Double down, good or bad?

Ralph just thinking off the top of my head.Because most speakers report "nominal" impedance and thier real impedance curve is all over the place, a doubling down amp would create serious spectral balance problems.
Looking at a frequency versus impedance curve like my Martin Logan CLS the high frequencies(2 ohms) would be driven 800 watts where the Low frequencies (8ohms) would be driven at 200 watts. Intuitively this would seem to cause spectral balance problems.
Does this make any sense?

Atmasphere, we're definately on the same page as far as the system-matching aspect of different amplifiers being optimum for different loudspeakers, especially when comparing among various speakers and amplifiers that use very different technologies and design approaches. But, er, well take this statement:

Power Theory (or Power Paradigm) is where the amp seeks to make constant power into all loads. It will not succeed, but that is the goal. The Dynaco ST-70 is a good example, 4,8,16 ohms its 35 watts. Our own MA-2 is another, 4,8,16 ohm 220 watts. Some transistor amps fall into this category.

I'm sorry, but the reasons why a ST-70 and a MA-2 both have constant power ratings into 4,8, and 16 ohms are completely different from each other! Further, a ST-70 has a much lower output impedance than that rated for the MA-2, and thus will interact with the loudspeaker impedance to a much different degree.

To use your B&W 802 example . . . according to Stereophile's measurements, this loudspeaker varies from a low of about 3 ohms in the mid-bass, with a peak of over 21 ohms in the midrange. Looking at my notes from the last time I measured a stock ST-70, it had an output impedance of about half an ohm over most of the audioband, from the 8-ohm tap . . . so I'll take an educated guess and assume it's about 0.29 ohms from the 4-ohm tap, which is what you would use for the 802.

So a ST-70 driving a B&W 802 would thus have about a 0.68dB response peak in the midrange due to the interaction of the amplifier output impedance and the speaker's impedance curve. For comparison, a hypothetical traditional solid-state amplifier (0.05 ohm output impedance) would have a 0.12dB response variation. But the MA-2 (published 1.75 ohms output impedance) would have a peak of 2.3dB! And for the MA-1 and M-60, the deviation is even greater . . . 4.04dB and 5.93dB respectively.

Now we're in complete agreement that the B&W 802 is a bit of an extreme case, and also that it's a poor match to an Atma-Sphere amp. And I'm not suggesting this is an inherently bad thing about Atma-Sphere amps (just a "system misapplication" if you will), or that the Dyna is a stellar match either . . . I'm personally a fan of the ST-70 but am also very familiar with its myriad shortcomings. But the ST-70 can hardly be considered a "Power Paradigm" amplifier because of its comparatively low output impedance.

Let me again re-iterate my original point: The suitability of an amplifier for driving a particular speaker simply CANNOT be inferred from looking at its clipping-power ratings into various load impedances! Ever. Period. It's output impedance that makes the difference.

Two secondary points: First, historically, there has been no Paradigm Shift - common practice loudspeaker design has ALWAYS been about constant voltage with frequency . . . as most vintage hi-fi tube amplifiers (such as the ST-70) have low output impedances, especially when compared to loudspeaker impedance curves of the day. Second, this is NOT a tube/transistor thing . . . there are many examples of solid-state amps with high output impedances in addition to tube amps with low output impedances.

Incidentally I actually commend Atma-Sphere for publishing their output-impedance specifications . . .

Peterayer, you are right, the Eggleston is designed around Voltage Paradigm rules, but some of the Pass amplifiers are not. You can find quite a bit of information on Nelson Pass' website regarding that. BTW his papers on distortion are excellent.

Bob_reynolds, Sure:
A transistor amp will make too much power at high frequencies on an ESL because ESLs have a low impedance at high frequencies, often the difference between the bass and highs can be as much as 8X difference in power response in an amplifier that can double power. Gregadd, this answers your question as well.

In the case of horns, the drivers are highly reactive due to tight gaps in the voice coils, and produce a lot of back EMF. When presented to the feedback network of an amplifier, this back EMF causes the input of the amplifier to misbehave- the voltages at that time do not represent the actual correction that the amp needs. So it tends to make excess harmonics and so sounds shrill.

In the case the the mbl, it is an easy 4 ohm load with an 8 ohm peak on the midrange driver. The designer expects the amp to throttle back its power, but an amp that makes constant power will not do so and so will have excessive upper midrange.

In the case of the B&W, the woofers are in parallel and are 3 db less efficient than the mids and highs. An amplifier with constant power response will drive the woofers with 3db less power than intended.

In all cases it is inappropriate power response. This is the major reason why you get mismatch between amps and speakers, although I would be remiss if I did not point out that distortion in both transistor and tube amplifiers also plays a significant role in what we hear as tonal aberration.

