Where should I go next? Where are my weak links?

Regarding the question about the impedance match between amplifier and speaker, see Figure 1 in Stereophile's measurements of the speaker, and JA's comments in the paragraph just above the figure.

IMO the wide variation of the speaker's impedance as a function of frequency does NOT necessarily mean that driving the speaker with a tube amp having high output impedance is a problem. It just means that the resulting sonics will vary more widely depending on what amplifier is being used than if the speaker had a flatter impedance curve.

Regards,
-- Al

Some further comments on the amplifier-to-speaker impedance compatibility issue:

It can be calculated that the interaction of the speaker's impedance dip to about 4 ohms at 20 kHz and the amplifier's 2 ohm output impedance will result in a frequency response rolloff of about 3.5 db at 20 KHz. The impedance dip to about 8.5 ohms in the area of 250 Hz will result in a frequency response dip of less than 1.8 db.

Neither number seems to me to be all that large. Furthermore, it seems very conceivable that the speaker was voiced with tube amps in mind, which would mean that its design may anticipate and compensate for those impedance interactions. Note in Figure 5 of JA's measurements, which shows nearfield anechoic frequency response, that the response is shelved upwards by about 3 db in the 10 to 20 kHz region!

The review noted much larger frequency response deviations due to interaction with the output impedance of the Shindo Haut-Brion amplifier they were using. My guess is that the output impedance of that amp is considerably higher than 2 ohms. The review indicated that the Shindo provided only a single output tap, which was nominally rated for use with 16 ohm speakers. That would seem consistent with it having a significantly higher output impedance than most tube amps provide.

Regards,
-- Al

02-26-12: Rauliruegas
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?

Hi Raul,

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