I just bought FE83en and would like to use it above 500hz with a 6/db crossover on an open baffle. But to do this I need to flatten the impedience at FS. So when I plug the FS of 165hz, RE 7.5 ohms, QES 4.06 and QES 1.057 in a seriese notch calculator it calls for : 121.7 uf, 7.65 mh and a RC of 9.45 ohms. Ok but my question is can I use other values for L and C as long as they are in resonance at 165hz. For example could I use 25 uf and 37 mh and a RC of 9.45 ohms or am I stuck using that 121.7uf cap and 7.65 mh inductor.
Yes, you can, but the cost will be the attenuation and phase. Any filter LC particularly, need to work over a definite impedance, and it gives some particular values of L (Inductance) and C (Capacitance) according to them. The Resistive part of the filter, is in few words, is to accommodate those reactive elements to the impedances related to it and give determined values of attenuation, or may for part specific of the filter, like a T shunt for example.
Are you reducing level at all of the Fostex to match the woofers? Then just parallel a resistor to the Fostex of about 50-100% of the impedance at Zmax and see if that gets you close enough. Normally this is high enough resistance applied to lower Fs magnitude, without reducing nominal impedance very much.
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