The ohms Trick

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ejspain

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If I have an amp capable of 8, 4, and 2ohms loads, and my Impression are rated at 4ohms, how do I know when the amp is playing at 4ohms? Want to get the most juice from the amp possible.
 
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JonFo

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Speakers present a varying level of resistance to the amp, depending on frequency. Manufactures list an average Ohm load for a given model.
ESL speakers will dip down to close (or below for older models like the CLS) to 2 Ohms at >10KHz.

So your amp is seeing loads anywhere from 6 Ohms down to 2 Ohms, depending on content. Your amp will deliver power into those loads as it can.

Ideally, amps should be 'load invariant' as Bob Carver would say, able to deliver a doubling of power for every halving of the load impedance, all the way down to 2 Ohms. Sunfires, Sanders, and others can do that. Your Marantz, as nice a unit as it is, cannot quite do that, but unless you hear something amiss, there is probably nothing to worry about. Bench test specs for the M7055
 

ejspain

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Speakers present a varying level of resistance to the amp, depending on frequency. Manufactures list an average Ohm load for a given model.
ESL speakers will dip down to close (or below for older models like the CLS) to 2 Ohms at >10KHz.

So your amp is seeing loads anywhere from 6 Ohms down to 2 Ohms, depending on content. Your amp will deliver power into those loads as it can.

Ideally, amps should be 'load invariant' as Bob Carver would say, able to deliver a doubling of power for every halving of the load impedance, all the way down to 2 Ohms. Sunfires, Sanders, and others can do that. Your Marantz, as nice a unit as it is, cannot quite do that, but unless you hear something amiss, there is probably nothing to worry about. Bench test specs for the M7055
WOW!! Perfect explanation @JonFo I just learned something. Contrary to what my responses have been, I've REALLY been pondering a new amp. After a little over a month breaking in the 11As, they are becoming more revealing and telling the truth about the power I'm feeding them. And the specs you shared explains why. Been reading a bit on the Parasound A31.
 
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Nuri58

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No need to worry. 200W is 200W - 2, 4, 8 ohms so it will olay loud and clear. But the issue is the heat it generates if you crank it up to loudly (and try to exeed the 200W as the 4 ohms essentially demands double up of current). I have a 8 ohm Arcam bridged p429 rated at 2×275w driving my fronts and thats what it deliveres despite the LS are rated 4 ohms - trust me sound pressure is more than adequate. Modern equipment will shot down if you exceedd its capabilities (might be a device out there's not doing that though). Also read about it at ML's own site where they claim not having heard about issues. I wonder if you could not just add a 4 ohm resistor between thr LS cable and th LS itself? Could be an impact on the sound i guess

PS tube amps are different so the above does not apply.
 

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I'm using a Parasound A31 with a pair of Theos and a Motif X and am very happy with it, a clean and transparent sound, though I suspect the Conrad Johnson MET1 preamp in the system has something to do with that as well. It operates in Class A for the first seven or so wpc. I've recently been dabbling with biamping the Theos and it's a snap to match amp levels as the A31 has input level controls (A31 into the stat panels).
 

ejspain

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I'm using a Parasound A31 with a pair of Theos and a Motif X and am very happy with it, a clean and transparent sound, though I suspect the Conrad Johnson MET1 preamp in the system has something to do with that as well. It operates in Class A for the first seven or so wpc. I've recently been dabbling with biamping the Theos and it's a snap to match amp levels as the A31 has input level controls (A31 into the stat panels).
Yea I've been reading a lot of good things about the A31. I think the 11As would love the 400W of clean, undistorted power coming down the line at 4ohms.
 

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You should also consider the Anthem MCA 225 mk 2 amp, it puts out 400w at 4 ohms. Does a wonderful job with my classic 9’s, driving both the stat panel and woofers in bi-wire setup. Your panels only need power with the internal amp for the woofers.
 

