Low pass filter positioning on subwoofer

Hi, i recently build a back loaded box for my 18" woofer driver and I also used a low pass LC filter. I noticed that inserting the filter at the uotput of the aplifier does not work at all, no filtering action. Inserting it at the input, filtering so the input signal, gives the result that I was looking for. I was wondering why this happens, so I can understand better how filter for audio application works.

Thanks for responses.
 
Immagine 2024-07-30 135705.png

this is the filter. Unfortunatly I know only the value of the capacitor, 47pF, because the components i used are all very old and without any description on it.
 
Immagine 2024-07-30 141113.png

I'm very sorry... this is the actual filter. The only value I know si the capacitor, 47pF. I don't the value of the inductor and I have no way to mesure it. looking at some similar inductor the value could be around 0,220 mH or something, but I cant be sure of that.