tube amps and electrostatics

Bifwynne
EPDR is not simple to work out you need Matlabs program that cost + the equipment to measure both parameters, unless you know the resistance and phase (which Stereophile do give) then all you need is the program.

Here is a link to the EPDR discussions on Stereophile with John Atkinson editor who's not using it yet and Keith Howard who does uses it from HiFi News & Record Review.

http://www.stereophile.com/content/epdr-wheres-formula-footnotes-1

Cheers George

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