Current amp vs Voltage amp
I think that you'll find this thread and this one to be informative. Also, if you haven't already, see Atmasphere's paper on Paradigms in Amplifier Design. Regards, -- Al |
Al, Ralph and OP. As Al and Ralph know, I have been acutely, maybe obsessively, interested in the OP's Q. I drive a pair of Paradigm S8s (v3) with an ARC VS-115 tube amp. I can't think of a worse match because the S8s have one of the most wacko impedance curve and phase angle plots I have ever seen. Indeed, when I called Paradigm, I was told the S8s were designed and voiced to be driven by a high current, high power SS amp. OTOH, ARC and Paradigm said I could still get away with my VS-115 -- whatever that means. I was feeling a bit down until I read the review and bench test reports on two ARC tube amps. Stereophile's report on the Ref 150 and Soundstage's report on the VS-115 (my amp). Both use about 12 to 14 dbs of negative feedback, which I will touch on below. Now here's the interesting point that I always overlooked. Take a look at the graphs that report the FR output results of both amps when driving a standard dummy load. I copied the URL sites of both reports. They dummy loads are pretty similar and may be standardized. Does power output as a function of frequency vary -- yes!. But not as much as I would have thought: +/- 1 db, or so with both amps driving the dummy load off the 8 ohm taps. Could that variance "flavor" the presentation? I think so. John Atkinson's comments (re the Ref 150) about this phenomenom (sp?) are interesting: "All three taps offer quite a low source impedance for a transformer-coupled design; as a result, the modulation of the amplifier's frequency response, due to the Ohm's Law action between that impedance and that of our standard simulated loudspeaker, was relatively mild. From the 8 ohm tap (fig.1, gray trace), it was ±0.8dB; the 4 ohm tap offered ±0.4dB, the 16 ohm tap ±1dB." In other words, driving a speaker off the 4 ohm tap resulted in a lower variance of FR as a function of frequency. Up until now, I had been driving my speakers off the 8 ohm tap. I always thought the presentation was a bit "forward." I think I now know why. The S8's 28 ohm impedance peak at the 2.2K Hz crossover point should have resulted in an exaggerated FR output and I think it did. Even at 1 or 2 db, I think it changed the acoustic presentation. I recently switched off to the 4 ohm tap. At times I think the presentation is less defined, maybe flatter. But I turned up the gain a bit and I think the detail is all there. Even the bass is flatter, more extended, maybe more honest. I've been using the 8 ohm tap for so long, I need to re-educate my ears. Time will tell. Perhaps Al and Ralph will chime in here. But I think the reason for my experience may be that the use of negative feedback lowered my amp's output impedance. This may have the effect of making my tube amp perform somewhat "SS-like" when presented with varying impedance curves. Dunno. Well that's all I have to say, which has been a lot. I look forward to reading Al's and Ralph's responses. The URLs I referred to are posted below. http://www.soundstagenetwork.com/measurements/amplifiers/arc_vs115/ http://www.soundstagemagazine.com/measurements/test_amplifiers.htm http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements http://www.stereophile.com/reference/60/index.html |
I always tell owners of ARC to try the 4 ohm tap. Some like it better some not so much. Note that there aren't many true 8 ohm impedance speakers especially just past the woofer impedance peak. Woofers usually dip to around 3-6 ohms. You might even get better bass control and definition off that tap. |
Hi Bruce (Bifwynne), I've looked at the references you provided, and read your post, and I think that everything you've said is essentially correct. Basically, your VS-115 has a lower output impedance than many or most other tube amps, on a given tap. The significant amount of negative feedback it uses is presumably a major reason for that. And it can be presumed that the output impedance of its 4 ohm tap is approximately half of the output impedance of its 8 ohm tap. The lower the output impedance of a tube amp, the more closely the effects of the interaction of that output impedance with the impedance vs. frequency characteristics of the speaker will approach those of a solid state amplifier (which will have near zero output impedance, in most cases). The one slight qualification I would make to your post (which you probably already realize) is to emphasize that JA's reference to obtaining a flatter frequency response with the 4 ohm tap than with the 8 ohm tap applies to his "standard simulated loudspeaker load," which has impedance characteristics that are quite different than those of your (and many other) speakers. As you probably already realize, for that and other reasons a generalization should not be drawn that 4 ohm taps will inevitably provide flatter frequency response than 8 ohm taps. It depends on the speaker. In this particular case, though, given that your speakers were voiced for solid state amps, it can be expected that lower output impedance will result in a flatter response, everything else being equal. Best regards, -- Al |
Thanks Al. One thing that the reports I cited answered for me was the magnitude of the FR variance. I didn't know how to convert the impedance and phase angle data into useable information. As you can see from both reports, the ARC Ref 150 and VS-115 use roughly the same amounts of NF and have similar output impedance stats. Further, the amps were tested by different people at difference times which gives me some confidence that the data is reliable. As I mentioned above, it appears that using the 4 ohm tap should yield a better FR result. I think it just might be doing that. Short of having an acoustician do precise measurements, I'll go by my ears. Just have to get use to a different acoustic presentation off the 4 ohm tap. This post and others like it provides important information for folks who want to use tube amps. I think the take-a-ways are the White Paper Paradigms present the extreme cases. As we can now see, my tube amp doesn't neatly fit into the Power Paradigm category. The other take-a-way is that folks looking to match tube amps with speakers should be somewhat mindful about the speaker's impedance and phase angle swings and their tube amp's output impedance. Of course, there's no substituting for a serious listen. My thanks to Al and Ralph for hanging in there with me. |
