I would like to ask for the sentece below in the the red box if fp2=400Hz, fp2=100Hz and fp1=60Hz then I can assume that fL=fp2=400Hz? And the other case if fp2=300Hz, fp2=100Hz and fp1=60Hz then fL=fp1+fp2+fp3=460Hz?

I ask this because I saw a problem where fp2=500Hz, fp2=100Hz and fp1=60Hz and calculate that fL=fp1+fp2+fp3=660Hz.This is correct?I think from the theory below should give us fL=500Hz.

## Best Answer

The statement below the red boxed text is fundamentally wrong because you cannot simply numerically add the frequencies of several cascaded filters and produce a number that has any accurate meaning. There might be some particular cases where it has some semi coincidental accuracy but these situations are not obvious and it would be naive to assume it will work. Given the usage of free sim tools I would advise against using this formula in favour of performing a simulation.