two polarized capacitors to get a non-polarized capacitor for a tweeter

[peters8]

Hi guys!
I've a simple question for you: I've found two polarized capacitors (a simple type of cross-over as you know) on the tweeters of a pair of vintage speakers.
Each capacitor has the following specs : 25 uF/100V.
I've to replace them with a good polypropylene capacitor...but I don't understand what is the correct uF value to buy.
Could you help me, please?
Thank you in advance for the patience!
Best regards

 

[NAD80]

Question is what speakers are they? Are the caps wired together? Parallel or series?. Yes you can replace them with polypropylene cap. But as the value of the cap goes up the cost of the cap really goes up. I have bought off of Parts Express, the Dayton line of caps. And depending where the cap is in the speaker crossover film caps might not be good. Midrange and tweeter film caps would be good. On the woofer not so much. As for values replace with the same value. Voltage min would be what was in the original cap. Hope this helps peters8. If I haven't before Welcome to AK.

 

[mhardy6647]

Assuming (???) the two capacitors are paralleled with each other (which I would think they'd have to be to pass a "music" waveform), the capacitances are additive by Ohm's law. Really? 25 uF? 2 x 25 uF in parallel would be 50 uF.

50 uF first order XO into 8 ohms would yield 400 Hz XO frequency, or 800 Hz into 4 ohms.
http://www.erseaudio.com/First-Order-2-Way

Was this for midrange?

Sounds either like an ultra-cheap loudspeaker and/or a field-installation (hack job)?

 

[peters8]

Hi guys and thank you for your replies.
I believe that a good picture of these two capacitors is the best solution...I'm still a newbie!
Here's the picture:

This is the simple cross-over on this 2 way speakers...of course the two capacitors (they're the original ones,about 40 years old!!!) are connected to the tweeter; the woofer is connected directly to the cable, without any cross-over element.
Both capacitors have a value of 25 uF.
I hope this can help.
Now, I'll wait for your advice in order to replace these ugly and old capacitors with a better (and new, of course!) one.
Thank you, guys, for your kindness.
Best regards!

 

[elitopus]

Those caps are in series. The total value is half of the marked values. 12.5uf or around that is what you need.

You could get 12uf and .47uf caps for 12.47uf. That would be close enough. Parts express has those sizes in a few different brands

 

[MCM_Fan]

Those caps are in series. The total value is half of the marked values. 12.5uf or around that is what you need.

You could get 12uf and .47uf caps for 12.47uf. That would be close enough. Parts express has those sizes in a few different brands

Note to the OP, if you do go with a 12uF and a 0.47uF you will need to connect them in parallel for the values to be additive. If you connect a 12uF and a 0.47uF in series, like your original caps the resultant value will be will be 0.452uF.

For caps wired in parallel:

c = c1 + c2

For caps in series:

1/c = 1/c1 + 1/c2

Film caps are better quality and will last longer than electrolytics. However, a film cap will be considerably larger than an electrolytic cap of the same value. You'll need to consider the physical size of your replacement caps, just to make sure there is enough room to mount them in your crossover.

Thankfully, Parts Express lists physical dimensions for all their caps. You can combine whatever values you like, in parallel, that add up to the desired 12.5uF. My Infinity Qb speakers also use a 12.5uF cap in the crossover. I ended up using Dayton Audio caps in 8.2uF and 4.3uF to get the desired 12.5uF needed when I rebuilt my crossovers.

 

[elitopus]

Note to the OP, if you do go with a 12uF and a 0.47uF you will need to connect them in parallel

Yes I forgot to mention that. Thanks

 

[peters8]

Ok, guys, perfet!
Thank you very much!
Regards