As someone who builds speakers commercially, there aren't any devices that will actually monitor a speaker's temperature. I think what you mean is perhaps, wattage? The speaker's temperature arises from the coil, which is what moves to produce sound. In large speakers, I've seen manufacturers attach some sort of sensors pointing at the moving coil to produce an estimate, but for the speakers used in the Macbooks, they are so thin that this would be a near impossible feat. Maybe Apple uses an estimation from the DSP based on the watts supplied vs time. But, certainly, you cannot attach any sort of device to the coil without making it distort or non-functional.
I know that Apple like to supply the speakers with slightly more power (Watts) than they can deal with to get them loud, but I haven't seen nor heard of this temperature monitoring so far. I couldn't find anything related to it either. Please share citations, if you have.
You're probably right. I looked at Neumann ("Independent soft clip, peak and thermo limiters for woofer and tweeter; Woofer excursion limiter; thermo limiter for the electronics and amplifiers") and Genelec (https://www.genelec.com/key-technologies/protection-circuitr...) for info - as they're the reference in the monitoring world - and my guess is that it's implemented like Apple, via some simulation function from time-integrated wattage and frequency to bool (limit on/off).
Apple isn't the first to use advanced limiters to get the most of loudspeakers, if I remember well, this trick is what allowed Devialet to make the Phantom what it is.
Which is why loudspeaker measurements should _always_ include something like this: http://0x0.st/XG1y.png
I don't know what apple is doing, but in theory, it should be possible to measure ohmic resistance of the coil, and infer temperature via PTC coefficient of coil material. The effect isn't very big at temperature differences you could tolerate in a loudspeaker coil though (~0,5%/K).
I know that Apple like to supply the speakers with slightly more power (Watts) than they can deal with to get them loud, but I haven't seen nor heard of this temperature monitoring so far. I couldn't find anything related to it either. Please share citations, if you have.