Concentric-tube resonators

Model and set-up

Reference

Measured transmission loss

• Perforated tube, inner diameter 50.8 mm, in a chamber of 76.2 mm; holes 2.49 mm in a 0.81 mm wall.
• Two lengths: 66.7 mm with 3.7 % open area (the paper’s Fig. 6) and 257.2 mm with 3.8 % (Fig. 7).
• Perforate impedance: Sullivan and Crocker’s own fit to their measured perforate; air at 20 °C, no mean flow, anechoic ends.

How to read the result

• The measured values are read from the paper’s figures (about ±3 % in frequency and ±1.5 dB), so the comparison is generous and says so.
• The 3-D finite-element resonance sits below the measured one and is converged in the mesh. At this size (k r = 0.9 at the resonance) the field is no longer plane, which a 1-D model cannot show.
• Main peaks in the plotted run: 20.9 dB at 2020 Hz against about 21.5 dB at 2175 Hz measured (Fig. 6), and 16.4 dB at 2280 Hz against about 18.8 dB at 2400 Hz (Fig. 7).
• The low-frequency humps are within 1 dB of the measurement.