Conversation so far:
What is JEM?
Vai designed the Ibanez JEM guitar, a unique instrument that incorporated a series of groundbreaking designs.
What was unique about it?
The guitar was designed with a sharper body shape, a large cutaway around the neck, twenty-four frets, a fully floating tremolo system.

Question: What was different about its sound?
Self-contained rewrite: What was different about the sound of the Ibanez JEM guitar?