From Drumtacs:
Not just a dampener! Drumtacs are selective. A single tac placed about an inch from the rim will remove only the high frequency overtone and leave a deeper focused sound with improved response and increased attack. As the Tac is moved toward the center of the drum more frequencies are removed and dampening occurs. Problem Drums with a nasty buzz or ring can often be tamed with drum tacs… try two!!! One on the batter head and one on the resonant (bottom) head.