The frequency, wavelength, and speed do not change. Waves which move from one medium to another are said to have been refracted . When this occurs, the frequency does not change, but both the velocity and wavelength do, as does the diection of the wave. When traveling into a medium of higher velocity, the wavelength is higher and the angle of refraction is greater than the angle of incidence. Similarly, if the speed is lower, the wavelength is smaller and the angle of refraction is smaller than the angle of incidence.
Diffraction is the abilty of waves to bend round corners.
High frequency sound tend to travel in a straight line and are not refracted. Interference is the combination of two or more waves of the same frequency but different amplitudes . Waves that are in phase add constructively and their amplitudes add together. When two or more waves of the same amplitude but different frequencies are combined together, beats are produced. The beat frequency is the difference in the frequecies.