Transistors and tubes are the same speed (speed works out to bandwidth, so imagine how it was that color television was possible with tubes; color television requires some bandwidth!).
It is the output transformer of a tube amp that usually limits its speed. However, delivering the 'current' to play bass on an ESL is no problem at all for a tube amp, in fact generally speaking transistors are less able to deliver the power needed, simply on account of the fact that the bass region of most ESLs is also the region of the highest impedance, which is often ten times higher than it is at 15-20KHz. |
hi everyone,
I had actually pose my opinion in another article, but I think this subject here is more suited and I wish senior members would share their valuable knowledge & experiences.
We had seen many varieties of impedance coupled with varying phase angles charts, especially from ESL speakers when they behave like a giant cap into high freq.
When some audiophiles describe tubes amp suit well for ESL, we are assuming the tubes would handle the voltage & current needed by the speakers optimally, at a certain range of frequencies. because, generally tubes cannot provide enough high current into magnetic coils when required for high excursion of speaker drivers into low bass and high frequencies due to same reasons too.
Now, I do not know how tubes behave given the ever changing phase angle in relation to impedance,(voltage leads or lags before/after the current), but I suspect that tube can offer more "fluctuation" or "more tolerant" to out of phase signals when required by the speaker to produce music. I believe tubes are naturally more "forgiving"(tubes can give more voltage without rising current) as compared to output transistors when facing these out of phase requirements posed by speakers, especially ESLs. I guess transistors usually have a tighter range to work with electrical signal. transistors are generally linear devices am I right? my bet is that transistors work best when voltage and current are output simultaneously(meaning linear), to provide the power needed by speakers, so if transistors need to work beyond its specification(non-linear, as required by out of phase angle signal), it would clip even before it reaches its full rated power(watt) regardless it is a single or multiple transistors trying to provide power into a given load.
base on above assumption, I perceive that tubes would better suited for ESLs but there are caveats, that's the songs the listener is playing should not contain low bass & high notes i.e. no punching bass, no high pitch like triangles or in harps, electric guitars etc.. (please also bear in mind tubes are slower in response, transistors are faster)
just my two cents |
Do what the maker recommends.
It'll all work. It's just a matter of how well. The maker should know best what works best. Once you've done that, then you are in a position to try something different and see how that works in comparison. You never quite know what will sound best to someone, however its much easier to determine what will perform best from a technical perspective. Optimal performance is usually the best place to start. Where one ends up after that might still be different, but at least you know you started out on the right road.
If you need an adaptor, impedance or otherwise in order to make things work well, you probably did not start out on the right road. |
An informative review from HiFi World there Al, however from my own in-room measurements 92 to 96 db peaks were demanding 120 to 140 Watts of the amplifier, therefore I must say that I am somewhat sceptical of the reviews 'more than adequate' power recommendation of 50 Watts! |
A simple way to hear what negative effects they have, is to put them on an amp that has no problem driving a speaker.
Then you will hear what negative effects they have when they are in.
In my view they are interim fix, to allow an amp that has problems driving the speaker, to make it usable with that speaker. And I use the word "usable" lightly.
A owner is far better off getting the right amp for the speaker, or the right speaker for that amp to start with.
Cheers George
|
Hard to say Al, he's not said what phenomena he ran into with any specificity.
Paul Speltz is very supportive though and often has suggestions for how to sort things out should one run into problems. |
Ralph, take a look at the impedance curve for the CLX, shown at the bottom of this page. Could it be that Tsushima1's negative experience with the Zero was the result of the speaker's extremely high impedance at low frequencies being multiplied 2 or 3 or 4 times, resulting in the tube amplifiers he used running essentially unloaded at low frequencies? Or, at best, running into impedances at low frequencies that were non-optimal for the output taps provided on the amplifiers? Best regards, -- Al |
Atmosphere, I did not, as there was nothing radically unusual in any of the three valve amplifier models ( two pentode PP and one Ultra Linear ) that I experimented with, the latter being right on the recommended minimum for CLX's and therefore in theory should have produced the most perceivable improvement, if any, of the three.
