Thor Mjölnir IEM

Beryllium copper is only 2% beryllium. Or less. A set of pure Beryllium golf clubs, assuming half a cubic foot volume = 1 set of golf clubs, would come to ~$130,000 USD in raw material cost. Your golf clubs are 300x cheaper because they are an alloy, not because Beryllium is cheap. Acquiring small amounts of pure Beryllium, ready to cast from a company like Materion would be difficult. Most suppliers wouldn't bother with an order that small. Then assuming you don't have the ability to cast it yourself you have to contract someone to cast... a microns thin film shaped into a dome, to be sold in a consumer audio product instead of... aerospace, scientific instrumentation, nuclear power, x-ray equipment and the multitude of other applications that demand high prices for critical applications, then you may begin to see why the economies of scale do not work in favor of a pure beryllium loudspeaker of any size. It's more likely AlBeMet or similar alloy or a coating of a standard polymer. unless he has found a remarkably cheap supplier of small quantities of beryllium foil.

He sure did.