Help needed for crossover design for supertweeter

Are you using t90a? If so you can use just a cap. 1. -1.5 should work. You might have to try both values buy cheap caps to see. Then replace with dorfs

I a m using a Visaton TL 16 H 8 OHM,

Technische Daten:
Nennbelastbarkeit mit Hochpassfilter 150 W (12 dB/Okt.; 7500 Hz)
Musikbelastbarkeit mit Hochpassfilter 200 W (12 dB/Okt.; 7500 Hz)
Nennimpedanz Z 8 Ohm
Übertragungsbereich (-10 dB) 2200–35000 Hz
Mittlerer Schalldruckpegel 100 dB (1 W/1 m)
Resonanzfrequenz fs 6000 Hz
Magnetische Induktion 1,6 T
Magnetischer Fluss 200 µWb
Obere Polplattenhöhe 2,5 mm
Schwingspulendurchmesser 16 mm
Gewicht netto 1,3 kg
Gleichstromwiderstand Rdc 6,9 Ohm
Schwingspuleninduktivität L 0,17 mH

It does depend on what the electrical phase is doing on the tweeter/midrange of your speakers up around 10kHz. a second order filter on the super tweeter could introduce phase issues which you will hear quite noticeably. John's suggestion of the first order with just a cap will introduce only one pole in the phase, which will start at +90 degrees and drop to around +48 degrees at the 10kHz crossover point. Depending on what the other drivers are doing around this frequency will determine how successful it is. You may want to experiment with connecting the s'tweeters out of phase. A good RTA software will show you what is going on.

In my case I use a second order network between the midbass and midrange. By inverting the connection on the midrange the phase of these two drivers is practically identical across the entire spectrum. I also reversed phase on my Fostex T500AmkII horn tweeters so that the phase difference between the midrange and tweeters is at most 40 degrees at the xover point and is about 30 degrees at 20kHz. This is by far the best I have been able to get things to sound using passives after amplification.

I hope this helps some.