As I say, entirely unexpected considering the due diligence before purchase! |
^^ Did you speak to Paul about it? Your experience is unusual (although much depends on the amp too). |
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I have to say that my own expearience of the Zero's into ML CLX's would seem to parallel with MrLoFi's, given the many favourable endorsements on line I was most surprised to find that IMHO the Zero's rather than opening up the presentation produced the opposite effect within my system
( Configuration and polarity checked and double checked for user error) |
I've had a pair of Zero's given to me, to me they are a band aid fix for an amp that not right for the speaker it's being use on, and the disadvantages far outweigh the advantages.
Your far better off getting the right amp for that speaker.
PS: I gave the Zero's away as well.
Cheers George
|
Yet they sound perfect and well extended when driven by my big current pushing solid state monoblock amps. 'Current pushing'? This sounds like a misconception to me. Again, Martin Logan is specific about the amplifier to use with their speaker because they have made the speaker so hard to drive. 0.5 ohms is hard on all amps, not just tubes! What you want to consider is how the amplifier distorts when presented with a low impedance- and in this case, **all** amplifiers, tube or solid state, will have higher distortion which will result in brightness. I suspect this is why Paul Speltz got a letter from Steve McCormick, wherein Steve described how even though his amps can drive 4 ohms effortlessly and with double the power of the 8 ohm load, the fact was that they sounded better (smoother, greater detail) when using the ZEROs to drive the same load. The simple fact is that you don't want an amplifier to work hard- it will have greater distortion which is to say it will sound harsher and with less detail. George, you should give a set of ZEROs a try with your Rogue amplifiers. I think you will find that by using them, they keep up with your solid state amps in the highs. That is the experience of many people using the ZEROs. The ZERO website ( http://www.zeroimpedance.com) has many comments in that regard. |
Yes Al and that why I say a Quad 57 is voiced around a low power low current tube amp, but with Martin Logan's statement:
"Quote:
However, it is important that the amplifier be stable operating into varying impedance loads: an ideally stable amplifier will typically be able to deliver nearly twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms." Quote:
This is why my ML Monoliths have very subdued/rolled off character in the uppermid/highs and dynamics when driven from my tube Rogue 120 monoblocks.
Yet they sound perfect and well extended when driven by my big current pushing solid state monoblock amps.
Cheers George
|
Again, though, as I indicated in my previous post George's comments mainly address frequency response at the amplifier output/speaker input. And flat frequency response at those points does not necessarily mean that the acoustic output of the speaker will have flat frequency response.
Ralph (Atmasphere) stated above that "in an ESL, the efficiency is fairly constant despite the impedance." ("Efficiency" referring to acoustic power out vs. electrical power in). I believe that is generally true. But even if we assume that the efficiency of a given ESL is just a little bit closer to being constant across the frequency range than it is to mirroring the impedance curve, then the minimal variation of amplifier output voltage as a function of load impedance that is characteristic of almost all solid state amps (assuming they are operated within the limits of their voltage, current, power, and thermal capabilities), and hence the increase in power delivery that will occur as impedance decreases, will result in greater frequency response variation in the acoustic output of that ESL than would result with a tube amplifier (operated within its capabilities) whose output impedance is some relatively high value, and whose output voltage therefore varies significantly as a function of varying load impedance.
Apologies for the long sentence :-)
Regards,
-- Al
|
|
Here is an Audio Research Reference 150 considered by many to be a tube amp with better drive than most. It's only being asked to drive 2.83v hardly taxing. Look at the black trace in the link, this is Sterophile's simulated (rather easy speaker load), the 150 is having a hard time staying flat.(I can show you an impedance graph of their simulated speaker load, I have it somewhere it's not as nasty as the ML's) Then look what happens to it when it has to drive a straight 2ohm load (green trace) it's really starting to take a dive in the upper mids/highs. What do you think will happen to the highs into a 1ohm capacitive load of the ML's http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements#dgk5iym3Akuwqg5H.97Cheers George |
An amp like say a Krell or similar, will remain almost flat in it's response across the frequency spectrum.
All you need to do is look at the simulated speaker load graphs of amps at 1/3 power on Stereophile to see what happens to them if they have, high'ish output impedance or can't deliver current, many tube amps exhibit this, and even many Mosfets, they are far from the ideal flat.