A note on terminology: Unless there are some extremely unusual exceptions out there, all audio power amplifiers amplify both voltage and current, so the terminology in the subject line of the thread is a bit misleading. Solid state amplifiers having near zero output impedance are sometimes referred to as being voltage sources, meaning that for a given input voltage their output voltage will remain constant regardless of load impedance (within the limits of their capability). Referring to them as being voltage sources is accurate terminology, to a very close approximation. (The reason it is a very close approximation, rather than being exact, is that no real world amplifier can have an output impedance that is exactly zero). Tube amplifiers, having significant output impedances, are sometimes referred to as being current sources, which strictly speaking would mean that for a given input voltage the current they output would remain constant regardless of load impedance (within the limits of their capability). That is NOT accurate terminology, except in the extremely loose sense that their output current will vary LESS as a function of load impedance than in the case of an amplifier having near zero output impedance. It may be helpful to read this Wikipedia writeup on the voltage divider effect. In the first figure, consider Z1 as representing the output impedance of the amplifier, and Z2 as representing the impedance of the speaker, which will be different at different frequencies. Regards, -- Al |
Hi Unsound, I suspect it to be true that more often than not speakers having widely varying impedances will provide flatter frequency responses when driven by solid state amps. But if so, that would simply be because more often than not speakers are designed and voiced with the expectation they they are most likely to be used with solid state amplifiers. But there are certainly a great many speakers having widely varying impedances that will do better with tube amps than with solid state amps. Many electrostatics are notable examples, along with a goodly number of dynamic (box-type) speakers. The effects of amplifier/speaker impedance interactions are, of course, just one of a great many factors affecting the frequency response and tonal balance of a speaker. Which kind of amplifier stands the best chance of being optimal after all those factors net out depends, as Atmasphere has said in similar threads in the past, mainly on the intentions of the designer. Best regards, -- Al |
I copied below John Atkinson's bench tests of the Revel Ultima Salon 2, a speaker that most would agree is a very high end performer. While the impedance and phase angle plots are more "user friendly" than my Paradigm S8s, it is important to note that even the mighty Revel's impedance plots have peaks and valleys. The low being a little less than 4 ohms in the bass region, with a high of 14 ohms in the mid/treble FR range. So . . . based on the comments above, I would expect that if the Revels were driven by a "pure" Power Paradigm amp with a relatively high output impedance, the acoustic presentation could very well be colored to some extent in the mid/treble FR range. But as Al said, such may not necessarily be the case because many tube amps are configured to have lower output impedances than one might expect, probably because of NF. In light of the bench test results of the ARC Ref 150 and VS-115, see above, if those amps were used to drive the Revels, I surmise that the acoustic coloration might not be too far off, especially if the 4 ohm taps are used. I don't know if the Ref 150 or VS-115 have enough "oomph" to get the best out of the Revels, but I don't think you would get a headache listening to them. Btw, I seem to recall that the Revel web site recommends a high current/high output SS amp to get the best results out of the Revels. I understand that the Revels are somewhat inefficient. I hope our membership reads these OPs because I think there is much to learn. I think this OP and other OPs are asking good questions. Btw, btw, as I am retraining my ears to get used to listening to my S8s driven off the 4 ohm tap, I don't think the S8s sound all that bad -- maybe even better than before. It's probably all in my head. ;>') Cheers, http://www.stereophile.com/content/revel-ultima-salon2-loudspeaker-measurements |
05-05-13: UnsoundSensitivity, defined as the sound pressure level (SPL) generated by the speaker at a given distance, in response to a given voltage at its input terminals, at a given frequency, is what it is for a given speaker. If the impedance of the speaker varies widely as a function of frequency, and if the speaker is driven by a tube amplifier having significant output impedance, then the voltage that appears at the input terminals of the speaker, which will be essentially the same as the amplifier's OUTPUT voltage, will vary significantly as a function of frequency, for a given INPUT voltage to the amplifier. If the same speaker is driven by a solid state amplifier having near zero output impedance, then the voltage that appears at the input terminals of the speaker will NOT vary significantly as a function of frequency, for a given INPUT voltage to the amplifier. What matters is minimizing the variation of SPL, as a function of frequency, for a given INPUT voltage to the amplifier. Which of those two scenarios will produce the best results in that respect depends on the design of the particular speaker, and what kind of amplifier the designer envisioned it being used with. Deadlyvj, thanks for providing the interesting link. A bottom line summary seems to me to be contained in this quote: Due to voltage driving, the sonic performance of virtually all loudspeaker systems is severely impaired by the diverse electromotive forces (see above) induced in the voice coil motor corrupting the ideal behaviour of the amplifier interface....I think that commenting on that intelligently would require both study of the details that are contained in his book, and more knowledge of speaker design than I possess. But his thesis, as I see it, does not change the fact that if a speaker has wide variations of impedance as a function of frequency, it is likely to perform best with an amplifier having whatever kind of output impedance the designer envisioned it being used with. Best regards, -- Al |
