Audio Systems: design a rumble (high-pass) filter for turntable, digital wireless communication, internal vibration

Question
What would be the best design for a high pass filter to cut out frequencies below about 20hz from the phono output.  I want to do this to avoid damage to my small ported speakers.  My lightly warped records produce noticeable excursions in the woofer.  I would prefer if the filter could be passive, and it would have to be either wired between the phono output and the amp or between the amp and speakers (preferably between the record player any amplifier).  I would like to design and build my own filter because I am only 16 and can't really afford expensive audio equipment, though I wish I could :)  Thanks for any help you could give.

Answer
It's been a very long time since I did that kind of tinkering. Try this website.

http://www.newwaveinstruments.com/resources/rf_microwave_resources/digital_wirel...

They describe both passive and active filters. You could do a little experiment however before you go down that path. Make absolutely certain; that your speakers and turntable are completely isolated; your turntable is on a very solid surface with no vibrations; place a piece of foam rubber under the turntable; make sure the cartridge headshell is seated all the way into the tonearm; you are properly grounding your turntable ground cable to your amplifier; your tonearm is perfectly parallel to the vinyl when it is playing; your stylus is good; you are not getting internal vibration from a worn turntable belt.