QUOTE(Jon S @ Apr 1 2008, 10:52 AM)

I'm not sure you will get much in the way of meaningful results out of this. There are far too many variables other than the material of the recorder – the player, make and quality of the recorder, conditions under which it’s being played, the equipment used to record it, etc. could all affect the results apart from the material. To be scientific about it you would have to eliminate all variables other than the material of the instrument. You would need identical recorders (other than material), played under the same conditions, by the same person (or preferably a machine), to get comparable results.
Regardless of other external factors, the material the instrument is made from will have an inherent effect on the tonal qualities of the instrument.
As a starting point, research and make a list of all the woods used to make recorders. Next do a Wiki/Google search for all those woods - NB. some woods are know by more than one name. If you use Wikipedia, it should have some information about the densities of the wood and the density does have an effect on how the recorder will sound. Your next job is to find out how these denisities will affect the tone, but I'll leave that for you to research. Write up and present your information in a clear and factual way.
As Jon S has said, there are many other factors which can affect the tonal characteristics, but I would say that these are very much beyond the scope of GCSE(?).