S : Sound and Vibration Terms, Definitions, Units, Measurements ...
S/N • signal-to-noise ratio
Sabin
Sabine
Sabine Absorption
Sabine Absorption Coefficient
Sabine Reverberation Time Equation
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.
SAW - surface acoustic wave, under
rayleigh waves
Scattering
Schroeder Method for calculating the
reverberation time from the impulse noise decay curve. The
backward curve integration algorithm was developed by Manfred Schroeder at Bell Labs in the nineteen-sixties.
EDT : Early Decay Time based on the impulse decay curve, 0 dB to -10 dB
T10 decay time based on the impulse decay curve, -5 dB to -15 dB
T20 decay time based on the impulse decay curve, -5 dB to -25 dB
T30 decay time based on the impulse decay curve, -5 dB to -35 dB
The
Schroeder Method is also known as
Backward Curve Integration
Second (s) the second, symbol s, is the name of the SI base unit of time.
0.001 s = 1 ms (millisecond) and 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
SEL • sound exposure level
Self-induced Oscillation Definition IEC 801-24-04, a continuing
oscillation that is generated in a system when non oscillatory energy is supplied, also known as
self-excited oscillation
See also other oscillation terms
SENEL • single event noise exposure level
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. Superseded by
real time analysis, these days.
Shear Wave
Shock rapid
transient transmission of mechanical energy.
Shock Pulse Definition IEC 801-24-27, excitation of a system characterised by rise and fall in a time interval short in comparison with the half-period of any
mode of oscillation of the system
Duration of Shock Pulse Definition IEC 801-24-28, time required for the instantaneous value of an excitation to rise from some stated fraction of its maximum value and to decay to the same fractional value
Short Leq
SI Units are the world's most widely used system of measurement units devised around the convenience of the number 10.
There are 7 base units from which other units are derived and therefore known as SI derived units.
SI Unit prefixes are used together with a SI unit to form decimal multiples or submultiples of the unit
Factor | Name | Symbol | Multiplying Factor |
1012 | tera | T | 1,000,000,000,000 |
109 | giga | G | 1,000,000,000 |
106 | mega | M | 1,000,000 |
103 | kilo | k | 1,000 |
10-3 | milli | m | 0.001 |
10-6 | micro | μ | 0.000.001 |
10-9 | nano | n | 0.000.000.001 |
10-12 | pico | p | 0.000.000.000.001 |
Examples: 10-6 g = 1 μg = 1 microgram or one millionth of a gram.
Example of a derived unit: Watt (symbol: W) is the SI derived unit of sound power, equivalent J/s. SI base unit kg·m2·s-3
Sideband in frequency domain functions, pairs of frequencies with similar amplitude that appear equally spaced on either side of a centre frequency - produced by modulation.
Signal-to-Noise Ratio is the difference in
dB between the measured sound level and the
noise floor due to other sources present. Ideally this should be greater than 10dB.
SIL • sound intensity level
SIL • speech interference level.
Simple Sound Source
Sine Wave or Pure Tone characterised by it's frequency (number of cycles per second) or it's wavelength (distance it travels within a period) and the amplitude .
Single Event Noise Exposure Level (SENEL) there are two variations of this term
1:- the dB(A) level which if it lasted for one second would produce the same
A-weighted
sound energy as the actual event.
2:- similar except the start and end of the measurement is defined, usually as 10 dB below the
Lmax
See also • T10 and SEL (sound exposure level)
Single Number Rating (SNR) a single number rating system for hearing protectors. This method requires a C-weighted
average sound level measurement for each 'noise risk' area and the manufacturers SNR figure for the specific protector..
See also other hearing protector procedures
Single Number Rating (SNR) a rating system for duct silencers.
SLM • sound level meter
SNR, see the • Single Number Rating(s) above
Sones a unit to compare the loudness of two sounds.
By definition one sone = 40 phons and also equals 40 dB on the equal loudness contours.
