Do we really need to change out capacitors in crossovers?

[rcarlton]

Anytime I hear the same paradigm trotted out about the importance of changing capacitors in a crossover, I wonder. I had not tested this truism until now, and held it to be good advise. My testing is limited (OK, extremely limited). I built an ESR meter to test the capacitors in my 1989 LaScalas. Guess what? They all tested good! Could replacing capacitors be unnecessary? More testing to follow.

[Guest " "]

" Could replacing capacitors be unnecessary?"

There have been reports of "bad ones".

Most of the Klipsch xovers I have are not recapped, and they sound fine, so I may not have any of the "bad ones". I think I have AA, AL's, AL3's, B-1's, AB-1's, E-2's, AK-2's, K500_5000's, etc.

Sure, I can change the caps, and they will sound different, but so will removing all the terminal wires, knocking off the corrosion, and reconnecting the wire terminals.

It's part of the hobby, some folks roll tubes, some folks roll speaker wire, some folks roll capacitors.

[BEC]

I would expect capacitors from 1989 to be reasonably good. Try some from the 70s.

What did they read in ESR?

Bob Crites

[George Roland]

I had a pair of 1977 K-Horns and purchased Bob Crites's replacement crossovers with all new parts. This made a major improvement in sound quality and a "believer" out of me.

George!

[Groomlakearea51]

BEC's right. Having had a bazillion heritage speakers over the years (all of which are usually pre-90's), and using one type as an example, the old aerovox caps in the 70's just mostly dried out. A good "benchmark" or rule of thumb.... would be if they are over 20 years old, they could probably stand replacing. There are a number of factors involved; heat, humidity, etc. that generally make the oil filled go downhill. The 80's types seem to hold up better, with a couple of exceptions, but I believe that one of the reasons that new caps sound better is probably related to the ever closer and more accurate tolerances during manufacture. Any change in something that relates to inductance, capacitance, etc. is going to make the sound different. Usually better. Just IMHO.

[JJkizak]

Capacitors (in the 1960's) were designed to last 20 years at the maximum. Some exceptions would be Bell Labs/Western Electric stuff. Today? unknown. The Crites and Deans networks contain the newest stuff going design wise in all catagories (except Dean doesn't put nameplates and serial numbers on them, not sure about Crites), but they do work better than the old ones in my opinion.

JJK

[rcarlton]

I would expect capacitors from 1989 to be reasonably good. Try some from the 70s.

What did they read in ESR?

Bob Crites

Capacitor ESR Ohms XOVER 1 ESR Ohms XOVER 2

2 MFD 0.86 0.94

2 MFD 1.0 1.0

2 MFD 0.90 0.91

8 MFD 0.24 0.26

8 MFD 0.21 0.21

30 MFD 0.15 0.15

All passed the test based on the chart with the meter.

[BEC]

Those 2 uF caps are terrible. I would throw out any over 0.4 ohms.

Actually I would be surprised to find any that bad in a 1989 crossover. Remember that each crossover has two of the 2 uF caps in series in the tweeter circuit. That is about 2 ohms that should not be there in series with the tweeter.

Bob Crites

[rcarlton]

Those 2 uF caps are terrible. I would throw out any over 0.4 ohms.

Actually I would be surprised to find any that bad in a 1989 crossover. Remember that each crossover has two of the 2 uF caps in series in the tweeter circuit. That is about 2 ohms that should not be there in series with the tweeter.

Bob Crites

Bob,

According to the chart with the ESR meter the 2 ufd capacitor would be considered bad if it had a reading of ~60 ESR Ohms.

[BEC]

I have no idea what their chart means. I bought one of those meters several years ago myself thinking it might be a nice carry-along meter to use in a tool kit. I never got any meaningful results measuring with it. My ESR meter cost me about $550.00 and I have not been able to find one any cheaper that really gives meaningful measurements.

