Low pass filter help

[ifrythings]

I wasn't sure were to put this so forgive me if I have it in the wrong place.

I got a unpowered sub a few days ago and I want to power it, but the amplifier I have to put in it has no filters on it so I want to make a low pass filter.

btw I don't know much about filters so if I should have a 1st order or second order please tell me.

I think this is a 2nd order (correct me if I'm wrong) filter with a 12db roll off, my problem is I want to be able to change the roll off frequence for it, were would I put a pot in the first resistor or second?

I used this formula 1/2pi(R1*R2*C1*C2)^.5 (not sure if thats the right one) to get a cut off frequency of 157 Hz.

will this work?

 

[illusionxx]

You can use the spreadsheet here.
I had to add the .zip file extension to be able to unzip it.