But Ralph, I think you may have mentioned yourself that if a "pure" Power Paradigm tube amp that doesn't use negative feedback and that has a somewhat high output impedance is matched up with a speaker having a "bumpy" impedance curve, there could be coloration of the acoustic presentation. Ergo, the need and importance of matching this type of amp with a speaker having a relatively benign impedance curve. The problem, I think, is that those types of speakers are in the minority of what's out there in the market. As I may have mentioned, some of the "big name" speakers like Magico and the Revel Ultima Salon 2 have impedance curves that would make a "pure" Power Paradigm amp dizzy. Or am I missing something . . . again as usual?? The ear has a tipping point where it will favor colorations due to distortion **over** actual frequency response errors. On top of that you can't count on flat frequency response from any speaker. The Power Paradigm favors the idea that the equipment be designed to obey human hearing perceptual rules (as opposed to arbitrary specs on paper- the Voltage Paradigm); with this in mind, it can be seen that it might be more important to keep distortion down over trying for a perfectly flat frequency response. Of course, if the frequency response is really messed up that won't do either, so you are correct that some care must be taken. In general though, if the speaker is a Power Paradigm device as is the amp, there are no worries. The problem comes in when you try to mix the two technologies- in that case you can always count on a tonal aberration. Just to be clear- its not important that the speaker have a flat impedance curve- it just has to be designed to work with the power response of the amp. If I can quote Duke Lejeurne of Audiokinesis. Duke starts out his comments by quoting another poster on that thread:
Drew Eckert wrote:
"Some audiophile amplifiers have silly high output impedances which interact with the speaker's varying impedance to change the frequency response and this is exacerbated with low load impedances. Output Transformer Less Tube amps are especially bad although single ended triodes without global feedback can also have problems.
"For instance an Atmasphere M-60 Mk.II.2 has a 4.1 Ohm output impedance.
"Driving a 3-way speaker with impedance varying from 16 to 64 Ohms this would cause a 1.4dB output difference between the minimum and maximum impedances.
"With 4 to 16 Ohm impedance the difference would be 4dB. This is not atypical for a 3-way...."
In reply, I'd like to point out that, with the same 4 to 16 ohm impedance difference described here, the power that a transistor amp puts out varies by 6 dB, because it is putting out constant voltage rather than constant wattage. Why does the audio world accept this without a blink, and yet think there's a problem when a tube amp exhibits less variance in power output into the same load??
It is because the audio world is accustomed to the way transistor amps behave, and most speakers are designed to work well with transistor amps. The designer designs the speaker to sound right when driven by an amplifier that puts out 1 watt into the 8-ohm portion of its curve, 2 watts into the 4-ohm portion of its curve, and 1/2 watt into the 16-ohm portion of its curve, all at the same time (2.83 volts).
Now, what if the designer's goal was a speaker that works great with an amplifier that puts out approximately constant wattage, regardless of the impedance curve (within reason)? Well that can be done just as easily, but there are fewer amplifiers designed that way out there, so his potential market is smaller.
These two approaches to amplifier and speaker design have a name: Voltage paradigm, and power paradigm. You can read more about the subject here:
www.atma-sphere
At this point Duke put a link to the Power Paradigm article. Continuing:
Okay, what kind of amplifier sounds best? Boy that's a long debate for another day, but a lot of people familiar with many types of amps prefer the sound of a good OTL or SET amp, assuming a good speaker pairing, and that includes yours truly. Some speaker manufacturers give priority to building speakers that will work best with power paradigm amps because they believe that combination sounds best, and just accept that they are fishing in a smaller pond.
Is it possible to build a speaker that works well with both types of amps?
Yes, by keeping the impedance curve as smooth as possible, the speaker will work well with both types of amps. And with such a speaker, you can really make an apples-to-apples comparison of the different amplifier types, rather than actually evaluating whether a (typically roller-coaster impedance) speaker synergizes best with a voltage paradigm amp or a power paradigm amp.
