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Capacitor upgrade in crossover - You CAN'T handle the TRUTH! - Part 3

Audiofire

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1. Hides the "bad sound quality" as not measurable distortions?
What about a discussion on the effect of dielectric absorption? Couldn't this make a difference to the sound in crossovers? Some audiofool capacitors have oil inside and that could possibly affect the sound, some even perceiving that as improved sound.

Edit: Just found something. Dielectric absorption is another non-issue apparently.

"With a 22k load resistor, the maximum 'recovered' voltage is 4.45mV, at 1.2ms after the short is removed (-81dB). Remember that this was after charging the cap to 50V for 500 seconds, then shorted for one second. This is not a normal audio circuit, and no audio circuit will subject a capacitor to anything even approaching the conditions used here.

"Caps in audio circuits are simply not charged and discharged in this manner. To do so would cause signals to be generated that, after amplification, would mean instantaneous speaker disintegration. These tests are silly - they prove nothing, but are regularly hailed by some audiophiles as some kind of 'proof' that they can hear a difference because it can be measured. It is forgotten in the excitement that the signals and tests that form such proof will never occur in a real audio system that is not in the process of blowing up.

"I have heard claims that the voltage recovery characteristic causes distortion similar to reverberation. What complete rubbish! If it were that simple to create reverb, one can be sure that no-one would have ever bothered with reverb springs, plates, or digital delays. Utter nonsense - it simply does not happen."

Source:
Rod Elliott. Capacitor Characteristics.
 
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SIY

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What about a discussion on the effect of dielectric absorption? Couldn't this make a difference to the sound in crossovers? Some audiofool capacitors have oil inside and that could possibly affect the sound, some even perceiving that as improved sound.

Edit: Just found something. Dielectric absorption is another non-issue apparently.

"With a 22k load resistor, the maximum 'recovered' voltage is 4.45mV, at 1.2ms after the short is removed (-81dB). Remember that this was after charging the cap to 50V for 500 seconds, then shorted for one second. This is not a normal audio circuit, and no audio circuit will subject a capacitor to anything even approaching the conditions used here.

"Caps in audio circuits are simply not charged and discharged in this manner. To do so would cause signals to be generated that, after amplification, would mean instantaneous speaker disintegration. These tests are silly - they prove nothing, but are regularly hailed by some audiophiles as some kind of 'proof' that they can hear a difference because it can be measured. It is forgotten in the excitement that the signals and tests that form such proof will never occur in a real audio system that is not in the process of blowing up.

"I have heard claims that the voltage recovery characteristic causes distortion similar to reverberation. What complete rubbish! If it were that simple to create reverb, one can be sure that no-one would have ever bothered with reverb springs, plates, or digital delays. Utter nonsense - it simply does not happen."

Source:
Rod Elliott. Capacitor Characteristics.
Glad you found that, Rod’s article is very good. Caps are second only to wire in the amount of mysticism and superstition surrounding them. I posted a bunch of debunking measurements which got some folks upset.

Good.
 

ToriCatcher

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Hello @ctrl
Just finished reading the whole series, it was very interesting. Thank you for posting it.
A small query, I was told by a reputable audio engineer that the maximal voltage of a capacitor can also have an effect, even audibly changing the tonality of the speaker.
Can you talk a little about the possible effects of say, changing an 50v electrolytic cap to 100, 250 or 400 volts maximum? (Assuming the caps are chosen to high value accuracy, as you did in your tests, and it seems improbable the 50v limit would be exceeded in actual use). I even saw the claim that such an increase in max voltage can reduce distortion.
Thanks a lot.
 

Audiofire

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A small query, I was told by a reputable audio engineer that the maximal voltage of a capacitor can also have an effect, even audibly changing the tonality of the speaker.
This probably has something to do with voltage transients. Does someone know what the maximum realistic voltage surge is for passive crossovers? I think it is well within 50 volts. This is much like when I asked about dielectric absorption, and the test from Rod showed that there was not any distortion. Other parameters that could have any effect are ripple current and ESR, but I don't know. If the audio engineer didn't explain in a verifiable way, there is always the possibility that he/she doesn't really know what he/she is talking about either.
 
