I am doing an experiment about standing waves in a resonance tube. I use a bucket of water, a waterproof tube (open at both ends), and a frequency generator app. I have two set-ups, A and B:
A. Setting the frequency to be constant and dipping the tube into the bucket of water until I hear resonance that signifies standing waves. I record the effective length of tube at which this occurs, from the part where the tube touches the water to the other end. Then, I compute the corresponding wavelengths.
B. Setting the length to be constant but with increasing frequency. I record the frequency at which the standing waves occur and compute the wavelengths.
Using the formula for the speed of sound $v =$ wavelength x frequency, I have solved the experimental speed of sound. Now, using the room temperature to solve for the theoretical speed of sound, I found out that the Set B resulted to less deviation from this theoretical value compared to the case of Set A. Is this expected in general? What do you think are the main sources of error?