1. The problem statement, all variables and given/known data Two sound sources 15m apart producing identical 229 Hz sounds. As you move from one to the other, you hear beat frequency of 2.5. How fast are you moving? 2. Relevant equations The question asks for the velocity of the observer Vo. The trick here is to use the standing wave model to get the solution, NOT the doppler reflection equation. 3. The attempt at a solution I used the doppler reflection equation to get a speed of 1.87 m/s. This was to see if my answer is wrong or right. I started by getting the different frequencies from the beat equation (assuming one is 229 and the other is below/higher than that), and then I got the wavelengths. I solved for the change in wavelengths and divided that by the reciprocal of the beat frequency (time) to get a velocity of 0.4 m/s. Any ideas what I'm doing wrong?