Bob_reynolds, Matin Logan has worked for years to try to make their speakers work with transistors. But ESLs in general do not behave quite the way you describe. Most of them are looking for the same amount of power to make a given amount of output, regardless of frequency or impedance. This has largely to do with the fact that their impedance curve is based loosely on a capacitor and has nothing to do with resonance. This is why amps with constant power response will be flatter in frequency response on Quads and Sound Labs, where a transistor amp will be making too much energy at high frequencies, and not enough in the bass. BTW this is a problem with Martin Logans too, despite their years of work to prevent it.

The Voltage Paradigm works best (insofar as frequency response is concerned) when dealing with speakers that have a box/driver resonance of some sort like found in an acoustic suspension speaker (although oddly enough, the very first acoustic suspension speaker, the Acoustic Research AR-1 was a Power Paradigm device and was built for amps that had a high output impedance).

Contrary to your assertion, a Power Paradigm device like an ESL, horn, or some types of box speakers (like the AR-1, but also Coincidents, Merlins and Wilsons) do **not** have to have a flat impedance curve to get flat uncolored response! All that has to happen is that the speaker be tailored in some way to deal with the constant power response of the amp. In the old days when horns were one of the few games in town, the speaker was equipped with controls to vary the output of the drivers, not to deal with room issues, but to assist the amplifier/speaker interface in getting tonally-flat response. Often all that is needed is that the impedance be *high* enough, beyond that the devil may care about the actual value.

In modern Power Paradigm designs, for example a bass reflex, using Theil/Small parameters the designer of the enclosure would set the port at a lower frequency than a designer of the same size box and driver would if in the Voltage Paradigm. Using Power Paradigm rules, the port would be set at some point wherein the amplifier will drive that set of frequencies a little harder (simultaneously avoiding the box resonance and extending the low frequency bandwidth to a lower point than possible using Voltage Paradigm rules), where if using Voltage Paradigm rules the port would be asking for considerably less power from the amp. But in either case the impedance curve would be anything but flat!

Hi Atmasphere,

I do have some other thoughts from what you posted above about driving certain speakers with specific electronics, especially tubes. First off, I respect highly what you and others have to say in regards to the technical aspects of certain types of equipment. Granted, you design and sell tube amps; specifically of the Output Transformer Less variety (OTL). You even stated your self that certain electronics and speakers do not match well and the only way to know for sure is in real world listening tests. I am listening to some great music right now (vinyl of course) on my all tube setup and kicking the crap out of my B&W 800’s with live energetic and excellent sounds from a pair of little 140 watt mono amps and the bass, midrange and highs are all excellent. The 800‘s replaced the B&W 802’s I had before (gave them to the wife for HD TV). The reason I am letting you know this information is so that I can impart from you some real world conclusions about tube amps and speakers that contradict your statements, not that I disagree with in your electronics prowess; it is that I do not agree that phase angle distortion and wicked impedance curves are going to stop people from enjoying music with certain electronics, and these electronics you seemed to limit yourself to because you have not heard all of the combinations either.

From what I have read in this post alone, your amps cannot drive B&W 802 because your amps are designed for a certain paradigm that contradicts what B&W may be using for their design paradigms, so perhaps a mismatch there. While other manufacturers are designing tube amps that do work with low impedance speakers such as Martin Logans, Magnepan and B&W’s. Obviously these types of tube amps are designed with a certain paradigm to match the low impedance of these types of speakers.

Your statement as read below:

“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?”

So based on your own admission that you do not know of any amps that do this, I think I am not off the mark by stating that perhaps there are some in production and being used now. I know this particular amplifier design is considered a “Power Paradigm” as it has an external 6x 3300 Microfarad capacitors (Elkos) power supply in addition to the regular on-board power supply. The amp is a class A/B with a pentode push pull design and very minimal negative feedback. It is somewhat of a hybrid amplifier as the owners manual states but the outboard power supply provides impulse power as you stated, perhaps in the 10ms realm that you mention and enough to give big speakers the additional current from the amps to drive them easily. Then I start to get confused when I look at your posts stating;

*tube amp with B&W 802 =>weak bass

“and other speakers (like the B&W 802) that are more effectively driven by transistors.”

“In all cases it is inappropriate power response. This is the major reason why you get mismatch between amps and speakers, although I would be remiss if I did not point out that distortion in both transistor and tube amplifiers also plays a significant role in what we hear as tonal aberration.”

Based on your statements and my real world experiences, I am not just an audio geek but an IT engineer by trade; I have to absolutely refute your statements and have conclusions quite the opposite from what you stated.

