Thanks George. Is it a gross simplification to view EPDR as a "refined" version of impedance which will provide a clue about the load an amp is facing when driving a speaker at various frequencies?? For example, the EPDR of the Wilson Alexis at one point was .9 ohms, which I assume is not particularly amp friendly.
Also, as a practical matter, most impedance and phase angle curves vary significantly as a function of frequency. So what's the deal if a speaker's EPDR in the bass region is .9 ohms (ala the Alexis), but the bandwidth saddle is only say, ... 50 Hz?
Thanks again George.
Bruce |
George, I did a web search for an article that explains EPDR. I found an article authored by Keith Howard printed in Stereophile (July 2007), here:
http://www.stereophile.com/reference/707heavy/index.html
Mr. Howard explains in simple to understand concepts what I have been seeking for some time. Namely an article that folds impedance and phase angle stats together in a way that provides useful information about speaker and amp compatibility.
If Messrs. Howard or Atkinson, or you too George, get around to starting up the SPCA (Society for the Prevention of Cruelty to Amplifiers), send me an application form.
And as usual, we audio dummies are at the mercy of an industry that is not as transparent as it should be. To quote Mr. Howard, "[EPDR] import seems not to have suffused audiophile consciousness. Speaker reviews don't address this issue, and neither do many speaker manufacturers, who are apparently happy to throw the output-device dissipation problem over the fence for amplifier designers to deal with."
Speaking just for myself, I'm embarrassed to call myself an audiophile for not having better quantifiably grasped these concepts a long time ago. What I wound up slapping together is hard to call a system. More the result of sheer dumb luck.
Good night Gracie,
Bruce |
Bifwynne, speakers get a reputation for being 'hard to drive' for a reason. What you might want to think about is the impact on the amp. It does not matter tube or transistor, if the amp is driving a hard to drive load the result will be more distortion from the amp.
For this reason you are usually better off, if sound quality is your goal, to get a speaker with higher impedance (as they are often easier to drive), regardless of the type of amp. Now if **sound pressure** is your goal, then a lower impedance speaker can help if you have a transistor amp.
But usually in high end audio we are more concerned with finesse. So this is something to consider! FWIW, most loudspeaker designers have not sorted out this simple fact that I have posted above. So you will continue to see lower impedances regardless of the speaker technology.
IOW if you were simply able to raise the impedance of a speaker without changing anything else, it would sound better as the amp driving it will sound smoother and more detailed due to a reduction of distortion. ESLs are no different and this is why the ESLs with higher impedance curves also have the most loyal following (they sound better). That is why the *ancient* Quad ESL57 is still around and still has loyal fans. Its easy to drive. |
Ralph, maybe my aim is way off. Instead of picking on amp manufacturers, maybe it's the speaker manufacturers who should be taken out to the woodshed.
But first, let me be generous by at least asking if it's the nature of the beast and the laws of physics that is the reason conventional cone speakers have flaky impedance and phase angle curves? Stated differently, is it possible to design a cone speaker that performs well *AND* has benign impedance and phase angle curves? And is also reasonably sensitive??
I imagine the "SET-heads" must use such speakers or else SET amps just wouldn't do the job.
Bruce |
Is it only flaky if the amp can't handle it? Perhaps the speakers performance benefits from it? |
Stated differently, is it possible to design a cone speaker that performs well *AND* has benign impedance and phase angle curves? And is also reasonably sensitive??
yes! Roy Johnson of Green Mountain Audio has been doing this for a long time now. He's well known but not an audiophile household name like, say, B&W. But his speakers are all cone-driver types & they are often 6 Ohms & they have very little phase shift in the 200Hz-8KHz band (we're talking 10 degrees or less) & outside this band the phase shift is more but nowhere near the speakers that are members of the Society for the Cruetly to Amplifiers. Green Mountain Audio speakers are easy to drive - a 30W/ch RM10 from Roger Modjeski will drive many of his stand-mount speakers to sufficiently high SPL. The Green Mountain Audio speakers are in the 90dB sensitivity range. here is a link to his Rio speaker design notes: http://greenmountainaudio.com/storage/speakers/rio/Rio-Design-Concept.pdfi realize that no phase plot is given but one can assume from the flatness of the impedance curve that the phase is also relatively flat (note that wild impedance curves & wild phase curves are related - when you see one, you see the other. Do an empirical check to convince yourself). here's a review of the Callisto speakers on 6moons: http://www.6moons.com/audioreviews/gma2/callisto.htmlThe Green Mountain Audio speakers always sound like music on all your genres of music. I recently heard them again at RMAF2013 & they once again delighted. Stereophile gave Green Mountain Audio some very good press: http://www.stereophile.com/content/marigo-whirls-green-mountain Roy Johnson on the left (& Marigo Audio Labs owner on Ron Hedrick on the right). For me speakers from the company are really the best & I can't seem to listen to any other type of speaker as they seem "broken" to me (my understanding is that the Apogee Scintilla also has a 1st order x-over). No financial or otherwise implied relationship with Green Mountain Audio. Just a happy former owner. Thanks. |
Thanks for the heads-up George. I'll do some checking. At this point, more from dumb luck, I may have a combo that works ok because my ARC Ref 150 has muscle power and a large reserve power supply, plus my speakers are reasonably sensitive (92 db). Otherwise, I would have been another hapless victim. I'll be smarter next time when I upgrade speakers. That's for sure. |
Bifwynne, another speaker you might look at is Audiokinesis. His speakers are not only more efficient, they are also very easy loads (some of them are 16 ohms) without crazy phase angles, yet also quite musical and good bass extension.
