Current amp vs Voltage amp

Historically speakers with lower impedances are more likely to be able to produce wave form fidelity than speakers with higher impedances.

[facepalm]I can't let that one pass[/facepalm]. Its well known for decades that the Quad ESLs have had very low distortion (re.: 'wave form fidelity'[sic]), some of the lowest out there. Yet the ESL57 and 63s both have a fairly high impedance.

In fact impedance has nothing whatsoever to do with waveform fidelity in a loudspeaker. That is entirely a matter of design.

There are many good reasons for speakers to have a low impedances and the market place has proven this for a long time now.

The 'good reasons' are sound *pressure*, not sound *quality*. I recommend you reread my previous comments. Its one thing if I say it- I own a small company that makes tube amps. But its another thing entirely when transistor amp manufacturers say that, and especially when that is re-enforced by the distortion measurements. We are talking about distortion that is audible too. Go ask Paul Speltz to show you that letter from Steve McCormick.

More challenging impedance loads would seem to go hand in hand with getting a more full range sound out of a smaller speaker design that will fit in well to most user's living/listening space.

For less full range applications especially in smaller rooms, there would appear to be more viable/affordable options in well designed higher impedance speakers.

However, the trend over time for most things is to become smaller and more efficient and also usually more cost effective and usable accordingly. The old paradigms have their strengths, but do not hold up well from an overall end user perspective these days. Too big, too expensive, and more maintenance required to keep things running well over time. But they can and often do sound really good. As do a lot of voltage based systems that leverage modern technology.

Its not valid to base decisions today on technology from 40 years ago. It is a different story now. THough I do love nostalgia including tubes and even Victrolas and have the Victorian styled home to potentially put these things in to prove it, the game continues to change, so one has to keep an eye on the ball!

Mapman, I'm not sure where you are holding with SS vs tube amps. But I think it's important to restate for emphasis sake that what Al and Ralph have been trying to explain all along is IME accurate.

If you read my posts about the SS/tube amp Paradigms and varying speaker impedances, I think Al was spot on when he said that an important factor, maybe the most important factor, is a tube amp's output impedance. The lower it is, the more "SS-like" it will perform.

I posted bench test reports from Stereophile and Soundstage for the ARC Ref 150 and ARC VS-115 (my amp). I found John Atkinson's comments quite interesting. He said that the FR output performance of the Ref 150 significantly "flattened" when driving a simulated speaker load off the 4 ohm taps as compared to the 8 ohm tap. Atkinson measured the Ref 150's output impedance to be lower off the 4 ohm taps as compared to the 8 ohm taps.

That result is consistent with what AL said about tube amps having low output impedance performing somewhat "SS-like" when driving speakers that were designed and voiced to be driven by a SS amp -- like mine.

Of course the reason the Ref 150 and VS-115 have low output impedance attributes is likely because of NF, which as Ralph says introduces odd ordered harmonics. So in the end, I guess it comes down to design trade-offs, with respect to both speakers and amps.

Bottom line: My Paradigm S8s have an impedance peak of 28 ohms at 2.2K Hz, which corresponds to the midrange/tweeter x-over point. In contrast, there is an impedance "saddle" of 4 ohms at 100 Hz. Paradigm advised me that the S8s were designed and voiced to be driven by a high current/high output SS amp. Ooopps.

I always thought the S8s sounded a bit "forward" when driving them off the VS-115's 8 ohm taps. At Al's and Ralph's suggestion, I tried the 4 ohm taps. I had to get used to the change in presentation, but now I like it better. Less listener fatigue, less forward, slightly crisper bass, and so forth. My anecdotal experience is consistent with what Atkinson predicted when he bench tested the Ref 150.

Not sure what else to say. Seems to me that if one can pick up a great speaker with relatively flat impedance and phase angle plots, the issue of tube versus SS amp compatibility will be largely mooted. But based on my read of reviews on some of the "big boy" speakers out there, like Magicos and Revel Salons, you are looking at speakers that need to be driven by some monster SS amps to sound their best. But don't take my word for it. Pull some of the bench test reviews and see for yourself.

Cheers and thanks again Ralph and Al for your patience and help.

Bifwynne,

What you relate sounds fine and does not surprise me. Whatever the details, paying attention to impedance matching between components pays off. Its a fundamental thing to get right, sometimes harder than others.

I just do not buy into the assertion that power paradigm and no negative feedback is the only way to make music sound real. It is based on sound theory perhaps, but in practice is not consistent with what I have heard in both cases over the years.

Cheers!

I just do not buy into the assertion that power paradigm and no negative feedback is the only way to make music sound real.

That's fine but it will not change the reality:

The problem here is that the human ear is more sensitive to odd ordered harmonics than almost anything else. Add on top of that that the ear is most sensitive at higher frequencies (FWIW the human ear is tuned to be more sensitive to bird song frequencies, something that comes from our forebears as a survival trait); the result is we can hear odd ordered harmonic content that is hard to measure on the bench.

We constantly hear how the ear is insensitive to this or that (for example we cannot detect the phase of a sine wave at all) but this is certainly an exception, and for a very good reason: the ear uses odd ordered harmonics to figure out how loud a sound is. This is vital to our survival- if you can't figure out how loud certain sounds are, you might soon be dead!

The thing about negative feedback is it does two things- one thing we like, the ability to servo-control the output of the amp so it will produce flat frequency response on *certain* speakers. The other thing it does is reduce distortion overall while actually adding odd ordered harmonic distortion.

When you add odd ordered harmonics even in trace amounts, it is audible because of what I have already explained. The result is it won't/can't sound real. You don't violate a fundamental human hearing perceptual rule without a price!

Get rid of the feedback get rid of this problem! But now you have to sort out how to get flat frequency response and low distortion without feedback. There are ways to reduce distortion, but how do you get the flat frequency response?

Use Power Paradigm design rules.

Many speaker designers do this, whether consciously or not, depending a great deal on the sort of amplifier that they like to listen to.

The Voltage Paradigm will work fine if you can build an amplifier that is simultaneously free of odd ordered harmonics and can also behave as a voltage source. That is the leading edge of the envelope in amplifier technology; so far no-one has been able to do it. There are some very notable amplifiers IMO that point the way- Ayre, Pass and I am also a fan of Berning, although the latter might be considered more of a hybrid approach. I suspect class D has something to offer here as well.