Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
The tweeter is 4Ω, yes. So you're right that a textbook Butterworth filter would require a 20uF capacitor. But like so many other things in audio, sometimes textbook values don't apply or are only marginally applicable. Some things are downright counter-intuitive.
This one isn't too bizarre, it's more just the fact that any first-order crossover is really more of a blending of sources than a splitter of sources. The crossover point should more properly be seen as a crossover band with wide overlap. It's not so much a crossover point as it is a crossover range, and that range is pretty wide.
First-order networks have both adjacent drivers pretty much completely on for at least two octaves. In this case, the midwoofer and tweeter share the range from 1kHz to 4kHz. So it's really a crossover range of 1kHz to 4kHz, but if I had to pick a single frequency to call the crossover point, I'd split the difference and call it 2kHz. You can see the peak impedance happens about there too - An intersection where the midwoofer circuit impedance is rising but the tweeter circuit impedance is falling - they are equal around 2kHz.
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