Originally Posted by
Ian Mackenzie
Ted,
1. Air core inductors are generally better as they offer best performance for mid / high pass filters as they will not saturate. Iron core have a benefit of low dcr for sub woofers and tend to be ower cost. I think JBL used iron core for low production cost given even their iron core had relatively high DCR.
2. I have made split air cores for attenuation without any problems, Giskard posted a spead sheet for calculations some time back. The benefit is attentuation of the voltage via the coils rather than wasted power dissipated in voltage drop across the resistors.
I still think an L pad is very useful for fine adjustment of attentuation while the split coils provide the bulk of the attenuation (see 3145 network).
Once you find the exact settings, the L pad can be replaced by high quality Mills power resistors for the best sonic performance.
While fun to make, passive crossovers are at best a wet rag attempt at filter design and better results can be attained at lower cost with a hi performance fully adjustable active crossover.* They don't waste power and you have more control over the crossover parameters.
*see hi end active crossover project.
Ian