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  • Active acoustics


    Electronically generated background sound of a specified level and frequency content, that is introduced into occupied environments to provide masking of intrusive noises and to enhance speech privacy.


    Alpha w - αw (Weighted Sound Absorption Coefficient)


    A single-number rating for random incidence sound absorption coefficients determined in accordance with EN ISO 11654. With this method measured values obtained in accordance with EN ISO 20354 are converted into octave bands at 250, 500, 1000, 2000 and 4000 Hz and are plotted on a graph. A standard reference curve is then shifted towards the measured values until a 'best fit' is obtained. The derived value of αw will vary between 0.00 and 1.00 but is only expressed in multiples of 0.05 eg αw = 0.65.

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  • Bandraster


    A wider than normal (50-150 mm) exposed grid system, mainly used with lay-in planks, that can be used to define the ceiling module in linear, square or rectangular layouts. Bandraster is also used to provide a location for partition systems.




    BioGuard is a special treatment applied to Knauf Armstrong mineral and metal tiles providing good cleanability, resistant to popular disinfectants and protection against bio-contamination, helping to prevent the build-up of mould, mildew and bacteria.’




    A tile edge detail used with Prelude 24 mm (or Bandraster) visible grid, resulting in a flat ceiling plane.

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  • Clean Room


    A room for research, product assembly or health care where the air quality for dust, lint, or airborne pathogens is critical. Such areas usually have smooth room surfaces to prevent dust collections and air supply systems using HEPA filters to keep dust, lint, etc. to a specified minimum level.


    These minimum levels are categorised into ‘ISO Classes’ from ISO 9 to ISO 1.




    A metal tile edge detail that enables the tile to be clipped into concealed suspension bars with a resulting fully concealed grid appearance but still retaining individual tile demountability and easy access to the void.

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  • Dnfw (Weighted Suspended Ceiling Normalised Level Difference)


    A single-number rating of the laboratory measurement of room-to-room airborne sound insulation of a suspended ceiling with a plenum above it. The rating is determined by test methods conducted to BS EN ISO 140-3:1995 and rated in accordance with BS EN ISO 717-1:1997.


    Some products may have Dncw values published. These are valid although Dnfw, which is essentially the same as Dncw, has superseded it.


    Durability — High resistance to surface damage 


    The ability of a ceiling tile to withstand vigorous cleaning, scrubbing or scratching.

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  • Euroclass


    The harmonised European classification for the fire reaction performance of building materials which may appear (in descending order of importance) as A1, A2, B, C, D, E or F.

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  • Fire Reaction


    Is the surface burning of materials and the rate at which they contribute to the growth of a developing fire within a particular area.


    Fire Resistance


    Is (after the fire has developed) the prevention of the fire from spreading through the building and attacking and destroying elements of the structure.




    The number of times per second in Hertz (Hz) at which sound pressure waves are generated by a source.

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  • Hertz (Hz)


    The unit of frequency measurement. One cycle per second is one Hertz.


    High-Pressure Cleaning


    The use of superior quality fibreglass facing on the Parafon Hygien product means that it can be cleaned using a high-pressure water spray (max 80 bar). The application must be in the form of a fan spray of min 30° and not a high-pressure 'cutting jet'. The suggested minimum distance between the nozzle and the ceiling tile should not be less than 300 mm and the angle of application should be 45°.




    A metal tile edge detail that enables the tile to be hooked onto concealed suspension bars with a resulting fully concealed grid appearance but still retaining individual tile demountability and easy access to the void.


    Humidity Resistance


    A ceiling tile's ability to withstand levels of moisture without sagging. Standard tiles and panels are designed for installation within a normal occupancy condition range of 15 to 35°C and maximum 70% RH. When temperature and humidity resistance are expected to exceed these ranges, the use of 95% or 100% RH products should be considered.

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  • ISO Classes


    These are examples of a classification system for a 'measured environment' known as a cleanroom. It limits the number of particles greater than a specified size within a specified volume of air, as defined by the standard BS EN ISO 14644-1. The levels are measured from ‘ISO Class 9’ to ‘ISO Class 1’ — allowing for the least particles.

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  • Laminated Ceiling Product


    A mineral fibre product with decorative surface laminates such as glass wool scrim or polyester film.


    Light Reflectance 


    Light reflectance of a surface is its property of reflecting light. The measure of light reflectance is that fraction of the specified incident light which is reflected by the surface, expressed as a percentage value.

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  • Main Runner


    The main support element of an exposed tee ceiling suspension system which is hung from the structure.




    An angled, rebated tile edge detail used with Prelude 15 or Interlude HRC grid, minimising the visibility of the exposed grid system.


    MicroLook 90


    A 90⁰ rebated tile edge detail used with Prelude 15 or Interlude HRC, minimising the visibility of the exposed grid system or with Silhouette grid making the face of the grid flush with the face of the tile.


    MicroLook BE


    A 90⁰ bevelled tile edge detail used with Silhouette grid, making the face of the grid flush with the face of the tile, or with Prelude 15 grid.

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  • NRC (Noise Reduction Coefficent)


    A single-number descriptor for random incidence sound absorption coefficients. Defined in ASTM 423 90a, as the arithmetical average, to the nearest multiple of 0.05, of the measured sound absorption coefficients at the four one-third octave band centre frequencies of 250, 500, 1000 and 2000 Hz.

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  • Octave


    A frequency interval wherein the higher frequency is twice the lower frequency.


