequency
Definition
The number of cycles per second.
Term
Oscillation
Definition
Any back and forth movement between two states.
Term
Vibration
Definition
Mechanical oscillation with elasticity acting as the restoring force.
Term
Sinusoidal motion
Definition
The motion of an object in which changes in displacement, velocity, and acceleration are sinusoidal functions of time.
Term
Periodic motion.
Definition
A motion that repeats itself in regular intervals until stopped by an external force.
Term
Harmonic motion
Definition
A motion in thich the acceleration of the object is directly proportional but opposite in direction to the displacement of the object from its equilibrium position.
Term
Waveform
Definition
A function representing changes of any physical quantity as a function of time.
Term
Propagation
Definition
Process of conveying energy through space via a wave motion.
Term
Mechanic wave
Definition
Transfer of mechanic energy from one molecule to another.
Term
Medium
Definition
A substance that occupies a space; can be solid, fluid, or gas.
Term
Mechanic disturbance.
Definition
Any event that causes a change in medium at a specific location.
Term
Longitudinal waves
Definition
Waves in which the particles of the medium are displaced in the same direction as the wave propagation.
Term
Compression
Definition
Bunching of particles causing increased density.
Term
Rarefaction
Definition
Spreading of particles causing decreased density.
Term
Transverse waves
Definition
Particles of a medium are displaced in a directon that is perpendicular to the direction of wave propagation.
Term
Surface waves
Definition
Complex waves created when a mechanic disturbance arrives at a border between two media having different densities; combination of transverse and longitudinal waves.
Term
Sound
Definition
A disturbance in an elastic medium that propogated through the medium as a longitudinal wave; a stimulus that causes an auditory sensation.
Term
Speed of sound
Definition
The rate at which energy propagates through a medium.
Term
Wavelength
Definition
The distance in space between two adjacent identical points of a propagating wave.
Term
Sound energy
Definition
The energy transferred from the vibrating source to the medium and propagates through the medium in the form of density changes.
Term
Infrasound
Definition
Very low frequency sounds that cannot be heard (below 20Hz).
Term
Ultrasound
Definition
Very high frquency sounds that cannot be heard (above 20kHz).
Term
Pure tone
Definition
Tone with only one frequency.
Term
Complex tone
Definition
Tone with more than one frequency.
Term
Deterministic sounds
Definition
Sounds where maginitude at different points in time can be predicted.
Term
Stochastic sounds
Definition
Sounds where future behavior cannot be predicted; random.
Term
Stationary noise
Definition
Random sound with acoustic properties that do not vary much over time.
Term
Nonstationary noise
Definition
Noise content and intensity change randomly and noise properties cannot be predicted over time.
Term
Phase difference
Definition
The absolute difference between that phases of two waveforms with neither considered as a point of reference; maximum difference = 180 degrees.
Term
Phase shift
Definition
The relationship between the phase of one waveform and another where one is considered the point of reference.
Term
In-phase
Definition
When two waveforms have the same frequency and phase.
Term
Out-of-phase
Definition
When two waveforms have the same frequency, but different phases.
Term
Instantaneous magnitude
Definition
The magnitude of a waveform observed at any given time.
Term
Amplitude
Definition
The maximum/peak magnitude of a waveform.
Term
Peak-to-peak magnitude
Definition
The whole range of magnitude changes within one period.
Term
Average magintude
Definition
The average value of the magnitude calculated across the whole period of a waveform.
Term
Root mean square (RMS) magnitude
Definition
Constant magnitude derived from the root of the mean of the squares of the instantaneous magnitudes calculated across the waveform's period.
Term
Stiffness
Definition
A mechanical property of an elastic object that describes its opposition to the change of its dimensions by an external force.
Term
Closed system
Definition
A system that does not exchange its energy with the environment; no loss of energy.
Term
Open system
Definition
A system that loses part of its energy to the surrounding environment due to the effect of friction.