Drew's numbers above illustrate an argument in favor of using a high impedance speaker with a low-output-impedance amp: The amp's output is approximately constant-power when the speaker's impedance is varying between 16 and 64 ohms, but the amp's power output changes significantly when the speaker's impedance varies between 4 and 16 ohms (same 4-to-1 variance in both cases). Also note, in both cases the amp's power output change vs speaker impedance is in the opposite direction of what happens with a voltage-paradigm (solid state) amp, and this is probably the main reason why simply dropping a specialty tube amp into your current system is a roll of the dice (and the odds are against you) unless you already know your current speaker is a good match.
Back to the original question, what's with 4 ohm speakers if they're harder to drive, well in general they can play louder with a solid state amp, and most people have solid state amps, so they get more sound per dollar with 4 ohm speakers (quantity outsells quality). Also, most woofers are 8 ohms, so if the designer wants to use two such woofers, he has to choose between series connection (16 ohms) and parallel connection (4 ohms). Most choose parallel connection because 4 ohm speakers outsell 16 ohm speakers. I believe that most amps - tube or solid state - sound better into a 16 ohm load, so my home audio two-woofer designs are 16 ohm loads (whereas my prosound two-woofer designs are 4 ohm loads, because there we're trying to maximize available SPL with solid state amps). What do I do about the typical halving of maxium power from solid state amps when driving a 16 ohm load? I start out with speakers that are about 3 dB more efficient, and of course pay a corresponding price in box size vs bass extension. However there is one "free lunch" to using power paradign amps: They generate equal or even increased, rather than reduced, power into the speaker's virtually inevitable bass impedance peaks, and if we keep this in mind and design our box accordingly, we get back most of the bass extension we otherwise would have lost when we traded off in the direction of higher efficiency.
So I take the position that, all else being equal, 16 ohm speakers sound better than 4 or 8 ohm speakers, and that power-paradigm amps are well worth seeking out matching speakers for.
Duke
dealer/manufacturer/power paradigm groupie
this is taken from the speakers forum: http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1368259003&openflup&13&4#13 |
Harking back to Mapman quoting Einstein... the only way to really get a handle on this is to get yourself to a show or an audio club and listen. See what floats your boat. Right now I am listening to an 18 wpc SET amp driving 97 dB high impedance speakers in a 14 x 23 x 8' room. I have to use 10 db attenuators to get the volume control up to 10:30 and it's about as loud as I ever want it. Plenty of bass. Vocals/midrange sound RIGHT. Source is 16/44.1 Pandora, so it's not the ultimate in detail, but it sounds pretty darn good to me. Go to RMAF and hear Ralph's 60 watt OTLs, driving the Audio Classic horns to near rock concert levels in one of the very big exhibition (not sleeping) rooms will show you that you do not need a mammoth amp (ss or tube)to provide mammoth sound w minimal distortion. OK, the cost is a little heat. Maybe you live in Phoenix and that is a game changer for you. That's cool (pun intended). Give a Berning ZOTL amp a try. Long tube life, auto-bias, compact, pretty cool running- certainly cooler than many ss amps biased into class A. |
Thanks again as usual Ralph and Al. Just want to re-post 2 links that answer in part how NF may work with tube amps driving “mountainous” impedance curve speakers.
The links show bench test measurements of 2 different ARC tube amps: (a) the new REF 150 as tested by John Atkinson of Stereophile in 2012; and (b) the VS-115 as tested by Soundstage in 2008. You'll note that both techs drove the amps into simulated speaker loads. Links of the simulated loads are also copied. While the simulated loads are not identical, they are both pretty steep in the same FR areas.
What I thought interesting is that both amps had roughly similar output impedance and NF specs. Also the output FR of both amps driving the simulated loads followed a similar pattern of reducing the impedance “mountains” into “small hills.”
I realize the only way to really know whatÂ’s happening is to mic an actual speakerÂ’s FR output. But having said that, I suspect that an otherwise flat FR speaker that was designed to be driven by a low impedance SS amp, if driven by one of the ARC amps would be in the same actual "FR" neighborhood.
Acoustic colorations? Yes, some. Wild fluctuations – doubtful, given the bench test results. Possibly +/- 1 db or less, especially if the 4 ohm taps are used.
