Speaker impedance for dummies

[DocG]

Hi all,

In my search for a pair of 'destination speakers' and matching amplification, I went for a demo of the Quad ESL-2805s last friday. They sounded just gorgeous, so back home - still high - I read some reviews of the other ESLs in the range.

The ESL-2912 brochure suggests a benign impedance curve, with a nominal impedance of 8 Ohm, and variation of 4-20 Ohm, suggesting they're an easy load for any amp. In a Hifinews review however, the lab report measures (and I quote) "a minimum modulus of 2.7 Ohm at 20 Hz. Impedance phase angle at low frequencies is high enough to lower the EPDR (equivalent peak dissipation resistance) to a minimum of 1.4 Ohm at 69 Hz, but as the ESL-2912's impedance will be level-dependent at LF, the dip to 3 Ohm modulus at 7.5 kHz and to 1.6 Ohm EPDR at 1.1 kHz are more relevant and suggest a moderately difficult amplifier load." (End of quote). Does anyone understand what this is all about? Do Quad give wrong specs? Or are these different things altogether? And what could be the relevance for matching an amplifier? Need for high current? And I thought ESLs were voltage-driven...

On a different note: can anyone tell me when the withdrawal symptoms start to wane after having heard Quads? I had a two hour exposure the day before yesterday...

 

[proffski]

What methods and apparatus did QUAD and What Hi Fi use? A friend is using two ESL-2912s both pairs driven by MF KW amplifier with no apparent distress and they sound just divine!

 

[chebby]

On a different note: can anyone tell me when the withdrawal symptoms start to wane after having heard Quads? I had a two hour exposure the day before yesterday...

About 10 years in my case. (After hearing the original ESL 63s in an all Quad amp/tuner set-up and a live Radio 3 afternoon broadcast.)

 

[DocG]

On a different note: can anyone tell me when the withdrawal symptoms start to wane after having heard Quads? I had a two hour exposure the day before yesterday...

About 10 years in my case. (After hearing the original ESL 63s in an all Quad amp/tuner set-up and a live Radio 3 afternoon broadcast.)

Is that: 10 years and ongoing? Or are you over it by now? If not, we might start a self-help group. "Hello, my name is DocG and I'm a Quadoholic"

 

[DocG]

What methods and apparatus did QUAD and What Hi Fi use?

Beat me...

Any idea what EPDR is, prof? Or "3 Ohm modulus at 7.5 kHz"?

 

[CnoEvil]

I would probably get an amp that's stable into 2 Ohms, just to be on the safe side.

 

[DocG]

I would probably get an amp that's stable into 2 Ohms, just to be on the safe side.

I agree that wouldn't harm. But few manufacturers give power ratings into 4, let alone into 2 Ohm. For their own Elite Stereo amp, Quad only quotes 2 x 85 W into 8 Ohm, while it certainly did a proper job last friday. So, any tips 'n tricks to spot the capable amps?

I could ask Quad of course, but odds are small they would recommend other brands, IMO.

 

[CnoEvil]

I would probably get an amp that's stable into 2 Ohms, just to be on the safe side.

I agree that wouldn't harm. But few manufacturers give power ratings into 4, let alone into 2 Ohm. For their own Elite Stereo amp, Quad only quotes 2 x 85 W into 8 Ohm, while it certainly did a proper job last friday. So, any tips 'n tricks to spot the capable amps?

I could ask Quad of course, but odds are small they would recommend other brands, IMO.

