First time when i tried to build Woofer circuit i face multiple problems because i was trying to build it with rc filter, i have got results very close to what i am searching for but unfortunately not those results that i was searching for. i have googled a lot. after a long searching i get into the 2.1 channel speakers ciruits. in there i found an extra ic that is used for making low pass filter or bass filter. actually there are two types of filters RC filter's and active filters. RC Filters are built around using resisters and capacitors, and Active Filters are built with IC's called as "op amp" they produce little sound but better for active filters. resisters and capacitors are used in this circuit for making a chain reaction to completely eliminate high frequency sounds. through this you can make either LOW pas filter (Bass Filter) or High pass Filter (Treble filter). different values are used to get different results. normally the circuit used for Low Pass Filter (bass Filter) is given below. I have found this after a very long search so please appreciate that i have shared this with you guys to easily make good woofer circuit. normally ic 4558 is used but you can use any ic with same proerties. ic 4 is active filter unit.