Analysis of active noise control plants using identification and signal processing methodology

In active noise control (ANC), to support the control
systems design and controllers parameterisation, it is important to become
familiar with plant features and possess its good parametric model. Due to
significant complexity of coupled acoustic and electric phenomena, it is not
feasible to build a sufficiently precise phenomenological model, although a
physical analysis is obviously very useful. The experimental methodology
developed in this paper provides information on passive features of ANC plants
as well as offers some guidelines, supported by theoretical explanations, for
the choice of sampling rate, system configuration and set-up. It is also
proposed how this methodology can be applied to examine non-linear effects and
evaluate the associated performance limitations. Plant non-stationarity is also
checked. Next, the procedure for determining parametric model of the plant of
proper structure is given. Within this stage, non-minimum phase phenomena of two
kinds are widely discussed. Although the analysis presented in this paper is
general, as the example for experiments, an active personal hearing protection
device (APHPD) applied to the artificial head is used. It is a representation of
compact acoustic plants (CAP). Such plants are characterised by the fact that
due to the geometrical arrangement of loudspeakers and microphones, in discrete
control, transmission times of acoustic waves are shorter than the transmission
times of corresponding electric signals.