Nothing weird. They're made to suit and suitable for signal coupling or bypass capacitors in tube amplifiers where the anode voltage potential may be in 3 figures.

Somehow I don't fancy paper in oil caps for speaker crossover, as it may veil the sonics, takes time to break in, reduce some sparkle in the highs and slow down the pace. Polypropylene caps are usually a more popular choice, but for the modder, anything can fit in because you're altering the sound to your personal taste, even if it means altering the response curve of the loudspeaker.
By reducing the cap value from 7uf to smaller value, you're actually narrowing the high frequency range to the tweeter. Less mids to the tweeter, and you may find a roll off in the midrange. The smaller the capacitance in series to the tweeter results in blocking more low frequencies whilst allowing high frequencies to pass through. A bypass capacitor to ground encourages high frequencies to bypass to ground, and thats usually at the woofer or LF driver to block any high frequencies outputting to the LF driver. Thats where the high freqencies are "crossover" to the HF driver. In other words the woofer takes care of low frequencies and the highs are passed on to the HF driver. The RC network determines the point it crossover, minimal overlap for flattest frequency response and match the tonal character of the speaker drivers.

This post has been edited by bsl555: Jan 5 2009, 01:21 AM

I was refering to your diagram in the 1st page and thinking thats the actual crossover in the Kef. If the 7uf is "normally not there", what's the actual circuit?
The manufacturer selected values are likely best matched to the characteristics of the speaker drivers. You're rolling about the cap values are likely to result in adding something somewhere and deprive something somewhere else.

A speaker crossover is actually a frequency divider and doing a balancing act. However you mod it will NOT extend the frequency range beyond the extent of the speaker design and potential. In practice you're altering its tone.