02-26-12: RauliruegasHi Raul,
Now, I can't see clear which your point. Are you trying to say that the Manley is a right amp for those speakers? or are you trying to diminish the impedance mistmatch between Manley and Zu? which your point?
... Trying to match electrical impedances between any other audio links but the amplifier/speakers always is important an almost all of us take care about: I repeat, which the difference with the amplifier/speaker impedanmce matching? why almost all do not care about? which is the explanation behind this audiophile behavior other than ignorance?
I'm not saying that the match is unimportant. Basically what I am saying is that it seems plausible to me that the speaker could be designed to sound its best when driven by a tube amp having significant output impedance, and it may not sound its best when driven by a solid state amp having near zero output impedance.
Speakers having relatively high sensitivity are often designed that way. See Atmasphere's paradigm paper for further background on that.
I certainly agree with you that using an amplifier having a 2 ohm output impedance with this speaker will result in a somewhat different frequency response than using a solid state amplifier having near zero output impedance, as the calculations in my previous post indicated. However, that does not necessarily mean that the frequency response when driven by the solid state amplifier is "better" or more neutral or more accurate, either subjectively or objectively.
The bottom line, putting aside subjective preferences, is what kind of amplifier the speaker was designed and intended to be used with. Some speakers are clearly designed to be used with solid state amplifiers, others are clearly designed to be used with tube amplifiers, and many others straddle the fence.
The likelihood that the Essence is designed to provide good results when used with a tube amplifier is given plausibility by the upwardly shelved top octave that I referred to (that measurement presumably having been taken with a solid state signal source), which will almost exactly cancel the top octave rolloff resulting from the interaction between the speaker impedance and the 2 ohm amplifier impedance. It is also given plausibility by the good sonic results that have been described by the OP and by the Stereophile reviewers, and by the fact that a lot of people successfully use high sensitivity speakers such as the Zu's with tube amps.
Regards,
-- Al