Snare drum resonant heads are Snare Drum Heads that are placed at the bottom of the snare drum. Once you hit the batter head, the resonant head will start reverberating along with the batter head. As a result, the snare mat starts to rattle against the resonant head which provides that characteristic snare sound. You can get the exact sound you want from the snare mat by tuning the tension of the resonant head as well as that of the snare mat. As resonant heads are relatively thin, they are not suited for use as Snare Drum Batter Head.