Attenuation is the gradual loss of intensity of any kind of flux as it travels through a medium.

I is the intensity - there is an exponential relationship between the thickness of the material (x) and the reduction in intensity.

ρ is the density of the medium

μ is the attenuation coefficient

- The greater the density - the more attenuation there is. These calculations are done for particular frequencies.

- Sound is the brain's response to the impact of acoustic waves (vibrations) within the human ear. The amount of energy contained in those waves depends on their amplitude. The larger the amplitude the louder the sound. However the ear's response to sound is not equal for all frequencies - so high amplitude waves that are not detected well by the human hearing system will sound quieter than low amplitude ones that are within the range the ear is best tuned to. See frequency response notes.

- Sound attenuation is the conversion of the energy of acoustic waves into heat energy of the medium. All of the vibration is difficult to remove as the medium itslef vibrates. Sound engineers try do 'sound proof' rooms.To remove as much noise as possible they make the waves vibrate the medium they travel through at a frequency outside the range of human perception. If the objects themselves move at a frequency within the range which can be heard, the sound is simply transmitted.

- Most noises are a combination of frequencies it is therefore difficult to make it all go away. The subjective nature of noise complicates attenuation further. One person may not mind low frequency sound but is irritated by high frequencies. Another person may be just the opposite.

- No single material that can attenuate well across the full sound spectrum.

- Most materials are effective at converting only a very limited frequency range (narrow spectrum). If it is thick enough, any material will eventually convert all sound energy to heat. However, achieving effective wide spectrum sound reduction within a limited space requires that different materials be composited together in a compatible manner. These layered materials are called laminates. The types of materials used, the sequence in which they are laminated and the method of construction all determine their effectiveness.

- All sound attenuation materials are a compromise. The compromise may be space, weight, complexity, cost or any combination of factors. For many reasons, what is effective in one situation is not suitable for another. A 25cm thick concrete wall is fine for attenuating sound along a motorway but isn't great for a motorboat! The engineer must decide which soundproofing material is best for which project.