Instructables
Picture of DIY Drum and Cymbal Silencers
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Drums are loud. Silencers can turn boom boom paaasshh into click click tick.  If your goal is to eliminate the drumminess of your drum kit, then Mass Loaded Vinyl (MLV) is your new friend.  From 1/8" MLV, cut discs to fit the heads of your toms, and rings to lay on the cymbals. MLV has an amazing ability to stifle a cymbal  (you'll have to do something different for the bass drum, like stuff it full of plushies, and wrap the beater with a cloth) Not totally silent, but compared to before, they'll be  library drums.
  I made a set of these and pretty much hated them. Sounded almost like my pillow drums, but "clickier".  Since having played pillows for the past eight weeks, I want a more drum-like sound from my drums!  After about a half minute, I took them off. I like the sound much better without them.  Sorry, my neighbors!