Basic Sinusoidal Vibration and Acoustics Flashcards

50 vocabulary flashcards reviewing essential concepts, formulas, and definitions from the lecture notes on basic sinusoidal vibration, wave propagation, acoustics, decibels, and sound interference.

Brownian motion

The continuous random motion of air molecules.

Static pressure

Pressure created by air molecules that changes due to vibration and is proportional to the density of the molecules.

Density (D)

The number of molecules per unit area, expressed as $\text{mass} / \text{area}$.

Pressure (p)

The force per unit area generated by the movement of air molecules.

Heating air

An action that does not increase air molecule density, but increases air molecule acceleration, resulting in higher pressure.

Energy (E)

The measure of work created by the force generated by the movement of air molecules.

Power (P)

The rate at which work is done, defined by the formula $P = E / T$.

Sound pressure squared (p^2)

In acoustics, a value that is directly proportional to sound power ($P$), energy ($E$), and intensity ($I$).

Vibration

The movement of an object from one point in space to another point, then usually back to the first point.

Inertia

The resistance of an object to any change in its state of motion.

Elasticity

The restoring property of an object to return to its resting state.

Oscillation

A motion in which an object shows regular fluctuation in value, position, and/or state at a mean value.

Wave

A disturbance or oscillation that travels through matter or space, accompanied by a transfer of energy.

Propagation

The transmission or transference of energy through a medium.

Electromagnetic wave

A transverse wave that does not require a medium to propagate.

Mechanical wave

A disturbance traveling in an elastic medium (such as air, glass, or metal) that requires a medium to propagate.

Longitudinal wave

A type of mechanical wave in which particles of the medium move parallel to the direction in which the wave travels.

Compressions (Condensation)

Regions of increased pressure in a wave where molecules are tightly packed together due to the outward motion of the source.

Rarefactions

Regions of decreased or negative pressure gaps in a wave caused by the inward motion of the source.

Transverse wave

A wave in which particles of the medium move perpendicular to the direction in which the wave travels.

Cycle

One complete oscillation of vibration.

Period (Pr)

The time it takes to complete one cycle of vibration.

Range of human hearing

The range of audible sound frequencies spanning from $20\,\text{Hz}$ to $20{,}000\,\text{Hz}$.

Peak amplitude

The maximum distance moved from $0$ in one direction.

Peak to peak amplitude

The total distance moved from the maximum negative position to the maximum positive position.

Root mean square (rms) amplitude

The calculated average distance moved for a complex wave, found by squaring individual amplitudes, taking their mean, and taking the square root.

In phase

A condition in which waves have the same starting phase and their energies combine.

Out of phase

A condition in which waves have different starting phases and their energies cancel each other out, making the sound quieter.

Frequency sweep

A series of sounds in which frequency increases with time.

Amplitude sweep

A sound sweep in which amplitude increases with time.

Wavelength (\lambda)

The distance between compression in one cycle and compression in the next, or rarefaction in one cycle and rarefaction in the next.

Speed of sound (c)

The velocity of sound in air, defined as $350\,\text{meters/sec}$.

10^-16 cm or 10^-12 m

What are the references for intensity 10log()

Decibel (dB)

A unit for expressing the ratio between two sound pressures or powers, equal to $1/10\,\text{bel}$.

20 µPa

the reference pressure for 20log()

Reference power (I_0)

The baseline reference sound intensity defined as $10^{-16}\,\text{watts/cm}^2$ (in cm) or $10^{-12}\,\text{w/m}^2$ (in m).

Starting phase

The initial position of a vibration relative to a reference position, where one complete sinusoid cycle corresponds to $360^\circ$.

Inverse Square Law

The principle stating that sound intensity is inversely proportional to the square of the distance ($r^2$) from the source, dropping by $6\,\text{dB}$ each time distance doubles.

Constructive interference

A condition in which similar points of two waves overlap, producing a final wave with an amplitude larger than the original waves.

Destructive interference

A condition in which opposite points of two waves overlap, producing a final wave with an amplitude smaller than the original waves.

Characteristic impedance

A property of a medium determining how easily sound travels through it or how resistant it is to sound wave transmission.

Nodes

Points of zero displacement in a standing wave where destructive interference occurs.

Antinodes

Points of maximum displacement in a standing wave produced by constructive interference.

Sound shadow

A region of reduced intensity or amplitude created when a sound wave is influenced by an obstacle in the sound field.

Reverberation time

The time required for reflected sound pressure to drop to a defined proportion of its original sound pressure.

Pure tone

A sound that consists of only one single frequency.

Complex sound

A sound containing multiple component frequencies, formed by the addition of simple sinusoids.

Fourier's Theorem

The theorem stating that any time/pressure waveform can be expressed as a sum of sinusoidal time/pressure waveforms.

Fundamental frequency (f_0)

The lowest frequency sine wave component of a complex wave.

Harmonics

The frequencies of component waves in a complex sound that are integer multiples of the fundamental frequency.