I know that for a stationary wave to form, two waves must be travelling in opposite directions with same frequency, amplitude, and superpose... and i know this is usually done when the incident wave is reflected off a denser medium and so undergoes a phase change of 180 degrees, however, can stationary waves be formed between waves travelling in opposite directions where they are not 180 degrees out of phase? say a wave was reflected off a less dense medium and did not undergo inversion,,, would it still form a stationary wave with the incident wave?