Hi andy2, what is your opinion on the 1uF foil caps (C2 and C7), why JT omitted it in the SE crossover?
Before answering your question, let me just take a moment discussing the physics behind capacitor and inductor. Think of them as the ying and yang of circuit design. I am not sure if you're technically inclined but they act opposite of each other. The capacitor acts to slow down a current whereas the inductor acts as to speed up a current. Mathematically a capacitor is an integrator (a process of averaging) and an inductor is a differentiator (a process of diffrentiation which emphasizing the extreme).
To make thing a bit more complicated, the larger the capacitor, it carries extra parasitic that is not part of the capacitor. The lower quality of the capacitor, the higher amount of parasitic. Therefore, there is a need to have a smaller capacitor in parallel for the higher frequency to get through bypassing all the parasitic of the large capacitor. If you have a really good capacitor, it would have less parasitic so it will not degrade the treble frequency so bypass capacitor may not be needed.
So the purpose of C2 and C7 are meant to provide an extra path for the higher frequency signal therefore to improve the transient of the treble frequency. Now it's a matter of implementation. If you think your main capacitor is good enough, then C2 and C7 may not be needed. So it's your call. Although C2 and C7 improves the treble transient, the problem with running a large capacitor and a much smaller capacitor together is it may introduce jitter since the signal path is now unequal. Another way to implement it is to equally split the capacitance value in half. For example, if you want 14uf, it might be better to have two 7uf vs. one 13uf and one 1uf. Both implementation both adds up to 14uf, but the physics will be different hence the difference effect in treble. At the end, it'a a matter of fine tuning.
For comparison purpose, most speakers have separate tweeter and midrange driver, therefor the tweeter xover on those speakers have very small capacitor in the signal path which is around 4.7uf to 6.8uf. For the CS2.4, if you count up all the cap in the signal path (14uf + 28uf = 42uf), that is quite a bit so the bypass cap is probably more important. Listening to the CS2.4 and my own design, I do feel my speakers have that extra treble details that is hard to describe but it's there. Some have mentioned that after the cap upgrade on the CS2.4, there is extra air and transparency so it may have something to do with that,