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-   -   Non-Polar Electrolytic vs. Polypropylene Film Capacitors (http://www.diyaudio.com/forums/parts/117452-non-polar-electrolytic-vs-polypropylene-film-capacitors.html)

gtforme00 14th February 2008 07:27 PM

Non-Polar Electrolytic vs. Polypropylene Film Capacitors
 
This isn't what you think! While there certainly are subjective preferences on these parts, I would like to present to this community the results of some tests I have performed today. The parts tested are all currently available, value oriented parts from Madisound, Parts-Express, or MCM.

-Measurements were made using the HP 4192A Impedance Analyzer (Calibrated this year).Three measurement frequencies were used: 100Hz, 1kHz, 10kHz.
-Signal voltage was 1VRMS.
-The series equivalent circuit model was used for calculations.
-Measurements presented are the capacitance, equivalent series resistance, and dissipation factor respectively.

  • 3.3uF Panasonic Polypropylene Film 200V (Madisound surplus)
    0.10 kHz 3.313 uF <0.1 Ohm <0.01% DF
    1.00 kHz 3.306 uF <0.01 Ohm <0.01% DF
    10.0 kHz 3.31 uF 0.005 Ohm 0.1% DF
  • 3.3uF Bennic XPP 250VDC (Which are on sale this month at MCM)
    0.10 kHz 3.313 uF <0.1 Ohm <0.01% DF
    1.00 kHz 3.306 uF <0.01 Ohm <0.01% DF
    10.0 kHz 3.28 uF 0.002 Ohm <0.1% DF
  • 4.7uF Non-Polar Electrolytic 100V (From Parts-Express)
    0.10 kHz 4.989 uF <5 Ohm 1.45% DF
    1.00 kHz 4.826 uF 0.93 Ohm 2.8% DF
    10.0 kHz 4.7 uF 0.264 Ohm 7.8% DF
  • 5.0uF GE Polypropylene 400VDC (Surplus from Madisound)
    0.10 kHz 4.93 uF 0.001 Ohm 0.1% DF
    1.00 kHz 4.92 uF <0.01 Ohm <0.01% DF
    10.0 kHz 4.93 uF <0.01 Ohm <0.01% DF
  • 10uF Madisound Surplus 100VDC
    0.10 kHz 10.1 uF <0.01 Ohm <0.01% DF
    1.00 kHz 10.07 uF <0.01 Ohm 0.04% DF
    10.0 kHz 10.1 uF 0.003 Ohm 0.2% DF
  • 10uF Dayton MPT 250VDC (From Parts-Express)
    0.10 kHz 10.005 uF <0.1 Ohm <0.01% DF
    1.00 kHz 9.98 uF <0.01 Ohm 0.03% DF
    10.0 kHz 9.99 uF 0.001 Ohm 0.1% DF
  • 12uF Bennic XPP 250VDC (Which are on sale this month at MCM)
    0.10 kHz 12.05 uF <0.1 Ohm <0.01% DF
    1.00 kHz 12.03 uF <0.01 Ohm <0.01% DF
    10.0 kHz 12.04 uF 0.001 Ohm <0.1% DF
  • 12uF Bennic Non-Polar Electrolytic (From Madisound)
    0.10 kHz 12.675 uF 3.45 Ohm 2.7% DF
    1.00 kHz 12.12 uF 0.40 Ohm 3.0% DF
    10.0 kHz 11.74 uF 0.073 Ohm 5.4% DF
  • 31uF Bennic Non-Polar Electrolytic (From Madisound)
    0.10 kHz 32.3 uF 1.60 Ohm 3.2% DF
    1.00 kHz 30.5 uF 0.241 Ohm 4.6% DF
    10.0 kHz 29 uF 0.057 Ohm 10% DF
  • 33uF Non-Polar Electrolytic (From Parts-Express)
    0.10 kHz 33.9 uF 1.78 Ohm 3.8% DF
    1.00 kHz 32.1 uF 0.170 Ohm 5.4% DF
    10.0 kHz 31 uF 0.047 Ohm 9% DF

Impressions.
Non-polar electrolytics are pretty lossy compared to polypropylene. I have always heard that, but never quantified it. Notice how the capacitance drops with frequency and the dissipation factor rises in the electrolytic capacitors.

Electrolytics are not very linear with frequency, we see a 10% change from 100Hz to 10000Hz! (this does NOT imply they cause non-linear distortion due to this fact, please don't misunderstand). The polypropylene capacitors by comparison are fairly linear in capacitance with frequency and most have dissipation factors too low to reliably measure.

Notice the high series resistance of the electrolytics compared to polypropylene. This does not seem to me to be a negligible amount of resistance in crossover design, after all, don't we model inductors with this much series resistance? I do not have experience with crossover design software beyond Speaker Workshop, and do not know if any of them can model the non-linear resistance of an electrolytic capacitor. It would seem to me that this would be particularly important for midbass drivers in a 3 or more way. The Qts of the driver-enclosure system will be affected by this series resistance.

Anyone else care to comment on this?