Term
Free vibration
Definition
The back and forth vibration of a system in which no additional energy is added once it is set into motion.
Term
Resonant frequency
Definition
The natural frequency at which a system will vibrate when left alone.
Term
Forced vibration
Definition
A vibration in which a system is forced to vibrate by an applied force.
Term
Friction
Definition
The force that opposes the relative motion of two bodies in contact and causes the conversion of system energy into heat.
Term
Damping
Definition
The loss of energy in a vibrating system due to dissipation to the surrounding environment; causes a gradual decrease in amplitude.
Term
Minimally damped system
Definition
Very little system friction.
Term
Critically damped system
Definition
Indicates the most rapid response to a sudden change of force without overshooting the equilibrium.
Term
Heavily damped
Definition
A lot of system friction.
Term
Time constant
Definition
Specifies time in seconds after which the amplitude of vibration decreases by ~63%.
Term
Rise time
Definition
The overall duration needed to change from 10% to 90% of a waveform's peak.
Term
Steady-state time
Definition
The time period during which a waveform has a relatively constant amplitude.
Term
Fall time
Definition
The time needed for a waveform to change from 90% to 10% of its peak value.
Term
Resonance curve
Definition
The dependence of the amplitude of vibrationof the frequency of the driving force.
Term
Complex vibration
Definition
The sum of two or more simple vibrations.
Term
Fourier theorem
Definition
Any complex waveform is the sum of various sinusoids of varying amplitude, frequency, and phase.
Term
Aperiodic vibration
Definition
A vibration without a repeating pattern.
Term
Periodic vibration
Definition
Vibratory motion in which an object returns to the same point in space at equal periods of time during the motion.
Term
Waveform synthesis
Definition
The process of combining several sine waves into a complex waveform.
Term
Harmonics
Definition
Whole-number multiple frequency components of a complex waveform.
Term
Greatest common factor
Definition
The largest common factor from a group of harmonically related components is equal to its fundamental.
Term
Missing fundamental
Definition
When the GCF of a set of harmonics is not present in the waveform.
Term
Periodicity
Definition
The concept that a periodic waveform repeats itself for an infinite amount of time.
Term
Noise
Definition
Random sequence of events resulting from the combination of a large number of unrelated frequencies.
Term
Transient
Definition
A brief, single event that ceases to exist after a very short time.
Term
Complex inharmonic motion
Definition
The sum of a finite number of frequencies that does not repeat its pattern within an observed period of time.
Term
Waveform analysis
Definition
The process of taking complex waveforms apart into individual components.
Term
Time domain
Definition
Representation of a phenomenon as a function of time.
Term
Spectrum
Definition
A graphical representation of a complex waveform showing the waveform energy (amplitude) of the individual components (y-axis) arranged in order of frequency (x-axis).
Term
Frequency domain
Definition
Representation of a phenomenon as a function of frequency.
Term
Line spectrum
Definition
A spectrum that consists of one or more separate vertical lines.
Term
Amplitude/frequency spectrum
Definition
Displays the amplitude of various vector quantities associated with the components (velocity, force, displacement, etc.).
Term
Continuous spectrum
Definition
A spectrum in which the energy of spread across a wide range of frequencies rather than at discrete sinusoidal components.
Term
Power spectrum
Definition
Displays the power (energy) of the components.
Term
Nodes
Definition
The points of the vibrating system at which displacement remains zero.
Term
Antinodes
Definition
The points at which the vibration magnitude is greatest.
Term
Mode of vibration
Definition
The specific vibration pattern of a vibrating system associated with each rosonance frequency of the system.
Term
Impedance
Definition
The opposition to the flow of energy through a system and any change in its state.
Term
Resistance (R)
Definition
The opposition of a system to movement caused by friction.
Term
Reactance (X)
Definition
The opposition of a system to a change in its state by the system's ability to store energy and prevent its transfer to or from another system.
Term
Mass reactance
Definition
The ability of the mass to store energy.
