GCSE required practical to prove the wave equation

I'm interested that it been suggested that the stationary wave demonstration should be used to illustrate the equation wave speed = frequency x wavelength as well as the ripple tank. It requires explaining that two "loops" make up one wavelength and requires trust that the wave speed remains constant if the same tension is on the string. It can then show that if you double the frequency, the wavelength halves (ie number of "loops" doubles). It's the first time I've tried it with weighted string. I've previously used a clamped piece of thin rubber tubing. On the string, I could only get 4 "loops" but I've have up to 8 on the rubber tubing.