hi everyone,
I had actually pose my opinion in another article, but I think this subject here is more suited and I wish senior members would share their valuable knowledge & experiences.
We had seen many varieties of impedance coupled with varying phase angles charts, especially from ESL speakers when they behave like a giant cap into high freq.
When some audiophiles describe tubes amp suit well for ESL, we are assuming the tubes would handle the voltage & current needed by the speakers optimally, at a certain range of frequencies. because, generally tubes cannot provide enough high current into magnetic coils when required for high excursion of speaker drivers into low bass and high frequencies due to same reasons too.
Now, I do not know how tubes behave given the ever changing phase angle in relation to impedance,(voltage leads or lags before/after the current), but I suspect that tube can offer more "fluctuation" or "more tolerant" to out of phase signals when required by the speaker to produce music. I believe tubes are naturally more "forgiving"(tubes can give more voltage without rising current) as compared to output transistors when facing these out of phase requirements posed by speakers, especially ESLs. I guess transistors usually have a tighter range to work with electrical signal. transistors are generally linear devices am I right? my bet is that transistors work best when voltage and current are output simultaneously(meaning linear), to provide the power needed by speakers, so if transistors need to work beyond its specification(non-linear, as required by out of phase angle signal), it would clip even before it reaches its full rated power(watt) regardless it is a single or multiple transistors trying to provide power into a given load.
base on above assumption, I perceive that tubes would better suited for ESLs but there are caveats, that's the songs the listener is playing should not contain low bass & high notes i.e. no punching bass, no high pitch like triangles or in harps, electric guitars etc.. (please also bear in mind tubes are slower in response, transistors are faster)
just my two cents