Double down, good or bad?

Magfan, voltage source / current source are Voltage Paradigm terms. A Current Source amplifier is one with a high output impedance. The Power paradigm term for this is 'power amplifier' since such amplifiers attempt to make constant power into all loads rather than constant voltage.

The two approaches require different speaker design considerations! Neither requires a flat impedance curve, but it you want to compare the two types of amplifiers, you need a speaker with a flat impedance curve and an adequate minimum impedance (8 ohms as opposed to 4 for example).

in the case of the B&W 802 you need to have 3 db more power into the 4 ohm woofer load as you do into the mids and highs because the woofers are 3 db less efficient. I am ignoring the effects of feedback here and doubtless there are amps that don't quite double power that can do OK on this speaker.

Atmasphere, it still seems that you have confused the fact that the maximum clipping power of an amplifier is simply not any kind of indicator of its output impedance. And as you well know, as long as a given amplifier is below clipping, it is the output impedance, NOT the maximum clipping power, that determines how much a given (complete) loudspeaker's frequency response will vary simply as a result of its non-linear impedance characteristics.

Incidentally in a loudspeaker design, it is NOT the efficiency and impedance of the drivers that are the biggest factor in determining how much impedance variation there is across the spectrum. In fact, most older (i.e. 1960s) loudspeakers have far more than 3dB efficiency difference between the direct-radiating bass/mid-bass driver(s) and their horn mids and highs. And these are speakers that you would consider to have relatively flat impedance curves, and are very "OTL-friendly".

Rather, it is the relationship of the bass drivers to the cabinet, and the choices made in crossover design, that are the key factors in determining the impedance curve of a complete loudspeaker. Which also of course has nothing to do with Paradigms of Philosophy or Increasing Cheapness on the part of loudspeaker designers, and especially has nothing to do with the Rise of Negative Feedback . . .

It's true that loudspeaker designers over the past several decades have indeed moved toward designs that rely less on mechanical damping within the drivers themselves, and more in the combined behavior of loudspeaker cabinet. But this shift is attributable to the monumentally influential work of the Austrialian A. Neville Thiele in the 1960s, and the continuation/publishing of his work by Richard Small in the JAES in the 1970s - for which we have the equations and parameters that bear their two names. Also hugely important was the work of Edgar Villchur in acoustic-suspension loudspeakers and dome radiators, and the huge advances in materials science . . .

These and many other truly scientific efforts are what we have to thank for the amazingly high level of sound reproduction that we enjoy today . . . so you'll forgive me if I bristle at a crumudgeonly, dogmatic analysis that attempts to force it into those old unsolveable harps of "tubes-vs-transistors" and "feedback=bad".

Sorry Unsound, it's been way too many years since I've had a Threshold amp on the bench, or looked at a schematic of one, to comment intelligently. I seem to remember the Stasis output stage resembling the complimentary-feedback-pair configuration . . . which is pretty similar in behavior to a conventional emitter-follower arrangement . . . but I could be completely wrong.

Magfan, if we're going to actually go down the road on amplifier stability . . . then the main thing is for the designer to accurately analyze the phase margin across the ENTIRE bandwidth of the amplifier - and this can be a challange with one (i.e. the vast majority) that uses a tranresistance amp for voltage gain, as this is the one configuration of a bipolar transistor where the gain is highly beta-dependent. Usually the open-loop gain follows a first-order slope over most of the audio spectrum, making the phase margin 90 degrees into a resistive load. So it's usually a capacitive load that causes the alarming decrease in phase margin, hence the use of an output inductor (and frequently a parallel Zobel network) within the amplifier.

The Power paradigm term for this is 'power amplifier' since such amplifiers attempt to make constant power into all loads rather than constant voltage.

Er, no, unless you're inventing your own terminology here.

A voltage amplifier amplifies voltage, as in a small-signal transconductance stage. A current amplifier amplifies current, as in a cathode- or emitter-follower. So . . . a "power amplifier" amplifies both, as in the output stage of a typical transformer-coupled tube amp.

As a complete device, an audio "power amplifier" of course must amplify both in order to be of much use, hence its name.

Kirkus, you are right in most of your posts and apparently either did not read something somewhere in mine or misinterpreted it. First, I'm not talking about clipping here- at all. I am well aware of the significance of the woofer in the box! The very point of a woofer in the box is that there is a resonance. Voltage paradigm amplifiers ('voltage source' amps) will throttle back their power as they encounter the resonant peak of the box, and so not exacerbate that resonance. That is the basis of the theory of the idea of making an amp that is a 'voltage source'.

Maybe you missed the link, so here it is again:
http://www.atma-sphere.com/papers/paradigm_paper2.html

Before the Voltage paradigm was proposed (MacIntosh and EV were two proponents in the 50s and 60s) the Power paradigm was the only game in town. I have had to create the terms 'Voltage Paradigm' and 'Power Paradigm' simply because the industry is mum on this subject in general- its inconvenient.

Yet the web audio forums are full of people that are constantly harping about aspects the the conflict between these two paradigms- tubes vs transistors is one of those debates that seems to arise from this conflict. But if you think my posts are *about* tubes vs transistors you have missed the point entirely!

The Voltage Paradigm uses a sort of short hand nomenclature that leads to confusion and I think this is happening for you in this case. Of course all amplifiers are power amplifiers, what the Voltage Paradigm seeks to do is call an amplifier a 'voltage source' when it refers to an amplifier that makes constant voltage into any load (i.e. doubles its power as the load impedance is cut in half). Amplifiers that have a high output impedance and make (or attempt to make) constant power are termed 'current source' amplifiers.

What is important to note here is the word paradigm. If you are operating solely within a paradigm, anything outside that paradigm can be construed as blasphemy.

The Power Paradigm amplifier is a 'power source', i.e. it will make constant power into any load. That is the voltage and current will both vary. I don't know of an amp that does this but that is the ideal, just as there are no true 'constant voltage' amplifiers out there either- that is the ideal. Does this clarify things?