A subject I have never had any experience with (unintentionally, all my slides have had square crooks so far) but I recently picked up a Bach corp slide with a round crook.

So what's the difference and why is the square crook the "standard" today?

If it's the same than for trumpet, the difference is that "it's different".

I have had a trumpet with both tuning slides, and there was (slight) a difference in feel, not (at all) in sound. And if you tried one for long enough, you would probably find the opposite difference when trying the other.

I think that there is almost as much difference between 2 similar slides than between a round and square crooked one.

[quote="SamBTbrn"]A subject I have never had any experience with (unintentionally, all my slides have had square crooks so far) but I recently picked up a Bach corp slide with a round crook.

So what's the difference and why is the square crook the "standard" today?[/quote]

I don't think it's any more "standard" now than it ever was in the past. Bach trombones have always had dual-radius (square) crooks, and King trombones have always had single-radius (round) crooks. (I'm generalizing here; King may have had dual-radius crooks a long time ago.) Your single-radius Bach slide may have been modified. It was pretty common for awhile for people to swap their Bach crook with a King crook to change the way the instrument blows. As for what the difference is, you'll probably get as many different opinions as there are people who answer.

I believe the truly "square" crooks exist, with an actual straight section between radii, on the p-bone and maybe the Bach 16 or 16M (someone help me out on that). There was a small bore Bach I played like that one time with a truly square crook and it was not nice. The dual radius large Bach crooks aren't "square" like that, per se. Just dual radius. They can be nice.