Annex C: Glossary

  1. Glossary

    Glossary

    The definitions given below are for the purposes of this document only, and are not intended to be rigorous. Fuller definitions of the various acoustical terms are to be found in the relevant British Standards listed in Annex D.

    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 20354:1993.

    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 material such as mineral wool used to close the gap in a cavity wall.

    Ctr

    The correction to a sound insulation quantity (such as DnT,w) to take account of a specific sound spectrum. See BS EN ISO 717-1:1997.

    dB

    (See decibel)

    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 140-4:1998.

    DnT,w

    A single-number quantity which characterises the airborne sound insulation between rooms. See BS EN ISO 717-1:1997.

    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 717-1:1997. See BS EN ISO 717-1:1997.

    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’). See BS EN 29052-1:1992 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 the direct path.

    Floating floor

    A floating floor consists of a floating layer and resilient layer (see also resilient layer and floating layer).

    Floating layer

    A surface layer that rests on a resilient layer and is therefore isolated from the base floor and the surrounding walls (see also resilient layer).

    Framed wall

    A partition consisting of board or boards connected to both sides of a wood or metal frame.

    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 the frequency of a sound (formerly called 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.

    Independent ceiling

    A ceiling which is fixed independently of a separating floor or an internal floor (see separating floor and internal floor).

    Internal floor

    Any floor that is not a separating floor (see separating floor).

    Intermediate landing

    A landing between two floors (see also landing).

    Internal wall

    Any wall that does not have a separating function.

    Isolation

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

    Landing

    A platform or part of floor structure at the end of a flight of stairs or ramp.

    LnT

    The impact sound pressure level in a stated frequency band, corrected for the reverberation time. See BS EN ISO 140-7:1998.

    LnT,w

    A single-number quantity used to characterise the impact sound insulation of floors. See BS EN ISO 717-2:1997.

    Mass per unit area

    Mass per unit area is expressed in terms of kilograms per square metre (kg/m²).

    Noise

    Noise is unwanted sound.

    Octave band

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

    One-third octave band

    A frequency band in which the upper limit of the band is 2^1/3 times the frequency of the lower limit.

    Rw

    A single-number quantity which characterises the airborne sound insulation of a material or building element in the laboratory. See BS EN ISO 717-1:1997.

    Resilient layer

    A layer that isolates a floating layer from a base floor and surrounding walls.

    Reverberation

    The persistence of sound in a space after a sound source has been stopped.

    Reverberation time

    The time, in seconds, taken for the sound to decay by 60dB after a sound source has been stopped.

    Separating floor

    Floor that separates flats or rooms for residential purposes.

    Separating wall

    Wall that separates adjoining dwelling-houses, flats or rooms for residential purposes.

    Sound pressure level

    A quantity related to the physical intensity of a sound.

    Sound reduction index (R)

    A quantity, measured in a laboratory, which characterises the sound insulating properties of a material or building element in a stated frequency band. See BS EN ISO 140-3:1995.

    Spectrum

    The composition of a particular sound in terms of separate frequency bands.

    Structure-borne sound

    Sound which is carried via the structure of a building.

    UKAS

    United Kingdom Accreditation Service.

    ΔLw

    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 BS EN ISO 717-2:1997.