If you seal a loudspeaker at the end of a tube and close the other end of the tube you will get standing waves; but what are the boundary conditions at the speaker for the sound pressure wave? Pressure =0 or Pressure = MAX? I find no mention of this in the literature. To find out I performed a simple experiment with a 622 mm long PVC tube. I placed a small microphone connected to an oscilloscope at one end (flush with the wall and sealed) and a speaker connected to a signal generator at the other end. I swept the signal and I observed the first resonance at a frequency f = 276 Hz; corresponding to a wavelength of lambda = 1244mm = 2L, indicating that the speaker is a hard boundary or a pressure antinode. This result implies the air particle displacement at the speaker must be zero as pressure and particle displacement waves have a phase delay of Pi/2. So the air at the speaker does not move....and this sounds like a paradox to me since the speaker is a piston and must be displacing the air adjacent to it. Any ideas?