very interesting to read the Andrew jones post, what struck me most was that speaker was not designed to flat frequency response and danny trying to get a more flatter response will make it sound different than what that speaker was loved for? well then every brand and might every speaker be called to have their own signature sound?
Due to the fact (or it seems) that Danny never creates complete measurements (at least +-90° hor and ver) of loudspeakers or a corresponding loudspeaker simulation for his crossover updates, certain information such as sound power, PIR, DI ... which have actually been standard in the design of loudspeakers for years, sometimes decades, are missing.
I don't have exact data on the said Elac speaker. The original crossover frequency was 2.5-3kHz, which is exactly in the range where the tweeter tends to widen its radiation due to the baffle dimensions and edge diffraction.
Therefore, the high crossover frequency helps to prevent an increase in sound power in this frequency range, and the horizontal radiation will probably be more even.
All this is lost with the low crossover frequency of 1.8kHz that Danny has chosen. If then the frequency response is made as smooth as possible, it is very likely that this results in a extreme widening in the radiation in the range 2-4kHz.
In order for such a speaker not to sound aggressive or unpleasant at high sound pressure levels, you need a heavily damped listening room that suppresses the lateral reflections, as these reflections will have a hump in the 2-4kHz range.
This effect can also be observed very nicely with the X-LS Encore, for example. If Danny had tuned the speaker to the smoothest possible frequency response, then in the worst case it would look like the FR normalized to the axial frequency response.
Normalized horizontal FR Encore
This speaker would be unbearable.
However, Danny did not do that and did not smooth the 1.5dB dip in the 2-4kHz range due to the edge diffraction but left it unchanged.
On-axis FR Encore
This helps to ensure that there is only a slightly increased PIR (and SP) in the 2-4kHz range - yet this is often perceived as too obtrusive or aggressive in a normally damped room.
PIR Encore
Had the crossover frequency been placed around 2.5kHz, as with the Elac, PIR and SP would have been relatively balanced, with a slight dip (due to vertical cancellations) - many find this more pleasant.
In most cases it is not enough to make the on-axis FR smoother in order to achieve a tonal improvement.
The reality is a bit more complex, which is how I would interpret Andrew Jones' statements.