I realize that the “cost” of using the NF is TIM and odd ordered harmonic distortion as Ralph, Al and others have explained, but isn’t that part of the amp designer’s decision trade-offs??
http://www.stereophile.com/reference/60/index.html
http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements
http://www.soundstagenetwork.com/measurements/amplifiers/arc_vs115/
http://www.soundstagemagazine.com/measurements/test_amplifiers.htm |
Regardless of design paradigm, isn't it the frequency response and distortion measured in the end that matter? These are components designed with certain criteria in mind that are obviously not interchangeable and must be matched together somehow. Its important to be aware of the technical details that matter, like impedance characteristics, to have the best chance of getting best results, but in the end, I do not think either paradigm can be measured as definitively better, although I suspect that the way these things are usually determined, via certain accepted distortion measurements, etc., that the common voltage paradigm measures better when done correctly. Of course doing it correctly is a big if given the multitude of choices, in lieu of a reliable consultant or knowledge needed to make the right decisions. Power paradigm has the advantage in that the smaller minority group of vendors that follow it these days offer good consulting on how to make it work. They have to, otherwise confusion and dissatisfaction might reign, as it often does in the more "open" volatege paradigm world. Knowledge is a key ingredient for good sound, so you need it regardless and when you find a good source of knowledge that you trust, I'd say go for it in that it is likely the ticket needed for good results, if you can afford it. |
THis interactive chart is a fantastic reference resource. Not only does it help you understand how music works, but also relates that to ear sensitivity, ie frequencies that our ears are most sensitive to, at least normally. So when looking at frequency response curves for a particular setup for example, compare what is measured to ear sensitivity as indicated. Also consider the harmonic elements that comprise various instruments in the recording as indicated in the chart. That should help one really assess what is going on when they listen better. I have a framed copy of a poster of this chart hanging in my main listening room for easy reference when needed. The paper is not interactive though unfortunately... :^). |
Great chart Mapman. The chart also provides insight into why a speaker may subjectively sound bright or flat (i.e., dull). The chart shows that our ears are very sensitive to midrange frequencies. So, if our audio rig emphasizes frequencies in the 2K to 3K range, the speaker may sound "bright." And I assume the opposite is also true. |
One additional factor to consider is how individuals hear. I doubt any two people hear exactly the same plus all our hearing changes as we age. Those 50 or over may be challenged to hear test tones much above 10-12Khz or so. That can be a mixed blessing when it comes to how gear sounds in that younger ears may have greater sensitivity in that range. Age might be one of the most telling factors regarding what "sounds good" if such a study were done I believe. Also note that the chart indicates that even though we may not "hear" higher frequencies, we may still be affected by them via other senses. |
Regardless of design paradigm, isn't it the frequency response and distortion measured in the end that matter? These are components designed with certain criteria in mind that are obviously not interchangeable and must be matched together somehow. Its important to be aware of the technical details that matter, like impedance characteristics, to have the best chance of getting best results, but in the end, I do not think either paradigm can be measured as definitively better, although I suspect that the way these things are usually determined, via certain accepted distortion measurements, etc., that the common voltage paradigm measures better when done correctly. Mapman, Put in a nutshell, to answer the first question above, 'no' is the short answer. The longer answer is that the ear cares about certain distortions and others not so much. In addition, the ear will interpret (as I have mentioned previously) some distortions as tonality, and will favor them over actual frequency response errors or accuracy. An excellent example is how some amps can sound bright, but measure the frequency response and they are perfectly flat. This is because trace elements of odd ordered harmonics are interpreted by the ear as brightness even though it does not show on the instruments. Another way of looking at this is that the Voltage Paradigm for the most part ignores human hearing rules, opting instead for arbitrary figures on paper. In essence, an example of the Emperor's New Clothes. I do not think that this was done on purpose, its just how things have worked out in the history of the last 45-50 years or so. You have to understand that back in those days, there was very little that was understood about how the ear actually perceives sound. So the Voltage model was set up around low distortion and flat frequency response. In the interim, we have learned a lot about human hearing, but one thing I find amusing is that one of the earlier