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ToriCatcher

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This probably has something to do with voltage transients. Does someone know what the maximum realistic voltage surge is for passive crossovers? I think it is well within 50 volts. This is much like when I asked about dielectric absorption, and the test from Rod showed that there was not any distortion. Other parameters that could have any effect are ripple current and ESR, but I don't know. If the audio engineer didn't explain in a verifiable way, there is always the possibility that he/she doesn't really know what he/she is talking about either.
Although a possibility, I like to give the benefit of the doubt until it is impossible. Especially as the whole thing was a favor and he has no interest in the matter.
 

fineMen

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Can you talk a little about the possible effects of say, changing an 50v electrolytic cap to 100, 250 or 400 volts maximum? (Assuming the caps are chosen to high value accuracy, as you did in your tests, and it seems improbable the 50v limit would be exceeded in actual use). I even saw the claim that such an increase in max voltage can reduce distortion.
Thanks a lot.

The claim is nonsense. You don't care about 30% of intermodulation in the speakers transducers, but are willing to pay multiple for an upgrade which effect is in the +/-0,000000..x% region?
 

Audiofire

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Although a possibility, I like to give the benefit of the doubt until it is impossible.
Please see this for a verifiable explanation, the lower ESR with a higher voltage is probably a parameter that can have any effect:
 

R Swerdlow

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This probably has something to do with voltage transients. Does someone know what the maximum realistic voltage surge is for passive crossovers? I think it is well within 50 volts.
Maximum voltage depends on the time frame for measurement. Well under 50 volts is probably true for average voltage. But for transients, it may be much higher.

Years ago, I met an EE named Bob Cordell at a DIY speaker building meeting in the Maryland, Washington, Virginia area. In the past, he made a living designing audio amplifiers, and he published a text book on the subject. He had switched to other fields in electronics, but he still kept a finger in audio, more as a hobby than a profession.

Cordell ran a demo that addressed the question of how powerful an amplifier we really need – if your goal is to never allow the amp to go into clipping. He rigged up ways to measure voltage & wattage both for very brief transients (about 20 microseconds) and an average for about 15 seconds. He played the same musical passage on the same speakers as he tested two different amps, one about 100 watts and the other about 250 watts. The music was a standard popular music with a female voice, played at modest levels not louder than conversation among listeners. He wrote a brief description of his Peak/Average meters.

The average wattage & voltage values were low during the passage, much less than 50V. But the brief transients (a rim-shot on a snare drum) had voltage peaks much higher than 100V, as high as 150V if I remember correctly. The 100 watt amp clipped during each rim-shot, but the 250 watt amp did not.

I'm not sure exactly what that means for caps in passive crossovers. But it does suggest that brief voltage surges of 100 to 150 volts occur more often that we might guess.
 
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Audiofire

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The average wattage & voltage values were low during the passage, much less than 50V. But the brief transients (a steady rim-shot on a snare drum) had voltage peaks much higher than 100V, as high as 150V if I remember correctly. The 100 watt amp clipped during each rim-shot, but the 250 watt amp did not.
Thank you, that is just another reason why film capacitors are probably the only right choice for speakers from a durability standpoint. They often have voltage ratings of 250 volts or well above. The radial type film capacitors can be rather cheap and the best choice for passive crossovers.
 
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ctrl

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A small query, I was told by a reputable audio engineer that the maximal voltage of a capacitor can also have an effect, even audibly changing the tonality of the speaker.
Can you talk a little about the possible effects of say, changing an 50v electrolytic cap to 100, 250 or 400 volts maximum?
With "standard" film capacitors, the dielectric strength is so good that distortion due to high voltage is practically irrelevant.

With electrolytic capacitors, the dielectric strength is significantly lower and therefore the distortions are significantly greater, but still at a very low level.

