Sabine
The originator of the Sabine reverberation equation. Wallace Clement Sabine, a founder of modern architectural acoustics (1868- 1919). Developed a relationship between reverberation time and the amount

of acoustic absorption in a room. Designed Boston Symphony Hall, considered being one of the best concert halls in the world.

Sine wave
The simplest form of periodic wave motion, expressed by the equation y=sin x, where x is degrees and y is voltage or sound pressure level. All other forms can be created by adding (mixing) a number of sine waves. The wave form of a “Pure tone” is a sine wave.

Sound
A pressure fluctuation, usually in the range of audible frequencies, resulting from a displacement of a gas, liquid, or solid, that can be detected by a mechanical or electromechanical transducer (e.g., a barometer, microphone, or the human ear). Sound propagation as sound waves in gas or liquids or vibrations in solid materials.

Sound absorption
Sound absorption is a material property which describes how well sound waves are absorbed in a material. When a sound wave is absorbed, it simply means that the sound wave is transferred into another kind of energy i.e. heat.
See also sound absorption coefficient.

Sound absorption coefficient
See absorption coefficient

Sound attenuation
The reduction in the intensity or the sound pressure level of sound, which is transmitted from one point to another.

Sound bridge
Analogue to thermal bridges in heat insulation constructions sound bridges transmit sound energy as structure borne sound between two part of a construction, which (besides the sound bridges) are not mechanically connected.
Typical example in building acoustics is the steel studs in double wall constructions (e.g. gypsum wall).

Sound bridges can reduce the sound insulation with many dB’s and be the main transmission path for sound transmission.

Sound insulation
The reduction of sound transmission through a building element.
Sound insulation material: Special material increasing the sound insulation of a construction as e.g. Rockwool.

Sound intensity
Average rate of sound energy transmitted in a specified direction at a point through a unit area normal to this direction at the point considered. Unit, watt per square meter (W/m{sup 2}); symbol, I.

Sound intensity level LI
Sound intensity I expressed as dB value:

LI=10*log(I/Io) dB

The reference value Io=10-12 W/m2 is defined so that the sound pressure

level and the sound intensity level in propagation direction in a free sound field

have the same dB values.

Sound power
The acoustic energy in W emitted from a sound source or transmitted through a defined transmission path (e.g. a duct).

Sound power level
The sound power expressed in dB
Sound power level in dB

Sound pressure
Sound pressure p (or acoustic pressure) is the measurement in Pascals of the root mean square (RMS) pressure deviation (from atmospheric pressure) caused by a sound wave passing through a fixed point. The symbol for pressure is the lower case p. The upper case P is the symbol for power. This is often misprinted. The unit is Pa=Pascals.

Sound pressure level (SPL)
The sound pressure level is the sound pressure p expressed as dB value:
The reference value po corresponds to the average hearing threshold for the human ear.

Sound reflection
See reflection

Sound reduction index R
See also: Rw·R’w:weighted sound reduction index, dB. Acoustic property of a bulkhead / deck (partition) for reduction of air borne noise.

Sound Transmission Class (STC)
A single number rating according to ASTM E413 Classification for Rating sound insulation of the sound transmission loss (sound reduction) similar to the Rw weighting acc. to ISO 717. The STC includes frequencies from 125 Hz to 4000 Hz, the Rw from 100 Hz to 3150 Hz.

Sound transmission coefficient, r
[dimensionless]---of a partition, in a specified frequency band, the fraction of the airborne sound power incident on the partition that is transmitted by the partition and radiated on the other side.

Sound waves
See sound

Specific airflow resistance Rs
According to ISO 9053 the quotient of the air pressure difference across the specimen divided by the linear velocity, measured outside the specimen, of airflow through the specimen.
For a homogeneous material the quotient of the specific airflow resistance divided by its thickness is called the airflow resistivity r.
The airflow resistance is a main product property of porous materials influencing the sound absorption in the material.

Spectrum
In mathematics, physics and signal processing, the frequency spectrum is a representation of a signal or other function in terms of frequency (in the “frequency domain”).
In audio, the frequency range is basically 20 Hz to 20,000 Hz. The frequency spectrum sometimes refers to the distribution of these frequencies. For example, bass-heavy sounds have a large frequency content in the low end (20 Hz- 200 Hz) of the spectrum.
E.g. the spectrum of background noise can be described in octave bands.

Speech intelligibility
A measure of the intelligibility of speech that indicates the ease of understanding speech. It is a complex function of psychoacoustics, signal-to-noise ratio of the sound source, and direct-to-reverberant energy within the listening environment. The intelligibility of speech (usually measured in the presence of noise or distortion) can be measured as Speech Transmission Index STI.

Speech Transmission Index - STI (%)
The measurement method for STI includes frequencies from 125-8000 Hz and results in a value between 0 and 1 which can be interpreted according to following subjective scale. The STI is a local parameter measured between a single speaker point and a single receiver point.

Speed of sound
(Also velocity of sound.) Usually taken as the mean value of the phase speed of an acoustic (or sound) wave. In an ideal, stationary gas the speed of sound c is a thermodynamic property depending only on the equilibrium state of the gas and is given by where is the ratio of specifi c heat capacities, at constant

pressure and volume, respectively; R is the gas constant; and T is absolute temperature.
For normal air, for t=20°C ⇒ c ≈ 340 m/s In water the speed is about 1500 m/s. In solid materials the sound propagation depends on the wave form. For longitudinal waves the speed in m/s is about:
Glass 5,500-6,000
Aluminium, Steel 5,100
Wood 3,400-4,500
Concrete 4,000
Brick 3,600
Ice 3,100
Water 1,500
Mineral Wool 180

Standing waves
A resonance condition in an enclosed space in which sound waves travelling in one direction interact with the refl ections on hard walls travelling in the opposite direction, resulting in a stable condition as a standing wave. Standing waves in a room are characterized by sound pressure maxima in a distance of

half a wave length.

Structure borne sound / noise
As a result of airborne or impact excitation the building constructions are vibrating. The machines standing on or attached to the building constructions cause also vibration of the constructions. The components of vibration in the range of audible sound are called the structure borne sound. Generally they are the propagation of different forms of waves (bending, longitudinal, transversal, etc.), that is the vibrations are also propagating. They reach even rooms where there is no sound source operating. The normal component of the vibrations to the surface of the building constructions is responsible for sound radiation.