tweeter capacitor

Guys,

I'm getting ready to install some Ambient Tweeters up high in my doors.  I need to find out what microfared cap I need to run to get a 10k crossover point at 6db.  The crossover chart states for 4ohm it's 4 microfarads and at 2ohm it's 8 microfarads. 

Here's the problem, I have a 4 ohm tweeter, but my amp is at a 2 ohm load.  So do I run a 4 or 8 microfarad?    I forget if the value is from the tweeter or what the load on my amp is!!! 

Any help would really be appreciated!  Thanks in advance.

The amp load does not factor into the equation.   Only the impedance of the tweeter. 

I've never heard of anything like this before, why not? Why should you have an ambient set? Shouldn't the tweeter in a basic 2way set take care of 10+kH?

The main reason for an ambient tweeter set is to raise the imaging in your car.  That's why you want to put it at 10k and above.

http://www.bostonacoustics.com/Manuals/Neo5Tech.pdf

CDT audio put out a set of those, too.  The high-mount tweeters come with a control that connects to the auxiliary tweeter output of the CDT crossover that's used for the components.   The idea is to raise the front stage if you don't feel it is "in front of you" using just the regular components in door locations.

Here's something on this:  http://www.cdtaudio.com/pdf/Image_Enhancement_flyer.pdf

And there is a more expensive unit available that provides far greater crossover slope with a complete two-way 24 db crossover.  This effectively cuts the sound at ~10K from the regular door-mounted tweeters and sends that information to the dashboard mounts.