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Marvin
06-01-2009, 10:50 AM
A little help please.
I have always heard that the capacitors in crossovers will leak over time. Leak meaning the dielectric material that makes a capacitor do what it does breaks down. This causes frequencies that should be trapped to "leak" through to the other driver. This means that frequencies will go to the drivers that they were supposed to be filtered from. This causes inefficient reproduction of sound.

Audio theory is not my strong point so I am looking for a little help here. The crossovers I am referring to are 35 year old Altec N800-8K. Also, why such a difference in Capacitor prices if all they really do is filter out unwanted frequencies. Maybe an explanation will help me understand.
Thanks,
Marvin

grumpy
06-01-2009, 11:02 AM
"leaky caps" term is often referred to when diagnosing tube amps... the dc-blocking
function becomes less effective. In regard to speaker use, they should read as an
open circuit at DC (multi-megohms) and measure at the correct capacitance value using
appropriate test equipment and methods.

Cost range? Different materials and manufacturing methods for different uses and
markets.

Marvin
06-01-2009, 01:23 PM
So what you are telling me is my original Capacitors are probably OK assuming they are physically in tact? And what I understood about Leaking capacitors is incorrect. I'm just curious.

Also, I see where the same rated caps can range from a couple of bucks to around $50. Is more costly better? If so, in what way?

I'm just trying to learn and understand. Knowledge is golden...
Thanks,
Marvin

grumpy
06-01-2009, 09:02 PM
Your capacitors may very well be performing their intended function.

Good appearance is not a guarantee, but if they look bad (bulging,
discoloration, material coming out...), there is a good chance that they
should be replaced.

Dielectric materials vary in their durability and lifetime, so there is some
possibility of them "going bad" depending on their use, environment, type,
etc... If you think something is wrong, it may be worth learning how to
check out electrical components.

If you had an expected voltage out/in curve for the crossover with the
l-pad set to a known ratio, and with resistive loads in place of the speakers...
with the proper equipment, you could make some measurements to verify
if the crossover (as a black box) is performing to spec.

Add a microphone and you might as well also measure the entire system
response; hopefully with some published spec to compare it to (not always
an option), or at least an idea of what looks reasonable or faulty.

Otherwise, individual component measurements (possibly requiring some
de-soldering and disassembly) are another option.

Or... rebuild the crossover from scratch with components that may or may
not be an improvement from the originals (without a thorough understanding
of the components, their limitations, and how some of those
limitations may have actually been used intentionally by the designer, swapping
in audio jewelry is no guarantee of success).

Or... re-design the crossover to suit the drivers and your sense of value vs. cost.

Feel free to read up on the various audio merits of capacitor types, or
perhaps someone else will respond with their experiences, opinions, thoughts,
etc...

Do you have reason to expect a problem?

Marvin
06-02-2009, 07:25 AM
Grumpy,
Thanks for your response. I must admit I am pretty ignorant when it comes to audio theory, as I'm sure you can tell, Ha. I don't know if I have a problem with the crossovers or not. I do know I had to replace the diaphragms due to one of them burned from an accidental overdriven situation. But, now that I have had them (HF drivers) restored everything sounds pretty good. But sense my 846B's are over 35 years old I was curious as to the crossovers needing attention. I understand from the forum that there may be something I can do to improve the sound quality. Mainly adjusting the crossovers.

Your explanation is quite thorough, but I must admit it is a bit over my head. And the old saying "if it ain't broke, don't fix it" comes to mind. I just remember hearing that certain components can deteriorate over time. Humidity, heat, and cold being factors contributing to the problem. I have refreshed the surround on the LF drivers with acetone as per Great Planes Audio's suggestion and had the HF drivers restored. So, the only thing left is the crossovers to fully refurbish the 846's.

I don't have the test equipment you mention so I just have to go with my gut and some helpful advice from more knowledgeable people like yourself. I did get a response from someone here on the forum who mentioned "tweaking" the crossovers. I would assume that meant replacing the capacitors. I know one thing for sure, I'm getting pretty confused.
Thanks again for all your help. At least I am getting some knowledge.
Marvin

spkrman57
06-02-2009, 07:41 AM
I live on the east side of Columbus and can help you restore your crossovers.

Actually, I could probably show you better crossover designs for your system than the original stock ones!

If you are interested send me a PM with your phone nr and we can chat about it some.

Regards, Ron



So what you are telling me is my original Capacitors are probably OK assuming they are physically in tact? And what I understood about Leaking capacitors is incorrect. I'm just curious.

Also, I see where the same rated caps can range from a couple of bucks to around $50. Is more costly better? If so, in what way?

I'm just trying to learn and understand. Knowledge is golden...
Thanks,
Marvin

grumpy
06-02-2009, 07:46 AM
Guess I got a bit long-winded. Maintenance on the drivers is a great way to keep the
things running the way they were made to sound. Going further, or 'hot-rodding' them
can be fun (which this should be), and sometimes beneficial (sometimes, not so much).

There are quite a few threads here regarding 'tweaking' your specific speakers....
worth a search and read if that's your bent :)

Edit: Sounds like you're in capable hands w/ Ron.

spkrman57
06-02-2009, 11:15 AM
We have narrowed down the necessary action to be performed on his Valencia's. It seems the 806's have been taken care of by Bill @ Great Plains and the 416's have been rotated and the excess goop cleaned up.

I asked Marvin to get the cap values of the crossovers so we can get them replaced with MPP Dayton audiograde from Parts Express. I will assist in any way needed. I don't see the need to replace the coils unless they are not working. I can test them in the future when the new caps are installed.

Regard, Ron