Timpani

The Timpani or Kettle Drums were the first percussion instruments to be accepted into the orchestra.  They consist of a large hollow metal shell across which a tight, thin plastic membrane is stretched.  When this drum skin is struck, a wave is established and reflected, producing a vibrating column of air within the body itself.  The pitch of the note can be changed by adjusting the tension of the membrane.  Tightening it forces it to vibrate faster and thus raises its pitch.   Until relatively recently, several Timpani were required, tuned to different notes or ample time to retune them was needed during the piece.  Modern Timpani have a pedal which allows the pitch to be varied immediately.

Approximate Range	1 octave
Diameter	55cm - 85cm