Term
Stiffness reactance
Definition
The ability of the stiffnes to store energy.
Term
Conductance (G)
Definition
The wase with which energy travels through a friction element in the system.
Term
Susceptance (B)
Definition
The ease with which energy travels through a stiffness element in the system.
Term
Mass susceptance
Definition
The ease with which energy flows through a mass.
Term
Sitffness susceptance
Definition
The ease with which energy travels through s spring element.
Term
Admittance
Definition
The ease with which a system can vibrate due to an applied force.
Term
Impedance matching
Definition
The practice of making the impedance of the source of power equal to the impedance of the load to transfer as much energy as possible from the source to the load.
Term
Mass dominated
Definition
If mass reactance is greater than stiffness reactance.
Term
Stiffness dominated
Definition
If stiffness reactance is greater than mass reactance.
Term
Sound absorption
Definition
Sound wave will lose energy due to absorption by the medium and surrounding boundaries.
Term
Absorption coefficient
Definition
The ability of a medium and its boundaries to absorb the energy of sound waves.
Term
Sound reflection
Definition
The bouncing of sound waves off of a boundary.
Term
Sound refraction
Definition
The bending of sound waves due to a change in the speed of sound propagation; caused by sound waves entering a different medium or changes in temperature.
Term
Incident wave
Definition
The original, incoming sound wave.
Term
Total internal reflection
Definition
A situation where 100% of the sound energy reaching a boundary is reflected back into the original medium.
Term
Critical angle of incidence
Definition
The smallest angle of incidence for which total internal reflection can occur.
Term
Thermal effect
Definition
The effect of bending sound waves away from the ground when warmer air is nearer to the ground and colder air is above it.
Term
Inverse thermal effect
Definition
When colder air is closer to the ground and warmer air is above it, waves bend toward the ground.
Term
Reverberation time
Definition
The time needed for a sound pressure to decrease 1000 times after the sound source ceases its operation.
Term
Reverberation
Definition
The reflected sound energy within an enclosed space.
Term
Reverberation chamber
Definition
Closed spaces with highly reflective surfaces that do not absorb sound waves.
Term
Anechoic chambers
Definition
Rooms with very soft walls, ceilings, etc. that absorb most of the sound energy.
Term
Acoustic shadow
Definition
An area behind a boundary that the direct sound waves does not enter.
Term
Sound diffraction
Definition
The phenomenon of sound waves bending around objects and through openings in barriers.
Term
Constructive interference
Definition
An increase in amplitude of sound waves when two or more sund waves travel through the same space and are in-phase.
Term
Destructive interference
Definition
A decrease in the amplitude of at least one sound wave when two sound waves travel through the same space and are out-of-phase.
Term
Beats
Definition
Slow, periodic amplitude fluctuations caused when two sine waves that are very close to each other in frequency interfere with one another.
Term
Sound field
Definition
A space containing sound waves.
Term
Near field
Definition
The resulting vibrations in a sound pressure near the sound source; characterized by large and nonuniform maxima and minima in acoustic pressure that gradually disappear into a uniform signal with increasing distance from the source.
Term
Far field
Definition
The region of uniformly decreasing sound pressure (1/r) observed far away from the sound source.
Term
Direct sound field
Definition
Sound field created by a sound source in an unbound space.
Term
Free field
Definition
Sound field in which sound propagation is not affected by objects or boundaries.
Term
Indirect field
Definition
Sound field where sound energy reflected from space boundaries dominates the sound energy propagating from the sound source.
Term
Diffuse sound field
Definition
And area filled with sound energy from random reflections coming from all directions and in which all SPLs are the same.
Term
Critical distance
Definition
The distance from the sound source where the intensity of both fields is about equal.
Term
Signal-to-noise ratio
Definition
The ratio of intensity of a signal to the intensity of a noise.
Term
End correction
Definition
Additional length added to a mass of a vibrating system to determine the resonance frequency of a tube with an open end.
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