Crossover cap value tolerances

[ZeroG]

OK, this may seem a bit like I've already answered my question before we start, but this concerns speaker XO cap values when replacing an old electrolytic with a film cap.

For example, on my last recap, the XO had a 2.2uF electrolytic cap, with 20% tolerance. That means the cap can vary from 1.76uF to 2.64 uF (+/- 20%) and still be within range.

But the designer had a reason to select a 2.2 uF cap, so it figures that the closer the replacement comes to an actual cap value of 2.2uF, the better - right?

The replacement 2.0 uF Dayton film cap measures 1.9uF, which is well within the 20% tolerances mentioned above. But I have a bunch of 0.1 caps, so paralleling a few then brings it up to the actual 2.2uF as per the design.

Is this a waste of time and effort? Does it really matter, or is the 2.0 cap just hunky dory as is?

Also - if the 20% tolerance is toward the high side, does that mean the tweeter crosses over a little lower?

 

[spkrdtr]

Your 2.0 uF caps are fine. If you have the 0.1 uF caps, go ahead and parallel them with the 2.0's.

If the 20% tol. is on the high side the xover point will be a little higher.
If you could look at the affect +- 20% has on a speaker's response, you wouldn't even have created your thread.

 

[ZeroG]

If you could look at the affect +- 20% has on a speaker's response, you wouldn't even have created your thread.

That was the point, actually. I've recapped dozens of speakers, and had been wondering just what "close enough" actually does to the sound. Without a scope and/or the ability to A/B the difference in sound 20-20Khz
it becomes a matter of memory. Typically I have liked the change, but after having a recent conversation with a speaker designer who couldn't stress loudly enough the selection of crossover points and caps, I wanted to hear some other points of view.

 

[Dave1027]

For example, on my last recap, the XO had a 2.2uF electrolytic cap, with 20% tolerance. That means the cap can vary from 1.76uF to 2.64 uF (+/- 20%) and still be within range....


Is this a waste of time and effort? Does it really matter, or is the 2.0 cap just hunky dory as is?

Yes, it will matter. There is a big audible difference between a 1.9uf and a 2.2uf. The audible difference between 1.76 and 2.64 is night and day. The other side of it is that you may end up liking the sound of the 1.9uf so if it's not too much trouble you should try it.

My opinion is that if you care enough about sound quality and you take the time to recap you should be concerned with tolerances. Just because the speakers came with 20% tolerence caps does not mean it's acceptable to remain with that tolerance.

 

[spkrdtr]

I point out to my customers for whom I do xo upgrades, using tight tol. components is somewhat analgous to using matched drivers. The transfer functions between the two speakers will be 'matched' with 1 or 5% tol. parts.

OTOH, if you look at crossover slope responses in the area of the knee, you'll see they shift very little with minor changes in cap values. The summed response in a dynamic (music) environment will be next to impossible to determine which is which.

 

[ZeroG]

Yes, it will matter. There is a big audible difference between a 1.9uf and a 2.2uf. The audible difference between 1.76 and 2.64 is night and day. The other side of it is that you may end up liking the sound of the 1.9uf so if it's not too much trouble you should try it.

My opinion is that if you care enough about sound quality and you take the time to recap you should be concerned with tolerances. Just because the speakers came with 20% tolerence caps does not mean it's acceptable to remain with that tolerance.

Agreed, one should always match the rated value. But if the cap has a 20% tolerance (a 40% spread!), then while recapping it makes sense to try to hit the mark by paralleling up. Further, I've noticed that even with higher grade MPP like Sidereal (yes, they were old), the measured value was at least 10% LOWER than the rating. Since I started measuring the replacement caps for the last few months (when it fits my meter), it seems that they always measure lower but not higher. Might be just chance but it did seem odd, especially for what was a pretty expensive cap in its day.

 

[automojo]

Personally, I would get a good quality cap, that has the tightest tolerance you can find ,10%- 3-5% even better, and be happy.
Just use the value of the o.e. cap.
You may, or may not here a difference in each-hard to say. Some ears are more sensitive-but I imagine the difference would be small.
IMHO, the biggest thing is getting your network back into spec. Second, using better quality modern caps that have lower ESR, which can have a audible effect.