Anyway, just think of what their so called good 2 uF cap would do in your tweeter circuit. Let's make it easy. If you had a cap that measured 40 ohms ESR. Their chart would call it good. Now put the signal to an 8 ohm tweeter through a capacitor with an ESR of 40 ohms. You would loose 80 percent of the signal as heat making it through the capacitor. Even if a capacitor or series of two capacitors just had an ESR of 2 ohms, that is enough to cost you 25 percent of your signal to the tweeter.

Also thinking of this term ESR (Equivalent Series Resistance) another way, any ESR at all is bad. ESR is a measurement of all bad qualities of a capacitor. That is ESR is anything a capacitor does other than act just as a capacitance. Well, perfect capacitors would have "0" ESR. In practice we can't get to "perfect" but we can get close with good polyproplyene caps. Most I use would measure around 0.02 ohms ESR. I can hear the difference if a cap is as bad as 0.5 ohms ESR in a tweeter circuit when I replace it with a good one of 0.02 ohms ESR.

Bob Crites

[Groomlakearea51]

BEC: Great explanation! Very useful info!!

[wsu99999]

To help answer your question, I saw no difference when I changed the caps in my 1976 LS's. I did hear a difference when I removed the magnetic screw. Weather it was psychological or not I don't k now. I am in the process of mailing my old caps to bob to see if they were bad and when I hear from him I can let you know more. Thanks bob for offering that to me - I really appreciate it.

[Islander]

To help answer your question, I saw no difference when I changed the caps in my 1976 LS's.

I can only speak for my case, but when I replaced the caps in my 1974 La Scalas, the improved clarity was immediately noticeable. I'm glad I did it.

[joeydingo]

I had Bob change the caps out in my '67 KHorns and noticed a big improvement. I didn't bother to ask what the readings were on the old caps, and not even sure he checked, but I did send the entire crossovers to him so he could fully test all components in the crossovers.

I kind of expected to have him tell me something or another was wrong with my 40 year old crossovers and I ought to buy a nice pair of his new ones----but NOPE, he just replaced the caps, said they tested fine and shipped my vintage crossovers back to me. And I'd have bought his new crossovers without a whimper had he said I needed them.

A good, honest man.

[Guest " "]

" Let's make it easy. If you had a cap that measured 40 ohms ESR. Their
chart would call it good. Now put the signal to an 8 ohm tweeter
through a capacitor with an ESR of 40 ohms. You would loose 80 percent
of the signal as heat making it through the capacitor. "

40ohms would also shift the crossover frequency between the mid driver and the tweet.

" I can hear the difference if a cap is as bad as 0.5 ohms ESR in a
tweeter circuit when I replace it with a good one of 0.02 ohms ESR. "

Like many, you have a very musical ear....thats about a .337 db difference (guessing)

[Guest " "]

"I have no idea what their chart means. "

right from the blue esr meter manual

//////////////////

What is bad ESR?

There is a chart of 3 X normal average ESR for various capacitor values and voltage ratings on the meter front
panel. There is no one bad value; it depends upon the rating of the capacitor you are testing.

In general, a capacitor with bad ESR will read at least 2 – 3 times the values given for a new capacitor by the
manufacturer. The values shown on the chart are generally 3 times the manufacturer’s specs. A really bad one
might be 10 times the values shown or more.

With experience you will be able recognize bad ones without consulting the chart.

//////////////////////////////////////////

so it seems you need to know the esr of good like caps, before you can jugde if the reading is 3x times the value indicated. I would imagine different types of caps would have different esr's even if they were new?

[Guest " "]

Here's a chart from another ESR meter product.

[DrWho]

An ESR measurement without frequency is rather meaningless...

Take a look at the equation for calculating ESR:
ESR = DF / (2 x PI x f x C)

The implication being that it changes dramatically with frequency. The other implication is that higher ESR with lower capacitance is normal for the same dissipation factor.

A capacitor measuring 40ohms at 100Hz is going to be 0.4ohms at 1kHz, or 0.04ohms at 10kHz.

[Blvdre]

Thanks for that Mike, that put it in context. So in all but a first order crossover (no cap in the low pass), the cap is in parallel with the woofer, so a higher ESR would not seem to be a big deal, as compared to a band or high pass filter. I'm sure there's more to that story, though.