A new method to generate mode waves in ducts by rigid splitters

In duct acoustics experiments, a controller is often required to generate the desired modes while suppressing all other cut-on modes. The present paper proposes a new method to actualize such a duct mode controller in the absence of flow by inserting in-duct rigid splitters in the sound source section. The interval between adjacent splitters is determined to ensure only plane wave propagating and each region separated by the splitters contains a loudspeaker flush mounted on the duct wall. The plane waves in each region can be easily controlled through properly setting the amplitude and phase of the corresponding loudspeaker, which finally generating a particular dominant mode in the experimental section. The relation between the settings of loudspeakers and the desired mode number is deterministic and the complex amplitudes of loudspeakers are controlled separately.