I was going to write some quibbles, but instead I will just point you to this article from Roger Sanders. While the amp he talks about has long been superseded, the problems about ESL's and phase angles and currents remains true. http://www.enjoythemusic.com/magazine/manufacture/0702/ Best, E |
Hi Al, There are flat impedance speakers out there, which is often accomplished with additional impedance normalizing circuits in the crossover. Certainly a niche. In these cases it is rightfully argued that the output impedance of amplifiers will have negligible effect on the frequency response. If this was Atma’s argument I would leave it alone. His repeated disinformation that the high output impedance is BETTER because it has constant power output regardless of impedance is nonsense. In no measurable case is it ever better. The measurements by SoundState and Stereophile are consistent. With "normal" speakers high impedance causes significant deviation from ideal. Of course, buy what you like. Best, E |
@atmasphere I am saying your entire argument is bunk, because the ideal audio amplifier is a voltage source, not a current source. In essence you are also arguing for amplifiers of TINY damping factor being ideal. Not supported by anyone but you. In fact, the amplifier I quoted, has a damping factor of around 0.8. That's about 400x worse than even a mediocre solid state amps. Complementing the amplifier design, speakers are measured by the output vs. frequency based on constant input voltage. For your theory to be at all accurate, speakers would have to have flat power efficiency (input vs. output) and ....they don't! The power efficiency of almost all multi-way speakers varies tremendously based on frequency. The LAST thing on earth you want is a constant current amplifier, unless you want your output to look like your impedance curve. If you are right, then man, 10 Ohms is too low. You should make amps with 30 or 50 ohms at the output, you would get even more ideal current sources! << hahahahah >> You know, it is a real shame that you take this tack, because I actually think you have a lot of fans, and built good products, but I've gotten really tired of you constantly hammering the superiority of high output impedance amps as a feature based on false and misleading (that's your own phrase) statements you repeat over and over again. Best, E |
Theory is too difficult to do in these forums, especially without graphs, but let’s talk some real world effects. SoundStage Magazine online has a review for the Atma-Sphere MA-1 Mk II.2 mono-blocks: http://www.soundstage.com/revequip/atmasphere_ma1ii2.htm with an excellent set of measurements which to illustrate what the output impedance problem is with typical tube amps and how much it is. The very first graph shows how the amp interacts with the complicated impedance of real world speakers. See the green line? That is what the electrical output looks like when driving a simulated speaker load. The frequency response can vary around +-3 dB (a bad thing) when driving an NHT: http://www.soundstage.com/measurements/atmasphere_ma1_mkii2/ I think this is quite typical behavior for tube amps. Most solid state speakers would be quite flat, debunking the idea that solid state amps have a harder time, ever. Despite the impression Atma tries to give, almost all speakers are designed as voltage-dependent devices. I know, I make them. :) That is, the prime quality we seek is to have a smooth and controlled frequency response for a given input VOLTAGE, not power. The power is going to vary up and down based on the crossover, drivers and even cabinet. We like to assume the amps driving our speakers is what is called an "ideal voltage source." where current (and power) output will vary based on the speaker, but the output voltage is purely a function of the input signal. This gets harder to do with high output impedance amps, or low impedance speakers. If your amp’s impedance is high enough, it will become an ideal "current source" where the output current has nothing to do with the load, and therefore the voltage at the speaker will vary wildly with the speker’s impedance. Atma-sphere has a unique perspective on this issue, and seems to constantly be suggesting a current source is ideal. He stands very much alone in this area. That being said, the question of sound quality and amp/speaker matching is purely subjective, and you should listen for yourself. I'm pretty sure my favorite tube amps of all time, the CJ Premiere 8s were quite high in output impedance, but I'm not going to try to sell new physics to convince anyone to buy them. Best, E |
