Acoustics and Lighting Systems: Properties of Sound

Vocabulary flashcards based on lecture notes covering the basic properties of sound, acoustics, frequencies, speed through various materials, and architectural sound phenomena.

Acoustics

A branch of science that deals with the control and propagation of sound.

Objectives of Acoustics

1. To reinforce needed sound; 2. to eliminate unwanted sound; 3. to prevent unwanted sound from being transmitted into an enclosed space.

Sound

A physical wave or series of vibrations originating from a vibrating body, acting as a pressure wave in an elastic medium.

Airborne Sound

A type of sound for which the medium is air.

Structure Borne Sound

A type of sound for which the medium is building materials such as concrete, wood, or glass.

Rarefaction

The instantaneous, local reduction in density of a gas due to the passage of a sound wave, characterized as the elongation of sound.

Frequencies

Vibrations from a body measured in cycles per second ($cps$) or vibrations per second ($vps$).

Sound Waves

The movement resulting from the combination of compressions and rarefactions in the surrounding air.

Masking of Sound

Also referred to as molecular sound, it occurs when a sound is covered up or absorbed by another sound.

Soporific Effect

An effect brought about by a low steady sound, such as White Noise.

Wave Length ($WL$)

The distance between two crests, representing the distance traveled by sound.

Reflection

A property occurring on flat, rigid, and smooth surfaces like walls, ceilings, plastered surfaces, and sandwich panels.

Resonance

The phenomenon that occurs when a vibrating body initiates another body to vibrate in harmony with it, reinforcing sound at specific frequencies.

Frequency and Resonance Relationship

Low frequencies have more resonance than high frequencies because they have longer wavelengths and more multipliers relative to room dimensions.

Speed of Sound in Concrete

$3700\,\text{m/sec}$ or $12,100\,\text{ft/sec}$.

Speed of Sound in Steel

$4900\,\text{m/sec}$ or $16,000\,\text{ft/sec}$.

Speed of Sound in Glass

$5000\,\text{m/sec}$ or $16,400\,\text{ft/sec}$.

Speed of Sound in Aluminum

$5800\,\text{m/sec}$ or $19,000\,\text{ft/sec}$.

Speed of Sound in Air ($22^{\circ}\,C$ / $72^{\circ}\,F$)

Approximately $344\,\text{m/sec}$ or $1130\,\text{ft/sec}$, which can result in architectural defects like echoes and reverberations.

Echoes

Reflected sounds reaching an observer delayed by more than about $0.058\,\text{seconds}$ relative to the direct sound.

Reverberation

A long succession of reflections in a room that continues before the sound dies away to inaudibility.

Inverse Square Law

A principle stating that sound intensity diminishes inversely as the square of the distance from the source increases.