Building Utilities 3: Acoustics and Lighting Practice Flashcards

A vocabulary-focused flashcard set detailing technical acoustical terms, formulas, and physical phenomena from the Building Utilities 3 lecture notes.

Absorbing Materials

Materials that dissipate acoustic energy within their structure as heat and/or mechanical energy of vibration, often specifically designed for boundary surfaces of rooms or cavities.

Absorption

The ability of a material to absorb acoustical energy, measured in sabins; defined as the product of area ($s$) and the absorption coefficient ($\alpha$).

Absorption Coefficient (\alpha)

The fraction of sound energy impinging on a surface that is absorbed by that surface.

Acoustics

The science of sound, including its generation, transmission, and effects of sound waves, and the technology of designing spaces to meet hearing needs.

Acoustical Impedance

The resistance to the flow of acoustical energy, measured in rayls at specific frequencies, which is affected by density and fiber diameter.

Airborne Sound

Sound that is transmitted through air by a series of oscillating pressure fluctuations.

Air Column

An air space enclosed on at least five sides which produces sound wave characteristics, such as pipes in a pipe organ.

Amplitude

The maximum displacement of the conductor molecules during each cycle of a sound wave.

Architectural Acoustics

The science and technology of controlling sound in and around buildings.

Attenuation

The lessening or reduction of sound level, for example from $80\,dB$ to $70\,dB$.

Complex Tone

A sound sensation characterized by more than one frequency.

Compression

In sound, the concentration of the conductor molecules to produce a high-pitch layer of sound.

Cycle

One complete displacement of a particle.

Damping

Energy dissipation in an oscillating system that prevents a system from oscillating freely.

Decibel (dB)

The basic metric unit for describing the magnitude of sound, calculated as $20$ times the logarithm to the base $10$ of the ratio of the sound pressure to a reference pressure of $0.0002\,dyne\,cm^{-2}$.

Diffuse Sound Field

A sound field in which the intensity of the sound is independent of its direction and sound energy flow is equal in all directions.

Echo

Sound waves which have been reflected back to a listener with sufficient magnitude and time delay.

Flutter Echo

A rapid succession of echoes caused by reflection of sound back and forth between two parallel walls.

Frequency

The number of complete oscillation cycles per unit of time, often measured in hertz ($Hz$).

Fundamental Frequency

The lowest frequency present in a complex tone.

Hertz (Hz)

A measure of frequency equivalent to cycles per second ($CPS$).

Infrasound

Noise of a frequency less than $20\,Hz$, which is below the normal lower audible limit of the human ear.

Intensity (I)

The average rate of sound energy flow per unit area in a direction perpendicular to the area, expressed as $I = \frac{P}{A}$.

Inverse Square Law

A principle stating that under free-field conditions, sound intensity varies inversely with the square of the distance from the source, expressed as $\frac{I_1}{I_2} = (\frac{d_2}{d_1})^2$.

Masking

The obscuring or covering up of one sound by another.

Noise Isolation Class (NIC)

A single number rating derived from Noise Reduction ($NR$) used to rate sound insulation.

Octave

A frequency band whose upper limit is twice the lower limit.

Phon

A unit used to measure loudness level.

Pitch

The subjective attribute of an auditory sensation that enables sounds to be ordered on a scale from low to high frequency.

Pure Tone

A vibration produced at a single frequency, characterized by the period formula $T_p = \frac{1}{f}$.

Resonance

A state in which the forces of oscillation of a system occur at or near a natural frequency of that system.

Reverberation

The persistence of sound in an enclosed space as a result of repeated reflection or scattering.

Reverberation Time

The time in seconds required for a sound level at a specific frequency to decrease $60\,dB$ after the source stops.

Sabin

The unit of measure of acoustical absorption equivalent to a square foot of perfectly absorptive material, named after Wallace Clement Sabine.

Sound Transmission Class (STC)

A single number rating of the sound insulation value of a partition, door, or window.

Sound Transmission Loss (STL)

The difference in decibels of the sound pressure level on the receiver side of a barrier compared to the source side.

Splay

A slight offset in angle (as little as $\frac{5}{8}\,in$ per foot) from a flat plane, used to prevent flutter echoes.

Structureborne Sound

Sound transmission through solid material by means of vibrations or waves in the material.

Threshold of Audibility

The minimum sound pressure level capable of evoking an auditory sensation.

Ultrasonic

Sound above the audible range with a frequency greater than $20,000\,Hz$.

Velocity of Sound in Air

The rate of travel of sound, considered a constant $330\,m/s$ or approximately $1130\,ft/s$ in architectural acoustics.

Wavelength (\lambda)

The distance sound travels during one cycle of vibration, calculated as $\lambda = \frac{v}{f}$.

Presbycusis

The condition of diminished hearing sensitivity attributed to advancing age.

Sociocusis

Permanent hearing damage caused by prolonged and repeated exposure to daily intense sound and noise.

Nosocusis

Hearing loss attributed to sickness (such as mumps), drugs, or accidents.

Tinnitus

A condition characterized by high-pitched ringing in the ears.

Helmholtz Resonator

A volume or cavity resonator consisting of an enclosed body of air connected to the surrounding space by a narrow neck, used to absorb maximum energy in a narrow low-frequency band.

NRC (Noise Reduction Coefficient)

The arithmetic average of sound absorption coefficients at $250$, $500$, $1000$, and $2000\,Hz$, expressed as $NRC = \frac{\alpha_{250} + \alpha_{500} + \alpha_{1000} + \alpha_{2000}}{4}$.

Sabine Formula

An empirical equation for reverberation time: $T = 0.05 \frac{V}{a}$, where $T$ is time, $V$ is room volume ($ft^3$), and $a$ is total room absorption (sabins).

Bass Trap

Acoustic foam elements placed in room corners to absorb low-frequency sound energy and reduce resonance.