Expert 1000 Pro

[Zappydev]

According to the physics I learned in skool, matt black should run cooler than shiny polished metal ....

There are 3 ways of losing (or absorbing) heat, radiation, conduction and convection.
Matt black, a "perfect black body" is the ultimate for radiant emission or absorption, but at hifi equipment temperatures radiant heat loss is negligibly small, so whilst black would be better it will be infinitesimally better.
The means of heat loss in hifi equipment is conduction from where the heat is generated in whatever active device to the surface of the casing or heat sinks, whence convection whisks it away.

In a Class-A amp where standing dissipation is some hundreds of watts, substantial fins with a considerable area for heat transfer to the air is needed. For Class D (and the Devialet AHD type) where the actual efficiency is high so most of the used power actually goes to the speaker and very little is wasted as heat, the surface area of case needed to dissipate this tiny amount of waste is small. Efficient conduction from the silicon junctions to the case is the important bit.

I understand people's confusion. There is lots of mis-use of terms. In cars (one of my responsibilities was cooling system for Formula 1 car where we had to dissipate over 500,000 watts of heat, a somewhat bigger problem than an AHD amp...) the "radiator" is not actually a radiator (it dissipates heat by forced convection) in the same way the "shock absorber" does not absorb shocks (it is a damper).

Excellent clarification - thank you!