How important is the efficiency of a speaker to you?

Dear @daveyf   .: You are rigth and I was lucky enough to found out all the power supply, protection circuit, input electrical circuit electrolithics at its original values through the best of the best caps: Vishay.

When I did it ( less than 2 years ago ) and I listened again what I listened was and is nothing less than stunnig for say the least. I bougth my 20.6 second hand and I did it to been paired with a pair of 20.5s that I owned too in a bi-amp configuration and latter on that I learned I sold the 20.5s

" The amplifier performed beautifully, showing maximum distortion of 0.42% THD + N at 20 kHz. This distortion level would not be audible on music and is comparable to published ratings for high - quality tube amps driving standard loads; here, we were using one-fourth of the amplifier's minimum rated load! "

 but in that 20's monoblocks review ( not the 20.6 that are even better ) that  THD does noit changes even at 1 ohm where the 20's  shoiwed 800 watts. Even those reviewers made this experiment with the monobloks:

"" An enthusiastic reviewer might call a beefy amplifier an "arc welder" as an exaggerated compliment to its ruggedness and current -handling capacity. However, no one would really expect an amplifier to actually melt steel. Almost no one, that is, except this reviewing team. We say this amplifier is an arc welder and back up this statement with a photograph (Fig. B1) of two 0.05 -inch steel plates welded together by a pair of Mark Levinson No. 20s. Arc welding is accomplished by creating an electric arc that melts metal. The molten sections of the items to be joined flow together and are then allowed to cool. In practice, the power source is connected to the two pieces to be joined and to a flux - coated welding rod. The arc is struck by momentarily shorting the rod to the work pieces. The flux is vaporized, forming an ionic conducting path for the arc and cleaning the metal. The arc stabilizes at about 100 amperes and 30 V (creating temperatures of 3,000° F), depending on the thickness of the metal and welding rod. If this sounds like the world's worst amplifier load, you're right! Coauthor Clark summoned Paul Grzebik to carry out the task. Paul has the reputation, in Detroit's technical community, for a willingness to try anything once, from building a parade float to scaling a TV transmitting tower. He readily agreed to our assignment. Clark drove both No. 20 amps with a 1 -kHz square wave to full output into a series resistor mixing network that combined both amplifier Fig. B1-Results of the arc -welding experiment. outputs in parallel to obtain the high current needed. After experimentation (and several blown line fuses), approximately 1 ohm was found to deliver the maximum current for starting and sustaining the arc. Wearing a mask and gloves (the intense blue light from the arc can burn the unprotected retina, while molten metal can splatter on the hands), Grzebik began welding. The arc turned out to be a fairly effective plasma tweeter, creating strong 1 - kHz square -wave sound radiation that required wearing ear protectors as well. Grzebik completed a small weld and, impressed, pronounced it satisfactory. After the welding, the No. 20s, still only lukewarm, were again put on the test bench. Distortion tests verified that no change in their performance had resulted from this extraordinary exercise. What's the point? With this test, Clark verified his confidence in the exceptional output capability and comprehensive protection built into these amplifiers. A few other amps might be able to weld steel without destroying themselves, but the No. 20s were certain to survive the experiment. One note: Don't attempt this feat yourself unless you are an accomplished welder, have the proper equipment, and are using amplifiers with extraordinary protection circuitry and output stages that can handle current extremes. Injury to yourself and destruction of lesser amplifiers may result. Don't expect manufacturers to repair your damaged amp under warranty, either! "

So,  we don't have to care on what  that tube manufacturer posted because it does not happens exactly as that. The very old 20's proved that and that design comes from 1986.

As always, there are designers and designers and J.Curl is really good . Remember the Vendetta Research phono stage? came from J.Curl and several other electronics designs as the Parasound and the like.

R.

@atmasphere   :0)

@rauliruegas  If you are happy with owning an arc welding machine, more power. Personally, I prefer to listen to music, and as such I generally prefer the lower powered amps, most particularly of the tube variety. I am in 100% agreement with what @atmasphere stated above. 

If a speaker requires an amp/ arc welder up front to drive it, then IMO, there is a problem with the speaker design. YMMV.

If a speaker requires an amp/ arc welder up front to drive it, then IMO, there is a problem with the speaker design. YMMV.

Exactly! Such speakers border on criminal as there simply aren't amps that sound like music that can drive them nor would they be all that musical due to thermal compression.

I look at it this way- if you can't drive it well with 100 Watts (in most rooms), its a problem. That is because the ear hears sound pressure on a logarithmic scale. So to get twice as loud (perceptually) that you can get with 100 Watt, you need 10x more- and 1000 Watt amps that sound like music don't seem to exist although class D is getting close with amps that can make 600 Watts or so.

The problem (again) is getting enough Gain Bandwidth Product in the design such that it can support the gain of the amp along with the feedback it has (together, known as 'loop gain'). If not, and this applies to almost all amplifiers ever made prior to about 2000 or so, you get distortion rising with frequency with its attendant unpleasantness- this is a good portion of the reason feedback has gotten a bad rap in high end audio. 

Its not feedback's fault so much as poor execution of feedback.

Plus a 1000 Watt amp would not be able to make up for the thermal compression that would be present- as I mentioned before, as you try to turn it up to get around the problem, it just gets worse. 

This has been discussed ad nauseum here on Audiogon. Low impedances can lower sensitivity which can make amps work harder to produce power and increase amp distortions. The degree to which the amp distorts due to this depends on the stoutness of the amp. The greater the loudspeakers sensitivity the more likely it will be a more open gateway to what distortions are still presented by upstream components, including but not limited from the amp. What is often less discussed is that varying impedances can strain amps too, and is more likely to present difficult phase angles to the amp as well. It is far easier to present and maintain a steady impedance by lowering the impedance of loudspeaker than visa versa. Electro-mechanical components are much more difficult to make perform well than purely electrical components. The variance between loudspeakers is typically much greater than between decently designed amps. This might suggest that more leaway be given to loudpspeakers than amps. As has previously (and wisely) suggested here; speakers designers have to choose what paramters and associated compromises combine to best meet ultimate design goals. Some if not most of the best measuring loudpseakers have lower impedances, and ergo lower sensitivity. There are a bountiful number of well designed amps that can handle such loads with minimal consequence.

Dear @daveyf  : First than all I'm a MUSIC lover and each single week at least I ttend to enjoy Live MUSIC and this " attitude " I have it for the last 25+ years.

I hate to listen the system Hardware and my room/system is builded through several years around nothing less than MUSIC but to enjoy MUSIC in my home we all need some kind of source/hardware.

I used tube electronics over 10+ years till I learned.

My ADS L2030 " old " speakers has 95db efficiency, no there is no single design problem with:

Vintage Holy Grail ADS L2030 High Fidelity Stereo Speakers and ADS C2000 Control Photo #1889387 - Aussie Audio Mart

The other gentleman ixs totally wrong, maybe he need to talk with J.Curl about that design or learn in other way about that specific design. I really don't care on his post that only shows high ignorance in tha specific regards amps.

R.