Current amp vs Voltage amp

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.

Bombaywalla,
I appreciate your perspective and input.It does seem the existence of high power SS amps can allow certain speaker faults to be some what masked by applying brute force as a remedy.
Regards,

Charles1dad -- Bombaywalla makes a fair point that many fine speakers have roller coaster impedance and phase angle plots. As I posted above, even the "mighty" Revel Ultima Salon 2's impedance plot is a bit of rock and roll.

OTOH, I think Bombaywalla's comment about me being in "sonic hell" may be a bit extreme. As I also posted above, the ARC Ref 150 and VS-115 amps were bench tested by different labs. Yet the results were consistent. As Ralph and Al explained, the use of NF reduces the output impedance of the amp, thereby making them more amenable to driving speakers with roller coaster impedance and phase angle plots. That is, somewhat SS-like.

Al also made a very important comment that even though the ARC amps FR plots were pretty flat at the speaker input interface, the most important stat is what comes out of the business end of the speaker. In the case of the S8s, they are rated, and have been bench tested to be very flat -- when driven by SS amps.

I surmise that by using the 4 ohm tap on my VS-115, which as Al thinks might reduce the output impedance of the VS-115, the S8's FR output might approach that achieved with a SS amp. Based on my subjective experience, since switching over to the 4 ohm taps, I think the S8s have a tighter bass response and are less forward as compared to using the 8 ohm taps.

BTW, I seem to recall that ARC uses Wilsons to voice their amps.

Bottom line: if I were to switch out my speakers to the Revels, I would probably also switch to a high current/high power SS amp, as recommended by Revel. At least Revel was honest enough to tell the consumer the type of amp that should be used.

P.S. Bombaywalla -- I think it's unfair to imply that the S8s are junk. I have no intention of starting a speaker war, but suffice to say, I think if properly tweaked and set up, they do a very credible job.

Bifwynne,
I have zero interest in any speaker war scenario, we all have our individual taste and there`s no point in taking that any further. I thought Bombaywalla`s opinion on speaker design-engineering choice/compromise was worthwhile and logical.
Regards,

I think that Bombaywalla may, somewhat understandably, have misconstrued Bruce's situation. AFAIK he hasn't had nearly as much interaction with Bruce and his speaker/amplifier concerns as I (and Ralph) have had. Bruce is certainly not in "speaker hell." He's just trying to develop as good an understanding as possible of the speaker/amplifier interface, which is certainly to his credit, and something that is likely to be helpful in the future.

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.

Best regards,
-- Al