George,
From the Stereophile review:
A first-order crossover can be achieved, not with a series capacitor but with a single inductor, this connected in parallel with the tweeter. The parallel inductor connection terminates the high-frequency driver well, helping to control its natural fundamental resonance. For the inductor to give a defined filter characteristic, however, there must be a series impedance; in the case of the Extrema, a resistor (fig.B). This resistor/inductor combination appears wired across the speaker input terminals; it will dissipate power over the speaker’s entire frequency range, mainly according to the resistor value.
image: https://www.stereophile.com/images/archivesart/sfefigB.jpg
Fig.B Conventional first-order high-pass crossover filter (top) vs "Sine-Cap" filter (bottom).
In the case of the Extrema, the series resistor for the treble section is typically 20 ohms. This provides the required source impedance for the crossover inductor, and also correctly attenuates the treble unit by the required 4dB or so. Yet with the Extrema’s nominal 8 ohm drivers, the total system impedance does not fall below a 4 ohm minimum—it is nominally a 5 ohm-rated design.
Read more at https://www.stereophile.com/standloudspeakers/915/index.html#C1tSeYjx17owvP01.99
Maybe OP should disconnect the jumper and test the treble section and mid/woofer section separately.
