Ambient Noise | The totally encompassing sound in a given situation at a given time, usually composed of sound from all the noise sources in the area. |
Background Noise | The steady existing noise level present without contribution from any intermittent sources. The A-weighted sound pressure level of the residual noise at the assessment position that is exceeded for 90 per cent of a given time interval, T (LAF90,T). |
dB | Decibel - The scale in which sound pressure level is expressed. It is defined as 20 times the logarithm of the ratio between the RMS pressure of the sound field and the reference pressure of 20 micro-pascals (20 μPa). |
dB(A) | An ‘A-weighted decibel’ - a measure of the overall noise level of sound across the audible frequency range (20 Hz – 20 kHz) with A-frequency weighting (i.e. ‘A’–weighting) to compensate for the varying sensitivity of the human ear to sound at different frequencies. |
Hertz | The unit of sound frequency in cycles per second. |
LA90 | A-weighted, sound level just exceeded for 90% of the measurement period and calculated by statistical analysis. See also the background noise level. |
LAeq | A-weighted, equivalent continuous sound level. |
LAFmax | A-weighted, maximum, sound level measured with a fast time-constant - maximum is not peak. |
Lden | day-evening-night noise level, the A-weighted, Leq (equivalent noise level) over a whole day, but with a penalty of 10 dB(A) for night-time noise (23:00-07:00) and 5 dB(A) for evening noise (19:00-23:00), also known as the day evening night noise indicator. |
LAE | The A-Weighted, sound exposure level. |
DnT,w | The weighted standardized level difference - The single figure number which characterises the airborne sound insulation performance of a separating element in accordance with EN ISO 717-1 standardized to a reverberation time of 0.5s. |
L’nT,w | The weighted standardized impact sound insulation level – This is the single figure number used to characterize the impact sound insulation performance of a separating floor in accordance with EN ISO 717-2 standardized to a reverberation time of 0.5s. |
RW | Weighted sound reduction index - a single number quantity which characterises the airborne sound insulation of a material or building element over a range of frequencies, based on laboratory measurements |
Reverberation Time | The time taken for the sound pressure level in a room to decay by 60dB after the sound source has been turned off. |
∆Lw | The measured improvement of impact sound insulation resulting from the installation of a floor covering or floating floor on a test floor in a laboratory (See I.S. EN ISO 717-2). |
Absorption | When sound is incident on a surface, a proportion of the sound is absorbed by the surface and a proportion of the sound is reflected off the surface. Sound absorption coefficient outlines the effectiveness of the material at absorbing the sound. Sound absorption coefficient ranges from 0 – 1, 0 representing all of the sound being reflected and 1 representing full absorption of the sound. |
DnT(Tmf,max),w | The SDG 02-05-03 weighted standardized level difference - The single figure number which characterises the airborne sound insulation performance of a separating element in accordance with EN ISO 717-1 standardized to the appropriate Tmf,max of the receive room. |
L’nT(Tmf,max),w | The SDG 02-05-03 weighted standardized impact sound insulation level – This is the single figure number used to characterize the impact sound insulation performance of a separating floor in accordance with EN ISO 717-2 standardized to the appropriate Tmf,max of the receive room. |
Tmf,max | SDG 02-05-03 sets out the acoustic requirements for reverberation time in the mid-frequencies 500Hz, 1000Hz and 2000Hz. Tmf,max describes the upper limit of these mid-frequency reverberation times. |
LAeq,30min | The equivalent continuous sound pressure level averaged over a duration of 30-minute period. SDG 02-05-03 outlines the upper limit for internal ambient noise levels within classrooms in terms of LAeq,30min. |
PPV | Peak Particle Velocity (PPV) is defined as the instantaneous maximum velocity reached by a vibrating element as it oscillates about its rest position and is measured in mm/s. |
VDV | Vibration Dose Value (VDV) is an assessment of the effect of building vibration on the people within. As defined in BS 6472:2008 the VDV is the fourth root of the integral of the fourth power of acceleration after it has been frequency-weighted (as defined in BS6472: 2008). The frequency-weighted acceleration is measured in m/s2 and the time period over which the VDV is measured is in seconds therefore VDVs is cited in terms of m/s1.75. |
