newbie, help with low-pass filter

I just want to ad a simple filter to a pair of small mid-bass speakers. These are in the rear doors of my truck. The rear seats stay folded down basically covering the speakers so all I want back there is bass. The speakers are 4 ohm 6.5" drivers rated at 50Hz-5kHz. These are drivers only with no built-in tweeters.

I would like to just cut out the highs to these speakers anywhere from 1-5kHz. I can only find select components at my local electronics store so not sure which way to go. What I bought was a choke rated at .68mH. This could be used for a simple first order filter by what I can figure should cut out about 1kHz and up.

Or, I can use a 10uF capacitor with a .33mH choke for a simple second order filter. What I can figure is I needed a 9.95uF cap with a .636mH choke. Will the 10uF/.33mH be close enough? If I use this should I swap the +/- wires for correct polarization?

Also, the capacitors are non-polarized and the chokes are RF Filters. Are these the correct parts?

Which way should I go, the first order or second order filter? Thanks for all help!
Yes it's permanent. I replaced the front two speakers with a good set of co-axils that sound fine. It has a good sounding set of tweeters up front, too. And the factory 6-disk changer is also fine with me. I just thought in the back, with the speakers covered, just do the bass deal. When I ordered the drivers for the back I didn't realize they would not come filtered...duh :-( When I installed them they sounded terrible (distortion). So, on when my jorney for filters. I'll try the parts store again for the 500 range components. Thanks again for the help!
Originally posted by micfly with the speakers covered,

Now there's an idea. Why don't you stuff a blanket or pillow up against them and see what you think of the sound. Just don't impede the cone travel. The thicker the blanket, the lower the frequency. :D

When I installed them they sounded terrible (distortion)

What kind of distortion were you hearing?
I'm sure the distortion is from all the highs these speakers can't reproduce. It's just when I open the doors and stick my ear up near them, otherwise up front most people wouldn't notice.

BTW, still wondering, If I go with the 2nd order should I swap the +/- wires? Also, if I get close on the part specs is that ok?

If you're using RF chokes they will probaly saturate as soon as any real power goes though them and the result will sound bad and possibly be a fire hazard.

The distortion you can hear is because your amp/headunit is clipping. Fitting a low-pass filter will help this to some extent by rounding off the waveform, but it will not do sod all for the fundamental problem that you are overdriving your amp/headunit.