A 10dB increase, from 40 to 50 phons sounds twice as loud, so 50 phons = 2 sones and the following table applies:-
40 phon = 1 sone
50 phon = 2 sones
60 phon = 4 sones
70 phon = 8 sones
80 phon = 16 sones
90 phon = 32 sones ... and so on
Sone Definition IEC 801-29-04, unit of
loudness, equal to the loudness of a
pure tone presented frontally as a
plane wave of frequency 1,000 Hz and a
sound pressure level of 40 dB, re 20 μPa
● Note 1 : the loudness of a sound that is judged by the listener to be n times that of the 1-sone tone is n sones.
Sound Absorption
Sound Absorption Coefficient
Sound Absorption Loss
Sound Analyser under
Spectrum Analyser.
Sound Diffraction
Sound Diffuse Field
Sound Diffusion
Sound Dose
Sound Density under
Sound Energy Density
Sound Energy
Sound Energy Density
Sound Energy Flux
Sound Energy Flux Density
Sound Energy Flux Density Level
Sound Exposure
Sound Exposure Level
Sound Exposure Meter
Sound Fields
Sound Field Quantities •
inverse square law •
particle displacement •
particle velocity •
sound pressure
Sound Flanking under
sound insulation
Sound Flux under
sound energy flux
Sound Insulation
Sound Intensity
Sound Isolation between Rooms under sound insulation, sound isolation
Sound Level
Sound Level Difference under sound insulation, level difference
Sound Level Meter
Sound Level Meter Classes
See also the IEC Definition of Level
Sound Localisation
Sound Particle Acceleration.
Sound Particle Displacement.
Sound Particle Velocity.
Sound Power
Sound Power Absorption Coefficient
Sound Power Density
Sound Power Level
Sound Power Quantity
Sound Power Reflection Coefficient
Sound Power Through a Surface Element
Sound Pressure
Sound Pressure Level
Sound Pressure Reflection Coefficient
Sound Reduction Coefficient under noise reduction coefficient
Sound Reduction Index under sound insulation
Sound Reference Levels
Sound Reflection when a sound wave reaches the boundary between one
medium and another medium, a portion of the wave undergoes reflection and a portion of the wave undergoes transmission across the boundary
See also reflected sound wave
Sound Spectrum Definition IEC 801-21-15, representation of the magnitudes (and sometimes of the phases) of the components of a
complex sound as a function of frequency.
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 Class (STC)
Sound Transmission Loss (STL)
Sound Units : the common unit across the range of sound levels is the
dB (decibel), which is used to compress the immense range of our hearing into manageable numbers.
The SI units for the main individual absolute sound levels are :
Sound Intensity = W/m2 (watt per metre-squared)
Sound Power = W (watt)
Sound Pressure = Pa (pascal)
Sound Velocity Level under
particle velocity level
Sound Volume Velocity under
volume velocity
Sound Waves
Sound Wavelengths
Sound Wave Velocity
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
Spatial Frequency is a measure of how often sinusoidal components of the structure repeat per unit of distance. The SI unit of spatial frequency is cycles per meter.
Specific Acoustic Admittance Definition IEC 801-25-38, reciprocal of the
specific acoustic impedance
Specific Acoustic Resistance Definition IEC 801-25-36, Real part of the
specific acoustic impedance
Specific Energy the energy per unit mass. SI derived unit
J/kg (joule per kilogram).
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 a wave, when multiplied by an appropriate factor, will give the power carried by the wave, per unit frequency, known as the
power spectral density of the wave and is commonly expressed in
watts per
hertz (W/Hz).
Spectral Density Definition IEC 801-21-43, limit as the bandwidth approaches zero, of the mean square value of a field quantity divided by bandwidth. The kind of field quantity must be specified, such as sound pressure, particle velocity, particle acceleration. Also known as spectrum density
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 Leakage
Spectral Lines the number of constant bandwidth lines used in the measurement of spectra.
Spectrum Adaption Term (C and Ctr)
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
Spectrum Density Definition IEC 801-21-43, limit as the bandwidth approaches zero, of the
mean square value of a field quantity divided by bandwidth. The kind of field quantity must be specified, such as
sound pressure,
particle velocity, particle acceleration.
