Capacitor type selection help for high pass

[RandyJ]

Hi guys,I'm making a 2-way bookshelf speaker for myself now. I want to use 3rd order for high pass. But the simulation result is the value of second Cap in series is very large,is 26 mF. I want to employ polypropylene for all the series Caps, but this one is really too big, and will not be cheap. Could i employ an electrolitic Cap for the second one, or an electrolitic one paralleled with a small PP Cap? Anybody compared with the sound of tweeter in these way? Please give me some advice. Thanks.

[Scott L]

I understand it was once fashionable to parallel caps. After further research this has proved to NOT be sonically so good.

I'm sorry, I do not know what country you are in, but a decent poly here in the United States costs 7 or 8 dollars.

Dayton DMPC-25 25uF 250V Polypropylene Capacitor | Parts-Express.com

[chlorofille]

Randy,

Do you mean 26uF ? 26mF is huge and must be some calculation mistake in your crossover.
For economical reasons, you can use an audio grade bipolar electrolytic cap.
An example would be a Mundorf Bipolar 22uF. You will need to parallel another 3.9uF to reach your 26uF.

[Scott L]

I meant it's not sonically so good to parallel dissimilar type caps. i.e an electrolytic and a polystyrene.

It's perfectly fine to parallel the same brand/type cap to reach a desired value. It's very good to be specific.

[Davey]

You might consider removing that capacitor and re-optimizing the remaining capacitor and inductor to achieve your target. My rule-of-thumb is, if that capacitor is approximately 27uF or larger then you can probably achieve a result without it.

Cheers,

Dave.

[RandyJ]

Many thanks,guys.
-Scott L,i agree with using the same type caps. I decide to use PP caps all.
-Davey, in my initial design, only using 26 uF cap could get good slope, FR curve and phase aligned with woofer. I will try your suggestion.
Here's another question. I don't know about the PP cap structure clearly. Is there difference in sound when i use 26 uF or 6 uF? I mean if large capacitance will bring disadvantage in sound, if i could get the same FR curve using 26 uF or 6uF.

[wolf_teeth]

You would change your sound drastically going from a 26uF to a 6uF. If this is on your tweeter as you say, it'll stop lower treble with a 6uF, where the 26uF will pass it. It's not so much a point of having bad sound with large or small values, but a point of where the cap rolls off the frequency response of the driver in its position in the circuit, according to the drivers' inherent frequncy response and impedance. The uF value decides where the capacitor influences the sound in the audio bandwidth.
Later,
Wolf