x-over calculation

[bigcatdairy]

hey guys, we should use the drivers' nominal impedences in calculation or we should use the ones at the cut-off freq point?

please let me know if anyone who has answer, thanks.

[Loren42]

The impedance at the desired crossover frequency is what you need. I am not sure what your definition of cut-off frequency is.

However, you will really need to measure the impedance curve yourself since speakers vary from the manufacture's published data. Remember, that impedance is the AC resistance and not the DC resistance that is quoted by the manufacture or measured on your DVM. I use Smith & Larson's Woofer Tester 2 to test mine.

Second, the impedance either side of the desired crossover frequency should be "flat" within an octave or more (depending on the selected slope of the crossover). This insures that the filter works as designed and does not adversely impact the filter slope.

Typically, a Zobel network is added to the woofer to flatten the impedance about the crossover frequency point. The Zobel does not impact the peaks at the woofer's resonance frequency. However, you can address those with additional network components if desired after the woofer is installed in the finished cabinet and remeasured.

To learn more I like this website as a way to understand the design process:

Passive Crossover Design