Chapter 5: The nature of sound Flashcards
wave motion
(wave) a change in energy concentration in a medium, which travels through space.
propagation
the process of converting energy through space via wave motion.
medium
a substance that occupies a space. (solid, fluid, gas) what the wave travels through
mechanical disturbance
an event that causes a change in a medium at a specific location.
longitudinal waves
particle motion in the same plane as wave motion.
waves in which the particles of the medium propagating the wave are displaced in the same direction as the wave propagation through the medium.
transverse waves
particles of medium are displaces perpendicular to direction of wave propagation.
wavelength
distance between compressed regions and the rarified regions.
the physical distance in space occupied by one period of a wave.
compression
a bunching of particles causing increased density.
rarefacation
a spreading of particles causing decreased density.
brownian motion
small random motion within a medium
sound source
a disturbance in an elastic medium that propagates through a medium as a longitudinal wave motion
sound
defined three basic ways
- a disturbance in an elastic medium that propagates through a medium as a longitudinal wave motion
- a stimulus that causes an auditory sensation
- an auditory sensation.
a systematic pressure disturbance in which a sound source creates regions of compression and rarefactions.
sound energy
energy that is transferred from vibration objects (sound source) to the medium and that propagates through the medium in the form of density changes.
atmospheric pressure
a constant pressure exerted by the atmosphere on the surface of the Earth.
the result in the weight of the atmosphere action on a specific surface.
speed of sound
the rate at which sound travels through a medium.
Cair=343 m/s
depends on the mediums density (P) kg/m3
and stiffness (K) N/m2 (or pascal)
density and stiffness affected by
temperature, pressure, and
molecular composition of medium,
Types of sound sources
Monopole (omnidirectional)
pulsating sphere with a fixed center in space and a radius (r) that varies in periodic patterns
(onion firework)
Types of sound sources
Dipole (bidirectional)
oscillating sphere
a set of two identical monopole sound sources pulsating out-of-phase and separated by a small distance as compared to the wavelength produced by the source.
wavefront
the imaginary line connection leading points (or connecting any other in-phase points) of wave propagating through a medium.
sound field
any area where sound waves are present
a space containing sound waves
pressure crated by sound waves varies throughout the sound field.
sound pressure
acoustic pressure
pressure caused by the vibration the sound source.
the magnitude of change in the local atmospheric pressure caused by the vibrations of a sound source.
Sound pressure (P) = Force(F)/Area (A)
unit is Pascal (Pa) =N/m2
how compressed or rarefied the particles are
particle displacement
indicates how far particles are displaced from their resting position.
particle velocity (v)
the velocity of a oscillating particle
directly related to the kinetic energy of the moving sound
NOT the speed of sound
particle displacement and sound pressure
are out of phase by 90 degrees
sound intensity
the amount of sound power that travels through a specific area of the wavefront surface.
how much sound power is transferred from the sound source to the surrounding area.
Inverse square Law
the farther something gets, the more energy is spread over a greater area and the intensity thus goes down.
*the law that states that in a free sound field the sound intensity is inversely proportional to the square of the distance from the sound source.
taxonomy
a scientific classification system. It divides a larger number of items into different categories in order to organize the items into smaller groups.
bandwidth
rage of frequencies listed from low to high
the frequency range of a sound spectrum defined by a specific drop of sound energy at the lowest and highest frequency of the bandwidth.
octave
doubling of a frequency.
acoustic impedance
the opposition to the flow of sound energy through a medium
amplitude distribution function
the function that represents the relative percetage of time that a waveform magnitude is equal to or greater than a given value
audible sound
a sound that can be heard
auditory signal
a signal that is intended to be heard
complex tone
a sound that has more than one but a finite number of sinusoidal components
compression
a bunching of particles causing an increased density in a medium; reduction of the signal dynamics.
continuous noise
a noise with relatively small fluctuations of levels within a period of observation.
deterministic sound
a sound in which the future behavior can be predicted mathematically or on the basis of previous observations
electromagnetic wave
a wave motion caused by an electric charge traveling through a system; does not require a medium and includes light and radio waves
mechanic wave
the transfer of mechanic energy from one molecule to another.
nonstationary noise
a noise in which the spectrum and intensity change randomly over time and space and in which the average value cannot be reasonably predicted.
overall sound power
the amount of power in the frequency range (bandwidth) of a sound.
plane wave
a wave with a waveform that has a straight surface.
power spectrum density
the average value of the power spectrum in a specific frequency band; that portion of the signal power contained in a 1 Hz wide bandwidth.
power spectrum density level
a logarithmic measure of the power spectrum density in dB in relation to some reference level (10 (-12)power W/m2
pure tone
a tone that has only one frequency component
quadrupole sound source
a sound source consisting of two adjacent and out-of-phase- dipole sound sources.
sound wave
a mechanic longitudinal wave propagating across a matter.
spherical wave
a wave that propagates in all directions in space in the shape of an expanding sphere; the sound wave produced by a monopole sound source.
stationary noise
a random sound that has average acoustic properties that do not vary over time or location in space.
stochastic (random) sound
see noise.
an aperiodic vibration; a complex vibration that consists of energy spread across a range of frequencies rather than consisting of discrete frequency components that are harmonically related; unwanted sound.
surface wave
a mechanical wave motion observed on the surface of water; composed of both transverse and longitudinal vibration patterns.
tone
a sound that has one (pure tone) or a finite (complex tone) number of distinct frequency components.
wave (wave motion)
a change in energy concentration in a medium, which travels across the space.
power spectrum density function
the average amount of sound power across all of the frequencies of the sound.
pink noise
a noise that has spectrum density that is inversely proportional to frequency.
white noise
a noise that consists of an infinite number of sinusoidal components having the same amplitude, but random phase, that are spread evenly across a wide frequency range; a noise that has a spectrum density that is independent of frequency.
