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find a used 10 inch or smaller car subwoofer. make a massive stiff cone out of card paper coated with pva glue. glue the cone to the center of the subwoofer on the edges of the dustcap . you might want to have surrounds around the edge of the cone connected to a sealed box. try playing dubstep music or something really bassy through it. you need a subwoofer amplifier or an amplifier with a powered sub output. http://onlinetonegenerator.com/ this site lets you generate constant tones.
you need to move a lot of air or have your head right next to the subs to actually hear that low. you can hear the difference with good headphones if you dont turn up the volume too loud.if the volume is up too loud you hear different frequencies because the woofer or headphones only makes clean sound when its moving in and out a certain distance. try turning down your subs, they probably go silent or quietly purr.