Robert D

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Speakers present a varying level of resistance to the amp, depending on frequency. Manufactures list an average Ohm load for a given model.
ESL speakers will dip down to close (or below for older models like the CLS) to 2 Ohms at >10KHz.

So your amp is seeing loads anywhere from 6 Ohms down to 2 Ohms, depending on content. Your amp will deliver power into those loads as it can.

Ideally, amps should be 'load invariant' as Bob Carver would say, able to deliver a doubling of power for every halving of the load impedance, all the way down to 2 Ohms. Sunfires, Sanders, and others can do that. Your Marantz, as nice a unit as it is, cannot quite do that, but unless you hear something amiss, there is probably nothing to worry about. Bench test specs for the M7055
Why is it that higher frequencies have lower impedance loads? I don't know why.
 

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Parasound seems pretty decent... neutral, clean power. I considered them when I decided to hitch my buggy to Bryston. The A31 equivalent would be the Bryston 6B-ST or 6B-SST (basically the exact same amplifier, which was released int he midst of their new model branding exercise). You can find them for about $2 - $2.5K second hand. If the original owner has the receipt from a dealer, you get the balance of the 20 (yes, Twenty!) year warranty.
 

Robert D

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Capacitive loads decrease in impedance as applied frequency increases.
I found this, its due to skin effect.

'Yes. The resistance does depend on frequency. The reason is 'skin effect'.
When an alternating current is passed through a conductor only a small portion of the conductor, usually called the skin depth carries the current. The value of skin depth is inversely proportional to frequency. As the frequency is increased, the skin depth decreases. But the value of ac resistance is directly proportional to frequency, or in other words, inversely proportional to skin depth. Thus, at higher frequencies, ac resistance is higher. This is the reason why we multiply the dc resistance by an empirical value 1.2 or 1.3 to calculate its ac equivalent."


I only took year one physics in college, so I don't think we ever learned this. It's also been over 30 years, lol.
 

Russr

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Good find. I would hazard a guess that the skin effect for ESLs and regular (magnetic motor) speakers is about the same.. .it "speaks to" (ha-ha) the nature of AC currents flowing more on the surface of a conductor. Those conductors would be speaker cables, components in X-Over circuits, etc.

As to why ESLs impedence drops like a bomb at higher frequencies, cast your mind back, if you will, to any classes/exposure you might have had to capacitors. In a circuit diagram, caps are symbolized as 2 parallel plates, with a conductor going off of each side into whatever circuit might be around them

Each plate will be able to "absorb" some charge, by collecting electrons on each plate. When in a DC (Direct Current) circuit (or something close to direct current, like a Low Pass filter), the gap between those plates will look like an open circuit, and signal will not go through.

But, when a capacitor is in a AC circuit, as one "side" is charged up, the other side DISCHARGES back into the circuit. This will then be seen by the circuit almost as a straight piece of wire (or a short circuit). When a circuit sees LOW resistance/impedance, the current increases.

Now, if you think about our beloved ESL's, you could think of the panels as some big-a$$ed capacitors. So as the amp's signal reaches the speakers, and the frequency Increases, the impedance seen by the amp Decreases and the current goes way-too-frikkin'high.

I might be totally off on the electro-mechanics of it, but that's how I'm thinking about things...

I had to dig deep for that... thanks for the trip down memory lane... just wish I'd passed more of the EE courses!
 

Robert D

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Good find. I would hazard a guess that the skin effect for ESLs and regular (magnetic motor) speakers is about the same.. .it "speaks to" (ha-ha) the nature of AC currents flowing more on the surface of a conductor. Those conductors would be speaker cables, components in X-Over circuits, etc.

As to why ESLs impedence drops like a bomb at higher frequencies, cast your mind back, if you will, to any classes/exposure you might have had to capacitors. In a circuit diagram, caps are symbolized as 2 parallel plates, with a conductor going off of each side into whatever circuit might be around them

Each plate will be able to "absorb" some charge, by collecting electrons on each plate. When in a DC (Direct Current) circuit (or something close to direct current, like a Low Pass filter), the gap between those plates will look like an open circuit, and signal will not go through.