I think you are correct that speaker manufacturers ought to be taken to task. Back in the old days when tubes were the only game in town, speakers were a lot more efficient and higher impedance. When the less expensive power of solid state came along, we saw both impedance and efficiency go down.
When transistors came along, amp manufactures realized they could build an amp with same power as a tube amp, but it might only cost 1/10th as much, yet they could still charge 90% of the tube amp retail cost. A similar thing was going on with speakers- its costs about 1/10th as much to build a lower efficiency driver (as opposed to a high efficiency driver). To get back some of the perceived loss of efficiency, the impedances headed south. IOW, its all about the dollars.
IMO its telling that you can have two speakers, one 10X more efficient, and the more efficient one can have the same bandwidth and be just as revealing, IOW not giving up anything for being more efficient.
I can't think of a good reason for a high end audio loudspeaker to be less than 8 ohms. I've mentioned this plenty of times before- the lower the impedance, the higher the distortion, making any amplifier harsher and less detailed due to the types of distortion and our human hearing/perceptual rules. IOW if you want to make a speaker that seems smoother and more revealing, all you have to do is increase its impedance (all other things being equal- same box characteristics, same crossover points). It will not be that the speaker itself is all that different, but the sound of the amp driving it will be! |
"ARC Ref 150 has muscle power and a large reserve power supply, plus my speakers are reasonably sensitive (92 db)"
That's a pretty solid combo on paper that should be capable of delivering the goods with the right tweaks.
No system is inherently good. Its what you do with it (the "smart" tweaks) that matter.
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"12-09-13: Bifwynne
George, I did a web search for an article that explains EPDR."
Good to see someone is starting to grasp it, I posted (link) 2 graphs of the B&W802D one that shows the impedance and phase angle as separate measurement lines, and the other graph in red that shows them combined to give the actual EPDR load the amp is seeing.
Note the big difference at 60hz and at 700-800hz where the load the amp sees, drops to almost 1 ohm (EPDR) from 3ohms (non EPDR)
http://www.stereo.net.au/forums/index.php?/topic/59228-class-d-amplification-explanation/#entry1010538
And look at the Wilson Alexia comment as well.
Cheers George |
These links will get you there better
B&W802D EPDR load
http://www.stereo.net.au/forums/uploads/monthly_12_2013/post-106386-0-82896500-1386705003.jpg
B&W802D non EPDR load
http://www.stereo.net.au/forums/uploads/monthly_12_2013/post-106386-0-58273700-1386705013.jpg
Cheers George |
The B&W 802D is, FWIW, an excellent example of Voltage Paradigm technology.
The woofers are each 8 ohms, but also 3db less efficient than the 8 ohm mid range and tweeter. They are in parallel, which requires the amplifier to double its power into the woofer load. This brings their output up by 3db, causing them to match with the rest of the speaker.
Yet the spec on the speaker says they are 'nominally 8 ohms'!
The requirement of the speaker is such that almost any amplifier driving it will have to have a fair amount of feedback to do so. This will cause the amp to be un-naturally bright. IMO this makes the speaker a poor choice as you will not be able to find an amplifier that will actually cause the combination to sound like real music.
This is not true of ESLs. |
"The requirement of the speaker is such that almost any amplifier driving it will have to have a fair amount of feedback to do so. This will cause the amp to be un-naturally bright. IMO this makes the speaker a poor choice as you will not be able to find an amplifier that will actually cause the combination to sound like real music."
B&Ws like those often tend to sound bright to me as well, but not always.
I'd compare those to my OHM Walsh speakers, which has impedance drop just below 3 ohm in teh mid bass region based on measures I have seen, but seldom ever sound naturally bright. There a single Walsh style driver does most of teh work up to 7khz or so. There is no driver efficiency mismatch issues to deal with in teh case of the OHM CLS driver. I suspect that might be part of the reason.
MY Bel Canto Class D amps use feedback as well. Brightness and/or fatigue is a non -issue.
