Bill had a Crosley radio on his desk. Going on Charles Sinclair's description, I tried to pinpoint exactly which by combing through images of dozens of models. You'll see the result in the book, but in any case, it would have been compact and stylish. Even the logo indicates that:
Bill's composer of choice was Mozart and he would listen while writing. He liked the Clarinet concerto. But his favorite was what is commonly known as "Eine kleine Nachtmusik."
A fitting choice for the maestro behind Batman.