Current amp vs Voltage amp

Frequency response flatness at the amplifier output/speaker input has no direct relevance. Speakers whose impedance varies significantly as a function of frequency, and that match most optimally with tube amps, can be presumed to require a non-flat frequency response at their input terminals to produce an acoustic output whose frequency response is flat. If such a speaker is mated with a solid state amplifier having near zero output impedance, frequency response flatness will have been optimized at the output of the amplifier, but it will be wrong at the output of the speaker.

hi Al, often it seems that a speaker manuf tries to find an amplifier that has an approximate H^-1(f) transfer function of that manuf's speaker so that the amplifier input-to-speaker output (which is sound) transfer function is more or less flat over the audio bandwidth.
As you would agree this is a very limiting way to design a speaker - change the amp (or another variable) & the performance falls off the cliff....

One of the reasons I chose the Daedalus speakers I have is that their combination of a pretty much flat impedance curve, high efficiency, and high power handling capability makes them suitable for use with just about any amplifier out there...

indeed good qualifications for a speaker to have. Empirically you will find that the people obsessing the least about amplifier-speaker interface are those that have understood the need for the speaker to have a relatively flat impedance & phase (let's not forget that phase response!) curves vs. frequency. Often in these speakers the curve is -3dB at 20KHz which I have been told by certain speaker manufs that this provides better in-room acoustics (vs. a speaker that has no turn-down at 20KHz). Such flat impedance speakers speak about the manuf ability to understand playback requirements & the ability to produce a product that is largely agnostic of the amplifier. Few such speaker manuf exist.....
I heard the Daedalus at RMAF one year - I remember that their sonics were very good. Best regards.

My understanding is that the S8s are ruler flat when driven by a solid state amp.

I doubt that, Bifwynne. With a SS amp, with the output impedance being very low (well into the sub-1 Ohm region), the amplifier is much less perturbed by the roller-coaster impedance & phase response of the speaker. The low output impedance of the amp allows it to sufficient source/sink current into the speaker to give you good sonics & dynamics (assumption is that the power amplifier has a robust power supply that is able to more or less double in wattage for each halving of the speaker impedance). So, the speaker will still have its roller-coaster impedance & phase responses but you will hear less of it with a SS amp.

Perhaps, using the 4 ohm taps lowers the amp's output impedance (maybe .5+ ohms) enough to smooth out the speaker's actual FR to approach a near zero output impedance of a SS amp. Dunno.

No, that's not what happens. The output impedance of a tube amp is dictated by the # of the tubes used in parallel in the output stage & the amount of global negative feedback used by the designer (each & every electronic output device - tube or transistor - inherently has local negative feedback in it. You cannot get away from this local feedback. To quote Nelson Pass in one of his White Papers "show me an electronic device & I will show you the local negative feedback").
Tubes usually have a very high output impedance relative to a speaker hence you have to jump thru some hoops to make a tube amp drive a speaker directly i.e. without output transformers. People like Atmasphere & Berning do that. And, back in the old days there was Harvey Rosenthal (?) who came up with the 1st zOTL amp (I think I'm remembering this correctly??)
The output transformer is put in place between the tube power output stage & the speaker input to buffer the tube amp from the wild swings in the impedance & phase of the speaker.
On the primary side of the output transformer, the tube power output stage sees a constant impedance. By working into a constant impedance, there is optimum power transfer from the tube output stage into the output transformer primary windings load impedance. So, the waters (if you may) are calm/serene.
On the secondary windings side of the power output transformer, the waters are rather choppy due to the speaker impedance & phase variations vs. freq. Several output taps are provided to match the speaker impedance such that there is more optimum power transfer between the secondary windings & the speaker input.
Some speakers are categorized as 8 Ohms speakers by their manuf. Then, use the 8 Ohm tap. Other are categorized at 4 Ohms speakers. Then, use the 4 Ohm tap. Still others are categorized as 6 Ohms speakers by their manuf. In this case, one needs to try both 8 & 4 Ohm taps to see which one is better. For example, the RM10 likes to use the 4 Ohm tap for a 6 Ohm speaker. The way this amp is designed it generates more power into the speaker. (I think I'm remembering this correctly??).
So, changing the output transformer tap merely provides a way to "tune" the power transfer towards more optimum between the tube power output stage & the speaker input. The amplifier output impedance does not change in the way your sentence reads.
FWIW.