I suspect that what Shadorne calls ’difficult’ (and for that matter the author at the link Erik provided) is the simple fact that solid state amps (even ones known for driving difficult loads) can’t make as much power into the relatively high impedance that the Quad presents at low frequencies. oh sure. Uh huh. If this had any basis in reality, at all, speaker testing would be based on power vs. frequency. It isn't. It is input voltage vs. frequency. Best, E |
So this brings me full circle. I've seen speakers that are hard to drive at the top end, at the bottom and all across the spectrum. The ESL speakers come by their low impedance and difficulties as do the full-range planar-magnetics (Apogee) via legitimate reasons. That is, the speaker technology itself poses challenges which the designers accept in exchange for other benefits. ESL's are essentially giant capacitors, no way to get around that. The sacrifice is made to submit the amplifiers to brutal loads in exchange for having a large single driver driven across it's surface (how well ESL's actually do this is arguable, but not for here). I think that with the worst of these panels, a lot of OK amps are going to perform quite a bit differently, which with "nice" speakers could perform nearly identically. And as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers. When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way. But this discernment does not make either the amplifier or the speaker more musical. It's just more demanding. Best, E |
All ESL panels I know of follow this descending impedance curve, which is a problem for a lot of amplifiers since most amplifier’s have rising impedance at the upper end of the frequency spectrum, resulting in an overall significant net loss of output. This is in addition to current limiting, which thanks to music being bass heavy, is less of a concern. Tube amplifiers rarely have the low output impedance (anywhere) that solid state amps do so they start at a disadvantage. However this is all basic electrical / and voltage dividing theorems. The final choices about matching any given amp to any given speaker has to include the speaker’s acoustic output and room. Given the impedance curves of the amps and speakers you can predict reliably that amp X’s electrical output will drop 6 dB at 20 kHz with a given speaker, but I can’t tell you if you’ll like it. :) Best, E |
@atmasphere Wrote this false and misleading statement (<----- a paraphrase of how atma has posted): The ’original Quad’ (as bdp24 put it) is an easy load to drive. Differences in damping between amps is one of the few things that **isn’t** audible on the speaker, owing to the fact that in the bass range the impedance is rather high. This reduces the difference heard between an amp with say 10:1 damping factor as opposed to one with 100:1. Rather than argue with someone desperate to be an authority, I submit this link: http://www.quadesl.com/quad_main.html Best, E |
Also want to say, we are lucky to be alive right now. There are some wonderful Women and Men making violins, violas and cello’s these days for relatively paltry sums compared to buying a Strad. Anyone who gets a chance to listen to an accomplished violinist should also be grateful for a chance to hear such remarkable craftsmanship. E |
So my previous remark was about violins. Any half hispanic, half asian lady, mostly single, concert violinist between 35 and 45 years old who would like to come to my home and prove I can’t tell the difference in which violin she’s playing, please let me know so I can arrange a time. Now, about amps. I can make speakers more "discerning" of amplifiers than others. I learned this trick from a famous speaker maker’s crossover. Lower the impedance and make it particularly reactive in the mid bass and voila, now you can tell the difference between several amplifiers which in a "Lesser" speaker you could not. This is a reason why I strive to make my speakers easy to drive. Easy to drive means they will sound great across a variety of amplifiers and electronics. I think this is part of what is going on. There are a lot of good modern amps which sound really similar. We live at a time when many amps sound free of glare and harshness or grain, smooth, extended and potent with easy to drive speakers, but not all speakers are easy to drive. :) For those who wish to be dominated by their speakers however, I can point you at some famous brands. :) Best, E |
The idea that you can’t tell the difference between a violin or viola you know very well and others is nonsense. Not only do they have a specific character, over time the fibers and resins break down depending on how they are played, which musician’s can tell, while listening or especially while playing. The elasticity of the entire piece changes over time. Ask any violin maker. Now, can I hear a recording and say "Aha, an early Stradivarious!" NO, i really can’t, but I am sure i could become accustomed to a particular instrument and hear it vs. others. Best, E |