But, when a capacitor is in a AC circuit, as one "side" is charged up, the other side DISCHARGES back into the circuit. This will then be seen by the circuit almost as a straight piece of wire (or a short circuit). When a circuit sees LOW resistance/impedance, the current increases.

Now, if you think about our beloved ESL's, you could think of the panels as some big-a$$ed capacitors. So as the amp's signal reaches the speakers, and the frequency Increases, the impedance seen by the amp Decreases and the current goes way-too-frikkin'high.

I might be totally off on the electro-mechanics of it, but that's how I'm thinking about things...

I had to dig deep for that... thanks for the trip down memory lane... just wish I'd passed more of the EE courses!
My degree is in Biology and exercise physiology, so I did the minimum of physics. I taught Biology and Chemistry in high school. Physics is probably my weakest area of science.
 

Brandon Hartwick

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I know everyone has an opinion on this, but if you're shopping for second hand amps I can't speak highly enough of the older class AB Jeff Rowland amps. They push lots of current and more importantly they're rock solid stable, the aggressive impedance curve of electrostatics won't be a problem. I drive my panels direct with no crossover and the amp doesn't mind.

You didn't ask and I'm not here to change your mind, but I had to put this out there lol.
 

JonFo

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I had to dig deep for that... thanks for the trip down memory lane... just wish I'd passed more of the EE courses!
Thanks for the erudite answers; I believe you are spot on.
From a wanna-be EE here who wishes he took some more EE courses in college.
 

Leporello

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I found this, its due to skin effect.

'Yes. The resistance does depend on frequency. The reason is 'skin effect'.
When an alternating current is passed through a conductor only a small portion of the conductor, usually called the skin depth carries the current. The value of skin depth is inversely proportional to frequency. As the frequency is increased, the skin depth decreases. But the value of ac resistance is directly proportional to frequency, or in other words, inversely proportional to skin depth. Thus, at higher frequencies, ac resistance is higher. This is the reason why we multiply the dc resistance by an empirical value 1.2 or 1.3 to calculate its ac equivalent."


I only took year one physics in college, so I don't think we ever learned this. It's also been over 30 years, lol.
1. Skin effect is negligible at audio frequencies over the conductor lengths used in audio systems. It's important at radio frequencies, and over the hundreds of mile lengths of power transmission lines. Don't know where that "empirical value" 1.2 or 1.3 comes from. Electrical current doesn't suddenly vanish below the skin depth, it falls to 1/e (about 37%) of its surface value. You can look up a treatment of skin effect in e.g. D.J. Jackson's "Classical Electrodynamics". You'll find that the skin depth at 20,000 hertz for copper is way deeper than the size of most conductors in audio systems.

2. I've got master's degrees in physics and electrical engineering, and do my best to explain things here, especially widely misunderstood things like amp and speaker impedance.

3. I drive my CLS II's with Parasound JC1 monoblocks, and couldn't be happier. I most definitely do not worry about extracting the maximum number of watts from them. They play way louder than I can stand to be in the rooms with them. They also reproduce the dynamic brilliance of the upper registers of a piano more convincingly than anything else I've heard.
 

Leporello

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Good find. I would hazard a guess that the skin effect for ESLs and regular (magnetic motor) speakers is about the same.. .it "speaks to" (ha-ha) the nature of AC currents flowing more on the surface of a conductor. Those conductors would be speaker cables, components in X-Over circuits, etc.

As to why ESLs impedence drops like a bomb at higher frequencies, cast your mind back, if you will, to any classes/exposure you might have had to capacitors. In a circuit diagram, caps are symbolized as 2 parallel plates, with a conductor going off of each side into whatever circuit might be around them

Each plate will be able to "absorb" some charge, by collecting electrons on each plate. When in a DC (Direct Current) circuit (or something close to direct current, like a Low Pass filter), the gap between those plates will look like an open circuit, and signal will not go through.

