TGD E 2014 – 0.1.4.1 – Definitions

0.1.4.1 For the purposes of this document, the following terms and definitions apply: Absorption – Conversion of sound energy to heat, often by the use of a porous material. Absorption coefficient – A quantity characterising the effectiveness of a sound absorbing surface. The proportion of sound energy absorbed is given as a number between zero (for a fully reflective surface) and one (for a fully absorptive surface). NOTE: Sound absorption coefficients determined from laboratory measurements may have values slightly larger than one. Refer to I.S. EN ISO 354. Absorptive material – Material that absorbs sound energy. Airborne sound – Sound which is propagated from a noise source through the medium of air, e.g. speech and sound from a television. Airborne sound insulation – Sound insulation that reduces transmission of airborne sound between buildings or parts of buildings. Air path – A direct or indirect air passage from one side of a structure to the other. Cavity stop – A proprietary product or material such as mineral wool used to close the gap in a cavity wall to minimise flanking sound transmission along the wall cavity. Cavity barrier – A construction provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space (refer to TGD B – Fire Safety). Decibel (dB) – The unit used for many acoustic quantities to indicate the level with respect to a reference level. Density – Mass per unit volume, expressed in kilograms per cubic metre (kg/m3). Direct transmission – Refers to the path of either airborne or impact sound through elements of construction. DnT – The difference in sound level between a pair of rooms, in a stated frequency band, corrected for the reverberation time. Refer to I.S. EN ISO 16283-1. DnT,w – The weighted standardised level difference. A single number quantity (weighted) which characterises the airborne sound insulation between rooms in accordance with I.S. EN ISO 717-1. Dynamic stiffness – A parameter used to describe the ability of a resilient material or wall tie to transmit vibration. Specimens with high dynamic stiffness (dynamically ‘stiff’) transmit more vibration than specimens with low dynamic stiffness (dynamically ‘soft’). Refer to I.S. EN 29052-1 for resilient materials. See BRE Information Paper IP 3/01 for wall ties. Flanking element – Any building element that contributes to sound transmission between rooms in a building that is not a separating floor or separating wall. Flanking transmission – Sound transmitted between rooms via flanking elements instead of directly through separating elements or along any path other than a direct path. Floating floor – A floating floor consists of a floating layer and resilient layer (see also floating layer and resilient layer). Floating layer – A surface layer that rests on a resilient layer and is isolated from the base floor and the surrounding walls (see also resilient layer). Frequency – The number of pressure variations (or cycles) per second that gives a sound its distinctive tone. The unit of frequency is the Hertz (Hz). Frequency band – A continuous range of frequencies between stated upper and lower limits (see also octave band and one-third octave band). Hertz (Hz) – The unit of frequency of a sound (cycles per second). Impact sound – Sound resulting from direct impact on a building element. Impact sound insulation – Sound insulation which reduces impact sound transmission from direct impacts such as footsteps on a building element. Internal floor – Any intermediate floor within a dwelling. Intermediate landing – A landing between two floors (see also landing). Internal wall – Any wall within a dwelling that does not have a separating function. Isolation – The absence of rigid connections between two or more parts

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