Tonehole Radiation Directivity: A Comparison of Theory to Measurements

Measurements have been conducted in an anechoic chamber for comparison to current linear acoustic theory for radiation directivity from a cylindrical pipe with toneholes. Time-delay spectrometry using an exponentially swept sine signal was employed to determine impulse responses at points external to the experimental air column. This technique is effective in clearly isolating nonlinear artifacts from the desired linear system response along the time axis, allowing the use of a strong driving signal without fear of nonlinear distortion. The experimental air column was positioned through a wall conduit into the anechoic chamber such that the driver and pipe input were located outside the chamber while the open pipe end and toneholes were inside the chamber, effectively isolating the source from the pickup. Measured results are compared to both frequency-domain, transmissionnetwork simulations, as well as time-domain, digital waveguide calculations.