Spectrum Density is also known as
spectral density
Spectrum Density Level Definition IEC 801-22-13, level of the limit, as the width of the band approaches zero, of the ratio of a specified quantity distributed within a frequency band to the width of the band.
● Note 1 : the kind of quantity must be specified, such as by (squared)
sound pressure spectrum level.
● Note 2 : in view of the fact that filters have finite bandwidths, practically the sound pressure spectrum level Lps is obtained for the centre frequency of the band by the formula: Lps = 10 log
10 (p
2/B) ÷ (p
o2/B
o) dB,
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) dB
Spectrum Level under
spectrum density level
Specular Reflection
Speech - Articulation Index (AI)
Speech - Articulation Intelligibility
Speech - Clarity
Speech - Intelligibility
Speech Interference Level (SIL)
Speech Interference Level (SIL3)
Speech Power
Speech Privacy
Speech Transmission Index (STI and STIPA)
Speed, in physics
speed and
velocity are different, they both relate to the distance travelled in time, but
velocity is a
vector quantity and includes information on the direction of travel
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.
The speed of sound (c), wavelength (λ) and frequency (f) are related by the formula c = λ·f
Speed of Sound Definition IEC 801-23-18, magnitude of the phase velocity of a free progressive sound wave
The speed of sound should not to be confused with the sound particle velocity.
Spelling
Spherical Wave
SPL • sound pressure level
SPP • speech privacy potential
square metre (m2) under
metre-squared
square root (√), the square root of a number is a smaller number that, when multiplied by itself equals the original number.
SRI • sound reduction index.
Standard Atmospheric Pressure
Standardized measurement in accordance with a Standard or 'Norm'.
Standardized Impact Sound Pressure Level (LnT)
Standardized Impact Sound Pressure Level (L'nT)
Standardized Level Difference (DnT)
Standard Reference Levels
Standing Wave
Static Pressure Definition IEC 801-21-18, at a point in a
medium the pressure that would exist at that point in the absence of
sound waves.
Static Pressure (symbol ps)
Stationary Signal a signal whose average statistical properties over a time interval of interest are constant. In general, the vibration signatures of rotating machines are stationary.
Stationary signals are either deterministic or random.
Statistical Analysis a calculation performed by a
sound level meter on the noise levels measured during the measurement period to describe the
L10, L90 etc., statistical levels of the noise.
STC • sound transmission class
STI • speech transmission index.
STIPA • speech transmission index for public address systems
STL • sound transmission loss
Stochastic the details of individual events may be unpredictable but the overall character of the sound is. For example rain falling, sound of insects, birds, etc.
Strength of a Monopole
Strength of a Simple Sound Source
Structure-borne Noise, noise caused by the vibration of elements of a structure, the source of which is within a building or structure with common elements, for example poor
impact sound insulation, building services plant, manufacturing machinery and local construction or demolition work.
a significant portion of the transmission path from source to receiver takes place in a solid structure rather than through the air.
Subharmonic Response
Superposition Principle under
Sound Waves.
Surface Acoustic Wave (SAW), under
rayleigh waves
Surface Area
Surface Normal
Surface Wavefront
SVL • sound velocity level, under
particle velocity level
SWL • sound power 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
Symbol of a Quantity Definition IEC 112-01-03, character or combination of characters denoting a quantity.
● Note 1 : a simple quantity symbol is preferably one, or in some cases two, letters of the Latin or Greek alphabets and may include subscripts, superscripts, or other modifying signs. The letters are in italic (sloping) type, using preferably a font with serifs. The subscripts and superscripts are printed either in roman (upright) type, or, when they denote quantities, variables, or running numbers, in italic (sloping) type. Also known as quantity symbol.
See • ISO 80000-1 and IEC 60027-1 for more details and for the combination of symbols.
Symmetry, exact reflection of form on opposite sides of a dividing line, plane or waveform.
Synchronous Averaging under
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
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