Research on active noise control and intensity with Professor Jiri Tichy 1984–2000

Abstract

Before Widrow [1] published the filtered-x algorithm in 1985, Warnaka et al. had a working prototype of a feedforward ANC which also pre-filtered the error path [2]. Tichy's role in this early patent was to break down the system into transfer functions that would align the LMS updates in time. Tichy also was an early investigator in acoustic intensity. By the mid-1990s, a robust frequency-domain ANC system was developed that combined both ANC and intensity to study the power flow and energy conversion in an ANC system [3]. In the early years of ANC, there was much controversy on how the additional energy from a secondary source could result in less energy radiated from a duct driven by a primary source. By using an Intensity error spectrum in a frequency domain ANC system, the power flow (active intensity) was minimized at various positions inside the duct to reveal how the active secondary source uses impedance to govern the radiated energy. This put the controversy to rest and provided clear objective evidence of how sound is actively “cancelled” or more precisely, how controlling waveguide impedance can control radiated sound power. Its an honor to have worked with Jiri.