Why are low impedance speakers harder to drive than high impedance speakers

Whoa, Ralph, you took my statement out of context. Here is what I actually said:

"Usually it comes down to approach: picking the speaker you love and then finding the right amp or vice versa, or in a fortuitous alignment of skill and circumstance, finding both without significant compromise."

Vice versa means "with the main items in the preceding statement the other way around", thus indicating your approach as one of two alternatives.

To say, as you did, that the first approach (speakers then amp) does not also work is counter indicated by many fine sounding audio systems selected based on that approach.

Best to you Ralph,
Dave

If one did a study of speaker size versus nominal impedance for speakers with good bass extension, I suspect an correlation would be seen between speaker size and impedance. Also a correlation between size and efficiency for certain.

Bottom line is way more people these days prefer speakers with smaller form factors that still do extended bass well to fit into their lifestyle and that puts more demand on the amps to do the work needed. Granted that there is also a motivation for makers to make speakers smaller as well to keep costs down and profits up.

Its much harder technically to get a lot of good sound out of a smaller package than a larger one. It requires higher quality drivers capable of more output with low distortion be designed. A lot of speaker innovation these days revolves around exactly that. Smaller speakers with better sound is the holy grail to a great extent. Some do it much better than others. Granted though it does COST more to make a larger speaker of certain high quality than a smaller one. more of anything always costs more.

Add in that amps are more efficient than ever and can do more work with smaller packages and less electricity and the story is complete.

Lower power tube amps SETs in particular but OTLs and others as well have to rely more on the speakers to pick up the slack and do the work more efficiently. That’s the speakers problem then, not the amps. But all buyers need is for the amp speaker combo together to be up to the task however that is achieved.

So not really a fair thing to judge the world from the perspective of low powered tube amps. Its a different paradigm as Atmasphere accurately refers to it that one can choose from if it fits their needs better, but obviously only a small % of even high end audio enthusiasts choose to go that way for good reason just as some do. Those are the facts. Its nice to have a choice of two different ways to do about things and still get excellent results. One side will never be made to see things the others way. Each is focused on doing things a different way for good reasons. Each approach will have its pros and cons compared to the other but pundits will naturally attempt to stage the comparison in terms favorable to their preferred approach.

Atmashere, the OP said nothing of ESL's. I did make mention of :  "Most typical speakers....".