Colloquia

Summary

Intensity probes are vector sensors used to measure the sound radiated from devices in their operating environment. However, these probes require careful calibration to be able to accurately measure the sound intensity, especially at low frequencies.

To ensure that intensity probes are calibrated to a sufficient degree at low frequencies, it is important to perform the calibration in an anechoic environment. Most passive methods struggle to sufficiently reduce sound reflections at these low frequencies. Active methods, i.e. methods using active microphones and speakers, may provide a solution. Here one such method, immersive wave propagation, is investigated for this purpose. This research focuses on the analytical and numerical implementation of immersive wave propagation for sound reflection removal.

To investigate the workings of immersive wave propagation for use in vector sensor calibration, a simplified one-dimensional finite difference time domain model is created with simulated white noise, hardware sample rate and actuator dynamics based on a lumped parameter model of a physical speaker. Immersive wave propagation is implemented using an idealized microphone array with an adjusted numerical implementation based on analytical physics-based equations that reduces the number of computations and allows for continuous operation. Wavelets are introduced into the numerical model and the pressure peaks of the generated and reflected wave are compared. In addition a hardware test is performed using a waveguide setup.

To further expand understanding of immersive wave propagation, analytical physics-based formulations for two- and three-dimensional cases are developed and investigated.

Results show that in idealized circumstances reflections can be significantly reduced using the developed formulation in the one-dimensional case, however performance severely degrades when actuator dynamics are not adequately compensated. Hardware results are inconclusive. The two-dimensional formulation results in a similar signal shape, but incorrect gains. A separate simulation shows that significant reduction in reflections can be achieved with limited actuators if both signal shape and gain are correct. The three-dimensional continuous operation formulation shows promising signal shapes and gains under idealized circumstances.