The adult male cicada possesses two ribbed membranes called tymbals, one on each side of its first abdominal segment. By contracting the tymbal muscle, the cicada buckles the membrane inward, producing a loud click. As the membrane snaps back, it clicks again. The two tymbals click alternately. Air sacs in the hollow abdominal cavity amplify the clicking sounds. The vibration travels through the body to the tympani, which amplify the sound further.