While most of the people think that sound of a clap comes from hands hitting each other,
It is more than that. !!!
The noise comes from a cavity of air that is compressed and pushed out of a small space.
Compressed air behaves like a resonator.
This is the same principle behind blowing across a battle's Mouth.
Palms create a cavity and the gap near the thumb acts like a neck.
The air escapes through the opening between thumb and index finger. This air jet vibrates and creates sound waves.
Faster air compresses the air more thus creating stronger air jets and louder pops.