rfidea wrote on Jun 30th, 2013, 12:29pm:There is nothing wrong at Wiki. You are mixing up the 3dB-frequency with the resonance frequency. The resonance frequency of your frequency is 15.9 kHz but that is not the 3dB frequency, which seems to be about 10.5 kHz.
The Q=0.5 means that your filter is NOT a Butterworth filter. A second order Butterworth filter has Q=1/sqrt(2)=0.707. A Butterworth filter has the same resonance frequency as 3dB-frequency, valid for all orders.
hi and many thanks for the reply. So this formula:fcut=1/2π(sqrt(R1R2C1C2) is valid only about butteworth filters .
so the formulas of fcut, depends on Q of the type of filter design (bessel,butterchebysec etc)....
So the Q=0.5 what is this? how can i know ?
Is there any rule of thumb?