Active sound profiling of narrowband signals for improving sound quality in an enclosed space

In this paper, an active sound profiling (ASP) system based on the command-FxLMS algorithm was implemented in an enclosed space for improving sound quality. This ASP system was designed to track a pre-defined target signal against rpm in order to actively reduce and enhance the disturbance signal from a rotating machine. The control system consists of an error microphone at a control point, a midrange loudspeaker and a subwoofer in the enclosed space with a digital signal processing board. The real-time control experiment with the ASP system was carried out in the enclosed space to track the target signal of 9 orders from C2 to C6 which was defined because the disturbance signal before control had poor sound quality. Sound pressure levels (SPLs) of the 9 orders were attenuated or enhanced over rpm. The root mean square values of the deviations between the SPLs after control and the target SPLs of the orders became about 1.62–5.23 dB, which were dramatically reduced compared to the deviations before control. This result showed that the ASP algorithm in the control experiment improved sound quality greatly.