Effect of filters on frequency response

[jordanstreet]

I’m interested in audio design and was messing around with NI Multisim building some basic filters. I created a 2nd order low pass filter with capacitors and found that the 2nd stage of the filter impacts the frequency response of 1st filter as illustrated below.

This would seem to indicate that you would run into issues designing more complex filters or tone stacks in a block by block manner as components in later blocks would affect the response of earlier blocks.

I don’t know why this is and was hoping someone here could explain it to me :)

http://img689.imageshack.us/img689/7316/filterinfluence.jpg

Thanks,
Jordan Street

 

[jim hardy]

your second stage loads down the first
separate their impedances by a decade at least - make 2nd stage 10K and 0.1uf

or use active filter.

ps didn't you want 2nd stage output across the cap? should get your 40 db/decade then.