Loudspeakers have we really made that much progress since the 1930s?

I personally think technology has Improved for boxed speakers. I had a pair of Linn Isobariks DMS speakers, which were considered up there with the best available back in the 1970's/ 80's. Today I think they are bested by the ELAC cheap as chips range. I do not know what has changed internally with Klipschorns since they were first thought of by Mr Klipsch in the 30's, but I think my 'new' but old Klipshorns sound rather good to my ears.

Great article by Art Dudley in October Stereophile.  He comes down squarely on the side of the best vintage speakers not having been surpassed or even equalled by modern speakers.

One reason for that sal is that Art doesn’t consider "vowel colorations" (as J. Gordon Holt coined them) particularly bothersome, or very high on his list of priorities in a loudspeaker. I couldn’t disagree more. The first good loudspeaker in that regard, it can be argued, was the Quad ESL, which ironically has not been surpassed!

I can remember puzzling over "vowel colorations" when JGH used that term many eons ago.  I wasn't sure what he meant then, and I really don't have any better understanding now.  Can you explain how you understand it?  It must be something I am not tuned into.

One reason for that sal is that Art doesn’t consider "vowel colorations" (as J. Gordon Holt coined them) particularly bothersome, or very high on his list of priorities in a loudspeaker. I couldn’t disagree more. The first good loudspeaker in that regard, it can be argued, was the Quad ESL, which ironically has not been surpassed!

Midrange naturalness and coherency is indeed a prime trait of the Quads, but there's more to overall naturalness here I find than they can achieve. While in some areas they may be unsurpassed, in others they don't even begin to approach much older designs, and this is true not only with the Quads but indeed most of contemporary loudspeaker designs. However, liking both vintage horn-type speakers and the Quad ESL's doesn't seem out of the question in the view of Mr. Dudley (nor mine):

And let me not miss this opportunity to preach: The Altec Valencia and the Quad ESL are polar opposites. The former is all about touch and impact and drama and the ability to present sonic detail in a musically convincing manner. The latter is about timbre and transparency and spatial relationships and presenting musical detail in a sonically convincing manner. Neither is terribly good at what the other does well. Both are superb, both are listenable, both are fun. Both are valid: I have nothing but respect for the person who chooses either, because either speaker is a window that looks out on at least half of what's going on. And that's more than you can say of most loudspeakers.

http://www.stereophile.com/content/listening-125-page-2#pJ5tiOBSqOagiOgK.97

I'd even preach a merger of sorts between the two is possible with currently built vintage-style all-hornspeakers using modern horn geometries, better cross-overs and cabinetry/materials (actually in the latest Stereophile Mr. Dudley hints at an upcoming review of a pair of speakers combining old and new). These may not yet approach the Quads on their core traits, but I'd wager the midrange from a great compression driver fitted to a well-built and -designed modern horn brings other vital qualities to the table like ease, presence and dynamic capabilities, while maintaining virtues that are not incompatible with stats and not least avoiding "vowel colorations." 

Prejudice still sticks to this old segment of speakers (and their contemporary siblings), or as Art goes about it his latest Stereophile article:

The fact is, contemporary audio consumers are even worse than contemporary audio designers when it comes to letting go of the things they think they know, in an effort to know something new about music playback - something new that is, in fact, very old. Modern designers and modern consumers alike must learn to ignore what they already know in the hope of gaining new ground.

[...]

Some - but far from all - vintage loudspeakers also leave out entire swaths of notes and their overtones. Take, for example, another well-loved Altec drive-unit, the 755. Introduced in 1948 by Western Electric, the 6"-diamter 755 was designed primarily to amplify voices, and so ignores frequencies below 70Hz and above 13kHz. What the 755 does it does with virtually perfect ease and impact and coherence and clarity and touch and nuance and physical presence. But listeners who are spoiled by generations of more modern loudspeakers that play notes from 20Hz to 20 kHz - but with virtually none of the 755's ease, impact and coherence - are usually deaf to the older driver's magic, until such a time as they can jettison musty expectations in favor of fresh ones. New expectations and old products go together nicely.