# The Cutoff frequency of bandpass filter

Given:

1. Center Frequency f0 = 2.2KHz
2. Q factor = 5

The problem I'm facing is this: How do I calculate the 2 cutoff frequencies of this band pass filter? I'm confused because my question says "The cutoff frequency is not always the -3dB point. This is only the case for Q = 0.707".

I found a website that calculates the cutoff for a band pass, and the results were:

[F1 = 20KHz to F2= 2.4KHz].

But when I simulate the circuit in Multisim, I have a huge difference between the results:

[F1= 1kHz and F2=5kHz].

I need a way to calculate the two cutoff frequencies. The system functions are given at the end of the figures:

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• "I'm confused because my question says "The cutoff frequency is not always the -3dB point." Are you sure that this statemenet was used in conjunction with your bandpass? I think, it applies - in particular - to LOWPASS stages. – LvW Nov 16 '16 at 8:29

The Q is always defined as $Q=f_O/\Delta f_{-3dB}$
The $|f2-f1|=\Delta f$. which are the -3dB values.