I've been using a Conn 14D single F horn for 2-3 years but need to upgrade to a double now. I got a chance to very briefly try a fellow band member's 6D. While I was very pleased with the smooth playing and crispness, I couldn't help but notice that the tone color and sound volume seemed a little slight in comparison to my 14D. I've heard that the 6D has a reputation for having a narrower and brighter tone, perhaps due to its more modest bore diameter. Perhaps the 14D single F has a wide bore along the lines of the 8D?
In any case, I'm curious about some of the other less-expensive doubles out there on the new and used horn market - and which ones are good for somebody who prefers a larger, mellower sound.