    Octave Band

    The audio frequency range is generally separated into octave bands as a matter of convenience, wherein each specific band is represented by its centre frequency, e.g. 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, and 16 kHz, which cover most of the audible frequency range.

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  • Perimeter Trim


    A right-angle shaped exposed grid section, either simple or stepped (Shadowline), that is installed around the ceiling perimeter to mask and support the cut edges of tiles and grid.


    Point load


    A load applied to a structure which is concentrated over a very small area. For example, the hangers of an information sign suspended below a ceiling grid, impose point loads where they are attached to it.


    Primary Cross Tee


    A grid element that is perpendicularly inserted into the main runner to space it and form different modules sizes.


    Privacy Index (PI)


    A measure of speech privacy, or lack of speech intelligibility, where the PI is calculated from the Articulation Index (AI) according to the following: PI = (1 - AI) * 100%.

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  • REI


    A European rating that describes three basic criteria for fire resistance as REI and these are defined as:

    - R = load-bearing (capacity to provide structural stability)

    - E = integrity (capacity to remain intact)

    - I = insulation (capacity to maintain a defined temperature on the unexposed side of the building element).

    Depending upon national market legislation and test performance, these letters may also appear as RE or EI and all three combinations will be followed by a number eg EI 30, indicating the minimum time in minutes that protection can or must be maintained.




    The persistence of sound in an enclosure, due to its continued reflection from the surfaces (walls, ceiling, floor, etc.), after the sound source has ceased. Reverberation is of significance in determining the quality and level of sound in an enclosure.


    Reverberation Time


    The time, in seconds, required for reverberant sound in an enclosure to decay to one-millionth (60 dB) of its original intensity after the cessation of the sound source. Reverberation time is frequency-dependent and is normally measured in one-third octave or octave bands.


    Rw (Weighted Sound Reduction Index)


    A single number rating of laboratory measurement of airborne sound reduction index. The rating is determined in accordance with EN ISO 717-1 from measurements made in accordance with EN 20140-3 over the third-octave band frequency range 100-3150 Hz.

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  • Scrubbability / Frequent Cleaning


    For applications where cleanliness is a priority, tiles may require cleaning beyond normal maintenance procedures. Ceilings with special facing material may offer superior performance. Metal ceilings may also be used for these applications.


    Secondary Cross Tee


    A grid element that is perpendicularly inserted into the primary cross tee to form different modules sizes.




    A tile or plank edge detail, with shiplap edges on two opposite sides and used with a concealed 'T' or 'Z' grid section to provide a concealed appearance but still retaining individual tile demountability and easy access to the void.


    Soft Fibre Ceilings


    A mineral fibre ceiling product manufactured with a high proportion of mineral wool and finished with a painted laminated scrim decorative facing. They are therefore more porous and lower in density than 'hard' mineral wool types and this results in tiles with very high sound absorption although their sound attenuation will be moderate.


    Sound Absorption


    The conversion of sound energy into heat (by friction) when passing through or striking a material or when causing a volume of air to resonate.


    Sound Attenuation


    A term used concerning the room-to-room transmission of sound via a common ceiling plenum.


    Sound Insulation


    A general term describing the reduction of airborne and structure-borne sound between separate spaces.


    Sound Masking


    The process by which masking sound is implemented to cover unwanted or intrusive sound (i.e. speech, equipment noise, etc.) and to enhance speech privacy.


    Sound Spectrum


    A representation of a sound wave (time-varying pressure wave) showing the frequency content and amplitude of the sound over the audio frequency range.


    Speech Privacy


    Refers to the lack of speech intelligibility from adjacent talkers. Several levels of speech privacy are defined in the ASTM standards, from Confidential privacy (meaning speech sounds can be heard but not understood), to Normal privacy (meaning that speech can be occasionally heard and understood but is generally non-intrusive), to Poor privacy (wherein all adjacent speech can be heard and understood). These levels can be related to ranges of PI representing each level of speech privacy.


    Structural Fire Protection


    The use of a tested ceiling system to provide additional fire resistance to a floor construction which has inadequate resistance of its own.

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  • Tegular


    Rebated tile edge detail used with Prelude 24 grid systems or Bandraster with Prelude 24 Cross Tees.


    Thermal conductivity (w/mk)


    The ability of the material to resist the transmission of heat through it. The lower the reported number, the better is the thermal insulation provided.

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  • Uniformly Distributed Load


    A load applied to a structure that is evenly distributed across the area where it is maintained. For example, a lay-in ceiling tile imposes a uniformly distributed load along the four flanges of the grid that supports it.

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  • Vector


    A tile edge detail, with grooves along two opposing edges, that is used with a Prelude 24 mm (or 24 & Bandraster) visible grid to provide a 'semi-concealed' appearance but still retaining individual tile demountability and easy access to the void.

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  • Washability / Occasional Cleaning


    Ceiling tiles can be cleaned with moist cloth or sponge damped in water containing mild soap or diluted detergent.


    Wet felt Mineral Fibre Ceilings


    Ceiling tiles or planks manufactured from a combination of the following naturally occurring, processed and recycled materials in varying proportions depending upon the tile type: mineral wool, clay, perlite, cellulose and starch mixed in a water-based process before being cured by heat. They are then finished with a water-based paint, or laminated scrim and paint, decorative facing. Wet felt technology allows considerable variation in the product's density and porosity which can be used to positively influence a wide range of technical performances of the finished products.

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