Formula for Q of 2nd order filter slope?

[brianp]

The reactance frequency of a given 12dB LC filter is defined as 1/ 2Pi x sqrt LC, regardless of the load impedance. But the Q of the slope changes if the load impedance is altered. I seem to have forgotten the formula to calculate the Q based on the impedance. Could anyone jog my memory?

[Jeff B.]

> The reactance frequency of a given 12dB LC
> filter is defined as 1/ 2Pi x sqrt LC,
> regardless of the load impedance. But the Q
> of the slope changes if the load impedance
> is altered. I seem to have forgotten the
> formula to calculate the Q based on the
> impedance. Could anyone jog my memory?

First make sure your values are in Farads and Henries and the formulas are:

Q=SQRT(((R^2)*C)/L)
F=1/(2*PI*SQRT(L*C))

Jeff