There's always the 35i. :shifty:

Quote from this review (under "Lab test report), "Where the AMS35i absolutely excelled was with its performance into 2 Ohm loads (for which it is not actually rated)...."

http://www.avhub.com.au/images/stories/australian-hifi/reviews/2011-03/Musical_Fidelity_AMS_35i_Amplifier_Review/musical_fidelity_ams35i_amplifier_review_lores.pdf

 

[matt49]

I agree that wouldn't harm. But few manufacturers give power ratings into 4, let alone into 2 Ohm. For their own Elite Stereo amp, Quad only quotes 2 x 85 W into 8 Ohm, while it certainly did a proper job last friday. So, any tips 'n tricks to spot the capable?

i have to confess ignorance on this. Would this be an example? (Also available in the form of the E560 integrated)

http://www.accuphase.com/model/a-35.html

 

[DocG]

Come on, guys! There must be more expensive options!

 

[CnoEvil]

Come on, guys! There must be more expensive options!.....

......Just go up the range.

Simples.

 

[proffski]

On a different note: can anyone tell me when the withdrawal symptoms start to wane after having heard Quads? I had a two hour exposure the day before yesterday...

About 10 years in my case. (After hearing the original ESL 63s in an all Quad amp/tuner set-up and a live Radio 3 afternoon broadcast.)

All I know is that when I visit said friend it can take weeks before start listening to music on my system, those electrostatics are that good!

 

[proffski]

What methods and apparatus did QUAD and What Hi Fi use?

Beat me...

Any idea what EPDR is, Proff? Or "3 Ohm modulus at 7.5 kHz"?

That would take a long time to explain in my terms, the more you look and delve into the complex way some loudspeakers can interact with and affect amplifier output stages would take most of the afternoon. Just remember that loudspeakers are not perfect resistors! And even a lot of those will have a measurable inductance! This link below may help answer a few questions maybe… I have yet to hear any domestic system which can give the huge dynamic contrast of a full blown orchestra. The article is a bit of an advert but the sentiment more or less spot on!

Links: http://www.enjoythemusic.com/magazine/manufacture/0708/ and this will pop a few eyeballs! http://www.stereophile.com/reference/707heavy/index.html

 

[Electro]

Probably a little excessive for quad panels but the Electrocompaniet AW 250 is quoted down to one ohm and is stable into loads down to 0.5 of an ohm as are all Electrocompaniet amps .
8 ohms 2 x 250 W 4 ohms 2 x 380 W 2 ohms 2 x 625 W 1 ohms 2 x 1100 W
http://www.electrocompaniet.no/products/classic/poweramp/aw250r.html

The original Electrocompaniet 25w amp from the late 70's is still considered by many people to be the best sounding amp for Quad panels and at the time was considered to be " The best sounding amplifier in the world " by many top HiFi journalists

That said the original 25w Electro amps spiritual successor is not an Electrocompaniet amp but still built buy one of the original designers .

The Abrahamsen SA1

http://www.classicseries.no/products.asp

http://www.classicseries.no/pic.asp

 

[matt49]

There's always the 35i. :shifty:

Quote from this review (under "Lab test report), "Where the AMS35i absolutely excelled was with its performance into 2 Ohm loads (for which it is not actually rated)...."

http://www.avhub.com.au/images/stories/australian-hifi/reviews/2011-03/Musical_Fidelity_AMS_35i_Amplifier_Review/musical_fidelity_ams35i_amplifier_review_lores.pdf

Mighty impressive test results there, Cno.

My local dealer says the AMS35is should arrive later this week. Early June I have demos of a Primare pre/power and Devialet. But realistically I think only the MF is now likely to stop me joining Mac in the Accuphase club.

(Apologies to the OP for taking the thread off topic.)

 

[CnoEvil]

Mighty impressive test results there, Cno.

My local dealer says the AMS35is should arrive later this week. Early June I have demos of a Primare pre/power and Devialet. But realistically I think only the MF is now likely to stop me joining Mac in the Accuphase club.

(Apologies to the OP for taking the thread off topic.)

Your place is already reserved. :shifty:

 

[DocG]

Mighty impressive test results there, Cno.

My local dealer says the AMS35is should arrive later this week. Early June I have demos of a Primare pre/power and Devialet. But realistically I think only the MF is now likely to stop me joining Mac in the Accuphase club.