Dw | Weighted Level Difference (Dw) a single integer number found by comparing the measured spectrum with the 'standard' curves in BS EN ISO 717 for airborne and impact insulation |
IIC (Impact Isolation Class) | Measures a floor assembly’s ability to absorb impact sound |
Octave Bands | Each octave band includes a frequency range where the upper frequency limit is twice that of its lower limit. I.E 1000Hz octave band contains noise energy at all frequencies from 707Hz to 1414Hz. |
A-Weighting | A-Weighting is a frequency dependent curve which is applied to sound pressure levels to achieve an expression of the relative loudness as perceived by the human ear. |
C-Weighting | C-Weighting is a frequency dependent curve that focuses on the effects of low-frequency sounds. It is typically used for high level measurements and peak sound measurements. |
Z-Weighting | Z-Weighting is the flat frequency response of 8Hz-20kHz (+/- 1.5dB). This displays the true properties of the noise without influence. Z-Weighting is often used for determining environmental noise and octave band analysis. |
LDay | Lday refers to the A-Weighted equivalent noise level (Leq) over the daytime period (07:00-23:00) |
LNight | LNight refers to the A-Weighted equivalent noise level (Leq) over the night-time period (23:00-07:00) |
LW | Sound power is the total energy radiated by a sound source. It is measured in watts (W) |
LP | Sound pressure a logarithmic measure of the RMS sound pressure of sound relative to a reference value. |
Sound Absorption | Absorption is the process of absorptive material taking in the energy of a sound pressure wave, instead of reflecting it away. The absorptive material converts the acoustic energy into heat energy. Sound absorption is a single number rating referred to as the sound absorption coefficient and ranges from 0-1. |
Sound Insulation | Sound Insulation materials are high density, massive materials (15kg/m3). They act as noise reducers by reflecting sound pressure waves away. |
Break-in Noise | Refers to the noise transmission into a building from an outside source. |
Break-out Noise | Refers to the noise transmission out of a building from an internal source. |
Flanking Transmission | Flanking transmission refers to the transmission of sound from a source room to an adjacent receiving room via paths other than the separating partition. |
Sound Reduction Index (SRI) | The SRI is the laboratory conducted measurements of the sound insulating properties of a material or building element. |
Ground Effect | Ground effect refers to the effect that the ground in between the source and the receiver has on the total attenuation. Soft ground provides up to 3dB attenuation over distances of 100m. Attenuation figures are source height and frequency dependant. |
Insertion Loss | Insertion Loss refers to the difference (dB) between the sound pressure level before and after attenuation has been applied. |
Perceived Noise Level | The dB value of the frequency-weighted sound pressure level is determined using a specified method that combines the sound pressure levels across 24 individual one-third octave bands ranging from 50Hz to 10kHz. |
Pink Noise | The definition of pink noise (IEC 801-21-11) refers to noise with a power spectral density that decreases in inverse proportion to frequency. |
Distance Attenuation | Distance attenuation refers to the phenomenon where the intensity of sound decreases as a receiver moves farther away from the sound source. As sound propagates from its origin, it spreads out over a larger area, akin to the expanding ripples on the surface of a pond. |
Resonant Frequency | The resonant frequency is defined as the specific frequency at which an object or system naturally oscillates or vibrates with the greatest amplitude or intensity. It is the frequency that corresponds to the system's natural mode of vibration or resonance. |
Early/First Reflections | Early reflection points, also known as first reflections, refer to the initial direct sound that reaches the listener's ears before the arrival of subsequent reflected sound. When sound propagates, it bounces off various surfaces, including not only the walls on the left and right but also the floor, ceiling, and everything in between. |