If we put aside the issue of damping for the moment, and so long as such a ss amplifier has the required output power, such a ss amplifier would almost always be able to provide more linear output regardless of whether they are ESL's or dynamic speakers, and that would hold true whether or not the impedance swings were wide or not. Whether or not thus would always be audible is of course another issue.:-) |
Hi Unsound, Yes, "such a ss amplifier would almost always be able to provide more linear output regardless of whether they are ESL's or dynamic speakers, and that would hold true whether or not the impedance swings were wide or not." (Assuming that by "linear" you are referring to flat frequency response). However, as I indicated that is not what matters. What matters, with respect to this issue, is the frequency response flatness of the output of the SPEAKER, as judged against the INPUT to the AMPLIFIER. Which in turn depends on how suitable the match is between amplifier output impedance and the design of the particular speaker. Frequency response flatness at the amplifier output/speaker input has no direct relevance. Speakers whose impedance varies significantly as a function of frequency, and that match most optimally with tube amps, can be presumed to require a non-flat frequency response at their input terminals to produce an acoustic output whose frequency response is flat. If such a speaker is mated with a solid state amplifier having near zero output impedance, frequency response flatness will have been optimized at the output of the amplifier, but it will be wrong at the output of the speaker. Best regards, -- Al |
@ Almarg, Hi, I was currious of your statement above, amps operate in a current mode and voltage mode?,, This is quite confussing to me,, My Krell 700cx clearly on all the technical papers, says this amp solely operates only in the current domain!, Krell is very famous for doing that!,, If you can study up on these technical papers for me, that would be cool!How can Krell make such a statement?,, thanks Almarg!,, cheers! |
Unsound, If the output impedance of the amplifier is a good match for the particular speaker, the output of the amplifier WILL adapt appropriately. Think of the amplifier as an amplifier having zero output impedance in series with a resistor whose value corresponds to the actual output impedance. If the impedance of the speaker varies significantly as a function of frequency, and if the amplifier's output impedance is significantly greater than zero (e.g., 1 or 2 or 3 ohms or so, as in the case of most tube amps), the voltage divider effect resulting from the interaction of that output impedance (corresponding to Z1 in the first figure of the reference) and the impedance of the speaker (corresponding to Z2 in the first figure of the reference) will result in the voltage at the amplifier output/speaker input varying as a function of frequency. If the amplifier's output impedance is a good match for the design of the particular speaker, that variation in amplifier output will result in minimal variation of the output of the speaker, as a function of frequency. Audiolabyrinth, I didn't say that amps operate in a current mode and a voltage mode. Actually, I don't know what that would mean, if anything. What I said is that amplifiers amplify both current and voltage. In other words, the voltage at their output is greater than the voltage at their input, and the current supplied by their output is greater than the current going into their input. You are probably referring to Krell's CAST concept, as described here. Note the statement in the first paragraph that "A Krell system connected in CAST transfers the signal in the current domain, throughout the signal path to the amplifier output stage where only one current to voltage conversion (I-to-V) takes place." Following that current to voltage conversion, at the output of the amplifier, both voltage and current would certainly be greater than at the input of the amplifier, or it wouldn't be able to drive the speakers to anything approaching reasonable volume. I see in the manual for the 700CX that its gain is spec'd at 26.4 db. That corresponds to an increase in voltage of about 20 times. And its 700 watt capability into 8 ohms certainly represents vastly more output current (actually, about 9.4 amperes, when the full 700 watts is being delivered into 8 ohms) than any preamp could ever supply to the amplifier's input. Best regards, -- Al |
Al, As always I appreciate your patient and clear explanations. What you eloquently describe is born out with simply listening. Either tube or SS amplifiers will be the best choice depending on the particular driven speaker's design characteristics. Just listen. There's no universal one fits all amplifier design that exists. It all begins with the intentions of the speaker designer. Best Regards, |
Frequency response flatness at the amplifier output/speaker input has no direct relevance. Speakers whose impedance varies significantly as a function of frequency, and that match most optimally with tube amps, can be presumed to require a non-flat frequency response at their input terminals to produce an acoustic output whose frequency response is flat. If such a speaker is mated with a solid state amplifier having near zero output impedance, frequency response flatness will have been optimized at the output of the amplifier, but it will be wrong at the output of the speaker. hi Al, often it seems that a speaker manuf tries to find an amplifier that has an approximate H^-1(f) transfer function of that manuf's speaker so that the amplifier input-to-speaker output (which is sound) transfer function is more or less flat over the audio bandwidth. As you would agree this is a very limiting way to design a speaker - change the amp (or another variable) & the performance falls off the cliff.... |
Hi Bombaywalla, Yes, agreed. As you certainly realize, any design involves a zillion or so tradeoffs and competing considerations, but it's still striking how some speakers can perform well with very diverse kinds of amplifiers, while other speakers cause the choice of amplifier to be very critical. One of the reasons I chose the Daedalus speakers I have is that their combination of a pretty much flat impedance curve, high efficiency, and high power handling capability makes them suitable for use with just about any amplifier out there, except for the really flea-powered types. The Coincidents that Charles uses are similar in that respect. Charles & Audiolabyrinth, thank you most kindly for the nice words. Best regards, -- Al |
