NC252MP (class D) vs. A250W4R (classAB) burst measurements into 4ohm//2.2uF load

[jimk1963]

I have been reading about it recently, modelling of speakers with LCR components that is, and it gets even more complicated when the mechanical effects starts to have an impact on the electrical characteristics. For electrostats, which is the edge case being discussed here, there is even an article that says for power and distortion measurements, electrostats can not be accurately modeled with linear components. I have shared the article in the other thread, but guess the discussion has moved on the social sciences side of things with cults and such, rather than the engineering one.

Not sure what drove your last comment, but to your reading that “for power and distortion measurements, electrostats can not be accurately modeled with linear components”, this is abundantly obvious to anyone who’s ever modeled circuits. LRC passives, without any modifications, are purely linear - you can never build a pure LRC circuit model that exhibits distortion. Distortion requires a nonlinearity(ies) somewhere in the system. Any model that hopes to simulate a circuit exhibiting distortion must therefore also include nonlinear elements.

The trick in circuit modeling is understanding when to apply linear modeling vs. more complex nonlinear modeling. For the discussions on this thread, we aren’t looking at amps being driven to high output levels where a speaker might distort and affect its equivalent circuit. Rather, the findings here (I think) are at low power where any decent speaker would/should be running well within its linear region. Unless e-stats have big distortion issues at low powers, we should be able to consider a passive LRC model for those as well. Whether this thread’s 2.2uF is good for that modeling, I have no idea.

 

[Deleted member 48726]

Not sure what drove your last comment, but to your reading that “for power and distortion measurements, electrostats can not be accurately modeled with linear components”, this is abundantly obvious to anyone who’s ever modeled circuits. LRC passives, without any modifications, are purely linear - you can never build a pure LRC circuit model that exhibits distortion. Distortion requires a nonlinearity(ies) somewhere in the system. Any model that hopes to simulate a circuit exhibiting distortion must therefore also include nonlinear elements.

The trick in circuit modeling is understanding when to apply linear modeling vs. more complex nonlinear modeling. For the discussions on this thread, we aren’t looking at amps being driven to high output levels where a speaker might distort and affect its equivalent circuit. Rather, the findings here (I think) are at low power where any decent speaker would/should be running well within its linear region. Unless e-stats have big distortion issues at low powers, we should be able to consider a passive LRC model for those as well. Whether this thread’s 2.2uF is good for that modeling, I have no idea.

IR to electrostats there should be some impedance / phase measurements out there from where an expert could model a dummy circuit to imitate correctly. Then do some "IRL" measurements to see what's what.

But actually I don't personally care as much for electrostats and edge cases, as I am more curious to whether the whole "all amplifiers sound the same" doctrine can be investigated properly when this door has been opened. -That's what I find most interesting. As I will swear I heard differences between an AVR and some other amps I later hooked up to the same set of speakers. I unfortunately don't have any electrical measurements of said speakers and none exist so I couldn't really prove anything when confronted with said sentence.

 

[jimk1963]

Impedance / phase diagrams as measured in reviews is as real as it gets as far as I'm concerned. Equivalent circuits are almost as good if we are aware of it's characteristics as you've described.

Still I'm not convinced that @pma 's test setup that started this whole thing is actually reflecting real load. At least from what I've learned the last few days it doesn't look quite right.

Agree, I think @pma is testing a worst case condition, rather than the impedance of any specific speaker (e-stats seem to come closest I guess, dunno). Still, it points out a unique weakness with Class D‘s architectural robustness that shouldn’t be forgotten.

When we evaluate RF power amps in hand-held devices, that may be driving an antenna, we have to account for potential VSWR problems like - someone removes the antenna. Depending on the transmission line length from PA to the connector, this can present a purely reactive load impedance that varies from a pure open circuit to a pure short circuit. We have to make sure the PA’s can withstand this without breaking into a self-destructive oscillation. I look at @pma ’s testing in a similar light. He’s pushing the amp to determine its stability/performance boundaries.

 

[fpitas]

Playing devil's advocate, I wonder if real speakers remain capacitive to 60kHz and above. Most tweeters tend to get inductive.

 

[jimk1963]

IR to electrostats there should be some impedance / phase measurements out there from where an expert could model a dummy circuit to imitate correctly. Then do some "IRL" measurements to see what's what.