I am living with both tube amps and B&W 802’s and 800’s and know for a fact with the right combination of tubes, I have realized that my amps can drive these speakers both to extremely loud SPL‘s and with deep enough bass that in some music you would think a subwoofer is on. In fact I thought at first when I gave up transistors to go with tubes, the bass may have appeared weak, but when I did some tube rolling, I realized that the amps have the capability to drive these speakers with great dynamic swings and effortlessly. The bass I was hearing had a natural taught and dry feel. It was what they call in German “Knackig”.

From what I am gathering about the posts, it seems as if the discussion is getting wrapped up in distortion levels mixed with phase angles and impedance curves versus the reality of actually driving certain speakers with watts and discounting other factors. I have heard a true 1 watt at 1 meter test done with various speakers and amps in a test lab in Germany to compare 1 watts vs. loudness. With a distortion level of only .05 at a given phase angle, no one is going to hear it, even at 1% at 96DB with loud rock music, it is not much of an issue, with an all tube setup at that loud of a SPL, someone is more susceptible to hear tube rush instead of harmonic distortion and clipping. We are talking about some serious minor issues. When a gross mismatch occurs, then obviously it will become known, but I just happen to have experiences that are totally opposite of what you are stating and therefore I cannot accept that all of your explanations are conclusive to every tube amp and speaker combination that is possible. I do like your amp designs and logical feedback in these forums, however as a user of the referenced products above with different experiences, I feel the need to convey my thoughts on the subject.

When I look at the spec sheet of a particular type of amp, I do not see why anyone having this type of amplifier would have a hard time driving a pair of B&W802’s or 800’s for that matter as I do without any issues. These are the specs for you if you are interested, note that there is less power at 8 ohms versus 4 ohms.

Output 140 W into 4 ohms (100 W into 8 ohms) Frequency response 3 Hz - 100 kHz Input impedance 210 kOhm Signal-to-noise ratio > 103 dB Damping factor 12 - constant from 20 Hz - 15 kHz Minimum load impedance 2 ohms

Its circuit incorporates additional reservoir capacitors to increase the current delivery of the power supply, counteract fluctuations in the supply voltage and suppress low frequency mains supply 'noise'.

A description of the outboard capacitance increasing power supplies:
The external current increasing power supply, Super Black Box, always results in an improvement in sound quality. The sound becomes more relaxed without losing pace; the subtle timbres of individual instruments become more defined, and the soundstage extends further into the distance. The improved stabilization of the power supply increases the pulse output of the power amplifier, making loudspeaker efficiency less critical. The amplifier will also handle speakers with impedances as low as 2 ohms.

Again I appreciate all of your technical answers to some of the inquiries here. So in light of what all has been said, however can it also be true some of the mentioned parameters such as phase angle and impedance variations when minimal do not affect sound as much as people think, at least listening pleasure. I am not saying that a big phase angle shift would not, but how many people have actually heard what a big phase angle shift does to sound, outside of incorrect match of speakers and amps and discovering that it “sounds“ bad. Often people hear other things from what an electronic measurements report sheet states, in cables, tubes, amps and speakers.

A Short story:
At the end of the day, when I packed my amps up in a McIntosh audio shop and disconnected them from the B&W 802‘s after a shootout with the MC501’s and 1201’s, the Mac amps were not happy campers nor was the owner of the shop. The customers asked what tubes amps I was using and how I made the speakers sound so good compared to the transistors. Of course the dealer stated you will never hear what a system will sound like until you get it home, but if it sounds like crap in the store, who wants to even take it home for a demo. I am not bashing Mac stuff, it sounds different and for me would make a great home cinema system, but the fact is other people heard the B&W 802’s with tubes in a Mac shop compared to premium Mac gear and preferred the particular tube amps I brought up to do the test and demo comparisons. For me that whole experience only reaffirmed that each individual must hear for themselves what will work and what will not work. The 1 watt at 1 meter test works real well. It is an easy test. if there is a lot more room to increase volume, then you probably have a good match. You are either going to like what you hear or not and if the phase angle is not perfect, do not be fooled to think that an amp can’t handle the load, it just might fool you.

Ciao,
Audioquest4life

Audioquest4life, first, phase angle and the like is really not part of the discussion- so far. As far as the 802s go, sure, you can make a tube amp drive them and have them sound fine. We have had customers do so in the past.

However, that is not the same as saying that they are sounding their best! If you were to put the speaker/amp combo in an anechoic chamber, you would easily measure the effect of the reduced woofer output (which is not the same as reduced low frequency **extension**).

The problem is that the speaker is intended for use by a voltage source, but I find that I prefer how it sounds with tube amplifiers as well, despite the reduced woofer output.