LC filter for audio (Ratio L/C)

[gain wire]

Hello all,

I must make this quick: what is the way to determine the proper ratio of inductance to capacitance when making an audio bandpass filter (1 st order, either series or parallel)?

Thank you!

 

[Elvee]

With a capacitor and an inductor, it isn't a 1st order filter, but a second order one.

Basically, the L/C ratio is the analogue of an impedance², which has to be compared with the load.

This sim shows the effect of an increasing L/C ratio, beginning with the green trace.

If you extrapolate to infinity, the circuit will become just a big inductance and a tiny capacitor, both having extremely high impedances at the frequency of interest, and allowing very little signal through, giving an extremely sharp peak.

This analysis neglects the Q of the reactive components themeselves.

 

[davidsrsb]

You must know both source and load resistances.
Passive audio filter design tables usually start with both at 600R