One must be aware that the sensitivity of a driver at 2.83V is already around 85-95dB@1m.
With a voltage of 10V, which corresponds to about 96-106dB@1m without lowering by voltage divider, very few will ever listen to music that loud.

At such high sound pressure levels the harmonic distortion of most loudspeakers is already above 1% (correspondingly high is usually IMD), but even electrolytic capacitors are still far below 1% distortion at these voltages.

In addition, @pma has made detailed measurements that show that even electrolytic capacitors are still below the distortion of even the best drivers - see the following posts in Part II (can be read quickly, only a few posts).
For "high power loudspeaker", you should of course only use electrolytic capacitors that have >=100VDC and not use the very cheap ones with only 63VDC dielectric strength.

And where it is financially reasonable, best to avoid electrolytic capacitors in the crossover - my rule of thumb, up to 15µF (and always in the high frequency range) I usually use film capacitors, what is above that is done with electrolytic capacitors.
 
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ctrl

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I'm not sure exactly what that means for caps in passive crossovers. But it does suggest that brief voltage surges of 100 to 150 volts occur more often that we might guess.
I think you have confused "watts" with "volts" here.
A 4 ohm speaker that requires peak voltages of 150V requires 5625W of amplifier power :eek:
Only people who live in a football stadium need that much power ;)
 

ToriCatcher

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With "standard" film capacitors, the dielectric strength is so good that distortion due to high voltage is practically irrelevant.

With electrolytic capacitors, the dielectric strength is significantly lower and therefore the distortions are significantly greater, but still at a very low level.

One must be aware that the sensitivity of a driver at 2.83V is already around 85-95dB@1m.
With a voltage of 10V, which corresponds to about 96-106dB@1m without lowering by voltage divider, very few will ever listen to music that loud.

At such high sound pressure levels the harmonic distortion of most loudspeakers is already above 1% (correspondingly high is usually IMD), but even electrolytic capacitors are still far below 1% distortion at these voltages.

In addition, @pma has made detailed measurements that show that even electrolytic capacitors are still below the distortion of even the best drivers - see the following posts in Part II (can be read quickly, only a few posts).
For "high power loudspeaker", you should of course only use electrolytic capacitors that have >=100VDC and not use the very cheap ones with only 63VDC dielectric strength.

And where it is financially reasonable, best to avoid electrolytic capacitors in the crossover - my rule of thumb, up to 15µF (and always in the high frequency range) I usually use film capacitors, what is above that is done with electrolytic capacitors.
Thanks for the response.
You only implicitly hinted that you estime there will be no change to tonality by changing between 400v, 250v, 100v or even 50v max. Is that really the case?
 
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ctrl

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You only implicitly hinted that you estime there will be no change to tonality by changing between 400v, 250v, 100v or even 50v max. Is that really the case?
In most cases, it won't matter. As I said, I would not use bipolar electrolytic capacitors with less than 100VDC.

It has been said in other posts that 250W peak power would be sufficient for the transient signals (in most cases).

That would be about 30VAC voltage for a 4 ohm speaker. The vast majority of speakers will have IMD and HD in the double digits at these sound pressure levels - so the contribution of electrolytic capacitors is very unlikely to matter at all.
 
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R Swerdlow

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I think you have confused "watts" with "volts" here.
A 4 ohm speaker that requires peak voltages of 150V requires 5625W of amplifier power :eek:
Only people who live in a football stadium need that much power ;)
That could easily be the case. I'm relying on memory of an afternoon more than 10 years ago. It could have been the peak voltage that becomes roughly 150 watts. The speakers were DIY 2-way tower speakers with ~6-8 ohm impedance.

The take home lesson was that transient (20 µsec) voltage peaks were significantly higher than the average voltages.

