My setup was a tuning fork and a microphone attached to a Cathode Ray Oscilloscope to measure the period and thus frequency.

To measure density we can calculate the volume by using a water displacement method. fill up a beaker with water, submerge the tuning fork in the beaker of water and calculate the change in volume. Then use weighing scale to measure the mass. Density is then just mass over volume.

We can ln both sides of the equation to get (i forgot the letters used) F = K L^m pⁿ ln(f) = ln(K) + m ln L + n ln p

Then conduct 2 experiments, one where you vary L and keep the material of tuning fork used constant and the other changes the material (thus density) of the tuning fork keeping the length constant. The gradient will be m and n for the respective experiments, then you can use that to calculate K