Thanks again, Tassie. Very useful information. As I understand it correctly, density surely determines the weight of the ply, so a different density could make a difference between two wood layers that have the same hardness & elasticity, althought mostly woods with same hardness & elasticity have also the same density.
But again, what are the effects of density then? Let's take Anigre and Koto. Hardness is the same, but Koto is more dense. In what way playing characteristics of Koto are different from Anigre?
You might find it interesting to read this: Wood! a blog by Ian Worz
- he gives some useful and interesting comments on the playing characteristics of different timbers, which you can use to draw your own conclusions about the effects of density. My guess (and it is nothing more than a guess) is that denser - and therefore heavier - timber would be faster than a timber of similar hardness given the extra weight, although my gut reaction is that it will be very small and probably very difficult to gauge. After all, we're really only talking a few grams here; it's not like the difference between a brick and feather!
I still maintain that modulus of elasticity is a big factor. JRSDallas's extraordinary contribution to Denis' Table Tennis World
points to the (complex) correlation between vibration and speed. It seems to me that a light timber (low density) with high stiffness (modulus of elasticity) is going to be faster than a heavier timber with low elasticity. Again there is a rough correlation between stiffness and hardness, but because all these qualities vary from timber to timber - and piece from piece within species! - it all adds up to a very complex puzzle.
In the end, lists like Ian Worz's and our very own list - The properties of different types of wood
give us good ideas about what we can expect from a particular timber.