So I was thinking about thermal ‘migration’ patterns and the flow of heat as it shifts ‘directions’ during warm up and how that would affect caps.
As Ted has shown us there can be ‘large’ changes to the amount of capacitance as the cap warms up. But while in the circuit and until a degree of equilibrium has been reached portions of the cap will be at variance with other portions. And as these areas are either being directly heated or are being warmed up by an adjoining area, these thermal effects will cause shifts in the amount of capacitance that will dynamically change.
Which means the ‘steady state’ capacitance that the cap presents to the circuit, won’t happen until thermal equilibrium has been reached.
Convection, radiation, conduction, these 3 types of thermal propagation methods each have unique properties of heat flow and transfer heat differently due to the proximity and the position of the heat source with respect to the location and proximity of the cap itself.
IOW different portions of the cap will heat up at different rates while then conducting that heat to the lower temp areas of the cap, until the cap has reached a degree of internal thermal homogeneity and then stabilizes.
The lead in wires, the outer case of any cap, each will conduct heat at different rates while acting at first as a ‘collector’ of heat to be absorbed into the internal structure of the cap. Not to mention the heat of the air that surrounds the cap, which in itself will contribute more heat as the cap continues to warm up. This changes the internal thermal flow pattern of the cap as its local environment shifts. And then when the cap begins to radiate heat away from itself into it’s local environment, which is a reversal of absorbing thermal energy during its earlier warm up stages, is yet another thermal flow pattern change.
And different types of caps will absorb thermal energy at different rates and in each of the three different ways, and so it goes.
And now apply this to resistors, transformers, inductors, active devices, even to an extent the ‘passive’ components like the circuit boards, the case, the wires, switches etc.
So to me it’s no wonder that we hear differences in the sonic signature as each unit warms up and approaches thermal stability. And why it can be ‘obvious’ when we do reach the optimal thermal equilibrium, since the entire circuit greatly reduces it’s fluctuations in operation, just due to heat migration pattern changes during warmup.
JJ