facts we discovered was that the ear uses odd ordered harmonics as a gauge of sound pressure. That was known by the mid-1960s. Yet the industry ignored it. The Power model rests on the idea that if we build the equipment to obey human hearing rules, the result will sound more like music. Well, if we are to obey one of the most fundamental hearing rules, we have to get rid of negative feedback, otherwise the result will always sound brighter and harsher than What Is Real. The evidence that this is not a topic of debate is all around us- probably the easiest to understand is that, over half a century after being declared obsolete, tubes are still with us (and we are still having these conversations). If the Voltage model was really the solution, it would have eclipsed all prior art and would be the only game in town. That it failed at that speaks volumes. Now in saying this I am not trying to make you or anyone else wrong. I would love the Voltage model to actually work, but IMO there are only a few examples that do; they represent a tiny minority, much smaller than the pond I am fishing from, to use Duke's apt expression. Its more a matter of what collectively we choose to ignore, things like the fact that the stereo can sound loud or shouty at times. Its been my experience that if the system is really working, you will never have any sense of volume from it, that is to say its relaxed even with 110db peaks. If you cringe at the thought of running the volume that high then you know exactly what I mean. Yet real music hits peaks like that all the time and we don't cringe. |
"This is because trace elements of odd ordered harmonics are interpreted by the ear as brightness even though it does not show on the instruments."
I have trouble understanding how the ear hears something as "bright" that does not evidence itself somehow when measured.
I've always taken that as some resulting frequency anomoly in one of those frequency ranges where the ear is most sensitive, but how serious can it be if not even measurable? Where is the evidence that the effect exists, much less the cause? |
"An excellent example is how some amps can sound bright, but measure the frequency response and they are perfectly flat. "
The ear sensitivity chart in the diagram I shared alone would seem to explain that. We don;t hear bass as well as other frequencies, so when response measures flat, bass may be less heard. But that is how our ears work, so it is what it is. ITs a clear alternate example of how we hear what otherwise measures differently. |
The huge unflatness of the ear sensitivity chart would also seem to debunk any claims one might make about being able to hear flat frequency response. If you hear it as being flat, it in fact cannot be. Significant equalization would have to be applied to the source to have any chance. At that point, what you hear as flat would no longer be natural, rather "enhanced" to make it sound that way to compensate for lack of flat response with our hearing. |
The huge unflatness of the ear sensitivity chart would also seem to debunk any claims one might make about being able to hear flat frequency response. If you hear it as being flat, it in fact cannot be. Significant equalization would have to be applied to the source to have any chance. At that point, what you hear as flat would no longer be natural, rather "enhanced" to make it sound that way to compensate for lack of flat response with our hearing. Its more complex than that, our ear/brain system can recognize acoustic environments and compensate for them... BTW I hope you are not suggesting that we need to compensate our ears with EQ. I have trouble understanding how the ear hears something as "bright" that does not evidence itself somehow when measured.
I've always taken that as some resulting frequency anomoly in one of those frequency ranges where the ear is most sensitive, but how serious can it be if not even measurable? Where is the evidence that the effect exists, much less the cause? If we can't measure it can it exist? Sure! Our instruments have limits of their own- noise being an excellent example (another being the tendency to quantify a phenomena as a reading on a meter...). When an amplifier has low harmonic distortion measurements, its often described as having such low distortion that its "buried in the noise of the instruments". The simple fact is that in regards to sensitivity to odd ordered harmonics, our ears are **more** sensitive than instruments. This is not hard to understand if you also know that the ear is that sensitive because it uses odd orders to gauge sound pressure- look at it as a survival trait. If you can't tell how loud a tiger is growling, you may well soon be dead. The ear needs to be pretty sensitive as a result. There are other things that the ear sucks at compared to instruments; this simply isn't one of them :) General Electric did the studies of this phenomena back in the 1960s. It was perhaps one of the first real forays into the hows and whys of human hearing perceptual rules. We have learned a lot more since then. |
"If we can't measure it can it exist? Sure!"
Sure. But some actual evidence always helps, especially in the often twilight zone of high end audio.
If you can't measure it, it does not prove it is not there, just that there is no evidence to substantiate it other than words and theories.
