Definitions

In this Technical Booklet the following 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 that sound absorption coefficients determined from laboratory measurements may have values slightly larger than one. See BS EN 20354. Absorptive material – material that absorbs sound energy. Airborne sound – sound propagating through the air. 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. Caulking – Process of sealing joints. Cavity stop – a proprietary product or a material such as mineral wool used to close the gap in a cavity wall to control flanking transmission. Ctr – the correction to a sound insulation quantity (such as DnT,w) to take account of a specific sound spectrum. See BS EN ISO 717-1. 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 – the process in which sound that is incident on one side of a building element is radiated by the other side. DnT – the difference in sound level between a pair of rooms, in a stated frequency band, corrected for the reverberation time. See BS EN ISO 140-4. DnT,w – a single-number quantity which characterises the airborne sound insulation between rooms. See BS EN ISO 717-1. DnT,w + Ctr – a single-number quantity which characterises the airborne sound insulation between rooms using noise spectrum no. 2 as defined in BS EN ISO 717-1. Dwelling – is defined in regulation 2 in Part A of the Building Regulations.