Ch 3 Sound and Its Measurement Flashcards
Brownian Motion
The rapid and random movement of air particles. Can be affected by the heat in an environment.
Elasticity
The springiness of molecules in a medium. The greater distance between molecules, the greater elasticity.
Waves
The succession of molecules being shoved together and then pulled apart.
Compressions
Where molecules are pushed together, becoming compressed.
Rarefactions
When molecules are pulled apart, becoming less dense.
Transverse Waves
A wave where the molecular motion is perpendicular to the direction of wave motion.
Longitudinal Waves
A type of wave where the molecules move along the same axis as the wave itself when a force is applied.
Cycle
The time it takes for one wave, which is one compression and one rarefaction, to go by.
Frequency
Cycles per second.
Ocsillation
One cycle of vibration, which starts from any part of a wave and goes to the same part of the next wave.
Sine Wave (Sinusoidal Wave)
A type of wave that takes one oscillation and uses it for a number of mathematical analyses that are important in the study of acoustics. The wave starts at 0 degrees.
Pure Tone
When a body oscillates sinusoidally, showing only one frequency of vibration with no tones superimposed.
Cosine Wave
Same as the sine wave, but instead of starting at 0 degrees, it starts at 90 degrees.
Free Vibration
Vibration that has no outside fore being added to perpetuate the swinging.
Forced Vibration
A vibration that an outside force is added to that controls the vibration, causing it to continue unaltered until the outside force is removed.
Period
The amount of time it takes for one cycle to occur.
Frequency
Frequency = 1/Period
Measured in Hz
Greater mass on an oscillating system
Increase in mass decreases velocity
Compliance
Reciprocal of stiffness. As compliance increases, the frequency at which the body is most easily made to vibrate decreases.
Resonant Frequency
A natural rate of vibration of a mass, which is the frequency at which it is most easily set into vibration and at which the magnitude of vibration is greatest and decays most slowly.
Amplitude
The measurement of a wave from it’s equilibrium point to it’s highest point (crest) or it’s lowest point (trough)
Velocity
The speech with which a wave travels from the source to another point.
Wavelength
A measurement from any point on a sinusoidal wave to the same point on the next cycle of the wave. The formula for determining wavelength is w=v/f. Can also be shown as v=fw or f=v/w.
Phase
When the starting and ending points of cycles from different waves are aligned so that the 0 degree point of each angle is lined up with the other.
Cancellation
When two tones have an identical frequency, but are 180 degrees out of phase with each other. When this occurs, the waves cancel each other out.
Beats
Changes in amplitude which are perceived by the ear as beats.
Complex Wave
A sound that contains a number of different frequencies, amplitudes, and phase relationships.
Fourier first showed that any complex wave can be analyzed in terms of its?
Sinusoidal components
Harmonics
Tones that occur over a fundamental.
Spectrum
A group of harmonics/overtones that starts at the fundamental and increases in frequency in increments of the fundamental. An example is a spectrum with a 100 Hz fundamental. The lowest sound in the harmonic spectrum is 100 Hz, whereas the next is 200 Hz, 300 Hz, etc.
Intensity
How far a body of sound travels
Dyne (d)
A unit for measuring small changes in the force of a sound.
Pressure
A force generated over a surface area
Work
When any mass, such as a group of air particles, is moved
Power
The capacity to exert physical force or energy
Intensity
Intensity (watts/cm^2) = power (watts) / 4pie x radius^2 (cm)
Decibel
A unit of measuring sound intensity. Decibels cannot be simply added or subtracted because they are logarithmic.
Intensity Level Equation
dB(IL) = 10 x log(Io/Ir)
Sound Pressure Level Equation
dB(SPL) = 10 x log(Po^2/Pr^2)
Sound-level meters
A device designated to measure the sound-pressure levels in various acoustical environments.
Hearing Level (HL)
The lowest sound intensity that stimulates normal hearing is called zero hearing level.
Threshold
The threshold of a pure tone is usually defined as the level at which the tone is so soft that it can be perceived only 50% of the time it is presented.
Sensation Level (SL)
The number of decibels of a sound above the threshold of a given individual.
