Non polarised electrolytics in speaker crossovers

[martin.m]

I have been reading an article on the Internet where the writer replaces the non polarised caps in a pair of vintage Hi Fi speakers with paper caps (in parallel to get the correct value). His theory is that the non polar caps still need a polarising voltage so can produce distortion and non linearity. The claim is that the audio performance is much improved with the paper caps fitted.

Is this a valid scientific theory or just more snake oil? There's not a huge expense involved but I suspect it is all a waste of time. This would apply to all speakers with a crossover unit, not just vintage ones. The article is here https://www.hifisystemcomponents.com...topic1121.html

[paulsherwin]

It's often a good idea to replace the electrolytics in old speaker crossovers, but that's because they're likely to be knackered by now. The hifi world seems to fetishise paper caps but I can't see why polyesters wouldn't sound exactly the same.

[martin.m]

Sorry, reading more closely the writer uses polyester capacitors but states they must be the "stacked layer" type so that they do not introduce any inductance. His point is that the non polar electrolytic types cause distortion.

Regards
Martin

[joebog1]

WOW !!!! I agree re Pauls comments, BUT at the same time electrolytics have some leakage and as a consequence might NOT be really good in cross overs. I say this mostly in respect to semi-conductor (transfer-resistor) amplifiers as they are directly connected to the voice coil. MOST valve amps are transformer coupled to the speaker so they are essentially isolated from the speaker. Any leakage will be largely assigned to weak bass or treble. (An electrolytic in treble circuits is not likely). Distortion?? I dont know! I have never bothered to measure the difference.

Plastic caps ( polyester, poly carbonate, polypropylene) are super cheap!! Good non polarised electros are, or can be expensive!!. I use plastic good quality caps. Unless you have a 1000 watt amp, 63 volt plastic is more than adequate. IF you want some extra security use 100 volt caps. BUT, YES change them over if you wish. IF they are more than 20 years old, CHANGE em for sure. Cost will be less than a couple of pints.

Joe

[Craig Sawyers]

Measurements by the late and great Cyril Bateman show that the harmonic distortion from non-polar electrolytics is almost as low as a polypropylene film capacitor. He measured 0.00042% *for no DC bias* in Capsound 6, which is far below audibility in any audio application, and even more so when the loudspeaker it feeds has large fractions of a percent distortion (they all do; it something loudspeaker manufacturers keep very quiet about!).

So any notion that a non-polar electrolytic causes distortion (or needs a DC bias!) in a loudspeaker crossover is simply audio paranoia.

The only reason to replace many decades old non-polars is if they have dried out, so their ESR has gone west and their value wandered. In which case replace them with new non-polars.

Craig

[dave cox]

I might pick film caps for better tolerance, both as manufactured and for drift with age. For the lower frequency elements film caps are likely to be prohibitively expensive and large so I would stick with (possibly selected for value) NP's.

Some manufactures might also have selected NP's for value but they won't do this for a value that isn't close to the nominal value as it doesn't make much economic sense!

Film caps are likely to have a somewhat lower ESR at higher audio frequencies but it won't be significant to an HF drive unit.

As pointed out already - they will all sound the same

dc

[Leon Crampin]

Power factor correction capacitors from old fluorescent units or motor phase-split capacitors from ancient Italian washing machines make excellent crossover capacitors. Space is not usually a consideration.

Electrolytics of any type are useless when they dry up, which is always the case with the Plessey devices which feature red/black end caps and yellow tape.

Leon.

[m0cemdave]

When I worked for a loudspeaker manufacturer (pro-audio, high power stuff) we always used plastic film types. Non-polarised electrolytics were considered cheapskate (or at least, "consumer grade" rather than "professional quality").

This was because of concerns over long term reliability / life expectancy, and the fact that they were only available with rather low voltage ratings and wide tolerances.

They are probably OK for consumer products, but we were making systems that were expected to have a long service life whilst maintaining their original specifications for as long as possible.

[Sideband]

IF there was any difference in sound quality it was probably because the old non-polarised caps were duff anyway. All he's done is to restore the speakers to original spec.