Thermal Distortion your loudspeaker most likely suffers from it. But do you care?

@atmasphere --

"Back when tubes were king, high efficiency speakers were very common because tube power was (and continues to be) expensive.

When solid state amps were commonplace, speaker efficiency started to go down.

The problem here is that it never helps to have an amplifier drive a speaker that is a difficult load and in particular low efficiency. The result will be higher distortion from the amplifier if nothing else, and that distortion usually manifests as higher ordered harmonics, to which the ear assigns the tonality of 'harsh and bright' and is keenly sensitive to their presence since it uses them to sense sound pressure.

So we've been hearing 'harsh and bright' for 50 years now. Some is the fault of amplifier design of course, but difficult to drive speakers don't help. 

So inefficient and low impedance speakers should be avoided if you want to get the most out of your amplifier dollar investment."

But what makes a speaker a difficult load also and not least involves the effects of passive cross-overs (unless this is implicit to what you're saying here, but it's unclear to me) in terms of their complexity and the (steep) phase angles presented, not to mention smearing of the signal here.

This is interesting due to observations I've made going from passive to active speaker designs (with the same speakers), where I've found going active with solid state amps makes for a sound more akin to the sonic imprinting of SET's; passive sounds more sluggish, heavier even and less resolved (but to some more pleasing this way), whereas active makes for a more transiently clean (less smeared), less grainy and more liquid and open presentation. Easier on the ears, and more fleshed out.

I'd have cherished the opportunity of using 16 ohm versions of the drivers used in my speakers (not least the compression driver, which is available in a 16 ohm version), having then both high efficiency, high impedance and passive filter-less speakers. I would assume though passive filters and their negation to be a similarly or even more important means of making the amp seeing into an easier load, certainly bypassing more complex passive filters. A "purer" low impedance load seems preferable to a higher ditto marred by steep phase angles, but I guess it also depends on the specific amp. 

I only turned it up for a minute!

@johnk actually I am going to walk back may earlier post.

If the crossover or other electronics in a planer speaker are not suffering compression, then it is entirely reasonable for you to have mentioned it.

so it’s a sage post,
 

apologies sir.

Crossover components most certainly can get hot enough for thermal compression to be an issue.  A friend of mine who repairs gear showed me a couple of inductors he took out of a pair of speakers that where played at a really high volume level.  Remarkably, the drivers were not blown, but the plastic formers for the inductors completely melted--what was left was a spool of wire sitting in a pool of plastic.

Can anyone confirm my lay understanding that Zobel Networks do, in fact, have a significant, if not great, effect on the SQ when applied correctly to a speaker?

AKA, “Deulund-Mundorf Ultra Speaker Purifiers” sold on AG.

k