A quick lesson in acoustic attenuation
Sound is the result of the disturbance of the eardrum by the impact of acoustic waves (vibration). The amount of energy contained in those waves (amplitude) and the time between the impact of consecutive waves (frequency) determines the strength of the disturbance of the eardrum (volume).
Noise is often thought of as simply being too much volume. While this is one type of noise, there are also others. A particular frequency or combination of frequencies may be low in volume but still be considered noise.
Sound attenuation is the conversion of the energy contained in acoustic waves into heat. This is accomplished by making the waves move other objects at a frequency outside the range of human perception.
Whatever the definitions, most people simply want to make it all go away. Clear enough but not all that easy. The subjective nature of noise complicates attenuation. One person may not mind low frequency sound but is irritated by high frequencies. Another person may be just the opposite.
Why not just reduce all frequencies?
While that is usually the goal, no single material accomplishes this. Most materials are effective at converting only a very limited frequency range. With enough thickness, any material will eventually convert all sound energy to heat. However, achieving effective sound reduction within a limited space requires different materials to be composited together. When constructing these laminates, the type of materials used, the sequence in which they are laminated and the method of construction all combine to determine their effectiveness.
Why are some sound attenuation materials better than others?
All sound attenuation materials are a compromise. The compromise may be space, weight, complexity, cost or any combination of factors. What is effective in one situation is not suitable for another. A 12″ thick concrete wall is fine for attenuating sound along a freeway but isn’t great for a vehicle. Deciding whether to trade performance for cost, or thickness for weight are choices users must make based on their needs.
Many “soundproofing” materials on the market are little more than one or more generic foams glued together with a Mylar facing. Coming up with a superior sound attenuation product requires innovation, research, testing and engineering expertise.
