My friend Prof. Chen-Gia Tsai, a brilliant musicologist who has solid background in physics and ethnic music, posted some comments on whether the materials of wind instruments affect their tones. He also pointed his readers to an interesting study.
In summary, the presenter of the study asked the audience to tell, without looking, the difference between two performance of a lightweight cherry wood flute and a concrete flute, which are of identical design except for their materials, and no one was able to tell their sonic differences. Chen-Gia pointed out that the sounds of wind instruments are affected by only their reeds and the air cylinder inside the instruments. As long as one can make two identical surfaces, the sound will be the same. He also noted that it's easier to bend metal materials freely in order to achieve specific shapes and woods may contain holes that affect the tone.
These are my responds to Chen-Gia's posting. I left my comments in Chinese on his blog. Here's the English translation. Disclaimer: I am no physicist so my assumption below comes from my limited knowledge of acoustics.
I suspect that performers perceive a more mellow tone from instruments made of wood because the softer wood surface actually damps higher harmonics. The same phenomena can be observed in different echoing effects between a metal room (or pipe) and a wood room.
Chen-Gia also pointed out that sometimes the vibration of the thinned instrument bore matters. I confirmed that from my experience: if one holds the brass bore tightly (from the outside, so the air stream stays unaffected) when playing, its tone is less "bright" (less higher harmonics). I suspect that instruments made of wood cannot rely its tones on the bore vibration.
About the study quoted, I also suspect that the reason nobody in the conference audience was able to tell the difference is due to lack of proper vocabulary, or they thought the differences between the two demonstrations could come from the unavoidable differences made by the performer.
That study also points out people's different perception on gold flutes and silver flutes. My personal observation on that is: gold flutes are much more expensive and its owners are usually committed professional performers. To the general audience, most sounds they hear on gold flutes come from professional players, who are likely to play better anyway. For a silver flute owner, even if the skill is comparable, a quick try on somebody else's gold flute is more challenging because every flute is different (a slight change in turbulence within the mouthpiece will result in very different tone) and it does take a while to get used to a new flute. Therefore, the testing sound produced by a silver flute player may not be optimal. Galway's flute is custom made -- for him.
Besides, in reality, gold flutes may differ from silver flutes not only on the material but also on some detail designs -- as a pricey car not only has a higher end engine but also better material in its shifting stick. People see the stick and conclude the car runs better. They may be right, although for a wrong reason. It's very difficult for musicians to make a fair comparison because of lack of access to identical flutes made of very different materials.
Finally, I personally react to the material of mouthpieces and the overall weight of an instrument when I play. That makes a totally objective comparison even harder.