Why Recap Speakers and When?

Scorpion8

Addicted Member
Howdy --

Been searching AK and reading old threads about recapping speakers. This was a good one: http://audiokarma.org/forums/showthread.php?t=74979&highlight=recapping+speakers.

My question however isn't answered in any of the posts. At what point does a speaker need to be re-capped? How many years after original purchase? How long in storage without any use before it's time to re-cap? Do the caps last longer if the speaker hasn't been played, or if it's been in constant use?

Thanks for the help!
 
I tend to think that 25 years is a good rule of thumb, based on stuff I've read and my own limited experience. A cap will "dry out" over time which will limit it's ability to pass signal (there may be more to it than). Case in point: my recently purchased Seeburg DSS1's Altec driver's output was virtually non-existent 'til I replaced the x/o cap.
Whether to use electrolytic or polypropylene (or better) caps is mostly a matter preference. Replacing old electolytics with polypro's can net a cleaner, often somewhat brighter sound, but doesn't necessarily maintain the speaker's original sonics. Just depends on what your after, I reckon. - Mark
 
As mentioned, caps deteriorate over time. Manufacturers tend to use inexpensive components when making crossovers too. Higher quality caps, non-inductive resistors, robust inductors and better wiring can make a huge difference in performance. Also replacing those awful "clip" type terminations with quality binding posts helps.
 
If I replace a cap it's because I noticed a problem in SQ or if I replace a driver like a tweeter. I have several 30+ old speakers that have the same caps in them and they still sound very good. As a matter of fact the Heritage speakers (36yo) I just replaced the tweeter caps when I put in new tweeters. The only other cap in the crossover was for the mid and it still sounds fine.
 
I can guarantee you caps can drift way off value as they age. In this case, it means the cap in question and its related driver are no longer crossed at their intended frequency regardless of sound quality.
 
Over time the crossover caps get high in ESR. ESR (equivalent series resistance) is the sum of all the losses in the cap expressed as a value of an equivalent resistor in series. The average 30 year old film and foil cap like the one in the picture will still test good for capacitance but be high in ESR. Most read around 1 ohm ESR at that age, but the sky is the limit. The one in the picture has an ESR of 68 ohms. The tweeter signal was not going to make it through this cap even though the capacitance is still pretty good at 1.9 uF. ESR meters like the one in the picture will set you back over $500.00 in case you want to run right out and get one for testing your caps.

Good caps (polypropylene) will read around a few hundredths of an ohm when new.

Bob Crites
 

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Will old(25+yrs. old) x-over caps harm drivers in the path? That would be my only concern. Thanks for that ESR info. :thmbsp:
 
The old bad caps are not likely to hurt the drivers but a case could be made for how that is possible. When the caps increase in ESR, the impedance of the circuit changes and therefore the crossover frequency points will also change. When this crossover point changes enough, you have drivers trying to produce frequencies not inside their operating range.

Bad sound and loss of efficiency is the best reason to change them.

Bob Crites
 
Are there any guidelines on ESR of electrolytic capacitors vs. film types?

What I'm afraid of is replacing old electrolytics with new film capacitors, and the lower ESR of the new caps giving the tweeters more volume, resulting in my nice old speakers turning into shrieking monsters.

How about a polypropylene film cap + small resistor to approximate the electrolytic? That'd give the presumed benefits of low distortion yet preserve the original ESR, wouldn't it?
 
shocley said:
Are there any guidelines on ESR of electrolytic capacitors vs. film types?

What I'm afraid of is replacing old electrolytics with new film capacitors, and the lower ESR of the new caps giving the tweeters more volume, resulting in my nice old speakers turning into shrieking monsters.

How about a polypropylene film cap + small resistor to approximate the electrolytic? That'd give the presumed benefits of low distortion yet preserve the original ESR, wouldn't it?

Electrolytics also have an ESR about equivalent to Polypropylene caps then they are new. They go up in ESR over the years just like others. Mylar caps start out life with an ESR higher than I like to see in caps.

Absoultely the worst new caps I have tested are the new expensive PIO caps. ESR is just at about the point where I would replace them when they are brand new. The ones I tested were at about 1/2 ohm.

