Acoustics and Sound Wave Fundamentals

Vocabulary practice flashcards covering wave properties, formulas, acoustics, resonance, and tube dynamics from the study notes.

Pressure

Force per unit area, measured in $dynes/cm^2$.

Frequency

The number of repetitions per unit time, measured in Hertz ($Hz$). Calculated as $\text{Frequency} = \frac{1}{\text{Time}}$.

Octaves Up Formula

Formula to find the frequency $n$ octaves above a base frequency ($F_b$): $F_b \times 2^n$.

Octaves Down Formula

Formula to find the frequency $n$ octaves below a base frequency ($F_b$): $F_b \times 2^{-n}$.

Human Range of Hearing

The range of sound frequencies detectable by the human ear, spanning from $20TokHz$ or $20,000TokHz$ ($20TokHz$).

Period

The duration required to complete one full cycle, calculated as $\text{Time} = \frac{1}{\text{Frequency}}$.

Wavelength ($\lambda$)

The spatial length of a wave cycle, given by $\lambda = \frac{c}{f}$, where $c$ is the speed of sound in $m/s$ and $f$ is frequency in $Hz$.

Speed of Sound ($c$)

A constant value of $331.4\,m/s$ at $0^\circ C$, which adjusts by $0.6\,m/s$ per $^\circ C$ of temperature variation.

Threshold of Hearing Reference Point

The standard baseline acoustic pressure level for human hearing, defined as $0.0002\,dynes/cm^2$.

dB SPL Formula

Calculated sound pressure level equation: $\text{dB SPL} = 20 \times \log_{10}\left(\frac{P_x}{P_r}\right)$, where $P_r = 0.0002\,dynes/cm^2$.

Absolute Pressure Level vs. Relative Sound Pressure Level

Absolute pressure is measured directly in $dynes/cm^2$, while relative sound pressure level is measured on a logarithmic scale in $\text{dB SPL}$.

Combining Identical Sound Waves

When two sound waves with the same amplitude are combined, total pressure ($dynes$) remains unchanged, but sound pressure level increases by $6\,dB$.

Damping

The reduction in amplitude of a wave over time caused by resistance or friction (inertia).

Amplitude

The magnitude of displacement of a wave, determined by force applied in the opposite direction, which does not affect frequency.

Phase ($\phi$)

The point reached in a wave cycle measured as an angle in degrees, where $0^\circ$ is the start of a sine wave, progressing through $90^\circ$, $180^\circ$, $270^\circ$, and $360^\circ$.

Sine Wave

A wave shape representing a pure tone consisting of a single, isolated frequency.

Complex Wave

A sound wave composed of a combination of more than one frequency.

Interference

An interaction that occurs when multiple forces act simultaneously on particles of a medium.

Complex Periodic Wave

A wave composed of multiple frequencies that exhibits a discernable, repeating pattern over time.

Complex Aperiodic Wave

A complex wave containing all frequencies within a given range without any discernable repeating pattern (e.g., white noise).

Fundamental Frequency ($f_0$)

The lowest frequency component in a complex periodic wave.

Harmonics

Higher frequency components of a complex wave that exist as whole-number integer multiples of the fundamental frequency.

Sawtooth Wave

A staircase-shaped complex wave where the amplitude of harmonic $n$ is given by $A_n = \left(\frac{1}{n}\right) \times A_1$.

Resonance

An increase in amplitude that occurs when an object or system vibrates at its preferred natural frequency.

Mechanical Resonance

Resonance requiring an external periodic force applied at the correct timing to increase amplitude.

Acoustic Resonance

Resonance involving multiple frequencies that produces a change in the output frequency and amplitude response.

Standing Waves

A wave pattern created when two identical waves with the same frequency move in opposite directions within the same medium.

Nodes

Positions along a standing wave where there is zero particle displacement.

Anti-nodes

Positions along a standing wave where particle displacement reaches maximum amplitude.

Open Tube Resonance

Resonance in a tube open at both ends, supporting all harmonic multiples ($2\times$, $3\times$, $4\times$) with length $L = \frac{\lambda}{2}$ and $\lambda = 2 \times L$.

Closed Tube Resonance

Resonance in a tube closed at one end, supporting only odd harmonic multiples ($3\times$, $5\times$, $7\times$) with length $L = \frac{\lambda}{4}$ and $\lambda = 4 \times L$.