Absorption : The changing of energy to heat which reduces the amount of energy which can be reflected.

Absorption Coefficient: The amount of sound energy which is absorbed at any surface, this can vary with frequency and the angle at which the sound hits the panel.

Acoustics : The science of sound.

Ambient Noise : The background noise in an area or environment, a composite of sound from many sources both near and far.

Amplitude: Amplitude measures a waves magnitude of oscillation or put simply, the magnitude of the maximum disturbance of the medium during one wave.

Audible frequency range: The range of sound frequencies normally heard by the human ear. The audible range spans from 20Hz to 20,000Hz.

Baffle: A free hanging sound absorbing unit used for reduction of reverberation and noise levels.

Bass: The lower range of audible frequencies.

Class 1: Class 1 is a classification for BS 476: Part 7: 1987 (As amended) Classification of the Spread of Flame of Products. This test is intended to measure the lateral spread of flame along the surface of an internal wall or ceiling lining product. The results are expressed as a classification based on the rate and extent of the flame spread. The highest Classification in this test is Class 1.

Class 0: Class 0 is the highest class required in the Building regulations. It is the highest classification for BS 476: Part 6: 1981 Fire Propagation for Products. This test can be carried out in order to assess the performance of internal wall and ceiling linings and give a comparative measure of its contribution to the growth of a fire.

Cycles per Second: The number of oscillations which occur in the time frame of 1 second.

Damp: To cause a loss or dissipation of vibrational energy in solid media and structures.

Decibel (dB): The standard measure of loudness. dB is a ratio of two quantities on a logarithmic scale.

dB(A): The frequency response curve which resembles the normal frequency hearing curve for most people.

Diffraction: A change in the direction of propagation of sound energy caused when a sound wave encounters an obstacle or an abrupt change in a surface.

Diffusion: The scattering of random reflections of a sound wave from a surface. Diffusion can create a sensation of sound coming equally from all directions.

Echo: An echo happens when a reflected sound produces a distinct repetition of an original sound.

Flame Spread: The measure of the time it takes for a flame to spread across a surface.

Flanking Transmission: Transmission of sound from a source to a receiving location through the adjoining parts of a structure.

Flutter Echoes: Flutter echoes often occur in long narrow spaces with parallel walls. They are short echoes produced in small reverberative spaces.

Frequency: The rate at which sound pressure varies.

Hertz (Hz): Frequency of sound. The same as cycles per second.

Helmholtz Resonator: Also referred to as a narrow cavity absorber. These resonators are usually some form of cavity in a rigid structure with a narrow neck to the outside air. These absorbers can have a perforated cover or slats over a cavity.

Isolate: A dampening mechanism made as part of an assembly or system, which reduces structure borne vibrations from passing through to a neighbouring area.

KHz: Frequency in thousands e.g. 1 KHz = 1,000Hz

Loudness: A subjective judgement of the intensity of a sound.

Noise: Unwanted sounds which a listener does not wish to hear.

Noise Reduction (NR): The difference in sound pressure level between any two points along the path of sound propagation.

Noise Reduction Coefficient (NRC): The arithmetic average of the products sound absorption coefficient measured over four octave bands.

Octave: An octave is a doubling or halving of frequency.

Pitch: The perceived frequency of a tone.

Reactive absorber: An absorber which involves the effect of mass and compliance as well as resistance.

Reflection: Sound is reflected just as light is with the angle of incidence equalling the angle of reflection.

Refraction: The bending of sound waves when they cross a boundary of layered material with different sound velocities.

Resonance: A reinforcement of sound due to echoes adding in phase with the original source.

Resonant frequency: The frequency at which resonance exists.

Reverberation: The persistence of sound which one hears after the original sound has ceased.

Reverberation Time: The time taken for a sound to decay by 60 decibels once the original sound has ceased.

Sabin: A unit of sound absorption based on a one square foot of material.

Sabine: The originator of the Sabine reverberation equation.

Sound: Sound is a vibrational disturbance which caused vibrations in the air which in turn caused vibrations in the ear drum.

Sound Absorption Coefficient: This measures the absorptive property of a material. Ideally, the majority of the energy is absorbed and then the rest is reflected.

Sound Attenuation: The reduction in intensity of a sound signal.

Sound Insulation: The capacity of a structure to prevent sound from reaching a receiving location.

Sound Transmission Class (STC): A single number rating system which represents the sound transmission loss of a wall.

Sound Transmission Loss (TL): The reduction of magnitude of sound between two locations.

Sound Waves: Sound travels in waves, the length of the wave is determined by the frequency and amplitude or volume determines the height of the waves.

Speech Intelligibility: The ability for a listener to understand speech clearly, this can be particularly problematic in classrooms and other teaching environments.

Wavelength: The distance a sound wave travels to complete one cycle.