And the simulated speaker load that Stereophile uses is not as savage as what we're talking about here with the ML's, and things like Wilson Watt/puppy, Alexandria etc.
Cheers George
|
George,
Would it also be true than that an amp that can't make power into higher impedances is also a "tone control" of sorts?
Respectfully,
Lee |
Sorry guys amp that can't keep it's end up at those 1ohms loads, will not have a flat frequency response from 20hz to 20khz no matter what level it's being played at. It becomes a tone control, end of story.
Cheers George
|
Atmasphere,
Thank you very much for your response.
So, if I understand correctly, for the most part an ESL will be as efficent (output approximately the same sound pressure level or volume) at a given amplifier output, say 1W, regardless of the impedance? I assume at the impedance extreme of the ESL (less than say 2ohms) the SPL will be reduced?
I hear reference of "less musical energy" at the upper registers. Effect being these upper frequency sounds are by nature "softer/lower" in volume compared to lower frequencies and less amplifier output is required?
Again my apologies for my simplistic understanding.
Lee |
Hvowell, said earlier:
Now is the reason this type of amp works is (assuming the speaker has a sensitivity (SPL) of 85db/1W into 8 ohms)
.25W into 32ohms = 85db
.50W into 16ohms = 85db
1W inot 8 ohms = 85db
2W into 4 ohms = 85db
4W into 2 ohms = 85db
so the SPL remains constant into all impedances?
The reason this is not so is because in the case of an ESL, the impedance curve is **not** an efficiency curve. The fact is that the impedance curve is based on a capacitor more than anything else. This makes ESLs fundamentally different from dynamic drivers in a box. In an ESL, the efficiency is fairly constant despite the impedance. Generally speaking, ESLs have an impedance curve that varies by about 10:1 over the range of the speaker, which makes any one of them tricky for all amps. The reason they work at all with solid state amps is due to the negative feedback loop in the amplifier which allows the amp to adapt somewhat (reduce its output at higher frequencies) to the lower impedance at high frequencies. Despite that its a common complain that a transistor amp will be too bright on an ESL (not the least of which is that negative feedback in and of itself can cause brightness; likely a topic for another thread). For example the Sound Labs, early Quads and Audiostatics are easily driven with tubes as the matching transformer in the speaker sets the bass impedance fairly high (usually over 16 ohms). OTOH, Martin Logan use the matching transformer to set the bass impedance at about 4-5 ohms, making the 20KHz about 0.5 ohms. This is why they want an amplifier that can double power reliably into low impedances, else they would simply not be getting any highs at all! Note: George is mis-using the word 'stability' and 'stable' in his comments (it may not be his fault; this is a common mis-use of the word). Stability in an amplifier is how well the amplifier resists *oscillation*. For example our smaller amplifiers, like the M-60 (which is an OTL) are perfectly stable driving 4 ohms even though they don't make as much power doing so. OTOH some transistor amplifier are unstable driving capacitive loads (IOW they can go into oscillation) even though they can double power as the load impedance is cut in half. We have customers driving Martin-Logan ESLs quite successfully using either our old Z-Music autoformers from years ago or the ZEROs. Both allow our amps to drive the ML ESLs with ease with no high frequency softness. I've heard one of these systems; if anything to me the combination might have been a little bright, but some of that may have been caused by the solid state preamp that was also in the signal chain. |
Simple ... it's a function of the transducer system itself. That is what is meant by how the speaker is voiced.
Take a simple example. A speaker system may present an impedance load of 20ohms at the mid/tweeter x-over point. Yet, assuming the drivers are phase coherent at the x-over point, and if the speakers are well designed, the FR should be flat over the x-over point. Similarly, a speaker's impedance function even outside the x-over points may fluctuate. But still, the driver system emits a level FR SPL. It's about how the speaker was voiced.
