We should reject hard-to-drive speakers more often

@atmasphere wrote:

The signal itself is the source of dynamic contrast. Loudspeakers only take away from that; if you value dynamic contrast, using a speaker that has the least thermal compression will bring you closer to your goal. In this light, ESLs have the least thermal compression owing to no voice coil at all; a close runner up is higher efficiency loudspeakers [...]

Which only gets you so far being ESL's have the lesser macro-dynamic range compared to horns/high efficiency designs, unless extremely (unrealistically?) large and rid of bass signals. Before thermal compression would ever become an issue with horns, other potential factors like horn material resonance and truncated horn size in the midbass horn in particular would be the primary concerns. While ESL's don't compress per se - and as such some of their implementations can have an advantage over low eff. direct radiating, dynamic driver designs - it's well known that when they limit out they do so abruptly, not least when applied full-range. 

Apogees have a voice coil and so thermal compression is possible.

If we are talking about the original Apogee true ribbon 1 Ohm speakers, this would be news to me.

Technically Atmasphere is correct, they use the aluminum panel as the voice coil, and they still use magnets. I highly doubt that apogee's suffer from thermal compression, the area is much larger to dissipate heat. I listened to a pair of Diva's that were driven by over 2,000 watts and they had effortless dynamics.

Technically Atmasphere is correct, they use the aluminum panel as the voice coil,

That’s just it. They are a panel, not a coil. There’s no "coil" there. They are however electromagnetic instead of electrostatic. In addition, the very large size and direct exposure to ambient temperature makes them behave in an entirely different manner thermally than a tightly wound coil in limited distance between round magnets.

I’m going to go with the Wikipedia article, that specifically calls a voice coil as consisting of a former, collar and winding, as proving these speakers have no voice coil to speak of.  Even if they did, the reasons for thermal compression in actual voice coil speakers can't possibly apply here.

https://en.wikipedia.org/wiki/Voice_coil

If we are talking about the original Apogee true ribbon 1 Ohm speakers, this would be news to me.

Technically Atmasphere is correct, they use the aluminum panel as the voice coil

the reasons for thermal compression in actual voice coil speakers can't possibly apply here.

Hence my use of the word 'possible'... In the case of a magnetic panel speaker like the Apogee, the 'voice coil' for lack of a better term can be heated.  It seems to me that would take some power. If it heats, then less current can be applied because the impedance is higher. That's what causes thermal compression. The thing about thermal compression is that it can happen with individual bass notes; IOW the 'voice coil' is heating and cooling dynamically with the music. If the speaker is using a magnetic principle then this can happen. How much it happens is a different matter.