| Your crossover will need to contain two filters; a low pass and a high pass. You are correct that the low pass filter would need to be 4 ohms. This can be accomplished a few ways. You can find a 4 ohm filter, you can use two 8 ohm filters, or you can roll your own. I recommend the third choice. Crossover design can be simple or extremely complicated, depending on your goals. I am not an expert but I can say that with a little guidance from an expert you can produce very good results that will be an improvement on any off the shelf design available.
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Hoof Hearted | 