One of the reasons I chose the Daedalus speakers I have is that their combination of a pretty much flat impedance curve, high efficiency, and high power handling capability makes them suitable for use with just about any amplifier out there...indeed good qualifications for a speaker to have. Empirically you will find that the people obsessing the least about amplifier-speaker interface are those that have understood the need for the speaker to have a relatively flat impedance & phase (let's not forget that phase response!) curves vs. frequency. Often in these speakers the curve is -3dB at 20KHz which I have been told by certain speaker manufs that this provides better in-room acoustics (vs. a speaker that has no turn-down at 20KHz). Such flat impedance speakers speak about the manuf ability to understand playback requirements & the ability to produce a product that is largely agnostic of the amplifier. Few such speaker manuf exist..... I heard the Daedalus at RMAF one year - I remember that their sonics were very good. Best regards. |
Al and Bombaywalla, it's a shame that only now am I starting to appreciate the import of impedance and phase angles plots. Had I known this before, I would have approached my speaker and amp purchases differently. As I posted above, even the "mighty" Revel Ultima Salons have roller coaster impedance curves, albeit more tube friendly than my S8s. At least Revel had the curtesy of including in their sales literature advice that their speakers sound best when driven by a high current/high power SS amp. At this point, I'm standing pat for now. As I mentioned, I switched over to the 4 ohm taps on my ARC VS-115 tube amp. I think the S8s sound less forward because the midrange is toned down. Although the bench test reports I posted on the ARC Ref 150 and VS-115 suggest that using the 4 ohm taps smooth out the FR variations at the amps' outputs, I'm not sure how that translates into speaker output. My understanding is that the S8s are ruler flat when driven by a solid state amp. Perhaps, using the 4 ohm taps lowers the amp's output impedance (maybe .5+ ohms) enough to smooth out the speaker's actual FR to approach a near zero output impedance of a SS amp. Dunno. If my wife would let me switch out gear, I'm not sure whether I would flip the speakers or the amp. The S8s are the darlings of the reviewer community, especially because of the Be tweeters and top grade engineering, R&D and QC that goes into their manufacture. The VS-115 also has garnered high grades. If I was to flip speakers, I probably would opt for the Revel Studio 2s, but would need to also flip for a high quality tube amp, maybe the new Ayre VX-5. Dunno??? |
Sorry I got to this late. It seems there are some things that need clarifying. If I am not beating a dead horse too much... Bifwynne, by adding negative feedback to an amplifier you do indeed move the amp towards the Voltage Paradigm. This is because as you surmised the 'output impedance' is lowered. I paraphrased the term because it is misunderstood however, and that is where the clarification comes in. Unsound, you might want to pay attention to this. Under the Voltage Paradigm, you have the term 'output impedance'. The term has a definition which is not intuitive. It refers to the amount of servo gain that the amplifier has which allows it to react to a load. It does not refer to the actual output impedance of the amp, as measured by any other field of endeavor in the world of electronics. How can we know this? The answer is simple. If the output impedance were indeed lowered, the amp could drive a progressively lower and lower impedance. It might even make more power. But we see by adding feedback to an amplifier that the output power into lower impedances does not change. IOW, what is happening is that the feedback gives the amp the ability to adapt to its load within certain limits by taking samples of its performance and using that as an error correction. The only way you can really get a lower output impedance is with bigger output transformers, more tubes or more transistors. The extra ability to drive a lower impedance does not come out of thin air or feedback- to do so would violate a fundamental rule of electronics known as Kirchoff's Law. The difference between the Voltage and Power Paradigms has more to do with feedback then tubes/transistors. With regards to Current Source, Power Source and Voltage Source: If the amp has a lot of voltage feedback it could become a Voltage Source. Most Transistor amps attempt to be Voltage Sources (and most of them run a lot of feedback). What this means is given a sine wave input signal, and a load of variable impedance (like a typical box speaker), the output voltage will always be the same. Note that with this model (the Voltage Paradigm) the *current* will vary as the load impedance varies. This is how such an amp can double power as impedance is cut in half, as with half the impedance the current will be double. Under the Power Paradigm the amplifier will attempt to make constant power into any load rather than constant voltage (there is a little math of note here, Power = Voltage X Current). IOW a Power Source. This is the behavior of a tube amp without voltage feedback. Depending on the load variation, both output voltage and output current will vary. Under the Power Paradigm, the output impedance of the amplifier is in fact the actual impedance of the output section of the amp. An amplifier can also be a Current Source, although there has never been a paradigm of design, test and measurement that has evolved around it. This type of operation is done by using current feedback rather than voltage feedback. Constant Current amps tend to have a very high output impedance by any measure, often well above 50 ohms. This does not mean that they cannot work with conventional speakers. Nelson Pass as done a lot of work in this area in recent years. |
