Unless you are willing to completely rely on trial and error procedures, start your network design project by measuring the impedance of the drivers and correcting the impedance if necessary with a RC filter.
If you choose a crossover point in a range where the driver's frequency response is changing rapidly off-axis, the off-axis response will have large response anomalies.
Large variations in the off-axis response degrade the power response the listener perceives. Reflected and reverberant response will be significantly different from the on-axis response, and generally devalue the overall quality.
Selecting the best slope is important, both to protect the tweeter (in particular), and to ensure that the drivers are all operated within their optimum frequency and power handling ranges.
A 6dB/octave (first-order) filter has the most predictable response, and is affected less by impedance variations than higher orders. On the negative side, the loudspeaker drivers will be producing sound at frequencies that are very likely outside their upper or lower limits.
12dB/octave (second-order) filters are better at keeping unwanted frequencies out of the individual speakers, but are more complex, and are affected by impedance variations to a much greater degree. The tolerance of the components used will also have a greater effect. The capacitance used must remain predictable and constant over time and power, which specifically excludes the use of bipolar electrolytics.
A 18dB/octave (third-order) filter requires closer tolerances than a second order, and is again even more susceptible to any impedance variations than the 12dB filter.
24dB/octave (fourth-order) filters increases the complexity and tolerance requirements even further - a point must be reached where the requirements versus the complexity and sensitivity will balance out.
How does it work?
For this example i use a second order (12dB) Highpass crossover network for 1 kHz.
The capacitor and also the inductor both have a specific resistant at any frequency.
Crossover Networks for Loudspeakers