(Apologies to the OP for taking the thread off topic.)

Your place is already reserved. :shifty:

Now that I found a dealer nearby, who stocks the 35i, you should really stop recommending it! The temptation becomes too tangible! :hand:

 

[CnoEvil]

Mighty impressive test results there, Cno.

My local dealer says the AMS35is should arrive later this week. Early June I have demos of a Primare pre/power and Devialet. But realistically I think only the MF is now likely to stop me joining Mac in the Accuphase club.

(Apologies to the OP for taking the thread off topic.)

Your place is already reserved. :shifty:

Now that I found a dealer nearby, who stocks the 35i, you should really stop recommending it! The temptation becomes too tangible! :hand:

:silenced: :shifty:

 

[DocG]

There's always the 35i. :shifty:

Quote from this review (under "Lab test report), "Where the AMS35i absolutely excelled was with its performance into 2 Ohm loads (for which it is not actually rated)...."

http://www.avhub.com.au/images/stories/australian-hifi/reviews/2011-03/Musical_Fidelity_AMS_35i_Amplifier_Review/musical_fidelity_ams35i_amplifier_review_lores.pdf

Mighty impressive test results there, Cno.

My local dealer says the AMS35is should arrive later this week. Early June I have demos of a Primare pre/power and Devialet. But realistically I think only the MF is now likely to stop me joining Mac in the Accuphase club.

(Apologies to the OP for taking the thread off topic.)

No need for apologies, Matt! Just keep us posted; I'm especially interested in your thoughts on the Devialet - planning a listen in a couple of weeks' time myself.

 

[CnoEvil]

I'm especially interested in your thoughts on the Devialet - planning a listen in a couple of weeks' time myself.

That's just postponing the inevitable.........Oh!........ :silenced:

 

[DocG]

That would take a long time to explain in my terms, the more you look and delve into the complex way some loudspeakers can interact with and affect amplifier output stages would take most of the afternoon.

That's exactly the answer I was afraid of getting...

Just remember that loudspeakers are not perfect resistors! And even a lot of those will have a measurable inductance! This link below may help answer a few questions maybe… I have yet to hear any domestic system which can give the huge dynamic contrast of a full blown orchestra. The article is a bit of an advert but the sentiment more or less spot on!

Links: http://www.enjoythemusic.com/magazine/manufacture/0708/ and this will pop a few eyeballs http://www.stereophile.com/reference/707heavy/index.html

... But these references do indeed shed a light on the matter. I had seen (and read) the Stereophile article before, but at the time didn't understand a jot of it. Now, with the Simon Thacher article as a step-up, it all makes so much more sense! Thank you for that, proff! It makes one wonder why the EPDR is not more generally used.

i'm still in doubt if the Quads are member of the Society for Cruelty to Amplifiers, though...

 

[oldric_naubhoff]

What methods and apparatus did QUAD and What Hi Fi use?

Beat me...

Any idea what EPDR is, Proff? Or "3 Ohm modulus at 7.5 kHz"?

That would take a long time to explain in my terms, the more you look and delve into the complex way some loudspeakers can interact with and affect amplifier output stages would take most of the afternoon. Just remember that loudspeakers are not perfect resistors! And even a lot of those will have a measurable inductance! This link below may help answer a few questions maybe… I have yet to hear any domestic system which can give the huge dynamic contrast of a full blown orchestra. The article is a bit of an advert but the sentiment more or less spot on!