There are some, but not many, speakers whose impedance function is near linear. Unless the impedance level is either ridiculously low or high, and the phase angle plots are not wacko, such a speaker could very well be both SS and tube (Power Paradigm) friendly. Just throwing this out there, but I think Maggies might represent a somewhat level 4 ohm load and pretty benign phase angles. I'm sure there others. |
Now is the reason this type of amp works is (assuming the speaker has a sensitivity (SPL) of 85db/1W into 8 ohms)
.25W into 32ohms = 85db
.50W into 16ohms = 85db
1W inot 8 ohms = 85db
2W into 4 ohms = 85db
4W into 2 ohms = 85db
so the SPL remains constant into all impedances?
Can anyone please comment on the above as to its accuracy? If correct, I dont understand this electrical concept as it pertains to how the speaker plays various notes at the intended (recorded) levels?
Considering a very simplistic example, if a bass note and mid range piano note are recorded at the same level and are played at the same moment, and assuming the speakers impedance at the bass note frequency is different from the speakers impedance at the piano note frequency, how then are the level of these two notes played through the speaker at the intended playback level? At the moment these two notes are played, does the speaker draw a constant output, (voltage/cureent) from the amplifier? If so, lets say it is 1W. If the above speaker sensitivity question is true, how can both notes be played at the same level at 1W being drawn from the amplifier?
Thank you, Lee |
Unless the amp is being tortured by the load and sensitivity of the speakers:
See this article:
http://www.stereophile.com/reference/707heavy#ovW5G38gcYb8whWE.97 |
"important to know whether the ESL was voiced to be driven by a SS or tube amp."
I own myself a pair of ML Monoliths III's with quite new fresh panels.
If I drive them with a my pair of Rogue 120 tube amps, they have highs but they are very distant and too polite, if I drive them with my solid state amps (similar to big Krells) low output impedance and gobs of current the high are where they should be and you know all about cymbal crashes.
And this thread is about the right amp for ML's not Quad 57, which I agree were most probably voiced with low power tube amps.
For Martin Logan to mention an amp should double into 4 from 8 and then increase again into 2ohm, this means current. And they also want one that's stable into capacitive loads like ESL's.
And lets face it a stable amp can be a 5 watter and have no current ability, so long as it doesn't ring or oscillate it's stable, current ability has nothing to do with stability into capacitive loads as ESL present.
Cheers George
|
George, you posted "[a]ll you have to do is look at Stereophile speaker simulated load graphs of tube amps especially to see that they cannot give a flat frequency response into those types of loads, especially ones that dip down to 1ohms."
I generally concur, but as I am sure you know, not all tube amps are made the same. For example, take a look at JA's bench measurements of my amp, the ARC Ref 150:
http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements#52FW4Aq5RbfXP6dv.97
As you can see, the amp's voltage output plot is a bit wavy when a simulated load is plugged into the amp's 8 ohm taps. That said, JA mentioned that "[t]he figures for the 8 ohm tap [ranged between] 1 and 1.4 ohms; for the 4 ohm tap, they [ranged between] 0.55 and 0.87 ohm." I surmise that the same simulated load would be less wavy if plugged into the amp's 4 ohm taps.
Now ... an actual "off the bench" report from me. If you get a chance, check some of my posts on the "DEQX Game Changer" thread. I bought a DEQX PreMATE, which effects both time domain alignment adjustments and room equalization correction.
To set up the DEQX, actual mic'd measurement are taken at the listener position. The FR of my speakers was frankly a mess. I surmise most of the FR aberrations were caused by room anomalies, not by my amp's output impedance interactions with the speaker. Btw, I drive my speakers off the 4 ohm taps.
One other point of interest. I sent Al my DEQX data files for review and comment. I think Al might concur with my observations. And right now, my speakers are pretty well adjusted via the DEQX. I am enjoying a very pleasant musical experience.
So, based on the foregoing, I suspect that if my amp/speaker combo was checked in an anechoic chamber, my tube amp/speaker FR plots would measure pretty close to the results obtained if my speakers were driven by a high quality SS amp under similar conditions.
Last point. The reason my amp's output impedance is low'ish and output voltage somewhat constant is because ARC uses a prudent amount of negative feedback. There is also some sort of local negative feedback effect achieved by reason of a circuit configuration between the power tubes and the output trannies. Ralph or Al can better explain how that works.
Kudos to all for the good comments.