I auditioned modern Quad ESLs prior to trying the OHMs. They were a reference standard for me as I heard them in every area except microdynamics. The OHM sound resembles that ES sound with the right amp + the macrodynamics one associated with a traditional dynamic driver. |
"They were a reference standard for me as I heard them in every area except microdynamics. "
Whoops, mean't to say macrodynamics there actually. Sorry. ES speakers I have heard tend to have microdynamics in spades. |
****Whoops, mean't to say macrodynamics there actually. Sorry. ES speakers I have heard tend to have microdynamics in spades.****
Phew!!! Had me worried there for about a second or two. |
Ralph, what you say makes a lot of sense. Notably, take a look at some of the Class A speakers profiled on Stereophile's 2013 List of Recommended Components, here:
http://www.stereophile.com/content/2013-recommended-components-loudspeakers
Most if not all the selected speakers (including B&W 800-Ds)seem to have the type of impedance characteristics you referred to above.
Based on discussions with Paradigm, I'm pretty sure my speakers were also voiced to be driven by a high current SS amp. FWIW, I understand that my version of the Signature 8 (v3) was redesigned whereby the woofers are now 3 db more sensitive. As a result, the mid and tweeter drivers were "unpadded" to be driven full bore. So, the current v3 version has a rated sensitivity of 92 db verses the v2 version, which was 89 db.
I gather that 3 db is a considerable increase in sensitivity. As such, based on what you said above, the S8 v3s are an easier load, regardless of whatever type amp is being used.
Nevertheless, I also gather than even though any type of amp should be less stressed driving the S8s, one is still left with the issue of acoustic coloration, the amount of which is dependent, in large part, on the amp's output impedance. Ergo, the caveat that some tube amps might not be a good candidate, particularly those not using any or very little NF. The same point also being relevant to many other speakers as well, which if technically correct, is an important take-a-way point.
Thanks again Ralph. |
Ralph thank you for the explanations. It really helps. I cannot find a impedance graph on my speakers. Is it hard to measure? With what Ralph has said I would like to do that. It seems that would help me optimize my system. Just curious. Thanks. I hope I did't hijack the thread. |
Impedance can be measured with a potentiometer of about 50 ohms or so, a signal generator and a DVM. It takes some time, as with this technique you have to put points on a graph.
You put the pot in series with the speaker and drive the combo with the generator. The pot is wired as a rheostat, and adjusted until you see the same voltage drop across the resistor as you see across the speaker terminals. You then measure the value of the pot and plot it on the graph for that frequency. Then you move the frequency and repeat. This takes time to do 20-20KHz, but it works well.
However there are computer programs now that can make the job a bit easier.
The impedance of the speaker does not tell you if it is Voltage or Power paradigm- its easier to find that out by asking the manufacturer what sort of amp they use. But this can be handy to sort out if you have a difficult load in the impedance curve- as we all know, some amps might overheat or the like if the impedance is too low. So it is very useful for that sort of thing.
It was using a technique like this that some Sound Lab customers discovered a few years ago what the Sound Lab impedance curve really was (and it was a lot different then Sound Lab had said at the time). Apparently Sound Lab had used a simulation that had a bug in it. This has resulted in Sound Lab making some changes that not only made the speaker a lot easier to drive for any amplifier, but also made for a better sounding speaker. |
12-10-13: Bombaywalla: RE: Stereophile review of Green Mountain Speakers driven by OTL:
They may have given the speakers themselves a good review, but not when it's driven by an OTL amp. And it's those impedances/phase that cause it to act like a tone control.
Stereophile: Listening review of the Green Mountain Diamantes, half way down the page.
http://www.stereophile.com/floorloudspeakers/694green/index.html
And then the measurments by JA to back up what SS heard, first paragraph:
http://www.stereophile.com/content/green-mountain-audio-diamante-loudspeaker-measurements
Cheers George |
Thanks for this info Georgelofi. The Diamantes were Green Mtn Audio's 1st offering back in 1994. Not a bad start - much better than most other speakers in the market at that time. There has been considerable advance since then & I believe that Roy Johnson has gotten the phase angles down much more so that the newer model speakers are more amplifier agnostic. I think now Roy Johnson is agreeable to the Atma-sphere M60 amplifier driving his speakers. |
I need to point out to you Bombaywalla that this Green Mountain speaker is far from being a hard load, if fact it's quite easy.
As it's a 6ohm average with a not so bad phase angle of -30degrees.
The worst load frequency for an amp happens where they cross at 100hz where the impedance is 6.5ohms with -25degrees phase angle.
So this speaker can be regarded as quite an easy one for amps to drive.
Cheers George |
Not to worry, enjoy the speakers; there are amplifiers up to the task, and with more to spare. |
^^ Yup! We shown with Roy's speakers at audio shows in the past. Never had a problem with them. |