But actually I don't personally care as much for electrostats and edge cases, as I am more curious to whether the whole "all amplifiers sound the same" doctrine can be investigated properly when this door has been opened. -That's what I find most interesting. As I will swear I heard differences between an AVR and some other amps I later hooked up to the same set of speakers. I unfortunately don't have any electrical measurements of said speakers and none exist so I couldn't really prove anything when confronted with said sentence.

Same here. People have complained about Class D hissing and “dryness” for example… Would be great to shed some light on that, even with mainstream, non-fringe speakers.

 

[fpitas]

Same here. People have complained about Class D hissing and “dryness” for example… Would be great to shed some light on that, even with mainstream, non-fringe speakers.

From what I've seen, the hissing business is mainly from active speakers. Hard to tell what the problem might be there.

 

[Deleted member 48726]

Agree, I think @pma is testing a worst case condition, rather than the impedance of any specific speaker (e-stats seem to come closest I guess, dunno). Still, it points out a unique weakness with Class D‘s architectural robustness that shouldn’t be forgotten.

When we evaluate RF power amps in hand-held devices, that may be driving an antenna, we have to account for potential VSWR problems like - someone removes the antenna. Depending on the transmission line length from PA to the connector, this can present a purely reactive load impedance that varies from a pure open circuit to a pure short circuit. We have to make sure the PA’s can withstand this without breaking into a self-destructive oscillation. I look at @pma ’s testing in a similar light. He’s pushing the amp to determine its stability/performance boundaries.

Yeah, maybe. We don't know. I don't know much about e-stats but looking at for example these measurements it doesn't seem right though. And I don't know if this speaker is proper representation of e-stats either. EDIT: And actually it becomes highly inductive > 20000 Hz.
-------
@ 10000 Hz
Z = 2 ohm
Phase ~ 55 ° cap.
-->
Xc = 1,64 ohm
C = 10,8 uF
-------

MartinLogan Montis loudspeaker Measurements

Sidebar 3: Measurements I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the MartinLogan Montis's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield and spatially averaged room responses. A note on these measurements is in order:

www.stereophile.com

 

[jimk1963]

Yeah, maybe. We don't know. I don't know much about e-stats but looking at for example these measurements it doesn't seem right though. And I don't know if this speaker is proper representation of e-stats either. EDIT: And actually it becomes highly inductive > 20000 Hz.
-------
@ 10000 Hz
Z = 2 ohm
Phase ~ 55 ° cap.
-->
Xc = 1,64 ohm
C = 10,8 uF
-------

MartinLogan Montis loudspeaker Measurements

Sidebar 3: Measurements I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the MartinLogan Montis's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield and spatially averaged room responses. A note on these measurements is in order:

www.stereophile.com

View attachment 275195

Good example. This speaker is pretty capacitive below a few hundred Hz but certainly not after that. Pretty sure we won’t find any speaker that looks like a parallel 4 ohm + 2.2uF. But I’m still not convinced that “ends the discussion”, per se. Not obvious to me, for example, if a more highly inductive load causes similar strange clad D behavior. Your graph here shows that speakers can present as inductive, in this case at the higher frequencies.

i suppose a preliminary conclusion might be this?? (1) findings here probably don’t translate to most speakers, therefore class D amps tested here will not exhibit these problems; (2) not all class D amps behave the same way under severe loads, so caveat emptor (@amp started another thread where a different class D amp had no problem with this large capacitIve load); (3) this testing sheds light on unique properties of class D, that designers and customers should be mindful of, for design verification and speaker selection, respectively.

 

[Deleted member 48726]

Good example. This speaker is pretty capacitive below a few hundred Hz but certainly not after that. Pretty sure we won’t find any speaker that looks like a parallel 4 ohm + 2.2uF. But I’m still not convinced that “ends the discussion”, per se. Not obvious to me, for example, if a more highly inductive load causes similar strange clad D behavior. Your graph here shows that speakers can present as inductive, in this case at the higher frequencies.

i suppose a preliminary conclusion might be this?? (1) findings here probably don’t translate to most speakers, therefore class D amps tested here will not exhibit these problems; (2) not all class D amps behave the same way under severe loads, so caveat emptor (@amp started another thread where a different class D amp had no problem with this large capacitIve load); (3) this testing sheds light on unique properties of class D, that designers and customers should be mindful of, for design verification and speaker selection, respectively.

I am not for ending the discussion. On the contrary I think that more investigation is needed and find it most interesting.
I think it opens up for more questions and hope to see more tests.

 

[levimax]

What about AMT tweeters? Do they have high capacitance like electro stats? Seems like the same technology but I am not sure. I looked at some spec sheets and they did not mention capacitance but that does not nessisarily mean anything.