My understanding is that the S8s are ruler flat when driven by a solid state amp.I doubt that, Bifwynne. With a SS amp, with the output impedance being very low (well into the sub-1 Ohm region), the amplifier is much less perturbed by the roller-coaster impedance & phase response of the speaker. The low output impedance of the amp allows it to sufficient source/sink current into the speaker to give you good sonics & dynamics (assumption is that the power amplifier has a robust power supply that is able to more or less double in wattage for each halving of the speaker impedance). So, the speaker will still have its roller-coaster impedance & phase responses but you will hear less of it with a SS amp. Perhaps, using the 4 ohm taps lowers the amp's output impedance (maybe .5+ ohms) enough to smooth out the speaker's actual FR to approach a near zero output impedance of a SS amp. Dunno.No, that's not what happens. The output impedance of a tube amp is dictated by the # of the tubes used in parallel in the output stage & the amount of global negative feedback used by the designer (each & every electronic output device - tube or transistor - inherently has local negative feedback in it. You cannot get away from this local feedback. To quote Nelson Pass in one of his White Papers "show me an electronic device & I will show you the local negative feedback"). Tubes usually have a very high output impedance relative to a speaker hence you have to jump thru some hoops to make a tube amp drive a speaker directly i.e. without output transformers. People like Atmasphere & Berning do that. And, back in the old days there was Harvey Rosenthal (?) who came up with the 1st zOTL amp (I think I'm remembering this correctly??) The output transformer is put in place between the tube power output stage & the speaker input to buffer the tube amp from the wild swings in the impedance & phase of the speaker. On the primary side of the output transformer, the tube power output stage sees a constant impedance. By working into a constant impedance, there is optimum power transfer from the tube output stage into the output transformer primary windings load impedance. So, the waters (if you may) are calm/serene. On the secondary windings side of the power output transformer, the waters are rather choppy due to the speaker impedance & phase variations vs. freq. Several output taps are provided to match the speaker impedance such that there is more optimum power transfer between the secondary windings & the speaker input. Some speakers are categorized as 8 Ohms speakers by their manuf. Then, use the 8 Ohm tap. Other are categorized at 4 Ohms speakers. Then, use the 4 Ohm tap. Still others are categorized as 6 Ohms speakers by their manuf. In this case, one needs to try both 8 & 4 Ohm taps to see which one is better. For example, the RM10 likes to use the 4 Ohm tap for a 6 Ohm speaker. The way this amp is designed it generates more power into the speaker. (I think I'm remembering this correctly??). So, changing the output transformer tap merely provides a way to "tune" the power transfer towards more optimum between the tube power output stage & the speaker input. The amplifier output impedance does not change in the way your sentence reads. FWIW. The S8s are the darlings of the reviewer community, especially because of the Be tweeters and top grade engineering, R&D and QC that goes into their manufacture.so what?? are these reviewers your friends i.e. do you trust their judgements & opinions? Do you know them personally? have you been to their house & Listened to their resp. systems? Are their music tastes aligned with yours? If yes, to all the above questions, then, I would buy what they recommend. Otherwise, it's just a review to be taken with a grain of salt. Who cares about the Be tweeter, the fit & finish & the QC when the speaker manuf does not possess the fundamentals of speaker design??? Get the physics right then let's talk Be tweeter, the fit & finish & the QC. Otherwise, this is all marketing hype disguised to hide fundamental flaws in the speaker performance as you have found out the hard way. Atleast, this is my take on the matter. YMMV. |
People like Atmasphere & Berning do that. And, back in the old days there was Harvey Rosenthal (?) who came up with the 1st zOTL amp (I think I'm remembering this correctly??) No. Harvey Rosenberg had a contract for a while with David Berning (which never went anywhere), at or near that time he coined the 'ZOTL' term, which refers to David's amplifiers (which employ an unusual output transformer, one lacking the usual limitations of normal output transformers; IOW not an OTL, and a brilliant design regardless). The output transformer is put in place between the tube power output stage & the speaker input to buffer the tube amp from the wild swings in the impedance & phase of the speaker. This set of comments are incorrect. The transformer does not buffer impedance or phase at all. It *transforms* it (hence the term). So whatever swings of impedance seen in the load are translated to much higher impedances which are what the tubes see. If the impedance of the load is too low, the tubes will make distortion and less power; if too high the transformer will ring (distort). That is why taps are provided. This is also why a lot of designers see the need for negative feedback, to tame the distortion of mismatched loads on the tubes due to impedance variation in the load, as well as the distortion of the transformer itself. You can have impedance variations in the load and have it work perfectly fine with an amplifier that has no feedback; that is to say that feedback is not required for a neutral presentation on a speaker that has a variable impedance curve. It turns out that the ear has a tipping point where it will favor tonality due to distortion over actual frequency response variation (and FWIW, just look at the charts of any speaker- **no-one** in the world has actual flat frequency response from any speaker; this is why I see the Voltage Paradigm as an entirely failed concept, not the least of which it ignores human hearing rules). IOW its often far more important to have low distortion in many cases than perfect voltage response. As Bifwynn found out, it is the interface between the amp and speaker that is far more important than the cost of either the amp or the speaker. When you understand the Voltage and Power Paradigm concepts essentially you take a lot of the guesswork out of matching amps and speakers. Imagine the money saved if the industry actually talked openly about this! |
