I had a nice long talk about this with Dr. Thomas Moore, the science editor of the ITG Journal. He is an expert on trumpet acoustics. You should check his work out at Rollins College in Florida.
In any case, he deosn't feel cryo does much for most trumpets. It is apparently well known in the metalurgy business that brass doesn't respond to any great extent to this treatment. SOLDER however, does.
Dr. Moore was guessing that any changes perceived by a trumpeter could have been caused by changes in the solder joints caused by cryo treatment. He also guessed they'd be subtle, at best.
He has NOT doen a study on this yet.
I did participate in the TPIN Freeze Off a few years ago. We did a double blind test on four horns: A Bach, A Benge, A Najoom and a Blackburn. Several trumpeters played the horns and filled out questionairres before and after freezing. One horn was left unfrozen as a placebo. The players were, Mark Ponzo of NIU, John Hagstrom of the CSO, Stanton Kramer (a local amateur) and myself. Wayne Tanabe, along with the engineer, John Lynch (the TPIN Lynch, not the Asymmetric mouthpiece guy) ran the tests.
The results of the test were moderately inconclusive. No surprise there, knowing what I know now.
I couldn't detect anyting different about the Bach comparing before and after. It turned out it was the placebo. I hated the Benge before and after, so that seemed to taint my point of view. The Najoom didn't seem much different.
The striking thing was the Balckburn. It was solid heavy horn and it I didn't care for it's playing characterisitics before freezing. However, AFTER, it was like a different horn. I loved it. It played much freer and just lit up when I blew it.
Now, there was a significant time gap between the before and after testing. I could have simply changed my mind about the way the horn felt. It was just a different day. I did seem quite noticable, though. Using Dr. Moore's thinking, there could have been more solder on that horn and this brought about the change.
In any case, the less than striking OVERALL results lead me to believe that cryo treament is not going to do much. This is a change of position on my part, but again, this is a case of "if I knew then what I know now." I think we often convince ourselves something works if we really want it to. I think I was succumbing to that. Oh well...
I won't call cryo treatment a scam though. That's doesn't seem fair. I think it was an honest empirical attempt to improve brasswinds. It just turns out that it doesn't really do that much.
So I am not voting as my option "not a scam but doesn't work" isn't up there.
Check out Dr. Moore's ideas.
Peace.
Nick