TheX-Ray Spectrum Model shows the effect of varying the high voltage (kVp), added filtration and ripple in the high voltage supply to the X-ray tube. The physical mechanisms by which X-rays are produced are Bremsstrahlung (in which collisions of the cathode electrons convert some of their energy into X-ray photons) and characteristic X-rays (in which the cathode electrons kick an inner shell electron out of an atom, and an X-ray photon is release when one of the atom's outer shell electron transitions to the inner shell). Changing the accelerating voltage of the cathode electrons (i.e. changing kVp) affects both mechanisms of X-ray production. Adding filtration to the X-ray beam reduces its intensity, but does not reduce all energy X-rays equally.

The X-Ray Spectrum Model was created by Michael Gallis using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. You can examine and modify this compiled EJS model if you run the model (double click on the model's jar file), right-click within a plot, and select "Open Ejs Model" from the pop-up menu. You must, of course, have EJS installed on your computer. 

Please note that this resource requires at least version 1.6 of Java (JRE).