### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 2pSA5. Active control in three-dimensional enclosures using multiple
secondary sources and error sensors.

**Scott D. Sommerfeldt
**

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John W. Parkins
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*Appl. Res. Lab. and Graduate Program in Acoustics, Penn State Univ., P.O.
Box 30, State College, PA 16804
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The use of multiple secondary sources and multiple error sensors can
significantly improve global attenuation whether one employs a control method
based on the squared pressure or energy density. A single source positioned
close to a pressure node will be inefficient at exciting the corresponding
mode, therefore the secondary modes will dominate the pressure field, and
attenuation is unlikely at the related frequency. Increasing the number of
secondary sources improves the probability that at least one source will not
lie close to a pressure node, thereby mitigating this problem. Problems also
arise when error sensors are close to nodes. Adding multiple error sensors
increases the probability that the sensors will be able to observe the dominant
modes, which will yield improved attenuation. Using a greater number of error
sensors than secondary sources will yield a determined control system, with a
unique optimal solution. If more sources are used than sensors, an
underdetermined control system will result which can be uniquely solved by
adding more constraints to the system, such as minimum effort. The performance
of the energy density versus squared pressure control methods are compared as
they relate to the use of multiple secondary sources and multiple error
sensors.