Low pass filter


2008-01-25 7:48 pm
my question is that I used the low pass filter topology sallen-key with tda2030 and ne5532 to use as 2.1 system for computer and when tested the sound still coming out from the woofer , is that right or am wrong that should hear only the low frequency ( boomy ) and the result isnt what what I wanted , is there way to move around to get the deep bass ???? and stop the music coming out the woofer ?????

thank you all


2011-12-27 4:22 am

You are correct, low pass filter lets only low frequencies pass unaffected (as they were). Low pass filters attenuate (weaken) frequencies above their cut-off frequency. The cut-off frequency does not mean "sounds above are cut-off", it only means "sounds above will be weaker".

Sallen-Key filters attenuate by 12 dB / octave (doubled frequency), so if your cut-off frequency is 150Hz, you'll have -12dB @ 300Hz, -24dB @ 600Hz, [email protected] 1200Hz and so on. That's why you still hear other than low frequencies from woofer. You can cascade (put many in a line) filters to achieve stronger attenuation.