Open-open pipes resonate at the same half-wavelength frequencies as closed pipes.

Evidence

There are two other pairs of boundary arrangements that can support standing waves. The first, shown in Figure 1.35 and 1.36, is the case of a boundedto-unbounded propagation boundary at both ends. An example would be a tube or pipe that is open at both ends. In this situation, the pressure component is zero at the boundaries, whereas the velocity component is at a maximum, as shown in Figures 1.35 and 1.36. Like the hard reflecting boundaries, the minimum frequency for a standing wave occurs when there is precisely half a wavelength between the two boundaries, and at all subsequent multiples of this frequency. This means that Equation 1.35 can also be used to calculate the standing wave frequencies for this boundary arrangement. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 404

Categorization

• DEFINE: Sets out the resonance rule for a tube open at both ends (pressure zero, velocity maximum at boundaries).
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 404
• XREF: connects to: Open and stopped organ pipes correspond to open-open and open-closed acoustic tubes. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1181