Heat transfer in Speaker Enclosures
Another factor to consider when looking at wadding is isothermal propagation. As a sound pressure wave travels through a medium which conducts heat more readily than air (such as most absorbent materials mentioned above), the higher temperature regions lose heat more quickly to the surrounding lower temperature areas. The result is that sound velocity is slower than it is in air (which is a very poor thermal conductor). The condition is termed isothermic. This has a useful effect. The time taken for a sound wave to travel through an absorbent filled enclosure is longer, so the enclosure is effectively larger to the sound wave. Thus the same sonic effect can be achieved from an absorbent filled enclosure, as with a larger one that is unfilled.