Cheers,
Bruce |
Great posts by Bruce (Bifwynne), with which I fully concur. 09-13-15: Georgelofi
... amps that cannot deliver current at those low loads ... cannot give a flat frequency response into those types of loads, especially ones that dip down to 1ohms. This is true, but I would emphasize the word "into." The frequency response characteristics of the signal at the input terminals of a speaker that will result in flat frequency response in the acoustic output of the speaker will depend on the design of the particular speaker. As Bruce said, it is "important to know whether the ESL was voiced to be driven by a SS or tube amp." And in that regard it is worth noting that the Quad ESL57 was designed before solid state amps existed. Although admittedly, as I believe you (George) mentioned earlier in this thread or in another similar thread, the vintage Mark Levinson ML-2 solid state amp in particular, rated at only 25 watts or thereabouts into 8 ohms but capable of supplying huge amounts of current into low impedances, is considered by many to have been a good match for the ESL57. While at the same time that speaker has been and still is used with tube amplification by many audiophiles. Regards, -- Al |
The fact is they want an amp that are stable and also that can double it's wattage from 8ohms down to 4 ohms and yet still increase even to 2ohms, (which means an amp that can do good current)
This means that if an amp cannot do this, then at the low 1ohms or 2ohms that their (ML) speakers present to an amp, then that amp will then start to behave like a tone control, and not stay flat in frequency response over the entire impedance range of speaker it's driving.
As simulated speaker load graphs will show you of amps that cannot deliver current at those low loads, therefore their frequency response will not be flat.
All you have to do is look at Stereophile speaker simulated load graphs of tube amps especially to see that they cannot give a flat frequency response into those types of loads, especially ones that dip down to 1ohms.
If you need proof I will post links for you to see what happens, but I think you should go and look for yourself.
Cheers George
|
George, that's a pretty clear clue that ML advises that the owner should use a rock stable SS amp. I don't know how low the impedance gets ... but that is a factor to consider when picking an amp.
This issue has come up before .. possibly in this thread. I'm a tube guy, so I'll let the SS guys weight in. I seem to recall that Ralph thinks Zeros can help in these situations. Never used em' so I stop here.
|
Once again from the Martin Logan website. They should know their own speakers.
"Quote:
However, it is important that the amplifier be stable operating into varying impedance loads: an ideally stable amplifier will typically be able to deliver nearly twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms." Quote:
Cheers George
|
Generally yes ... reason ... there's much less energy called for in the high frequencies. If your music source required the amp to push 100 watts of power into the tweeter, not sure what would blow first ... your ears or the tweeter.
Most of the power demands placed on an amp are in the bass/low midrange. Much less power demands in the upper end. |
Maybe that's why my VAC 30/30 worked so well with my SL-3's.
If this is the case for ESL's, that leaves me with 1 question. Does it matter? To make low notes, the amp needs to make the speaker move a lot of air. Not so for high frequencies. So, for example, if the amp needs to produce a low note at 2 ohms, or if it needs to produce a high note at 2 ohms, wouldn't the amp have an easier time with the high note even though the resistance is the same? |
Going out on a limb here by getting technical than I should. But I recall reading posts from some our tech members that described the "common" ESL impedance function to be like capacitor. That is high impedance at low frequencies and low impedance (sometimes very low) at high frequencies. Indeed, some of the posts said that only amps that are stable driving such loads need apply.
I think another important question to think about is whether the ESLs were voiced to be driven by a SS or tube amp. As Ralph Karsten (Atmasphere) has explained in his white paper, most SS amps operate under the Voltage Paradigm, i.e., these amps have a very low output impedance and maintain constant output voltage. Under this model, power (i.e., watts) delivered to the speaker will inversely vary with the speaker's impedance, i.e., less watts at high impedances; more watts at low impedances.
By contrast, many tube amp have higher output impedances and operate under the Power Paradigm. In such cases, power (watts) will not vary as much with changes in speaker impedances.
The main point is that as long as the amp is operating within its safe operating range, it's more important to know whether the ESL was voiced to be driven by a SS or tube amp.
