Audio Capacitors

There's no need to shout. Please turn your CAPS LOCK OFF!

Designing a proper crossover network for a speaker system requires a lot more information than just a single crossover frequency and choosing a capacitor type. When I did build my own speakers I liked using polypropylene dielectric capacitors. You should use non-polarized capacitors. All Poly-caps are non-polarized. Some Poly-caps do have a lead marking that indicates which lead is the outside wrap. There is no "best" component, just personal preferences and logistic concerns.

The most critical thing to prevent tweeter damage is paradoxically a large enough power amplifier to prevent clipping distortion from sending DC voltages to your speakers.

http://www.circuitstoday.com/tweeter-crossover-circuit
The complete tweeter schematic is shown below. including calculations for determining components,,,

http://www.diyaudio.com/forums/multi-way/189847-introduction-designing-crossovers-without-measurement-2.html

The OP didn't say what kind of tweeter he/she is using. It could be piezo or electrostatic, whilst the diagram and DIYAudio's advice presumes a voicecoil tweeter.

Perhaps the OP might care to say a little more about what sort of tweeter it is?

OP, your keyboard is clipping. Turn down the gain or get a bigger keyboard.

Total Harmonic Distortion!

One with a cut-off frequency above 1800 Hz.

High-pass filter - Wikipedia, the free encyclopedia

Some good audio capacitors are:

Polystyrene,

Polypropylene,

Use less extent, polycarbonate or Teflon tend to have good performance. It will be good if you know more unbiased reviews.