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A covering, usually of insulating material, on pipe or ductsLoudness
The subjective judgement of the intensity of a sound.

Natural frequency

The frequency at which a resiliently mounted mass when set into vibration would vibrate under the influence of gravity alone with no additional forces or constraints.


Solids that reflect light of certain wavelengths, without producing appreciable luminescence these are used in solids and paints to achieve a desired colour.


Chains of molecules formed by the chemical combination of two or more identical combining units called monomers.


Materials suitable for use at high temperatures; usually used for thermal insulating or thermal barriers composed of aluminas, silicas, etc.


The persistence of sound within a space after the source has ceased, due to repeated reflections at the boundaries of the space (walls)

Reverberation time

The time it takes for a reverberant sound of a given frequency to decay by 60dB after the source is cut off.


A means of converting Nox gasses (nitrogen oxides) with the aid of a catalyst into Nitrogen and water. SCR's use ammonia as the reducing agent. This prevents Nox gasses entering the atmosphere where they can combine with cloud moisture to produce the strong inorganic acid – Nitric Acid.

Slag cements

Cements made from blast furnace slag.

Sound Power Level (SPL)

A value equal to 10 times the logarithm to the base 10 of the ratio of total acoustic power emitted by a source to a reference pressure normally 2 x 105 N/m2.

Spray Drying

The production of a solid product by the atomization of a liquid solution into a heated vessel which evaporates the liquid. The dry particles fall to the bottom of the vessel.

White Noise

Noise of a statistically random nature having equal energy at every frequency between set limits.

Wood Pulp

Wood which has been broken down, to a fine powdered substance called pulp through mechanical or chemical processes.