S

Sabin
The measure of sound absorption of a surface equivalent to 1 ft 2 of a perfectly absorptive material (named after Wallace Clement Sabine, a pioneer in architectural acoustics).

Sabine Formula
A formula developed by Wallace Clement Sabine that allows designers to plan reverberation time in a room in advance of construction and occupancy.

Scattering
An irregular diffraction of sound in many directions.

Signal to Noise Ratio
The difference between the nominal or maximum operating level and the noise floor in dB.

Slap Back
A discrete reflection from a nearby surface.

Sonic Boom
An extremely loud sound of short duration heard at an observation point, produced by a plane (or any other vehicle) that goes past the observation point at a speed greater than the speed of sound.

Sound
Vibrations in a medium, usually in the frequency range capable of producing the sensation of hearing.

Sound Absorption Coefficient
The ratio of sound-absorbing effectiveness (at a specific frequency) of 1 ft 2 of acoustical absorbent to 1 ft 2 of perfectly absorptive material; usually expressed as a decimal value between 1.0 (perfect absorption and 0 (perfect reflection)

Sound Barrier
A material that when placed around a source of noise inhibits the transmission of that noise beyond the barrier. Also, anything physical or an environment that interferes with communication or listening. For example, a poor acoustical environment can be a barrier to good listening and especially so for persons with a hearing impairment.

Sound Control
The application of acoustical principles to the design of structures, equipment, and spaces to permit them to function properly and to create the desired environment for the activities intended.

Sound Intensity (I)
The average rate of sound energy flow through a unit area in a given direction. The unit of sound intensity is watts per square metre (W/m 2 )

Sound Level
A measure of sound pressure level as determined by instrumentation with standardised frequency-weighting characteristics (e.g., A scale sound level in dBA).

Sound Lock
In architectural acoustics, a small space that works as a buffer between a source room and a receiving room. A sound lock is usually connected to the source and receiving rooms with sound retardant doors.

Sound Power
The rate at which sound energy is radiated, expressed in watts.

Sound Power Level
A power expressed in dB above the standard reference level of 1 picowatt.

Sound Pressure
The change in pressure at a point due to sound energy relative to the static pressure at that point without the sound wave.

Sound Pressure Level
A measure of the magnitude of sound pressure on a logarithmic scale; a value equal to 20 times the logarithm to the base 10 of the ratio of a sound pressure o a reference pressure (reference pressure is usually taken to be 2 x 10 -5 N/m 2 ).

Sound Reinforcement
Refers to the beneficial reinforcement of a sound signal provided by sound-reflecting surfaces or by a loudspeaker system.

Sound Transmission
The propagation of sound energy through various media.

Sound Transmission Class (STC)
A rating of the laboratory-derived airborne sound transmission loss data for a structure determined in accordance with the procedure of ASTME E 90 and E 413.

Sound Transmission Loss (TL)
TL of a partition or floor is equal to 10 log (l/t), where t =transmission coefficient of the partition. The unit of TL is dB. TL is a measure of the sound insulation of a partition, and generally varies with the frequency of sound.

Source Room
The room that contains the noise source(s).

Spectrum
The description of a sound wave’s components of frequency and amplitude.

Speech Intelligibility
It is the ratio percentage of discrete speech units correctly recognised by a listener. It is measured by the Speech Transmission Index and denotes the acoustical quality of the enclosed space.

Standing Wave
When sound waves are reflected between two parallel hard reflecting walls, the interference pattern set up between the forward going waves and backward going waves. Standing waves are formed whenever the distance between the walls of an enclosure is an integer multiple of half the wavelength of sound.

Structure-Borne Sound
Sound energy transmitted through solid elements of a building structure.