Btw, I think Ralph has suggested using ZERO autoformers to simulate higher speaker impedance. The theory is that Zeros can help amps manage the very low speaker impedances presented by some ESLs at high frequencies. |
That seems to be the opposite of what it is for most other speakers. Maybe there's something unique about that particular design. |
The quad has an impedance in excess of 32 ohms under 100HZ, with just under 2ohms impedance at about 10KHZ.
Lee |
"If I understand correctly than, for the Quad ESL this means only 6.25W/12.5W in the lower frequencies while 100W into the higher frequencies?"
No. Its the opposite.
If I understand correctly than, for the Quad ESL this means 100 watts in the lower frequencies while 6.25W/12.5W into the higher frequencies?" |
This is all well beyond my understanding and wondering can someone comment on a question concerning the voltage vs power model? I believe I read two, perhaps more, points of view?
Concerning an ESL such as the Quad "57" referenced earlier with a SS amp "doubling" the amps output as the impedance is halved (assume)
25W into 8ohms
50W into 4ohms
100W into 2ohms
would not the output be also "halved" as the impedance rises above 8ohms
12.5W into 16ohms
6.25W into 32ohms
If I understand correctly than, for the Quad ESL this means only 6.25W/12.5W in the lower frequencies while 100W into the higher frequencies?
Now is the reason this type of amp works is (assuming the speaker has a sensitivity (SPL) of 85db/1W into 8 ohms)
.25W into 32ohms = 85db
.50W into 16ohms = 85db
1W inot 8 ohms = 85db
2W into 4 ohms = 85db
4W into 2 ohms = 85db
so the SPL remains constant into all impedances?
Thank you everyone for all the previous information, so very informative!
Lee
|
If you want a tube amplifier to mate with ELS speakers, that excels effortlessly and with outright awesome dynamic contrasts, very low level resolution, go the the CAT and never look back. |
Funny to read this thread about autoformers.
Probably 6-7 years ago, I added a McIntosh SS amp to my arsenal that uses autoformers. At the time, I was also using Steve McCormack's platinum modded amps too. I compared them and shared my thoughts with Steve about the improvements possible with adding an autoformer as an additional mod for his amps and suggested the Paul Speltz product.
He noticed the same thing and, apparently, even wrote about it. I've been inactive in this hobby for quite some time, so it's fascinating to see this recent discussion of something I was dealing with when I last was “involved" in the hobby.
I echo everything Atmasphere is saying and can vouch first hand...not because I was prejudiced or persuaded by forums or audiophile "authority"...but because I discovered this phenomenon organically...almost by accident. |
04-11-14: Atmasphere'Stable' means that the amp won't oscillate when presented with the load in question. Stable is a given with any amp, you may have missed the rest of the Martin Logan quote for the type of amp they recommend for their speakers. And to get these sort of figures, the amps need low output impedance, to get it. So here it is again. " Be able to deliver NEARLY twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms." In other words for the uninitiated, what's needed is an amp that can ALMOST double it's 8ohm wattage for each halving of load. EG: 8ohm-100watts 4ohm-200watts 2ohm-400watts Cheers George |
However, it is important that the amplifier be stable operating into varying impedance loads: an ideally stable amplifier will typically be able to deliver nearly twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms. 'Stable' means that the amp won't oscillate when presented with the load in question. Atmasphere, perhaps I'm not seeing the same things you are? Perhaps. Take a look at Fig 4 at the link you provided. |
..unless there is nobody out there willing to play along..... |
Where did ML ever pick up that crazy paradigm?