But, when a capacitor is in a AC circuit, as one "side" is charged up, the other side DISCHARGES back into the circuit. This will then be seen by the circuit almost as a straight piece of wire (or a short circuit). When a circuit sees LOW resistance/impedance, the current increases.

Now, if you think about our beloved ESL's, you could think of the panels as some big-a$$ed capacitors. So as the amp's signal reaches the speakers, and the frequency Increases, the impedance seen by the amp Decreases and the current goes way-too-frikkin'high.

I might be totally off on the electro-mechanics of it, but that's how I'm thinking about things...

I had to dig deep for that... thanks for the trip down memory lane... just wish I'd passed more of the EE courses!
Ideally, the moving charged diaphragm of the ESL, doing work on the surrounding air, would mitigate the 1/f impedance effects of the capacitive plates of an ESL, just as the back emf generated from a voice coil, doing work on the surrounding air, mitigates the inductive effects of a dynamic speaker. But we live in the real world so, yes, an ESL looks like a capacitor at high frequencies while a dynamic speaker looks like an inductor. Most amps don't care that a voice coil looks like a pure resistance at DC.

Also, the step-up transformer of an ESL reflects back more capacitance than seen by measuring the speaker stators directly.
 

Robert D

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1. Skin effect is negligible at audio frequencies over the conductor lengths used in audio systems. It's important at radio frequencies, and over the hundreds of mile lengths of power transmission lines. Don't know where that "empirical value" 1.2 or 1.3 comes from. Electrical current doesn't suddenly vanish below the skin depth, it falls to 1/e (about 37%) of its surface value. You can look up a treatment of skin effect in e.g. D.J. Jackson's "Classical Electrodynamics". You'll find that the skin depth at 20,000 hertz for copper is way deeper than the size of most conductors in audio systems.

2. I've got master's degrees in physics and electrical engineering, and do my best to explain things here, especially widely misunderstood things like amp and speaker impedance.

3. I drive my CLS II's with Parasound JC1 monoblocks, and couldn't be happier. I most definitely do not worry about extracting the maximum number of watts from them. They play way louder than I can stand to be in the rooms with them. They also reproduce the dynamic brilliance of the upper registers of a piano more convincingly than anything else I've heard.
So what do you think the main reason is for why the impedance drops as frequency of the electrical signal goes up in our home stereo systems? I guess this doesn't happen in cone speakers, for the reasons already discussed concerning electrostat panels?
 

ejspain

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1. Skin effect is negligible at audio frequencies over the conductor lengths used in audio systems. It's important at radio frequencies, and over the hundreds of mile lengths of power transmission lines. Don't know where that "empirical value" 1.2 or 1.3 comes from. Electrical current doesn't suddenly vanish below the skin depth, it falls to 1/e (about 37%) of its surface value. You can look up a treatment of skin effect in e.g. D.J. Jackson's "Classical Electrodynamics". You'll find that the skin depth at 20,000 hertz for copper is way deeper than the size of most conductors in audio systems.

2. I've got master's degrees in physics and electrical engineering, and do my best to explain things here, especially widely misunderstood things like amp and speaker impedance.

3. I drive my CLS II's with Parasound JC1 monoblocks, and couldn't be happier. I most definitely do not worry about extracting the maximum number of watts from them. They play way louder than I can stand to be in the rooms with them. They also reproduce the dynamic brilliance of the upper registers of a piano more convincingly than anything else I've heard.
Great to hear you're pleased with the JC1s driving the CLSs. Would love having the mono's but in my case, in my space, and costs, I think I'll get as good a performance from the A31 dishing out 400W @4ohms (for 2 channel listening) and a very decent 250W @8ohms (for movies). This should make my Impressions very happy compared to what they're getting plus it's kind of justified in my relatively small space (13' x 18' x 10').
 
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