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About those dried out capacitors...

beansprout

beansprout

New Member
So I have a pair of Polk Audio RTA 12 speakers which I purchased around 1981 or so. Since they are 37 years old I thought they would benefit from a crossover rebuild. I've never attempted a rebuild like that, but being handy with a soldering iron and having some understanding of electronics I thought I'd give it a try.
The RTA's were nice for this since the crossover is mounted to the top of the speaker, just under a top grill assembly with very easy access. I purchased all new capacitors; 8 per speaker. Some of the capacitors were doubled or put in parallel to equal the old capacitance.
After the rebuild was complete, I gave them a listen and thought they sounded darn nice. Of course, I couldn't really do a side by side comparison, but again I thought they sounded really nice.
I decided to check the old capacitance values with the capacitor checker on my fluke meter and was surprised to find they were very close to their rated values and in some cases spot-on.
So I wonder, can something other than capacitance affect the quality of sound with an old or cheap capacitor?
 

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Whether or not people here agree with me or not, capacitors of different manufacture affect the sound you end up with, and pages and pages of threads have beat this to death. i stuffed the least expensive PP caps in my Dahlquist DQ 10's that I had for 35 plus years, and the change was so great I was in shock. The complete range was changed from top to bottom IMO.
 
beansprout said:
....So I wonder, can something other than capacitance affect the quality of sound with an old or cheap capacitor?
Click to expand...

That would be a yes. There many more characteristics to a capacitor than capacitance, but they're harder for most people to measure.
 
beansprout said:
Some of the capacitors were doubled or put in parallel to equal the old capacitance.
Click to expand...
I've heard changing the configuration of the capacitors (placing in parallel) can affect the sound characteristics of the speaker. I had some KLH speakers which I replaced the crossover caps. They originally had a pair of electrolytic caps in parallel for the high freq. response. I added the capacitance of the two caps and replaced them with a single cap. The resulting highs coming from the speaker became almost ear-piercing afterwards. I placed them back to their original (parallel) configuration which improved the sound.
 
beansprout said:
So I have a pair of Polk Audio RTA 12 speakers which I purchased around 1981 or so. Since they are 37 years old I thought they would benefit from a crossover rebuild. I've never attempted a rebuild like that, but being handy with a soldering iron and having some understanding of electronics I thought I'd give it a try.
The RTA's were nice for this since the crossover is mounted to the top of the speaker, just under a top grill assembly with very easy access. I purchased all new capacitors; 8 per speaker. Some of the capacitors were doubled or put in parallel to equal the old capacitance.
After the rebuild was complete, I gave them a listen and thought they sounded darn nice. Of course, I couldn't really do a side by side comparison, but again I thought they sounded really nice.
I decided to check the old capacitance values with the capacitor checker on my fluke meter and was surprised to find they were very close to their rated values and in some cases spot-on.
So I wonder, can something other than capacitance affect the quality of sound with an old or cheap capacitor?
Click to expand...

BTW, you can do a side by side, before and after comparison. Make changes to one speaker, leave the other as is, hook them up (one on left, one on right), put your preamp in mono mode, and compare.
 
Thanks for the responses. Wish I would have thought of the spark1 idea for side by side comparison. I was going to sell these speakers as I thought they were the least listenable of the three pairs I have, but after the rebuild I'm having second thoughts...
Is there such a thing as an adjustable capacitor so you could change capacitance as you listen and pick out the value you like best? I'm guessing not as it's probably high level calculations for a target sound, but it would be pretty cool if they were available for math challenged people like myself.
 
A true high value variable capacitor isn't practical, but there have been lots of switched decade capacitor substitution boxes made. For speaker tuning, it might be easiest to find a rotary switch and some surplus caps and make one. Since you'll use a lot of low value caps, the cost should be low. If suitable switches and caps can be found, a binary arrangement will use fewer caps. Cornell-Dubilier made some like that, but they've usually drifted way out of tolerance by now. do a Google image search on capacitor substitution box.
 
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