Bifwynne, by adding negative feedback to an amplifier you do indeed move the amp towards the Voltage Paradigm. This is because as you surmised the 'output impedance' is lowered. I paraphrased the term because it is misunderstood however, and that is where the clarification comes in. Unsound, you might want to pay attention to this.Ralph, thanks for your characteristically erudite inputs. I think I understand this, and it seems to make sense to me. At the same time, though, referring to the conventional and intuitive definition of "output impedance," isn't it true that the output impedance of a tube amp for its 4 ohm tap will be about one-half of its value for the 8 ohm tap? And if so, regardless of whether the amp uses feedback from its output or not, won't that reduced output impedance reduce the frequency response variations at the amplifier output/speaker input terminals that would result from the interaction of that output impedance with the impedance vs. frequency variations of the speaker? Albeit at the possible cost of compromising the performance of the amplifier itself, depending on how well the amp can handle the mismatch that may result. That often being a subjectively more significant consideration, as you pointed out in your second post. Best regards, -- Al |
Why are there speakers designed with widely fluctuating impedances and steep phase angles in the first place? Why is there not more of an effort to build speakers with flatter impedance curves and gentler phase angles? Is the availablility of many high power solid state amplifiers to compensate for this their bail out safety net? Is there the belief these types of speakers sound better than those with easier load characteristics? Regards, |
Why are there speakers designed with widely fluctuating impedances and steep phase angles in the first place? Why is there not more of an effort to build speakers with flatter impedance curves and gentler phase angles?IMO, it is because building a speaker with a flat impedance & phase curves requires some serious engineering & knowledge of physics. Not every speaker manuf has that; in fact, most do not. They cover this up with marketing hype - computer-aided design, CNC manuf, lustrous finish, exotic woods, Berrylium & Diamond drivers, blah, blah. There are several trade-offs in manuf speakers such as on-axis & off-axis response, power handling, sensitivity, resonances, tuning the port, bass overhang, etc, etc. I am no speaker designer expert but I've spoken with a few manuf in the many years I've indulged in this hobby. Most of these speaker manuf will make certain trade-offs that will yield wild/roller-coaster impedance & phase curves. With the wide availability of class-AB high power power amps, they figure that some amp on the market will drive their speaker. And, coupled with this is the reliance by the speaker manuf that many, many listeners will not know the difference & not know any better. A speaker that is distorting due to impedance & phase mis-management can be sold to these people as one having more "details" in the sound. Also, such speakers have a "wow" factor - hear a demo in the audio store or in-factory. The person is sold & buys the speaker. A little while later you read a "listener's fatigue" post on Audiogon from this person! This is gradually changing & will force the speaker manuf to wise-up & not output junk designs but the process is slow. That is why I hear: ARC used to voice their amps with Vandersteen, Avalon with Spectral & MIT cables, B&W voiced with Classe amps & so on. Deviate from this combination & you will be in sonic hell (as Bifwynne! :-) I'm sure that there are other (better) reasons & I hope that some other more knowledgeable members chime in. |
Charles1dad -- Bombaywalla makes a fair point that many fine speakers have roller coaster impedance and phase angle plots. As I posted above, even the "mighty" Revel Ultima Salon 2's impedance plot is a bit of rock and roll. OTOH, I think Bombaywalla's comment about me being in "sonic hell" may be a bit extreme. As I also posted above, the ARC Ref 150 and VS-115 amps were bench tested by different labs. Yet the results were consistent. As Ralph and Al explained, the use of NF reduces the output impedance of the amp, thereby making them more amenable to driving speakers with roller coaster impedance and phase angle plots. That is, somewhat SS-like. Al also made a very important comment that even though the ARC amps FR plots were pretty flat at the speaker input interface, the most important stat is what comes out of the business end of the speaker. In the case of the S8s, they are rated, and have been bench tested to be very flat -- when driven by SS amps. I surmise that by using the 4 ohm tap on my VS-115, which as Al thinks might reduce the output impedance of the VS-115, the S8's FR output might approach that achieved with a SS amp. Based on my subjective experience, since switching over to the 4 ohm taps, I think the S8s have a tighter bass response and are less forward as compared to using the 8 ohm taps. BTW, I seem to recall that ARC uses Wilsons to voice their amps. Bottom line: if I were to switch out my speakers to the Revels, I would probably also switch to a high current/high power SS amp, as recommended by Revel. At least Revel was honest enough to tell the consumer the type of amp that should be used. P.S. Bombaywalla -- I think it's unfair to imply that the S8s are junk. I have no intention of starting a speaker war, but suffice to say, I think if properly tweaked and set up, they do a very credible job. |
I think that Bombaywalla may, somewhat understandably, have misconstrued Bruce's situation. AFAIK he hasn't had nearly as much interaction with Bruce and his speaker/amplifier concerns as I (and Ralph) have had. Bruce is certainly not in "speaker hell." He's just trying to develop as good an understanding as possible of the speaker/amplifier interface, which is certainly to his credit, and something that is likely to be helpful in the future. Bombaywalla, I would add just one point to your IMO excellent list of reasons for the proliferation of speakers having problematical impedance curves. And that is that there seems to be a tendency among many audiophiles to equate the ability of a speaker or other component to resolve hardware differences with its ability to resolve musical information. Thus, if on the basis of reviews, user comments, etc., a speaker acquires the reputation of making amplifier selection particularly critical, it will in the minds of many audiophiles create an expectation that it will resolve musical information and detail better than a speaker for which amplifier selection is less critical. While of course, as this thread makes clear, that is by no means necessarily the case. Best regards, -- Al |