I think most of us reading this thread agree that inexpensive metalized polypropylene (MPP) capacitors, rated at 250VDC / 150VAC are the 1st choice for building crossovers. All of the MPP caps I've had my hands on measure a capacitance value almost exactly what their label states, well within the ±5% specification. These are the inexpensive Taiwanese MPP caps sold in the USA by Parts Express or Madisound. If I can't find one with the needed capacitance, I'll order a 400VDC / 250VAC Solen or Audyn Q4 cap, but I avoid anything at higher prices than those.

It's been years since I bought a non-polar electrolytic (NPE) cap. I found that many of them measured beyond their ±10% tolerance values, when they were new! It took about 10-20 NPE caps just to find two that measured within spec. Compared to that, MPP caps are a bargain.
 

SIY

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In some speaker designs, the caps are specified with voltages low enough that they will fail before the drivers do. That is a good thing.
 

Audiofire

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It's been years since I bought a non-polar electrolytic (NPE) cap. I found that many of them measured beyond their ±10% tolerance values. It took about 10-20 NPE caps just to find two that measured within spec. Compared to that, MPP caps are a bargain.
Another reason why an electrolytic cap with a higher voltage rating can change "the tonality of the speaker" when it might as well be the different capacitance that had any effect, not the voltage (matching capacitance on each channel can be good for the audible quality though).
 
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ToriCatcher

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Another reason why an electrolytic cap with a higher voltage rating can change "the tonality of the speaker" when it might as well be a different capacitance that had any effect, not the voltage (matching capacitance on each channel can be good for the audible quality though).
Of course what I meant is a situation where everything but maximum voltage is the same.

In most cases, it won't matter. As I said, I would not use bipolar electrolytic capacitors with less than 100VDC.

It has been said in other posts that 250W peak power would be sufficient for the transient signals (in most cases).

That would be about 30VAC voltage for a 4 ohm speaker. The vast majority of speakers will have IMD and HD in the double digits at these sound pressure levels - so the contribution of electrolytic capacitors is very unlikely to matter at all.
Thanks again.
Another question regarding your interesting series of posts, what about differences of film vs electroytic after heating (semi prolonged normal use)? Did you happen to look at that?


Alas, regarding voltages, I am left with the question what would be the effect of changing the caps of an old beloved set of speakers of mine that did originally come with 50v electrolytic capacitors.
 
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fineMen

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In some speaker designs, the caps are specified with voltages low enough that they will fail before the drivers do. That is a good thing.
Even if it is only a hint, the current is also limited! For that reason I can not make, for example, an impedance equalization in the bass with electrolytic capacitors. The stomping in contemporary music lay just where the resonant circuit acts, and often has -3dB level. The current capacity is usually not written on the part, and can be shockingly low.

In the further the case lies nevertheless as clear as day. If the money is left, it is worth in almost all cases to buy a better tranducer than to think about expensive and stupidly expensive capacitors. If you don't have one of the ten best drivers at hand, an electrolytic capacitor will do. Then you just take an MKT or so, because it no longer depends on the few dollars.
 

fineMen

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Alas, regarding voltages, I am letf with the question what would be the effect of changing the caps of an old beloved set of speakers of mine that did originally come with 50v electrolytic capacitors.
My guess is probably right, you don't have a measurement system? Then you should better do nothing. That will not work.
 

Audiofire

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Thanks again.
Another question regarding your interesting series of posts, what about differences of film vs electroytic after heating (semi prolonged normal use)? Did you happen to look at that?


Alas, regarding voltages, I am left with the question what would be the effect of changing the caps of an old beloved set of speakers of mine that did originally come with 50v electrolytic capacitors.
Temperature can affect capacitance and ESR, but this should happen rather uniformly if all capacitors are the same age and type. The difference from a lower ESR comes in the form of higher volume level, because more voltage can get through from what I understand. That would explain why tonality is changed by giving more sound pressure to a certain speaker driver.

If there are only electrolytic capacitors in there, it will work all right to replace. A difference usually comes when only some of them are electrolytic and they are changed with film capacitors. The bad sound quality comes from electrolytic caps that have a deteriorated capacitance and ESR, which will only become more deteriorated if the temperature is increased.
 
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