 

[DonH56]

Most of the ESLs I have measured do go low in impedance at high frequency because of the panel capacitance, but the actual phase angle seen by the amplifier is inductive due to the coupling/biasing transformer. The impedance is low, but inductive rather than capacitance from around the upper midrange up.

Edit: Note that is not the case for the Martin-Logan Montis @Holdt posted above; it is mostly capacitive until above 20 kHz. I wonder if the crossover or something else is going on with that one...

 

[PeterOo]

I am not for ending the discussion. On the contrary I think that more investigation is needed and find it most interesting.
I think it opens up for more questions and hope to see more tests.

Reproducing these results with actual ESLs would be most valuable. Now we are discussing the effect of an unproven assumption: 4ohm // 2.2uF is representative of a relevant number of commercially available (electrostatic) loudspeakers. Not just 2 or 3 extreme designs.

 

[3ll3d00d]

I would think it's more a function of crossover design than anything else

There was an example of this posted in avs recently, no measurements to verify unfortunately so can't say it's exactly this problem but does illustrate how it can happen with "normal" speakers

https://www.avsforum.com/threads/official-jtr-speaker-thread.1165099/page-2180#post-62344161

 

[dougi]

What about AMT tweeters? Do they have high capacitance like electro stats? Seems like the same technology but I am not sure. I looked at some spec sheets and they did not mention capacitance but that does not nessisarily mean anything.

I don't know, but again it may depend on the crossover. Stereophile measurements of one Audiovector shows -ve phase at high frequencies but an Alto audio less so.

 

[sonder]

It's my birthday at the weekend.

I was about to pull the trigger on a NC252MP based amp to power my Triangle Borea BR03s, because I feel my topping pa3s is struggling particularly on bass heavy tracks played a bit louder, midrange can distort a bit, feel the speakers just just need more power available.

Any issues with this pairing, I'm new and don't understand this thread fully, but leaning towards a hypecore NC***MP.

Advice for the uninformed?

 

[antcollinet]

It's my birthday at the weekend.

I was about to pull the trigger on a NC252MP based amp to power my Triangle Borea BR03s, because I feel my topping pa3s is struggling particularly on bass heavy tracks played a bit louder, midrange can distort a bit, feel the speakers just just need more power available.

Any issues with this pairing, I'm new and don't understand this thread fully, but leaning towards a hypecore NC***MP.

Advice for the uninformed?

The PA3 doesn't have oodles of power, it is true. But also the reveiw here states the speakers you have have some midrange port resonances - which might be what you are hearing at higher volume.

There is nothing wrong with the parimg of the NC amp with the speakers, but if what you are hearing comes from the spakers and not the amp, then it won't solve the problem.

If I were you I'd try to borrow (From a dealer? From a friend?) a higher power amp, and see if it solves your problem before comitting. Or buy from a supplier with a no questions return policy.

 

[Ruffy]

For a passive speaker, the crossover has such a drastic effect the individual driver response alone is meaningless. Now for an active speaker where the amp directly drives each driver, it's important.

Yeah I understand that, I wonder though what magnitude of effect having two crossovers in parallel would have in some of these speakers. Some crossovers have upwards of 10 elements affecting phase and impedance, I would’ve thought 2 in parallel would make for a more difficult load, only measurement would tell though.

Cheers, Andrew

 

[sonder]

There is nothing wrong with the parimg of the NC amp with the speakers, but if what you are hearing comes from the speakers and not the amp, then it won't solve the problem.

Perfect, thanks.

Honestly, if it turns out to be the speakers, I'll move them elsewhere in the house where they're less used and stick something else at the end of the NP***MP based setup.

I'm not particularly constrained by budget and feel I have simple requirements, roon server -> (anything) -> my ears - for 8-12 hours a day - constrained listening environment and speaker placement. The audio world is a minefield to navigate, wherever I turn, and the more I research and read the more of a minefield and rabbit hole it becomes.

 

[SIY]

What about AMT tweeters? Do they have high capacitance like electro stats?

I've measured two of them, both of which were almost pure resistances.

 

[SIY]

The ESLs I've measured (admittedly a limited sample) show a capacitance in series with a resistance. So a more realistic load, even for an edge case, is the 2u2 in series with (say) 1R. If there's a resistor in parallel, we must remember that the modulus of the impedance will be lower than the resistance and adjust our power calculations accordingly.