The S8s are the darlings of the reviewer community, especially because of the Be tweeters and top grade engineering, R&D and QC that goes into their manufacture.

so what?? are these reviewers your friends i.e. do you trust their judgements & opinions? Do you know them personally? have you been to their house & Listened to their resp. systems? Are their music tastes aligned with yours?
If yes, to all the above questions, then, I would buy what they recommend. Otherwise, it's just a review to be taken with a grain of salt.
Who cares about the Be tweeter, the fit & finish & the QC when the speaker manuf does not possess the fundamentals of speaker design??? Get the physics right then let's talk Be tweeter, the fit & finish & the QC. Otherwise, this is all marketing hype disguised to hide fundamental flaws in the speaker performance as you have found out the hard way. Atleast, this is my take on the matter. YMMV.

Why are there speakers designed with widely fluctuating impedances and steep phase angles in the first place? Why is there not more of an effort to build speakers with flatter impedance curves and gentler phase angles?

IMO, it is because building a speaker with a flat impedance & phase curves requires some serious engineering & knowledge of physics. Not every speaker manuf has that; in fact, most do not. They cover this up with marketing hype - computer-aided design, CNC manuf, lustrous finish, exotic woods, Berrylium & Diamond drivers, blah, blah.
There are several trade-offs in manuf speakers such as on-axis & off-axis response, power handling, sensitivity, resonances, tuning the port, bass overhang, etc, etc. I am no speaker designer expert but I've spoken with a few manuf in the many years I've indulged in this hobby.
Most of these speaker manuf will make certain trade-offs that will yield wild/roller-coaster impedance & phase curves. With the wide availability of class-AB high power power amps, they figure that some amp on the market will drive their speaker. And, coupled with this is the reliance by the speaker manuf that many, many listeners will not know the difference & not know any better. A speaker that is distorting due to impedance & phase mis-management can be sold to these people as one having more "details" in the sound. Also, such speakers have a "wow" factor - hear a demo in the audio store or in-factory. The person is sold & buys the speaker. A little while later you read a "listener's fatigue" post on Audiogon from this person!
This is gradually changing & will force the speaker manuf to wise-up & not output junk designs but the process is slow.
That is why I hear: ARC used to voice their amps with Vandersteen, Avalon with Spectral & MIT cables, B&W voiced with Classe amps & so on. Deviate from this combination & you will be in sonic hell (as Bifwynne! :-)
I'm sure that there are other (better) reasons & I hope that some other more knowledgeable members chime in.

P.S. Bombaywalla -- I think it's unfair to imply that the S8s are junk.

Bifwynne, sorry I never intended to call the Paradigm S8s to be junk. In my post I meant to say that the marketplace is littered with speakers with very mediocre/poor performance. The comment was not intended to single out any one speaker product. I have NO intention of starting a speaker war here; I would like to be very clear on this point.

OTOH, I think Bombaywalla's comment about me being in "sonic hell" may be a bit extreme.

LOL! :-D OK, it might have been.
But, I took my ques from the following statements Bifwynne wrote in his various posts:

I drive a pair of Paradigm S8s (v3) with an ARC VS-115 tube amp. I can't think of a worse match because the S8s have one of the most wacko impedance curve and phase angle plots....

I was feeling a bit down....

If I was to flip speakers, I probably would opt for the Revel Studio 2s, but would need to also flip for a high quality tube amp, maybe the new Ayre VX-5. Dunno???

- there's confusion! He's thinking of flipping equipment. I inferred (now I know incorrectly) that he was hitting rock-bottom w/ his present components.

Bombaywalla, I would add just one point to your IMO excellent list of reasons for the proliferation of speakers having problematical impedance curves. And that is that there seems to be a tendency among many audiophiles to equate the ability of a speaker or other component to resolve hardware differences with its ability to resolve musical information. Thus, if on the basis of reviews, user comments, etc., a speaker acquires the reputation of making amplifier selection particularly critical, it will in the minds of many audiophiles create an expectation that it will resolve musical information and detail better than a speaker for which amplifier selection is less critical. While of course, as this thread makes clear, that is by no means necessarily the case.

well-said Al!
best regards.

Does it truly demand that much more high level engineering expertise to build flatter impedance speakers with better phase angles?

i personally think 'yes'. Empirically, we can all get this info by merely looking at the offerings in the marketplace. How many of the available speakers afford the user the use of a wide range of amplifiers with minimal hit in sonic performance? Each one of these speaker manuf claims to be highly qualified. Are they?