P.S. Bombaywalla -- I think it's unfair to imply that the S8s are junk.Bifwynne, sorry I never intended to call the Paradigm S8s to be junk. In my post I meant to say that the marketplace is littered with speakers with very mediocre/poor performance. The comment was not intended to single out any one speaker product. I have NO intention of starting a speaker war here; I would like to be very clear on this point. OTOH, I think Bombaywalla's comment about me being in "sonic hell" may be a bit extreme.LOL! :-D OK, it might have been. But, I took my ques from the following statements Bifwynne wrote in his various posts: I drive a pair of Paradigm S8s (v3) with an ARC VS-115 tube amp. I can't think of a worse match because the S8s have one of the most wacko impedance curve and phase angle plots.... I was feeling a bit down.... If I was to flip speakers, I probably would opt for the Revel Studio 2s, but would need to also flip for a high quality tube amp, maybe the new Ayre VX-5. Dunno???- there's confusion! He's thinking of flipping equipment. I inferred (now I know incorrectly) that he was hitting rock-bottom w/ his present components. |
Bombaywalla, I would add just one point to your IMO excellent list of reasons for the proliferation of speakers having problematical impedance curves. And that is that there seems to be a tendency among many audiophiles to equate the ability of a speaker or other component to resolve hardware differences with its ability to resolve musical information. Thus, if on the basis of reviews, user comments, etc., a speaker acquires the reputation of making amplifier selection particularly critical, it will in the minds of many audiophiles create an expectation that it will resolve musical information and detail better than a speaker for which amplifier selection is less critical. While of course, as this thread makes clear, that is by no means necessarily the case.well-said Al! best regards. |
No offence taken Bombaywalla. Actually, in some of my private communications with Al and Ralph, I too mused that it would be a great boon to the hobby if speaker designers could, with the flip of a switch, change the electronic crossover for SS or tube application. It might require an external crossover -- dunno. But I too take great exception when the industry doesn't disclose the simple fact like Revel, that "so and so speaker is designed to be driven by a [___] amp." Further, where are the tube amp manufacturers? No disclosure there either. The modus operandi is plug and play. IMO, bad form. |
This thread is very educational and thought provoking and comments here are well informed. It really asks the obvious question, why on earth do we have such a high number of these roller coaster impedance speakers? What is their upside. Does it truly demand that much more high level engineering expertise to build flatter impedance speakers with better phase angles? If that's the case then those who are capable of doing this deserve more respect and recognition for their achievement. It's a superior speaker when it allows the buyer more flexibility with amplifier selection. |
Unsound -- fair point. But if nothing else changes, A'gon members who read this post and other like it will realize that it takes more than lip service to think it's an easy task to match speakers and amps. Not sure this is true, but I surmise that most (not all) of the hi-end speakers on the market have roller coaster impedance and phase angle plots. Al and Ralph have made this point many times -- it's important to understand what the designer had in mind when designing a particular speaker. As I mentioned above, my S8s are advertised to have a pretty flat FR plot, as confirmed in a number of independent bench tests. And maybe it's true. But as I also mentioned above, it was only after I called Paradigm that I learned for a fact that my speakers love high current/high power SS amps. Almost eats them up for desert. So the lesson for the rest of us is that until there is more disclosure, caveat emptor is the rule. If one is interested in a particular speaker, unless the sales literature recommends a particular type of amp, call the factory and ask questions until you get a credible answer. Let's face it, speakers and amps can cost a lot of bucks. The smart consumer will ask questions to ensure the pieces fit together. Cheers and I hope our fellow members will read this post. |
Bifwynne, Good post.Why should the burden be on amplifier designers to build larger,more complex and expensive models in order to manage these inefficient and difficult to drive speakers?That`s putting the cart before the horse. Bombaywalla`s point is quite sound, why not better design/engineering from the speaker manufacturers to avoid these problems? |
Charles1dad, I'm not an engineer, but try to be a pragmatist. I also stayed at a Holiday Inn last night. LOL :>') I think others have made the point that amp and speaker designers have to make trade-offs to achieve a certain result at a certain price point. I appreciate that there are a number of "tube friendly" speakers on the market (I am aware of at least 3 or 4 off the top of my head), but I suspect that most are not. Consequently, I surmise that most speaker designers assume that their gear will be driven by high output SS gear and if compromises have to be made, it could be impedance and phase angle attributes. So maybe the real issue is that while tube amps possess certain sonic attributes that SS amps can only hope to mimic, perhaps if something has to "give," tube amp manufacturers will have to figure out a way to make their products able to do double duty and handle speakers that are designed and voiced to be driven by SS amps. Ralph and Al have made a point that such amps are heavy and costly. Perhaps that will be the design challenge of tube amp manufacturers if they want to compete in the present and future marketplace. In the meantime, I have tweaked and configured my gear whereby I am better able to enjoy the music without experiencing listener fatigue. I don't know how flat the FRs of my S8s are, but the output is musical. I'm standing down for now with respect to switching out gear. Next time, I'll be a little smarter when putting gear together. We all live and learn. |