Regards,
David

Conrad Hoffman 15th February 2008 06:08 AM

I've never been a fan of non-polar electrolytics, in fact I think they're often inferior to standard electrolytics. As a general rule, polypropylene caps are similar to polystyrene, with very low DF. Teflon is better, but impractical in any value I'm interested in. Mylar (polyester) is worse, and many people can't stand them. It's easy to measure the differences in DF, but with a good bridge, not an impedance analyzer. Still, I find the wide range curves you can generate with the impedance analyzer more useful. Personally, I don't find the differences that great, though I prefer polypropylene. I avoid electrolytics of any type in the signal path, with the exception of power amp feedback circuits, just because most other types are impractically large. I use active crossovers, so there's no need for electrolytics there! I've yet to see convincing tests that show high end caps to be any better than similar type and value of common inexpensive caps.

gtforme00 15th February 2008 02:30 PM

Conrad,

Thanks for the response! All of this came about as a result of a current project to clone the NHT M3.3. Jack Hidley graciously provided me with the schematics and the drivers are available here. This is by far the most complicated crossover I've built, and I want to know exactly what I am getting with the components I am buying. I wonder if NHT made allowance for the series resistance of the electrolytics used in the midbass and midrange crossovers?

For my self-designed projects, anything over 2-way has received active crossovers. I whole heartedly agree that they are superior to passive crossovers! With the current prices of passive components, they are a whole lot less expensive as well!

Conrad Hoffman 15th February 2008 03:50 PM

You might also find this interesting from back when I was making comparisons between mostly film types-

http://members.rpa.net/~choffman/cap_compare.xls

cuibono 15th February 2008 03:57 PM

Thank you both for doing all that work and sharing it. I wish more people actually took the time and made the effort rather than just talk.

I never realized how much capacitance drops with frequency..

gtforme00 15th February 2008 04:04 PM

Thank you! I greatly appreciate you taking the time to post this information. I will add this to my reference library of test results. Do you have more information about the bridge you used to measure these results?

Conrad Hoffman 15th February 2008 06:18 PM

I'm fortunate to have periodic access to an Agilent E4980A. That has capabilities out to 2MHz, and I did all the spreadsheet measurements using that. At home I use a combination of the GR1615 standards bridge, which excels at accuracy and low DF, the GR716C, which can get to near 1MHz, but none of my antiques can measure large values at high frequencies like the $16K Agilent.

gtforme00 15th February 2008 07:19 PM

You are quite welcome. This information was gathered with a personal interest, but I considered it valuable to share as I have not found it available in condensed form, especially for "everyman" style capacitors.

I have noticed an error in my original post, and have not the ability to change it. The Madisound 10uF surplus capacitor should read 10.1 uF at 10kHz, not 100.7uF.

Regards,
David

AndrewT 16th February 2008 11:48 AM

Quote:

Originally posted by gtforme00
I have noticed an error in my original post, and have not the ability to change it. The Madisound 10uF surplus capacitor should read 10.1 uF at 10kHz, not 100.7uF.

ask the Mods to substitute your corrected script for the erroneous version.

gtforme00 19th February 2008 04:05 PM

Would a moderator please make the above correction?

An update to my inquiry on capacitor ESR and crossover design.

First, I was a bit redundant in specifying both ESR and DF, as they are inextricably linked for a given frequency. DF = 2*PI*F*ESR*C*(100 for percent). However, it is nice to see the ESR to get a grasp of the resistance each capacitor represents.

Second, in private conversations with a loudspeaker engineer (The above mentioned Jack Hidley from NHT) he confirmed that an experienced designer will take into account the ESR of both capacitors and inductors. Furthermore he stated that the ESR was taken into account in the design I am cloning (NHT M3.3) and that I should try to match the Dissipation Factors given in the specifications. This was good for me to discover, as I had purchased at least one film capacitor to replace an electrolytic, a substitution which I will no longer be using.

Now, it is very common to hear discussion of Inductor ESR, but this is the first confirmation I have seen that capacitor ESR should be considered when designing loudspeakers. This does NOT automatically invalidate all designs which have not taken this into account. The differences among the ESRs of various types of film capacitors are fairly small, however there is a significant difference between the ESR of film type capacitors and that of electrolytics. The practice of swapping electrolytics for film capacitors to "improve" a design is immediately called into question.

There is no paradigm breaking news here, and to some this may even be old news. This is just one more small block of knowledge to add to the vast amount of information available on this forum.

So what practical lessons should we take away from this experiment? If one is designing a crossover with electrolytics, one should be aware that the ESR of the capacitor will have a small effect on the drivers actual response, and that some software is not capable of modeling this (in my experience Speaker Workshop). Similarly, if an existing design has an electrolytic, be aware that there will be a deviation from the design if a film type capacitor is substituted. Whether this deviation will be perceived subjectively as an improvement is outside the scope of this discussion.

I hope that this discussion has been as informative for the readers as it has been for the author.

Regards,
David

P.S. Next up, can I measure "voltage coefficient of capacitance", and how do different types of capacitors compare?


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