Plus once it is determined to exist the next question is how important is it really?
ANy issue can seem quite grand on its own. But put it into the big picture along with all the rest, and maybe it is not really the biggest nut to crack? All designers have their pet peeves that determine their approach. Designs are different as a result as are the results themselves. Which is best? Each woth their salt thinks their own most likely. How to determine who is right and who is wrong? Evidence certainly helps. Substantial evidence often takes a long time to accumulate to the point where determinations can be. But time usually tells in the end. We'll see.... |
Atmasphere, I've found that chart to be a useful tool to help me understand audio better. What I have heard over the years is consistent with what the chart tells me.
IS there some way you can reconcile the theory you support with the chart? For example, do the harmonic loudness artifacts you describe commonly fall into the frequency ranges depicted that ears are most sensitive to? That sound plausible to me. If what you say is at least consistent with the chart, that adds something to the case IMHO.
My understanding as documented on the source site is the human ear sensitivity data depicted in the chart is based on data collected "testing large sample groups" and is based on ISO standard 226 (2003) for human equal loudness contours, whatever the blue heck that is. |
I have to tell you that this tube vs solid state discussion and other discussions are typically biased against solid state and towards tube. As I have mentioned previously in other posts, I have heard many excellent tube amps. But, I have also heard just as many excellent solid state amps. Good Design/engineering is just that. Take it home, plug it in and listen for your self. Some like the "tube" sound. I have listened for decades and I can tell you that what I usually hear is the specific design of the circuitry of the particular amp. I have heard tube amps that had terrible sound stage, dynamics, etc. Same with solid state amps. Some times it has to do with system integration or room dynamics or actual design of the tube amp. We can talk harmonic distortion till the cows come home. But, the real test is long term listening in your home on your system. If it works and you smile and you are "there", then that's it. Show me a tube amp that people say is really great and I'll show you a solid state amp that matches it or better it. It depends on the design/construction/circuitry, engineering of either. If I had the money right now, I would purchase two Audio Research REF 250 amps. I have heard them and they are incredible. Better than the best like priced solid state amps? Couldn't tell you since I haven't heard them. But, I'm not prejudiced. I know good design and engineering when I hear it or see it. What would be better is to have forums where solid state amp designers and tube amp designers sit and answer questions and discuss these issues. Then, you will have a more fair discussion and I guarantee that you will have better insite and information.
enjoy (no really, enjoy) |
Minor1 said: I know good design and engineering when I hear it or see it. Not to be contrary, but unless I miss my guess, neither you nor anyone else has ever "heard" a "design". You may have heard a system based on a component whose designer made trade-offs and design decisions that ultimately yielded a sound that conformed to your aesthetic. Now when you say: What would be better is to have forums where solid state amp designers and tube amp designers sit and answer questions and discuss these issues. Then, you will have a more fair discussion and I guarantee that you will have better insite [sic] and information. I say, right on bro!!! |
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Audiogon often seems a magnet for unique or differing perspectives on good sound. SS is old hat and boring. Does not attract much attention these days as a technology. Class D amps are newer and get a lot of attention here. Tubes are cooler and more unique these days, as is vinyl.
I'm working on building more appreciation for Walsh style speakers here on A'gon myself in that I believe Lincoln Walsh used his engineering experience with radar systems in WW2 to get dynamic speakers right while the rest of the world missed the boat. Pretty radical....