If that's the case then those who are capable of doing this deserve more respect and recognition for their achievement.

indeed they do! they really do as they have 'got' it. These particular speaker manuf rarely toot their own horn as a result they get forgotten & taken over by those who have eye-candy for speakers. IMO.

05-09-13: Charles1dad
Attempting to make tube amps more compatible to drive certain speakers could potentially result in a loss of their instrinsic "sonic attributes".

I think 'yes' if you don't make the tube amp big (& resultingly expensive). This seems to be the opinion of Al & Atmasphere as well. see quote below from Bifynne's post-

tube amp manufacturers will have to figure out a way to make their products able to do double duty and handle speakers that are designed and voiced to be driven by SS amps. Ralph and Al have made a point that such amps are heavy and costly.

For example, TRL (Tube Research Labs) makes a 800W/ch tube amp that can drive an Apogee Full Range speaker:
http://www.tuberesearchlabs.com/products/gt800.htm
no price mentioned. if you have to ask, you can't afford them! ;-)
They also make a 400W/ch power amp which is expensive!
http://www.tuberesearchlabs.com/products/gt400.htm & I believe that this will also drive a Full Range.
Steve Wolcott also makes some high power tube amps (might not be able to drive an Apogee but I'm sure that they can drive other tough speaker loads):
http://www.wolcottaudio.com/WA_presence.htm

yeah, the upshot is that to keep from losing it's tube attributes the tube amp will have to be big, bulky & expensive to drive tough loads.

In the Power Paradigm the box design puts the peak at a lower frequency to take advantage of the extra energy- but again netting fairly flat frequency response, but wiht the additional benefit of bass extension, which might well be up to half an octave.

Atmasphere, what does this mean?
The box resonance peak is where it is. How does the Power Paradigm amplifier move that peak to a lower frequency?
If the resistance in the bass region goes up (due to a box resonance) then the current into that higher resistance goes down. the voltage must go up to keep constant power. Where does the bass extension come from?

A good example is an ESL, whose impedance curve is based on a capacitor. It really works a lot better if the amp makes constant power rather than constant voltage.

I believe that a traditional SS amp (one that was not designed for an ESL in mind) will likely sound mediocre 'cuz of the high capacitance load that will tend to make that amp oscillate & eventually fail. OTOH, if a SS amp is designed with an ESL in mind (& a few names come to mind that are being used successfully with ESLs & planars) then these SS amps will be effective.

The answer here is quite simply, such amps that can drive such loads are usually incapable of sounding like real music, as they have design features that violate human hearing/perceptual rules.

I'm afraid that I do not agree with this either. Again, a few examples come to mind where amps that have been designed to tackle tough-load speakers do sound very musical.
I agree that copious amounts of global negative feedback totally ruin the sonics of the amplifier. However, there are a few manuf who have figured out how to tackle hard speaker loads & yet sound musical.

I believe that a traditional SS amp (one that was not designed for an ESL in mind) will likely sound mediocre 'cuz of the high capacitance load that will tend to make that amp oscillate & eventually fail. OTOH, if a SS amp is designed with an ESL in mind (& a few names come to mind that are being used successfully with ESLs & planars) then these SS amps will be effective.

Belief and reality are usually two different things. In this case I invite you to do the math. How much power will an ideal 400 watt SS amp make into 30 ohms and into 3 ohms? If you answer 'about 100 watts and about 900 watts' then you have some grasp of the problem.

Atmasphere, it was not clear to me what was being referred to. Al cleared that up for me - you were referring to speaker design & not amp design. I figured you were speaking of amp design given your vocation.
The "I believe" part was a way of writing in the English language. Maybe I should have written "I believe it to be true....".

Re. the math problem you cited, yes, I did get those values.
So? The amps I'm thinking of are capable of generating these kinds of wattages & sounding musical at the same time. Indeed that's what I was thinking in the 1st place when I wrote that post.....

But as we saw in the ESL example, the model falls apart.

nah! your ESL example, I think, is a bad one. There are several SS amps manuf that have ESLs in mind & they do sound very good with ESLs. Yes, if you pair a SS amp not designed to take a high capacitative load then it will destructively fail immediately/over time. Your example assumes that one would take a SS amp not designed for high capacitative loads & pair it with an ESL & then complain about the sonics. Give both the manuf of ESL amps & the listener the benefit of doubt that they will be using an ESL amp for an ESL speaker & then compare tube vs. SS power amps for ESLs.
Maybe there is another example that you could cite where the voltage paradigm fails? Thanks.