S/N : Signal-to-Noise ratio the difference between the nominal or maximum operating level and the noise floor in dB
Sampling Frequency the rate at which a continuous waveform is digitised, given in Hz.
Sampling Interval how long the data is measured at each sample point.
Sampling Theorem says that ideally a signal should be sampled at a rate twice its highest frequency component.
Scalar Quantity a quantity fully described by a magnitude or numerical value, for example density, mass and speed. As opposed to a vector quantity which has both magnitude and direction, for example acceleration, force and velocity
Scalar Quantities may be added, subtracted or multiplied like ordinary numbers, vector quantities can not.
Second : s the second, symbol s, is the name of the SI base unit of time.
0.001 s = 1 ms millisecond : 0.000001 s = 1 μs microsecond
Seismic relating to earthquakes or other vibration in the earth
Seismic Reflection the reflection of waves at boundaries between different rock formations
Seismic Refraction the refraction of waves passing through formations of 'earth' having different seismic velocities
Seismic Velocity the velocity of wave propagation in particular ground or rock formation
Seismogram a record produced by a seismograph
Seismograph A measuring instrument for detecting and measuring the intensity and direction and duration of movements of the ground (as in ground-borne vibration) - Certified Seismographs
Serial Frequency Analysis the measurement of octave or third octave bands of noise where a single filter is stepped across the different bands one at a time, suitable mainly for steady noise signals only. Superseded, in the main, by real time analysis.
Shock rapid transient transmission of mechanical energy.
SI Units is the world's most widely system of units devised around the convenience of the number 10.
There are 7 base units from which other units are derived and known as SI derived units.SI Unit prefixes : used together with a SI unit to form decimal multiples or submultiples of the unit
Example 10-6 g = 1 μg = 1 microgram or one millionth of a gram.
Signal-to-Noise ratio the difference between the nominal or maximum operating level and the noise floor in dB
Single Event Noise Exposure Level : SENEL there are two variations of this term:-
Both are similar on the sound exposure level : SEL but we believe the second was developed to take account of single events like aircraft noise where the Lmax is important but the duration should also be taken factored in. An event with a higher Lmax can have a lower SEL than a longer event.
Single Number Rating : SNR a single number rating system for hearing protectors - BS EN ISO 4869
See also : Noise Reduction Rating - NNR used in the USA.
Single Number Rating : SNR a rating system for duct silencers.
Slow Time Weighting - also known as Slow Response and Slow Time Constant.
SNR : see Single Number Rating above
Sones a unit to compare the loudness of two sounds.
Sound any pressure variation that the human ear can detect. Depending on the medium, sound extends and affects a greater area (propagates) at different speeds. In air, sound propagates at a speed of approximately 343 m/s. In liquids and solids, the propagation velocity is greater - 1480 m/s in water and 5120 m/s in steel, for example.
Sound Analyser under Spectrum Analyser.
Sound Flux under Sound Energy Flux
Complex Sound Source, is composed of various sources, multiple frequencies and directivity patterns.
Sound Speed Gradient the speed of sound decreases with decreasing temperature and creates a negative sound speed gradient. An increase in temperature results in a positive sound speed gradient
Sound Transmission passage of a sound wave through a medium or series of media.
Sound Velocity Level under Particle Velocity Level
Spatial Averaging taking measurements at various positions and averaging the results. Mandatory in Sound Insulation measurements and recommended anywhere multiple reflections are present.
See also other types of Averaging
Specific Acoustic Impedance (z) the ratio of the effective sound pressure at a point in an acoustic medium to the effective particle velocity at that point. z = p/v the SI units are Pa·s/m3 or rayls in MKS units.
Specific Noise noise from the source under investigation as defined in BS 4142 Method for rating industrial noise affecting mixed residential and industrial areas. The specific noise is compared to the background noise to assess the likelihood of complaints.
Specific Volume : v the number of cubic metres occupied by one kilogram of the substance : m3/kg.
Spectra is the plural of spectrum
The Spectral Density of the wave, when multiplied by an appropriate factor, will give the power carried by the wave, per unit frequency, known as the power spectral density (PSD) of the signal and is commonly expressed in watts per Hertz (W/Hz).
Spectral Density Limit as the bandwidth approaches zero, of the mean square value of a field quantity divided by bandwidth.
See also : Energy Spectral Density.
Spectral Lines the number of constant bandwidth lines used in the measurement of spectra.
Spectrum the description of a sound wave's resolution into its components of frequency and amplitude.
Spectrum Analyser an instrument to analyse a sound or vibration wave into it's frequency components. A spectrum analyser converts a signal from the time domain into the frequency domain,. The FFT, Octave and 1/3-octave analysers are the most common type today, but there are many other types.
Spectrum Averaging a short term spectrum analysis may include information due to external sources, for example background noise. Repeating the measurements over a longer period and averaging the spectra will cause any random signals to be 'discarded' and your confidence in the measurement will improve.
See also other types of Averaging
where p and po are respectively the given field quantity and the reference quantity; B and Bo are respectively the effective bandwidth of the filter and the reference bandwidth of 1 Hz.
When Lp is the band sound pressure level observed through the filter, the above relation reduces to Lps = Lp - Log10 (B/Bo) dBSpectrum Level is also known as Spectrum Density Level
Speech - Articulation Index : AI
Speech - Articulation Intelligibility
Speech - Intelligibility
Speech Interference Level : SIL
Speech Interference Level : SIL3
Speech Transmission Index : STI and STIPA
Speed of Sound : c ≈ 331.5 + 0.60 T(°C), at 20 °C, the speed of sound in air is approximately 343 m/s and the decrease of speed with temperature is referred to as a negative sound speed gradient. The speed of sound is also dependent, to a minor extent, on atmospheric pressure and relative humidity.
Sound travels faster in liquids and solids. For example the speed of sound in water is 1,480 m/s and for iron 5,120 m/s, these values are also temperature dependent, also giving rise to Sound Speed Gradients.
Speed of Sound should not to be confused with Sound Particle Velocity.
square metre : m2 : Area
square root : √ the square root of a number is a smaller number that, when multiplied by itself equals the original number.
Standard Atmospheric Pressure : atm atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface. Standard Atmospheric Pressure is equal to 101.325 kPa the preferred SI units or 8760 mmHg and 1013.25 millibars.
Standardized measurement in accordance with a Standard or 'Norm'.
Stationary Signal a stationary signal is a signal whose average statistical properties over a time interval of interest are constant. In general, the vibration signatures of rotating machines are stationary.
Statistical Analysis a calculation performed by a Sound Level Meter on the noise levels measured during the measurement period to describe the Statistical Levels Ln of the noise.
Stochastic details of individual events may be unpredictable but the overall character of the sound is. For example rain falling, sound of insects, birds, etc.
Structure-borne Noise a significant portion of the transmission path from source to receiver takes place in a solid structure rather than through the air.
Superposition principle under Sound Waves.
SVL : Sound Velocity Level under Particle Velocity Level
Symbols : The names, symbols and definitions for quantities and units of acoustics are given in BS EN ISO 80000-8 - BSI copyright precludes us publishing any standard. However we can state 'well-known' general facts
See ISO 80000-1 and IEC 60027-1 for more details and for the combination of symbols.
Synchronous Averaging see Time Domain Averaging.
System of Units set of base units and derived units, together with their multiples and submultiples, defined in accordance with given rules, for a given system of quantities - see the SI units above