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The odd ordered harmonics are perceived as sound pressure level comment is interesting to me. I recently switched from all tube amplification to a very good tube preamp and very low distortion and high current solid state amps. Musical transients are now much more impactful and realistic spls are acheived and not perceived as loud, (lack of odd order harmonic distortion?)Very happy with the results with one caveat. Using my sound meter I am now regularly listening to music in the mid 90 to low 100 db range and starting to get some evidence that I'm affecting my hearing. Maybe I was better off with the even ordered tube harmonic distortion satiety at about 10 to 15 db less sound pressure level and not going deaf. Go figure. |
05-24-13: Mapman
... I believe Lincoln Walsh used his engineering experience with radar systems in WW2 to get dynamic speakers right while the rest of the world missed the boat. Pretty radical. Interestingly, as far as I am aware he was also the only manufacturer of consumer-oriented audio power amplifiers utilizing the 300B directly heated triode power tube, between the earliest days of hifi and the resurgence of interest in that tube that occurred in the last three decades or so. Also, some of his amplifiers used 2A3 DHT power tubes, and similar comments apply to them, with the slight qualification that his use of 2A3s was preceded by their use in the power amplifier sections of certain high end radios of the 1930s. Those Brook Electronics Company amplifiers are highly collectable these days, and go for big $$$ on the rare occasions when they appear for sale. Best, -- Al |
So, individual technical peeves and preferences aside, in the end here are things I think really matter regarding choice of amp and speakers to match.
1) If limited frequency range down to only 50-60 hz or so is your game, the world is your oyster. Many many good combos of both SS or tube amps and speakers to do that.
2) If full range frequency response flat to down below 40 hz or so is your target, now you have some important choices to make, especially for a larger room in that in the end, however you achieve it large volumes of air must be highly pressurized at low frequencies to achieve the goal. Choices are:
1) modest or low power tube amp + higher efficiency larger speakers. The lower power the amp the larger the speakers will need to be. Soft clipping of transients at high volumes is still clipping so you have to avoid that!
2) Higher power SS or tube amp with smaller speakers. Lower efficiency speakers will also still require more power. Class D amps may be the emerging technical solution that best addresses this. Otherwise those high power amps needed will be large , heavy, expensive to buy, and expensive to run as well. |
Of course, for full range scenario, nothing wrong with using a low power SS amp in place of a tube amp. Or a larger tube amp with smaller speakers, although this is where the size and power required of the tube amp will result in limited good choices. Again, soft clipping is still clipping, so none of that allowed! :^) |
I suppose another scenario would be like Petepapp describes, and you want to preserve your hearing. Soft clipping may be a good thing there, so a smaller tube amp might fit the bill for a full range solution with smaller speakers. |
Very good point. Is it odd ordered harmonic distortion that causes damage within the average spl range we listen at? Will I preserve my hearing ability switching to tubes? |
Distortion or not, high volume levels if overdone will damage your ears . Unfortunately many musicians(this includes classical un amplified genre also) suffer significant hearing loss over the years due to excessive SPL environments. Be careful and preserve your precious hearing sense.
Regards, |
My old XA100.5 monoblocks ( 100 watt classA) were superior in drive, control, slamm and dynamics compared to my older heavy Modified Musical Fidelity Nu-Vista-300. This one measured far over 2 times 350 watts ( 8 ohm) |
I naturally, and I bet I'm not the only one, tend to turn up the volume until I perceive the "sweet spot". Since odd ordered harmonics are our sound pressure clue, their absence (relative term), with very clean reproduction will tend to promote increased listening levels. It does not sound loud even though it is. My solution, since I listen several hours daily, is to use a sound meter to monitor spls. I'm using a free droid app. Sometimes I even pay attention to it. |
Since I have set up my system to be absent of loudness cues, it frees me to set the volume to the level that seems appropriate for what I am listening to. A solo guitar being quieter than a full orchestra for example. For example, do the harmonic loudness artifacts you describe commonly fall into the frequency ranges depicted that ears are most sensitive to? The answer to this question is usually 'yes'. The reason is that the amplifier has to work harder to reproduce the lower frequencies. Their harmonics will often show up in the 'birdsong' region. I can provide a simple test that shows how important this odd ordered thing really is. It can be done with simple equipment and is quantifiable. I've offered it before. If anyone here is interested, just say so. |
Thanks Jake. I think the impedance/phased angle plots are demanding as reported in Stereophile mainly because of the 2 ohm dip and 4-5 ohm range. But other than that, the impedance is quite flat between 4 and 5 ohms across the freq. band. The low bass peaks are typical. Nevertheless, it does demonstrate the VS-115's impressive performance capability. How many amps out there can push power into such low impedance loads?? |
Atmasphere, I am interested to see what you have. If you can't pull up my email you'll get a personal response from mine in a few days. |