I guess it's always easier to put the burden on the other guy :-) That's a pretty safe bet no matter which way one thinks technically. |
From the Marin Logan website:
Quote:
However, it is important that the amplifier be stable operating into varying impedance loads: an ideally stable amplifier will typically be able to deliver nearly twice its rated 8 Ohm wattage into 4 Ohms, and should again increase into 2 Ohms. Quote:
Cheers George
|
04-09-14: Unsound
Unless there is some sort of internal eq or the impedance actually compensates for the drivers-crossover/speaker systems inherent deviations from flat frequency response (something that has been done to some degree in crossover designs from other manufactures, but something I've yet to hear attributed to ML designs), I'd hazard a guess that it might be reasonable to extrapolate that the sound output to somewhat mimic the impedance/frequency graphs provided. As I indicated I have no specific knowledge of the behavior of Martin-Logan speakers. But keep in mind that application of a voltage which is constant as a function of frequency will result in power delivery which progressively increases as impedance decreases. (In saying that I'm oversimplifying a bit by ignoring phase angle effects). As you'll realize, what a speaker basically does is to convert some fraction of the electrical power supplied to it into acoustical power. And as Ralph pointed out earlier, the efficiency of an ESL (power out vs. power in) does not decrease in step with impedance as frequency increases, but instead remains pretty much constant as I understand it. So in the absence of specific indications to the contrary I see no reason to expect flat frequency response in (in terms of voltage) to result in flat frequency response out. As I see it the usefulness of TJN's measurements is that they provide insight into the DIRECTION in which tonality will be affected as a function of amplifier output impedance. But they provide essentially no insight into what output impedance will be optimal. Best regards, -- Al |
Atmasphere, perhaps I'm not seeing the same things you are?
And, Bifwynne's post re: MLs amplifier recommendations seem to suggest amplifier characteristics that are at odds with your post
"...IOW the ML ESLs are a low impedance Power Paradigm loudspeaker." |
Al, thank you. I thought I might have missed something. Still, the last paragraph seems to suggest what I think most could reasonably expect:
"...Figs.5-7 show the measured impedances of the 2Ce, Angelus, and Aerius. Note that the Sonic Frontiers' frequency-response deviations when driving these loudspeakers show the same general trends as the impedance magnitudes of each respective loudspeaker. That is, the peaks and dips in the responses correspond closely to the peaks and dips in the impedance plots. The impedance plot therefore gives a general indication as to just how a given loudspeaker's response will change when used with an amplifier having a high output impedance.—Thomas J. Norton"
Unless there is some sort of internal eq or the impedance actually compensates for the drivers-crossover/speaker systems inherent deviations from flat frequency response (something that has been done to some degree in crossover designs from other manufactures, but something I've yet to hear attributed to ML designs), I'd hazard a guess that it might be reasonable to extrapolate that the sound output to somewhat mimic the impedance/frequency graphs provided. |
Wrm57, the easiest rule of thumb is ask the designer what sort of amplifier they designed the speaker for. |
:) Yes- damping factor is different from "output impedance" in that it gives you an idea of the servo performance of the circuit, it it has any. Unsound, what you see from that graph is the woofer driver in a box, combined with the impedance curve of the ESL. The Aerius is a hybrid speaker. Interestingly, we also see that as ML speakers go, this one is less severe, dropping to a fairly manageable 2 ohms at 20KHz. If I can draw your attention to the letter that is appended to this article, you can see from it why the ZERO works as well as it does, effectively lowering the output impedance of a zero feedback tube amplifier into the range where it might conform with the parameters laid out in the letter. The response plots initially do seem to suggest that the speaker is Voltage Paradigm, since such amplifiers seem capable of producing flat frequency response. I feel its important to point out that the amplifiers in question all show a peak in response as I forecast, which seems to start up at about 7KHz, and increasing with frequency as the impedance of the speaker continues to drop. Since the ear can hear a change in a spectrum of frequencies much better that it can with a single frequency, we now see that there is a correlation between the measurements and subjective listening experience wherein the amplifiers are causing the speaker to have brightness on the top end. As I have mentioned before, this is a common complaint when combining ESLs and transistors. The whole point of the Voltage Paradigm when it was proposed way back in the late 1950s and into the 1960s was that it would eliminate tonal coloration due to frequency response errors. What we see from these measurements is that isn't happening. Now the Power Paradigm does not make any such guarantee. Instead, it seeks to keep the kinds of distortion to which the ear is most sensitive to a minimum. This is does because the ear translates such distortions to tonality, the idea being that there is a tipping point in the brain where the tonality of distortion can be more pronounced than actual frequency response errors. If this pans out correctly, it may well mean that the result will seem more linear, even when the frequency response does not seem to be quite as flat. IOW, this whole thing has to do with how we perceive sound as opposed to how we measure it. Its a classic argument, and as I pointed out in my article about the Voltage and Power Paradigms ( http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php) this argument has been around ever since the Voltage Paradigm was introduced. |