Remember that ESR is a measurement of everthing a cap does that is not what a cap should do. If you want to attenuate a signal, the absolute worst way to do that is to depend on getting attenuation from poor performance of caps. That poor performance is not a stable thing. It will continue to get worse with age.

So, in most cases when new caps are put into a crossover the high end gets brighter. That is when you should consider break-in time. That is for your ears not the cap. The speakers are likely sounding just like they did when they left the factory. You have perhaps not ever heard them sound that way or it has been a very long time since you heard them sound right.

Bob Crites
 
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BECtoo said:
Electrolytics also have an ESR about equivalent to Polypropylene caps then they are new. They go up in ESR over the years just like others. Mylar caps start out life with an ESR higher than I like to see in caps.

... The ones I tested were at about 1/2 ohm.


At the risk of turning this into electronics for dummies, two questions.

1. What is a "good" ESR value? For example, for the electrolytic caps that I need for speakers I wish to refurb, one supplier that lists ESR lists the IMP/ESR anywhere from 40.3 to 80.5 ohms.

2. Is there any problem in replacing electrolytic with metallized polypropylene, of course using caps with the same uF and V values?
 
subdermis2000 said:
At the risk of turning this into electronics for dummies, two questions.

1. What is a "good" ESR value? For example, for the electrolytic caps that I need for speakers I wish to refurb, one supplier that lists ESR lists the IMP/ESR anywhere from 40.3 to 80.5 ohms.

2. Is there any problem in replacing electrolytic with metallized polypropylene, of course using caps with the same uF and V values?

In all cases, for any use, as low as possible is best for ESR in a capacitor.

I like to see values of around 0.05 ohm or less in new caps. Most good new polypropylene caps test in the 0.02 ohm area.

Perhaps the spec you quoted above would be milliohms or thousandths of an ohm. A capacitor of 40 to 80 ohms would be worthless for any application I can think of.

The picture I have attached is showing a test of a good cap. You can see that the ESR is about 13 thousandths of an ohm and the capacitance is within about 1.6% of the stated value. A very good cap.

Bob Crites
 

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Oops, missed answering the question about substituting polypropylene caps for electrolytics. That is a good question too.

Ok, for every case, I would prefer to use a polpropylene in place of an electrolytic cap. In some cases, though, that is not practical. If you have a woofer roll off cap, for instance and its value is high like 68 or 100 uF, the cost and size of a polypropylene is prohibitive. Also, the job that cap is performing as a woofer roll off, is more like that of a trash can than anything else. In other words, it takes frequencies we don't want to hear out of that driver and sends them to ground. We do not listen to any music through that cap and its job then, is relatively unimportant. I would use an electrolytic there.

Bob Crites
 
If i might add my two cents worth here, you cannot go wrong with the Solens, i swear by them in all my Altec 2 way networks.

I'd just like to add a point that i haven't seen mentioned and that is in regard to handling of your new caps. Wether it's an electrolytic, poly, or film and foil, a capacitor is a hermetically sealed device. When the seal is compromized, it threatens both the ESR and uF value of the cap, and degradation begins immediately upon the seal being broken. The main point to be concerned with is where the leads exit the cap body. It's a good idea to avoid applying much stress at that point and i've seen posters on other threads recommend using hemostats or locking needlenose pliers to hold the leads while bending, soldering, or otherwise terminating those leads. Some of the larger solens get rather heavy, and i like to add a small amount of epoxy to reinforce that area where the lead exits the cap body.

I have also learned to always test every cap before installation in a circuit. Capacitor makers also make mistakes and have bad days too!

Just my two cents worth.
 
The following question is in regards to use with vintage Jensen speakers, circa 1962. I'll be using values of 33uF to 35uF, and 4uF.

Out of curiousity, has anyone used Axon (True Caps), Dayton (DMPC or PMPC), or Solen (PA or PB) in a standard 1st order (6dB) filter configuration for a 3 way application; and bypassed them with .1uF Sonicap Gen II's ???

My main concern is about poor/high ESR levels on the main caps. I'm not too worried about the Gen II's since their ESR is generally excellent.

I prefer not to buy $$$ of caps simply for testing purposes and see how they all stack up.

. . Falcon
 
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