I have nothing to add to the fine theoretical explanations that have been given in this thread, but it is the case that my Colin Goldie Overton D and C whistles sound much better after they have been played for a while. It may be my inagination–but I don’t think so–that both of my polymer (a fancy word for a good plastic, I think) Silkstone whistles (a D and a B-Flat) sound better after they have been played for a while as well. Minds greater than mine have figured this stuff out and designed accordingly, I believe.
I have a host of --OK, several–whistles that seem ready to go when picked up, including whistles by Mack Hoover, John Sindt, and Michael Burke. These are, by and large, whistles with thinner walls than the ones that benefit from warming up. Perhaps it is that the thinner walls, by virtue of their smaller mass, simply get up to optimal temp. more quickly.
My two cents’ worth,
Tom D.
Tom D.