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The measured improvement of impact sound insulation as result of installing a floor covering or floating floor. Result is based on installing on a laboratory test floor to BS EN ISO 717-2:1997

‘A’ Weighting

Frequency dependent weighting based on the human hearing range.


Conversion of sound energy to heat, usually through the use of an acoustic panel or material

Airborne Noise

Refers to a sound that radiates through the air and, if not treated correctly, can pass through partitions. Referred to in documents such as Approved Document E. 


Is a correction value used to adjust measurements associated with airborne noise for site testing, to take in to account low frequency noise when used in conjunction with DnTw. Standard defining this is BS EN ISO 717.

May also be identified by C (A-weighted pink noise spectrum) or Ctr (A-weighted urban traffic noise spectrum).

Decibel (dB)

More commonly shown as dB, the unit for decibel based on the logarithmic scale for sound intensity.

Decibel  (A-Weighted) (dBA)

More commonly identified as dB(A) or dBA, show an expression of relative loudness of sounds in air as perceived by the human ear. A Weighted values are adjusted to show a reduction in low frequency sounds, compared with unweighted decibels, in which no adjustments are made for audio frequency.


Mass per unit volume. kg/m³ for example (kilogram = unit)

Refers to the on-site testing for sound insulation between areas and derived as the sum of all paths, for airborne noise. The main path is normally the separating partition however this measurement also takes into account flanking transmission, widows, ventilation and other junctions within the building fabric. DnTw may need to be corrected for low frequency sound (see +Ctr) Dw relates to the onsite sound insulation and the nT element allows for the normalization of revereberation (allows all sound insulation results to be compared equally regardless of reverberation differences)
Flanking Transmission

Refers to a sound that is transmitted around a partition due to a weakness in how the partitions interact at the junction between one or more of them and includes the effectiveness of how acoustic materials are installed. Flanking noise is included as this can be a potentially major and costly issue to resolve. 


The number of pressure variations (or cycles) per second that gives a sound its distinctive tone. the unit of frequency is the Hertz (Hz)

Hertz (Hz)

Represented by Hz and is the unit representing sound frequency (sound wave oscillations per second). One Hertz (1Hz) equals one vibration per second with audible sources to the human ear ranging from 20Hertz to 20,000 Hertz (20Hz – 20,000Hz)

Impact Noise

Refers to a sound that is transmitted through a partition (relating to floors only) as a result of an impact directly on to the structure and is connected to sound insulation. Impact has been included as a separate entity to Sound Insulation above given that it is referred to in acoustics when looking at floor partitions in all architectural applications. 


The absence of rigid connections between two or more parts of a structure.


Refers to the on-site testing for weighted and standardized impact sound pressure levels between the floor/ceiling construction of a dwelling. See BS EN ISO 717-2:1997

LAeqT (Equivalent continuous sound pressure level)

The average of the total sound energy with A frequency weighting over a specified time period. Commonly used as a descriptor of human perception of sound over time.


Minimum sound pressure levels recorded during the measuring process


Maximum sound pressure levels recorded during the measuring process


Percentile sound pressure level exceeded for 10% of the measuring process, A weighted through statistical analysis


Percentile sound pressure level exceeded for 90% of the measuring process, A weighted through statistical analysis


Daily personal noise exposure dose


Measured exposure to noise over a working week (40 hours, 5 Days)

NCR (Noise Reduction Coefficient)

An average of the sound coefficients across the 250, 500, 1000 and 2000Hz frequency bands. Gives a single figure measurement for how effective a product absorbs sound.


Noise is unwanted sound

Octave Bands

Show the audio spectrum divided in to 10 equal parts and defined in the Iso standards as 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz and 16kHz.

This spectrum can be refined further by sub dividing the audio spectrum in to 33 bands to form third octave bands.

One-third octave bands

A frequency band in which the upper limit of the band is 2.33 times the frequency of the lower limit.

Resilient Layer

A layer that isolates one element from another.


Reverberation (Reverb) is defined as a persistence of sound, that continues after the sound is produced and is often mistakenly described as an echo (which occurs when a pulse of sound can be heard twice).  Reverb is created when sound reflects off of hard surfaces causing numerous reflections that build up and decay as the sound is absorbed by the surfaces of objects within the space.

Reverberation Time

Reverb is measured using a sound meter and predefined noise source to a level where the sound ecays to acceptable levels.

RT60 – How long a sound takes to decay to 60dB (Rt10, RT15, RT20 & RT30 are also options if required)

Tmf – Is the mid-frequency reverberation time produced by taking an average of the 500Hz, 1kHz and 2kHz frequency bands. 


Used in identify the sound reduction value of as single entity when tested under laboratory condiditons. For example 50dB Rrepresents a sound reduction of 50dB

Sound Classification

Is a designation given to how well a material or product absorbs sound energy with A being the best and E being the worst.

Sound Absorption Coefficients

Are measured at set frequencies and represent by a value between 0 and 1 (0 = 0% absorption and 1 = 100%) and is represented by the symbol α.

Sound Insulation

Sound insulation refers to the practice of preventing noise being transmitted from one space to another, ensuring that sound levels in the receiving space are at acceptable levels. Basic sound insulation is the noise level within one space minus the noise level in the receiving room.

Sound Power level SWL, Lw

Sound Power Level (measure of the total power radiated by a source)

Sound Pressure level SPL, Lp

Sound Pressure level (expressed in decibels as measured by a sound level meter)

Sound Reductio Index (R)

Designing effective acoustic solutions

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