Links: http://www.enjoythemusic.com/magazine/manufacture/0708/ and this will pop a few eyeballs!

http://www.stereophile.com/reference/707heavy/index.html

I see proffski beat me to it. that article from stereophile is a great one to explain what EPDR is, if you can grasp the technicalities behind it. in a nutshell with most speakers it's not the impedance minimum that may be asking the amp work toughest but a higher impedance point where electrical phase shift is high. of course, if the impedance minimum is joint by a high phase shift then there's no good news. however, AFAIK the impedance minima are not usually the points where phase shift is high. EDPR (equivalent peak dissipation resistance) then is a measure of speaker impedance that takes electrical phase shift into equation.

the best case scenario from the amp's POW would be a flat impedance curve with no electrical phase shift, i.e. purely resistive load. ribbon speakers come closer than other designs to that ideal. the worst speakers for an amp to drive are modern dynamic speakers and ESLs IMO.

now DocG, as for your question regarding severity of Quad's 2912 impedance plot. I wish I could see the plot they come up with in Hi-Fi News but I'd wager it would look completely different from what I would expect it to look like. for instance there's the impedance + shift plot of Quad 2805 from Stereophile review:

you can see there their impedance is very high for most of the audioband just dropping below 4 Ohms only around 10k Hz. also the electrical phase shift is rather benign (+/- 20 deg.) with two exceptions: low bass and high treble. for instance the combination of ca. 5.5 Ohms and -45 deg shift at 15k Hz will be felt a lot more stressful on amp than the impedance minimum at 10k Hz. also the phase shift in deep bass is very high too but the impedance plot in that region is very high - minimum of 12.5 Ohms at 20 Hz - so it will ameliorate that phase shift severity somehow. unfortunately I can't yet calculate EDPR from impedance and shift values so I don't know what EDPRs at 20Hz and 15k Hz in 2805 would be but from the results in hi-fi news review I can only assume Quad made some changes in the driving electronics of the 12 version speakers. so now they would have impedance plots more like in typical ESLs.

as for amp suggestions. if you're going to pursue the way of an ESL afficionado or you're going to choose some tough to drive modern dynamic speakers you'd better choose an amp which is stable into 2 Ohm continuous load. my suggestions are Accuphase (class A or more powerful AB), Musical Fidelity (class A), Audia Flight (class A power amps), AM Audio (class A integrated and power amps) and of course Krell. but the highest recommendation based on VFM goes to AM Audio. those are no-feedback (read: much better) class A amps with measured performance that rivals that of feedback amps and in some way surpasses. you probably noted class A repeats often. and for a reason. a well designed class A will always have well sorted power supply; mandatory for handling those low impedance loads. there is a good reason why you won't find class A at a budget level. also, I would steer away from tube amps for driving ESLs. there's a high chance of clipping at low impedances (tubes are no good for low impedances). but clipping from tube amps does not sound as bad as from solid state feedback amps. still, distortion is distortion, no matter how it sounds like. I personally prefer clarity and realism.

re: the other link from proffski to the ETM article. while there's absolutely nothing wrong with the logic behind the design of that amp you surely don't need an amp capable to deliver 120dB with conjunction with the speakers in your room. IMO and IME 100 - 105dB transients is absolutely enough for a lifelike experience.

hope this helps.

 

[DocG]

I'm especially interested in your thoughts on the Devialet - planning a listen in a couple of weeks' time myself.

That's just postponing the inevitable.........Oh!........ :silenced:

 

[DocG]

Thanks for your elaborate complements, Oldric.

So, should I go Quad, I'll have some more searching to do... (might end up in Cno's club after all...)

Ever looked into the Sanders ESL amp, Oldric? Any thoughts welcome!

First (and IMO by far most important) step however will be convincing the wife we need these black monoliths in our living room. Talking of a challenge! All tips wholeheartedly appreciated.

 

[matt49]

my suggestions are Accuphase (class A or more powerful AB), Musical Fidelity (class A), Audia Flight (class A power amps), AM Audio (class A integrated and power amps) and of course Krell.

Oldric, thanks as ever for your informed comments. I'm interested that you say "of course Krell". Based only on one demo of the new Krell S-550i, the Krell sound seems a long way away from, say, Accuphase. I got a harshness from the Krell that said "class AB" to me. But that was just one demo, of course.

Matt