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I did a little reading on crossovers this morning, a simple HP crossover consists of a capacitor(s). My friends Alpine Type S' are crackling when he turns it up, plus he always has the bass turned up too loud.

The local rat shack doesn't carry a single cap. with the value I need, so I was going to wire two cap.s in parallel. I plan on getting a 220uF cap and a 100uF cap, in parallel this will "produce" a 320uF cap and create a HP cut off of about 125 Hertz. I beleive the roll off will be 6db right?

Is this a good plan? Just doing this too save some money (~$10) instead of buying "bass blockers" from crutchfield.

The two caps from radio shack:
http://www.radioshack.com/product/index ... Id=2102485
http://www.radioshack.com/product/index ... Id=2102484

Also, I noticed the pictures show the case of the capacitors have an arrow (usually to show which lead is negative), but does it really matter when used in the application of a crossover? Both are going to be connected to a positive source, just in series.

anyone?

What impedance are the speakers? Yes, a single cap ill rolloff at 6db. I believe you're going to need caps that DON'T have an arrow, since it's AC. AC moves back and forth, not just one way like DC. I believe these are called bipolar caps.
If your speaker is 4 ohms, then 320uF (220+100, in parallel) is correct.

For reference: http://www.partsexpress.com/webpage.cfm?WebPage_ID=146

pretty sure the speakers are 4 ohm (i'll test em with a meter to be sure though).

radioshack lists those capacitors (the links I posted) for use with speakers, maybe it's a generic photo? weird.

"These capacitors are generally non-polarized electrolytics, polypropylene, or Mylar and consist of interleaved layers of foil and insulating material."
-http://www.termpro.com/articles/xover.html

could I find non-polarized caps. at any local place?

I would guess Radio Shack would have both types. I'm not really sure what places carry electronics, unfortunately. Parts Express and Madisound both carry some decent stuff.

a single capacitor would be a 1st order filter, which is 6dB/octave. that's more shallow than the speaker's own natural 12dB roll off.
What you need is at least a cap and a choke, to make a second order filter for 12dB roll off.
Build it for about 125Hz, or just get a "bass blocker" which is a filter pre-made for you.

http://www.the12volt.com has great databases on filter building.
first through third-order and zobel.
Forget radio shack for filter components though. They don't carry non-polarized mylar capacitors, which are what you want for this.
theirs are all polarized and won't work in this situation.
Talk to a car audio shop for what you need, or look online at sites like partsexpress.com for the parts you need. PAC makes decent stuff for this.

partsexpress will have the capacitor & parts you need... and cheap. my capacitors for my tweeters (when i had a set of dayton tweeters in my saturn) were like $.50 each.