Posted by Ian Easton on May 08, 2002 at 08:37:59:
For want of a better term I'll call the Yamaha YEB 381's 5th rotor a 'manual compensator', as suggested in a thread below.
I've played several of these horns, as well as many 321s (ie without the 5th). To my mind, it seems a very neat way of addressing intonation problems. I wonder why this design hasn't been employed wore widely, and why Yamaha (whom I've E-mailed) no longer provides this option from the factory or as a retrofit.