### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 2aEA9. Implementation of fast transversal filters for active structural
acoustic control.

**Marcus J. Bronzel
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Christopher R. Fuller
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*Vib. and Acoust. Lab., Virginia Tech., Blacksburg, VA 24061-0238
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The design of an optimal feedforward controller in active noise control
applications for controlling the sound radiation from a vibrating structure can
be seen as a system identification problem. Most control implementations use a
stochastic gradient search algorithm to adaptively identify the impulse
response of the optimal control filter. The convergence properties of the
widely used filtered-x LMS algorithm depend on the signal properties of the
filtered reference signals. Sensing the reference signals from the vibrating
structure is inevitable in most real applications and will effectively result
in structural filtering of the unknown noise source. The filtered reference
signals from a structural sensor generally exhibit a large eigenvalue spread
resulting in poor convergence properties of the adaptive controller. A new
extended-filtered-x approach has been developed which makes the implementation
of fast RLS type algorithms possible. These algorithms are based on an
orthogonal projection of the predictor error into the subspace of the filtered
reference signals and therefore converge independent from the underlying signal
statistics. Experiments for active control of noise from a vibrating plate have
been conducted which demonstrate the superior control performance of fast
transversal filters.