Bringing conductors closer together moves them more towards being a capacitive load. Spacing them further apart makes them less capacitive and moves them more towards the inductive side of reactance.
When one can find equal amounts of capacitance and inductance at the same point, the reactance is effectively nulled. While this can be achieved, it typically varies with frequency. As frequency rises, wavelengths are shortened and the gap between conductors appears to widen. That is why zip cord is more inductive than a twisted pair given the same amount of insulation around each conductor. Both start out relatively even at very low frequencies but the gap between inductive reactance and capacitive reactance widens as frequency climbs.
The twisted pair has more intimate contact area between the two conductors as they spiral around each other. This increases capacitance / lowers inductance. The zip cord has only one continual point of contact along their lengths and is therefore more isolated from each other. As a result, inductance is increased and capacitance lowered.
As a side note, anyone that has tinkered with speaker crossovers knows that putting increased inductance in series with a speaker will roll off high frequency response. Hence, the lack of treble clarity and extension when using zip cord with thick insulation.
As one can tell, this is a very simplified example. If you want further proof, take some Goertz speaker cable and separate the conductors. Not only will it no longer be a high capacitance design, the total impedance will be drastically altered. Sean
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