Tube Watts vs. Solid State Watts - Any credence?

The manufacturer recommends 50-180 watts and received wisdom seems to be that the speakers respond better to solid state watts (what does that mean)?
Mikey8811

I've not looked at the Vienna Acoustics Kiss speaker impedance & phase plots but if this is the wisdom that has been imparted to you then it would mean that the VA Kiss has some wild impedances & phase angles in the bass region where the actual impedance is quite low where a tube amp would have difficulty sourcing large amounts of current to have a controlled bass response. In such a case a s.s. amp would do better esp. if it can double down for each halving of the load impedance. This would be an expensive s.s. amp since it would have a very robust power supply. Heavy chassis, heavy power xformer, large heatsinks, high cost but it would give you a tight bass response while a tube amp would give you flabby bass response unless you spent $$$ to get a large tube amp.

10-09-15: Djfst
High end audio is definitely tricky. For example, I'm running a Primaluna Dialogue HP Integrated Amp with EL34 tubes to Sonus Faber Olympica III Speakers which are 91db efficient and are 4ohms rated according to specs. The Primaluna has 4ohm taps and 8ohm taps, and the 4ohm speakers sound far better on the 8ohm taps.

I found your speaker measurements here:
http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1285:nrc-measurements-sonus-faber-olympica-iii-loudspeakers&catid=77:loudspeaker-measurements&Itemid=153
if you scroll down & look at the 2 plots "impedance magnitude variation" & "phase angle" you can see that this speaker has capacitive phase angles in the bass region to, oh, ~150Hz. The impedance is complex i.e. has a x+jy sort of form. So, the real part of the speaker impedance into the power amp is delivering current is not 4 Ohms as printed on the back of the speaker but less than 4 Ohms due to the capacitive (reactive) phase angle. So, any power amp would be asked to deliver more current than originally thought (since you are thinking it's a 4 Ohm speaker) & this can tax the power amp.

When you connect your SF to the 8 Ohms tap, the power amp is being asked to deliver more current into the lower (4 Ohms) speaker impedance compared to when you have it connected to the 4 Ohms tap. The higher current delivered yields a better bass response.
The plots show the speaker is mostly inductive in the 150Hz-2.5KHz. So, when high voltages are present in the mid-bass-to-mid-range little current is asked from the power amp due to this inductive impedance nature of this speaker in this region (the math omitted deliberately). And, in the high-freq even tho the speaker become capacitive there is not much energy in those frequencies so the power amp is not taxed much.
So, it seems to make sense that this SF speaker would sound better on the 8 Ohms tap.

Bombaywalla, as you probably know, my amp is the ARC Ref 150 SE. I mention this because ARC designed my amp, and indeed, most of its tube amps, using NFB. In the case of the Ref 150 SE, I believe the NFB stat is 14 db.

Ralph has written quite a bit about the negative trade-offs of using NFB. Do you consider 14db to be "a lot of global negative feedback"??

FWIW, ARC describes its Ref 150 circuit topology as follows:

"Output stage coupling is a combination of “ultralinear” and Audio Research’s patented “partially cathode-coupled” topology, which is superior to conventional pentode or triode operation."

Whatever that means. :) LOL

10-10-15: Inna
I don't remember where but once I read that someone was comparing the sound of 100 wt Gryphon with 600 wt Krell, both transistor amps. Same speakers,forgot what that was. Besides sounding a lot better in every respect, Gryphon also sounded more powerful. Dynamic speakers, this I remember.
What are the possible explanations?

Impossible to tell without knowing how the testing/comparison was made... My guess is they did not level match, or make quick switches between components - the two main factors that our senses need, in order to make a proper evaluation...

Bombaywalla, I just caught your post re the Soundstage measurements of the SF speaker. I surmise that you would agree with the general view of many that when deciding on a tube amp's output taps to use for a particular speaker, that one should use the taps that sound best to that person's ears.

That said, if I was asked to guess what would be the best output tap selection for the SF speakers based JUST on graphs and NOT ears, I might have guessed the 4 ohm taps would be optimal. Here's why.

Btw, I assume the SFs were voiced to be driven by a SS amp. I also tracked down a J Atkinson bench test report of the Prima Luna HP amp. JA's output impedance measurements are pretty typical: 4 ohm taps (between 1.1 and 1.3 ohms); 8 ohm taps (about double the 4 ohm taps).

First off, the SFs are moderately sensitive. Soundstage reports 88.3 db. That bodes well when worrying about driving speakers with rough impedance and phase angle plots in the bass frequencies.

Second point. As JA reports, the amp's output voltage will vary with speaker load because of the amp's "high'ish" output impedance. Presumably, the amp's output voltage should vary less off the 4 ohm taps because output impedance is half that of the 8 ohm taps.

Third point. The Soundstage report shows that SF's FR drops off pretty sharply below 70 or 80 Hz. I suspect that the owner may be using a self powered subwoofer. If so, my reactions are even more on point.

Fourth point. The Soundstage report also shows that the SF's impedance ranges between 3 and 5 ohms between 50 and 100 Hz. In addition, the SFs are mildly capacitive (neg. 23 degrees or so) in that frequency range. Could be worse. Further, speaker impedance stays at 5 ohms or below up to 1000 Hz.

Conclusion. All in, my guess ... based JUST on the numbers ... is that the 4 ohm taps would yield a cleaner sound with less frequency response variation because of the amp's output impedance off the 4 ohm taps. In addition, the back impedance off the primary taps of the output trannies would probably be a better impedance match for the tubes because the amp is asked to deliver most of its power output in the 3 to 5 ohm range.

All the "techno" BS aside, I recommend that the owner of the SFs and the Prima Luna gear should use the taps that sound best to his ears.