Perhaps slightly off topic...
My observation on amps and "difficult" speakers - ie: those with low impedances at some frequencies in the spectrum
With Quad ESL's (63 / 989) - which can be difficult but not overly so... a robust AVR (Onkyo 876 / Integra 70.4) with 140W/ch provided almost as good performance as the Quad 606 140W/ch amps... I thought the Quad amps were better... but would I be able to differentiate them in a blind test? - not sure.
Here is where I move slightly off topic.
Due to the dreaded WAF - I had to find a non planar, more compact speaker solution, and settled on Gallo Ref 3.2 as the most "planar sounding" speaker that met the requirements of WAF....
These speakers can be quite difficult to drive, with bass dropping to 3 ohm, and the tweeter dropping to 1.6ohm.
To sound decent - the amp has to be able to provide the relevant Voltage consistently across the entire frequency range...
140W @ 8ohm is around 95V ... but that same 95V into 1.6 ohm is 705W... and of course buckets of current.
Pretty much any amp can drive an 8 ohm speaker within its rating.
Few and far between are the amps that can maintain that performance when your load drops down below 2 ohm (and for some speakers below 1 ohm !!!)
1st requirement with low impedances.... is that the amp should not overheat, bust into flames and expire ... (some used to do that!)
2nd It should remain stable - depending on design and topology, some amps increase distortion substantially as they struggle down into the low impedances - sound gets nasty, and the nasties spread throughout the frequency range
3rd It should have sufficient power to provide the desired SPL continuous and peak, consistently throughout the frequency range.
Typically, that means 75db continuous with peaks of +20db or 105db SPL at the MLP
You can do various calculations to work out what that means with various amps - but lots of highly regarded amps don't do well under the "difficult speaker" conditions.
In my case - the best value solution has ended up being the Crown XLS series pro amps.
Capable / Rated for 1200W into 2ohm - they easily drive a difficult speaker cleanly. (and they are merely cruising while doing so!)
A 100W AVR - which sounds just fine with "normal" 8ohm speakers, sounded muddy, constrained, veiled into the Gallo speakers.
The big 140W AVR's sounded quite good, the Quad 606 sounded a little better... in this case consistently and noticeably so... but the Crown XLS was consistently better yet - I have experimented back and forth, swapping the options in and out over a number of years... and for these speakers, the Crown XLS remains king.
Could I find alternatives that would meet the requirements set by these speakers and my listening room etc... absolutely... but nowhere near the $250 I paid for a used pro XLS (!) - and they can still be found out there at around that price.
Keeping an eye on amps.... it seems that I would need to look at US$2500 + to match or better what I have at present... and whether it would actually provide an audible improvement is anyones guess.
I believe some panels (Soundlab?) drop down to 0.5 ohm - so the struggle for an appropriate amp is very real indeed!
