Help for making a musical instrument (percussion)?!!?

Question

How do u calculate the length of the hollow metal rod for different frequencies? What formulas do u use?

Answer 1

There are several ways you can go about it, but the easiest is to just cut a length, ring it and then trim it until it matches a tuning fork or a piano. The reason I say this is because there is more to getting the right tone than just the length of a rod. There is also the type of metal and the thickness.
But once you have one rod or tube in the correct pitch, the rest is pretty easy as long as you use the same thicknesses and types of metal, you can calculate the frequencies based on length with respect to each other. For example, F1/F2 = (L2/L1)^2 where F1 and F2 are frequencies and L1 and L2 are lengths. This is of course a rough calculation but will get you pretty close. In general, cutting a rod in half will raise the frequency x 4 or double the octave.
A really good way to find this info is to google "wind chime physics". I am enclosing a couple of good links below.
Have fun!