Glad Shushu you pointed it out. The LS treble can overstate things easily. But it's also the source of some of the most "airy" space that help in its specificity of the images. The closer gap between speakers creates a holographic space that connects the whole stage together. Almost mono-like stability.
On the excess energy at 1kHz., and this has been reported and explained by no less than Derek Hughes himself of spendor that there is a rise 1-3 dB in the 900-1.2 kHz region when the surround gets weaker over time.
That has been minimized to some extent but still inavoidable despite the change from butyl was it to pvc. The change has resulted in less nasality. A little more neutral less tizzy sweeter treble as well. The terms "bark" (for the bass hump) and "squak" for the treble that some of the drop-in replacements like studio 3 from Rogers and the Harbeth P3es as well as spendor S3/5 have been removed and corrected. As a result, they don't sound like the LS3/5a at all. I can attest to this coz I also own a Rogers Studio 3. The Studio 3 is rated "G" by "HiFi Choice" mag while the LS3/5A is given an "A." No, "A" does not mean excellent. It stands for the rating "average." My JPW P1 even rates better than the LS3/5A!
Yet I find the LS still an expressive speaker on human voice and most instruments of music.
And these are the two most important aspects I think of its design for the broadcast that makes the LS3/5A the "better" tool for the industry. Why it found its way into the homes of people like us is quite another story to tell.
Could it be that most good recordings, the ones that simulate "live" as really "live" come thru easily like it is with the LS3/5A? Even "poor" recordings are being helped in a way that you can still enjoy them specially on most acoustical music. I have a lot of el cheapo Laserlight, Naxos, and some european classical collection that I enjoy immensely on them.
On the "nasality" issue. This appears to me as its own coloration to the sound for the same reason that a more "neutral" sounding speakers may also sound thinner and emaciated. I think the LS3/5A was not designed to sound like most commercial "hifi" speakers out in the market. If that was the only requirement for the BBC's broadcast, there would have been no need for the development of the LS3/5A.