Does it truly demand that much more high level engineering expertise to build flatter impedance speakers with better phase angles?i personally think 'yes'. Empirically, we can all get this info by merely looking at the offerings in the marketplace. How many of the available speakers afford the user the use of a wide range of amplifiers with minimal hit in sonic performance? Each one of these speaker manuf claims to be highly qualified. Are they? If that's the case then those who are capable of doing this deserve more respect and recognition for their achievement.indeed they do! they really do as they have 'got' it. These particular speaker manuf rarely toot their own horn as a result they get forgotten & taken over by those who have eye-candy for speakers. IMO. |
This is a great discussion about the factors that go into good sound from a technical perspective. Speaker/amp matching is perhaps the most important fundamental to get right first to achieve best results IMHO. Every system must have an amp and speakers and other things might help compensate but cannot replace a good amp/speaker match. I am in the camp that says the happy path is to get the fundamentals right from a technical perspective first and tweak from there. Nothing is more fundamental than making sure the amp is up to the task of GETTING THE MOST out of the speakers. |
ALso, shame on the high end audio industry for not making it easier for buyers to get the most out of these products. It would not be hard to come up with a quantitative system for the benefit of buyers to identify quality of amp/speaker matches. But the reality is its up to the buyer to be educated enough to make these decisions. Good luck! I suppose such a system would take a lot of the mystique out of high end audio, for better or for worse. I guess if it were beneficial to the vendors to do something like that, they would. |
05-09-13: Charles1dadI think 'yes' if you don't make the tube amp big (& resultingly expensive). This seems to be the opinion of Al & Atmasphere as well. see quote below from Bifynne's post- tube amp manufacturers will have to figure out a way to make their products able to do double duty and handle speakers that are designed and voiced to be driven by SS amps. Ralph and Al have made a point that such amps are heavy and costly. For example, TRL (Tube Research Labs) makes a 800W/ch tube amp that can drive an Apogee Full Range speaker: http://www.tuberesearchlabs.com/products/gt800.htm no price mentioned. if you have to ask, you can't afford them! ;-) They also make a 400W/ch power amp which is expensive! http://www.tuberesearchlabs.com/products/gt400.htm & I believe that this will also drive a Full Range. Steve Wolcott also makes some high power tube amps (might not be able to drive an Apogee but I'm sure that they can drive other tough speaker loads): http://www.wolcottaudio.com/WA_presence.htm yeah, the upshot is that to keep from losing it's tube attributes the tube amp will have to be big, bulky & expensive to drive tough loads. |
One of the most interesting recent developments in audio to me is that newer high efficiency amplifiers at affordable price points now offer an alternative to easier to drive higher efficiency speakers, which is a popular current high end paradigm for optimizing performance. Full range, quality high efficiency speakers tend to be big and expensive. NEwer high efficiency amplifier technology is capable of taking a lot of the technical guesswork out of the equation and driving most ANY speaker well. PLus they are small and affordable! Watch out! There's a new and very talented kid on the block! Of course, a good technical match alone does not assure that a listener will like what they hear, but it does provide a solid foundation to work with from there. |
Why are there speakers designed with widely fluctuating impedances and steep phase angles in the first place? A woofer in a box will have a resonance that is expressed as a peak in impedance. If there is no accommodation for this fact either in the amp or the speaker, the result will be too much energy at the impedance peak. In the Voltage Paradigm the amplifier power is throttled back. This effectively insures flat frequency response. In the Power Paradigm the box design puts the peak at a lower frequency to take advantage of the extra energy- but again netting fairly flat frequency response, but wiht the additional benefit of bass extension, which might well be up to half an octave. Some speakers don't have impedance curves based on box resonance. With such speakers, the Voltage model falls apart. A good example is an ESL, whose impedance curve is based on a capacitor. It really works a lot better if the amp makes constant power rather than constant voltage. That way the amp can make power in the bass regions where the impedance is high. This is why transistor amps tend to be bright and bass shy on ESLs- and typically why owners of ESLs and transistors put the speaker too close to the rear wall, to get bass reinforcement. They are not realizing the full potential of the speaker. Anytime a Voltage Paradigm product is used with a Power Paradigm product, a tonal aberration will occur. We audiophiles call that 'equipment matching'. One could also ask why amp designers choose not to build amps that can deal with such loads? (This question is posed in the context of 'difficult' loads with low impedance or high phase angles) The answer here is quite simply, such amps that can drive such loads are usually incapable of sounding like real music, as they have design features that violate human hearing/perceptual rules. One common example is the application of negative feedback, which, due to propagation delays in the amplifier circuit, causes ringing distortion, typically odd ordered harmonics (5th, 7th and 9th) which are used by the ear to sort out how loud a sound is. This is a pretty fundamental hearing rule. Amps that violate it have the coloration of brightness and also come off as harsh. If you want to get away from that you have to figure out how to make a low distortion amp that uses no feedback. As stated earlier, distortion often take precedence over actual frequency response errors by the human ear, IOW its more important to have low distortion than it is to have perfectly flat frequency response (which can't be counted on in the best of circumstances anyway). |
