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[Stephen Kirby]

Thermal mass.  The more of it, the slower the cooling.  With a wooden cover the magnet was attempting to reach equilibrium with the surrounding air.  With the metal cover the surrounding air was warmer as the plate took time to cool off.

In the PCBA world, the thermal mass of different components substantially complicates the reflow profile used on the in-line ovens used to solder SMT boards.  Smaller scale but same effect.

There's also the ability of something to absorb or radiate heat.  Back in my youth of hot rodding VWs some folks would polish engine parts like the valve covers.  This reduced heat dissipation meant the engines were more likely to run hot or overheat.  Leaving a rough surface meant more radiating area and less internal reflection.  Better yet was painting them crackle black.

Many laptops and such make use of thermal pipes or conduits to get heat from inside the box nearer to an outside surface or some place airflow can be found.  In a speaker this could take the form of copper bars running from the magnet or pole piece to inside a port.  Or the back panel (which does have the disadvantage of absorbing sunlight IR.

[Jeremy Young]

I had a really nerdy post about heat transfer that I decided wasn't worth posting so I deleted it.  I'm glad Stephen didn't hold back.


As my brother-in-law the mechanical engineer would say, technically it's "specific heat capacity" and not "thermal mass" if you really want to split hairs, but I don't haha.

Surface area is great (add fins to your heat sink) but even better if you can put a front on it to make a "chimney" to drive some convection air currents and make it a more active heat dump.  Same way a baseboard heater works (or doesn't work if the front panel is removed). 

Keeping the metal out of direct sunlight would be key, paint it white or maybe a chrome finish would reduce direct solar radiation gains that would otherwise very easily make the metal heat sink hotter than the ambient air temp. Then we'd need to figure out how to keep people from stacking them or cutting themselves on the exposed metal.....sorry to wreck a perfectly good conversation about limiters with thermodynamics.

[ProSoundWeb Community]