RC Low Pass Filter help

[sanyoboy]

Hi Guys, I made a RC low pass filter to place on the line into my sub woofer amp but I don't think its working, sounds no different than with no RC Low pass filter.

My setup is PC > karaoke mic amp to left and right speakers + steal Left channel for sub > circuit > amp > sub woofer.

Here's a picture.

The circles are RCA female connectors.

I am using a 100v 15uF cap it has no polarity marking what so ever. Only writing with capacitance the company and the voltage on one side. I am using the side with no writing as positive. It hasn't blown yet so I am guessing its right or just not passing any audio hence its not working.

Is it my capacitor backward or is it the fact its coming out of a karaoke mic amp or something else?

[MrSlack]

Bit hacky but that may work. I've done similar things in the past. The 3db point of that filter is ~88Hz but there a couple of issues with it. Firstly the roll off is still pretty slow on a simple RC filter and at low frequencies that may not be audible. You can improve that by using two or more identical filters one after the other or picking a different filter model (twin-t etc). Note that as each stage operates as a divider, the output will reduce considerably! Secondly the thing will modify the impedance of the source considerably so it may merely reduce the volume and crush any noticable filter effects; use an active filter (op amp) for each stage. Probably a tl072 can be run single rail in an active filter config off a 9v battery for this job without causing any nasty side effects as it's consumer line level.

Edit: just to add, back in the summer of 1992 I built two active speakers using the same method instead of crossover networks. Still work today and sound rather good!

[Zero999]

What's the cut-off frequency?