I've seen a lot of King trumpets advertised as "Dual Bore" and a while back, I managed to land one on ebay--a Symphony Silver Sonic--but absent a regular medium or large bore horn to compare side-by side, it's hard to attriute any specific playing characteistc or advanage to that elemet of its architecture.
More recently, I pulled my MartinTroubadour down off the display rack where it hangs, and discovered while lubricating the main tuning side that it too was a dual bore design. Most recently, I discovered the same thing about my Rudy Muck Citation, and a Benetone, and an Acme, so am now pushed to answer the question: "Why"?. Looking at the geometry of thetrumpet, this configuratio gives the player a tapered leadpipe, a 3-4" section of cylindrical tubing in the upper leg of the tuning slide, about 3" of tapered tubing in the curved portion of the slide, and then back to cylindrical as the air passes through the valve block, ultimately tapering up again in the bell. Fortunately Ive got a reasonablecontrol horn to compare these against but so far, the comparison has been less than enlightening.
So, with apologies to the little old lady who did the Wendy's ad: Where's the beef? What is the supposed advantage / selling point of this design? What's it supposed to do for me as a player. I'm looking for it, but I can't feel it or hear it.