Super tweeter for FullRange Driver

Your plan makes a lot of sense to me, and imo the T90A is a good choice. My first commercial effort used a fullrange driver augmented by a rear-firing T90A.

In a case like this, where you don’t have the benefit of measurements, you find the capacitor value for the supertweeter by trial and error. There is simply not enough information available to reliably predict what the correct value should be. I’d recommend you not go over 3 microfarads, and I’ll go out on a limb and toss out 1.5 microfarads as a suggested starting point.

Capacitor values add when you wire them in parallel. If you want to end up with a boutique capacitor, find the correct value using inexpensive film capacitors before you spend the big bucks on a boutique cap. Capacitor quality cannot make up for not using the right value.

I don’t think you’ll end up with an impedance curve that will cause your amp any distress. There is very little energy in the top octave so an impedance dip up there is unlikely to be an issue, and the capacitor in series with the tweeter will keep the net impedance from dropping very low anyway.

Duke

Thanks for the response Duke. Do you suggest I throw in a resistor or two to help attenuate the volume, or some kind of Lpad? I'm guessing the T90As will be significantly louder than the Audio Nirvanas due to there higher sensitivity. 

ak, I would try without first but if they run too hot then yes but you want to put it in front of the capacitor or you will change your cross over point.